Poly(glycolide) multi-arm star polymers: Improved solubility via limited arm length

Abstract

SummaryDue to the low solubility of poly(glycolic acid) (PGA), its use is generally limited to the synthesis of random copolyesters with other hydroxy acids, such as lactic acid, or to applications that permit direct processing from the polymer melt. Insolubility is generally observed for PGA when the degree of polymerization exceeds 20. Here we present a strategy that allows the preparation of PGA-based multi-arm structures which significantly exceed the molecular weight of processable oligomeric linear PGA (<1000 g/mol). This was achieved by the use of a multifunctional hyperbranched polyglycerol (PG) macroinitiator and the tin(II)-2-ethylhexanoate catalyzed ring-opening polymerization of glycolide in the melt. With this strategy it is possible to combine high molecular weight with good molecular weight control (up to 16,000 g/mol, PDI = 1.4–1.7), resulting in PGA multi-arm star block copolymers containing more than 90 wt % GA. The successful linkage of PGA arms and PG core via this core first/grafting from strategy was confirmed by detailed NMR and SEC characterization. Various PG/glycolide ratios were employed to vary the length of the PGA arms. Besides fluorinated solvents, the materials were soluble in DMF and DMSO up to an average arm length of 12 glycolic acid units. Reduction in the T g and the melting temperature compared to the homopolymer PGA should lead to simplified processing conditions. The findings contribute to broadening the range of biomedical applications of PGA.

Microbial mediated dimerization of fattyacids of sunflower oil: An effective role of lipase and biosurfactant

“…This could be due to the increase in length of the fatty acid units after polymerization . These observations were similar to the observations made by a number of researchers on polymers …”

Polyglycerol Hyperbranched Polyesters: Synthesis, Properties and Pharmaceutical and Biomedical Applications

“…Amorphous polyesters produced with pure glycerol gave PGSuc with the lowest T g (−10.9 • C) and T g increased with decreasing glycerol purity (Table 1). Reaction temperatures of [180][181][182][183][184][185][186][187][188][189][190] • C are quite high and some highly branched polyesters, leading to insoluble gels, were obtained. To avoid this PGSuc was also synthesized at lower temperatures (indicative conditions: 135 • C for 24 h) with toluene and 1:1 or 2:1 diacid:glycerol molar ratio [18].…”

Hyperbranched aliphatic polyether polyols

“…Polyglycolide became soluble in several organic solvents upon attachment as arms to a hbPG core. 164 Just recently, hbPEG, 102 which is somewhat related to hbPG, was also used as a macroinitiator for the ROP of L-lactide to yield MSPs with molecular weights up to 800 kg mol À1 . 165 In addition, hbPG was functionalized with suitable initiator groups by esterification for controlled radical polymerization of the arms, for example, by ATRP.…”