Biodegradable polymers with variable architectures via ring‐expansion polymerization

Abstract

Kinetically controlled ring‐expansion polymerizations (REPs) are defined syntheses generating cyclic oligomers and polymers without linear intermediates and without equilibration reactions. This review reports syntheses of cyclic metal alkoxides and their use as initiators for REPs of lactones, cyclic diesters, and cyclocarbonates. In addition to homopolyesters, telechelic oligoesters or polyesters, random copolyesters, and A–B–A triblock copolymers can be prepared by these REPs. The in situ combination of REPs with condensation (mostly acylation) reactions allows a broad variation of end groups. The in situ combination of REPs with polycondensation enables various chain‐extension reactions, including the syntheses of multiblock copolymers. With spirocyclic initiators, four‐armed stars with functional end groups may be prepared. The in situ combination of REPs with condensation reactions of trifunctional or multifunctional reagents makes a broad variety of networks accessible. The average segment lengths may be controlled via the monomer/initiator ratios of the REP. All materials produced via the aforementioned REP processes are biodegradable and nontoxic, and this allows for biomedical and pharmaceutical applications. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4723–4742, 2004

Cyclic polymers: Synthetic strategies and physical properties

“…First examples of REPs were published in 1994, 207,208 based on lactones as monomers. Since then, numerous articles have appeared dealing with REPs of cyclic esters (lactones, cyclic diesters, cyclocarbonates) initiated by cyclic covalent metal alkoxides.…”

“…Since then, numerous articles have appeared dealing with REPs of cyclic esters (lactones, cyclic diesters, cyclocarbonates) initiated by cyclic covalent metal alkoxides. 207 This working field was elaborated in four directions. Since REPs of cyclic esters by means of cyclic tin alkoxides represent the oldest and most widely studied group of all REPs, this part will be discussed first.…”

“…228,229 In addition to cyclic homopolyesters, cyclic copolyesters having random or block sequences were prepared. 207,[230][231][232][233][234][235][236][237][238] Cyclic diblock copolyesters were accessible in two ways. First, two lactones were polymerized in a sequential manner, under conditions preventing transesterification.…”

A novel strategy towards cyclic aliphatic (co)polyesters

“…Anyway, the cyclization is not very effective, contamination by undesired polycondensates is a concern and requires an additional and tedious step of purification by fractionation. Therefore, the quest for more efficient cyclization methods remains a challenging priority, even though several clever strategies have been explored as reported in the literatures [25][26][27][28]. Remarkably, Bielawski et al have initiated the ring-opening metathesis polymerization of cyclooctene by a cyclic ruthenium carbene, so leading to macrocyclic poly(cyclooctene) (M n = 6·10 5 -1.1·10 6 g/mol) by intramolecular chain transfer.…”

“…Cyclic poly(methyl acrylate) was accordingly formed with a predetermined molecular weight (M n = 8.2·10 3 g/mol) without high dilution by intramolecular chain termination. Kricheldorf et al [27] initiated ring-opening polymerization of lactones and lactides by a series of cyclic tin dialkoxide and the growing chains are macrocycles linked by an endocyclic living tin dialkoxide. In a typical example, cyclization was stabilized by the insertion of 1,3-dithian-2-one into the Sn-O bond with formation of macrocyclic precursor.…”