Synthesis, Hydrolytic Degradation Behavior, and Surface Properties of Poly(alkyl glycolide)-Polyglycolide Copolymers

Given the environmental impact of polymers on our daily lives, the development of biodegradable polymers is becoming increasingly critical. Poly(diisobutyl glycolide)-polyglycolide (PDIBG-PGA) and poly(diisopropyl glycolide)-polyglycolide (PDIPG-PGA) copolymers, which are structurally similar to polylactic-<i>co</i>-glycolic acid (PLGA) polyesters frequently used in the field of biomaterials, were synthesized via ring-opening polymerization (ROP) of glycolide with l-diisobutyl glycolide (l-DIBG) or l-diisopropyl glycolide (l-DIPG), respectively, in various molecular weights (<i>M</i> _w ^GPC: 15.5-40.0 kDa) and in high yields (up to 85.0%). The wettability characteristics of biodegradable polymers are important not only in air but also for their behavior in underwater environments. PDIBG-PGA silica composites, due to their amphiphilic nature, exhibited water contact angles between 72° and 85° in air, unaffected by the increasing addition of hydrophilic silica nanoparticles. However, underwater-oil contact angles increased from 75° to 165° as a result of the higher silica nanoparticle content and enhanced surface roughness. When the silica content reached 30%, the surface demonstrated self-cleaning and oil-repellent properties underwater, attributed to the Cassie state, which trapped air within the surface's hierarchical roughness. Furthermore, the surface free energy (SFE) values of PDIBG-PGA and PDIPG-PGA copolymer films were evaluated using the Owens-Wendt method, which revealed an increasing underwater hexadecane contact angle as the polar component interactions increased. Differential scanning calorimetry analysis revealed that all synthesized copolymers were amorphous, and the glass transition temperatures (<i>T</i> _g) increased with the increase in the molecular weight of the copolymers (for instance, <i>M</i> _n ^GPC: 9560 g/mol → <i>T</i> _g: 25.1 °C vs <i>M</i> _n ^GPC: 20,850 g/mol → <i>T</i> _g: 32.3 °C for PDIBG-PGA; <i>M</i> _n ^GPC: 10,670 g/mol → <i>T</i> _g: 37.7 °C vs <i>M</i> _n ^GPC: 23,360 g/mol → <i>T</i> _g: 42.3 °C for PDIPG-PGA). The molecular weight decreases of 88.3% and 76.5% and mass losses of 36.7% and 12.3% were observed for PDIBG-PGA and PDIPG-PGA copolymers after 8 weeks of hydrolytic degradation, respectively. The faster degradation of PDIBG-PGA (<i>T</i> _g: 25.1 °C) than PDIPG-PGA (<i>T</i> _g: 37.7 °C) may be attributed to the <i>T</i> _g below the hydrolytic degradation temperature (37 °C) because of an increase in the mobility of PDIBG-PGA polymer chains, allowing water molecules to transfer more easily through the matrix.