Abstract
AbstractThe free‐radical copolymerizability of 3(2‐methyl)6‐methylpyridazinone (I) with styrene (St)(M1) has been reinvestigated at varying reaction conditions (solvent, monomer concentration, and reaction temperature). The copolymerization rates in protic solvents were not proportional to the monomer concentration. The overall activation energies in protic solvents were much affected by the monomer concentration. The results might be ascribed to the viscosity effect on the termination reaction, because the protic solvent was found to interact with I through hydrogen bonding to form a 1:1 complex which changed the viscosity of the reaction mixture. The monomer reactivity ratios were strongly affected by the reaction conditions. This might be explained by taking account of the solvation to the carbonyl group of I in the transition state, because clear relationships were not obtained by plots of log 1/r1 against the values of both vCO and vCC stretching frequencies of I, but the values of both ΔΔH‡(ΔH‡11 − ΔH‡12) and ΔΔS‡(ΔS‡11 − ΔS‡12) decreased linearly with a decrease of the monomer concentration in order of benzene ∼ dimethylformamide < ethanol < phenol < acetic acid systems.
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