Friction of copolymers of methyl α-n-alkylacrylates (alkyl ⩾ C16H33) and n-octadecyl methacrylate with methyl methacrylate

Abstract A comparative study was made of the friction and wear properties of homopolymers and copolymers (with methyl methacrylate (MMA)) of methyl α-n-hexadecylacrylate (MHDA), methyl α-n-octadecylacrylate (MODA) and n-octadecyl methacrylate (ODMA). In the first two compounds the long alkyl side chain is attached to the polymer backbone, whereas in the last it is adjacent to the carboxyl group that is attached to the polymer backbone. The friction data obtained for homopolymers and copolymers (thin films on glass or steel) of MHDA, MODA and ODMA were similar. The coefficient of friction μ decreased rapidly at a low concentration of MHDA, MODA or ODMA in the copolymers, then decreased more slowly. At about 50 mol.% μ (copolymer) ≈ μ(homopolymer) and further increases in the concentrations of these monomers in the copolymer led to a slight decrease in μ to the limit of the μ value for the homopolymer (μ ≈ 0.10). The durability of thin films (about 3700–4100 A thick) of the copolymers increased with the concentration of MHDA, MODA or ODMA up to 21–25 mol.%. However, 100% MHDA and MODA have lower durabilities than some of the copolymers. All homopolymers and copolymers show higher durabilities than poly-MMA and the durabilities of some of the copolymers approach that of poly-ODMA, which has the highest durability in the series of polymers studied. The lower durabilities of poly-MHDA and poly-MODA ( M n values 7083 and 1320) compared with that of poly-ODMA ( M n = 1.9 × 10 5 ) may be related to their low molecular weights. In all cases the durability of the homopolymers and copolymers was greater on glass than on steel. Available evidence indicates that the decrease in μ and the increase in durability of the copolymers studied is attributable to the long alkyl side chain and not to the polymer backbone. Further, the effect of the long alkyl side chain on μ and on durability is related to its flexibility and capability of orientation during the rubbing process.