Ketene acetals ring-opening copolymerization

The living R-ROP of cyclic ketene acetals was achieved with nitroxy-mediated polymerization (NMP) (29), ATRP (30), and RAFT (31) methods to afford the polyesters with low polydispersities. Recently, it has been reported that the block and random copolymers with vinyl monomers showing low polydispersities could also be obtained by living radical ring-opening copolymerizations (32, 33). 

Fig. 31. Preparation of biodegradable PS by incorporating ester linkages into the backbone via ring-opening copolymerization of styrene with a cyclic ketene acetal.

Ring-opening polymerizations and copolymerizations also offer novel routes to polyesters and polyketones. These polymers are not otherwise available by radical polymerization. Finally, ring-opening copolymerization can be used to give end-functional polymers. For example, copolymerization of ketene acetals with, for example, S, and basic hydrolysis of the ester linkages in the resultant copolymer offers a route to a,co-difunctional polymers. 

Related work had shown that the nitrogen analogs of the cyclic ketene acetals were readily synthesized and would polymerize with essentially 100% ring opening. For this reason their copolymerization with a variety of monomers was undertaken (6). 

Since the monomer I would copolymerize with a wide variety of comonomers with the introduction of an ester group into the main chain, this appeared to make possible the preparation of biodegradable addition polymers. Copolymerization of ethylene and the ketene acetal I at 120°C produced a series of copolymers containing ester groups in the backbone of the copolymer, again with quantitative ring opening. 

The free radical polymerizations of cyclic ketene acetals have recently evoked a lot of interest (10-13). TTie oly(e-caprolactone) (PCL) can be synthesized by free radical ring opening polymerization (10). The copolymerization of its monomer, 2-methylene-l,3-dioxepane (MDO), with some vinyl monomers resulted in an aliphatic ester backbone, as well as the pendant functional groups from the vinyl monomers (10). By free radical polymerization of MDO and the vinyl monomers vinylphosphonic acid (VPA), dimethylvinylphosphonate (VPE) and acrylic acid (AA), we synthesized a series of biodegradable copolymers including PCL... 

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