Emulsion copolymerization ofD,L-lactide and glycolide in supercritical carbon dioxide

Abstract

Biodegradable polyesters were synthesized via an emulsion polymerization in supercritical carbon dioxide (SC‐CO2). Copolymers of lactide and glycolide were synthesized in SC‐CO2 with stannous octoate as the ring‐opening catalyst and a fluorocarbon polymer surfactant as an emulsifying agent. The conversion of lactide and glycolide was monitored with respect to the reaction time and temperature with 1H NMR spectroscopy. The conversion of glycolide surpassed 99% within 72 h for an SC‐CO2 phase maintained at 200 bar and 70 °C. Under the same conditions, lactide conversion reached 65% after 72 h of polymerization. Unpolymerized monomer was removed after the reaction by extraction with an SC‐CO2 mobile phase. The molecular weights of all the copolymers were measured by gel permeation chromatography. Weight‐average molecular weights (Mw) ranged between 2500 and 30,200 g/mol and polydispersity indices ranged from 1.4 to 2.3 for polymerization times of 6 and 48 h, respectively. Although the molecular weight increased significantly during the first 48 h of reaction, there was no significant difference in the Mw for polymerization times of 48 and 72 h. Emulsion polymerization within the benign solvent SC‐CO2 demonstrated improved conversion and molecular weight versus polymers synthesized without surfactant. The emulsion polymerization of lactide and glycolide copolymers in SC‐CO2 is proposed as a novel production technique for high‐purity, biodegradable polymers. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 562–570, 2001

Ring-opening copolymerization of L-lactide and ɛ-caprolactone in supercritical carbon dioxide using triblock oligomers of caprolactone and PEG as stabilizers

“…The emulsion and precipitation syntheses of poly(D,L-lactide-co-glycolide) using a CO 2 soluble SB, poly(perfluoroocytyl), were reported by Hile and Pishko. 29,30 Bratton et al 31,32 used blocks of PCL with KrytoxFSL and PCL-perfluoropolyether-PCL as SBs in PLLA synthesis in scCO 2 . A series of fluorinated diblock and triblock copolymers of PCL and poly(heptadecafluorodecylacrylate) were synthesized as SBs by the ring-opening polymerization of e-CL and atom transfer radical polymerization of the acrylate by Grignard et al 33 They used these copolymers in the dispersion ringopening polymerization of e-CL in scCO 2 .…”

Synthesis and Characterization of a Novel Degradable Aliphatic Polyester that Contains Monomeric Lactate Sequences

“…[6][7][8] However, the catalysts used to initiate ROP are difficult to remove from the resulting polymer [9] and the purity of the polymer is quite important for biomaterial applications. [10] In addition, the preparation of lactide is complicated and expensive. [11] Thus, it is of significant merit to develop a new route for preparing LAbased polymers while retaining their degradability.…”

Controlled polymerisation and purification of branched poly(lactic acid) surfactants in supercritical carbon dioxide

“…ScCO 2 has been reported to strongly depress the melt temperature of L-lactide from ∼95°C to ∼50°C, 31,33,37 and through view cell studies we were able to visualise a similar trend for D,L-lactide, which has a higher T m (∼130°C). D-Sorbitol has an ambient T m of 95°C.…”

“…23 An alternative to using toxic organic solvents is the use of supercritical fluids and in particular carbon dioxide (scCO 2 ), which is an environmentally benign, low cost and tuneable solvent that can be easily tuned by altering temperature and pressure. 28 Consequently, there has been significant interest in the ROP of cyclic esters in scCO 2 , 23,28,29 and also in the purification of the resulting polymers, [30][31][32] 30 In this particular study the different extractions were assessed individually, and only limited information is available on the conditions required for purification. However, when compared against conventional purification methods clear advantages are seen.…”