Ring expansion polymer synthesis

Many works on the synthesis of cyclic polymers and block copolymers using kinetically controlled ring-expansion polymerizations of cyclic monomers, such as lactones and lactides with various types of cyclic tin initiators, were reviewed by Kricheldorf [147,148]. Kricheldorfs group continued the synthesis of cyclic polymers, and their recent works have focused on the following. Polycondensations of 4,4/-difluorodiphenylsulfone with tris(4-hydroxy phenyl)ethane were performed in DMSO to give multi-cyclic poly(ether sulfone)s derived from tris(4-hydroxyphenyl)ethane [149]. 

Scheme 1.4 Ring-expansion polymerization and the subsequent covalent linking for the synthesis of ring polymers (Li et al, 2006).

Kudo, H., Makino, S., Kameyama, A., and Nishikubo, T. (2005) Synthesis of cyclic polymers ring-expansion reaction of cyclic S-dithioester with thiiranes. Macromolecules, 38,5964-5969. 

However, the cyclization usually gives a mixture of linear and cyclic polymers that are difficult to separate. The synthesis of cyclic polymers from cyclic alkoxyamine by ring-expansion polymerization (Figure 20) can represent a suitable... 

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