Chain copolymerization ring-opening reaction

The synthesis of elastomers by step, chain, and ring-opening polymerizations is reviewed. These reactions are characterized as to the process variables which must be controlled to achieve the synthesis and crosslinking of an elastomer of the required structure. Both radical and ionic chain polymerizations are discussed as well as the structural variations possible through copolymerization and s tereoregularity. 

By means of a ring-opening polymerization of the condensation type Vlasov et al. [50] synthesized polypeptide based MAIs with azo groups in the polymeric backbone. The method is based on the reaction of a hydracide derivative of AIBN and a N-carboxy anhydride. Containing one central azo group in the polymer main chain, the polymeric azo initiator was used for initiating block copolymerizations of styrene and various methacrylamides. 

Poly(bisphenol-A-carbonate) under pseudoideal reaction conditions was investigated, and the cyclic polycarbonate was obtained as the main product. In the system, the interface of the water/toluene mixture might have favored the cyclization reaction between the polar end groups [88]. Cyclic carbonates during the (Salen)CrCl catalyzed CCh/cyclohexene oxide copolymerization process in the presence of ionic initiators was also obtained [89]. The cyclic carbonate is produced via the backbiting mechanism, and the process is assumed to take place via a metal alkoxide (polymer chain) intermediate. Subsequent ring-opening of the cyclic carbonate with concomitant formation of polyether and CO2 was fast at the reaction temperatures from 80 to 100 °C). 

In many systems, however, the analysis of the cationic copolymerization of heterocyclic monomers is complicated by two factors (1) at least some of the homo- and cross-propagation reactions may be reversible (2) redistribution of the sequences of comonomers within the chain may occur as a result of chain transfer to polymer. Therefore, the conventional treatment involving four irreversible propagation steps is rarely applicable in cationic ring-opening copolymerization. Instead, the diad model should involve four reversible reactions, i.e., eight rate constants... 

The above listed monomers polymerize exclusively by cationic ring-opening polymerization. Polymerization of cyclic imino ethers has been reviewed by Saegusa1,4,). In this section we follow mostly the conclusions of the Kyoto group summarizing the applied synthetic methods. Subsequently we describe initiating systems, peculiarities of chain growth, side reactions, copolymerization systems and possible applications, in this order. 

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