Poly(3,4-epoxycyclohexylmethyl acrylate) Synthesis and Use in the Preparation of an Exceptionally Hard yet Flexible Organic Polymer Coating

Despite the commercial availability of 3,4-epoxycyclohexylmethyl acrylate (ECMA), its homopolymerization is not reported. In this study, liquid viscous poly(3,4-epoxycyclohexylmethyl acrylate) (PECMA) is synthesized via free radical polymerization and fractionated to obtain samples with varying molecular weights. After casting with a cationic photoinitiator and photocuring of the resultant film to cross-link the epoxide groups via ring-opening polymerization, a hard solid coating is formed. For fully cured coatings, hardness (H) increases with the molecular weight of PECMA. At a weight-average molecular weight (Mw) of 14.5 kDa, the H value of the fully cured coating reached 0.78 ± 0.02 GPa, over five times that of poly(ethylene terephthalate) (PET) and three times that of polystyrene (PS), representing the highest H value reported for an organic material. This exceptional hardness correlates with excellent wear resistance, as no wear tracks are observed after 250 abrasion cycles with steel wool under 13 kPa. The coating also exhibits high transparency, with 97% transmittance at 500 nm for a 50 μm-thick film, and remains thermally stable up to 300 °C. These properties indicate that PECMA holds significant potential for diverse applications.