WO2009074532A1

WO2009074532A1 - Elastomeric flexibilizer for thermosets

Info

Publication number: WO2009074532A1
Application number: PCT/EP2008/067009
Authority: WO
Inventors: Laurent Gervat; Nicolas Passade-Boupat; Robert J Barsotti
Original assignee: Arkema France
Priority date: 2007-12-10
Filing date: 2008-12-08
Publication date: 2009-06-18
Also published as: TW200938581A

Abstract

The invention relates to elastomeric block copolymers useful as flexibilizers for thermoset materials and in particular for epoxy materials. The elastomeric block copolymers provide a large decrease in the modulus of the epoxy material, without a significant decrease in the Tg of the material. The flexibilizers of the invention form a unique, non-particulate morphology within the thermoset matrix. This unique morphology is found at a use level of below 20 weight percent of the block copolymers.

Description

ELASTOMERIC FLEXIBILIZER FOR THERMOSETS

Field of the Invention:

The invention relates to elastomeric block copolymers useful as flexibilizers for thermoset materials and in particular for epoxy materials. The elastomeric block copolymers impart a large decrease in the modulus of the epoxy material, without a significant decrease in the Tg of the material. The flexibilizers of the invention form a unique, non-particulate morphology within the thermoset matrix. This unique morphology is found at a use level of below 20 weight percent of the block copolymers.

Background of the Invention:

Epoxy resins are a class of thermosetting polymers widely used in structural adhesives, composites, surface coatings, and laminates due to their high strength, low creep, low cure shrinkage, resistance to corrosion, and excellent adhesion. A major shortcoming is the inherent brittle nature of the epoxies in the cured state, as well as their stiffness which inhibits various industrial applications.

Core-shell polymers have been incorporated as a discrete phase of rubber particles into a rigid polymer matrix to provide toughening. Block copolymers, and in particular amphiphilic block copolymers, have also been used to toughen epoxy and other thermoset polymers. The amphiphilic block copolymers (epoxy miscible segment and epoxy immiscible segment) containing a rubbery component toughen epoxy resins through self-assembly of the amphiphilic block prior to epoxy cure. PEO- based amphiphilic block copolymers are described in WO 2006/052727.

Similar self-assembling amphiphilic block copolymers of poly( ethylene oxide) - b-poly(propylene oxide) for use in epoxy resin modification are known (Macromolecules, 2000, 33, 5235-5244.)

US 2004/0247881 describes the use of an amphiphilic block copolymer as an epoxy modifier for a specific class of flame retardant epoxy resin. Examples are given of polyether-based block copolymers and of reactive poly(methyl methacrylate-co-glycidyl methacrylate) -b- poly(2-ethylhexylmetacrylate.

US 2004/0034124 (Arkema) describes the use of SBM, BM, and MBM block copolymers to toughen thermoset materials. The block copolymers are used at levels of from 1-80 percent. In each of these, the epoxy-compatible block makes up at least 50 weight percent of the block copolymer

Each of the epoxy-modifier systems in the art form discrete individual modifier particles in the epoxy - resulting in toughening of the epoxy resin. While these block copolymers of the art can be used to toughen the thermoset (epoxy) materials, they do little to increase the flexibility (decrease the modulus) of the thermoset material. Traditional epoxy "fiexibilizers" are additives which lower the matrix Tg, such as carboxy-terminated butadiene acrylonitrile (CTBN). These materials must be used at high loading levels (around 40%) to provide a large decrease in modulus. At these loading levels, large decreases in the Tg of the eposy matrix occur. Fiexibilizers for epoxy systems are known. These fiexibilizers work by lowering the Tg of the thermoset material. Unfortunately, many applications for epoxy and other thermoset materials require a high Tg - for use at high temperatures. Surprisingly, it has now been found that elastomeric block copolymers, either functionalized or unfunctionalized, can be used to dramatically lower the modulus of thermoset resins, without a significant loss of Tg. These epoxy-modifϊer systems require low (less than 20%) of block copolymer modifier, yet form a continuous polymer phase within the epoxy matrix.

Summary of the Invention: The invention relates to a flexible thermoset composition comprising from 1 to less than 20 weight percent of an elastomeric block copolymer; where the elastomeric block copolymer forms a continuous polymer phase. Preferably the flexible thermoset composition has a modulus that is at least 50 percent lower than that of the unmodified thermoset resin, and the Tg of the thermoset composition is less than 1O⁰C lower than that of the unmodified thermoset resin.

The invention also relates to a process for producing a flexible thermoset composition comprising the step of blending from 1 to less than 20 weight percent of an elastomeric block copolymer into the thermoset resin; where the elastomeric block copolymer forms a continuous polymer phase.

Brief Description of the Drawings

Figures 1 and 2: Are Transmission Electron Microscopy (TEM) and Atomic Force Microscopy (AFM) micrographs of a comparative modified epoxy (Example 1), showing discrete particle morphology.

Figures 3 and 4: Are TEM and AFM micrographs of an epoxy resin modified with the elastomeric block copolymer of the invention (Example 2). Note the continuous polymer phase.

Figure 5: Is a DMA plot showing the large modulus drop in the epoxy composition of the invention, compared to an unmodified epoxy and an epoxy having a block copolymer (comparative) forming particulate domains. Figure 6: Is a DMA plot showing the tan δ of the modified and unmodified epoxies. The maximum value correspond to the δ transition (or glass transition temperature) of the different systems which are all the same

Figures 7, 8, 9 and 10: Are AFM micrographs of an epoxy resin modified with the elastomeric block copolymer of the invention (Example 4). Note the nearly continuous polymer phase.

Figure 11 and 12: Are AFM micrographs of an epoxy resin modified with the elastomeric block copolymer of the invention (Example 5). Note the continuous polymer phase.

Detailed Description of the Invention

The invention relates to elastomeric block copolymers useful as flexibilizers for thermoset materials and in particular for epoxy materials. The elastomeric block copolymers provide a large decrease in the modulus of the epoxy material, without a significant decrease in the Tg of the material. By "block copolymer" as used herein means both true block polymers, which could be di-blocks, tri-blocks, or multiblocks; graft block copolymers or branched block copolymers, also known as linear star polymers; and gradient polymers or gradient block copolymers. Gradient polymers are linear polymers whose composition changes gradually along the polymer chains, potentially ranging from a random to a block-like structure. When a copolymer segment is synthesized using a controlled radical polymerization (CRP) technique such as nitroxide-mediated polymerization, it is termed a gradient or 'profiled' copolymer. This type of copolymer is different than a polymer obtained by a traditional free radical process and will be dependant on the monomer composition, control agent, and polymerization conditions. For example, when polymerizing a monomer mix by traditional free radical polymerizations, a statistical copolymer is produced, as the composition of the monomer mix remains static over the lifetime of the growing chain (approximately 1 second). Furthermore, due to the constant production of free radicals throughout the reaction, the composition of the chains will be non-uniform. During a controlled radical polymerization the chains remain active throughout the polymerization, thus the composition is uniform and is dependant on the corresponding monomer mix with respect to the reaction time. Thus in a two monomer system where one monomer reacts faster than the other, the distribution or 'profile' of the monomer units will be such that one monomer unit is higher in concentration at one end of the polymer segment. Each block of the block copolymers may itself be a homopolymer, a random copolymer, a random terpolymer or a gradient polymer.

Gradient block copolymers can be formed for example by allowing unreacted monomer from a 1^st block continue to react in the formation of a second block. Thus in an A-B block gradient copolymer, the A block is formed first and when the monomer(s) for the B block are added, the unreacted A block monomer(s) is kept in the mixture to react leading to an A-B block copolymer with a gradient of the A block in the B block. Preferred block polymers are A-B diblock and A-B-A triblock copolymer. Each block itself may be a homopolymer, a random co-polymer (where co-polymer includes terpolymer and other combinations of two or more different monomers), or a gradient polymer.

By "elastomeric" block copolymer, as used herein, is meant that the copolymer contains at least one elastomeric block, the elastomeric block(s) makes up more than 50 mole percent of the copolymer, preferably more than 70 percent, more preferably over 75 percent and most preferably over 80 percent. The elastomeric block has a Tg of less than +2O⁰C, preferably less than O⁰C, and more preferably less than -2O⁰C. All blocks of the block copolymer may be elastomeric, or the block copolymer may have one or more elastomeric blocks and one or more non-elastomeric blocks. The non-elastomer block has a Tg of at least 2O⁰C greater than that of the elastomeric block, preferably a Tg above 2O⁰C, more preferably above 5O⁰C and even more preferably above 75 ⁰C,

Elastomeric Block Copolymers

The elastomeric block copolymer of the invention contains at least one elastomeric (soft) block that is incompatible with the thermoset material and at least one block that is compatible with the thermoset resin. The thermoset-compatible block(s) can be elastomeric and have Tgs below ambient temperature, making the entire block copolymer a "liquid", or can be hard (non-elastomeric) blocks generally having a glass transition temperature (Tg) of greater than 2O⁰C, and more preferably greater than 5O⁰C. The thermoset-compatible block can be chosen from any thermopolymer meeting the Tg requirements. Preferably, the thermoset-compatible block is composed of one or more ethylenically unsaturated monomers, including, but not limited to (meth)acrylates, styrenics, vinyl acetates, polyethers, polyesters, and acrylamides. In one embodiment the thermoset-compatible block is formed primarily of methacrylate ester units, styrenic units, or a mixture thereof. Methacrylate esters useful in the invention include, but are not limited to, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, sec-butyl methacrylate, tert- butyl methacrylate, amyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, cycloheyl methacrylate, 2-ethylhexyl methacrylate, pentadecyl methacrylate, dodecyl methacrylate, isobornyl methacrylate, phenyl methacrylate, benzyl methacrylate, phnoxyethyl methacrylate, 2 -hydroxy ethyl methacrylate and 2-methoxyethyl methacrylate. Styrenic monomer units include styrene, and derivatives thereof such as, but not limited to, alpha-methyl styrene, and para methyl styrene. If the thermoset- compatible block is a hard block, it preferably contains at least 60 percent by weight, and preferably at least 80 percent by weight of methyl methacrylate units, with the remainder being alkyl acrylate units. The choice of copolymer type and amount can be selected to provide specific performance properties for a given end-use.

The elastomeric block(s) that are incompatible with the thermoset material generally have a Tg of less than 2O⁰C, and preferably less than O⁰C. Preferred elastomeric blocks include polymers and copolymers of alkyl acrylates, dienes, styrenics, and mixtures thereof. In one embodiment, the elastomeric block incompatible with the thermoset resin contans no polyether structures. Preferably the elastomeric block is composed mainly of acrylate ester units. Acrylate ester units useful in forming the soft block include, but are not limited to, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, tert-butyl acrylate, amyl acrylate, isoamyl acrylate, n-hexyl acrylate, cycloheyl acrylate, 2- ethylhexyl acrylate, pentadecyl acrylate, dodecyl acrylate, isobornyl acrylate, phenyl acrylate, benzyl acrylate, phnoxyethyl acrylate, 2 -hydroxy ethyl acrylate and 2- methoxy ethyl acrylate. Preferably the acrylate ester units are chosen from methyl acrylate, ethyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate and octyl acrylate. Useful dienes include, but are not limited to isoprene and butadiene.

In one preferred embodiment, the block copolymer is made of methylmethacrylate and butyl acrylate blocks. The butyl acrylate level in the block copolymer can be fine-tuned to provide good scratch resistance. In a second preferred embodiment, the block copolymer is composed of primarily methylacrylate and butyl acrylate blocks.

The acrylic block polymer of the invention is formed by a controlled radical polymerization process. Examples of controlled radical polymerization techniques will be evident to those skilled in the art, and include, but are not limited to, atom transfer radical polymerization (ATRP), reversible addition fragmentation chain transfer polymerization (RAFT), nitroxide-mediated polymerization (NMP), boron-mediated polymerization, and catalytic chain transfer polymerization (CCT). Descriptions and comparisons of these types of polymerizations are described in the ACS Symposium Series 768 entitled Controlled/Living Radical Polymerization: Progress in ATRP, NMP, and RAFT, edited by Krzystof Matyjaszewski, American Chemical Society, Washington, D. C, 2000. In principle, any living or controlled polymerization technique, compatible with the monomer choices, can be utilized to make the block copolymer. One preferred method of controlled radical polymerization is nitroxide-mediated CRP. Nitroxide- mediated CRP is preferred as it allows for the use of a larger variety of monomers in the triblock copolymer, including the use of acrylics, acrylamides, and especially acid functional acrylics.

Nitroxide-mediated polymerization can occur in bulk, solvent, and aqueous polymerization media, and can be used in existing equipment at reaction times and temperature similar to other free radical polymerizations. One advantage of nitroxide- mediated CRP is that the nitroxide is generally innocuous and can remain in the reaction mix, while other CRP techniques often require the removal of the control compounds from the final polymer. Furthermore, stringent purification of the reagents is not needed.

The mechanism for this control may be represented diagrammatically as below:

M with M representing a polymerizable monomer and P representing the growing polymer chain.

The key to the control is associated with the constants Kdeact, k_act and k_p (T. Fukuda and A. Goto, Macromolecules 1999, 32, pages 618 to 623). If the ratio kieact/kact is too high, the polymerization is blocked, whereas when the ratio kp/kdeact is too high or when the ratio kdeac/k_act is too low though, the polymerization is uncontrolled.

It has been found (P. Tordo et al, Polym. Prep. 1997, 38, pages 729 and 730; and CJ. Hawker et al., Polym. mater. Sci. Eng., 1999, 80, pages 90 and 91) that β-substituted alkoxyamines make it possible to initiate and control efficiently the polymerization of several types of monomers, whereas TEMPO-based alkoxyamines [such as (2',2',6',6'- tetramethyl-1 '-piperidyloxy-)methylbenzene mentioned in Macromolecules 1996, 29, pages 5245-5254] control only the polymerizations of styrene and styrenic derivatives. TEMPO and TEMPO-based alkoxyamines are not suited to the controlled polymerization of acrylics. The nitroxide -mediated CRP process is described in, US 6,255,448, US 2002/0040117 and WO 00/71501 , incorporated herein by reference. The above-stated patents describe the nitroxide-mediated polymerization by a variety of processes. Each of these processes can be used to synthesize polymers described in the present invention.

In one process the free radical polymerization or copolymerization is carried-out under the usual conditions for the monomer or monomers under consideration, as known to those skilled in the art, with the difference being that a β-substituted stable free radical is added to the mixture. Depending on the monomer or monomers which it is desired to polymerize, it may be necessary to introduce a traditional free radical initiator into the polymerization mixture as will be evident to those skilled in the art.

Another process describes the polymerization of the monomer or monomers under consideration using a alkoxyamine obtained from β-substituted nitroxides of formula (I) wherein A represents a mono -or polyvalent structure and R_L represents a mole weight of more than 15 and is a monovalent radical, and n > 1.

Another process describes the formation of polyvalent alkoxyamines of formula (I), based on the reaction of multifunctional monomers, such as, but not limited to, acrylate monomers and alkoxyamines at controlled temperatures. The multifunctional alkoxyamines of formula (I), wherein n > 2, may then be utilized to synthesize linear, star, and/or branched polymeric and copolymeric materials from the monomer or monomers under consideration.

Another process describes the preparation of multimodal polymers where at least one of the monomers under consideration is subjected to free radical polymerization in the presence of several alkoxyamines comprising the sequence of formula (I), wherein n is a non-zero integer and the alkoxyamines exhibit different values of n. The alkoxyamines and nitroxyls (which nitroxyls may also be prepared by known methods separately from the corresponding alkoxyamine) as described above are well known in the art. Their synthesis is described for example in US Pat. No. 6,255,448 and WO 00/40526. One useful stable free radical is N-ϊ-butyl-N-[l-diethylphosphono-(2,2,- dimethylpropyl)]nitroxide (DEPN), which has the following structure:

DEPN

The DEPN radical may be linked to an isobutyric acid radical or an ester or amide thereof. A useful initiator is iBA-DEPN initiator, which has the following structure, in which SGl is the DEPN group.

iBA-DEPN initiator when heated separates into two free radicals, one of which initiates polymerization and one of which, the SGl nitroxide radical, reversibly terminates polymerization. The SGl nitroxide radical dissociates from methacrylates above about 25 ⁰C and disassociates from acrylates above about 90 ⁰C.

Other useful initiators include esters and amides Of CH₃CH(SGl)CO₂H. If esters or amides are used, they are preferably derived from lower alkyl alcohols or amines, respectively, for example, the methyl ester, CH₃CH(SGl)CO₂CH₃. Polyfunctional esters, for example the diester of 1 ,6-hexanediol [CH₃CH(SGl)Cθ2]2[(CH2)e], can also be used. Difunctional initiators can be used to prepare symmetrical A-B-A block copolymers. Initiators with higher functionality, for example the tetraester of pentaerythritol [CH₃CH(SG I)CO₂CH₂^C], can be used to prepare star copolymers of the type 1(BA)_n, in which I is the initiator and n is the functionality of the initiator. Typically, a monofunctional alkoxyamine is used to prepare an AB block copolymer. A difunctional alkoxyamine can be used to produce a triblock ABA copolymer. However, a triblock copolymer can also be made from a monofunctional alkoxyamine by extending an AB diblock copolymer with an additional A segment (i.e., three sequential reactions of an A segment, then a B segment, then another A segment). Another method for making a triblock copolymer from a monofunctional alkoxyamine is to first react the monofunctional alkoxyamine with a diacrylate (such as butanediol diacrylate) to create a difunctional alkoxyamine. None of the reactions require the addition of further initiation source (such as an organic peroxide), though in some cases, peroxides might be used during the course of the reaction to "chase" residual monomer. If it is preferred to preserve the "living" character of the nitroxide terminated chain ends, the "chasing" step is carried out at a temperature below the nitroxide dissociation temperature as will be evident to those skilled in the art.

The copolymerization may be carried out under conditions well known to those skilled in the art, taking into account the monomers under consideration and the desired product. Thus, the polymerization or copolymerization may be performed, for example, in bulk, in solution, in emulsion or in suspension, at temperatures ranging from 0 °C to 250 ⁰C and preferably ranging from 25 ⁰C to 150 ⁰C.

"Sequenced" block copolymers may be produced by 1) polymerizing a monomer or a mixture of monomers in the presence of an alkoxyamine at a temperature ranging from 25 ⁰C to 250 ⁰C and preferably ranging from 25 ⁰C to 150 °C; 2) allowing the temperature to fall and optionally evaporating off the residual monomer(s); 3) introducing a new monomer(s) mixture into the reaction mixture; and 4) raising the temperature to polymerize the new monomer or mixture of monomers. This process may be repeated to form additional blocks. Polymers made by this process will have nitroxide end groups. They can remain on the end of the polymer chains or be removed by an additional processing step.

At any point during the synthesis process a further initiation source (such as an organic peroxide), might be used to create a composite material containing a mixture of controlled block structures and homopolymers. Depending on the monomer(s) present, the non-block structures could be homopolymers or random copolymers. Furthermore, these homopolymers or random copolymers may be primarily hydrophobic or hydrophilic in nature, again dependant upon the monomer(s) present.

The block co-polymers have a controlled molecular weight and molecular weight distribution. Preferably the weight average molecular weight (M_w) of the co-polymer is from 1 ,000 to 1 ,000,000 g/mol, and more preferably from 5,000 to 300,000 g/mol, most preferably less than 200,000 g/mol. The molecular weight distribution, as measured by the ratio of the weight average molecular weight to the number average molecular weight (M_w/M_n), or polydispersity, is generally less than 4.0, preferably equal to or less than 2.5, and more preferably equal to or less than 2.0 or below. Polydispersities of equal to or less than 1.5 or below, and equal to or less than 1.3 or below, may be obtained by the method of the invention.

In one embodiment of the invention, the epoxy-compatible block contains from 1 to 50 mole percent of functionality and preferably from 1-20 mole percent. This enables the functionalized block to either react with the epoxy matrix or to increase compatibility of the functionalized block with the epoxy matrix. The functionality can be incorporated into the block polymer either through the use of functional monomers, or by post- polymerization functionalization. Useful functional groups include acids, hydroxides, acrylamides and glycidyl groups. Functional monomers useful for incorporating functional groups into the acrylic block polymer include, but are not limited to, acrylic acid, methacrylic acid, glycidal methacrylate, dimethyl acrylamide, hydroxyethyl methacrylate.

In one embodiment, the block copolymer of the invention is an all-acrylic copolymer - meaning that at least 10 percent, preferably at least 50 percent, and more preferably at least 80 weight percent of each block is composed of (meth)acrylic monomer units.

The block copolymer may be used as an emulsion or solution, or may be isolated into a powder by means known in the art, such as, but not limited to, spray drying, vacuum drying, freeze drying, coagulation, or may be isolated as a pellets by means of degassing extruder. Thermoset material

The elastomeric block copolymer of the invention is used to modify a thermoset resin. Thermoset resins include, but are not limited to, epoxy resins, cyanoacrylates, bismalimides , unsaturated polyester resins, polyurethanes, polyacrylics and vinyl ester resins, and phenolic resins. In one preferred embodiment, the thermoset resin is an epoxy resin.

Epoxy resins useful in the present invention are those having at least two oxirane functional groups, which can be polymerized by ring-opening. Preferred epoxy resins are those that are liquids at 25⁰C. The epoxy resins may be aliphatic, cycloaliphatic, heterocyclic or aromatic. Useful epoxy resins include, but are not limited to epoxy resins of, resorcinol diglycidyl ether, bisphenol A diglycidyl ether, triglycidyl-p-amino-phenol, bromobisphenol F diglycidyl ether, the triglycidyl ether of m-amino-phenol, tetraglycidylmethylenedianiline, the triglycidyl ether of (trihydroxy-phenyl)methane, polyglycidyl ethers of phenol-formaldehyde novolak, polyglycidyl ethers of ortho-cresol novolak and tetraglycidyl ethers of tetraphenyl-ethane. Mixtures of at least two of these resins can also be used.

Hardeners react with epoxy resins to form a cross-linked material. Generally useful hardeners are those that react at room temperature or higher. Examples of useful hardeners include, but are not limited to: acid anyhydrides, aromatic or aliphatic polyamines, including diaminodiphenyl sulphone (DDS), methylenedianiline, 4,4,'- methylenebis(3-chloro-2, 6-diethyl-aniline (MCDEA) or 4,4'- methylenebis(2,6-diethyl- aniline (M-DEA), dicyandiamide (DICY) and its derivatives, imidazoles, polycarboxylic acids and polyphenols.

Properties

The block copolymer additive of the invention provides flexibility to the thermoset composition. This increase in flexibility occurs without a significant decrease in the Tg of the thermoset composition. The modulus of an elatomeric block copolymer- modifϊed epoxy composition was found to be lowered by over 25 percent, over 50 percent, over 75 percent, and even over 100 percent, while the Tg of the thermoset material decreased by less thanl5°C, 1O⁰C, and even by less than 5⁰C. While not being bound by any particular theory, it is believed that the flexibility of the modified epoxy composition of the invention, with little change in Tg, is related to the observation that the elastomeric block copolymer forms a continuous polymer phase within the thermoset matrix, and not discrete particles. By a continuous polymer phase is meant that the polymer additive phase can be traced continuously for at least 5 microns, and where the continuous polymer phase has an aspect ratio of greater than 10. The continuous polymer phase of the invention does not include morphologies such as wormlike micelles, wormlike vesicles, spherical nanostructures, or large (greater than 1 micron) rubber particles. Examples of the continuous polymer phase morphologies can be seen in the figures of the invenention, and include, but are not limited to rings, lameller, and long fiber-type structures.

This morphology is particularly unexpected, since the epoxy composition contains only low levels of block copolymer - levels of 20 percent or less, and more particularly of only 10 percent or less. Block copolymers having lower concentrations of elastomeric blocks were found to form into discrete particular morphologies, and these act as tougheners of the thermoset rather than flexibilizers.

The block copolymer may be blended into the thermoplastic matrix in any manner known in the art, including but not limited to melt blending, extrusion blending, solvent blending, shear mixing at room or elevated temperature (160⁰C for example). As the curing progresses the molecular weight of the epoxy increases and phase separation occurs leading to the formation of the continuous polymer phases, due to thermodynamic forces (dependant on cure kinetics and blend compatibility).

Uses of the flexible, high Tg modified epoxy of the invention include, but are not limited to: flexible copper clad laminates for flexiblie printed wire boards, flexible coatings, flexible structural adhesives (both acrylic and epoxy adhesives).

EXAMPLES

Example 1 (Comparative) (E21)

A modified epoxy composition containing 10 weight percent of E21 (synthesized following US2004/0034124 patent, SBM with a composition 33/33/33) in a bisphenol A diglycidyl ether (DGEBA) + methylene diethylaniline (MDEA) in a stoichiometric ratio of epoxy to N-H amino groups) epoxy matrix was formed by curing 4h at 160⁰C and 6h at 240⁰C. TEM (Transmission Electronic Microscopy) and AFM (Atomic Force Microscopy) (define acronyms) images were obtained, and are shown in Figures 1 and 2.

Example 2 (of the Invention)

An block copolymer composed of 80 weight percent polybutyl acrylate and 20 weight percent polymethyl methacrylate blocks was synthesized in the bulk by controlled radical polymerization in the presence of an alkoxyamine based on the nitroxide SGl ,.

The block copolymer was blended at 10 weight percent with DGEBA and MDEA in a stoichiometric ratio of epoxy to N-H amino groups.

The mixture was blended and poured into a glass reactor and cured 4h at 160⁰C and 6h at 240⁰C. TEM and AFM images were taken, and are shown in Figures 3 and 4. Note that the block copolymer of Example 2 does not form the spherical morphology seen with other block copolymer of Example 1 and other block copolymers having a lower percentage of elastomeric block. Instead, the block copolymer organises in a lamellar structure.

A DMTA (Dynamic Mechanical Thermal Analysis) analysis was performed on Comparative Example 1 and Example 2, with the plots shown in Figure 5 and 6.

As can be seen in the DMTA scan, a much greater modulus drop is seen for the modified epoxy of Example 2, as compared to modified Example 1. It is also noted that the Tg of the modified epoxy composition is maintained. (Figure 5 and Table 1) Epoxy flexibilizers currently in use generally resulting a large decrease in Tg.

TABLE 1

Table 2 shows the change in the tensile properties of the DGEBA+MDEA system with and without the addition of the block copolymer of Example 2

TABLE 2

A solvent analysis (solvent up-takes at saturation in Water, Methyl Ethyl Ketone

(MEK) or Toluene) was performed on comparative Example 1 and Example 2, with the results shown in Table 3:

TABLE 3

% Weight uptake at saturation in

DGEBA+MDEA

Water MEK Toluene

Neat system 1,4 30,5 8,0

+ 10% E21 1,8 30,4 9,1

+ 10% ECL 33 1,4 26,6 27,7

The solvent resistance of the system is slightly affected by the continuous structure, in particular with Toluene. But the water resistance is preserved. Example 3 (comparative) DGEBA/DICY unmodified

A DGEBA/ dicyandiamide (DICY) epoxy resin with the DGEBA having a molecular mass of 372 g/mol was used as the control (unmodified). A ratio of 100 parts DGEBA resin to 4.5 parts DICY was used with 0.4 parts of a commercial accelerator provided by Air Products known as Amicure UR. The DGEBA and DICY were blended and cured at 19O⁰C for 70 minutes.

Example 4 (DGEBA/DICY 10% modifier loading)

A block copolymer consisting of a polymethyl acrylate block and a polybutylacrylate block, the former having a molecular weight of 20 kg/mol, the latter having a molecular weight of 30 kg/mol, was polymerized by nitroxide mediated polymerization. 491.51g of methyl acrylate was added to a IL stainless steel polymerization reactor and degassed with nitrogen for 10 minutes. 7.473g of iB A-DEPN (BlocBuilder from Arkema Inc.) alkoxyamine were added to the monomer and the mixture was heated under pressure to 11O⁰C. The mixture was polymerized for 2.5 hours, reaching 74% conversion. The 74% pMA solution was saved for further experiments. To add butyl acrylate to the first block, 100.6g of the above PMA solution was added to The same IL reactor as above with 253.8g butyl acrylate, 38.4g additional methyl acrylate, and 102. Ig toluene. The mixture was polymerized for 2 hours at 112- 115⁰C until 67% conversion of butyl acrylate and 65% conversion of methyl acrylate. Residual monomer and solvent were removed from the polymer at 11O⁰C under full vacuum for 2 hours.

The elastomeric block copolymer was blended into the DGEBA/DICY epoxy resin of Example 3, and cured at 19O⁰C for 70 minutes.

Example 5

Example 4 was repeated using a block copolymer consisting of a polymethyl acrylate block and a polybutyl acrylate block, the former having a molecular weight of 20kg/mol, the latter having a molecular weight of 50 kg/mol, was made using the same first block solution as example 4 (75%pMA in methyl acrylate). To add butyl acrylate to the first block, 115.73g of the above PMA solution was added to a round bottom flask with 302.7g of butyl acrylate. The residual methyl acrylate was removed in vacuuo at 65⁰C, creating a solution of 22.3%PMA in butyl acrylate. 72.9g of this solution plus 24.8g of toluene were added to a 100ml glass reactor with overhead mixing. The mixture was polymerized for 1.5 hours at 112-115⁰C until 50% conversion of butyl acrylate. Residual monomer and solvent were removed at 9O⁰C under full vacuum for 2 hours. The elastomeric block copolymer was blended into the DGEBA/DICY epoxy resin of Example 3, and cured at 19O⁰C for 70 minutes.

The modified and unmodified epoxy resins of Examples 3, 4 and 5 were measured by tensile and fiexural testing according to the procedures provided by ASTM. Tensile testing is carried out until failure of the specimen is realized. Fiexural testing is carried out in three point bending mode.

The glass transition temperature of the material was measured by Dynamic Mechanical Analysis on cured samples using a Rheometrics Scientific RDA-111 strain rheometer. The rheometer was installed with a torsion rectangular geometry with approximate dimensions of 2'" 0.5'" ¹A". Dynamic temperature ramp experiments were done at a frequency of 1 Hz and heating rate of 2 deg. C/ min. All experiments were performed under nitrogen atmosphere. The glass transition temperature is taken at the maximum of tan δ. The results are shown in Table 4, and the AFM images are shown in Figures 7, 8, 9 and 10 (Example 4) and Figures 11 and 12 (Example 5):

TABLE 4

Claims

What Is claimed is:

1. A flexible thermoset composition comprising from 1 to less than 20 weight percent of an elastomeric block copolymer; wherein the elastomeric block copolymer comprises a continuous polymer phase.

2. The flexible thermoset composition of claim 1, wherein the modulus is at least 25 percent lower than that of the unmodified thermoset resin, and the Tg of the thermoset composition is less than 15⁰C lower than that of the unmodified thermoset resin.

3. The flexible thermoset composition of claim 2, wherein the modulus is at least 50 percent lower than that of the unmodified thermoset resin, and the Tg of the thermoset composition is less than 1O⁰C lower than that of the unmodified thermoset resin.

4. The flexible thermoset composition of claim 1 , wherein said thermoset composition comprises an epoxy resin.

5. The flexible thermoset composition of claim 1 , wherein said elastomeric block copolymer contains at least 50 (mole/weight) percent of elastomeric block(s).

6. The flexible thermoset composition of claim 1 , wherein said elastomeric block copolymer contains at least 70 (mole/weight) percent of elastomeric block(s).

7. The flexible thermoset composition of claim 1 , comprising from 3 to 10 weight percent of an elastomeric block copolymer.

8. The flexible thermoset composition of claim 1 , wherein said elastomeric block copolymer is an all-acrylic copolymer.

9. The flexible thermoset composition of claim 8, wherein said elastomeric block copolymer comprises a non-elastomeric block comprising methylmethacrylate units, and an elastomeric block comprising butyl acrylate units.

10. The flexible thermoset composition of claim 1 , wherein said elastomeric block copolymer is a functionalize copolymer, comprising from 1 to 50 moles of functionality.

11. The flexible thermoset composition of claim 1 comprising a flexible copper clad laminate for flexible printed wire boards, flexible coatings, or flexible structural adhesives.

12. A process for producing a flexible thermoset composition comprising the step of blending from 1 to less than 20 weight percent of an elastomeric block copolymer into the thermoset resin; wherein the elastomeric block copolymer comprises a continuous polymer phase.

13. The process of claim 12, wherein said elastomeric block copolymer is formed by a controlled radical polymerization process.

14. The process of claim 12, wherein the modulus of the thermoset composition is at least 50 percent lower than that of the unmodified thermoset resin, and the Tg of the thermoset composition is less than 1O⁰C lower than that of the unmodified thermoset resin.

15. The process of claim 14, wherein the modulus of the thermoset composition is at least 75 percent lower than that of the unmodified thermoset resin, and the Tg of the thermoset composition is less than 5⁰C lower than that of the unmodified thermoset resin.