High molecular weight poly (L‐lactic acid) clay nanocomposites via solid‐state polymerization

Abstract

We propose here, a novel technique to synthesize high molecular weight (MW) poly (L-lactic acid)-clay nanocomposite (PLACN), via solid state polymerization (SSP). We synthesize prepolymer of PLACN (pre-PLACN) from both, L-lactic acid and L-lactide, as starting materials. Synthesis of pre-PLACN from L-lactic acid is carried out via in situ melt polycondensation (MP) of L-lactic acid oligomer, followed by SSP, to achieve high MW PLACN (M w $ 138,000 Da). In case of L-lactide as the starting material, we prepare L-lactide-clay intercalated mixture which yields moderate MW pre-PLACN during subsequent ring opening polymerization (ROP). Interestingly, ROP is performed by using hydroxyl functionalized ternary catalyst system (L-lactide-Sn(II) octoate-oligo (L-lactic acid) complex), which provides the terminal hydroxyl end-groups, required for step-growth SSP. Pre-PLACN MW is now increased to M w $ 127,000 Da, by the subsequent SSP process. 1 H NMR analyses confirm that these endgroups, are indeed consumed during SSP. During SSP, the PLACN also achieves up to 90% crystallinity, which may be due to the synchronization of the slow stepgrowth SSP of poly(L-lactic acid) (PLA) with the crystallization kinetics. Optical purity of PLACNs is similar to that of neat PLA, whereas the thermal stability of PLACNs is significantly superior. As evidenced by wideangle X-ray scattering/small-angle X-ray scattering analyses and in line with the literature, both, intercalated and exfoliated PLACN morphologies, have been synthesized, by suitable selection of clays. We also verify the correlation between the PLA semicrystalline morphology and the PLACN morphology, which is consistent with those of PLACN synthesized by other techniques. POLYM. COM-POS., 32:497-

Direct condensation of lactic acid in the presence or absence of supported zirconium sulfate

“…This work considers SSP in a much lower temperature range as opposed to that in the Refs. , , , and . In the current work, self‐sticking particles were observed using higher reaction temperatures.…”

“…Some of the results are consistent with those obtained by other authors. The presence of this work is still justified in terms of Brønsted acid catalysis and different reaction conditions since Lewis acids have been used in other experiments . Supported ZS is found to be an efficient and enantioselective catalyst for the SSP of short‐chain prepolymers.…”

“…reported SSP of PLA reaching high MW PLA for the first time in 2001. Today, several SSP studies of PLA exists including the synthesis of nanocomposite PLA . Most SSP articles refer exclusively to weight average MWs based on polystyrene standards (PS).…”

Control of thermal degradation of poly(lactic acid) using functional polysilsesquioxane microspheres as chain extenders

“…For example, the free radical branching/linking of PLA has been introduced during the melt mixing process in an extruder or kneader in the presence of trace amounts of various peroxides as radical initiators . Also, the solid‐state postpolymerization technique has been utilized to obtain high‐molecular‐weight PLA . Recently, “chain extenders,” the functional additives that are used to link the end groups of these low‐molecular‐weight PLA to obtain high‐molecular‐weight PLA, are considered to be an easy‐to‐apply alternative for many industries and have attracted much attention .…”

Synthesis and characterization of PLA nanocomposites containing nanosilica modified with different organosilanes I. Effect of the organosilanes on the properties of nanocomposites: Macromolecular, morphological, and rheologic characterization

“…In the last years, the study of potentially biodegradable nanocomposites, mainly based on PLA polymers, has intensified, in order to improve the properties of the material and to find new applications 14–17…”