Linear and Branched Architectures from the Polymerization of Lactide with Glycidol

Abstract

Samples of polylactide (PLA) were synthesized by initiating lactide ring opening with glycidol using Sn(Oct) 2 catalyst. Under low-temperature solution polymerization conditions, epoxide ring opening is precluded, leading to predominately linear epoxide capped PLA. With high-temperature bulk polymerization, simultaneous lactide and epoxide ring opening leads to hyperbranched polyesters characterized by linear PLA segments separating glycerol branch points. Molecular weights and extent of branching were determined by gel permeation chromatography (GPC), and the presence of branching was confirmed by solution viscosity measurements and g′ calculations. Solution polymerizations yielded linear samples with controlled number-average molecular weights in the range 4800-19 200 g/mol. Number-average molecular weights of branched samples from bulk polymerization ranged from 19 800 to 100 800 g/mol. The branched samples exhibited relatively low polydispersity indices (PDI) in the range 1.48-2.00. Glass transition temperatures of branched samples were determined by differential scanning calorimetry and were found to be lower compared with literature values for linear PLA of similar molecular weight.

Synthesis of branched poly(lactic acid) bearing a castor oil core and its plasticization effect on poly(lactic acid)

“…19,20,28 In this study, castor oil, which has three secondary hydroxyl groups, was used as an initiator for the polymerization of lactide. LLA or D,L-lactide was polymerized using tin(II) octanoate in bulk.…”

“…[14][15][16][17][18][19][20] The branched polymers were produced by ring-opening polymerization of lactide using initiators with more than three hydroxyl groups. Some of the typical initiators were pentaerythritol, dipentaerythritol, myo-inositol, glycerol and polyglycidol.…”

“…18 The hyperbranched polymers were obtained by the copolymerization of lactide with glycidol or 2,2-bis(hydroxymethyl)butyric acid using tin(II) octanoate as a catalyst. 19,20 Considerable efforts have been made to enhance the flexibility of PLLA, and thereby overcome its inherent brittleness by blending PLLA with low-molecular-weight plasticizers or other polymers. Various compounds have thus far been used to achieve good plasticization effects in PLLA.…”

Reactive extrusion of poly(L‐lactic acid) with glycidol

“…Because the pendant hydroxyl groups are less reactive than the primary hydroxyl groups, higher temperature and longer time of reaction are required to produce branches. 15 In a reactive extrusion process of limited residence time, we can expect predominant formation of linear chain extended PLLA containing pendant hydroxyl groups.…”

“…The latter is not expected to have the same mobility as a chain end, and hence the overall reduction of the mobile chain end concentration causes the improvement in T g and T m . Because extensive branching typically leads to lowering of T g and T m compared with linear PLLA, 15 the increase in T g and T m seen for PLLA-A suggests that the reactive extrusion process resulted in the formation primarily chain extended linear polymers. Similar trends in T g and T m , albeit of lower magnitude, were observed for PLLA-B with respect to concentration of glycidol and residence time.…”