Nonstoichiometric polycondensation I. synthesis of polythioether from dibromomethane and 4,4′‐thiobisbenzenethiol

High molecular weight poly(phenylene thioether) (3) was successfully obtained by the polycondensation of 4,4′‐thiobisbenzenethiol (1) and dibromomethane (2) with a variety of feed ratios in the presence of 1,8‐diazabicyclo[5,4,0]undec‐7‐ene (DBU) in 1‐methyl‐2‐pyrrolidinone (NMP) at 75°C. The resulting polymer showed the maximum inherent viscosity (ηinh) of 0.50 dL/g in 4 h when 1.5 equivalents excess of 2 was used. The model reaction using benzenethiol (4) and dichloromethane (5) in the presence of DBU in deuterated dimethylsulfoxide (DMSO‐d6) at 25°C indicated that the rate of the second nucleophilic displacement reaction (k2) is 61 times faster than that of the first one (k1). The maximum of theoretical molecular weights calculated at various stoichiometric imbalance (S) under the condition of k2/k1 = 61 showed a good agreement with the experimental molecular weights at specific polymerization times.