Synthesis and characterization of polylactides with different branched architectures

Abstract

Star-shaped and comb-like poly(L-Lactide)s (PLA) are produced by employing multifunctional initiators, and hyperbranched structure is prepared using a cyclic co-monomer with hydroxyl group. FTIR, size exclusion chromatography, and H-NMR techniques are employed to characterize the synthesized polymers, validating the formation of desired structures with chain lengths above the critical length for entanglement. After characterization of the synthesized polymers, the effect of branching on PLA properties is investigated by comparing the crystallization and rheological behavior of branched PLAs to those of a linear commercial grade. Differential scanning calorimetry and optical microscopy observations reveal a remark-able improvement in PLA crystallization due to the nucleation role of branching points. Moreover, synthesized polylactides exhibit strain hardening behavior during elongational viscosity measurements by a sentmanat extension rheometer platform. Significant improvements in crystallization and elongational rheology behavior of the synthesized polymers support the achievement of branched polymer structures.

Effect of chemical and physical branching on rheological behavior of polylactide

“…Proton nuclear magnetic resonance ( 1 H-NMR) analysis was done and confirmed the formation of branched structures as expected from the type of initiators and reaction condition. Details of this characterization are reported elsewhere [Nouri et al (2015)]. Linear PLA was the semicrystalline grade 4032D from NatureWorks.…”

Synthesis and characterization of well‐defined random and block copolymers of ε‐caprolactone with l‐lactide as an additive for toughening polylactide: Influence of the molecular architecture

“…[11][12][13][14][15][16][17][18] In several reviews, researchers have comprehensively surveyed the literature in this area. 19,20 Star-shaped polymers are characterized by a low melt viscosity and a lower T g and are less crystalline and more compact in size compared to linear polymers of similar molecular weights.…”

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

“…Peaks corresponding to PLA end groups (methine protons) are shifted further upfield compared to when incorporated in the polymer backbone (δ = 4.17-4.25 vs. 5.08-5.21 ppm), identified previously when synthesising branched PLA (with 2 to 22 initiating hydroxyl groups). [12][13][14][45][46][47] This shift is used to determine the chain length of each PLA arm (ESI eqn (S1B) †). [12][13][14]45 DSC analysis was performed using a TA-Q2000 DSC (TA Instruments).…”

“…[8][9][10] Branched PLA could potentially represent a viable route to delivering such non-petrochemical based replacements. These materials can be synthesised via the ring opening polymerisation (ROP) of D,L-lactide using a range of polyhydroxyl co-initiators, including pentaerythritol, [11][12][13][14][15][16] dipentaerythritol 11,16 and ethylene glycol 5,17 or sugar alcohols, such as glycerol 5,12,14,18 and sorbitol 5,6,19 ( Fig. 1) which are renewably sourced and considered to be non-toxic.…”

“…In conventional and commercial operations, residual reagents are removed by several purification steps requiring high temperature devolatilisation, 41 or by use of potentially toxic organic solvents (dissolving the crude product in chloroform or DCM, followed by precipitation in methanol) and then drying under high vacuum, often for several days. 13,15,16,22,42 In this paper we report a new strategy for controlled ROP of D,L-lactide in scCO 2 using D-sorbitol as a co-initiator. Our target is to synthesise branched PLA, with targeted molecular weight and also to demonstrate control of the degree of branching by changing the ratio of D,L-lactide : D-sorbitol.…”