1967 Volume 40 Issue 9 Pages 2139-2145
To investigate the steric effect of β-substituents of styrene derivatives on their reactivities in radical copolymerization, fourteen cis- and trans-β-alkylstyrenes were synthesized and copolymerized with acrylonitrile. The reactivities of β-alkylstyrenes toward the acrylonitrile radical decreased in the order: CH3>C2H5\gtrsimn-C3H7\gtrsimn-C4H9>iso-C3H7>s-C4H9>t-C4H9 in both the cis- and trans-series. Linear relationships were found between the relative reactivities and Taft’s or Hancock’s steric parameter. These relationships and the study of the monomer structures led to the following conclusions: 1) The low reactivity of β-alkylstyrenes in radical polymerization is to be attributed to the steric hindrance of β-alkyl substituents. 2) The effect of the hyper conjugation of the β-alkyl groups is not important. 3) The difference in the reactivities among intramolecularly-hindered cis-β-alkylstyrenes is due not to the difference in resonance of the monomer, but to the difference in the steric hindrance of the β-alkyl groups toward the attacking radicals.
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