POLY(BETA-HYDROXYNONANOATE) AND POLYSTYRENE OR POLY(METHYL METHACRYLATE) GRAFT-COPOLYMERS - MICROSTRUCTURE CHARACTERISTICS AND MECHANICAL AND THERMAL-BEHAVIOR

Active polymers containing peroxide groups were synthesized via polyme rization of styrene or methyl methacrylate with oligo(adipoyl 2,5-dime thylhexane-2,5-diyl peroxide) (OAHP) or oligo(2,5-dimethylhexane-2,5-d iyl 4,4'-azobis(4-cyanoperoxyvalerate)) (LUAB). Poly(beta-hydroxynonan oate) (PHN) and the active polymer were mixed, and free radical grafti ng reactions were carried out to optimize mechanical and viscoelastic properties of PHN. The ''active'' vinyl polymers polystyrene (PS) and poly(methyl methacrylate) (PMMA) were grafted onto PHN chains or cleav ed them, depending on the PHN/active polymer mass ratio and the peroxy gen content of the active polymer. The increase in tensile strength (f ) and strain (epsilon) was observed to be maximum in graft copolymers having vinyl polymer contents less than 20 wt.-%. SEM micrographs show ed surface topography. Phase-separated graft copolymers reveal dispers ed phase particles, micrometer and submicrometer sized particles, and holes in the micrographs. The SEM observations are also wholly consist ent with the glass transition temperature behavior obtained from diffe rential scanning calorimetric (DSC) measurements.