|Title of Invention||
A PROCESS FOR PRODUCING ACRYLIC COPOLYMERS WITH PENDENT PHENOL FUNCTIONS
|Abstract||This invention relates to film forming acrylic copolymers with pendant phenol group which are useful as adhesives. The copolymers are prepared by copolymerising an alkenyl cyanide monomer, an acrylic acid ester monomer and a monomer containing an unsaturation and a phenol group in the presence of a free radical initiator. The copolymer is separated and may be cast into films for forming adhesives.|
This invention relates to a process for producing aery1ic copolymers with pendant phenol functions.
These, copolymers are useful as single component thermoplastic and two component thermoset film adhesive for bonding different substrates including metals and rubber.
Film adhesives have great application potentiality in high-tech areas like aerospace. The bonding requirements in these areas are generally met by use of glue like and solvent-based resinous polymeric adhesives. Use of film adhesive faci1itates the bonding manoeuvre and helps regulate the glue thickness and minimise wastage of adhesive and accumulation of dead weight which is very critical when weight saving; becomes a matter of concern. A few number of film adhesives for structural and nonstructural applications have been reported. Some of these film adhesive and their applications have been cited by E-Lavins and J A Snelgrove in the Hand Book of Adhesive (Editor, Skiest, Publisher, Van Nostrand and Reinold, 1977) and by L T Eby and H P Brown in Treatise on Adhesion and Adhesives (Editor, R L Patrick, Publisher, Marcel Dekker, 1966). Majority of the reported film adhesives ar& based on high molecular weight epoxy resin and a few Ar» based on acrylic copolymers. Two component vinyl acetal-phenolics constitute another less-preferred film adhesive. The decreased preference is due to the condensation nature of the cure reaction which generates voids in the bond, thereby weakening it. Epoxy film adhesive dominate the industry and this system invokes need for blending with polymers such as nylon.
rubber etc. to confer film-forming characteristics. The physical and adhesive properties are hence dictated by the nature of the additives. Those based on acrylic fi1ms uses vinyl polymerisation for crosslinking which is unpredictable in aerobic conditions due to interference of atmospheric oxygen acting as polymerisation inhibitor. Whereas the present invention dislcoses thermoplastic and thermoset film adhesives formed from phenol-functiona1 acrylic polymers with built—in film forming characteristics wherein the thermoset adhesive undergoes faci1e cure by addition reaction without evolution of volatile byproducts and the thermoplastics, simply by melting and consolidation. Both systems have very good shelf-life at ambient conditions.
The main objective of this invention is to provide a method for synthesising high molecular weight polymers with pendant phenol functions having built-in film-forming characteristics- Such phenol functional polymer is produced by free radica1 copolymerisation of a mixture of three vinyl monomers in a solvent - One such monomer is an alkeny1 cyanide monomer typically acrylonitrile or methacrylonitrile, preference being given to the former. The second monomer of the mixture is constituted by an acrylic acid ester of alcohols such as methanol, ethanol, propanol, isopropanol, butanol, isobutanol, pentanol, isopentanol, or ethyl hexyl alcohol. Instead of acry1ates, the methacrylate esters of the above alcohols can also be used. The preferred monomer is butyl acrylate or ethyl
acrylate. The third component is a monomer containing both an unsaturation and a phenol group. The best example is ortho, para-, or meta- hydroxy phenyl maleimide or ortho-, para- or meta-hydroxy phenyl citraconimide- It may be optionally replaced by ortho-, para- or meta hydroxy phenyl itaconimide or ortho-, para- or meta hydroxy styrene. The free radical initiator used for polymerisation is one among the azo initiators typically azo bis-isobutyronitrile or azo bis cyanocyclohexane. Peroxides such as benzoyl peroxide, ditertiary butyl peroxide, diamy1 peroxide, eyelohexanone peroxide and butyl hydroperoxide can also be used as polymerisation catalysts. The polymerisation is done in an organic solvent selected among tetrahydrofuran (THF), dioxane, methyl ethyl ketone (MRK), methy 1 isobuty1 ketone (MIBK), dimethyol formamide (DMF) or dimethyl acetamide (DMAc) or their mixtures in any combination and proportion- Typically dimethyl f ormamide can be chosen as the solvent. The polymerisation is performed at temperatures between 60-90oC for 3 to 10 hours and the formed polymer is isolated by pouring the resinous solution to any nonsolvent. The nonsolvent can be chosen from among hydrocarbons, such as hexane, heptane, actane, cyclohexane or their mixtures in any combination and proportion. The nonsolvents can also be alcohols such as ethanol, methanol, propanol, isopropanol, or a mixtures of these in any combination and proportion. Typically, methanol can be chosen. In such a copolymer formulation, the alkyl acrylate part can vary from 55-65%, by weight, the ni tr i le monomer can vary between 20-35%. by
weight and the phenol functional monomer is varied from 3 to 15%
by weight. The free radical initiator is taken at a
concentration ranging from 0.05 to 0.2 percent by weight of the
total monomer -
The phenol group in the polymer offers amenability for structural modifications and crosslinking through its reactions with other functional electrophiles. Thus, the polymer can be crosslinked through reaction of the phenol groups with any polyelectrophile such as polyepoxide typically a diepoxide.
Accordingly the present invention provides process for producing acrylic copolymers wi th pendant phenol functions comprising copolymerising in a manner known perse an alkeny1 cyanide monomer, an acrylic acid ester monomer and a monomer containing both an unsaturation and a phenol group in the presence of a known free radical initiator and isolating the copolymer produced by methods konwn in the art.
The following examples illustrate the details of regarding the synthesis of the copolymer.
Process for phenol-functional acrylic polymers(PFAP)
59.5 parts of butyl acryllate and 31 parts of acrylonitrile are mixed with 9.5 parts of 4-maleimido phenol in 100 ml freshly distilled dimethyl formamide containing 0-10 part of azobisi sobutyroni trile 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 60-70°C and maintained at this temperature for 2 to 6 hours. The viscous solution is then poured drop-wise to 2 litres of methyl alcohol under agitation. The resinous polymer formed is separated by decanting the supernatant liquid- The entire precipitate is then dissolved in 150 parts of tetra hydro furan (THF) and then reprecipitated as described. The polymer is then dried at 40 to 50°C under vacuum for 4 to 7 hours. The polymer is formed in 80-9O% yield. The polymer is characterised by Gel Permeation Chromatography to determine the molecular weight (fin) in the range 50,000-60,000 with a polym dispersity index of 1.7 to 2.0. The infra red (IR) spectrum of the polymer shows an absorption at 1780 cm characteristic of the imide and at 1740 cm-1 due to ester carbonyl groups and a strong absorption at 2150 cm due to the nitrile group. The broad peak at 3300-3500 cm is indicative of the hydroxy1 groups.
Process for thermoplastic adhesive (TPA)
The polymer (PFAP) is dissolved in methyl ethyl ketone (MEK) to form a 107. (by weight) solution and is then poured in to a rectangulr mould containing polypropylene sheet fixed at the bottom. It is allowed to evaporate at room temperature for 24 hours. The amount of solution poured to the mould is regulated so as to have a thickness of 50 to 100 micron for the dry film. This film can be served as a thermoplastic adhesive.
The dry film is then cut into dumb-bell specimen for determining the tensile properties as per ASTM-method. Typically tensile strength, elongation and initial young's modulus are measured. Typica1 mechanical properties of the film are given in table 1.
The formed film is tested for its mechanical properties but after curing it following a step-wise cure schedule of 30 minutes each at 80°C, 100°C - Mechanical properties are included in table 1. Application of adhesive in bonding
The adhesive properties. Lap Shear Strength (LSS) and T-Peel Strength (TPS) of the film adhesives are determined using chromic acid-etched B-51-SWP aluminium alloy as per ASTM D-1002 and ASTM- D872 methods respectively. The film of reguired are a is cut and interposed between the joints with contact pressure. The step-wise cure schedule of 30 minutes each at 80°C, 100°C and 150°C is adopted both for thermop1astic adhesive (TPA) and thermoset adhesive (TSA), The aluminium alloy can be replaced by bi trile rubber in which case no etching is given.
Table gives the relative concentrations of the monomers employed for realising the phenol-functional acrylic polymers (PFAP) described therein.
Table gives typical mechanical properties of both thermoplastic adhesive (TPA) and cured thermoset adhesive (TSA).
Table 3 gives the LSS and TPS of both types of adhesive both for aluminium-aluminium and rubber-aluminium systems as described.
Scheme 1 depicts the synthesis of the polymer and curing of the thermoset adhesive resulting from it.
Table is Typical composition and, molecular characteristics of
phena1—functiona1 acrylic po1ymers (PFAP)
Table 2: Mechanical properties of the thermoplastic adhesive
(TPA) and cured thermoset adhesive (TSA). The numbers refer to
adhesives derived from corresponding PFAP) of table 1. (Examples
TPA-1 and TBA-1 are derived from PFAP-1)
Table 3: LSS (in kg/cm2) and T-peel strength (in kg/cm) of TPA and TSA polymers under ambient conditions
The advantages of the present invention are:
The film adhesives disclosed in the present invention
is easily synthesised and their composition and consequent1y the mechanical properties can be conveniently tailored.
The polymer readily forms film which is transparent and is stable at ambient conditions indefinitely-
The dry film can be rendered thermoplastic or thermoset through easy formulation while casting film from it-
The absence of condensation cure reaction avoids probability for formation of microvoids between bonded substrates.
It can be easily used as adhesive for different adherends for moderately load bearing applications.
Our copending application /MAS/99 disc loses and claims a process for producing thermosetting adhesive from the acrylic copolymers having pendant phenolic groups.
1. A process for producing acrylic copolymers with pendant phenol functions comprising copolymerising an alkenyl cyanide monomer, an acrylic acid ester monomer and hydroxy phenyl maleimide containing both an unsaturation and a phenol group, in the presence of a free radical initiator and isolating the copolymer produced.
2. The process as claimed in claim 1, wherein the alkenyl cyanide monomers is acrylonitrite or methacrylonitrile.
3. The process as claimed in claim 1, wherein the acrylic acid ester is an ester of methanol, ethanol, propanol, isopropanol, butanol, isobutanol, pentanol or ehtylhexyl alcohol.
4. The process as claimed in claim 1, wherein said monomer containing an unsaturation and a phenol group is selected from hyroxy phenyl citraconimide, hydroxy phenyl itaconimide and hydroxy styrene.
5. The process as claimed in claim 4, wherein said phenol group is located on ortho, meta or para positions with respect to the unsaturated group.
6. The process as claimed in claim 1, wherein the free radical initiator is an azo compound preferably azobis isobutyronitrile or azobis cyanocyclohexane.
7. The process as claimed in claims 1 and 2 wherein the
copolymerisation is carried in the presence of a peroxide catalyst.
8 • The process as c1 aimed in c1aim 3, wherein the perox ide catalyst is selected from benzoyl peroxide, ditertiary butyl peroxide, diamyl peroxide and eyelohexanone peroxide.
9, The process as claimed in claims 1-4 wherein the
polymerisation is carried at 60 to 90°C for 10 hours.
10. The process as claimed in claims 1-5, wherein said polymerisation is carried out in the presence of an organic solvent selected from tetra hydrofuranj dioxane, methyl ethyl ketone, methyl isobutyl ketone, dimethyLformamide, dimethylacetamide, either alone or in combination.
11. The process as claimed in claims 1-6, wherein 55 to 657-
by wt of alkyl acrylate monomer, 20-357. by weight of the nitrile
monomer and 3 to 157. by weight of phenol functional polymer are
12. The process as claimed in claims 1-7, wherein the
copolymer is cast into films by known methods.
13. The process as claimed in claim 12, wherein said thermoplastic film is cast on a support.
14. A process for producing acrylic polymers with pendant phenol groups substantially as herein described.
Dated this 21st day of April 1999
|Indian Patent Application Number||453/MAS/1999|
|PG Journal Number||50/2007|
|Date of Filing||21-Apr-1999|
|Name of Patentee||M/S. INDIAN SPACE RESEARCH ORGANISATION|
|Applicant Address||ANTARIKSH BHAVAN, NEW BEL ROAD, BANGALOR - 560 094,|
|PCT International Classification Number||C 08 F 216/00|
|PCT International Application Number||N/A|
|PCT International Filing date|