Block Copolymers Based on Ethylene Glycol, Glycidol and β-Butyrolactone with Tunable Thermal Properties, Solubility, and Hydrolytic Degradation

We report di- and triblock copolymers that combine hydrophilic polyethers—poly(ethylene glycol) monomethyl ether (mPEG) and polyglycidol (PGl)—with a hydrophobic, degradable polyester, poly(β-butyrolactone) (P(β-BL)). A mild hydrolysis method was developed to selectively remove acetal protecting groups from poly(ethoxy ethyl glycidyl ether) (PEEGE) without cleaving the β-butyrolactone polyester backbone, enabling the preparation of PGl-b-P(β-BL) and mPEG-b-PGl-b-P(β-BL) block copolymers. Thermal analysis revealed that the glass transition temperatures (Tg) of the copolymers could be tuned by varying block composition and length. Diblock copolymers containing the PGl segment were amorphous, with Tg values ranging from −2.7 to −19.9 °C. The presence of an mPEG segment in the triblock copolymers resulted in a further decrease in Tg, reaching values between −32.3 and −38.9 °C. Solubility and water affinity studies demonstrated that incorporation of hydrophilic polyether blocks enhances copolymer–solvent interactions, leading to increased wettability of the polymer-coated surface. The water contact angle for films formed from PGl-b-P(β-BL) decreased to 53 °C, while for mPEG-b-PGl-b-P(β-BL) copolymers, it was further reduced to 43 °C compared with the hydrophobic P(β-BL) film. Hydrolytic degradation experiments showed accelerated cleavage of the P(β-BL) segment in copolymers containing hydrophilic blocks compared to the P(β-BL) homopolymer, which is attributed to increased water accessibility and surface hydrophilicity. The most pronounced decrease in molar mass, reaching at least 50% relative to the initial non-degraded sample, was observed for the diblock copolymers, whereas the P(β-BL) sample showed only a marginal weight reduction of a few percent. Overall, this study demonstrates that the combination of hydrophilic mPEG and PGl blocks with P(β-BL) enables the design of block copolymers with tunable thermal properties, solubility, and degradation behavior, offering potential for a wide range of applications.