Living cationic polymers prepared from silyl-functional...

Details Living cationic polymers prepared from silyl-functional... Living cationic polymers prepared from silyl-functional...

1999-04-15

2001-02-27

Lipman, Bernard (Department: 1713)

Organic compounds -- part of the class 532-570 series

Organic compounds

Silicon containing

C525S284000, C526S194000

Reexamination Certificate

active

06194597

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a method for preparing a living cationic polymer. More particularly, the invention relates to a method for synthesizing a living polymer having a silyl-functional head group by reacting a cationically polymerizable monomer in the presence of a Lewis acid using a novel organosilane as the initiator. The resulting living polymer can be coupled to prepare a silyl-functional telechelic polymer.
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 arc crosslinkable 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. However, this method does not teach the preparation of a PIB having terminal silyl functionality or the preparation of a telechelic silyl-functional PIB.
To the contrary, 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 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.
Therefore, there is still a need for compounds which are capable of initiating a cationically polymerizable monomer to prepare a polymer having a reactive silicon-functional head group.
SUMMARY OF THE INVENTION
Applicants have now discovered 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 polymer having a silicon halide head group. The present invention, therefore, relates to a method for preparing a silyl-functional living cationic polymer, said method comprising reacting, in the presence of a Lewis acid,
(A) at least one cationically polymerizable monomer with
(B) an initiator 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 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.
The invention further relates to the above method wherein the living cationic polymer is subsequently quenched to form a stable product or is reacted in situ with a coupling agent to provide a coupled reactive silyl-functional telechelic polymer.
DETAILED DESCRIPTION OF THE INVENTION
The cationically polymerizable monomers contemplated in the present method include vinyl monomers which can stabilize a cation or propagating center due to the presence of an electron donating group, or by resonance. These can be selected from alkenes, such as isobutylene, butadiene, isoprene, methylbutene, 2-methylpentene; styrenics, such as styrene, p-methylstyrene, &agr;-methylstyrene and indene, inter alia. Alternatively, they can be vinyl ethers, such as isobutyl vinyl ether and methyl vinyl ether. The instant method contemplates the employ of one or more of the above described monomers.
In preferred embodiments of the present method, at least one monomer is selected from isobutylene, isoprene or a styrenic monomer. Preferably, at least 50 mole percent, and more preferably 80 mole percent, of the monomer used in the cationic polymerization is isobutylene. Most preferably, the entire monomer is isobutylene, this resulting in a living polyisobutylene (PIB) homopolymer.
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)—, in 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 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 to 10 but is preferably more than 1. More preferably, the ratio is 1 to 3. After the hydrosilation reaction, separation of the desired product (v) by a suitable method, such as fractional distillation, is recommended. In this case, it is highly recommended 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 arc platinum black, platinum metal on various solid supports (e.g., carbon), chloroplatinic acid, alcohol solutions of chloroplatinic acid, and complexes of chloroplatinic acid with liquid ethylenically unsaturated compounds such as olefins and organopolysiloxanes containing ethylenically unsaturated hydrocarbon radicals bonded to silicon. Preferred catalysts include a platinum complex catalyst produced by reacting chloroplatinic acid and divinyltetramethyldisiloxane, prepared according to U.S. Pat. No. 3,419,593 to Willing and a neutralized complex of platinous chloride and divinyltetramethyldisiloxane, prepared according to U.S. Pat. No. 5,175,3

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