Gamma Irradiation-Based Free Radical Grafting of N-Hydroxyethyl Acrylamide onto Poly[(R)-3-hydroxybutyrate]

This work demonstrates successful grafting of N-hydroxyethyl acrylamide (HEAA) onto poly[(R)-3-hydroxybutyrate] (P[(R)-3HB]), up to 156 wt.% using ⁶⁰Co gamma irradiation (10.1 kGy) and a 1:4 P[(R)-3HB]:HEAA molar ratio in ethyl acetate. The resulting N-hydroxyethyl acrylamide-grafted poly[(R)-3-hydroxybutyrate] (P3HB-HEAA) was comprehensively characterized using FTIR, NMR, SEM, DSC, TGA/DTG, tensile testing, and water uptake, and exhibited striking property changes relative to the native polymer. The modified material showed a T_g of 124°C, reduced melting enthalpy (ΔH_m = 12 J/g), increased T_d,10 and T_d,50 of 260°C and 340°C, respectively, increased elongation at break (ɛ = 65%), increased toughness (by 378%), exceptional water absorption capacity (610 wt.%), a markedly less ordered surface structure compared to the starting materials. These changes indicate formation of a less crystalline, highly hygroscopic, hydrogel-like system. HEAA grafting generated a biphasic architecture comprising a semicrystalline, structurally robust, P[(R)-3HB] backbone coupled with an amorphous, hydrogel-like HEAA surface layer, yielding a potentially biodegradable polymer with enhanced hydration capacity. The structure retains structural integrity while enabling substantial water uptake properties not accessible with either component alone. Combining mechanical strength with tuneable hydration behavior, HEAA-grafted P[(R)-3HB] expands the functional and commercial potential of P[(R)-3HB] into applications requiring simultaneous structural integrity, controlled swelling, and potential biocompatibility.