Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2000-05-16
2002-10-22
Lipman, Bernard (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S279000
Reexamination Certificate
active
06469115
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for preparing a room temperature vulcanizable polyisobutylene polymer. More particularly, the invention relates to a method for synthesizing a polyisobutylene having hydrolyzable silyl-functional groups positioned at or near molecular chain ends, said polymer being prepared by a living polymerization wherein isobutylene, a silyl-functional cationic initiator and a silyl-functional comonomer are reacted in the presence of a Lewis acid.
BACKGROUND OF THE INVENTION
Living anionic polymers are well known in the art but truly living cationic systems have only been developed more recently. By definition, termination and chain transfer rates are zero, or negligible, in such a living polymer so that the concentration of active centers remains approximately constant. Of particular commercial interest are living organic polymers which can be used to prepare telechelic oligomers and macromolecules having hydrolyzable silyl end groups since these can be used to formulate room temperature vulcanizable (RTV), moisture-curable sealants, caulks and adhesives, inter alia. Unlike the well known moisture-curable silicone RTVs, compositions based on polymers having a hydrocarbon backbone offer the advantage of low permeability, making them more suitable for gas barrier applications such as form-in-place gaskets, O-rings, rubber plugs/seals, and the like.
U.S. Pat. No. 4,829,130 to Licchelli et al. discloses a method for preparing silylated copolymers of isobutylene which are cross linkable upon exposure to moisture. In this case, isobutylene is copolymerized with a comonomer having a vinylic group attached to a silylalkyl group through a benzene ring connecting group. The product of this copolymerization is a polyisobutylene (PIB) having pendant silyl-functional groups along its main chain.
Likewise, U.S. Pat. No. 4,524,187 to Greco et al. teaches cross linkable polyisobutylene copolymers having pendant silyl functionality which is reactive with moisture. In this case, isobutylene is first reacted with a triene compound to form a copolymer having pendant vinyl groups, the latter then being silylated with a moisture-reactive hydridosilane or mercapto-functional silane.
Polymers having reactive silyl head groups were described by Kennedy et al. in
Advances in Polymer Science
, 43, 1-50 (1982). These workers discovered that initiators which included an SiCl or SiH group as well as a cationogenic moiety could be used to polymerize cationic systems such that the silicon-functional groups survived. The cationogenic moiety studied was the benzyl chloride group (i.e., —C
6
H
4
—CH
2
Cl) wherein &agr;-methylstyrene was polymerized in the presence of diethyl aluminum chloride as coinitiator. In this case, however, it was observed that the amount of —SiCl detected was only a small fraction of the theoretical, especially when more than one chlorine was present in the head group. Further, although these workers suggest that the SiCl groups may survive polymerization of isobutylene, they did not obtain quantitative confirmation thereof and did not demonstrate the new initiators in connection with this monomer. Thus, Kennedy et al. then turned to the investigation of systems having SiH terminal groups, such polymers being considered more promising intermediates which presented fewer experimental difficulties.
In copending application Ser. No. 292,333 filed on Apr. 15, 1999, we disclose the use of a novel class of compounds which, unlike the initiators taught by Kennedy et al., cited supra, can initiate cationic polymerization in a controlled manner to provide a living polymer having a silicon halide head group. This living polymer is prepared by reacting at least one cationically polymerizable monomer with the novel initiator, further described infra, in the presence of a Lewis acid. According to the above disclosure, the living cationic polymer may be further reacted with a coupling agent to provide a silyl-functional telechelic polymer. However, this method requires an exact stoichiometric amount of the coupling agent with respect to the living polymer chain, this often being difficult in large scale operations. Further, this method is relatively complicated and there is still a need for simpler means of synthesizing silyl-functional telechelic hydrocarbon polymers which can be readily cured by exposure to moisture.
SUMMARY OF THE INVENTION
It has now been discovered that a virtually telechelic, silyl-functional polyisobutylene can be prepared by reacting isobutylene, the above mentioned novel initiator, and a silyl-functional styryl comonomer in the presence of a Lewis acid.
The present invention, therefore, relates to a method comprising reacting, in the presence of a Lewis acid,
(A) isobutylene;
(B) an initiator of the formula
and;
(C) a styryl comonomer of the formula
wherein R is selected from H or methyl group, R′ is a divalent non-aromatic hydrocarbon group having 1 to 6 carbon atoms, R″ is independently selected from alkyl groups having 1 to 10 carbon atoms or aryl groups having 6 to 10 carbon atoms, R′″ is a divalent non-aromatic hydrocarbon group having 2 to 6 carbon atoms, X is independently a halogen group, Y is halogen and n is independently 1, 2 or 3.
The invention further relates to the virtually telechelic silyl-functional polymer prepared by the above method.
DETAILED DESCRIPTION OF THE INVENTION
Component (A) of the present invention is a monomer consisting essentially of isobutylene and may be either a substantially pure isobutylene (IB) monomer or a mixture of isobutylene with up to 20 mole percent of at least one monomer selected from 1-butene, 2-butene, isoprene, styrene, &agr;-methylstyrene or p-methylstyrene. These mixtures having a minor proportion of the above mentioned monomers are also referred to as “isobutylene” for the purposes herein. Preferably, component (A) is substantially pure (i.e., distilled) IB.
The reactive silyl-functional initiator (B) of the present invention is represented by the formula
wherein R is selected from H or methyl group, R′ is a divalent non-aromatic hydrocarbon group having 1 to 6 carbon atoms, R″ is selected from alkyl groups having 1 to 10 carbon atoms or aryl groups having 6 to 10 carbon atoms, X is halogen, Y is halogen and n is 1, 2 or 3. Specific examples of R″ include methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, n-octyl, 2-ethylhexyl, n-nonyl, n-decyl, phenyl and tolyl, methyl being preferred. The group R′ is exemplified by —CH
2
—, —CH
2
—CH
2
—, —CH
2
CH
2
CH
2
—, —CH
2
—C(Me)
2
— and —CH
2
═CH
2
—, and is preferably —CH
2
CH(Me)—, wherein Me hereinafter represents a methyl group. Specific examples of X and Y are fluorine, chlorine, bromine and iodine. Further, the moieties attached to the benzene ring of formula (i) may be in ortho, meta or para positions with respect to one another, the latter two isomers being preferred. Preferably, X and Y are chlorine and n is 2 or 3.
In a highly preferred embodiment of the instant method, the initiator has the formula
wherein n is 2 or 3.
The initiators of the present invention can be prepared by first carrying out a hydrosilation reaction between a dialkenyl benzene species (or an alkenyl-alkynyl benzene species) and a halosilane, as illustrated below for a preferred system wherein R′ is —CH
2
CH(Me)—:
in which R, R″, X and n are as defined above in connection with formula (i). In the above hydrosilation reaction, the molar ratio of component (iii) to component (iv) can be 0.3:1 to 10:1 but is preferably more than 1:1. More preferably, the ratio is 1:1 to 3:1. After the hydrosilation reaction, isolation of the desired product (v) by a suitable method, such as fractional distillation, is recommended. In this case, it is highly preferred that a radical scavenger, such as phenothiazine, be added to the mixture to prevent polymerization of the product and starting materials.
Suitable catalysts for the hydrosilation reaction are platinum black, platinum metal on var
Faust Rudolf
Hadjikyriacou Savvas E.
Roy Aroop Kumar
Suzuki Toshio
Dow Corning Corporation
Lipman Bernard
Weitz Alexander
Zombeck Alan
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