A new and promising method for the diversification of microbial polyesters based on chemical modifications is introduced. Poly(3-hydroxy alkanoate)-g-(poly(tetra hydrofuran)-b-poly(methylmethacrylate)) (PHA-g-(PTHF-b-PMMA)) multigraft copolymers were synthesized by the combination of cationic and free radical polymerization. PHA-g-PTHF graft copolymer was obtained by the cationic polymerization of THF initiated by the carbonium cations generated from the chlorinated PHAs, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHx) in the presence of AgSbF6. Therefore, PHA-g-PTHF graft copolymers with hydroxyl ends were produced. In the presence of Ce+4 salt, these hydroxyl ends of the graft copolymer can initiate the redox polymerization of MMA to obtain PHA-g-(PTHF-b-PMMA) multi-graft copolymer. Polymers obtained were purified by fractional precipitation. In this manner, their gamma-values (volume ratio of nonsolvent to the solvent) were also determined. Their molecular weights were determined by GPC technique. The structures were elucidated using H-1-NMR and FTIR spectroscopy. Thermal analyses of the products were carried out using differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA). (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 111: 2308-2317, 2009