Initiators for polymerization

Details Initiators for polymerization Initiators for polymerization

1991-11-25

1993-06-29

Schofer, Joseph L.

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

Synthetic resins

Polymers from only ethylenic monomers or processes of...

549 29, 549 41, 549 49, C08F 400, C07D33350

Patent

active

052235912

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to the use of compounds as initiators for cationic polymerization by means of thermal activation or photochemical activation (UV-irradiation) or activation by electron bombardment (EB). The polymerization-initiator consists of a heterocyclic, arylsubstituted or with an arylring fused sulfonium salt in combination with a non-nucleophilic anion. During the activation of the initiator, a carbon-sulfur bond is broken leading to formation of a sulfide and a carbocation (carbenium ion) within the same molecule. The carbocation initiates the polymerization. Since the activation does not lead to fragmentation of the initiator-molecule into smaller molecules, no low molecular weight sulfur-containing decomposition products form that otherwise would evaporate or migrate from the polymer causing bad smell. The ring-opening cationic initiators in the present invention thereby possess great enviromental advantages both during the polymerization and in handling of the polymer products.
The present invention relates also to some compounds which are novel compounds per se.


BACKGROUND

Cationic polymerization (for a recent review of the area, see: Comprehensive Polymer Science 1989, 3, 579 ff), in contrast to radical polymerization, is not inhibited by the presence of oxygen in air and proceeds after UV-initiation in the dark. Cationic polymerization is also complementary to radical polymerization with respect to polymerizable monomers. Thus, electron rich carbon-carbon double bonds (e.g. alkenyl ethers) are easily cationically polymerized while acrylate monomers are usually unreactive. Vinyl ethers however, do not homopolymerize under radical polymerization conditions. Epoxides is another commercially important class of monomers that polymerize readily under cationic conditions but are inert to radical polymerization.
The utility of cationic polymerization has strongly been tempered by the fact that previously developed cationic initiators have inferior technical properties such as unsatisfactory high initiation temperature and poor solubility in monomer blends and smelly decomposition products.
Strong proton acids (e.g. HClO.sub.4, HBF.sub.4) or Lewis acids (e.g. AlCl.sub.3, BF.sub.3) initiate cationic polymerization of for example vinyl ethers and epoxides. These acids have a very limited utility in a technical context, such as curing of a coating, mainly due to the immediate polymerization that occurs upon mixing initiator and monomer, i.e. the system has no "pot life".
This problem has been circumvented by developing "latent proton acids". They are structurally recognized by being aryl-substituted "onium-salts", e.g. sulfonium-, iodonium-, or arsonium-salts, with non-nucleophilic anions such as SbF.sub.6.sup.-, AsF.sub.6.sup.-, PF.sub.6.sup.-, and BF.sub.4.sup.-. These salts are stable, latent sources of the corresponding strong Bronsteds acid HSbF.sub.6, HAsF.sub.6, and HBF.sub.4 respectively, which are generated upon activation and initiate the polymerization. The salts are inactive until the activation occurs. A majority of this class of latent initiators require photochemical activation (irradiation by UV-light). (Belg. Pat. 828670, 1974; U.S. Pat. No. 3,981,897, 1976; Belg. Pat. 837782, 1970; Belg. Pat. 833472, 1976).
More recently, it has been shown that some sulfonium- and iodonium-salts can be thermally activated and utilized for the initiation of a cationic polymerization. Two methods for activation have been developed; redoxinitation (A. Ledwith, Polymer 1978, 19, 1217) and thermal initiation (Jap. Pat. 63.221.111, 1988, [CA 1989, 111, 40092y],; Jap. Pat. 63223002 1988 [CA 1989, 110, 173955h]; S. P. Pappas and L. W. Hill, J. Coating Technol., 1981, 53,43; S. P. Pappas and H. B. Feng, "Cationic Polymerization and Related Processes" ed. E. J. Goethals, Academic Press, New York, 1984; T. Endo and H. Uno, J. Polym. Sci., Polym. Lett. Ed., 1985, 23, 359; T. Endo and H. Arita, Makromol. Chem., Rapid Commun., 1985, 6, 137).
In common for these initiators is that the activation leads

REFERENCES:
patent: 4407759 (1983-10-01), Crivello
patent: 4417061 (1983-11-01), Crivello
Morio et al., Journ. of Applied Polymer Sci.; 32:5727-5732 (1986); "Thermoinitiated Cationic Polymerization of Epoxy Resins by Sulfonium Salts".
Endo et al.; Journ. of Polymer Sci.: Polymer Letters Edition; 23:359-363 (1985); "Thermoinititated Cationic Polymerization of Bicyclo Ortho Ester by Benzylsulfonium Salts".
Asahi Denka Kogyo K. K.; Chemical Abstracts; 99(18) (1983) 141034v & JP 5837003.

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