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Polymers with an amidinothio end group (-S-eNH are easily obtained1v2) by polymerization of a vinyl monomer with redox initiators involving thiourea (TU) as the reductant. Such end groups are reported to hydrolyse readily under alkaline conditions forming mercapto end groups. In the presence of air, intermolecular oxidative coupling of these chain ends takes place leading to an appreciable increase in intrinsic viscosity or molecular weight I). This sequence of reactions was employed in the pesent work with the objective of preparing block copolymers from a mixture of poly(methy1 methacrylate) and polystyrene, prepared separately from the respective monomers by Fei3-TU as redox initiator. NH, Nn CH3 NH II

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Copper(II)‐exchanged‐13X molecular sieves, prepared from four copper(II) salts, namely, sulfate, nitrate, chloride, and acetate, and their activities in the polymerization of N‐vinylcarbazole at a fixed copper ion exchange level were studied. From the kinetic characteristics of polymerization it was established that the variation in activities of the Cu‐exchanged sieves is due primarily to the difference in the pH of the original salt solution, which is responsible for the varying degree of proton exchange with the zeolite during copper ion exchange. A first‐order dependence of the rate of polymerization was observed with respect to H+ ion concentration of the original copper‐salt solution. It was further established that the rate of polymerization of exchanged copper ion, at a hypothetical zero proton concentration, is low. A mechanism of polymerization of NVC on copper‐exchanged‐13X zeolite was suggested on the basis of the results obtained.

SynopsisKinetics of polymerization of N-vinylcarbazole over CdIIk13X molecular sieves in toluene have been studied. The rate of polymerization (R,) has been found to be second order with respect to percent exchange level of CdII) and also to the NVC concentration a t all the reaction temperatures of 40, 50 and 60°C. The rate increases with decreasing pH of the original exchanging salt solution up to a pH of about 3.5, beyond which it falls. The overall activation energy of polymerization has been found to decrease with increase in monomer concentration, exchange level of WII), and the hydrogen ion concentration of the original exchange solution.Average degree of polymerization also follows a similar trend. A mechanism of polymerization involving simultaneous propagation on both metal ion WII) and proton on a zeolite surface has been suggested. The two propagation routes are characterized by an average activation energy of 10.36 kcal/mol and 5.40 kcal/mol on the metal ion and proton centers, respectively. EXPERIMENTAL MaterialsNVC (BASF, West Germany) was recrystallized from methanol by the standard p r o c e d~r e .~ Solvents such as toluene and methanol were of analytical grade. They were purified by standard procedures. Cobalt(I1) chloride, hexahydrate (AnalaR, BDH, UK) was used as such.Cobalt(I1) chloride solution was prepared at 0.2M concentration and the concentration was checked by chemical analysis. The pH of the solutions was varied by the addition of aqueous HC1 in a n appropriate amount and was measured by a digital pH meter at 35°C.