Equilibrium Polymerization of 7-(Alkoxycarbonyl)-7-cyano-1,4-benzoquinone Methides, Substituent Effect on Polymerizability, and Copolymerization with Styrene

Abstract

Polymerization kinetics of 7-(alkoxycarbonyl)-7-cyano-1,4-benzoquinone methides with alkoxy groups such as methoxy (3a), butoxy (3b), isopropoxy (3c), and sec-butoxy (3d) was investigated in chloroform in the presence of 2,2‘-azobis(isobutyronitrile) (AIBN) as an initiator. Their polymerizations were found to be typical equilibrium polymerization reactions, and on the basis of this polymerization behavior, the thermodynamic parameters of polymerization such as the enthalpy (ΔH) and entropy (ΔS) of polymerization were determined. To get information about the substituent effect on the homopolymerizability of 7-(alkoxycarbonyl)-7-cyano-1,4-benzoquinone methides, the ΔH values were compared with the substituent parameters for the alkyl group of the alkoxy substituents by means of a linear free energy relationship and the homopolymerizability was found to be determined mainly by the steric hindrance of the alkoxy groups. The copolymerization of 3a with styrene in chloroform with AIBN as an initiator was carried out above and below the equilibrium monomer concentration of 3a. Above the equilibrium monomer concentration of 3a, 3a copolymerized with styrene in a random fashion to afford the monomer reactivity ratios, r1(3a) = 4.70 ± 0.85 and r2(styrene) = 0.01 ± 0.01 at 60 °C. Alfrey−Price's Q and e values of 3a were calculated to be Q = 32 and e = +1.05, respectively, indicating that 3a is a highly conjugative (reactive) and electron-accepting monomer. On the other hand, below the equilibrium monomer concentration of 3a, 3a copolymerized with styrene in a perfectly alternating fashion. The change from random fashion to alternating one for this copolymerization was explained well in connection with the equilibrium polymerization behavior of 3a.