Glycidyl cinnamate : copolymerization with glycidyl ethers, in-situ NMR kinetics, and photocrosslinking

Abstract

The copolymerization of glycidyl cinnamate (GC) as a hitherto non-polymerizable, photoreactive epoxide structure to aliphatic polyether copolymers is described, using the monomer-activated epoxide ring-opening polymerization (MAROP). Ethoxyethyl glycidyl ether (EEGE) and GC are copolymerized employing triisobutylaluminum (i-Bu3Al) as a catalyst and tetraoctylammonium bromide (NOctBr4) as an initiator. The amount of GC varies from 3 mol% to 100 mol%, which results in apparent molecular weights in the range of 2600 to 4600 g mol−1 and dispersities (Đ) below 1.34. Studies of the microstructure by in-situ 1H NMR kinetics indicate a gradient-like distribution of EEGE and GC (reactivity ratios: rEEGE = 0.28; rGC = 3.6), applying the ideal copolymerization model for evaluation. A tentative explanation relies on differing bond lengths in the respective epoxide rings, as suggested by density functional theory (DFT) calculations. Mild and selective cleavage of the acetal protecting groups of EEGE is achieved using the acidic ionic resin Dowex, leaving the GC ester bonds intact (Mn = 1900–3700 g mol−1, Đ < 1.34). Thermal properties of the copolymers and the PGC homopolymer are investigated by differential scanning calorimetry (DSC). The crosslinking of P(G-co-GC) copolymers by UV irradiation allows hydrogel formation, which is confirmed by IR spectroscopy.