Cationic Polymerization of Phenylbutadienes. V. Cationic Copolymerization of Monophenyl-1,3-butadienes

Abstract

ABSTRACT:To obtain information about the transition state for the cationic polymerization of monophenylbutadienes, the ring-substituent and the temperature effects on the copolymerizability were investigated. Judging from the magnitude of the p+ values for the copolymerizations of styrene with ring-substituted 1-and 2-phenylbutadienes, it is suggested that the propagation of monophenylbutadiene proceeds through the transition state which involves an cyclic carbonium ion intermediate. The same interpretation could be applied for the attack of a cinnamyl-type cation onto monophenylbutadiene. The reactivity of monomers toward a styryl cation decreased according to the following order: 1-phenylbutadiene>styrene>2-phenylbutadiene. The lower reactivity of 2-phenylbutadiene in comparison with styrene may be ascribed to the enthalpy increase which overweighs the entropy increase in the transition state.KEY WORDS 1-Phenylbutadiene / 2-Phenylbutadiene / Ring-Substituent Effect / Temperature Effect / Transition State / In a previous paper,1 the authors reported the cationic copolymerization of l-phenyl-1,3-butadiene (1-PB) with olefinic monomers such as isobutene, styrene, and a-methylstyrene. The reactivities of these monomers toward a I-PB propagating end in methylene chloride decreased in the following order: a-methylstyrene > 1-PB > isobutene > styrene. This order has been explained in terms of the nucleophilicity of the monomers and the stability of the resulting cations.In general, the kinetic feature of the propagation depends on the steric and the electronic effects of both the monomer and the propagating end. In addition, the propagation rate is sensitively influenced by a slight difference of the geometrical structures for the transition state.In this work, the transition state for the cationic polymerization of monophenylbutadienes will be discussed on the basis of the reactivity difference in the copolymerization. EXPERIMENTALMaterials 1-PB and 2-phenyl-1,3-butadiene (2-PB) were prepared as described in previous papers. 2 • 3 276 l-p-Methylphenyl-1,3-butadiene (p-CH3-l-PB) and l-p-chlorophenyl-1,3-butadiene (p-Cl-1-PB) were synthesized from the corresponding benzaldehydes by the same method as 1-PB.l-mChlorophenyl-1,3-butadiene (m-Cl-1-PB) was synthesized by Meerwein arylation between butadiene and the corresponding diazonium salt, and subsequent dehydrochlorination by potassium hydroxide. 4 These monomers were all trans isomers.Ring-substituted-2-phenyl-1,3-butadienes including p-methoxy, p-methyl, and p-chloro groups were prepared from the corresponding acetophenones and vinylmagnesium bromide by Grignard reaction and subsequent dehydration by potassium bisulfate. The boiling points of these monomers were as follows: p-CH3-l-PB 87°C (7 mm); p-Cl-1-PB 98°C (7 mm); m-Cl-1-PB 100°C (8 mm); p-CH3O-2-PB 76°C (4 mm); p-CH3-2-PB 61-62°C (7 mm); p-Cl-2-PB 67-69°C (5 mm). The purities of these monomers were more than 99% according to gas chromatography. Styrene, p-methylstyrene, catalysts, and methylene chloride were ...

Carbocationic Polymerization

“…Considering the importance of carbocation stability, it is not surprising that in some instances reasonable correlation was obtained between log(1/r 1 ) and Hammett's σ or Brown's σ + values of the substituents of the second monomer. Examples are the copolymerization of α-methylstyrene with substituted styrenes (169) or styrene with substituted 1-and 2-phenylbutadienes (172). It is thus expected that ideal copolymerization (r 1 = r 2 = 1) in carbocationic systems is unlikely-the only reported ideal system is the copolymerization of isobutylene with β-pinene at −130/−120 • C in ethyl chloride initiated with "H 2 O"/EtAlCl combination (173).…”