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Sterically controlled cationic propagation in the ring‐opening polymerization of bicyclic acetals and bicyclic oxalactones
Author(s) -
Sumitomo Hiroshi,
Okada Masahiko
Publication year - 1986
Publication title -
makromolekulare chemie. macromolecular symposia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.257
H-Index - 76
eISSN - 1521-3900
pISSN - 0258-0322
DOI - 10.1002/masy.19860060105
Subject(s) - bicyclic molecule , cationic polymerization , polymerization , chemistry , ring opening polymerization , acetal , monomer , stereochemistry , polymer chemistry , organic chemistry , polymer
Sterically controlled cationic propagation in the ring‐opening polymerization of bicyclic acetals, which is important and attractive in relation to the chemical synthesis of structurally defined polysaccharides, involves a selective cleavage of acetal bonds, configurational changes of the asymmetrical acetal carbons, and the enantiomer selection at the chiral growing chain end. Also in the polymerization of a bicyclic oxalactone having bicyclo[3.2.1]octane skeleton resulting peculiarly in the selective formation of macrolides of specific ring sizes, the exclusive bond scission accompanied by the inversion of the configuration of the acetal carbon takes place, and, as a result, sequences of four or five consecutive monomer units of the same chirality form at a growing chain end. Optically pure cyclic tetramer and cyclic pentamer (20‐ and 25‐membered macrolides, respectively) were prepared by the oligomerization of a monomer mixture of 36 % optical purity under the reaction conditions where racemic monomer gave racemic cyclic dimer highly selectively, whereas optically active monomer afforded cyclic tetramer and cyclic pentamer, respectively. Ring‐opening polymerization of another two kinds of newly synthesized bicyclic lactones having bicyclo[2.2.2]octane skeleton was conducted by the use of cationic, anionic, and coordinated initiators. From 1 H and 13 C NMR analysis of the resulting polyesters and comparison of the spectra with those of model compounds, the mechanism of polymerization, together with the polymerization reactivity of the monomers, is discussed.