Preparation of Higher Molecular Weight Poly (L-lactic Acid) by Chain Extension

Abstract

High molecular weight poly (lactic acid) (PLA) was obtained by chain extending with hexamethylene diisocyanate (HDI). The influences of the amount of chain extender, reaction time, and molecular weight changes of prepolymers on the poly(lactic acid) were investigated. PLA prepolymer with a viscosity, average molecular weight (Mη) of 2 × 104 g/mol was synthesized froml-lactide using stannous octoate as the catalyst. After 20 min of chain extension at 175°C, the resulting polymer hadMwof 20.3 × 104 g/mol andMnof 10.5 × 104 g/mol. Both FT-IR and1H-NMR verified that the structure of PLA did not change either before chain extending or after. The optically active characterized that the chain extending-product was left handed. DSC and XRD results showed that both theTgand the crystallinity of PLA were lowered by chain-extension reaction. The crystalline transformation happened in PLA after chain extending, crystallineα′form toαform.

A journey across the solid state polymerization to assess the role of critical factors influencing the molecular weight of polylactic acid

“…In other words, using prepolymer with lower initial molecular weight leads to higher PLA molecular weight after polycondensation reaction. This observation agrees well with the other work's findings .…”

Thermoplastic Starch: A Possible Biodegradable Food Packaging Material—A Review

“…), implant devices (Fu and Kao ), and internal sutures because it has a low molecular weight and low cost (Liu et al . ).…”

Nanocomposites based on chain extended poly(l-lactic acid)/carboxylated carbon nanotubes: Crystallization kinetics and lamellar morphology

“…21 It was found that chain extension of PLLA influenced the kinetics of both isothermal and nonisothermal crystallization. 7,22…”

“…[1][2][3] PLLA can be found either in both completely amorphous or semi-crystalline forms, depending on its chemical structure (i.e., the enantiomeric content) and the processing conditions. [4][5][6][7] In addition, physicochemical characteristics of PLLA deserve deeper studies according to a more fundamental/basic point of view. It is well known that PLLA slowly crystallizes from the melt state, which allows preparing materials with tuned degrees of crystallinity and different lamellar morphologies by changing the thermal history.…”

“…21 It was found that chain extension of PLLA influenced the kinetics of both isothermal and nonisothermal crystallization. 7,22 Multiwalled carbon nanotubes (MWCNTs) attract more attention among nanoparticles due to their high efficiency as nucleating agents and their ability to control both the degree of crystallinity and the crystallization kinetics. [23][24][25] The effect derived from the presence of MWCNT in the increase of nucleation has been extensively reported, but the detailed understanding of the role of MWCNT in the growth of polymer crystals remains a complex topic.…”