Structures and thermal properties of chitosan-modified poly(methyl methacrylate)

The emulsion polymerization of methyl methacrylate in the presence of chito san with potassium persulfate (KPS) as an initiator was examined in a previ ous article. The free radicals that dissociated from KPS not only initiated the polymerization but also degraded the chitosan molecules. Therefore, in addition to its role as a cationic surfactant, chitosan also participated in the polymerization reaction. When the polymerization was complete, the l atex polymer consisted of poly(methyl methacrylate) (PMMA) homopolymer and chitosan-PMMA copolymer. In this article, the structures and thermal proper ties of latex polymers are examined. Gel permeation chromatography was used to measure the molecular weight of the PMMA homopolymer, with the copolyme r composition determined by an elemental analyzer. Scanning and transmissio n electronic microscopes were used to measure the size of latex particles f rom different reaction systems. The surface charges of latex particles at s everal different pH values were determined by the measurement of the zeta p otential. All results agreed with the reaction mechanism proposed in the pr evious article. Finally, the presence of rigid chitosan increased the glass -transition temperature of the final latex polymers. Thermogravimetric anal ysis showed that the degradation behavior of latex polymers was similar to the unzipping mechanism of PMMA, yet the presence of chitosan units hindere d the unzipping of the main chains in chitosan-PMMA copolymers. (C) 2001 Jo hn Wiley & Sons, Inc.