Experimental and mathematical modeling studies of styrene-acrylic acid copolymerization via the FRRPP process.

摘要

The F&barbelow;ree r&barbelow;adical r&barbelow;etrograde-p&barbelow;recipitation p&barbelow;olymerization (FRRPP) process is applied to styrene (St) homopolymerization and styrene-acrylic acid (St-AA) copolymerization systems in this study. Results show the gradual increase of conversion versus time, confirming the reaction-control feature of the FRRPP process. Logarithm of the molecular weights linearly increases with logarithm of the reaction times for both St homopolymerization and St-AA copolymerization via FRRPP, indicating that the FRRPP system is a polymerization process with physically entrapped active radicals. Additionally, it is found that general FRRPP features could be lost if a relatively large amount of AA is involved in the reaction system.; St-AA copolymers via FRRPP have a different structure/composition from those formed by solution polymerization. This is demonstrated by the observation that FRRPP products show amphiphilic characteristics. Furthermore, the preferential mutual reaction between styrene and acrylic acid and the nature of the FRRPP process provide justifications for the intention to generate tapered block copolymers in this study.; Phase equilibria for the poly(St-AA)/ ether/AA ternary and poly(St-AA)/ ether/St/AA quaternary systems are also investigated. Results indicate that the polymerization conducted in this study is indeed carried out in the phase separation region above the lower critical solution temperature (LCST) of the reaction solution.; Monomer reactivity ratios of St and AA, based on the terminal model, are determined using Kelen-Tudos method, nonlinear least square method, and integration composition equation. In addition, monomer reactivity ratios based on the penultimate model are also estimated.; PolySt-Poly(St-AA) copolymers prepared via FRRPP process are applied to wood flour/polystyrene composites as coupling agents in this study. The ultimate stress and strain are found to be improved. The molding temperature is found to mildly affect the performance of the coupling agent. Very high molding temperatures may impair the performance of the resulting composites.; Finally, a comprehensive mathematical framework is proposed for the St-AA copolymerization system via FRRPP. A predictive model is built upon the penultimate and terminal kinetic theories, incorporating diffusion-controlled reaction constants and the effect of phase separation. Specifically, the penultimate model is shown to have a good capability of predicting the conversion vs. time behavior for the St-AA copolymerization system.