No abstract

Degradation of polyacetals, polyoxiranes, polythiiranes, poly(ethylene disulfides) and poly(alkylene sulfides), initiated by cationic initiators, is a general phenomenom. The polyacetals lead to a mixture of monomer and cyclic oligomers; the polyoxiranes mainly to cyclic dimers. Cationic degradation of polythiiranes and poly(ethylene disulfides) leads to a variety of cyclic compounds the nature of which depends on the monomer substituents. Poly(alkylene sulfides) form the corresponding thiacycloalkanes. The mechanism of these degradations and the influence of substituents on the degradation products have been studied. Preliminary results on U.V. ‐ initiated cationic degradation of polythiiranes are reported.

Recent extensive studies have distinguished a special class of polymers which are able to form thermotropic mesophases despite the absence of mesogenes in their chemical structure [1]. In the most striking form the tendency to form such mesophases is displayed by polymers with flexible inorganic backbone, such as poly(diethylsiloxane)/PDES/. In this presentation recent results concerning mechanical and thermomechanical behaviour of a series of PDES mesophase elastomers are considered. Three types of PDES elastomers were studied: crosslinked samples prepared by peroxide vulcanization [2,3], crosslinked samples vulcanized by a multifunctional siloxane resin [4] and block copolymers with ladder polysilsesquioxane as the hard block and PDES as the soft block [5].

The highly living character of a number of cationic polymerizations has been used to synthesize new, well defined, segmented copolymers. This has been achieved by sequential monomer additions, by grafting reactions, by macromonomer copolymerizations as well as by transfer to polymer. In the present report, a number of examples of such polymers will be presented. The new materials are based on tetrahydrofurane (THF), alkyloxazolines (ROx), cyclic amines, cyclic acetals and cyclic sulfides.

SUMMARY:The application of numerical methods for the calculation of the molecular weight distribution of living ionic polymerization, carried out in the presence of monofunctional and polyfunctional transfer agents, is described. The methods used include the numerical solution of a system of differential equations by the Runge-Kutta-Merson procedure and the statistical Monte-Carlo approach. When a monofunctional transfer agent is used, the Runge-Kutta-Merson procedure is quite useful for the calculation of the molecular weight distribution for various polymerization systems. When a polymerization is carried out in the presence of a polyfunctional transfer agent, the mechanism includes the coupling of polymer chains. Due to the complexity of the system, the Runge-Kutta-Merson procedure is hardly applicable and problems of this type should be solved by a Monte Carlo simulation procedure. Once a computer program has been written, both methods allow the chemist to calculate the molecular weight distribution of a polymer as a function of the different kinetic parameters of the polymerization.