Synthesis and anionic ring-opening polymerization of crown-ether-like macrocyclic dilactones: An alternative route to PEG-containing polyesters and related networks

Linear aliphatic polyesters whose structure is made of short polyethylene glycol (PEG) segments connected along the chain by malonate units were synthesized from two PEG-containing macrolactones: 15,15-dimethyl-1,4,7,10,13-pentaoxacyclohexadecane-14,16-dione (1) and 5,8,11,14,17-pentaoxaspiro[2,15]octadecane-4,18-dione (2). Anionic ring-opening polymerization conditions using either thiophenolates or a p-nitrophenolate as initiators yielded poly(ether-ester)s of low to moderate molecular weights, with broad molecular weight distributions. When the monomer also contains an activated cyclopropane unit of the cyclopropane-1,1-dicarboxylate type (such as in 2) and harsher polymerization conditions are used (higher temperatures and bulkier counterions), opening of the cyclopropyl ring can compete with the dilactone polymerization, providing access to crosslinked materials.