Biodegaradable nanoporous microspheres by RAFT polymerization

INTRODUCTION Spherical polymeric particles have been intensively studied and synthesized by a variety of methods such as spray drying, emulsification methods and so on. Controlled radical polymerizations (CRP) including RAFT,... [ view full abstract ]

INTRODUCTION
Spherical polymeric particles have been intensively studied and synthesized by a variety of methods such as spray drying, emulsification methods and so on. Controlled radical polymerizations (CRP) including RAFT, ATRP, SFRP have been studied for past few decades due to their tolerance of impurities, the ready availability of many kinds of initiators, catalysts and monomers, their mild reaction conditions, and their ability to produce polymers with predetermined molecular weights and narrow polydispersities
In this study, nanoporous microspheres based on PMVK-b-PCL-b-PMVK block copolymers were fabricated by photodegradating PMVK blocks and evaluated their surfaces and internal structures by electron microscopies.

METHODS
Nanoporous nanoporous microspheres based on polycaprolactone (PCL) and photodegradable poly(methyl vinyl ketone) (PMVK) were synthesized and characterized. First, PCL based triblock copolymer was synthesized by RAFT polymerization followed by the fabrication of microsphere by emulsion method. Disk-shaped particles were then prepared by UV-irradiation with the microsphere. In order to polymerize by RAFT method, PCL based macro-CTA (chain transfer agent) was synthesized by reacting carboxylic acid-terminated CTA with PCL, and used for the synthesis of block copolymer with MVK. The morphology of the particles before and after UV irradiation were confirmed by SEM and TEM images and spherical microspheres were changed to disk-shaped forms, owing to collapsing of PMVK moieties by UV irradiation.

RESULTS AND DISCUSSION
As shown in Figure 1, fabricated microspheres had uniform size particles with approximately 5 um in diameter, and those from block copolymers had a nanoporous structures after UV exposure while PCL microspheres had kept the smooth surfaces. Spherical microspheres were gradually changed to disk-shaped forms as UV irradiation time increased, owing to collapsing of PMVK blocks by UV irradiation.

CONCLUSIONS
Nanoporous microshperes based on PCL and photodegradable polymethylvinylketone (PMVK) were synthesized and anticipated to enhance drug release and could find potential applications for biomaterials.

ACKNOWLEDGEMENTS
This work was supported by Basic Science Research Program (NRF-2014R1A1A4A01008897) through the Ministry of Education and National Research Foundation of Korea.