Propagation Rate Coefficient of Poly(N-isopropylacrylamide) in Water below Its Lower Critical Solution Temperature

• Published in: Macromolecules 2000-11, Vol.33 (23), p.8589-8596
• Main Authors: Ganachaud, François, Balic, Robert, Monteiro, M. J, Gilbert, R. G
• Format: Article
• Language: English
• Subjects: Applied sciences; Exact sciences and technology; Physicochemistry of polymers; Polymerization; Polymers and radiations
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma000619l

Pulsed laser polymerization (PLP) of N-isopropylacrylamide (NIPAM) in water was performed over the range 2−20 °C (below its lower critical solution temperature), to obtain propagation rate coefficients (k p). While the value of k p deduced from these data obeyed some of the consistency criteria for PLP (e.g., that the multiple points of inflection give the same apparent value of k p), the apparent k p so obtained depended on monomer and initiator concentrations. For monomer concentration ∼0.4−0.8 M, the temperature dependence is approximated by k p(apparent)/dm3 mol-1 s-1 = 108.7 exp(−24.5 kJ mol-1/RT). FTIR and osmometry measurements were used to infer the presence of significant amounts of dimer and to deduce the equilibrium constant for dimer formation. A model based on dimerization was derived to account for k p variations with monomer concentration but did not fit the experimental data, implying that a more complex treatment taking into account complexation with propagating chain ends or a bootstrap effect is required.