Transfer by weak acids in the slow‐initiation‐no‐termination (SINT) polymerization of butyl cyanoacrylate

The theory of slow‐initiation‐no‐termination polymerization has been extended to take account of transfer by added or adventitious transfer agents (T), giving equations relating the number‐average molecular weight (M̄n) to the ratios of concentrations of transfer agent to monomer ([T]0/[M]0) and of transfer to propagation rate constants (ktr/kp). The equations are shown to give a fair description of the M̄n values found in the polymerization of butyl cyanoacrylate by pyridine and by tetrabutylammonium acetate in presence of known concentrations of cyanoacetic, chloroacetic and acetic acids. Approximate values are yielded for the rate constant ratios, viz. 102(ktr/kp) ≈ 15,5 and 0,3, respectively (in tetrahydrofuran at 20°C). Conversely, the theory is shown to explain variations in M̄n values found in polymerizations of five different samples of this monomer, permitting characterization of the unknown concentrations of transfer‐causing impurity.