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: M_{n NMR} = 7000 g mol⁻¹ or M_{n 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.