Monomer reactivity ratios for acrylonitrile-methyl acrylate free-radical copolymerization

Nonlinear monomer reactivity ratios for the homogeneous free-radical copolymerization of acrylonitrile and methyl acrylate were determined from ¹H NMR and real-time Fourier transform infrared (FTIR) analyses. All ¹H NMR data were obtained on polymers isolated at low conversions (<10%), whereas the FTIR data were collected in situ. The copolymerizations were conducted in N,N-dimethylformamide at 62°C and were initiated with azobisisobutyronitrile. The real-time FTIR technique allowed for many data points to be collected for each feed composition, which enabled the calculation of copolymer compositions (dM ₁/dM ₂) with better accuracy. Monomer reactivity ratios were estimated with the Mayo-Lewis method and then were refined via a nonlinear least-squares analysis first suggested by Mortimer and Tidwell. Thus, monomer reactivity ratios at the 95% confidence level were determined to be 1.29 ± 0.2 and 0.96 ± 0.2 for acrylonitrile and methyl acrylate, respectively, which were valid under the specific system conditions (i.e., solvent and temperature) studied. The results are useful for the development of acrylonitrile (<90%) and methyl acrylate, melt-processable copolymer fibers and films, including precursors for carbon fibers.