Gobinda Saha

Preparation of Drug Delivery Biodegradable PLGA Nanocomposites and Foams by Supercritical COsub2 Expanded Ring Opening Polymerization and by Rapid Expansion from CHCIF2 Supercritical Solutions

Abstract : The synthesis of poly(lactic-co-glycolic acid) (PLGA) by the ring opening copolymerization of D,L-lactide and glycolide was performed at 110 deg C to 130 deg C using Sn(Oct)2 as catalyst, 1,10-decanediol as initiator in a supercritical sc-CO2 expanded medium at pressures of up to 2,500 psi. Due to the limited monomer solubility in sc-CO2 at low temperatures (70 deg C), only Mn=2,500 is typically obtained. However, molecular weight increases with both temperature and sc-CO2 pressure. Thus, Mn = 13,000 (PDI = 1.28) was obtained at 110 deg C - 130 deg C even in the absence of fluorinated surfactants. Biodegradable drug delivery nanocomposites based on dexamthasone and poly(lactic acid) (PLA) and poly(lactide-co-glycolide) (PLGA) were prepared by the rapid expansion of the corresponding supercritical CHCIF2 solutions (110 deg C, 200-300 bar) in air (RESS) and in toluene (RESOLV). The RESS process leads to a broad particle size distribution (100-500 nm) while the RESOLV generates a narrower distribution centered around 100 nm and is accompanied by the formation of a few large particles, most likely due to aggregation.

TiCp 2 Cl-Catalyzed Living Radical and Ring Opening Polymerizations Initiated from Epoxides and Aldehydes in the Synthesis of Linear, Graft and Branched Polymers

Ti(III)Cp2Cl-catalyzed radical ring opening (RRO) of epoxides or single electron transfer (SET) reduction of aldehydes generates Ti alkoxides and carbon centered radicals which add to styrene, initiating a radical polymerization. This polymerization is mediate in a living fashion by the reversible termination of growing chains with the TiCp2Cl metalloradical. In addition, polymers or monomers containing pendant epoxide groups (glycidyl methacrylate) can be used as substrates for radical grafting or branching reactions by self condensing vinyl polymerization. In addition, Ti alkoxides generated in situ by both epoxide RRO and aldehyde SET initiate the living ring opening polymerization of e-caprolactone. Thus, new initiators and catalysts are introduced for the synthesis of complex polymer architectures.