|Title of Invention||
A PROCESS FOR SYNTHESISING HIGH MOLECULAR WEIGHT ACRYLIC COPOLYMERS WITH PENDENT EPOXY GROUPS
|Abstract||This invention relates to a process for synthesising high molecular weight acrylic polymer with pendant epoxy functions by copolymersinmg a mixture of alkyl acrylate, alkenyl cyanide and a glycidyl ester of an unsaturated organic acid in the presence of a free radical initiator. The product is recovered by known methods.|
This invention relates to a process for synthesising high molecular weight acrylic copolymers with pendent epoxy functions. These copolymers are particularly suitable for fomulating tack-free, non-melting thin films useful as thermosetting film adhesives for bonding a variety of substrates including polyimide films. The epoxy functional acrylic polymer is formed by way of copolymerization of acrylic monomers in definite proportion and the polymer is formulated to form thin b-staged films undergo curing at higher temperature without melting.
Acrylic acid copolymers with pendant epoxy group may be synthesised by the following process.
A pendant epoxy-functional polymer is made by free radical copolymeriaation of a mixture of three vinyl monomers in a solvent. One such monomer is alkenyl cyanide monomer like acrylonitrile or methacrylonitrile. The second monomer of the mixture is an alkyl ester of acrylic or methacrylicacid where the alkyl part can be constituted by one among methyl, ethyl, propyl, butyl, pentyl, isopentyl, hexyl or ethyl hexyl group and preferably butyl group. The third component of the mixture is constituted by glycidyl ester of an unsaturated acid. Glycidyl acrylate or glycidyl methacrylate are examples. The free radical initiator used can be any a^o initiator, example aaobis isobutyronitrile or azoblscyanocycloheaxane or it can be any peroxide initiator such as benzoyl peroxide or ditertiary butyl peroxide. The polymerisation is done in an organic solvent
selected among tetrahydrofuran (THF), dioxane, methylethyl ketone (MEK), methyl isobutyl ketone (MIBK), dimethyl formamide (DMF), dimethyl acetamide (DMAc), N-methyl pyrrolidone (NMP) or dimethyl sulfoxide (DMSO) or a mixture of two or more of any of these solvents in any proportion. The preferred solvent is DMF. The polymerisation is performed at temperatures between 80-80^C. The reaction is carried out for 5-10 hours and the resultant polymer is isolated by pouring the resinous solution to any non solvent. The nonsolvant can be chosen from among hydrocarbons, such as hexane, heptane, octane, cyclohexane or their mixtures in any combination and proportion. The nonsolvent can also be an alcohols such as ethanol, methanol, propanol, isopropanol or a mixtures of these in any combination and proportion in the presence or absence of added water. The preferred one is methanol.
In such systems, the alkyl acrylate or methacrylate imparts the required flexibility whereas the polar nitrile component contributes to enhanced wetting, adhesion and cohesive strength of the polymers. The epoxy groups incorporated through suitable monomer serves as the functional group for curing of the film adhesive. The polymer is blended with a filler, preferably silica powder of particle size below 10 micron, an aliphatic diamine for curing part of the epoxy groups at room temperature and an aromatic diamine to induce curing of the remaining epoxy groups at higher temperature. The part curing at room temperature by the aliphatic amine prevents the melt-flow of the
resin on heating. The aliphatic diamine can be chosen among piperaaine or substituted piperazine or N,N' dialkyl alkane diamine where the alkane moiety can range from ethane to dodecan and the alkyl part from methyl to hexyl. The preferred diamine compound is piperazine. The aromatic diamine is chosen among 3,3- diamine diphenyl sulfone, 4,4-diamino diphenyl sulfone, 3,3-diamino diphenyl ketone, 4,4-diamino diphenyl ketone or a mixture of these in any proportion, preference being given to 4,4'diamino diphenyl sulfone.
In * such a copolymer formulation, the alkyl acrylate part can vary from 55-65% by weight, the nitrile monomer can vary between 20-35% by weight and the epoxy monomer content is varied such that the polymer has an epoxy functionality in the range 0.15-0.3 equivalents/kg. The free radical initiator is taken at a concentration ranging from 0.01 to 0.2 percent by weight of the total monomer. The silica filler in the polymer formulation is varied in the range 10-20% by weight of the polymer. The aliphatic and aromatic diamines are added such that each accounts for 50% of the epoxy groups on an equivalent basis. In this calculation, the aliphatic diamine and aromatic diamine are both considered to possess two functional groups each for reactj.on with epoxy groups of the polymer on a 1:1 equivalent basis.
Accordingly, the present invention provides a process for synthesising acrylic copolymers having a molecular weight in the range of 45,000-65,000 with pendant epoxy functions comprising the steps of solution copolymerising a mixture of an alkyl acrylate, an alkenyl cyanide and a glycidyl ester of an unsaturated organic acid at a temperature below 80°C in the presence of a free radical initiator, separating and isolating the copolymer.
The following examples illustrate the details of synthesis of the copolymer and the formulated film adhesive derived from it.
Example 1. Synthesis of epoxy-functional acrylic polymer (EFAP)
A mixture containing 39 parts of butyl acrylate, 21 parts of acrylonitrile, 1 part of glycidyl methacrylate and 39 parts of fresh distilled dimethyl formamide containing 0.1% (with respect to the three monomers) of azo-bis-isobutyronitrile, all taken in a 500 ml round bottomed flask fitted with a vacuum adaptor. The solution is cooled to -50°C or preferably -70°C and evacuated using a vacuum pump and then closed under vacuum. The solution is then kept in a water bath heated to 70°C and maintained at this temperature for 6 hours. The viscous solution is then poured drop-wise to 10 times its volume of methyl alcohol under agitation. The resinous polymer formed is separated by decanting the supernatant liquid. The precipitate is then dissolved in tetrahydrofuran (THF) to make approximately 10% (weight/weight) solution and then reprecipitated into methanol as described above. The polymer is then dried at 40 to 60oC under vacuum for 3 to 7 hours. The polymer is formed in 80-90%
yield. It is characterised by Gel Permeation Chromatography (GPC) to determine the number average molecular weight (Mn) which is in the range 45000-55000 with a poly dispersity of 1.7 to 2.0. The IR spectrum of the polymer shows an absorption at 1740 cm"^ characteristic of the ester carbonyl groups and a strong absorption at 2150 cm-1 due to the nitrile group derive from acrylonitrile. The weak peak at 910 cm-1 is indicative of the epoxy groups.
Table 1: Typical composition and molecular eharaoteristics of epoxy functional acrylic polymer
It is to be understood that the foregoing description and the appended claims do not exclude abvious equivalents known to persons skilled in the art.
Our copending application No. 452/MAS/99 describes and claim a process for producing tack-free non-melting acylic film adhesive made from high molecular weight acrylic copolymers ^ with pendant epoxy function.
1. A process for synthesising acrylic copolymers having a molecular weight in the
range of 45,000-65,000 with pendant epoxy functions comprising the steps of solution
copolymerising a mixture of an alkyl acrylate, an alkenyl cyanide and a glycidyl ester
of an unsaturated organic acid at a temperature below 80°C in the presence of a free
radical initiator, separating and isolating the copolymer.
2. The process as claimed in claim 1, wherein said alkyl acrylate monomer is
selected from methyl, ethyl, propyl, isopropyl, butyl, isobutyl, hexyl, or ethyl hexyl
ester of acrylic acid or methacrylic acid.
3. The process as claimed in claims 1 and 2 wherein said alkyl acrylate monomer constitutes 55 to 65% by weight of reaction mixture.
4. The process as claimed in claim 1, wherein said alkenyl cyanide is selected from acrylonitrile or methacrylonitrile and constitutes 25-35% by wt of the reaction mixture.
5. The process as claimed in claim 1, wherein the addition of glycidyl ester is
regulated such that the epoxy content of the polymer produced is in the range of 0,15
to 0.3 equivalent/kg.
6. The process as claimed in claim 1, wherein the free radical initiator is an aso compound preferably asobisisobutyronitrile or a2obisoyanocyclohexane.
7. The process as claimed in claim 1, wherein the free radical initiator is a peroxide compound preferably benzoyl peroxide, dicumyl peroxide, cyclohexanone peroxide or ditertiary
8. The process as claimed in claim 1, wherein said oopolymerisation is carried out in an organic solvent medium selected from tetrahydrofuran, dioxane, methyl ethyl ketone.
methyl isobutyl ketone, dimethyl formamide, dimethyl acetamide, N-methyl pyrolidone, or dimethyl sulphoxide either alone or in admixture.
9. The process as claimed in any of the claims 1-6 wherein the said polymerisation is carried out at 60-80oC for 5-10 hours.
10. The process as claimed in claims 1-9, wherein the said acrylic copolymer is cast into films by known methods.
11. A process for synthesising high molecular weight, film
forming acrylic copolymer with pendent epoxy functions
substantially as herein described.
|Indian Patent Application Number||451/MAS/1999|
|PG Journal Number||26/2007|
|Date of Filing||21-Apr-1999|
|Name of Patentee||INDIAN SPACE RESEARCH ORGANISATION|
|Applicant Address||ANTARIKSH BHAVAN, NEW BEL ROAD, BANGALORE-560 094.|
|PCT International Classification Number||C08F220/06|
|PCT International Application Number||N/A|
|PCT International Filing date|