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
2000-08-14
2002-07-16
Lipman, Bernard (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S333300, C525S342000
Reexamination Certificate
active
06420485
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to curable siloxane-grafted hydrocarbon copolymers which are useful in the formulation of sealant, caulk, adhesive and coating compositions. More particularly, the invention relates to silyl-functional copolymers prepared by reacting an isomonoolefin/vinyl aromatic copolymer with particular siloxanes in the presence of a free radical generator.
BACKGROUND OF THE INVENTION
Various organic polymers having moisture-sensitive silyl functionality are known in the art. Such systems may be prepared, for example, by hydrosilating a polymer having vinylic functionality along its main chain (or at terminal positions) with a reactive group-containing silane which also contains SiH functionality, the reaction being carried out in the presence of a catalyst such as platinum. When hydrocarbon polymers are so modified, they combine advantages inherent in moisture-curable silicone compositions with those of the hydrocarbon. That is, the modified polymer can be crosslinked via the reaction of hydrolyzable silyl groups at room temperature and the low gas and moisture permeability of the organic backbone is maintained. Therefore, such systems are eminently suitable for use as base polymers in sealants for gas barrier applications such as formed-in-place gaskets, O-rings, rubber plugs/seals, medical and food container caps, and the like. However, the hydrosilation methods conventionally used to prepare such modified polymers and their precursors are expensive and complicated.
A different approach for preparing certain polymers having moisture-sensitive silyl functionality has been suggested by Scott in U.S. Pat. No. 3,646,155. This patent teaches that polyethylene, or a copolymer of ethylene with minor portions of propylene and/or butylene, can be reacted with a silane which bears both an aliphatically unsaturated group as well as a hydrolyzable group, the reaction taking place in the molten state and in the presence of a free-radical generating compound. The resulting modified polyethylene was crosslinked by exposing it to moisture, typically steam. Of course, such an ethylene polymer or copolymer generally has a high molecular weight and must be processed at temperatures above the melt point (typically above 140° C. according to Scott). Further, all of the examples of the Scott patent indicate that the melt index, which is inversely related to melt viscosity, actually decreases upon modification with the silane. Scott points out that his cured compositions generally exhibit properties similar to those of corresponding peroxide-cured systems. However, it is clear that the moisture-curable modified polymers taught by Scott must be processed/fabricated at high temperatures and are certainly not suited for the production of room-temperature vulcanizable (RTV) sealant compositions.
Copending application Ser. No. 09/260,456 to Bahadur et al. discloses a method for the preparation of a moisture-curable silyl-functional copolymer wherein a copolymer of isobutylene and a conjugated diene having a number average molecular weight of about 5,000 to 500,000 is reacted with a silane having both an alkenyl group and a silicon-bonded hydrolyzable group, the reaction being carried out in the presence of a free-radical generator. The resulting copolymer exhibits a molecular weight and viscosity which are considerably lower than the corresponding values for the initial unmodified copolymer and it is an ideal base polymer for formulating RTV sealants for gas barrier applications. Likewise, copending application Ser. No. 09/260,455 to Chung et al. discloses a moisture-curable silylated copolymer which is prepared by reacting a copolymer comprising at least 50 mole percent of a C
4
to C
7
isomonoolefin and a vinyl aromatic monomer with a silane having unsaturated functionality as well as hydrolyzable functionality, the reaction being carried out in the presence of a free radical generator.
SUMMARY OF THE INVENTION
It has now been discovered that the methods employed in the above mentioned copending applications can be followed wherein the silane component is replaced with a siloxane containing a hydrolyzable silyl group separated from a silicon-bonded unsaturated group, or a silicon-bonded hydrogen, by a hydrocarbon linkage. It was particularly surprising that the SiH-functional siloxanes could be readily grafted to a hydrocarbon copolymer using the above mentioned methods. Since the aforementioned functional siloxanes have higher boiling points than the silanes described above, they can be grafted at higher temperatures than latter compounds while remaining relatively less volatile, a major consideration with respect to industrial hygiene in commercial production. Moreover, these siloxanes can also be prepared at a lower cost than a silane having a long alkenyl group such as hexenyltrimethoxysilane, the latter also being somewhat less volatile than a compound such as vinyltrimethoxysilane.
The present invention, therefore, relates to a silylated copolymer which is the reaction product of:
(A) an olefin copolymer prepared from at least 50 mole percent of at least one C
4
to C
7
isomonoolefin monomer and at least one vinyl aromatic monomer;
(B) a siloxane having the formula
Q-SiR2(OR
2
Si)
n
R″SiR′Y
2
wherein Q is a monovalent group selected from hydrogen or an olefinically unsaturated hydrocarbon group having 2 to 8 carbon atoms, R is an alkyl group having 1 to 4 carbon atoms, R″ is a divalent hydrocarbon group having 1 to 6 carbon atoms, Y is a hydrolyzable organic group, R′ is selected from R or Y and n is an integer having a value of 1 to 9; and
(C) a free radical generator.
DETAILED DESCRIPTION OF THE INVENTION
The copolymers of the invention may be characterized as the addition product of an olefin copolymer radical created by contact of copolymer (A) with a hydrolyzable siloxane (B) in the presence of a free radical generator (C), wherein the siloxane adds to the polymer backbone to produce a siloxane-grafted (siloxane-modified) copolymer product.
Olefin copolymers suitable for modification in accordance with this invention comprise copolymers prepared from monomer mixtures containing at least 50 mole % of at least one C
4
, to C
7
isomonoolefin and from about 0.1 to 50 mole percent of at least one vinyl aromatic monomer. Preferred vinyl aromatic monomers are mono-vinyl aromatics, such as styrene and alpha-methyl styrene; alkyl-substituted styrenes, such as t-butylstyrene; and para-alkyl substituted styrenes wherein the alkyl group contains from 1 to 4 carbon atoms, preferably para-methylstyrene. Suitable isomonoolefin monomers include isobutylene, isopentene, isohexene, isoheptene, and the like. Preferably, 100% of the isomonoolefinic monomer content is isobutylene. Further, it is preferred that component (A) is an elastomeric copolymer prepared from isobutylene and para-methylstyrene which contains about 0.1 to 20 mole % of para-methylstyrene. These copolymers (hereinafter referred to as IPMS) have a substantially homogeneous compositional distribution such that at least 95% by weight of the polymer has a para-methylstyrene content within 10% of the average para-methylstyrene content of the polymer. They are also characterized by a narrow molecular weight distribution (Mw/Mn) of less than about 5, more preferably less than about 3.5, a glass transition temperature (T
g
) below about −50° C. and a number average molecular weight (M
n
) in the range of about 2,000 to 1,000,000, preferably from about 10,000 to 200,000. These copolymers may be prepared by conventional cationic polymerization of the monomer mixture using a Lewis acid catalyst, as well known in the art (e.g., see U.S. Pat. No. 5,162,445).
Another class of olefin copolymers which are useful in the present invention are the metallocene-catalyzed copolymers comprising at least one C
4
to C
7
isomonoolefin and an alkylstyrene, particularly a C
1
to C
4
para-alkylstyrene, and most preferably para-methylstyrene (e.g., see U.S. Pat. No. 5,543,484). These copolymers
Shim Anne Katja
Suzuki Toshio
Dow Corning Corporation
Lipman Bernard
Weitz Alexander
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