WO2023139195A1

WO2023139195A1 - Polymer foams based on poly(meth)acrylimide

Info

Publication number: WO2023139195A1
Application number: PCT/EP2023/051330
Authority: WO
Inventors: Johannes Vorholz; Ralf Richter; Hartmut Elsässer; Jörg KRAFT; Andreas Weber; Wolfgang LULEY
Original assignee: Röhm Gmbh
Priority date: 2022-01-24
Filing date: 2023-01-20
Publication date: 2023-07-27

Abstract

The invention relates to a polymer foam F comprising (preferably consisting of) a polymer composition A comprising: (i) 0.1 to 100 wt.-%, preferably 1 to 99 wt.-%, more preferably 5 to 95 wt.-%, based on the total weight of the polymer composition A, of at least one poly(meth)acrylimide A-1, and (ii) 0 to 99.9 wt.-%, preferably 1 to 99 wt.-%, more preferably 5 to 95 wt.-%, based on the total weight of the polymer composition A, of at least one poly(vinylidene fluoride) A-2, wherein the polymer foam F is obtained by foaming the polymer composition A using a physical blowing agent B, preferably an inert gas. The invention further relates to a foamable polymer composition P for producing the polymer foam F, to processes for producing the polymer foam and to the use thereof.

Description

Polymer foams based on poly(meth)acrylimide

Technical field

The present invention relates to polymer foams based on polymer compositions of imidated poly(meth)acrylate, especially imidated poly(methyl methacrylate), and optionally poly(vinylidene fluoride). The inventive polymer foams exhibit good mechanical properties compared to standard foamed polymer systems.

Furthermore, the present invention is directed to a foamable polymer composition of imidated poly(meth)acrylate and optionally poly(vinylidene fluoride) in combination with at least one physical blowing agent B.

Moreover, the present invention relates to a process for producing the inventive polymer foam, to a process for producing the inventive foamable polymer composition as well as to the application thereof. For example, the polymer foams can be used as (light-weight) construction materials, in particular in automotive constructions, aviation construction or marine construction. Moreover, the polymer foams can be used as insulating materials or damping materials.

Polymer foams are materials typically used in applications where light-weight, flotation, thermal insulation, electrical insulation and cushioning effects are required. Foams made out of polystyrene (PS), polyethylene (PE), or polyurethanes (PUR) are widely known. However, foams made from these materials are limited in thermal resistance, chemical resistance, weathering resistance and ageing properties in general terms. Polymer foams of poly(vinyl chloride) (PVC) and polyetherimide (PEI) can overcome only some of these drawbacks.

Fluoropolymers, such a as poly(vinylidene fluoride), are known to have superior properties with respect to chemical resistance, flammability and water absorption. However, fluoropolymers typically exhibit low mechanical stability compared to other polymers. This reduces their applicability, in particular as construction materials.

EP 2 217 644 B1 discloses a process for making fluoropolymer foams with the use of non-gaseous blowing agents. The non-gaseous blowing agent can be combined with the fluoropolymer at temperature below the decomposition temperature of the non-gaseous blowing agent. Decomposition of the blowing agent can then be induced after the composition is brought in the desired shape.

EP 1 745 093 B1 discloses fluoropolymer foams which are cross-linked by irradiation with an electron beam or with gamma radiation and subsequently foamed using inert gasses as blowing agents. The process allows foaming at a temperature above the melting temperature of the fluoropolymer. Poly(meth)acrylimides are based on imidated poly(meth)acrylate, such as imidated poly(methyl methacrylate) (PMMA), and are a particular class of heat distortion-resistant thermoplastics. Shaped bodies made of this material can be exposed to significantly higher temperatures over prolonged periods than shaped bodies made of other thermoplastics, for example poly(methyl methacrylate) (PMMA). These high-performance thermoplastics are for example used for the coverage of lamps or light guides. US 2011/0015317 A-1 describes poly(meth)acrylamide having improved optical and color properties particularly under thermal load.

Furthermore, polymethacrylamides PMI are known which are prepared by thermal cyclisation and formation of imide ring structures in copolymers of (meth)acrylic acid and (meth)acrylonitrile under addition of ammonia-producing additives, such as urea. The preparation of poly(meth)acrylimides is known and disclosed, for example, in GB-B 1 078 425, GB-B 1 045 229, US-B 3 627 711 , or US-B 4 139 685.

It has been reported that the addition of poly(meth)acrylamide based on imidated poly(meth)acrylate allows the production of stable foams of polyetherblockamide, although the latter, if used alone, is not able to form stable foamed articles. An according autoclave process is described in WO 2020/078856 A-1 and WO 2020/079081 A-1 using physical blowing agents.

EP 0 635 537 A2 describes a process for producing poly(meth)acrylamide (based on imidated poly(meth)acrylate) foams using chemical blowing agents, such as Mg/AI/Si-hydroxide-hydrates. US 4,246,374 relates to an anhydrous process for the preparation of poly(meth)acrylamide by imidation reaction of poly(meth)acrylate with ammonia or an primary amine, which may optionally be foamed in the presence of chemical blowing agents. JP S 59115338 A discloses an expandable resin composition comprising polyolefins and poly(meth)acrylamide.

Polymer blends comprising poly(vinylidene fluoride) and poly(meth)acrylamide have been reported in the art and are taught to act as adhesive agent between polymer layers of incompatible polymers such as polyamides or poly(methyl methacrylate) and poly(vinylidene fluoride). Reference is made to EP 0 878 509 B1 and EP 0 637 511 B1 .

The production of polymer foams from untreated semi-crystalline polymers such as poly(vinylidene fluoride) is difficult because a tailored balance between molten and formed crystals is important to achieve an expandable melt stable enough to form a good foam. This becomes even more difficult when a blowing agent with a plasticizing effect is used that additionally reduces the viscosity of the polymer melt. Zhao et al. (J. Mater. Chem. C, 2018, 6, 3065-3073) observed for a poly(vinylidene fluoride) with a molecular weight of 300,000-330,000 g/mol a variation of the obtained foam density by a factor of 6 within a very narrow (4 K) temperature range below the melting temperature of the polymer of 172 °C when carbon dioxide was used as blowing agent. Foams with a density around 100 kg/m³ could be produced only within a very narrow temperature window of 3 K. Disclosure of the invention

It was surprisingly found that a polymer foam F comprising a polymer composition A based on poly(meth)acrylimides, in particular polymethylmethacrylimide (PMMI), and optionally poly(vinylidene fluorides), can be prepared over a broad compositional range from poly(vinylidene fluoride)-rich to pure poly(meth)acrylimide polymer foams, wherein the polymer foam F is obtained by foaming the polymer composition A using a physical blowing agent B. The obtained polymer foams F have in general uninform cell structures and exhibit good mechanical properties. Compared to pure poly(vinylidene fluoride) foams, in particular plastic flow is reduced. This allows the application as structural foam in curing processes at increased temperatures. In addition, the foam structure is improved, and low density foams can be obtained easily within a large temperature range.

Thus, the present invention is directed to a polymer foam for applications as light weight construction material, automotive construction material, insulating material or damping material, comprising at least one poly(meth)acrylimide, preferably at least one poly(meth)acrylalkylimide, especially polymethylmethacrylimide (PMMI), and optionally at least one poly(vinylidene fluoride). The polymer foam materials of the present invention could become an alternative to commonly known polymer foams, such as PET-, PMI-, PVC- or PEI-based materials as well as melamine-based polymer foams.

Unless otherwise stated, all amounts given in % refers to % by weight (wt.-%).

Detailed description of the invention

In particular, the present invention is directed to a polymer foam F comprising (preferably consisting of) a polymer composition A comprising:

(i) 0.1 to 100 wt.-%, preferably 1 to 99 wt.-%, more preferably 5 to 95 wt.-%, based on the total weight of the polymer composition A, of at least one poly(meth)acrylimide A-1 , and

(ii) 0 to 99.9 wt.-%, preferably 1 to 99 wt.-%, more preferably 5 to 95 wt.-%, based on the total weight of the polymer composition A, of at least one poly(vinylidene fluoride) A-2, wherein the polymer foam F is obtained by foaming the polymer composition A using a physical blowing agent B, preferably an inert gas, in particular carbon dioxide, nitrogen and mixtures of carbon dioxide and nitrogen.

In a further aspect, the invention relates to a foamable polymer composition P comprising (preferably consisting of): a) 67 to 99.99 wt.-%, preferably 77 to 99.99 wt.-%, more preferably 87 to 99.99 wt.-%, based on the total weight of the foamable polymer composition P, of a polymer composition A comprising:

(ii) 0 to 99.9 wt.-%, preferably 1 to 99 wt.-%, more preferably 5 to 95 wt.-%, based on the total weight of the polymer composition A, of at least one poly(vinylidene fluoride) A-2, and b) 0.01 to 33 wt.-%, preferably 0.01 to 23 wt.-%, more preferably 0.01 to 13 wt.-%, based on the total weight of the foamable polymer composition P, of at least one physical blowing agent B.

The present invention further relates to a process for producing a polymer foam F, wherein the process comprises the following process steps: a. Heating a polymer composition A comprising:

(ii) 0 to 99.9 wt.-%, preferably 1 to 99 wt.-%, more preferably 5 to 95 wt.-%, based on the total weight of the polymer composition A, of at least one poly(vinylidene fluoride) A-2, to a temperature T close to or above the glass transition temperature T_g, determined by differential scanning calorimetry (DSC), of the resulting mixture of polymer composition A and blowing agent B, often heating close to or above the glass transition temperature TgA, determined by differential scanning calorimetry (DSC), of the polymer composition A, particular to a temperature T > (TgA - 50°C), preferably T > (TgA - 10°C), more preferably T > (TgA - 5°C); b. Applying a physical blowing agent B to the polymer composition A; and c. Allowing the physical blowing agent B to expand by reduction of the applied pressure and/or increase of the temperature to obtain a polymer foam, wherein process step a is carried out before, after or simultaneous to process step b, and process step c is carried out after process step a and b.

Typically, the glass transition temperature T_g of the resulting mixture of polymer composition A and blowing agent B, and/or of the polymer composition A (TgA) is determined by differential scanning calorimetry (DSC), in particular utilizing a heating rate of 10K/min and preferably using inert gas atmosphere, e.g. nitrogen atmosphere. Determination of glass transition temperature of polymers via DSC is commonly known by a skilled person and can be carried out using an appropriate apparatus, e.g. using a Mettler Toledo DSC HC01. Typically, the melting temperature T_m, e.g. the melting temperature of the polymer composition A, is determined by differential scanning calorimetry (DSC), in particular utilizing the conditions mentioned above for determination of glass transition temperature.

In a further aspect, the invention relates to the use of a polymer composition A comprising:

(ii) 0 to 99.9 wt.-%, preferably 1 to 99 wt.-%, more preferably 5 to 95 wt.-%, based on the total weight of the polymer composition A, of at least one poly(vinylidene fluoride) A-2, for producing a polymer foam F or a foamable polymer composition P.

Moreover, the invention relates to the use of a polymer foam F according to the invention as light-weight construction material, in particular in automotive construction, aviation construction or marine construction. Moreover, the polymer foams can be used as insulating materials or damping materials. Polymer foam F

The inventive polymer foam F comprises (preferably consists of) a polymer composition A as described herein.

The polymer foam F may be an open, semi-open or closed cell polymer foam. In a preferred embodiment, the polymer foam F is a closed cell polymer foam. Closed-cell polymer foams F are in particular characterized by their good mechanical stability. On the other hand, open-cell polymer foams F are able to be infiltrated by gases and liquids. However, in applications for composite materials (such as light-weight composite materials), excessive infiltration with liquid components (e.g. adhesives) results in increased density of the foam and is therefore undesirable.

Depending on the foaming process, the polymer foam F has a great variety of density. Preferably, the polymer foam F has a density of 5 to 800 kg/m³. In a more preferred embodiment, the density of the polymer foam F may range from 20 to 500 kg/m³, more preferably from 50 to 250 kg/m³. The density may be adjusted during the foaming process, e.g. by the selection of the amount and nature of the physical blowing agent B, the foaming temperature and the foaming process, but also by the composition and optional pre-treatment (e.g. cross-linking reactions) of the polymer composition A. This allows the production of a polymer foam tailored for the desired application.

Following ASTM D 3576-04 standard, the apparent cell size in polymer foams can be determined from a microscopic image of the foam (e. g. using SEM) by counting the number of cell wall intersections along several lines of known length. The cell number density can be determined by counting all cells on a micrograph with known area dimensions assuming that the foam is isotropic. Cell sizes vary between 1 pm and 500 pm, preferably between 5 pm and 200 pm, more preferably between 7 pm and 100 pm. Typical cell number densities are between 10⁵ and 10¹° 1/cm³.

The polymer foam F is obtained by foaming the polymer composition A using a physical blowing agent B, preferably an inert gas, e.g. noble gas, carbon dioxide, nitrogen, in particular carbon dioxide, nitrogen and mixtures of carbon dioxide and nitrogen. Preferably, the polymer composition A comprises < 1 wt.- %, more preferably < 0.5 wt.-%, often < 0.1 wt.-%, based on the total weight of the polymer composition A, of a chemical blowing agent.

In a preferred embodiment, the polymer foam F comprises less than 5 wt.-%, more preferably less than 1 wt.-%, often less than 0.5 wt.-%, based on the total weight of the polymer composition A, of solid or liquid decomposition products of chemical blowing agents.

Polymer composition A

The polymer composition A comprises: (i) 0.1 to 100 wt.-%, preferably 1 to 99 wt.-%, more preferably 5 to 95 wt.-%, based on the total weight of the polymer composition A, of at least one poly(meth)acrylimide A-1 ; and

(ii) 0 to 99.9 wt.-%, preferably 1 to 99 wt.-%, more preferably 5 to 95 wt.-%, based on the total weight of the polymer composition A, of at least one poly(vinylidene fluoride) A-2,

In one embodiment of the invention, the polymer composition A comprises:

(i) 50.1 to 100 wt.-%, preferably 61 to 99 wt.-%, more preferably 69 to 98 wt.-%, based on the total weight of the polymer composition A, of at least one poly(meth)acrylimide A-1 ; and

(ii) 0 to 49.9 wt.-%, preferably 1 to 39 wt.-%, more preferably 2 to 31 wt.-%, based on the total weight of the polymer composition A, of at least one poly(vinylidene fluoride) A-2.

This embodiment is a poly(meth)acrylamide-rich polymer composition A, from which poly(meth)acrylamide-rich polymer foams may be prepared.

In an alternative embodiment of the invention, the polymer composition A comprises:

(i) 0.1 to 49.9 wt.-%, preferably 4 to 39 wt.-%, more preferably 7 to 31 wt.-%, based on the total weight of the polymer composition A, of at least one poly(meth)acrylimide A-1 ; and

(ii) 50.1 to 99.9 wt.-%, preferably 61 to 96 wt.-%, more preferably 69 to 93 wt.-%, based on the total weight of the polymer composition A, of at least one of at least one poly(vinylidene fluoride) A-2.

This embodiment is a poly(vinylidene fluoride)-rich polymer composition A, from which poly(vinylidene fluoride)-rich polymer foams may be prepared.

The polymer composition A may optionally comprise additives C, preferably selected from conventional auxiliaries and additives, to improve or adjust the properties of the polymer composition A and/or the polymer foam F produced therefrom, in particular with respect to the intended application.

Typically, polymer composition A may optionally comprise up to 30 wt.-%, based on the total weight of the polymer composition A, of at least one additive C. In one embodiment of the invention, the polymer composition A comprises 0 to 20 wt.-%, preferably 0 to 15 wt.-%, based on the total weight of the polymer composition A, of at least one additive C common for polymer compositions in order to adjust polymer properties to the demands of the intended application.

The polymer composition A may optionally comprise further polymers D, which are different from constituents A-1 and A-2, to improve or adjust the properties of the polymer composition A and/or the polymer foam F produced therefrom, in particular with respect to the intended application.

Typically, polymer composition A may optionally comprise up to 30 wt.-%, based on the total weight of the polymer composition A, of at least one further polymer D. In one embodiment of the invention, the polymer composition A comprises 0 to 20 wt.-%, preferably 0 to 15 wt.-%, based on the total weight of the polymer composition A, of at least one further polymer D in order to adjust polymer properties to the demands of the intended application. In other words, the polymer composition A comprises (or consists of):

(iii) 0 to 30 wt.-%, based on the total weight of the polymer composition A, of at least one additive C, and

(iv) 0 to 30 wt.-%, based on the total weight of the polymer composition A, of at least one further polymer D, which is different from constituents A-1 , A-2 and C.

The constituents A-1 , A-2, C, and D are described in detail in the following.

Poly(meth)acrylamide A-1

The inventive polymer composition A comprises one or more poly(meth)acrylimide A-1 , preferably at least on poly(meth)acrylalkylimide.

Generally, poly(meth)acylimide (also referred to as polyglutarimide) as used in the present invention refers to polymers which are obtained by imidation of (meth)acrylic polymers, in particular poly (meth)acryl alkyl esters, wherein typically two adjacent carboxyl or carboxylate groups react with ammonia or primary amines to form a cyclic imide. Typically, the at least one poly(meth)acrylimide A-1 is selected from at least partially imidated poly(meth)acrylate, preferably from at least partially imidated polyalkyl(meth)acrylates, more preferably from at least partially imidated polymethylmethacrylate. In a preferred embodiment, the at least one poly(meth)acrylimide A-1 is polymethylmethacrylimide (PMMI).

In terms of the present invention “(meth)acrylate” is meant to encompass methacrylates (such as methyl methacrylate, ethyl methacrylate etc.), acrylates such as methyl acrylate, ethyl acrylate, etc.), and mixtures thereof.

In terms of the present invention “polyalkyl (meth)acrylate” means a polymer comprising at least 30 wt.- %, preferably at least 40 wt.-%, more preferably at least 50 wt.-%, of alkyl (meth)acrylate monomer units and includes copolymers of alkyl (meth)acrylate monomers with one or more other co-polymerizable monomer(s).

For the purposes of the present invention, particular preference is given to Ci-Cis-alkyl (meth)acrylates, advantageously Ci-Cio-alkyl (meth)acrylates, in particular C1-C4-alkyl (meth)acrylates. Preferred alkyl methacrylates encompass methyl methacrylate (MMA), ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n butyl methacrylate, isobutyl methacrylate, tert.-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, isooctyl methacrylate, and ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, and also cycloalkyl methacrylates, for example cyclohexyl methacrylate, isobornyl methacrylate or ethylcyclohexyl methacrylate. Use of methyl methacrylate is particularly preferred. Preferred alkylacrylates encompass methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tert.-butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, isooctyl acrylate, nonyl acrylate, decyl acrylate, and ethylhexyl acrylate, and also cycloalkyl acrylates, for example cyclohexyl acrylate, isobornyl acrylate or ethylcyclohexyl acrylate.

Typically, the poly(meth)acrylimide A-1 is produced by at least partially imidation of poly(meth)acrylates via reactive extrusion, e.g. using a degassing extrudes, including reaction of poly(meth)acrylate with ammonia and/or a primary amine, such as a primary alkyl-substituted amine. Typically, such imidation reaction is carried out at high pressure and high temperature in the melt or in solution. Said imidation reaction processes are for example described in US 2,146,209 and US 4,246,374. Often phosphorous additives, such as hypophosphites, sodium benzene phosphinate or hypo phosphoric acid, are added during or after imidation reaction.

Preferably, the polymer composition A comprises at least on poly(meth)acrylimide A-1 , more preferably at least 50 wt.-%, based on the polymer composition A, of at least on poly(meth)acrylimide A-1 , which contains units of formula I:

in which

R¹ and R² are, independently from each other, hydrogen or Ci-Ce alkyl, preferably hydrogen or methyl; and

R³ is hydrogen, Ci-Cis-alkyl, Cs-Cs-cycloalkyl, Ce-Cio-aryl, or Ce-Cio-aryl-Ci-C4-alkyl, where these radicals may be up to trisubstituted by radicals selected from the group consisting of Ci-C4-alkyl, C1-C4- alkoxy and halogen.

In particular, the structure unit described in formula I is present in the poly(meth)acrylimide A-1 to an extent of at least 5 wt.-%, preferably of at least 15 % wt.-%, more preferably of at least 60 wt.-%.

Preferably, in the unit of formula (I) R¹ and R² are each methyl; and R³ is Ci-Cis-alkyl, more preferably Ci-Ce-alkyl, even more preferably methyl. Accordingly, the particularly preferred poly(meth)acrylimide A-1 contains (N-methyl)dimethylglutarimide units as units of formula (I). According to a preferred embodiment, the at least one poly(meth)acrylimide comprises at least 5 wt.-%, preferably at least 15 wt.-%, more preferably at least 60 wt.-%, based on the total poly(meth)acrylimide,

wherein the residues R¹; R² and R³ are independently from each other selected from Ci-Cis-alkyl, more preferably Ci-Ce-alkyl, even more preferably R³ is methyl, also preferably all residues R¹; R² and R³ are methyl.

As a result of the preparation, the poly(meth)acrylimide A-1 may contain not only units of formula (I) (i.e. glutarimide units) but also small amounts of (meth)acrylic acid units, (meth)acrylic acid anhydride units, and also residual (meth)acrylic ester units.

In a preferred embodiment the polymer composition A comprises at least 50 wt.-%, preferably at least 70 wt.-%, more preferably at least 80 wt.-%, based on the polymer composition A, of the at least one poly(meth)acrylimide A-1 , wherein the poly(meth)acrylimide A-1 contains units of formula (I) as defined above.

In a further preferred embodiment, the at least one poly(meth)acrylimide A-1 comprises: i) from 1 to 95 wt.-%, preferably from 20 to 92 wt.-%, more preferably 50 to 91 wt.-%, also preferably 50 to 95 wt.-%, based on the total weight of the poly(meth)acrylimide A-1 , units of formula I

ii) from 1 to 70 wt.-%, preferably from 2 to 60 wt.-%, more preferably 2 to 49 wt.%, also preferably

2 to 48 wt.-%, based on the total weight of the poly(meth)acrylimide A-1 , units of formula II

iii) from 1 to 20 wt.-%, preferably from 1 to 12 wt.-%, based on the total weight of the poly(meth)acrylimide A-1 , units of formula III

iv) from 0 to 15 wt.-%, preferably 0 to 10 wt.-%, also preferably 1 to 10 wt.-%, based on the total weight of the poly(meth)acrylimide A-1 , units of formula IV

R¹ and R² are, independently from each other, hydrogen or Ci-Ce alkyl, preferably hydrogen or methyl;

R³ is hydrogen, Ci-Cis-alkyl, Cs-Cs-cycloalkyl, Ce-Cio-aryl, or Ce-Cio-aryl-Ci-C4-alkyl, where these radicals may be up to trisubstituted by radicals selected from the group consisting of Ci- C4-alkyl, Ci-C4-alkoxy and halogen, and

R⁴ is Ci-Cia-alkyl, Cs-Ce-cycloalkyl, Ce-Cio-aryl, Ce-Cio-aryl-Ci-C4-alkyl, where these radicals may be up to trisubstituted by radicals selected from the group consisting of Ci-C4-alkyl, C1-C4- alkoxy and halogen.

More preferably the poly(meth)acrylimide A-1 is built up of (essentially consists of) repeating units selected from the units (I) to (IV) as described above. Preferably, in the unit of formulas (I) to (IV) R¹ and R² are each methyl; R³ is Ci-Cis-alkyl, more preferably Ci-Ce-alkyl, even more preferably methyl, and R⁴ is Ci-Cis-alkyl, more preferably Ci-Ce-alkyl, even more preferably methyl or ethyl. More preferably, R¹, R², R³ and R⁴ are methyl.

In addition, the poly(meth)acrylimide A-1 may contain further repeating units which arise, for example, from styrene, maleic acid or the anhydride thereof, itaconic acid or the anhydride thereof, vinylpyrrolidone, vinyl chloride or vinylidene chloride. Generally, the proportion of the comonomers, which cannot be cyclized or can be cyclized only with very great difficulty, should not exceed 30 wt.-%, preferably 20 wt.-% and particularly preferably 10 wt.-%, based on the weight of the monomers.

Preferred poly(meth)acrylimide A-1 is prepared from poly(meth)acrylates, such as polymethyl methacylate or copolymers thereof, by imidation reaction, preferably using ammonia and/or methylamine, so that 1 to 95 wt.-%, preferably 20 to 92 wt.-%, more preferably 50 to 91 wt.-% of the (meth)acrylic ester groups are imidated (degree of imidation). Generally, the degree of imidation may be determined via NMR spectroscopy.

Typically, the weight average molecularweights of the poly(meth)acrylimide A-1 is in the range of 50,000 to 200,000 g/mol, preferably 80,000 to 120,000 g/mol.

Preferably, the poly(meth)acrylimide A-1 used according to the present invention exhibits a melt volume rate (MVR) of < 20 cm³/10 min, preferably < 10 cm³/10 min, preferably from 0.2 to 20 cm³/10 min, also preferably from 1 .5 to 20 cm³/10 min, determined according to ISO 1133, at 260 °C using 10 kg load.

Preferably, the poly(meth)acrylimide A-1 used according to the present invention exhibits a Vicat softening temperature of at least 130 °C, more preferably of at least 150 °C, even more preferably of at least 170 °C, determined according to ISO 306 (B50) using a load of 50 N and utilizing a heating rate of 50 °C /h.

According to a preferred embodiment, the polymer composition A exhibits a Vicat softening temperature of at least 130 °C, more preferably of at least 150 °C, even more preferably of at least 170 °C, determined according to ISO 306 (B50) using a load of 50 N and utilizing a heating rate of 50 °C/h.

Poly(vinylidene fluoride) A-2

According to the present invention, poly(vinylidene fluorides) include foamable homo- and copolymer comprising repeating units derived from vinylidene fluoride (VDF) that they can be transformed by extrusion, injection molding, compression molding or other forming techniques known to those skilled in the art. The poly(vinylidene fluorides) can be semi-crystalline or amorphous. Preferably, it is semicrystalline. Preferably, the poly(vinylidene fluorides) can be radiation cross-linked. Poly(vinylidene fluorides) are commonly known thermoplastic fluoroplolymers, which are obtained via polymerization of vinylidene fluoride CH2=CF2 (1 ,1-difluoro ethylene), optionally together with suitable comonomers. Typically, poly(vinylidene fluorides) may be transparent in thin layers and appear milky white at higher thickness. Generally, poly(vinylidene fluorides) are synthesized by free radical polymerization in suspension or emulsion under controlled conditions of pressure and of temperature, e.g. at a temperature from 10-150°C and pressure of 10-300 atm. For example, poly(vinylidene fluorides) are often used for the production of films or sheets.

Preferably, the poly(vinylidene fluorides), used as component A-2, may be selected from vinylidene fluoride homopolymers (PVDF), as well as copolymers or terpolymers of vinylidene fluoride, wherein typically the amount of vinylidene fluoride units is at least 50 wt.-%, preferably at least 60 wt.-%, more preferably at least 70 wt.-%, based on the total weight of all monomer units in the poly(vinylidene fluorides). For example co- and/or terpolymers of vinylidene fluoride may be obtained by polymerization of vinylidene fluoride together with one or more co-monomers, selected from partly or fully fluorinated olefins, such as vinyl fluoride, trifluoro ethylene, tetrafluoro ethylene, 3, 3, 3-trifluoro-1 -propylene, 1 ,2,3,3, 3-pentafluoropropylene, 3,3,3,4,4-pentafluoro-1-butylene, hexafluoro propylene, and hexafluoro isobutylene; partly or fully chlorinated fluoro-olefins, such as chlorotrifluoroethylene; perfluorinated vinyl ethers, such as perfluoro methyl vinyl ether, perfluoro ethyl vinyl ether, perfluoro-n-propyl vinyl ether, and perfluoro-2-propoxypropyl vinyl ether; other fluorine-containing monomers, such as fluorovinyl sulfonic acid; olefins, such as ethylene or propylene.

According to a preferred embodiment the component A-2 comprises (preferably consists of) at least one poly(vinylidene fluoride), wherein the poly(vinylidene fluoride) is selected from homopolymers of vinylidene fluoride, and copolymers of vinylidene fluoride with one or more comonomer selected from vinyl fluoride, trifluoro ethylene, tetrafluoro ethylene, hexafluoro propylene, hexafluoro isobutylene, chlorotrifluoro ethylene, perfluoro methyl vinyl ether, and fluorovinyl sulfonic acid; more preferably selected from tetrafluoro ethylene, hexafluoro propylene, and chlorotrifluoro ethylene. In a particular preferred embodiment of the invention, the component A-2 comprises (preferably consists of) at least one poly(vinylidene fluoride), wherein the poly(vinylidene fluoride) is selected from homopolymers of vinylidene fluoride (PVDF).

The mass average molecular weight Mw of the poly(vinylidene fluoride) used as component A-2 is preferably 50,000 to 450,000 g/mol, more preferably 100,000 to 400,000 g/mol, more preferably 110,000 to 300,000 g/mol, also preferably 130,000 to 280,000 g/mol. Typically, the mass average molecular weight of the poly(vinylidene fluoride) can be measured via gel permeation chromatography (GPC), using dimethyl formamide (DMF) as a solvent and calibration using polystyrene standard.

In a particular preferred embodiments of the invention, the poly(vinylidene fluoride) is a PVDF homopolymer, i.e. a polymer with a proportion of 100 wt.-% of repeating units derived from vinylidene fluoride (VDF), based on the total weight of the poly(vinylidene fluoride). The PVDF homopolymers typically have a specific density (ASTM D792) of 1 .77 to 1 .79 g/cm3, a melting temperature, determined by differential scanning calorimetry (DSC), of about 172 to 173 °C, a glass transition temperature, determined by differential scanning calorimetry (DSC), of about -35 °C and a crystallization temperature of about 140 °C.

Typically, for the purposes of the invention commercially available grades of poly(vinylidene fluoride) may be utilized, such as Kureha KF polymers from Kureha Corporation, Japan (e.g. KF TH850, KF TH1000, and KF TH1100), Kynar® grades from Arkema (e.g. Kynar® 760, Kynar® 740, Kynar® 720, and Kynar® 710), 3M® Dyneon® grades from Dyneon, and Solei® grades from Solvay (e.g. Solef®1006, 1008, 1015, 5140, 6008, 6010, 6012, 60512, 11008, 21508,1 1010, 21510). For example, PVDF as described in EP 2046888, US 2016/0200884 A-1 and WO 2009/000566 can be used in the present invention.

Additives C

Optionally, the inventive polymer composition A may comprise one or more additives C, preferably selected from conventional auxiliaries and additives, for example selected from organic and inorganic particulate fillers, reinforcing fibers, lubricants, cross-linking agents, thermal stabilizers, light stabilizes, UV stabilizers, UV absorbers, antioxidants, plasticizers, processing aids, viscosity improvers, flame proofing agents, impact modifiers, scattering particles, soluble or insoluble dyes, pigments, antimicrobial agents and the like. Particularly, the properties of the inventive polymer composition A are not adversely affected by these additives and/or specific properties, such as optical appearance, weather, heat or chemical resistance, of the polymer composition A respectively of formed articles produced thereof may be improved.

Preferably, the inventive polymer composition A comprises at least one additive C, selected from crosslinking agents, thermal stabilizers, UV absorbers, and impact modifiers.

Typically, the additives C may be present in an amount of up to 30 wt.-%, preferably up to 20 wt.-%, more preferably up to 15 wt.-%, also preferably up to 10 wt.-%, based on the total weight of the polymer composition. Typically, the additive C may be present in an amount of 0.0001 to 20.0 wt.-%, also preferably 0.001 to 10.0 wt.-%, also preferably 0.0001 to 2.0 wt.-%, based on the total polymer composition.

In a particular preferred embodiment, the inventive polymer composition A comprises at least one crosslinking agent, which is capable of cross-linking the polymer chains (e.g. of the poly(meth)acrylimide) and to produce a cross-linked polymer matrix. Suitable cross-linking agents include those, that can form free radicals under radiation, in particular under beta or gamma radiation, and thus improves optional crosslinking of the polymer material via radiation exposure, e.g. by beta radiation, gamma radiation or e-beam radiation. Such cross-linking agent are for example described in WO 2007/106074 A2. Typically, the at least one cross-linking agent comprises two or more unsaturated groups including olefinic groups. Suitable unsaturated groups include (meth)acrylic groups (also referred to as (meth)acryloyl or (meth)acrylyl), vinyl, allyl, and the like. Preferably, the cross-linking agent may be selected from bifunctional (meth)acrylates, tri- or multifunctional (meth)acrylates, and other known cross-linkers, such as allyl methacrylate, allyl acrylate, and divinylbenzenes. Exemplary polyallylic compounds useful as cross-linking agents include those compounds comprising two or more allylic groups, for example, triallylisocyanurate (TAIC), triallylcyanurate (TAC), and combinations thereof.

Further, the cross-linking agents preferably include multifunctional (meth)acrylates, which are selected from esters of (meth)acrylic acid and a polyfunctional alcohol, typically selected from aliphatic diols, triols and/or tetraols containing 2-100 carbon atoms, e.g. propane diol, butane diol, hexane diol, octane diol, nonane diol, decane diol, eicosane diol, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, dodecaethylene glycol, tetradecaethylene glycol, propylene glycol, dipropyl glycol, tetradecapropylene glycol, trimethylolpropane pentaerythritol. Examples of suitable multifunctional (meth)acrylates are ethyleneglycol diacrylate, 1 ,6-hexanediol diacrylate, neopentylglycol di(meth)acrylate, ethyleneglycol dimethacrylate (EDMA), polyethyleneglycol di(meth)acrylates, polypropyleneglycol di(meth)acrylates, polybutyleneglycol di(meth)acrylates, 2,2-bis(4- (meth)acryloxyethoxyphenyl) propane, 2,2-bis(4-(meth)acryloxydiethoxyphenyl) propane, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, trimethylolpropane trimethacrylate, trimethylolpropane triacrylate (TMPTA), di(trimethylolpropane) tetra(meth)acrylate, and combinations thereof. Also included are N,N'-alkylene-bis-acrylamides.

Typically, the inventive polymer composition A may comprise 0.01 to 20 wt.-%, specifically 0.1 to 15 wt.- %, more specifically 1 to 10 wt.-%, and even more specifically 2 to 7 wt.-%, based on the total weight of the polymer composition, at least one cross-linking agent, preferably selected from triallylisocyanurate (TAIC), triallylcyanurate (TAC), ethyleneglycol dimethacrylate (EDMA), 1 ,4-butanediol dimethacrylate, divinylbenzene, and allyl (meth)acrylate, more preferably triallylisocyanurate (TAIC) and/or triallylcyanurate (TAC).

In one embodiment, the inventive polymer composition A may further comprise one or more thermal stabilizers as additive C. Thermal stabilizers as such are known to the skilled person and are described inter alia in Kunststoff-Handbuch, Bd. IX, S. 398, Carl-Hanser-Verlag, 1975. Examples of commonly used thermal stabilizers include but are not limited to p-methoxyphenylethacrylamide, diphenylmethacrylamide, sodium dodecyl phosphate, disodium monooctadecyl phosphate, disodium mono(3,6-dioxyoctadecyl)phosphate and alkylamino salts of mono- and dialkyl-substituted phosphoric acids described in WO 2005/021631 A-1 .

Typically, such thermal stabilizers may be present in an amount of 0.0001 to 2 wt.-%, especially 0.001 to 1 .0 wt.-%, based on the weight of the polymer composition. Further, the optional additives C may include commonly known light or UV stabilizers, such as UV absorbers, antioxidants and/or free radical scavengers, for example selected from benzophenone derivate UV absorbers, in particular hydroxyphenylbenztriazole derivatives (such as 2-(2'-hydroxy-5'- methyl-phenyl)benzotriazole, commercially available as Tinuvin® P, from BASF SE or 2-(2'-hydroxy-3'- dodecyl-5'-methyl-decyl)benzotriazole);oxanilide UV absorbers (such as N-(2-ethoxyphenyl)-N'-(2- ethylphenyl) ethanediamide, commercially available as Tinuvin® 312 from BASF SE), sterically hindered amine stabilizers (HALS) (such as bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate, 8-acetyl-3-dodecyl- 7,7,9,9-tetramethyl-1 ,3-8-triazaspiro(4,5)decane-2, 5-dione, bis(2,2,6,6-tetramethyl-4- piperidyl)succinate, poly(N-B-hydroxyethyl-2,2,6,6-tetramethyl-4-hydroxypiperidine succinic acid ester) and bis(N-methyl-2,2,6,6-tetramethyl-4-piperidyl) sebacate); and phenolic antioxidants (such as octadecyl 3-(3,5-di-te/Y.-butyl-4-hydroxyphenyl)propionate, commercially available as Irganox® 1076 from BASF SE). Preferably, commonly known UV absorbers are used as UV stabilizers, if needed.

Typically, such light or UV stabilizers may be present in an amount of 0.01 to 1 .5 wt.-%, especially 0.02 to 1 .0 wt.-%, based on the weight of the polymer composition.

In another embodiment, the polymer composition A can additionally comprise one or more impact modifiers in order to raise the impact strength. Suitable impact modifiers include core/shell polymers having a poly(butyl acrylate) or poly(butadiene) core and a shell of poly(methyl methacrylate) and/or poly(meth)acrylimide. In addition to these, other conventional modifiers can be used. For example, suitable butadiene-based impact modifies are as described in EP 0 018 640 A-1 . Typically, the optional impact modifies may be present in an amount of up to 30 wt.-%, preferably up to 20 wt.-%, more preferably from 5 to 30 wt.-%, based on the total weight of the polymer composition.

In terms of the present invention “particulate” or “particulate filler” means a component, additive and/or filler consisting essentially of particles having length to thickness ratio (L/D ratio) less than or equal to 100, preferably less than or equal to 20, more preferably less than or equal to 10. Typically, particulate fillers or particles includes particles having spheroidal, ellipsoid, acicular, lamellar and/or plate like forms.

Preferably, the organic particulate filler is selected from solid polymer particles essentially consisting of a polymer selected from poly(phenylene sulfone) (PPSU) (e.g. Ceramer® particles from Ceramer GmbH), fluoropolymers and perfluoropolymers, such as polytetrafluoroethylene (PTFE) (e.g. Polymist® PTFE from Solvay), perfluoroalkoxy alkane polymers (PFA) (e.g. Teflon®-PFA from DuPont or Dyneon®-PFA from Dyneon /3M), tetrafluoroethylene/ethylene copolymer (ETFE); and/or high molecular weight polyolefins (e.g. PE-HMW GHR® grades or PE-UHMW GUR® grades both available from Celanese). In a preferred embodiment, the organic particulate filler is composed of spheroidal polymer particles having a L/D ratio in the range from 1 to 3. Typically, the organic particulate filler is composed of polymer particles having a weight averaged particle diameter in the range of 1 to 100 pm, preferably 2 to 60 pm, more preferably 2 to 30 pm. For example, the organic particulate filler is utilized in form of a micronized polymer powder. Typically, the at least one inorganic particulate filler can be selected from known fillers, e.g. hard abrasive particles, such as oxides, cubic boron nitride (BN) and ceramic particles; or known solid-state lubricants, such as graphite, molybdenum disulfide (M0S2) and hexagonal boron nitride (BN). For example, suitable inorganic particulate fillers B2 are described in DE10329228A-1 , US 2013/0178565, and US 2005/0208313. There is no particular restriction on the size of the particles of the inorganic particulate filler. The average particle diameter 2 may be, for example, in the range from 5 nm to 100 pm, preferably 10 nm to 10 pm. Often it may be preferred to use the inorganic particulate filler in form of nanoparticles, typically having an average particle diameter in the range of 10 to 1000 nm, preferably 50 to 1000 nm. The particle sizes can be determined by means of dynamic light scattering (also known as photon correlation spectroscopy or quasi-elastic light scattering) or via electron microscopy, e.g. scanning electron microscopy (SEM) or transmission electron microscopy (TEM). For example, suitable inorganic particulate filler may be selected from metals, metalloids (including e.g. C, B, Si, and Ge) and compounds thereof, such as oxides, nitrides, carbides, borides, chalcogenides (e.g. sulfides and selenides), halides (e.g. chlorides), phosphates, carbonates, silicates, zirconates, and aluminates. Preferred embodiments include for example natural graphite, synthetic graphite, graphene, hexagonal boron nitride, cubic boron nitride, molybdenum disulfide, tungsten disulfide, silicon nitride, silicon carbide, boron carbide, copper nanoparticles, silver nanoparticles, silicon dioxide (e.g. fused silica, crystalline silica, natural silica), aluminum oxide; zinc oxide, titanium dioxide, cerium dioxide, zirconium dioxide, and calcium carbonate.

In terms of the present invention “fiber”, “reinforcing fiber”, or “fibrous filler” means a component, additive and/or filler consisting essentially of particles having an L/D ratio greater than 100.

Reinforcing fibers can be selected form short fibers and long fibers, wherein typically the average fiber length of short fibers is in the range from 0.1 to 1 mm, and typically the average fiber length of long fibers is in the range from >1 to 50 mm. The average fiber length of the fibers present in the finished polymer composition A can in particular alter as a consequence of the steps in the process (e.g. extrusion). Typically, the reinforcing fiber can be selected from commonly known reinforcing fibers, including inorganic reinforcing fibers, such as carbon fibers, boron fibers, glass fibers, silicate fibers , silica fibers, mineral fibers, ceramic fibers, and basalt fibers; organic polymer reinforcing fibers, such as aramid fibers, polyester fibers, nylon fibers, and polyethylene fibers; and natural fibers, such as wood fibers, flax fibers, hemp fibers, and sisal fibers. Suitable reinforcing fiber include, for example, glass fibers, such as E, A, C, ECR, R, S, D, and NE glasses and quartz, milled glass fiber, chopped glass fiber, and long glass fiber. Other suitable inorganic reinforcing fiber include single crystal fibers or whiskers made of silicon carbide, aluminum dioxide, boron carbide, silicon carbide, silicon nitride, graphite, iron, nickel, or copper. Other suitable inorganic reinforcing fiber include carbon fibers, stainless steel fibers, metal coated fibers, and the like. Moreover, also polymer fibers, such as polyamide fibers include nylon fibers (e.g. nylon 6; nylon 6,6; nylon 12; 10) and aramid fibers (e.g. Kevlar®, which is commercially available from E. I. duPont de Nemours), thermoplastic polyester fibers (e.g. polyethylene terephthalate and polybutylene terephthalate), fibers formed from acrylic polymers (e.g. polyacrylonitriles having at least about 35wt.-% acrylonitrile units, which can be copolymerized with other vinyl monomers such as vinyl acetate, vinyl chloride, styrene, vinylpyridine, acrylic esters or acrylamide), polyolefin fibers (e.g. comprising at least 85wt.-% of ethylene, propylene, or other olefins), fibers formed from polyvinyl chloride, polyvinylidene chloride, polytetrafluoroethylene, polyvinyl alcohol, polyimides, polyether sulfones, polyphenyl sulfones, polyetherketones, polyphenylene oxides, polyphenylene sulfides or polyacetals. Typical organic polymer reinforcing fibers are for example described in US-B 9,994,670. Typically, reinforcing fibers may be provided in the form of monofilament or multifilament fibers and can be used either alone or in combination with other types of fiber, for example, through coweaving.

Lubricants may be selected from liquid lubricants, such as silicon oil; waxes, such as polyolefine waxes, polyethylenglycol waxes, and other commonly known lubricants, such as fatty acids, fatty alcohols, fatty acid esters, and fatty acid amides. For example, conventional lubricants are described in R. Gachter, H. Muller, Kunststoffadditive, 3. Ed., page 443 ff., Hauser Verlag. Typically, fatty acids and fatty acid derivates suitable as lubricant are based on saturated or unsaturated carboxylic acids having 8 to 40, preferably 10 to 40, more preferably 16 to 22 carbon atoms, e.g. capric acid, palmitic acid, lauric acid, stearic acid, montanic acid, and behenic acid. For example, the at least lubricant may include fatty acid esters and/or fatty acid amides obtained from aliphatic saturated mono to tetra functional alcohols or amines having 2 to 40, preferably 2 to 6 carbon atoms, e.g. n-butanol, n-octanol, stearyl alcohol, ethylene glycol, propylene glycol, neopentyl glycol, pentaerythritol, stearyl amine, ethylene diamine, propylene diamine, hexamethylene diamine, di-(6-aminohexyl)amine. Preferably, the at least one lubricant may include glyceryl distearate, glyceryl tri(stearate), ethylene bis(stearamide) (EBS), glyceryl monopalmitate, glyceryl trilaurate, glyceryl monobehenate und pentaerythritol tetrastearate. Further, the at least one lubricant may include one or more polyethylene glycol and/or copolymers of ethylene oxide and propylene oxide, typically having a molecular weight in the range of 1000 bis 15000 g/mol. According to a preferred embodiment, the polymer composition A comprises 0 to 5 wt.-%, more preferably 0 to 3 wt.-%, more preferably 0 to 2 wt.-%, based on the total polymer composition, of at least one lubricant, wherein the lubricant is selected from silicon oil (i.e. liquid polymerized siloxane with organic side chains, e.g. polydimethylsiloxane). Preferably, the silicon oil exhibits a viscosity in the range from 5,000 to 100,000 mPas. The silicon oil may be used in form of a master-batch, e.g. ACCUREL® Si 755 from Evonik.

Further polymers D

The polymer composition A may comprise one or more other polymers, which form a homogenous blend with the at least one poly(meth)acrylimide A-1 and the at least one poly(vinylidene fluoride) A-2. For example, the other polymer in the polymer composition A may be selected from polyalkyl (meth)acrylate (e.g. polymethyl(meth)acrylate, more preferably polymethylmethacrylate (PMMA)), polycarbonate (PC), polyvinylchloride (PVC), polyamide (PA), styrene-acrylonitrile copolymer (SAN), thermoplastic polyesters and mixtures thereof. Foamable polymer composition P

The present invention further relates to a foamable polymer composition P comprising (preferably consisting of): a) 67 to 99.99 wt.-%, preferably 77 to 99.99 wt.-%, 87 to 99.99 wt.-%, based on the total weight of the foamable polymer composition P, of a polymer composition A comprising (preferably consisting of):

The polymer composition A, poly(meth)acrylimide A-1 and poly(vinylidene fluoride) A-2 as well as the preferred embodiments thereof are as defined herein above. The foamable polymer composition P may optionally comprise additives C and/or further polymers D as disclosed herein above.

The foamable polymer composition P is characterized by comprising at least one physical blowing agent B in an amount of 0.01 to 33 wt.-%, based on the total weight of the foamable polymer composition P, preferably 0.1 to 25 wt.-%, more preferably 1 to 20 wt.-%.

Physical blowing agent B

Any known physical blowing agent may be used as blowing agent B. Physical blowing agents according to the invention include chemical substances which develop their foaming properties by expansion without undergoing chemical reaction (e.g. decomposition reactions). Physical blowing agents B are typically dissolved in the polymer composition A prior to the expansion. Typical examples of physical blowing agent B include gases or volatile liquids such as air, nitrogen, carbon dioxide, noble gases, hydrogen, halogenated hydrocarbons (CFCs and HCFCs), alcohols, ethers, ketones, aromatic hydrocarbons and water. Particular examples include air, nitrogen, oxygen, argon, helium, carbon dioxide, i-butane, pentane, i-pentane, methyl chloride, methylene chloride, trichloroethylene, CChF (CFC-11), CCI2F2 (CFC-12, CCI2F-CCI2F (CFC-112), C2CI3F3 (CFC-113), CCIF2-CCIF2 (CFC-114), CHCI2F (HCFC-21), CHCIF2 (HCFC-22), CF3-CHCI2 (HCFC-123), CF3-CH2F (HFC-134a), CCI2F-CH3 (HFC-141 b), CCIF2-CH3 (HFC-142b), CHF2-CH3 (HFC-152a), CHF2-CHF-H3F5 (HFC-245a).

In a preferred embodiment, physical blowing agents B are selected from inert gases, i.e. gases which are inert towards chemical reactions towards the constituents of the polymer composition A. Preferred physical blowing agents B include noble gases, nitrogen, carbon dioxide and mixtures thereof, more preferably nitrogen (N2), carbon dioxide (CO2) and mixtures of N2 and CO2. Most preferably, the blowing agent B comprises or is carbon dioxide. It was found by the present inventors that carbon dioxide exhibits good compatibility with the constituents of the polymer composition A which allows a direct absorption of the blowing agent B by the polymer composition A under mild conditions (i.e. low temperatures, low pressures and/or reduced duration required for desired direct absorption). This preserves the properties of the polymer compositions A which under harsh conditions may deteriorate due to potential decomposition reactions of its constituents. Moreover, the required time for preparing the foamable polymer composition P may be reduced using carbon dioxide as blowing agent B.

Since chemical blowing agents produce decomposition products which remain in the polymer composition A and may alter the properties of the polymer composition A and the products produces thereof, it has been found that physical blowing agents B discussed above, in particular compared to nitrogen and most preferably carbon dioxide, are superior with respect to the properties of the polymer foam F as well as the foaming process.

Process for producing the polymer composition A

Furthermore, the present invention is directed to a process for producing the polymer composition A, as described above, comprising

(iv) 0 to 30 wt.-%, based on the total weight of the polymer composition A, of at least one further polymer D, which is different from constituents A-1 , A-2 and C; by mixing the constituents.

The preferred embodiments and the description of the components A, B, and optionally C and/or D, as mentioned in connection with the inventive polymer compositions, apply accordingly.

The polymer composition A is principally obtained by mixing the constituents A-1 , A-2 and optionally C in order to obtain as substantially homogeneous polymer blend. The term “substantially homogeneous polymer blend” includes solutions of the constituents A-1 , A-2 and optionally C as well as evenly dispersed mixtures thereof. The mixing is typically carried out using methods known per se, for example by processing via the elastoviscous or molten state, i.e. by kneading, rolling, calendering, extrusion, injection molding, pressing, sintering or other suitable processes. Preferably, the mixing of the components takes place via heating, preferably via melting, the constituents A-1 and A-2 and optionally adding the additives C. Preferably, the mixing is carried out at a temperature in the range from 150 to 350 °C, in particular from 200 to 300 °C. It is also possible to prepare the inventive polymer composition A by dry blending the constituents A-1 and A-2, and optionally additives C, and typically melting the mixture afterwards, wherein the constituents are typically present as powder, particles or granulates.

Preferably, the polymer composition A is produced via extrusion, typically utilizing a melt temperature typically in the range from 200 to 350 °C, in particular from 250 to 300 °C. Conventional mixing devices, such as single-screw or multi-screw extruders or extruders with an oscillating screw and optionally additionally with shear pins may be used.

Preferably, the polymer composition A may be obtained in form of a powder, a granulate, or a semifinished product, such as sheet, film, or bar.

Typically, the process for producing the polymer composition A comprises at least the following process steps: a-1 . Melting the at least the constituents A-1 and A-2 to form a molten polymer composition A, a-2. Extruding the molten polymer composition A to obtain granules, a-3. optionally injection molding of the granules to obtain a molded part or optionally extrusion of the granules to obtain an extruded sheet.

The process can be conducted, for example, as follows: Pellets formed from the constituents A-1 and A-2 are metered as a dry premixture or individually via gravimetric or volumetric metering balances into a compounder preheated to the appropriate temperature (e.g. twin-screw compounder from Coperion or Berstorff or single-screw compounder from Buss or other standard models). In the corresponding screw, at the appropriate speed, the pellets are heated to form a melt. In the compounder, the mixture is heated at a suitable screw speed to form a melt. The melt is pressed through a die plate to form melt strands. These melt strands can be cooled down in a water bath, for example to room temperature. The cooled and hardened strands are chopped into pellets in a strand pelletizer. Alternatively, they can be chopped into pellets and cooled down by means of underwater pelletization (obtainable, for example, from Econ, BKG, Gala). The pellets formed are dried in dry air dryers at 50 to 95°C, for example, for several hours to give a reduced water content, for example 0.001 % to 0.1 %. The dried pellets are then processed to molded articles such as sheets, for example on a multi-zone screw injection molding machine at a barrel temperature of 150 to 300°C. The injection mold is then cooled.

In one embodiment of to the present invention, the polymer composition A may optionally be crosslinked prior to expansion by irradiation with an electron beam or with gamma radiation wherein the radiation dose is from 5 to 200 kGy. Crosslinking can be obtained by use of crosslinking agents known to those skilled in the art (e.g. triallylcyanurate) and subsequent exposure to ionizing radiation (e.g. electron beam or gamma irradiation). Preferentially, no chemical crosslinking or crosslink promoters are used but only crosslinking by ionizing radiation is employed. Typical doses for irradiation crosslinking are in the range of 5 to 200 kGy, but a preferential range is 25 to 100 kGy. Process for producing the polymer foam F

In another aspect, the present invention is directed to a formed article made of the polymer composition A as described above. The polymer foam F may be obtained from the polymer composition A via a process as described below.

The polymer foam F is preferably obtained by a process comprising at least the following process steps: a. Heating a polymer composition A comprising:

(ii) 0 to 99.9 wt.-%, preferably 1 to 99 wt.-%, more preferably 5 to 95 wt.-%, based on the total weight of the polymer composition A, of at least one poly(vinylidene fluoride) A-2, to a temperature T close to or above the glass transition temperature T_g, determined by differential scanning calorimetry (DSC), of the resulting mixture of polymer composition A and blowing agent B, often close to or above the glass transition temperature TgA, determined by differential scanning calorimetry (DSC), of the polymer composition A, particular heating to a temperature T > (TgA - 50°C), preferably T > (TgA - 10°C); more preferably T > (TgA - 5°C); b. Applying at least one physical blowing agent B to the polymer composition A; and c. Allowing the at least one physical blowing agent B to expand by reduction of the applied pressure and/or increase of the temperature to obtain a polymer foam, wherein process step a is carried out before, after or simultaneous to process step b, and process step c is carried out after process step a and b.

In process step a, the polymer composition A is heated to a temperature T close to or above the glass transition temperature T_g, determined by differential scanning calorimetry (DSC), of the resulting mixture of polymer composition A and blowing agent B, often close to or above the glass transition temperature TgA, determined by differential scanning calorimetry (DSC), of the polymer composition A, particular to a temperature T > (TgA - 50°C), preferably T > (TgA - 10°C); more preferably T > (TgA - 5°C); typically above a temperature > 150°C.

It has been surprisingly found that this temperature T > (TgA - 10°C), preferably T > (TgA - 5°C), is sufficient to enable the direct absorption of the physical blowing agent B, in particular with physical blowing agents B having an electric dipole moment, in particular carbon dioxide (CO2), by the polymer composition A.

In process step b, the physical blowing agent B is applied to the polymer composition A. This may be achieved by applying a gaseous, physical blowing agent B to the heated polymer composition A obtained in process step a. In process step c, the physical blowing agent B incorporated in the polymer composition A, comprising constituents A-1 , A-2, B and optionally C and/or D, is allowed to expand. This may be achieved by reduction of the applied pressure and/or increase of the temperature. The foaming process may be promoted by reducing the applied pressure during and/or after the decomposition temperature is achieved. However, reduction of the applied pressure is often sufficient to expand the physical blowing agent B. The foaming process may be promoted by increasing the temperature above the evaporation temperature of the physical blowing agent B, in particular if a physical blowing agent B is used which is liquid at ambient temperature.

After foaming is completed, the obtained polymer foam F is preferably cooled below the glass transition temperature TgA, determined by differential scanning calorimetry (DSC), of the of the polymer composition A, comprising the constituents A-1 , A-2 and optionally D, preferably below 120°C, in particular below 100 °C, in order to stabilize the polymer foam F.

The process may be carried out in a so-called autoclave process or, alternatively, in a so-called extrusion process.

In one embodiment of the invention, the so-called autoclave process, the process for producing a polymer foam F comprises at least the following process steps: a. Heating a polymer composition A to a temperature T close to or above the glass transition temperature T_g, determined by differential scanning calorimetry (DSC), of the resulting mixture of polymer composition A and blowing agent B, often close to or above the glass transition temperature TgA, determined by differential scanning calorimetry (DSC), of the polymer composition A comprising A-1 , A-2 and optionally D; particular heating to a temperature T > (TgA - 50°C), preferably T > (TgA - 10°C); more preferably T > (TgA - 5°C); b. Introducing the polymer composition A into an autoclave and subjecting it to a physical blowing agent B; and c. Allowing the physical blowing agent B to expand by reduction of the applied pressure and/or increase of the temperature to obtain a polymer foam, wherein process step a is carried out before, after or simultaneous to process step b, and process step c is carried out after process step a and b.

The process can be conducted, for example, as follows: Molded articles of the polymer composition A as described herein (e.g. sheets) are saturated with physical blowing agent B (preferably CO2) in a standard autoclave at a pressure of preferably 100 to 400 bar and a temperature of preferably 80 to 180°C, more preferably 145 to 180°C, often 150 to 170°C, over a period of several hours. After desired saturation is achieved, the pressure is decreased a foaming then proceeds with spontaneous expansion. Preferably, the temperature is decreased below 150°C, more preferably below 145°C before pressure is decreased. In an alternative embodiment of the invention, the so-called extrusion process, the process for producing a polymer foam F comprises at least the following process steps: a. Heating a polymer composition A to a temperature T above the melting temperature T_m, determined by differential scanning calorimetry (DSC), of the constituents A-1 , A-2 and optionally D (i.e. above the melting temperature T_m of the polymer composition A); b. Applying at least one physical blowing agent B to the molten polymer composition A; and c. extruding the molten polymer composition A by means of a perforated plate or nozzle, thereby expanding the physical blowing agent B to obtain a polymer foam F.

It is apparent to the skilled person, that the process for producing a polymer foam F is typically combined with the process for producing a foamable polymer composition P, i.e. starting with the polymer composition A and introducing the physical blowing agent B is introduced during the process for preparation of the polymer foam.

The process can be conducted, for example, as follows: Pellets formed from polymer composition A are metered as a dry premixture or individually via gravimetric or volumetric metering balances into a compounder preheated to the appropriate temperature (e.g. twin-screw compounder from Coperion or Berstorff or single-screw compounder from Buss or other standard models). In the corresponding screw, at the appropriate speed, the pellets are heated to form a melt. The physical blowing agent B, for example CO2 or mixtures of CO2 and N2, is added to the melt and distributed therein. The die plate used here is, for example, a slot die corresponding to the desired geometry in terms of thickness and width. At this die, the melt will spontaneously expand (foam) on exit and cool down to give a foamed extrudate. In accordance with the desired geometry, the foamed extrudate can be drawn off either with the aid of a calender as a sheet or with the aid of other continuous draw-off devices (known from profile extrusion) and cooled down. After a successful cooling process, the foamed extrudate is cut to the corresponding desired length.

This process is a continuous process and is therefore preferred.

Process for producing the foamable polymer composition P

In another aspect, the invention is directed to a process for producing a foamable polymer composition P, comprising a) 67 to 99.99 wt.-%, preferably 77 to 99.99 wt.-%, 87 to 99.99 wt.-%, based on the total weight of the foamable polymer composition P, of a polymer composition A comprising:

The process comprises at least the process steps a. to b. for producing the polymer foam F as defined above. Prior to foaming the polymer composition according to process step c., the composition comprising at least constituents A-1 , A-2 and B, is cooled. The thus obtained foamable polymer composition may be transported, processed (e.g. cut) and subsequently foamed by a user or customer by heating the foamable polymer composition P. The required temperature depends in particular on the applied physical blowing agent B. Typically, the temperature is above the glass transition temperature T_gp, determined by differential scanning calorimetry (DSC), of the foamable polymer composition P. Often, in particular if a physical blowing agent B is used, a temperature below the melting temperature T_m, determined by differential scanning calorimetry (DSC), of the polymer composition P is sufficient.

In a preferred embodiment of this aspect of the invention, the at least one physical blowing agent B comprises carbon dioxide, nitrogen or mixtures of carbon dioxide and nitrogen, in particular carbon dioxide and mixtures of carbon dioxide and nitrogen. These allow a direct absorption of the physical blowing agent B by the polymer composition A and a subsequent foaming of the foamable polymer composition P under mild conditions. Thermal and mechanical stress of the polymer composition A and potential decomposition of its constituents is reduced.

The process therefore provides a mild production process, allows the compact transportation of the nonfoamed foamable polymer composition P and subsequent foaming without the need of expensive facilities for incorporation of the physical blowing agent B by an user or customer.

In one embodiment of to the present invention, the foamable polymer composition P may optionally be cross-linked prior to expansion by irradiation with ionizing radiation such as electron beam, beta radiation (p- radiation) or gamma radiation. Preferably, the radiation is carried out using electron beam, wherein the radiation dose is from 5 to 200 kGy. Crosslinking can be obtained by use of crosslinking agents known to those skilled in the art (e.g. triallylcyanurate) and subsequent exposure to ionizing radiation (e.g. electron beam, beta radiation (p -radiation) or gamma radiation). Preferentially, no chemical crosslinking or crosslink promoters are used but only crosslinking by ionizing radiation is employed. Typical doses for irradiation crosslinking are in the range of 5 to 200 kGy, but a preferential range is 25 to 100 kGy.

Process for cross-linking the polymer composition A, the foamable polymer composition P or the polymer foam F In a preferred embodiment the process for producing a polymer foam from the polymer composition A encompasses at least one step of cross-linking by exposing the polymer composition to radiation, preferably high energetic radiation, more preferably radiation selected from beta radiation (e.g. p- radiation (electron emission)), gamma radiation, electron beam, x-ray radiation, and UV/Vis radiation (i.e. by photo-cross-linking). The cross-linking by exposure with gamma radiation or electron beam, in particular electron beam, is preferred.

It is described in the state of the art that exposure to high energetic radiation, such as gamma radiation or beta radiation, induces cross-linking in the polymer material, e.g. polyethylene, polypropylene, and polyamides, and may improve the wear resistance of the material (e.g. WO 2007/106074 A2). This is often used for polymer material suitable for implants (see e.g. WO 98/01085 A-1). Generally, the term “gamma radiation” or “gamma ray” refers to electromagnetic radiation having a quantum energy of equal or more than 200 keV. Generally, the term “beta radiation” or “beta ray” refers to high-speed electron (p- radiation) or positron (p⁺ radiation) emitted by the radioactive decay of an atomic nucleus during the process of beta decay.

Typically, the polymer composition A is exposed to ionizing radiation, such as gamma radiation or electron beam, in the solid stage after its production. Further, it is possible to expose the polymer composition A, preferably in solid stage, after its production, preferably in form of a semi-finished product (e.g. sheet, film, or bar) or in form of an injection molded product. Typically, the exposure to ionizing radiation may be followed by a thermal treatment, such as re-melting or annealing, in particularto reduce the amounts of free radicals.

Preferably, the cross-linking by exposure to ionizing radiation, such as gamma radiation, is carried out using a polymer composition A comprising at least one cross-linking additive as described herein.

Application

The polymer foams F according to the invention are preferably used as construction material, such as light-weight construction material, in particular in automotive construction, aviation construction or marine construction. Moreover, the polymer foams can be used as insulating materials or damping materials.

The polymer foams F combine good mechanical properties with reduced plastic flow. Moreover, the polymer foams may be prepared over a broad compositional range and have uniform cell structures.

Description of the figure

Figures 1 to 4 show scanning electron microscope photographs of different polymer foams. Figure 1 shows a polymer foam according to the invention of 100 wt.-% polymethacrylmethylimid (A- 1.1) having a density p of 72 kg/m³.

Figure 2 shows a polymer foam according to the invention of 70 wt.-% polymethacrylmethylimid (A-1.1) and 30 wt.-% poly(vinylidene fluoride) (A-2) having a density p of 82 kg/m³.

Figure 3 shows a polymer foam according to the invention of 10 wt.-% polymethacrylmethylimid (A-1.1) and 90 wt.-% poly(vinylidene fluoride) (A-2) having a density p of 61 kg/m³.

Figure 4 shows a polymer foam of 100 wt.-% poly(vinylidene fluoride) (A-2) having a density p of about 287 kg/m³.

The invention is illustrated in more detail by the Figures, claims and the experimental examples and comparative examples.

Examples a. Components of polymer compositions

A-1.1 : Polymethacrylmethylimid (PMMI), prepared by reaction of polymethylmethacrylate with methylamine via reactive extrusion, wherein the obtained PMMI A-1.1 comprises about 75 wt.-% of unit according to formula I as described above with R1 , R2 and R3 being methyl. The PMMI A-1.1 exhibits a melt volume rate (MVR) of about 5 cm³/10 min, determined according to ISO 1133, at 260 °C using 10 kg load, and a Vicat softening temperature of about 150 °C, determined according to ISO 306 (B/50).

A-1.2: Polymethacrylmethylimid (PMMI), prepared by reaction of polymethylmethacrylate with methylamine via reactive extrusion, wherein the obtained PMMI A-1 .2 comprises about 90 wt.-% of unit according to formula I as described above with R1 , R2 and R3 being methyl. The PMMI A-1.1 exhibits a melt volume rate (MVR) of about 1.7 cm³/10 min, determined according to ISO 1133, at 260 °C using 10 kg load, and a Vicat softening temperature of about 170 °C, determined according to ISO 306 (B/50).

A-2: Kureha® KF T850, Kureha Corporation, poly(vinylidene fluoride) (PVDF) having a molecular weight of ~ 200,000 g/mol, density p of 1760 kg/m³, a glass transition temperature T_g of about - 45 °C and a melting temperature T_m of about 175 °C. b. Symbols and characterization methods

The following symbols and methods are used in the description of the preparation and characterization of the starting materials and products:

Glass transition temperatures T_g and melting temperatures T_m were determined by differential scanning calorimetry (DSC) using a Mettler Toledo DSC HC01. N2 (30mL/min) was used as purge gas during the entire measurement N2. Measurements took place in a perforated crucible for pressure equalization.

Cooling was effected with liquid nitrogen. The measurements started at -100°C, the sample was kept isothermal for 1 minute. Heating rate from -100°C to 200°C with 10K/min. Cooling rate from 200°C to - 100°C with -50K/min. At minus 100°C the sample was kept isothermal for 8 minutes. Heating rate from -100°C to 200°C with 10K/min. c. Preparation of polymer compositions A

The compounding of the polymer compositions as given in Table 1 was carried out on a co-rotating twin- screw extruder (ZSK30) at a temperature in the range of 220 °C to 285 °C and a screw rotational speed of about 200 min^-1. A cooling metal plate was used for pelletizing. The pelletizer was cooled with compressed air.

Table 1. Polymer compositions A

d. Preparation of foamable polymer compositions P and polymer foams F

Polymer foams were prepared in autoclaves. The polymer compositions as indicated below were introduced into an autoclave and CO2 was applied to the polymer composition at pressure and duration indicated in Table 2. The obtained, C02-comprising polymer compositions were foamed immediately after the C02-absorption by reducing the pressure to ambient pressure to result in polymer foams with the densities recited in Table 2. While low density foams may be prepared from the compositions according to the invention (cf. Ex. 2, 3, 6 in Table 2), pure PVDF (A-2) can be foamed only to polymer foams having densities above 255 kg/m³ under similar conditions (cf. Table 3, Comparative Examples 14 to 20).

Table 2. Process parameters

Table 3. Process parameters of the foaming process

¹ Pellets

² Density measurement via buoyancy method e. Mechanical Properties Further polymer foams F of Examples 21 to 52 are prepared as described above and having the compositions recited in Table 4 below. The foaming conditions are given in Tables 2 and 3 above. The obtained polymer foams F were characterized. The results and foaming processes applied are summarized in Table 4. Table 4. Polymer foams F

² In the case of materials in which no maximum in compressive stress before a deformation of 15% but plastic flow was observed, the compressive stress at 15% deformation is given instead. f. Conclusions

The polymer foams according to the invention may be prepare over a broad density range and a broad ratio of components A-1 to A-2 ranging from 9:1 to 1 :9

While pure PVDF foams show a strong tendency to plastic flow (cf. Comp. Ex. 46, 50), this tendency is reduced or disappears entirely for the polymer foams according to the invention (cf. Ex. 38, 42). No plastic flow behavior is observed for polymer foams according to the invention even below 100 kg/m³. Moreover, compared to pure PVDF foams, polymer foams according to the invention show better compressive mechanical properties with - at the same time - reduced densities Examples of inventive and comparative polymer foams are shown in Figures 1 to 4. The pure PVDF foam (Figure 4) shows a non-uniform and less advantageous cell structure, wherein the inventive foams (Figures 1 to 3) exhibit a uniform cell structure.

Claims

Patent Claims

1 . Polymer foam F comprising a polymer composition A comprising:

2. Polymer foam F according to claim 1 , wherein the least one poly(meth)acrylimide A-1 contains

R³ is hydrogen, Ci-Cis-alkyl, Cs-Cs-cycloalkyl, Ce-Cio-aryl, or Ce-Cio-aryl-Ci-C4-alkyl, where these radicals may be up to trisubstituted by radicals selected from the group consisting of Ci-C4-alkyl, Ci-C4-alkoxy and halogen.

3. Polymer foam F according to claim 1 or 2, wherein the at least one poly(meth)acrylimide A-1 comprises: i) from 1 to 95 wt.-%, preferably from 20 to 92 wt.-%, based on the total weight of the poly(meth)acrylimide A-1 , units of formula I

ii) from 1 to 70 wt.-%, preferably from 2 to 60 wt.-% based on the total weight of the poly(meth)acrylimide A-1 , units of formula II

iii) from 1 to 20 wt.-%, preferably from 1 to 12 wt.-% based on the total weight of the poly(meth)acrylimide A-1 , units of formula III

(III); and iv) from 0 to 15 wt.-%, preferably from 0 to 10 wt.-% based on the total weight of the poly(meth)acrylimide A-1 , units of formula IV

R³ is hydrogen, Ci-Cis-alkyl, Cs-Cs-cycloalkyl, Ce-Cio-aryl, or Ce-Cio-aryl-Ci-C4-alkyl, where these radicals may be up to trisubstituted by radicals selected from the group consisting of Ci-C4-alkyl, Ci-C4-alkoxy and halogen; and

R⁴ is Ci-Cia-alkyl, Cs-Ce-cycloalkyl, Ce-Cio-aryl, or Ce-Cio-aryl-Ci-C4-alkyl, where these radicals may be up to trisubstituted by radicals selected from the group consisting of Ci-C4-alkyl, C1-C4- alkoxy and halogen.

4. Polymer foam F according to claim 2 or 3, wherein R¹, R², R³ and R⁴ are methyl.

5. Polymer foam F according to any of claims 1 to 4, wherein the polymer foam F is a closed-cell polymer foam. Polymer foam F according to any of claims 1 to 5, wherein the polymer foam F has a density of 5 to 800 kg/m³, preferably 20 to 500 kg/m³, more preferably 50 to 250 kg/m³. Foamable polymer composition P comprising: a) 67 to 99.99 wt.-%, based on the total weight of the foamable polymer composition P, of a polymer composition A comprising:

(i) 0.1 to 100 wt.-%, preferably 1 to 99 wt.-%, more preferably 5 to 95 wt.-%, based on the total weight of the polymer composition A, of at least one poly(meth)acrylimide A-

1 , and

(ii) 0 to 99.9 wt.-%, preferably 1 to 99 wt.-%, more preferably 5 to 95 wt.-%, based on the total weight of the polymer composition A, of at least one poly(vinylidene fluoride) A-

2, and b) 0.01 to 33 wt.-%, based on the total weight of the foamable polymer composition P, of at least one physical blowing agent B. Foamable polymer composition P according to claim 7, wherein the at least one physical blowing agent B comprises at least one physical blowing agent selected from carbon dioxide, nitrogen or a mixture of carbon dioxide and nitrogen. Foamable polymer composition P according to claim 7 or 8, wherein the least one poly(meth)acrylimide A-1 contains units of formula (I)

R³ is hydrogen, Ci-Cia-alkyl, Cs-Cs-cycloalkyl, Ce-Cio-aryl, or Ce-Cio-aryl-Ci-C4-alkyl, where these radicals may be up to trisubstituted by radicals selected from the group consisting of Ci-C4-alkyl, Ci-C4-alkoxy and halogen. Polymer foam F obtained by foaming of a foamable polymer composition P according to any of claims 7 to 9. Process for producing a polymer foam F, wherein the process comprises the process steps: a. Heating a polymer composition A comprising: (i) 0.1 to 100 wt.-%, preferably 1 to 99 wt.-%, more preferably 5 to 95 wt.-%, based on the total weight of the polymer composition A, of at least one poly(meth)acrylimide A-

1 , and

2, to a temperature T close to or above the glass transition temperature T_g, determined by differential scanning calorimetry, of the resulting mixture of polymer composition A and blowing agent B; b. Applying at least one physical blowing agent B to the polymer composition A; and c. Allowing the physical blowing agent B to expand by reduction of the applied pressure and/or increase of the temperature to obtain a polymer foam, wherein process step a is carried out before, after or simultaneous to process step b, and process step c is carried out after process step a and b.

12. Process for producing a polymer foam F according to claim 11 , wherein the polymer composition A is cross-linked prior to expansion by irradiation with an electron beam, wherein the radiation dose is from 5 to 200 kGy.

13. Use of a polymer foam F according to any of claims 1 to 6 as construction material, in particular in automotive construction, aviation construction or marine construction, as insulating material or as damping material.

14. Polymer foam F comprising a polymer composition A comprising:

(ii) 0 to 99.9 wt.-%, preferably 1 to 99 wt.-%, more preferably 5 to 95 wt.-%, based on the total weight of the polymer composition A, of at least one poly(vinylidene fluoride) A-2, wherein the polymer foam F comprises less than 5 wt.-%, based on the total weight of the polymer composition A, of solid or liquid decomposition products of chemical blowing agents.

15. Polymer foam F comprising a polymer composition A comprising:

(ii) 0 to 99.9 wt.-%, preferably 1 to 99 wt.-%, more preferably 5 to 95 wt.-%, based on the total weight of the polymer composition A, of at least one poly(vinylidene fluoride) A-2, wherein the polymer foam F is obtained by foaming the polymer composition A using a physical blowing agent B, preferably an inert gas, e.g. noble gas, carbon dioxide, nitrogen, in particular carbon dioxide, nitrogen and mixtures of carbon dioxide and nitrogen, and wherein the polymer composition A comprises < 1 wt.-%, based on the total weight of the polymer composition A, of a chemical blowing agent.