Design and development of a poly(acrylonitrile-co-methyl methacrylate) copolymer to improve the viscoelastic and surface properties critical to scratch resistance†
Scratch resistance has become a coveted property for exterior applications as scratches not only reduce the life cycle and durability of a product but also affect its aesthetics. Poly(methyl methacrylate) [PMMA] based materials are often used for exterior applications despite their limited scratch resistance. This work focuses on the design, development and evaluation of methyl methacrylate (MMA) and acrylonitrile (AN) copolymers to improve the viscoelastic and surface properties critical to scratch resistance. In this work, a molecular modelling approach based on a quantitative structure–property relationship (QSPR) was employed to predict the desired properties such as elastic (E)-modulus and shear yield stress at different copolymer compositions. Thus, a series of poly(acrylonitrile-co-methyl methacrylate) [p(AN-co-MMA)] molecules with increasing AN content (∼35, 75 and 82% in copolymer) were prepared by solution polymerization and evaluated using a nano-indentation test to investigate the surface hardness and E-modulus on compression moulded films. Tests revealed a significant increase in the modulus and surface hardness for the copolymers compared with the homopolymer (E-modulus: 5.8 GPa and 4.5 GPa; surface hardness 0.32 GPa and 0.22 GPa respectively). The values increased with increasing AN content of the copolymers. Stress relaxation studies were also performed to validate the predictions of improved shear yield stress obtained from the molecular modelling approach. It is suggested that the incorporation of AN imparts structural rigidity to the copolymers and thereby improves the scratch resistance of the p(AN-co-MMA) copolymers. Thus, p(AN-co-MMA) are good candidates for applications requiring improved scratch resistance.