Active polymers containing peroxide groups were synthesized via polymerization of styrene or methyl methacrylate with oligo(adipoyl 2,5-dimethylhexane-2,5-diyl peroxide) (OAHP) or oligo(2,5-dimethylhexane-2,5-diyl 4,4'-azobis(4-cyanoperoxyvalerate)) (LUAB). Poly(beta-hydroxynonanoate) (PHN) and the active polymer were mixed, and free radical grafting 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 cleaved them, depending on the PHN/active polymer mass ratio and the peroxygen 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 showed surface topography. Phase-separated graft copolymers reveal dispersed phase particles, micrometer and submicrometer sized particles, and holes in the micrographs. The SEM observations are also wholly consistent with the glass transition temperature behavior obtained from differential scanning calorimetric (DSC) measurements.