Photopolymerized and acetylene-functionlized polyacrylates for photoclickable elastomers

The acetylene functional groups on polymer chains provide a photochemical access to modulate or actuate the properties of the polymer. We report here a photochemical way to actuate a polyacrylate to elastomers. High molecular weight acetylene functionalized homo- and copolymers of are prepared with a novel monomer, 2-(dimethylpropargyloxy)ethyl methacrylate, DMPOEMA, by photo-initiated free-radical polymerization (FRP) in solution at room temperature. The acetylene groups are tolerant of the solution photo FRP at 50 wt% concentration, but not tolerant to thermal FRP and photo FRP at 80 wt% concentration. Copolymers P(DMPOEMA-co-EA) with‾Mn in 12,500–15,100 g/mol were prepared with conversion up to 90% at 50% concentration and three monomer feed ratios. The feed ratio of DMPOEMA had slight effects on the polymerization rate, but effects on PDI at higher monomer conversion with prolonged photo-irradiation. The acetylene functionalized polyacrylates become photo-sensitive and are photo cross-linkable or photo clickable after solvent is removed. Real-time FT-IR study reveals that the photo cross-linking with a tri-thiol compound follows the normal thiol-yne photochemistry, and the photo cross-linking catalyzed with only photoinitiator results in diene units in the cross-linked polymer networks. These photo-treated polyacrylate exhibited designable elastomer properties: with Tg in −24 to −11 °C, more than 10 times increase of relative cross-linking density and resistant to solvents, improved stress, strain and elongation properties. This work paves a way for the acetylene functionalized (meth)acrylates as advanced photo-reactive material.