Silyl-functional pseudo-telechelic polyisobutylene terpolymers

Details Silyl-functional pseudo-telechelic polyisobutylene terpolymers Silyl-functional pseudo-telechelic polyisobutylene terpolymers

2000-10-03

2001-07-31

Teskin, Fred (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S135000, C526S185000, C526S238000, C525S326500, C525S384000, C524S547000

Reexamination Certificate

active

06268451

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 pseudo-telechelic polyisobutylene terpolymer having hydrolyzable silyl-functional groups statistically positioned near molecular chain ends, said polymer being prepared by a terpolymerization process wherein isobutylene, and two different silyl-functional monomers are reacted in the presence of a Lewis acid.
BACKGROUND OF THE INVENTION
Both silicone and organic polymers which contain reactive functional groups are known in the art. Of commercial interest are polyisobutylene (PIB) systems containing hydrolyzable silyl groups since they can be used to formulate moisture-curable sealants, caulks and adhesives, inter alia. Unlike the well known moisture-curable silicone room temperature vulcanizable (RTV) compositions, systems based on polymers having a PIB backbone offer the advantage of low permeability, making them eminently suitable for gas barrier applications such as formed-in-place gaskets, O-rings, rubber plugs/seals, and the like. In these PIB polymers it is particularly desirable that the functional groups reside at each end of the molecular chain. Such telechelic polymers offer an advantage in that the molecular weight between reactive groups can be controlled. Consequently, when a telechelic polymer is cured, the molecular weight between crosslinks (i.e., the network structure) and, therefore, ultimate mechanical properties of the product, can be controlled and essentially no “dangling” ends remain.
For example, U.S. Pat. No. 4,904,732 to Iwahara et al. discloses, inter alia, the preparation of a silyl-functional PIB polymer by hydrosilating a corresponding polymer which contains unsaturated groups. The resulting polymer can have an essentially telechelic structure and can be cured (e.g., by exposure to moisture). However, the total process suggested by Iwahara et al. is quite complicated and, therefore, expensive.
Using a different approach, U.S. Pat. No. 4,829,130 to Licchelli et al. discloses a method for preparing silylated copolymers of isobutylene which are 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. Ostensibly, the product of this statistical copolymerization is a polyisobutylene having pendant silyl-functional groups along its main chain and, although the process is relatively uncomplicated, the location of functional groups can not be controlled and the products are inherently inferior to silyl functional telechelic polymers.
Likewise, U.S. Pat. No. 4,524,187 to Greco et al. teaches crosslinkable polyisobutylene copolymers having pendant silyl functionality. 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. Again, control of functional group distribution is not possible.
Thus, there is still a need for simpler means of synthesizing a silyl-functional polyisobutylene which can be readily cured by exposure to moisture to form a crosslinked elastomer having properties which approach those of the corresponding telechelic system.
SUMMARY OF THE INVENTION
We have shown that polymers prepared according to the teachings of Licchelli et al., cited supra, do not exhibit a random distribution of silyl-functional groups, as implied by the disclosed process. Thus, when the reactivity ratio (i.e., the ratio of homo-propagation rate constant to cross-propagation rate constant) for the system comprising isobutylene and silyl-functional monomer is approximately 1, and the concentration of the silyl-functional monomer is much lower than that of isobutylene, the functional groups will be randomly distributed along the chain and the distribution of copolymer composition (i.e., molecule-to-molecule variation) will be narrow. However, when this ratio is significantly different from 1, as under the conditions described by Licchelli et al., there is a copolymer composition drift with conversion, and homo-polyisobutylene (not containing any silyl functionality) may also form at low or high conversion. Further, under these circumstances, the silyl functionality tends to congregate at one end of the polymer, resulting in a considerable presence of “dangling” ends having no functionality. This, in turn, leads to inferior mechanical properties, and greater surface tack, when the polymer is cured. These factors could explain the relatively low gel contents reported by Lichelli et al.
We have now found that, unlike the copolymers of Licchelli et al. and Greco et al., a pseudo-telechelic, silyl-functional polyisobutylene terpolymer can be prepared by reacting isobutylene, a comonomer derived from an isopropenyl-functional benzene and a comonomer derived from a vinyl-functional benzene in the presence of a Lewis acid. Unlike the copolymers disclosed in the above cited art, the terpolymers of the present invention exhibit a high gel content when cured (i.e., low extractables).
As used herein, the term “pseudo-telechelic” denotes a terpolymer having one type of reactive silyl-functional unit statistically concentrated near the head of the terpolymer chain and a slightly different type of reactive silyl-functional unit statistically concentrated at the tail of the terpolymer. This definition does not, of course, exclude the presence, albeit to a considerably lesser extent, of either of the above functional groups near the middle of the chain. This surprising result was only observed when the terpolymer was synthesized in a solvent medium wherein the reactivity ratio for the system isobutylene/vinylphenyl comonomer (described infra) is greater than 1 and the reactivity ratio of the system isobutylene/isopropenylphenyl comonomer (also described infra) is less than 1. Moreover, a collateral benefit of the instant method is that the molecular weight of the resulting pseudo-telechelic terpolymer can be controlled by adjusting the amount of the isopropenylphenyl comonomer (B). Again, this is desired as a means of controlling the viscosity of formulated, e.g., sealant products such that the latter can be readily applied in the field.
The present invention, therefore, relates to a method comprising reacting, in the presence of a Lewis acid and a solvent,
(A) an isobutylene monomer;
(B) an isopropenylphenyl comonomer having the formula
(C) a vinylphenyl comonomer of the formula
wherein R′ is a divalent non-aromatic hydrocarbon group having 2 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 hydrolyzable group and n is independently 1, 2 or 3, with the proviso that r
AC
is greater than 1 and r
AB
is less than 1, wherein r
AB
is the reactivity ratio of said isobutylene in the presence of said comonomer (B) and said solvent and r
AC
is the reactivity ratio of said isobutylene in the presence of said comonomer (C) and said solvent.
The invention further relates to the pseudo-telechelic silyl-functional terpolymer prepared by the above method.


REFERENCES:
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patent: 4829130 (1989-05-01), Liechelli et al.
patent: 4904732 (1990-02-01), Iwahara et al.
patent: 5247021 (1993-09-01), Fujisawa et al.
patent: 5260378 (1993-11-01), Gandini et al.
patent: 5478899 (1995-12-01), Bening
patent: 5527870 (1996-06-01), Maeda et al.
6001 Chemical Abstracts, 118 (993) Feb. 8, No. 6, p. 14, Columbus, Ohio USA.
Polymeric Materials Science and Engineering, Vol. 72, “Direct Initiation in Carbocationic Polymerization,”Robert Faust, et. al., University of Massachusetts Lowell.
Journal of Organometallic Chemistry, 156 (1978) 55-64, “Organoaluminum Chemistry and Its Application

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