Branched pentablock poly (L-lactide-co- -caprolactone) synthesis in scCO2

Pentablock poly(L-lactide-co- -caprolactone) (PLLA/PCL), with a central fluorinated segment and four PLLA/PCLA side chains was synthesized by sequential ring-opening polymerization (ROP) with stannous octoate catalyst in an environmentally benign and clean medium, scCO2. Copolymers of PLLA and PCL are extensively researched for biomedical applications. Fluorinated hydrocarbons are similarly promising for biomedicine, and especially for oxygen carrying substitute applications. Initially, a fluorinated reactive triblock stabilizer (prepolymer, PCL-FLKT-PCL) with inner fluorinated segment and PCL side chains was synthesized in bulk from a tetraol fluorinated alcohol (FLKT) with a 99% conversion. The prepolymer was then utilized for the synthesis of copolymers scCO2, where PLLA segments were successively incorporated to the ends of the prepolymer, forming a pentablock structure with four polyester side chains. Reactions were carried out at 75ºC and 4000- 4500 psi. Solubility studies of the prepolymer and the pentablock copolymer in scCO2 showed effective solubilization at the reaction temperature and pressure. The molecular weights of the products were measured with the aid of gel permeation chromatography; the prepolymer and the copolymer possessed average number molecular weights (Mn) in the range of 13,000 and 24,000 (for 96% conversion of LLA), respectively. Relatively low poly-dispersity indexes were obtained: 1.34 for the prepolymer and 1.08-1.34 for the pentablock copolymer. Material characterization was carried out by 1H-NMR, 13C-NMR, 19F-NMR, Differential Scanning Calorimetry (DSC), Gel Permeation Chromatography (GPC) and Scanning Electron Microscopy (SEM).