Work‐hardening Photopolymer from Renewable Photoactive 3,3’‐(2,5‐Furandiyl)bisacrylic Acid

The design of a photopolymer around a renewable furan‐derived chromophore is presented herein. An optimised semi‐continuous oxidation method using MnO(2) affords 2,5‐diformylfuran from 5‐(hydroxymethyl)furfural in gram quantities, allowing the subsequent synthesis of 3,3’‐(2,5‐furandiyl)bisacrylic acid in good yield and excellent stereoselectivity. The photoactivity of the diester of this monomer is confirmed by reaction under UV irradiation, and the proposed [2+2] cycloaddition mechanism supported further by TD‐DFT calculations. Oligoesters of the photoreactive furan diacid with various aliphatic diols are prepared via chemo‐ and enzyme‐catalysed polycondensation. The latter enzyme‐catalysed (Candida antarctica lipase B) method results in the highest M (n) (3.6 kDa), suggesting milder conditions employed with this protocol minimised unwanted side reactions, including untimely [2+2] cycloadditions, whilst preserving the monomer's photoactivity and stereoisomerism. The photoreactive polyester is solvent cast into a film where subsequent initiator‐free UV curing leads to an impressive increase in the material stiffness, with work‐hardening characteristics observed during tensile strength testing.