Polylactide Vitrimers

TLDR

Research on healing cross‑linked polymers is abundant, yet renewable cross‑linked polymers have received little attention. The study investigates the healing ability of polylactide‑based vitrimers containing Sn(Oct)₂. Vitrimers were synthesized by cross‑linking hydroxyl‑terminated star‑shaped polylactide with methylenediphenyl diisocyanate at IC:OH ratios of 0.6–1.1 and catalyst ratios of 0.013–0.050. The cross‑linked vitrimers showed lower plateau modulus and Tg at reduced IC:OH ratios, short relaxation times (<50 s at 140 °C), and healed fractured samples recovered up to 67 % elongation, 102 % tensile strength, and 133 % modulus.

Abstract

While much research has been aimed at new approaches to the healing of cross-linked polymers, there is a dearth of effort in the healing of renewable cross-linked polymers. In this study, the healing ability of renewable polylactide-based vitrimers containing Sn(Oct)2 was investigated. The vitrimers were prepared from hydroxyl-terminated star-shaped poly((±)-lactide) samples that were cross-linked with methylenediphenyl diisocyanate. Cross-linked samples were prepared with isocyanate:hydroxyl (IC:OH) ratios of 0.6:1 to 1.1:1 and initial catalyst:hydroxyl (Sn(Oct)2:OH) ratios ranging from 0.013:1 to 0.050:1. The plateau modulus and Tg values for the cross-linked samples decreased with decreasing IC:OH ratio. The materials were subjected to stress relaxation analyses, which confirmed that the materials not only were vitrimeric in nature but also exhibited remarkably short characteristic relaxation times of less than 50 s at 140 °C. Finally, vitrimers fractured in uniaxial tensile testing were healed by compression molding and exhibited up to 67% recovery of ultimate elongation, up to 102% recovery of tensile strength, and up to 133% recovery of tensile modulus values.