Synthesis and properties of ABA-triblock copolymers from polyester A-blocks and easily degradable polyacetal B-blocks†
Abstract
Novel, degradable amphiphilic ABA triblock copolymers with a polyacetal chain as the hydrophilic internal block and polyesters as external hydrophobic segments were designed and prepared for the first time in a controlled manner. Initially, α,ω-hydroxy-terminated polyacetals were obtained via the cationic polymerization of dioxolane (DXL) conducted in the presence of ethylene glycol as an initiator and triflic acid as a catalyst. In the next step, the resulting polyacetals were used as efficient macroinitiators in the ring-opening polymerization (ROP) of selected cyclic esters catalysed by tin(II) octoate (Sn(Oct)2). The length of the polyester blocks was varied by using different molar ratios of cyclic monomer (L-lactide or ε-caprolactone) to polyacetal macroinitiator (PDXL: Mn NMR = 7000 g mol−1 or Mn NMR = 2400 g mol−1). High conversions of cyclic esters (>95%) afforded block copolymers with monomodal molar mass distributions and molar masses ranging from 10 000 g mol−1 to 56 000 g mol−1. The formation of triblock block copolymers was proven by DOSY NMR. The resulting amphiphilic copolymers were characterized by 1H NMR, 13C NMR, SEC, DSC, and TGA. Additionally, the influence of the blocky copolymer structure on the degradability was investigated. Combining polyester blocks with polyacetal segments allowed the preparation of new materials with tuneable hydrophobic/hydrophilic balance and enhanced degradability.