No abstract

The effect of solvent in the homogeneous anionic copolymerization of styrene with p‐methylstyrene, p‐tert‐butylstyrene, and m‐methylstyrene has been determined. In nonpolar media where the gegenion is lithium, a nonhomogeneous distribution exists with the more basic monomer in higher concentration at the growing chain end which shows as an enhanced relative reactivity. This is depressed by the addition of a small amount of more polar solvent. The influence of temperature as a function of solvent has been determined for selected anionic systems. In nonpolar media, an increase of temperature favors incorporation of the less basic monomer whereas a more polar solvent has only a small effect and favors a more ideal copolymerization. In cationic copolymerization the effect of hyperconjugation has been demonstrated. This effect of hyperconjugation appears to be enhanced in polar media. The cationic copolymerizations of styrene with p‐tert‐butylstyrene in nitrobenzene shows a steric hindrance of the bulkier monomer on its incorporation into the copolymer. Determination of reactivity ratios as defined for radical systems does not fully characterize ionic copolymerizations.

No abstract