Detailed investigation of the propagation rate of urethane acrylates

Abstract

Temperature dependent propagation rate coefficients, k_p, are determined for four acrylate monomers containing a carbamate moiety via the pulsed laser polymerization-size exclusion chromatography (PLP-SEC) technique. Therefore, the Mark–Houwink–Kuhn–Sakurada coefficients K and a of the respective polymers were additionally determined via triple-detection SEC. The monomers under investigation were synthesized from hydroxyethyl acrylate, hydroxyl(iso)propyl acrylate as well as phenyl isocyanate and hexyl isocyanate, respectively, in all four possible combinations. For 2-(phenylcarbamoyloxy)ethyl acrylate (PhCEA) an activation energy of 14.3 kJ mol⁻¹ and a frequency factor of A = 1.2 × 10⁷ L·mol⁻¹ s⁻¹ are obtained for k_p. The MHKS parameters for poly(PhCEA) are K = 8.3 × 10⁻⁵ dL g⁻¹ and a = 0.677. For 2-(phenylcarbamoyloxy)isopropyl acrylate (PhCPA) an activation energy of 14.2 kJ mol⁻¹ and a frequency factor of A = 4.9 × 10⁶ L mol⁻¹ s⁻¹ are found for k_p and the MHKS parameters for poly(PhCPA) read K = 10.3 × 10⁻⁵ dL g⁻¹ and a = 0.657. The activation parameters of k_p of 2-(hexylcarbamoyloxy)ethyl acrylate (HCEA) are E_A = 13.3 kJ mol⁻¹ and A = 6.6 × 10⁶ L mol⁻¹ s⁻¹ with K = 36.0 × 10⁻⁵ dL g⁻¹ and a = 0.552 for poly(HCEA). For 2-(hexylcarbamoyloxy)isopropyl acrylate (HCPA) E_A is 14.1 kJ mol⁻¹ and A = 6.6 × 10⁶ L mol⁻¹ s⁻¹ with K = 26.0 × 10⁻⁵ dL g⁻¹ and a = 0.587 for poly(HCPA). All rate measurements were performed in 1 M solutions in butyl acetate. The fast propagating nature and reduced activation energy of the monomers may be understood on the basis of the increased nucleophilicity that is induced by the carbamate functionality present in all monomers. Rate-increasing effects from solvent polarity and/or from H-bonding can, however, not be excluded and might also contribute to the observed high propagation rates.