In this study hyperbranched polyacetals (HBPAs) were used as a new type of porogens to prepare porous biodegradable microspheres.HBPAs were synthesized through the transacetalization process

which was carried out with an AB2 type monomer of 4-(2-hydroxyethoxy)-benzaldehyde dimethyl acetal and a B2 type core of benzaldehyde dimethyl acetal catalyzed with pyridinium camphorsulfonate (PCS).The results demonstrated that HBPAs were highly pH sensitive.They degraded rapidly at pH 5.0

and barely degraded at pH 7.4.The porous biodegradable poly(lactic acid) (PLA) microspheres were prepared by blending HBPAs and PLA with the emulsion-solvent evaporation method and the blending microspheres were then placed in acidic conditions for 2 weeks.As HBPAs hydrolyzed faster than PLA

the HBPAs component was first degraded from the blending microspheres to form small pores in the PLA matrix.DSC results and degradation process of the blending microspheres showed that the phase separation appeared in the blending microspheres of HBPAs and PLA.This phase separation favored the hydrolysis of HBPAs in the blending microspheres.The pore size of the microspheres can be regulated by changing the weight ratio of HBPAs to PLA.With increasing the HBPAs amount

the pore size of the PLA microspheres increased in a linear manner.HBPAs

as a new type of porogens

offer a new method to prepare porous microspheres.