Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2000-03-03
2002-05-14
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S213000, C525S217000, C525S195000, C525S357000
Reexamination Certificate
active
06388018
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention:
This invention relates to graft copolymers containing cationic groups in the polymer chain.
2. Description of the Related Art:
It is well known to blend low Tg (glass transition) elastomers with more brittle thermoplastic polymers having a higher Tg to yield blends with improved toughness and impact strength. The desired properties are only obtained by achieving a fine dispersion of the elastomer in the thermoplastic polymer.
It is also well known to form blends of relatively highly unsaturated elastomers such as polybutadiene or natural rubber with elastomers having less or no ethylenic unsaturation, e.g., butyl rubber, halogenated butyl rubber, copolymers of isobutylene and a para-alkylstyrene, ethylene/propylene or ethylene/propylene/diene rubber and the like, in order to enhance the properties of vulcanizates based on such blends. Such property enhancement includes improved oil and grease resistance, improved resistance to oxygen and ozone degradation, improved abrasion resistance and improved impermeability to air, water vapor and many organic solvents.
One of the major problems associated with the formation of such blends is that most of these polymer components are mutually incompatible. Poor mutual adhesion at the blend phase boundaries in such systems results in a diminishment of physical properties of the polymer blend.
It is well established that the use of appropriately structured polymer compatibilizers as additives in such systems can markedly enhance physical properties. These additives are typically block or graft copolymers in which polymer segments interact in a favorable manner with each polymer phase of the blend. This “bridging” at the interfacial blend region enhances the interfacial adhesion, and improves the dispersion and size of the discrete blend phase and improves mechanical properties. Thus, for example, a block or graft copolymer containing both polybutadiene and polystyrene polymer units can serve as a compatibilizer in a polymer system comprising a blend of polystyrene and polybutadiene.
Analogs of halogenated butyl rubber have been recently discovered which comprise the halogenated product of a random copolymer of a C
4
to C
7
isomonoolefin, e.g. isobutylene, and a para-alkystyrene, e.g. para-methylstyrene, such as disclosed in U.S. Pat. No. 5,162,445. Although these materials are devoid of olefinic backbone unsaturation, the presence of a benzylic halogen, e.g. bromine, permits facile crosslinking or curing of the polymers using, for example, zinc oxide/stearic acid curing systems. In addition, functionalized versions of these copolymers may be prepared by nucleophilic substitution of the benzylic halogen present in the polymer molecules with a reagent reactive therewith to provide polymers containing amine, acid, ester, amide, onium and the like functionality. Grafted polymers may also be prepared by a graft-onto reaction wherein the halogenated copolymer is reacted in solution with a polymeric nucleophile such as polystyryl lithium. These graft-onto reactions lead to the production of solvent soluble grafted copolymers which are disclosed to be useful as compatibilizers for polymer blends, e.g., blends of polyisobutylene, butyl rubber or halogenated copolymers of isobutylene and para-methylstyrene with polystyrene.
SUMMARY OF THE INVENTION
The present invention provides graft copolymers which are polymeric onium salts of polymers and copolymers containing halogenated para-alkylstyrene units in the backbone polymer chain.
More specifically, the invention provides a graft copolymer containing cationic units in the polymer chain having the structure:
wherein R and R′ are independently selected from the group consisting of hydrogen and; a C
1
to C
4
alkyl group, Z is selected from the group consisting of nitrogen and phosphorous, R
1
and R
2
are the same or different alkyl radicals containing 1 to 4 carbon atoms, R
3
is a direct link or an organic radical containing 1 to 6 carbon atoms, X is halogen and PL is a polymer chain segment derived from at least one anionically polymerized monomer.
The invention also provides a process for preparing a graft copolymer comprising:
a) polymerizing one or a mixture of anionically polymerizable monomers under anionic polymerization conditions using, as a polymerization initiator, a compound having the formula R
1
R
2
Z R
3
—Li to form a polymer having the structure R
1
R
2
Z R
3
—PL; and
b) reacting said polymer under onium salt-forming conditions with a copolymer containing polymerized monomer units in the polymer chain having the structure:
wherein a graft copolymer containing cationic units pendant to the backbone polymer chain and having the structure described above is obtained.
Graft copolymers of this invention are useful as compatibilizers for immiscible polymer blends and are also useful in their own right as thermoplastic elastomers having improved mechanical properties.
DETAILED DESCRIPTION OF THE INVENTION
The graft copolymers within the scope of this invention differ from the graft copolymers disclosed in U.S. Pat. No. 5,162,445 in their structure and method of preparation. In the '445 patent, a “living” anionically polymerized polymer or a carboxylate thereof is subjected to a nucleophilic displacement reaction involving benzylic halogen present in a backbone polymer containing polymerized, halogenated para-methylstyrene. In the present invention, graft copolymers are prepared by reacting an anionically polymerized polymer polymerized using a tertiary amino or phosphino lithium initiator. Subsequent reaction of the phosphino or amino group present at the polymer end with a backbone polymer containing the benzylic halogen results in the formation of an ammonium or phosphonium cationic group situated between the backbone chain and the pendant graft polymer. This group enhances both the mechanical properties of the graft copolymer as well as the dispersion therein of a negatively charged filler materials such as carbon black and colloidal silica.
Polymers which may be used as the backbone segment in preparing the graft copolymers of this invention may be thermoplastic or elastomeric polymers. Suitable thermoplastic polymers include halogenated, e.g., brominated, poly (para-methylstyrene) and random copolymers of halogenated para-methylstyrene with one or more other monomers such as non-halogenated para-methylstyrene, styrene, t-butylstyrene, alpha-methylstyrene, acrylonitrile, alkylacrylates or methacrylates, butadiene and the like.
Suitable elastomeric copolymers used as the backbone segment include random halogenated copolymers of less than 50 wt % of a para-alkylstyrene such as para-methylstyrene and at least 50 wt % of one or more elastomer-forming monomers such as C
4
to C
7
isomonoolefin, butadiene, isoprene and the like.
Preferred copolymers forming the backbone segment of the graft copolymers are the halogenation product of random elastomeric copolymers of a C
4
to C
7
isomonoolefin, such as isobutylene, and a para-alkyl styrene comonomer, preferably para-methylstyrene containing at least about 80%, more preferably at least about 90% by weight of the para isomer, and wherein at least some of the alkyl substituent groups present in the styrene monomer units contain halogen. Preferred materials may be characterized as isobutylene interpolymers containing the following monomer units randomly spaced along the polymer chain:
wherein R and R′ are independently hydrogen, lower alkyl, preferably C
1
to C
4
alkyl, and X is bromine or chlorine, and wherein the interpolymer is otherwise substantially free of ring halogen or halogen in the polymer backbone chain. Preferably R and R′ are each hydrogen. Up to about 65 mole % of the para-alkylstyrene present in the interpolymer structure may be the halogenated structure (2) above, more preferably from about 5 to 60 mol %.
Most useful of such materials are elastomeric random copolymers of isobutylene and para-methylstyrene containing from about 0.5 to about
Fetters Lewis J.
Peiffer Dennis G.
Rucker Rebecca L.
Sissano Joseph A.
Wang Hsien-Chang
Asinovsky Olga
ExxonMobile Research and Engineering Company
Purwin Paul E.
Wang Joseph C.
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