Polymer and Materials Science
Wiley InterScience Backfile Collection 1832-2000
Chemistry and Pharmacology
4-Methylstyrene (S) was copolymerized with methyl methacrylate (M) or acrylonitrile (A) in benzene or N,N-dimethylformamide solution, respectively. The reactions were carried out at 50°C, using 2,2′-azoisobutyronitrile as free-radical initiator. The copolymer compositions were determined from oxygen (SM) or nitrogen (SA) analysis, 100 MHz 1H NMR, and 25 MHz 13C NMR spectra. These methods lead to the same results. Data plotted according to the Kelen-Tüdős (K-T) procedure indicate that the copolymerization of S with M can be adequately described by the terminal-unit model. The corresponding reactivity ratios (rS = 0,46 ± 0,02 and rM = 0,35 ± 0,02) were in good agreement with literature values and conform with the Q, e-scheme. On the other hand, the K-T plot for copolymerization of the SA system indicates deviations from the terminal model (rS = 0,27 ± 0,02 and rA = 0,10 ± 0,01) in the S- and A-rich regions. This departure was interpreted in terms of penultimate effects on the reactivity of the S- and A-ended radicals. The values of the corresponding reactivity ratios were as follows: rSS = 0,18 ± 0,03, rAS = 0,34 ± 0,04, rAA = 0,06 ± 0,01, and rSA = 0,13 ± 0,01. The theoretical curve of copolymer composition versus monomer feed, calculated with these parameters, is in excellent agreement with the experimental data. This finding shows that, on the basis of the composition data alone, the penultimate model provides an appropriate description of the copolymerization of S and A.
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