Eliminating the oxygen inhibition in the redox free radical polymerization of alicyclic polyurethane acrylate coatings: A study of the beneficial effect of paraffin wax

Abstract

Elimination of oxygen inhibition is still a challenge in the preparation of copolymers for steel bridge deck coatings industry by redox free radical polymerization (RFRP) technique in air and at room temperature. Herein, solvent-free paraffin wax composite alicyclic polyurethane acrylate (PW/APUA) coatings cured in air and at room temperature were developed by RFRP technique, and the efficacy and mechanism of oxygen inhibition elimination by paraffin wax during curing was investigated. The results of tensile, contact angle (CA) and water absorption (WA) tests showed that compared with pure APUA coating, the PW/APUA coatings exhibited superior mechanical properties and water resistance at room temperature, with tensile strength, elongation at break and CA up to 25.1 MPa, 204.23 % and 112.5°, respectively, and WA down to 0.008 %. Thermogravimetric analysis (TGA) suggested that the thermal initial decomposition of the coating increased from 180 °C to 200 °C after incorporation of paraffin wax. Differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA) indicated that two glass transition temperatures of PW/APUA coating with 0.3 % paraffin wax were −88.4 °C and 92.6 °C, respectively. Moreover, microstructural characterization of PW/APUA coatings revealed that paraffin wax eliminated oxygen inhibition by forming a dense barrier layer on the air contact surface of the APUA coating. Furthermore, the paraffin wax molecules co-crystallized with the non-polar groups of acrylates, but did not form new chemical bonds. This study provides a distinct and general strategy for eliminating oxygen inhibition of RFRP technology in air.