Comprehensive Understanding of Polyester Stereocomplexation

Abstract

We report a comprehensive understanding of the stereoselective interaction between two opposite enantiomeric polyesters prepared from the regio­selective copolymerization of chiral terminal epoxides and cyclic anhydrides. For many of the resultant polyesters, the interactions between polymer chains of opposite chirality are stronger than those of polymer chains with the same chirality, resulting in the formation of a stereocomplex with an enhanced melting point (T m) and crystallinity. The backbone, tacticity, steric hindrance of the pendant group, and molecular weight of the polyesters have significant effects on stereocomplex formation. Bulky substituent groups favor stereocomplexation, resulting in a greater rise in T m in comparison to the component enantiomeric polymers. The stereocomplex assembly of discrete (R)- and (S)-poly­(phenyl glycidyl ether-alt-phthalic anhydride)­s oligomers revealed that the minimum degree of polymerization required for stereocomplex formation is five. Raman spectroscopy and solid-state NMR studies indicate that stereocomplex formation significantly restricts the local mobilities of CO and C–H groups along the backbone of chains. The reduced mobility results in the enhanced spin–lattice relaxation time and both 1H and 13C downfield shifts due to the strong intermolecular interactions between R- and S-chains.

Properties Enhancement of High Molecular Weight Polylactide Using Stereocomplex Polylactide as a Nucleating Agent

“…Previous studies generally focus on the enhancement of PLA properties through the formation of s-PLA materials from PLLA and PDLA with various blending ratios [9][10][11][12][13][14][15]27]. The mechanical properties of s-PLA increase with an equivalent ratio of PLLA and PDLA, such as Young's modulus by up to 25% [24].…”

“…The addition of plasticizers into the PLA matrix can reduce its brittleness and enhance its life span. Mixing PLLA and PDLA enantiomers forma stereocomplex PLA (s-PLA) with a different crystal structure and higher thermal and mechanical properties [8][9][10]. Furthermore, the blending of PLA with nucleating agents could improve its thermal and mechanical properties as well as increasing its crystallinity.…”

Photoinduced Reversible Semicrystalline‐to‐Amorphous State Transitions of Stereoregular Azopolyesters

“…Photoinduced Reversible Transitions between Semicrystalline Stereocomplexes and Amorphous cis‐Azopolyesters . Recently, macromolecular stereocomplexation‐the formation of an interlocked orderly assembly of polymer chains with two different enantiomeric configurations‐has received much attention due to its ability to enhance thermal properties and reveal new crystalline behaviors that significantly differ from those of the component enantiomer [24, 25] . Serendipitously, we discovered that the synthesized chiral trans ‐polyesters could form stereocomplexes, upon mixing the ( R )‐ and ( S )‐enantiomers in a 1:1 mass ratio.…”

Recent Progress in Enhancing Poly(Lactic Acid) Stereocomplex Formation for Material Property Improvement

“…The most common and robust solution to produce reinforced PLA materials is via stereocomplex crystallization using enantiomeric pairs of poly (L-lactide) (PLLA) and poly (D-lactide) (PDLA), which can occur from both melt and solution state (Ikada et al, 1987). For a well-mixed PLLA and PDLA blend, multicenter hydrogen bonding interactions lead to a possible alternative arrangement of helical chains between L-lactyl and D-lactyl units with opposite chiral conformation for PLA stereocomplexation (SC) (Okihara et al, 2006;Wan et al, 2019). As opposed to homocrystallites (HCs) from enantiopure PLLA or PDLA, the blend of enantiomeric PLLA and PDLA provides enhanced intermolecular interactions through dipole-dipole interaction and hydrogen bonding, leading to more tightly packed chain conformations in a side-by-side manner within the SC crystal lattice (Tsuji, 2005), thus improving mechanical property, thermal stability, and hydrolytic resistance (Tsuji and Ikada, 1999).…”