Reactive compositions and polymers made therefrom

A reactive composition comprising a solution of about 25-65% by weight of an uncured elastomer in about 35-75% by weight of polymerizable vinyl monomer and a free radical peroxide polymerization initiator. The reactive composition is polymerized under anaerobic conditions without solvent to form a graft copolymer wherein the elastomer is in a continuous phase and the resinous vinyl polymer functions as a reinforcing filler. The resulting graft copolymer has a tensile modulus of at least about 5 MPa at 200% elongation and 1.0 MPa at 50% elongation.

BACKGROUND OF THE INVENTION 
This invention relates to novel reactive compositions of an elastomer 
dissolved in a vinyl monomer and graft copolymers prepared therefrom that 
are especially tough elastomers. 
The art is replete with compositions comprising mixtures of plastic resins 
and elastomeric materials. Many commonly used plastics such as 
poly(styrene), poly(methacrylate), the nylon resins, and so on, are 
subject to brittle fracture in their unmodified form, and it has become 
common to compound such resins with various proportions of rubber-like 
polymers to improve their resistance to breaking as the result of sharply 
applied stress. The sophistication of this art has also extended to the 
employment of elastomeric polymers that form ionic, covalent, or Van der 
Wals bonds with the host resin, it having been found that improvement of 
impact strength is even greater if some bonding occurs between the resin 
and the elastomeric toughening agent. Among the many patents describing 
such compositions, U.S. Pat. Nos. 3,489,822, 3,819,765 and 3,886,233 can 
be mentioned as representative. These patents describe compositions 
wherein minor amounts of ethylene-propylene (EP) copolymers or 
ethylene-propylene-diene (EPDM) elastomers are reacted with polymerizable 
monomers, such as styrene and acrylonitrile, to form grafted copolymers. 
Elastomers are vulcanized with a great variety of chemicals, depending on 
the composition of the host polymer. Sulfur and its compounds, various 
organic compounds, metal oxides and hydroxides, and a variety of organic 
peroxides are commonly used. U.S. Pat. No. 3,179,715 teaches that EP 
copolymers can be vulcanized by a co-curing reaction in mixtures 
containing about 5% to 29% styrene or divinylbenzene under the influence 
of organic peroxide free radical initiators to give a fairly tough rubber. 
The compounding and vulcanization of elastomers in conventional commercial 
practice is a complex process, involving mixing of polymer, fillers and 
curing agents in large and expensive equipment, processing on sheet-off 
mills, preparation of preformed portions of the resulting stock, and 
finally vulcanization at high temperatures in compression molding 
equipment. There is a great desire in the rubber industry to make greater 
use of the less complex injection molding methods normally used for 
fabricating objects of the thermoplastic resins by the plastics industry. 
Progress has been made in this direction by employing reactive materials 
such as the liquid isocyanate elastomers, which are mixed with curing and 
extending compounds in the course of injection molding to form 
polyurethane products. This process is known as liquid injection molding 
(LIM) or liquid reaction molding (LRM) and is described in, among other 
places, "Rubber Age", July 1975, pages 46-48. This type of system is used 
for forming polyurethane parts, for instance, and requires precise control 
of the metering of two or more reaction streams because proper 
stoichiometry of the reactants must be maintained. An analogous process 
using highly reactive but more conventional rubber compositions such as 
specially compounded SBR or EPDM rubbers of a less fluid nature is known 
as reaction injection molding (RIM). This process requires especially 
heavy duty processing equipment because of the high viscosity of the high 
molecular weight elastomers which are the major components of the 
compositions employed. One apparatus suitable for processing such 
compositions is described in U.S. Pat. No. 3,878,285 to Souffie. There is 
a need in the industry for less complex, less costly, and more easily 
processable compositions that can be used in the LIM and thermoset 
injection molding processes to give tough, high quality reinforced rubber 
objects. 
SUMMARY OF THE INVENTION 
It has now been discovered that stable reactive compositions can be made by 
dissolving an uncured elastomer in a polymerizable vinyl monomer. These 
reactive compositions remain stable when stored at ambient temperatures 
for extended periods of time. Subsequently, the reactive compositions can 
be heated to cause polymerization of the solution to a solid, tough 
elastomeric rubber. The novel reactive compositions comprise a solution of 
about 25-65% by weight, preferably 30-50% by weight, of an uncured 
elastomer, selected from the groups consisting of ethylene/higher 
.alpha.-olefin copolymers; natural rubber; ethylene/ethyl acrylate 
copolymers; styrene butadiene rubber; ethylene/vinyl acetate copolymers; 
polyisobutylenes; or polychloroprene, solubilized in 35-75% by weight, 
preferably 50-70% by weight, of a polymerizable vinyl monomer capable of 
dissolving said elastomer and a thermally activatable free-radical 
peroxide polymerization initiator. Preferably, the elastomer is an 
ethylene/propylene copolymer, optionally containing one or more 
nonconjugated dienes, and most preferably wherein the copolymer has an 
ethylene content of from about 50-80% by weight, most preferably 60-80% by 
weight, ethylene units. Any polymerizable vinyl monomer capable of 
solubilizing or dissolving in the uncured elastomer can be used in the 
reactive composition. The preferred polymerizable vinyl monomers are 
styrene, substituted styrenes, vinyl toluene, acrylic acid, methacrylic 
acid and esters thereof, vinyl acetate, acrylonitrile, and 
methacrylonitrile. The compositions are prepared by adding, in any order, 
elastomer, peroxide initiator, and polymerizable vinyl monomer to a vessel 
and mixing until the elastomer is in solution in the vinyl monomer. The 
resulting solution is a stable reactive composition that can be 
polymerized by heating into a tough, elastomeric graft copolymer wherein 
the elastomer is in the continuous phase and the resinous vinyl polymer 
forms a separate and discreet phase that functions as a reinforcing 
filler. More particularly, a graft copolymer made by injecting a solution 
of about 25-65% by weight of an uncured elastomer selected from the group 
consisting essentially of ethylene/higher .alpha.-olefin copolymers; 
natural rubber, ethylene/ethyl acrylate copolymers; styrene butadiene 
rubber; ethylene/vinyl acetate copolymers; polyisobutylenes; or 
polychloroprene, solubilized in about 35-75% by weight of a polymerizable 
vinyl monomer capable of dissolving said elastomer and a free radical 
peroxide polymerization initiator into a mold cavity and heating the 
solution to about 120.degree.-180.degree. C for about 2-40 minutes under 
anaerobic conditions without solvent for the reactants to obtain a graft 
copolymer wherein the vinyl monomer graft polymerizes on the elastomer, 
said elastomer being a continuous phase and the resinous vinyl polymer is 
a separate phase that functions as a reinforcing filler, thus resulting in 
a grafted copolymer having a tensile modulus in the absence of inorganic 
fillers of at least about 1.0 MPa at 50% elongation. The resulting graft 
copolymer consists essentially of an elastomer selected from the group 
consisting of ethylene/higher .alpha.-olefin copolymers; natural rubber; 
ethylene/ethyl acrylate copolymers; styrene butadiene rubber; ethylene 
vinyl acetate copolymers; polyisobutylenes; or polychloroprene comprising 
a continuous phase and resinous vinyl polymer which is a separate phase 
grafted to said elastomer that functions as a reinforcing filler, said 
grafted copolymer having a tensile modulus of at least about 5 MPa, 
preferably at least about 7 MPa at 200% elongation and at least about 1.0 
MPa at 50% elongation. 
DETAILED DESCRIPTION OF THE INVENTION 
The reactive compositions are prepared by mixing at ambient temperatures 
25-65% by weight uncured elastomer, 35-75% by weight polymerizable vinyl 
monomer and a thermally activatable free radical peroxide polymerization 
initiator. The uncured elastomers that are dissolved in the polymerizable 
monomer include ethylene/higher .alpha.-olefin copolymers, optionally 
containing one or more nonconjugated dienes. Generally, the amount of 
ethylene, higher .alpha.-olefin, nonconjugated dienes present in the 
copolymer is, by weight, 25-80% ethylene, 60-20% higher .alpha.-olefin and 
the balance nonconjugated diene. Usually, the higher .alpha.-olefin is 
propylene but other olefins such as 1-butene, 4-methyl-1-pentene, 
1-pentene, 1-heptene, and 1-decene can also be used. The nonconjugated 
dienes containing only one terminal double bond are, generally, acyclic 
dienes containing 6-22 carbon atoms, 1,4-hexadiene, ethylidenenorbornene, 
cyclopentadiene, 1,4-heptadiene, and 5-methylene-2-norbornene. Copolymers 
may also contain a second nonconjugated diene having two terminal double 
bonds, such as 1,7-octadiene, 1,4-pentadiene, 5-(5-hexenyl)-2-norbornene 
and norbornadiene. These copolymers are described in U.S. Pat. Nos. 
2,933,480, 3,260,708 and 3,819,591. 
One especially useful composition contains an uncured ethylene/higher 
.alpha.-olefin copolymer containing 60-80% by weight ethylene units. When 
such copolymer in particulate form is mixed with a polymerizable vinyl 
monomer, such as styrene, and heated briefly, e.g., 5-30 minutes, to a 
moderate temperature such as 50.degree.-60.degree. C, a solid solution of 
a free-flowing particulate composition is obtained wherein the vinyl 
monomer remains in monomeric form. By solid solution is meant a 
homogeneous composition containing monomer imbibed in the high molecular 
weight polymer that is solid at temperatures up to about 60.degree. C but 
that is easily converted to a more fluid, readily injection moldable state 
when heated to processing temperatures of about 65.degree. C or more 
depending on the particular composition employed. Such reactive 
compositions are easy to handle and can be readily polymerized at 
temperatures of 120.degree.-180.degree. C. 
Other suitable elastomers include natural rubber, butadiene/styrene 
polymers (SBR), polychloroprene (neoprene), ethylene/vinyl acetate 
copolymers, polyisobutylenes, and ethylene/ethyl acrylate copolymers. Such 
uncured elastomers are well known in the art. Ethylene/ethyl acrylate 
elastomers are disclosed in U.S. Pat. No. 3,904,588. 
The polymerizable vinyl monomer used in formulating the reactive 
composition must be capable of forming a liquid or solid solution with the 
uncured elastomer. A variety of vinyl monomers can be used, such as, for 
example, styrene, vinyltoluene and other substituted styrene monomers 
containing substituents on the aromatic ring, acrylic acid, methacrylic 
acid and esters thereof, vinyl acetate, acrylonitrile, methacrylonitrile 
and mixtures thereof, especially styrene-acrylonitrile, 
styrene-methacrylic acid and styrenemethyl methacrylate. Excellent results 
are obtained when monomeric styrene or styrene-methacrylic acid mixtures 
are used. 
The thermally activatable free radical peroxide polymerization initiators 
used with the vinyl monomer can be added to the composition in amounts of 
from 0.1-5%, usually 0.5-2% by weight of total polymeric composition. The 
peroxide used should be capable of polymerizing the vinyl monomer and 
initiating the graft copolymerization. Peroxide-type polymerization 
catalysts having the formula ROOR' where R is an organic radical and R' is 
an organic radical or hydrogen can be used. Representative examples 
include ditertiary butyl peroxide, tertiary butyl hydroperoxide, tertiary 
butyl perbenzoate, dicumyl peroxide, 2,5-dimethyl-2,5-bis(t-butyl 
peroxy)hexyne-3. The reactive compositions obtained by mixing at ambient 
temperature the uncured elastomer containing a free radical peroxide 
initiator and polymerizable vinyl monomer result in a stable, easy to 
handle solution that can be polymerized to a tough, elastomeric copolymer. 
The loss of solubility of the copolymer indicates that grafting of the 
vinyl monomer onto the copolymer has taken place. Quite advantageously 
these stable reactive solutions can be molded by LIM and conventional 
thermoset molding techniques. Reactive compositions prepared from 
ethylene/higher .alpha.-olefin copolymers having at least 60% by weight 
ethylene units are especially preferred because such compositions are 
free-flowing particulate solid solutions that are most convenient to use 
in injection molding operations. 
Conventional cross-linking aids used with peroxide initiators can be 
employed in the polymerization reaction and include polyunsaturated 
compounds such as m-phenylenebis-maleimide, triallyl cyanurate, 
triallylisocyanurate, divinylbenzene and the like. 
Polymerization and curing of the reactive solution is accomplished 
simultaneously by heating the solution to temperatures of about 
120.degree.-180.degree. C, usually 140.degree.-170.degree. C, for about 
2-40 minutes, depending on the activity or half-life of the initiator. The 
reactive solution is injection molded and polymerization is conducted in a 
mold cavity under anaerobic conditions without solvent. The resulting 
polymerized cured copolymer is a graft copolymer wherein the elastomer 
forms a continuous phase and the polymerized resinous vinyl polymer, e.g., 
polystyrene, forms a discreet phase. The graft copolymer has the 
characteristics of an elastomer in spite of the fact that a large portion 
of the graft copolymer is composed of non-elastomeric units. The resinous 
phase formed from the vinyl polymer acts as a reinforcing filler 
conferring surprisingly high tensile modulus and ultimate strength on the 
cured product. The graft copolymers made by the process of this invention 
have a tensile modulus of at least about 5 MPa, usually 7 MPa, at 200% 
elongation, and at 50% elongation of tensile modulus of at least about 1.0 
MPa, all in the absence of inorganic fillers. Many copolymers have a 200% 
tensile modulus of the order of 25-30 MPa. 
Injection molding is accomplished on an injection molding machine suitable 
for molding thermosetting materials. Compounds to be molded may contain an 
internal release agent such as stearic acid. In addition, the mold can be 
sprayed with inert release agents. The barrel of the molding machine is 
heated above 65.degree. C but below the temperature at which the chosen 
peroxide initiator rapidly decomposes. The compound is injected into a 
mold cavity heated to 120.degree.-180.degree. C and maintained under 
pressure until the part has cured, i.e., 2-40 minutes. Following the cure, 
the mold is opened and the part is stripped from the mold and allowed to 
cool. 
Compounding ingredients such as fillers, pigments, extenders, internal 
lubricants, etc., can also be advantageously employed in the 
polymerization process. 
The graft copolymers of this invention can be used in many applications 
where ethylene/higher .alpha.-olefin copolymers, e.g., EPDM's and SBR, 
have been used in the vulcanized state. Exemplary uses are in molded 
products, and fascia or sight-shields for automobiles and shoe components. 
The exact manner of fabricating such goods is apparent to one skilled in 
the art.