WO2021202121A1

WO2021202121A1 - Process of foaming cyclic olefin copolymer with a supercritical fluid

Info

Publication number: WO2021202121A1
Application number: PCT/US2021/023086
Authority: WO
Inventors: Gang Huang; Yujie SHENG; Liang Li; Ya Xian WANG; Yong Yang
Original assignee: Exxonmobil Chemical Patents Inc.
Priority date: 2020-03-31
Filing date: 2021-03-19
Publication date: 2021-10-07

Abstract

The present invention relates to a process of foaming cyclic olefin copolymer with the supercritical fluid, which comprises: (i) treating a polymer composition with the supercritical fluid at a foaming temperature, wherein the polymer to be foamed in the polymer composition is a cyclic olefin copolymer, and (ii) foaming the treated polymer composition obtained in step (i) to produce a foam, wherein the cyclic olefin copolymer is amorphous and the foaming temperature is in the range from about Tg to about Tsolid-liquid point + 10°C, or wherein the cyclic olefin copolymer is semi-crystalline and the foaming temperature is in the range from about Tc to about Tm + 10°C, wherein Tg is the glass transition temperature of the cyclic olefin copolymer, Tsolid-liquid point is the temperature of solid-liquid transition point of the cyclic olefin copolymer, Tc is the crystallization temperature of the cyclic olefin copolymer, and Tm is the melting point of the cyclic olefin copolymer.

Description

PROCESS OF FOAMING CYCLIC OLEFIN COPOLYMER WITH A

SUPERCRITICAL FLUID

INVENTORS: Gang Huang, Yujie Sheng, Liang Li, Yong Yang and Yaxian Wang

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of and priority to US Provisional Application No. 63/002,870 filed March 31, 2020, the disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

[0002] This invention relates generally to a process of foaming cyclic olefin copolymer with a supercritical fluid, and a foam obtainable by the process.

BACKGROUND OF THE INVENTION

[0003] There is a large and growing market for polymer foams. Low density foam with high stiffness, good thermal stability and good processability shows high demand. Cyclic olefin copolymer (COC) exhibits several advantages especially in foam application, such as high melt strength and strong extensional strain hardening, good barrier property, designable modulus and T_g in wide range.

[0004] However, there is still a need for a new process of preparing cyclic olefin copolymer foam having lower density, high stiffness, good thermal stability and good processability in lower cost.

SUMMARY OF THE INVENTION

[0005] In a first general aspect, this disclosure provides a process of foaming cyclic olefin copolymer with a supercritical fluid, which comprises:

(i) treating a polymer composition with the supercritical fluid at a foaming temperature, wherein the polymer to be foamed in the polymer composition is a cyclic olefin copolymer, and

(ii) foaming the treated polymer composition obtained in step (i) to produce a foam, wherein the cyclic olefin copolymer is amorphous and the foaming temperature is in the range from about T_g to about T_{solid-liquid point} + 10°C, or wherein the cyclic olefin copolymer is semi-crystalline and the foaming temperature is in the range from about T_c to about T_m + 10°C, wherein T_g is the glass transition temperature of the cyclic olefin copolymer, T_{solid-liquid point} is the temperature of solid-liquid transition point of the cyclic olefin copolymer,

Tc is the crystallization temperature of the cyclic olefin copolymer, and T_m is the melting point of the cyclic olefin copolymer.

[0006] In a second general aspect, this disclosure provides a foam obtainable by the process according to the present invention.

[0007] In a third general aspect, this disclosure provides the use of the foam according to the present invention in construction, insulation, cushion, protection foam or as rigid structure foam.

[0008] Certain aspects of the first, second, and third general aspects may include one or more of the following features.

[0009] In some aspects, the cyclic olefin copolymer is amorphous and the foaming temperature is in the range from about T_g + 10°C to about T_{solid-liquid point} +5°C.

[0010] In some aspects, the cyclic olefin copolymer is amorphous and the foaming temperature is in the range from about T_g + 15°C to about T_{solid-liquid point}, preferably from about T_g + 20°C to about T_{solid-liquid point} - 2°C, more preferably from about T_g + 25°C to about T_{solid-liquid point} - 5°C.

[0011] In some aspects, the cyclic olefin copolymer is semi-crystalline and the foaming temperature is in the range from about T_c +10°C to about T_m +5°C.

[0012] In some aspects, the cyclic olefin copolymer is semi-crystalline and the foaming temperature is in the range from about T_c +15°C to about T_m + 2°C.

[0013] In some aspects, the cyclic olefin copolymer is semi-crystalline and the foaming temperature is in the range from about T_c +20°C to about T_m, preferably from about T_c +20°C to about T_m-2°C.

[0014] In some aspects, the pressure in step (l) is in the range from about 3 MPa to about 30 MPa, preferably from about 5 MPa to about 25 MPa, more preferably from about 9 MPa to about 20 MPa, provided that a supercritical fluid is used in step (i).

[0015] In some aspects, the treating time in step (i) is at least 5 minutes, preferably at least 20 minutes, more preferably at least 25 minutes.

[0016] In some aspects, the polymer composition is in the form of sheet.

[0017] In some aspects, the polymer composition is in the form of bead.

[0018] In some aspects, water is additionally added in the treatment of step (i).

[0019] In some aspects, the average particle size of the bead is in the range from about

2 mm to about 2 cm. [0020] In some aspects, the cyclic olefin copolymer is amorphous and the loss factor tan d of the cyclic olefin copolymer at the foaming temperature is in the range from about 0.3 to about 0.7, preferably from about 0.35 to about 0.65; or the cyclic olefin copolymer is semi- crystalline and the foaming temperature is in the range from about T_m-20°C to about T_m + 10°C, preferably from about T_m -10°C to about T_m + 5°C, more preferably from about T_m -5°C to about Tm + 5°C.

[0021] In some aspects, the cyclic olefin copolymer is amorphous and the complex viscosity of the cyclic olefin copolymer at the foaming temperature and 1 Hz is in the range from about 3x10⁴ Pa·s to about 2x10⁵ Pa·s, preferably from about 4x10⁴ Pa·s to about 1x10⁵ Pa·s.

[0022] In some aspects, the amount of the supercritical fluid is in the range from about 1 wt.% to about 90 wt.%, preferably from about 1.5 wt.% to about 25 wt.%, more preferably from about 1.5 wt.% to about 10 wt.%, based on the total weight of the polymer composition and the supercritical fluid.

[0023] In some aspects, the supercritical fluid is selected from carbon dioxide, water, C₁- C₆-alkane, ethylene, propylene, methanol, ethanol, acetone, nitrogen, or a combination thereof. [0024] In some aspects, the expansion ratio is at least 3, preferably at least 4.

[0025] In some aspects, the cyclic olefin copolymer comprises cyclic olefin monomer units in an amount of from about 3 mol.% to about 70 mol.%, preferably from about 5 mol.% to about 65 mol.%, more preferably from about 5 to about 15 mol.% or from about 20 to about 65 mol.% based on the total amount of monomer units in the copolymer.

[0026] In some aspects, the cyclic olefin copolymer comprises cyclic olefin monomer selected from the group consisting of norbomene, tetracyclododecene, cyclopentene, dicyclopentadiene, ethyhdene norbomene, vinyl norbomene, cyclooctene, and cyclooctadiene. [0027] In some aspects, the cyclic olefin copolymer comprises at least one monomer other than the cyclic olefin monomer, which is selected from ethylene and a-olefin monomer.

[0028] In some aspects, the a-olefin monomer is selected from 1-propene, 1-butene, 1- hexene and 1-octene.

[0029] In some aspects, the process is carried out in batch mode or continuously.

[0030] In some aspects, the process is carried out in batch mode and step (ii) is carried out by dropping the pressure and the pressure drop rate in step (ii) is in the range from about 5 MPa/s to about 600 MPa/s, preferably from about 8 MPa/s to about 200 MPs/s.

[0031] In some aspects, the complex viscosity of the cyclic olefin copolymer, measured at about its melting temperature and 1 Hz, is from about 0.5x 10⁴ Pa·s to about 1.2x10⁵ Pa·s. [0032] In some aspects, the process additionally comprises subjecting the cyclic olefin copolymer to vacuum before step (i).

[0033] In some aspects, the density of the foam is in the range from about 0.03 g/cm³ to about 0.5 g/cm³, preferably from about 0.035 g/cm³ to about 0.4 g/cm³, more preferably from about 0.035 g/cm³ to about 0.3 g/cm³.

[0034] In some aspects, the foam has a tensile strength in the range from about 0.5 MPa to about 3 MPa and/or an elongation at break in the range from about 300% to about 900%.

DESCRIPTION OF THE DRAWING [0035] Figures 1A, 1B, and 1C (collectively referred to as Figure 1 below) shows the

Dynamical mechanical analysis of TOP AS™ 9903D-10, 9506F-500 and 5013F-04.

[0036] Figures 2A, 2B, and 2C (collectively referred to as Figure 2 below) shows the complex viscosities ofTOPAS™ 9903D-10, 9506F-500 and 5013F-04.

[0037] Figure 3 shows DSC curve ofTOPAS™ E-140. [0038] Figures 4A, 4B, and 4C (collectively referred to as Figure 4 below) shows the foaming temperature and corresponding expansion ratio at pressure drop rate around 10 MPa/s in example 1.

[0039] Figure 5 shows the density curve of the foam beads as a function of foaming temperature in example 2. [0040] Figure 6 shows the photos of the COC 5013F-04 foam beads obtained at different foaming temperature in example 2.

[0041] Figure 7 shows SEM images of the COC 5013F-04 foam beads (ER=28) in example 2.

[0042] Figure 8 shows the photo of foam sample obtained by extmsion foaming process (die temperature is 180°C, CO₂ content is 2 wt.%) in example 3.

[0043] Figure 9 shows SEM images of foam sample obtained by extrusion foaming process (die temperature is 180°C, CO₂ content is 2 wt.%) in example 3.

[0044] Figure 10 shows the density curve of the foam beads obtained in example 4 as a function of foaming temperature. [0045] Figure 11 shows the photos of the COC E-140 foam beads obtained at different foaming temperature in example 4.

[0046] Figure 12 shows SEM images of the COC E-140 foam beads (ER=19.6) in example 4. [0047] Figure 13 shows the foaming temperature and corresponding density of the foam samples obtained in example 5.

[0048] Figure 14 shows dynamical mechanical analysis of TOP AS™ E-140.

[0049] Figure 15 shows the tensile specimen and its size.

DETAILED DESCRIPTION OF THE INVENTION

[0050] Various specific embodiments, versions, and examples are described herein; including exemplary embodiments and definitions that are adopted for purposes of understanding the claimed invention. While the following detailed description gives specific preferred embodiments, those skilled in the art will appreciate that these embodiments are exemplary only and that the invention can be practiced in other ways. For purposes of determining infringement, the scope of the invention will refer to any one or more of the appended claims, including their equivalents, and elements or limitations that are equivalent to those that are recited. Any reference to the “invention” may refer to one or more, but not necessarily all, of the inventions defined by the claims.

[0051] As used herein, the term “copolymer” is meant to include polymers having two or more monomers, optionally, with other monomers, and may refer to interpolymers, terpolymers, etc. The term “polymer” as used herein includes, but is not limited to, homopolymers, copolymers, terpolymers, etc., and alloys thereof. The term “polymer” as used herein also includes impact, block, graft, random, and alternating copolymers. The term “polymer” shall further include all possible geometrical configurations unless otherwise specifically stated. Such configurations may include isotactic, syndiotactic and atactic symmetries.

[0052] A supercritical fluid means a substance at a temperature and pressure above its critical point, where distinct liquid and gas phases do not exist. The density of the supercritical fluid is close to liquid, but its viscosity is lower than liquid and its diffusion rate is faster than liquid.

[0053] The glass transition temperature (T_g) can be measured by DMA (dynamic mechanical analysis).

[0054] T_{solid-liquid point} is the temperature of solid-liquid transition point of the cyclic olefin copolymer. T_{solid-liquid point} of the cyclic olefin copolymer can also be measured by DMA. [0055] Tc is the crystallization temperature of the cyclic olefin copolymer. T_c can be measured by DSC (differential scanning calorimetry).

[0056] T_m is the melting point of the cyclic olefin copolymer. T_m can be measured by DSC. [0057] In one embodiment of the process according to the present invention, the cyclic olefin copolymer is amorphous and the foaming temperature is in the range from about T_g + 10°C tO about Tsolid-liquid point ^“t5°C, e.g., from about Tg + 15°C to about T_{solid-liquid point} +5°C. from about T_g + 20°C to about T_{solid-liquid point} +5°C, from about T_g + 25°C to about T_soiid-iiquid point +5°C, from about T_g + 30°C to about T_{solid-liquid point} +5°C, from about T_g + 35°C to about T_{solid-liquid point} 3 ( . from about T_g + 10 C to about T_{solid-liquid point}, from about T_g + 15 C to about T_{solid-liquid point}, from about Tg + 20°C to about T_soiid-uq_Uid point, from about T_g + 25°C to about T_{solid-liquid point}, from about T_g + 30°C to about T_{solid-liquid point}, from about T_g + 35°C to about T_{solid-liquid point}; from about T_g + 10°C to about T_{solid-liquid point} -2°C, from about T_g + 15°C to about T_Soiid-iiquid point - 2°C, from about T_g + 20°C to about T_{solid-liquid point} - 2°C, from about Tg Ί" 25 C tO about T_{solid-liquid point} - 2 C, from about Tg + 30 C tO about Tsolid-liquid point " 2 C, from about T_g + 35°C to about T_{solid-liquid point} - 2°C; from about T_g + 10°C to about T_soiid-iiquid point -5°C, from about T_g + 15°C to about T_{solid-liquid point} - 5°C, from about Tg + 20°C to about T_{solid-liquid point} - 5°C, from about T_{g '} 25°C to about T_{solid-liquid point} - 5°C, from about Tg ' 30°C tO about Tsolid-liquid point " 5 C, OG from about Tg + 35 C tO about Tsolid-liquid point " 5 C.

[0058] In one embodiment of the process according to the present invention, the cyclic olefin copolymer is semi-crystalline and the foaming temperature is in the range from about T_c +10°C to about T_m +5°C, e.g., from about T_c +15°C to about T_m +5°C, from about T_c +20°C to about T_m +5°C; from about T_c +10°C to about T_m +4°C, from about T_c +15°C to about T_m +4 C, from about T_c +20°C to about T_m +4°C; from about T_c +10°C to about T_m +3°C, from about T_c +15°C to about T_m +3°C, from about T_c +20°C to about T_m +3°C; from about T_c +10°C to about T_m +2°C, from about T_c +15°C to about T_m +2°C, from about T_c +20°C to about T_m+2°C; from about T_c +10°C to about T_m +1°C, from about T_c +15°C to about T_m +1°C, from about Tc +20°C to about T_m +1°C; from about T_c +10°C to about T_m, from about T_c +15°C to about Tm, from about T_c +20°C to about T_m; from about T_c +10°C to about T_m-2°C, from about Tc +15°C to about T_m-2°C, or from about T_c +20°C to about T_m-2°C.

[0059] In one embodiment of the process according to the present invention, the pressure in step (i) in the process of the present invention is in the range from about 3 MPa to about 30 MPa, preferably from about 5 MPa to about 25 MPa, more preferably from about 9 MPa to about 20 MPa, provided that a supercritical fluid is used in step (i).

[0060] In one embodiment of the process according to the present invention, the treating time in step (i) is at least 5 minutes, at least 20 minutes, or at least 25 minutes. Usually, the treating time is no more than 5 hours, for example no more than 4 hours, no more than 3 hours, or no more than 2 hours.

[0061] In one embodiment of the process according to the present invention, the polymer composition is in the form of sheet. The sheet can be produced by using a compressing molding machine.

[0062] In another embodiment of the process according to the present invention, the polymer composition is in the form of bead. The average particle size of the bead is in the range from about 2 mm to about 2 cm.

[0063] Water can be additionally added in the treatment of step (I), especially when the polymer composition is in the form of bead.

[0064] In one embodiment of the process according to the present invention, the cyclic olefin copolymer is amorphous and the loss factor tan δ of the cyclic olefin copolymer at the foaming temperature is in the range from about 0.3 to about 0.7, for example from about 0.31 to about 0.69, from about 0.32 to about 0.68, from about 0.33 to about 0.67, from about 0.34 to about 0.66, from about 0.35 to about 0.65, from about 0.36 to about 0.64, from about 0.37 to about 0.63, from about 0.38 to about 0.62, from about 0.39 to about 0.61, from about 0.4 to about 0.6. Elastic modulus (G ) and the viscous modulus (G”) of the polymer can be tested by rheology, e.g. DMA, for example by using an ARES-G2 rheometer (TA Instruments) with 8 mm parallel plates geometry. DMA can be performed in temperature range of 200 to 25°C with cooling rate 5°C/min, strain amplitude controlled in linear region, and frequency at 1 Hz. The complex viscosity of the polymer sample is determined as a square root of the sum of (G’)² and (G”)²· The loss factor tan d was determined as G”/G’.

[0065] In one embodiment of the process according to the present invention, the cyclic olefin copolymer is semi-crystalline and the foaming temperature is in the range from about Tm-20°C to about T_m+10°C, for example from about T_m-18°C to about T_m + 9°C, from about T_m-16°C to about T_m + 8°C, from about T_m-14°C to about T_m + 7°C, from about T_m-12°C to about Tm + 6°C, from about T_m-10°C to about T_m+5°C, from about T_m-8°C to about T_m + 5°C, from about T_m-5°C to about T_m + 5°C.

[0066] In one embodiment of the process according to the present invention, the cyclic olefin copolymer is amorphous and the complex viscosity of the cyclic olefin copolymer at the foaming temperature and 1 Hz is in the range from about 3x10⁴ Pa·s to about 2x10⁵ Pa·s, from about 4x10⁴ Pa·s to about 1x10⁵ Pa·s. The complex viscosity can be measured by rheology, for example DMA. [0067] In one embodiment of the process according to the present invention, the supercritical fluid can be selected from carbon dioxide, water, C₁-C₆-alkane, ethylene, propylene, methanol, ethanol, acetone, nitrogen, or a combination thereof, preferably carbon dioxide.

[0068] The supercritical fluid is typically added to the polymer composition in an amount sufficient to make a foam. In one example, an amount of supercritical fluid is from about 1 wt.% to about 90 wt.%, from about 1 wt.% to about 75 wt.%, from about 1 wt.% to about 50 wt.%, from about 1 wt.% to about 25 wt.%, from about 1 wt.% to about 10 wt.%, from about 1 wt.% to about 2.5 wt.%, from about 1.5 wt.% to about 2.5 wt.%, from about 1.5 wt.% to about 5 wt.%, from about 5 wt.% to about 75 wt.%, from about 5 wt.% to about 50 wt.%, or from about 5 wt.% to about 25 wt.%, based on the total weight of the polymer composition and the supercritical fluid.

[0069] In some aspects, the amount of supercntical fluid is sufficient to diffuse into the cyclic olefin copolymer to produce a homogenous composition. The amount of supercritical fluid can be altered to obtain a foam with the desired properties, such as density, stiffness, and cell content.

[0070] In some aspects, two or more supercritical fluids are used in step (i) of the process according to the present invention. In one example, the supercritical fluid includes carbon dioxide and a hydrocarbon (preferably C₁-C₆-alkane, ethylene, propylene). In another example, the supercritical fluid includes nitrogen and/or carbon dioxide.

[0071] In one embodiment of the process according to the present invention, the expansion ratio is at least 3, or at least 4, for example 5, 8, 10, 15, 20, 25, 30. The expansion ratio means the ratio of the volume of the polymer composition after foaming to the volume of the polymer composition before foaming.

[0072] In some aspects, the cyclic olefin copolymer includes cyclic olefin monomer units in an amount of from about 3 mol.% to about 70 mol.% based on the total amount of monomer units in the copolymer. For example, the cyclic olefin copolymer can include cyclic olefin monomer units in an amount of from about 5 mol.% to about 65 mol.%, preferably from about 5 mol.% to about 15 mol.%, from about 6 mol.% to 12 mol.% or from about 20 mol.% to about 65 mol.%, from about 20 mol.% to about 30 mol%, from about 30 mol.% to about 40 mol.%, from about 40 mol.% to about 50 mol.%, or from about 45 mol.% to about 55 mol.% based on the total amount of monomer units in the copolymer.

[0073] In some aspects, the cyclic olefin monomer has the formula:

wherein each R¹ is independently selected from H and C_1-6 alkyl; and each R² is independently selected from H, C_1-6 alkyl, C_1-6 alkenyl, and C_1-6 alkylidene. In the alternative, any two R² together with the carbon atoms to which they are attached form a C_3-8 cycloalkyl ring or C_3-8 cycloalkenyl ring, each of which is optionally substituted with 1 or 2 R²; or any two R², when attached to adjacent carbon atoms, form a bond (i.e., there is a double bond between the two adjacent carbon atoms).

[0074] Suitable examples of cyclic olefin monomers include norbomenes, tetracyclododecene, cyclopentene, dicyclopentadiene, cyclooctene, and cyclooctadiene. Suitable examples of norbomenes include bicyclo[2.2.1]hept-2-ene, ethylidene norbomene, and vinyl norbomene.

[0075] In some aspects, the cyclic olefin monomer is selected from any one of the following compounds:

In some aspects, the cyclic olefin monomer is a norbomene of formula [0076] In some aspects, the cyclic olefin copolymer comprises at least one monomer other than the cyclic olefin monomer, which is selected from ethylene and a-olefm monomer. In some aspects, the cyclic olefin copolymer includes ethylene monomer unit. In such aspects, the cyclic olefin copolymer can include ethylene monomer units in an amount from about 30 mol.% to about 95 mol.% based on the total amount of monomer units in the copolymer. For example, the cyclic olefin copolymer can include ethylene monomer units in an amount from about 35 mol.% to about 95 mol.%, preferably from 35 mol.% to about 90 mol.%, from about 85 mol.% to about 95 mol.%, from about 88 mol.% to about 92 mol.% or from about 45 mol.% to about 80 mol.%, from about 70 mol.% to about 80 mol%, from about 60 mol.% to about 70 mol.%, from about 50 mol.% to about 60 mol.%, or from about 45 mol.% to about 55 mol.% based on the total amount of monomer units in the copolymer.

[0077] In some aspects, the cyclic olefin copolymer includes at least one a-olefm monomer. Suitable examples of an a-olefm monomer include 1-propene, 1 -butene, 1 -hexene, and 1- octene. In one example, the cyclic olefin copolymer includes an a-olefm monomer units in an amount from about 1 mol.% to about 5 mol.%, or from about 1 mol.% to about 10 mol.% based on the total amount of monomer units in the copolymer.

[0078] The cyclic olefin copolymer can be branched or linear. For example, the cyclic olefin copolymer can have from 2 to 100 termini (e.g., 2 to 80, 2 to 75, 2 to 60, 2 to 50, 2 to 40, 2 to 35, 2 to 25, 2 to 10, 2 to 5, 4 to 20, 5 to 25, 10 to 50, 25 to 75, 3 to 6, 5 to 15 termini). In some aspects, the cyclic olefin copolymer is branched and has from 3 to 5, 4 to 6, 5 to 6, or 3 to 6 termini. In some aspects, the cyclic olefin copolymer is linear and therefore has 2 termini. [0079] The weight-average molecular weight (M_w) of the cyclic olefin copolymer can be between about 1,000 Da and about 250,000 Da. For example, the cyclic olefin copolymer can have an M_w of about 200,000 Da, about 195,000 Da, about 190,000 Da, about 185,000 Da, about 180,000 Da, about 175,000 Da, about 170,000 Da, about 165,000 Da, about 160,000 Da, about 155,000 Da, about 150,000 Da, about 145,000 Da, about 140,000 Da, about 135,000 Da, about 130,000 Da, about 125,000 Da, about 120,000 Da, about 115,000 Da, about 100,000 Da, about 90,000 Da, about 80,000 Da, about 70,000 Da, about 60,000 Da, about 50,000 Da, about 40,000 Da, about 30,000 Da, about 20,000 Da, and about 10,000 Da. The polydispersity index (PDI) (M_w/M_n) of the cyclic olefin copolymer can be between about 1.50 and about 3.00. For example, the cyclic olefin copolymer can have a PDI of about 2.95, about 2.90, about 2.85, about 2.80, about 2.75, about 2.70, about 2.65, about 2.60, about 2.55, about 2.50, about 2.45, about 2.40, about 2.35, about 2.30, about 2.25, about 2.20, about 2.15, about 2.10, about 2.05, about 2.00, about 1.90, about 1.80, about 1.70, about 1.60, or about 1.50.

[0080] In some aspects, the cyclic olefin copolymer is amorphous. As used herein, the term “amorphous” refers to a solid polymer in which the arrangement of polymer molecules is random and lacks the order characteristic of a crystal.

[0081] In certain aspects, the cyclic olefin copolymer is semi-crystalline. As used herein, the term “semi-crystalline” refers to a solid polymer containing areas of cry stallinity, in which the polymer matenal exhibits organized and tightly packed molecular chains. For example, the degree of crystallinity of the polymer is from about 1% to about 20%, from about 5% to about 15%, or from about 10% to about 40%. The cry stallinity of a polymer sample may be determined, for example, as a ratio of melting enthalpy of the polymer sample to the melting enthalpy of fully crystalline polymer, wherein the melting enthalpies are determined using differential scanning calorimeter (DSC) analysis. [0082] The crystallinity temperature of the cyclic olefin copolymer may be from about 40°C to about 100°C, or from about 70°C to about 95°C, as measured at atmospheric pressure using, for example, DSC analysis.

[0083] The melting point of the cyclic olefin copolymer may be from about 60°C to about 210°C, for example from about 70°C to about 200°C, from about 70°C to about 100°C, from about 120°C to about 200°C, or from about 130°C to about 200°C.

[0084] The glass-transition temperature of the cyclic olefin copolymer may be from about -20°C to about 180°C, or from about -10°C to about 170°C, for example from about 0°C to about 160°C, from about 0°C to about 30°C, from about 40°C to about 160°C, from about 50°C to about 150°C, from about 60°C to about 140°C, from about 70°C to about 130°C, or from about 80°C to about 120°C.

[0085] The T_{solid-liquid point} of the cyclic olefin copolymer may be from about 60°C to about 210°C, for example from about 70°C to about 200°C, from about 70°C to about 100°C, from about 120°C to about 200°C, or from about 130°C to about 200°C.

[0086] In some aspects, the density of the cyclic olefin copolymer is from about 0.8 g/cm³ to about 1 g/cm³, measured at atmospheric pressure, for example, by dividing mass of the polymer sample by its volume. For example, the density of the cyclic olefin copolymer is about 0.8 g/cm³, about 0.85 g/cm³, about 0.9 g/cm³, or about 0.95 g/cm³.

[0087] In some aspects, the complex viscosity of the cyclic olefin copolymer, measured at about its melting temperature and lHz, is from about 0.5x10⁴ Pa·s to about 1.2x10⁵ Pa·s, for example from about 0.6x10⁴ Pa·s to about 8x10⁴ Pa·s, or from about 0.8x10⁴ Pa·s to about 5x 10⁴ Pa·s. The complex viscosity can be measured by rheology, for example DMA.

[0088] In some aspects, the following holds: the cyclic olefin copolymer is a copolymer containing norbomene monomer units and ethylene monomer units; the amount of norbomene monomer units is from about 3 mol. % to about 60 mol. % based on the total amount of monomer units in the cyclic olefin copolymer; the cyclic olefin copolymer is amorphous or semi- crystalline with crystallinity from about 10% to about 35%, the crystallinity temperature of the cyclic olefin copolymer is from about 40°C to about 100°C; the glass-transition temperature of the cyclic olefin copolymer is from about -20°C to about 180°C; the melting point of the cyclic olefin copolymer is from about 60°C to about 210°C; the density of the cyclic olefin copolymer is from about 0.8 g/cm³ to about 1 g/cm³; and the complex viscosity of the cyclic olefin copolymer, measured at about its melting temperature and 1 Hz, is from about 0.5 x 10⁴ Pa·s to about 1.2x10⁵ Pa·s. [0089] In some aspects, the cyclic olefin copolymer is any one of the cyclic olefin copolymers described in US patent No. 9,982,081 or US patent publication No. 2018/0291128, which are incorporated herein by reference in their entirety. The cyclic olefin copolymer can be prepared by any one of the processes described in these documents. In one example, the cyclic olefin copolymer can be produced by a gas-phase polymerization process using a heterogeneous catalyst. In another example, the cyclic olefin copolymer can be produced by a solution polymerization process. Suitable examples of polymerization catalysts include Group 4 metallocenes.

[0090] In some aspects, the cyclic olefin copolymer contains at least one monomer containing a polar functional group. Suitable examples of such polar functional groups include hydroxy, aldehyde, acid, amine, amide, anhydride, and urea.

[0091] The cyclic olefin copolymers of this disclosure can possess one or more of numerous advantageous properties. Examples of such properties include good processability, as high melt strength and strong extensional strain hardening, good barrier property, designable modulus and T_g in wide range etc.

[0092] The polymer composition, in addition to the cyclic olefin copolymer, may include at least one additional component. In one example, the additional component is a surfactant. Suitable examples of surfactants include polysiloxanes (e.g., silicone surfactants and ethoxylated polysiloxane), ethoxylated fatty acids, salts of fatty acids, ethoxylated fatty alcohols, salts of sulfonated fatty alcohols, and fatty acid ester sorbitan ethoxylates. The polymer composition may also include a nucleating agent, a pigment, a colorant, a stabilizer, a fragrance, a flame retardant, or an odor masking agent. Such additives may assist in controlling size and amount of foam cells, and enhance stability of the foam.

[0093] In some aspects, step (ii) in the process according to the present invention is carried out using a pressure-drop technique. In this method, the pressure above the treated polymer composition is released such that to create a pressure drop to atmospheric pressure. In some aspects, step (ii) is performed at a pressure drop rate in a range from about 5 MPa/s to about 600MPa/s, for example from about 5 MPa/s to about 400MPa/s, from about 5 MPa/s to about 200MPa/s, from about 5 MPa/s to about lOOMPa/s, from about 5 MPa/s to about 50MPa/s, from about 5 MPa/s to about 20MPa/s, from about 8 MPa/s to about 400MPa/s, from about 8 MPa/s to about 200MPa/s, from about 8 MPa/s to about lOOMPa/s, from about 8 MPa/s to about 50MPa/s, from about 8 MPa/s to about 20MPa/s, from about 50 MPa/s to about 400MPa/s, from about 80 MPa/s to about 200MPa/s, from about 80 MPa/s to about 150MPa/s. [0094] The process according to the present invention can be carried out in batch mode or continuously.

[0095] In the batch mode, the cyclic olefin copolymer and supercritical fluid can be added to the autoclave, heated to the foaming temperature and maintained for designed time. After that, the pressure is released to obtain the foam. Alternatively, the autoclave can be heated to the foam temperature and then the cyclic olefin copolymer and supercntical fluid are added. [0096] When the process according to the present invention is carried out continuously, the cyclic olefin copolymer and supercritical fluid can be mixed in an extruder and then be extruded through die at the foaming temperature to obtain the foam. The cyclic olefin copolymer can be mixed with the supercritical fluid in the extruder at a temperature higher than T_m or T_soiid- liquid point of the COC.

[0097] A further aspect of the present invention is directed to a foam of the cyclic olefin copolymer obtainable by the process of the present invention. The density of the foam can be in the range from about 0.03 g/cm³ to about 0.5 g/cm³, from about 0.035 g/cm³ to about

0.4 g/cm³, from about 0.035 g/cm³ to about 0.35 g/cm³, from about 0.035 g/cm³ to about

0.3 g/cm³, from about 0.035 g/cm³ to about 0.2 g/cm³, from about 0.035 g/cm³ to about

0.1 g/cm³, from about 0.035 g/cm³ to about 0.08 g/cm³; from about 0.05 g/cm³ to about

0.5 g/cm³, from about 0.05 g/cm³ to about 0.4 g/cm³, from about 0.05 g/cm³ to about 0.3 g/cm³, from about 0.05 g/cm³ to about 0.2 g/cm³; from about 0.1 g/cm³ to about 0.5 g/cm³; from about 0.1 g/cm³ to about 0.4 g/cm³; or from about 0.1 g/cm³ to about 0.3 g/cm³. The density can be determined using a density kit according to ASTM D792 protocol.

[0098] The Shore A hardness of the foam according to the present invention can be in the range from about 40 to about 95, or from about 60 to about 90. The hardness can be measured according to ASTM D2240, for example by using an Asker A Durometer.

[0099] The foam according to the present invention has a tensile strength in the range from about 0.5 MPa to about 3 MPa and/or an elongation at break in the range from about 300% to about 900%. For example, the tensile strength of the foam can be in the range from about 0.8 MPa to about 2.5 MPa, from about 0.8 MPa to about 2.0 MPa, from about 0.8 MPa to about 1.5 MPa, from about 1.0 MPa to about 2.5 MPa, or from about 1.5 MPa to about 2.5 MPa. For example, the elongation at break of the foam can be in the range from about 300% to about 800%, from about 300% to about 700%, from about 300% to about 600%, from about 300% to about 500%, from about 400% to about 800%, from about 500% to about 800%, from about 600% to about 800%, or from about 400% to about 600%. [0100] The foam of the cyclic olefin copolymer according to the present invention has uniform cell. The average size of the cells of the foam can be in the range from about 20 μm to about 300 μm, from about 30 μm to about 250 μm, from about 50 μm to about 200 μm, from about 50 μm to about 150 μm, or from about 150 μm to about 250 μm, as determined, for example, using an optical microscope or a scanning electron microscope (SEM). The cell size can be determined, for example, according to ASTM D3576-98 protocol.

[0101] A further aspect of the present invention is directed to the use of the foam obtainable according to the process of the present invention in construction, insulation, cushion, protection foam and as rigid structure foam. [0102] The process of foaming cyclic olefin copolymer with the supercritical fluid according to the present invention is a cheap, simple, stable and recyclable process, shows wide foaming temperature and high expansion ratio and the resulted foam has high cell count, good mechanical properties and hardness and uniform cell size distribution.

Examples Materials and sample preparation

[0103] The cyclic olefin copolymers (TOPAS™ 5013F-04, 9506F-500, 9903D-10 and E- 140) used for foam preparation are commercially available from TOPAS Advanced Polymers. The properties of these copolymer are given in Table 1.

Table 1. Characteristics of COC

[0104] Dynamical mechanical analysis (DMA) of TOPAS™ 9903D-10, 9506F-500 and 5013F-04 were shown in Figure 1. The complex viscosities of TOPAS™ 9903D-10, 9506F- 500 and 5013F-04 were shown in Figure 2, respectively. Elastic modulus (G’) and the viscous modulus (G'') of the tested polymer sample were measured using an ARES-G2 rheometer (TA Instruments) with 8 mm parallel plates geometry, by the DMA test. DMA was performed in temperature range of 200 to 25°C with cooling rate 5°C/min, strain amplitude controlled in linear region, and frequency at 1 Hz. The complex viscosity of the polymer sample is determined as a square root of the sum of (G’)² and (G”)². The loss factor tan d of the polymer sample was determined as G”/G' In the curve of loss factor tan d vs temperature, the peak temperature corresponds to T_g and the temperature when tan d = 1 after rubber plateau corresponds to Tsoiid-Uquid point (i.e. if there are more than one point with tan d = 1 in the curve, T_{solid-liquid point} corresponds to the highest temperature at which tan d = 1).

[0105] The melting temperatures (T_m) and crystallization temperatures (T_c) of copolymers were measured using differential scanning calorimeter DSC 8000 (PerkinElmer) according to the following procedure. After the sample was installed, the system was vacuumed for 5 minutes. Each sample was heated from room temperature (ca. 23°C) during a first heating cycle at a constant heating rate of 10°C/min to 200°C in order to erase the thermal history of the polymer, held for approximately 3-5 minutes, then cooled at a constant cooling rate of 10°C/min to 20°C, held for approximately 3-5 minutes, then reheated at a constant heating rate of 10°C/min to 200°C for a second heating cycle. During the cooling and heating processes, the crystallization and melting patterns of the samples were recorded. The melting point and crystallization temperature were determined based on the second heating cycle in the DSC thermogram. DSC scan were obtained in J/g.

[0106] The DSC curve of TOPAS™ E-140 was shown in Figure 3.

[0107] The supercritical fluid used in the foaming experiments was CO₂.

General protocol for the foaming process Batch foaming process 1:

[0108] The batch foaming process 1 was carried out in an autoclave (500ml) with supercritical fluid CO₂. The autoclave was heated to a set temperature, and then a COC sheet sample ( 1 cm* lcm* lmm) was placed in the autoclave, CO₂ then was injected to purge air out of the autoclave for lmin, then the autoclave was sealed and locked, the vacuum pump and the corresponding valve were opened, the gas was exhausted, and the high pressure CO₂ was injected to target pressure (15MPa) to make CO₂ in supercritical phase. The sample then saturated in CO₂ for certain time (30 minutes). Then the pressure was quickly released under designed pressure drop rate (controlled by metering valve), and the foam was taken out and weighted.

Batch foaming process 2:

[0109] COC Pellets were put in a 2mm-thick mold and heated in a compression molding machine for melting. The resulted product was cut into 2cmx2cm sheets and put into the autoclave (600 ml). Then the CO₂ gas was pumped into the autoclave until the pressure was slightly lower than the target pressure. The temperature was increased in around 2°C/min to reach the target temperature. If the pressure was still lower than the target pressure, more CO₂ was added until pressure reached the target pressure. The temperature and pressure were maintained for 30 minutes for saturation. After that, the outlet valve of the autoclave was opened quickly to trigger a rapid pressure release and thus the sheets were foamed.

Bead foaming process:

[0110] Pellets, i.e., beads (the average diameter is around 1 to 2 cm) of COC and water were enclosed in a high pressure stainless vessel (3 L) equipped with a heating system. The water was used as a heat transfer medium. Under an appropriate stirring speed (200r/min), CO₂ was charged into the vessel to reach to a pressure lower than the target pressure. Then the vessel was heated to a target temperature and additional CO₂ was added to reach the target pressure as shown in table 4 and table 9 below. The heating process took 30 minutes to 60 minutes depending on the target temperature. After that, the depressurization occurred by opening the shut-off value and bead foams were obtained in a collection device. Extrusion foaming ( continuous process):

[0111] Extrusion foaming was carried out by using twin extruder (ZE25Ax30, Berstorff) and melt cooler system, wherein the melt cooler system was located between the extruder and the rod die. From hopper to die, the extruder was separated into 6 zones. Zone 1 was located under hopper and COC was charged from the hopper. Zone 2 and zone 3 were solid and melting zone. In Zone 4, CO₂ was injected. At zone 5 and 6, polymer melted and CO₂ were mixed to form a single phase solution. Melt cooler was connected with extruder and its temperature was controlled by three oil temperature controllers. The temperature of melt cooler was slightly lower than the temperature of zone 6. The screw speed was 180 rμm, the output was 3 kg/h, the rod die diameter was 2 mm, and the CO₂ content was selected to be 2 wt.%, 3 wt.%, or 4 wt.% based on the total weight of cyclic olefin copolymer and CO₂.

Methods for characterizing foams

[0112] Various properties of foam samples were determined (an average value was taken over three-time measurements). Table 2 summarizes the properties, as well as apparatuses and base protocols that were used to determine these properties. Table 2. Measured properties, apparatuses, and protocols

[0113] The density (p) of a solid foam sample were calculated using the following equations, where W is the weight and V is the volume of the sample: ρ≡W/V .

[0114] The volume of irregularly shaped foam samples was determined by Archimedes principle, by measuring buoyancy force upon submerging the foam sample into water. According to Archimedes principle, density of the foam sample can be determined according to the following equation, where po is the density of water at the test temperature and WB is apparent immersed weight:

[0115] The cell size of the foam was determined using a scanning electron microscope (SEM) and a carefully fractured or sliced foam sample cross-section according to ASTM D3576-98 protocol. Scanning electron microscope (FEI Quanta 450) were used for this measurement. The cell size was estimated by assuming that the foams were isotropic with a uniform distribution of spherical bubbles in all directions.

Example 1 - Batch foaming process by using TOP AS™ 5013F-04. 9506F-500. 9903D-10 [0116] The foaming of TOP AS™ 5013F-04, 9506F-500, 9903D-10 COC is earned out according to batch foaming process 1. In example 1 , foaming temperature is vaned to explore the temperature-dependent expansion ratio at pressure drop rate around 10 MPa/s. The foaming temperature and corresponding expansion ratio at pressure drop rate around 10 MPa/s in example 1 are shown in table 3 and figure 4. Table 3. The foaming temperature and corresponding expansion ratio at pressure drop rate around 10 MPa/s

[0117] By comparing foaming temperature with COC viscosities, storage modulus G'/loss modulus G” and loss factor tan δ. For the amorphous COC, it can be found that suitable foaming temperature, T_high related to the temperature of solid-liquid transition point (G’=G”) while T_low related to T_g. In addition, foam samples with high expansion ratio exhibit a suitable range of their rheology properties, that is tan d at the advantageous foaming temperature being in the range from about 0.3 to about 0.7 and/or viscosity (1 Hz) being in the range from about 3x10⁴ Pa·s to about 2x10⁵ Pa·s.

Example 2-Bead foaming process bv using TOP AS™ 5013F-04

[0118] Example 2 is carried out according to bead foaming process by using TOP AS™ 5013F-04. The foaming temperature is varied to explore the temperature-dependent expansion ratio at pressure drop rate around 10 MPa/s. The heating process took around 1 hour. The foaming temperature, the pressure, corresponding expansion ratio and density of the resulted foam beads in example 2 are shown in table 4. Table 4. The foaming temperature, the pressure, corresponding expansion ratio and density of the foam obtained by bead foaming process

[0119] The density curve of the foam beads as a function of foaming temperature in example 2 is shown in figure 5. The photos of the COC 5013F-04 foam beads obtained at different foaming temperature in example 2 are shown in figure 6. SEM images of the COC 5013F-04 foam beads (ER=28) in example 2 are shown in figure 7. The SEM images show high cell density with average cell size roughly around 50-100 μm in diameter and the cell wall is very thin. Example 3-Extrusion foaming process by using TOPAS™ 5013F-04

[0120] Example 3 is carried out according to extrusion foaming process by using TOPAS™ 5013F-04. The foaming temperature is varied to explore the temperature- dependent expansion ratio. The amount of CO₂ is also varied to explore its effect on foaming. [0121] The temperature in different zones of the extruder is shown in table 5. The temperature of oil controllers for the melt cooler and die temperature (corresponding to the foaming temperature), die pressure, the expansion ratio and the apparent density of the resulted foam are shown in table 6 (using 2 wt.% CO₂), table 7 (using 3 wt.% CO₂) and table 8 (using 4 wt.% CO₂).

Table 5. The temperature in different zones of the extruder

Table 6. The temperature of oil controllers for the melt cooler and die temperature, die pressure, the expansion ratio and the apparent density of the resulted foam by using

2 wt.% CO₂

Table 7. The temperature of oil controllers for the melt cooler and die temperature, die pressure, the expansion ratio and the apparent density of the resulted foam by using

3 wt.% CO₂

Table 8. The temperature of oil controllers for the melt cooler and die temperature, die pressure, the expansion ratio and the apparent density of the resulted foam by using

4 wt.% CO₂

[0122] The photo and SEM images of foam sample obtained by extrusion foaming process (die temperature is 180°C, CO₂ content is 2 wt.%) in example 3 are shown in figures 8 and 9, respectively.

[0123] For the extrusion foaming, the foamed samples of high quality are obtained at the temperature of 180 and 185°C with the CO₂ content being 2 wt.%, the cells are dense, the performance will be better, and the entire extrusion process is more stable. With CO₂ content increasing, the suitable foaming temperature decreased and the expansion ratio could be over 10 times.

Example 4-Bead foaming process bv using TOP AS™ E-140

[0124] Example 4 is carried out according to bead foaming process by using TOP AS™ E- 140. The foaming temperature is varied to explore the temperature-dependent expansion ratio at a pressure drop rate around 10 MPa/s. The heating process took around 30 minutes. The foaming temperature, the pressure, corresponding expansion ratio and density of the resulted foam beads in example 4 are shown in table 9.

Table 9. The foaming temperature, the pressure, corresponding expansion ratio and density of the foam obtained by bead foaming process

[0125] The density and expansion ratio curves of the foam beads obtained in example 4 as a function of foaming temperature are shown in figure 10. The photos of the COC E-140 foam beads obtained at different foaming temperature in example 4 are shown in figure 11. SEM images of the COC E-140 foam beads (ER=19.6) in example 4 are shown in figure 12. The SEM images show high cell density with average cell size roughly around 100 to 150 μm in diameter.

Example 5- Batch foaming process 2 by using TOPAS™ E-140

[0126] The foaming of TOPAS™ E-140 COC was carried out according to batch foaming process 2. In example 5, foaming temperature is varied to explore the temperature-dependent expansion ratio at a pressure drop rate around 10 MPa/s. The foaming temperature, corresponding expansion ratio and density of the foam samples obtained in example 5 are shown in table 10 and figure 13.

Table 10. The foaming temperature, pressure, corresponding expansion ratio and density of the foam samples by batch foaming process 2

[0127] Dynamical mechanical analysis of TOPAS™ E-140 is shown in Figure 14. The solid-liquid transition point (G’=G”) of E-140 is around 90°C. Combining the foaming temperature with DSC curves of E-140, it can be found suitable foaming temperature, wherein T_high of the foaming temperature relates to Tm while T_low relates to Tc. In this range, COC shows good elasticity and viscosity balanced, thus leading to good foamability.

[0128] Since the foamed sheets are not very flat directly after foaming, a secondary compression molding of 30 seconds or 60 seconds is applied to flatten them. The densities of the foamed sheets after flattening are shown in table 11 and their mechanical properties are shown in table 12.

Table 11. The densities of the foam sheets after secondary compression molding

Table 12. Tensile strength and elongation at break of E-140 foam sheets with different densities

[0129] The Mechanical properties (tensile strength and elongation at break) of E-140 foam sheets after flattening as shown in table 12 were tested according to IS037: 1994 using a universal tester (Gotech, Taiwan). The tensile specimen is of type 2 and its size is shown in the figure 15. The rate of stretching in the test is 500 mm/min. Example 6- Batch foaming process 2 by using TOPAS™ 5013F-04 [0130] The foaming of TOPAS™ 5013F-04 COC was carried out according to batch foaming process 2. COC 5013F-04 sheet is foamed at 165°C and 15 MPa. The pressure drop rate is around 10 MPa/s. The density of the foamed sheet is 0.094 g/cm³. Since the foamed sheet is not very flat directly after foaming, a secondary compression molding at 150°C for 60 seconds is applied to flatten it. The density of the foamed sheet after flattening is 0.167 g/ cm³ and Shore Hardness thereof is 86.8 ± 1.5 (Shore A, average of five measurement). OTHER EMBODIMENTS

[0131] It is to be understood that while the present application has been described in conjunction with the detailed description thereof, the foregoing description is intended to illustrate and not limit the scope of the present application, which is defined by the scope of the appended claims. Other aspects, advantages, and modifications are within the scope of the following claims.

Claims

Claims What is claimed is:

1. A process of foaming cyclic olefin copolymer with a supercritical fluid, which comprises:

(i) treating a polymer composition with the supercritical fluid at a foaming temperature, wherein the polymer to be foamed in the polymer composition is a cyclic olefin copolymer, and wherein the cyclic olefin copolymer is optionally subject to vacuum before step (i), and

(ii) foaming the treated polymer composition obtained in step (i) to produce a foam, wherein the cyclic olefin copolymer is amorphous and the foaming temperature is in the range from about T_g to about Tsoiid-nquid point + 10°C, or wherein the cyclic olefin copolymer is semi-ciystalline and the foaming temperature is in the range from about T_c to about T_m + 10°C, wherein T_g is the glass transition temperature of the cyclic olefin copolymer,

T soiid-iiquid point is the temperature of solid-liquid transition point of the cyclic olefin copolymer,

Tc is the crystallization temperature of the cyclic olefin copolymer, and Tm is the melting point of the cyclic olefin copolymer.

2. The process according to claim 1, wherein the cyclic olefin copolymer is amorphous and the foaming temperature is in the range from about T_g + 10°C to about T_{solid-liquid point} +5°C , T_g + 15°C to about T_{solid-liquid point}, preferably from about T_g + 20°C to about T_{solid-liquid point} - 2°C, more preferably from about T_g + 25 °C to about T_{solid-liquid point} - 5°C.

3. The process according to claim 1 or 2, wherein the cyclic olefin copolymer is semi- crystalline and the foaming temperature is in the range from about T_c +10°C to about T_m +5°C, preferably from about T_c +15°C to about T_m + 2°C, more preferably about T_c +20°C to about Tm, and more preferably from about T_c + 20°C to about T_m- 2°C.

4. The process according to any of claims 1 to 3, wherein the pressure in step (i) is in the range from about 3 MPa to about 30 MPa, preferably from about 5 MPa to about 25 MPa, more preferably from about 9 MPa to about 20 MPa, provided that a supercritical fluid is used in step (i).

5. The process according to any of claims 1 to 4, wherein the treating time in step (i) is at least 5 minutes, at least 20 minutes, preferably at least 25 minutes.

6. The process according to any of claims 1 to 5, wherein the polymer composition is in the form of sheet or bead, wherein when in the form of a bead, water is additionally added in the treatment of step (i).

7. The process according to claim 6, wherein polymer composition is in the form of a bead and the average particle size of the bead is in the range from about 2 mm to 2 about cm.

8. The process according to any of claims 1 to 7, wherein the cyclic olefin copolymer is amorphous and the loss factor tan d of the cyclic olefin copolymer at the foaming temperature is in the range from about 0.3 to about 0.7, preferably from about 0.35 to about 0.65; or the cyclic olefin copolymer is semi-crystalline and the foaming temperature is in the range from about Tm-20°C to about T_m + 10°C, preferably from about T_m -10°C to about T_m + 5°C, more preferably from about T_m -5°C to about T_m + 5°C.

9. The process according to any of claims 1 to 8, wherein the cyclic olefin copolymer is amorphous and the complex viscosity of the cyclic olefin copolymer at the foaming temperature and 1 Hz is in the range from about 3x10⁴ Pa·s to about 2x10⁵ Pa·s, preferably from about 4x10⁴ Pa·s to about 1x10⁵ Pa·s.

10. The process according to any of claims 1 to 9, wherein the amount of the supercritical fluid is in the range from about 1 wt.% to about 90 wt.%, preferably from about 1.5 wt.% to about 25 wt.%, more preferably from about 1.5 wt.% to about 10 wt.%, based on the total weight of the polymer composition and the supercritical fluid.

11. The process according to any of claims 1 to 10, wherein the supercritical fluid is selected from carbon dioxide, water, C₁-C₆-alkane, ethylene, propylene, methanol, ethanol, acetone, nitrogen, or a combination thereof.

12. The process according to any of claims 1 to 11, wherein the expansion ratio is at least 3, or at least 4, wherein the expansion ratio is the ratio of the volume of the polymer composition after foaming to the volume of the polymer composition before foaming.

13. The process according to any of claims 1 to 12, wherein the cyclic olefin copolymer comprises cyclic olefin monomer units in an amount of from about 3 mol.% to about 70 mol.%, preferably from about 5 mol.% to about 65 mol.%, more preferably from about 5 mol.% to about 15 mol.%, especially from about 20 mol.% to about 65 mol.% based on the total amount of monomer units in the copolymer.

14. The process according to any of claims 1 to 13, wherein the cyclic olefin copolymer comprises cyclic olefin monomer selected from the group consisting of norbomene, tetracyclododecene, cyclopentene, dicyclopentadiene, ethylidene norbomene, vinyl norbomene, cyclooctene, and cyclooctadiene, and wherein the cyclic olefin copolymer comprises at least one monomer other than the cyclic olefin monomer, which is selected from ethylene and a-olefin monomer.

15. The process according to claim 14, wherein the process is carried out in batch mode and step (ii) is carried out by dropping the pressure and the pressure drop rate in step (ii) is in the range from about 5 MPa/s to about 600 MPa/s, preferably from about 8 MPa/s to about 200 MPs/s.

16. The process according to any of claims 1 to 15, wherein the complex viscosity of the cyclic olefin copolymer, measured at about its melting temperature and 1 Hz, is from about 0.5x10⁴ Pa·s to about 1.2x10⁵ Pa·s.

17. A foam obtainable by the process according to any of claims 1 to 16, wherein the density of the foam is in the range from about 0.03 g/cm³ to about 0.5 g/cm³, preferably from about 0.035 g/cm³ to about 0.4 g/cm³, more preferably from about 0.035 g/cm³ to about 0.3 g/cm³, and wherein the foam has a tensile strength in the range from about 0.5 MPa to about 3 MPa and/or an elongation at break in the range from about 300% to about 900%.

18. Use of the foam according to claim 17 in construction, insulation, cushion, protection foam or as rigid structure foam.