Thermodynamic analysis of the reaction-induced phase separation of random copolymers of methyl methacrylate and N,N-dimethylacrylamide in the precursors of a polythiourethane network

E. R. SOULÉ; B. JAFFRENNOU; F. MÉCHIN; J. P. PASCAULT; J. BORRAJO; R. J. J. WILLIAMS

JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS

John Wiley

Año: 2006 vol. 44 p. 2821 - 2827

0887-6266

Poly(methyl methacrylate) (PMMA) and random copolymers of methyl methacrylate (MMA) and N,N-dimethylacrylamide (DMA) containing 7.5, 15 and 20 wt % DMA were dissolved in a stoichiometric mixture of m-xylylene diisocyanate and 4-mercapto-methyl-3,6-dithia-1,8-octanedithiol, precursors of a polythiourethane network. Phase separation that took place during polymerizations at 60, 90 and 120 ºC, exhibited a lower-critical-solution-temperature (LCST) behavior. Cloud-point conversions that were determined by iodometric titration of free thiol groups of samples chilled in ice at the cloud-point, increased with the weight fraction of DMA in the random copolymer. This may be used to control the cloud-point conversion and determine the characteristic size of dispersed domains. A thermodynamic analysis was performed using the Flory-Huggins equation, taking into account the polydispersities of both the thermoplastic and thermoset polymers, and using an interaction parameter depending on temperature and on the three binary interaction energies. A reasonable fitting of experimental curves was obtained with negative values for the interaction energies of the MMA-thermoset and DMA-thermoset pairs, and a positive value for the MMA-DMA pair.