Block copolymer synthesis optimal conditions

We investigated the chemoenzymatic synthesis of block copolymers combining eROP and ATRP using a bifunctional initiator. A detailed analysis of the reaction conditions revealed that a high block copolymer yield can be realized under optimized reaction conditions. Side reactions, such as the formation of PCL homopolymer, in the enzymatic polymerization of CL could be minimized to < 5 % by an optimized enzyme (hying procedure. Moreover, the structure of the bifunctional initiator was foimd to play a major role in the initiation behavior and hence, the yield of PCL macroinitiator. Block copolymers were obtained in a consecutive ATRP. Detailed analysis of the obtained polymer confirmed the presence of predominantly block copolymer structures. Optimization of the one-pot procedure proved more difficult. While the eROP was compatible with the ATRP catalyst, incompatibility with MMA as an ATRP monomer led to side-reactions. A successfiil one-pot synthesis could only be achieved by sequential addition of the ATRP components or partly with inert monomers such as /-butyl methacrylate. One-pot block copolymer synthesis was successful, however, in supercritical carbon dioxide. Side reactions such as those observed in organic solvents were not apparent. 

The chemoenzymatic cascade synthesis of block copolymers combining enzymatic ring opening polymerization (eROP) and atom transfer radical polymerization (ATRP) is reviewed. Factors like reaction condition and initiator structure were investigated and optimized prior to the polymerization. The synthesis of block copolymers was successful in two consecutive steps, i.e. eROP followed by ATRP as evident from SEC and GPEC analysis. While in the one-pot approach, block copolymers could be obtained by sequential addition of the ATRP catalyst, side reactions were observed when all components were present from the start of the reaction. A successful one-pot synthesis was achieved by conducting the reaction in supercritical carbon dioxide. 

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