The kinetics of the anionic polymerization of e-caprolactone, including the kinetics of macrocyclization and the kinetics of macrocycles propagation in THF solution, initiated with (CH,),SiONa, were investigated. Rate constants of propagation (kpCn,) and of back-biting (kdCn,) involving monomer and cyclic oligomers (macrocycles) with n = 2, 3, . . . monomeric units were determined for n 9 7 . It was found that starting from the tetramer kdCnin-1*4io*'and kp(n) -n0,7i0,15 (in Jacobson-Stockmayer's theory kpcn)n). This discrepancy is explained in terms of "conformational hindrance", increasing for small cycles with the increase of the ring size until a certain ring size is reached. This hindrance decreases the availability of some of the ester groups in the macrocyclics for attack of the growing species, lowering in this way the exponent in the dependence of kP(,,) on n from one to a lower value.(kp(n)n).

Polyurethane networks whose elastic chains are constituted of hydrophilic poly(l,3-dioxolane) of well-defined molecular weight were synthesized using an end-linking process. The poly(l,3-dioxolane) (PDXL) precursor polymers, fitted with OH functions at both chain ends, were prepared cationically in the presence of ethylene glycol. The latter compound is involved in the initiation reaction and provides the OH functions at the chain ends. The end-linking process, leading to the formation of the poly(l,3-dioxolane) network, involves the reaction of the precursor with a stoichiometric amount of a plurifunctional isocyanate, under conditions that minimize defects. The swelling behavior of the poly(l,3-dioxolane) networks is compared with that of poly(ethy1ene oxide) networks previously studied. 0 1990, HUthig & Wepf Verlag, Basel CCC 0025-1 16X/90/$03.00

The cationic polymerization of 1,3-dioxolane and 1.3-dioxepane has been investigated to prepare "living" polymers and then to use them for copolymerization. Carbenium hexafluoroantimonate salts that are good initiators for tetrahydrofuran polymerization have been tested but produce unsatisfactory results with these acetals. In contrast, triflic anhydride, another good initiator for tetrahydrofuran polymerization, allows molecular weight control. Attempts to prepare block copolymers of two acetals by adding the second one to the first one under living conditions were unsuccessful because of randomization through transacetalization. Block copolymers containing a central block of polydioxepane and outer blocks of I ,2-dimethoxyethylene could be prepared by addition of the latter to living polydioxepane. Active polydioxolane reacts readily with polystyrene and leads to the formation of graft copolymers in the absence of gel.LEONARD C. REIBEL, CLAUDE P. DURAND et EMILE FRANTA. Can. J . Chem. 63, 264 (1985).Nous avons Ctudit la polymCrisation cationique d'acetals cycliques tels que le dioxolanne-1,3 et le dioxepanne-1.3 en vuc de prCparer des systemes vivants et, partant de la, d'obtenir des copolym6res. Les sels (hexafluoroantimoniates) de carbCnium qui s'ktaient avCrCs Ctre de bons amorceurs pour la polymCrisation du tktrahydrofuranne donnent des rCsultats dCcevants avee les acCtals cycliques. Par contre l'emploi de I'anhydride de I'acide triflique, un autre bon amorceur de la polymCrisation du tktrahydrofuranne, permet de contrbler la masse molCculaire des polyacCtals formis. Nous avons tent6 d'obtenir des copolymeres sCquencCs de deux acCtals cycliques en preparant d'abord un poly-acCtal vivant avec I'un des monomkres et en ajoutant ensuite le deuxikme acCtal cyclique. Cependant le copolymkre obtenu prCsente une distribution statistique des deux monomkres due aux reactions de transacCtalisation. Par contre un copolymkre trisCquenc6 ayant une sequence centrale de polydioxepanne a pu Ctre prCparC en faisant rCagir sur du polydioxepanne-a,w vivant du dimCthoxy-l,2 Cthylkne. Des copolymeres greffks ont Cgalement t t C obtenus en faisant rCagir du polydioxolanne, porteur d'un site actif par chaine polymkre, sur du polystyrkne.

We have studied the reaction of 1,3‐dioxolane with trifluoromethanesulfonic acid in the presence of α,ω‐dihydroxypolytetrahydrofurane and α,ω ‐ dihydroxypolystyrene. Besides polymerization of 1,3‐dioxolane we have observed the occurence of a fast coupling reaction between the initial oligodiols. The mechanism has been studied using a monohydroxylated polystyrene and a model compound, 3‐phenyl‐1‐butanol. We have shown that coupling takes places through transacetalization even under the mild conditions used Ethylene glycol is produced and an acetal bridge is formed between oligodiols. Conditions have been found where high‐molecular‐weight polymer is formed through this polycondensation, in the absence of homopoly(1,3‐dioxolane).