Renewable Poly(α-methylene-γ-butyrolactone)Organogels Prepared by Postpolymerization Cross-Linking Reaction withDiamines

Sustainable polymers offer an environmentally friendly route to tunable soft functional materials. Here, a series of cross-linked gels derived from renewable α-methylene-γ-butyrolactone (MBL) were synthesized via thermally induced postpolymerization cross-linking. PMBL homopolymers were first prepared by free radical polymerization (FRP) or photo-ATRP to systematically vary molar mass and dispersity. Subsequent ring-opening amidation of pendant γ-butyrolactone units with diamine cross-linkers, namely, 1,6-hexanediamine (HexdiA) and 1,2-bis(2-aminoethoxy)ethane (BisEdiA), yielded covalently cross-linked networks. Structural characterization (1H NMR, ATR-FTIR, and TNBSA assays) confirmed efficient network formation, while rheological and swelling studies demonstrated highly tunable mechanical and thermoresponsive behavior. Cross-linking also raised the glass transition temperature up to ∼50 °C and improved thermal stability relative to the homopolymer. Control over precursor properties and cross-linker chemistry enabled precise adjustment of network density, mesh size (2–50 nm), and modulus (0.05–148 kPa). The gels exhibited nonmonotonic swelling characterized by transient overswelling and subsequent relaxation, while reaching equilibrium swelling values up to ∼8000% in DMSO and DMF. They displayed a temperature-dependent swelling–shrinkage–swelling pattern in DMF within the range −26 to 90 °C. Polymer–solvent interactions modeled by Flory–Huggins and network theories yielded ⟨χPMBL–DMSO⟩ = 0.435–0.460 and χgel = 0.51–0.53, with Mark–Houwink-Sakurada exponent a = 0.56. Hansen solubility parameters of the gels were found within dispersion values δD = 17–19 MPa0.5, polar values δP = 13–17 MPa0.5 and hydrogen bonding values δH = 8–12 MPa0.5. As a proof of concept, hydrophobic drug loading and release demonstrate the potential of PMBL as a renewable, tunable, and stimuli-responsive platform for soft organogels for controlled drug delivery.