Small molecule-free photocurable polymer films through [2+2] photocycloaddition

Photocurable materials are gaining increasing attention for their potential in functional polymer systems and advanced materials applications. However, many conventional systems rely on small molecule photoinitiators and/or monomers, raising concerns regarding toxicity, stability, and leaching. In this work, we report for the first time the development of a soft, hand-moldable, small molecule-free photocurable copolymer, poly(cinnamoyl ethyl acrylate-stat-lauryl methacrylate) [P(CEA-stat-LMA)], synthesised via a straightforward ‘one-pot’ process: reversible addition-fragmentation chain-transfer (RAFT) copolymerisation of 2-hydroxyethyl acrylate (HEA) and lauryl methacrylate (LMA), followed by Steglich esterification with cinnamic acid to convert HEA residues to cinnamoyl ethyl acrylate (CEA) repeat units. By tuning the CEA:LMA molar ratio, the glass transition temperature (Tg) and viscoelastic properties of the copolymer were finely controlled. Among the series, P(CEA73-stat-LMA42) demonstrated an optimal balance, yielding hand-moldability at room temperature coupled with the ability to be photo-crosslinked. Effective crosslinking via intermolecular [2+2] photocycloaddition was confirmed via UV–vis spectroscopy, Fourier transform infrared (FTIR) spectroscopy and gel permeation chromatography (GPC). Furthemore, rheological and tensile analyses revealed a transition from a ductile and moldable state to a robust elastic network, with a gel fraction reaching 80
2%. This combination of malleability prior to curing and enhanced mechanical integrity post-curing offers a versatile platform for fabricating custom-shaped, small molecule-free polymeric materials. Such systems hold great promise in next-generation photocurable materials, particularly in thin film applications where user-defined shaping and reliable curing are essential, such as wearable electronics, medical devices and soft robotics.