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

Abstract

Although the bi-functional monomer 3,4-epoxycyclohexylmethyl acrylate (ECMA) is commercially available, there are no reports on its homopolymerization. In this study, poly(3,4-epoxycyclohexylmethyl acrylate) (PECMA) is synthesized via free radical polymerization and PECMA is subsequently fractionated to obtain samples with varying molecular weights. A PECMA solution, containing a cationic photoinitiator, is cast and the solvent is evaporated to form a viscous liquid polymer film. Upon photolysis, the nanoindentation hardness (Hit) of the coating increases, and the epoxy group concentration decreases due to the epoxide ring-opening polymerization or crosslinking. For fully cured coatings, Hit increases with the molecular weight of PECMA. At a polystyrene-equivalent weight-average molecular weight (Mw) of 14.5 kDa, the Hit value of the fully cured coating reaches 0.78 ± 0.02 GPa. This hardness value is more than five times that of poly(ethylene terephthalate) (PET) and over three times that of polystyrene (PS) under identical testing conditions, representing the highest Hit value reported for an organic material to date. The high Hit value directly correlates with excellent wear resistance, as no wear tracks are observed on the coating after 250 abrasion cycles with steel wool under a pressure of 13 kPa. In contrast, both PET and PS exhibit significant wear tracks after just one abrasion cycle. The coating also demonstrates high transparency, with a transmittance of 97% at 500 nm for a 50 µm thick film, after accounting for the glass substrate's absorption. Additionally, thermogravimetric analysis shows that the polymer remains thermally stable up to 300 °C. These properties suggest that this hard, transparent, and thermally stable polymer, along with its copolymers, has significant potential for a wide range of applications.