Polyesteracetals via TBD Catalyzed Ring‐Opening Polymerization

Polyacetals represent a novel category of degradable polymers, exhibiting remarkable potential for utilization in biomedical and pharmaceutical applications due to their controllable degradation behavior under physiological conditions. The organocatalyst 1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene (TBD) was used for the ring‐opening polymerization (ROP) of 2‐methyl‐1,3‐dioxane‐4‐one. Whereas standard reaction conditions, suitable for lactide polymerization resulted in a polyester due to loss of acetaldehyde, the amount of esteracetal repeating units could be tailored by the polymerization conditions. Performing the ROP at −35°C at a monomer concentration of 15 mol L −1 maximized the incorporation of labile acetal groups to 50 mol%. The versatility of this polymerization system was demonstrated through the successful initiation with a wide range of alcohols, including 1‐pyrenemethanol for end‐group analysis via size exclusion chromatography with UV detection and matrix‐assisted laser desorption‐ionization mass spectrometry, as well as various macroinitiators such as mono‐ and bifunctional poly(ethylene glycol)s, poly(2‐ethyl‐2‐oxazoline), poly(2‐ n ‐nonyl‐2‐oxazoline), and poly(2‐ iso ‐propyl‐2‐oxazoline), thereby facilitating the synthesis of well‐defined block copolymers.

The ring‐opening polymerization (ROP) of a cyclic hemiacetal ester catalyzed by 1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene (TBD) yields statistical copolymers containing esteracetal as well as ester repeating units. Their ratio can be tailored through adjustment of the ROP conditions. The use of hydroxyl end‐functionalized poly(ethylene glycol)s and poly(2‐oxazoline)s as macroinitiators enables access to well‐defined block copolymers.