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 T g 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.

Polylactide (PLA) was melt blended with either polypropylene (PP) or a polypropylene based elastomer (PBE, Vistamaxx) in an effort to improve its mechanical properties. An ethylene−glycidyl methacrylate−methyl acrylate terpolymer (PEGMMA, Lotader) was utilized as compatibilizer through coupling to the end groups of PLA. Graft copolymers formed enhanced the adhesion between PLA and polyolefin phases and lowered the interfacial tension. The morphological, mechanical, and rheological properties of the PLA/polyolefin compatibilized blends were investigated, and the blends exhibited substantial improvement in elongation at break and tensile toughness as compared to the corresponding binary blends. The remarkable efficacy of PEGMMA as a reactive compatibilizing agent allows the bridging of two immiscible but important classes of thermoplastics, polylactide and polypropylene, and the production of ductile PLA/PP blend materials.

The synthesis of poly(thienylene vinylenes) (PTV) has been attracting attention due to the low band gaps and high electrical conductivities of these materials, making them applicable for charge storage devices, transparent conductive coatings, and electrochromic devices. Unsubstituted PTV is an intractable polymer that is usually synthesized via a processable precursor. This article reports the synthesis of conjugated polymers using solid-state metathesis conditions, demonstrating the efficiency of this methodology for preparation of a processable polymer, such a 3-dodecyl PTV (P3DDTV). The 3-dodecyl-2,5-dipropenylthiophene was synthesized and subsequently polymerized using ADMET conditions with Grubbs’ second-generation catalyst. The prepolymer film (M n = 4000 g/mol) was further polymerized in the solid state to give a final product with M n = 14 000 g/mol (a 3.5-fold increase while in the solid state). The polymer obtained by this methodology exhibited thermal (T g = 43 °C and T m = 115 °C) and electrochemical (optical band gap of 1.65 eV and HOMO energy level of 5.35 eV) properties similar to those of PTV polymers synthesized by ADMET polymerization using a high boiling solvent or by cross-coupling reactions.

No abstract

Semi-crystalline polylactide(PLA)/polyolefin multi-component blends were used as precursors for the generation of a new class of micro-cellular polymers. Either a polypropylene-based elastomer (PBE) or polypropylene (PP) homopolymer were utilized as dispersed phases at the 10 wt% level. An epoxy-functionalized terpolymer (PEGMMA) was introduced (1 wt%) as a reactive compatibilizer to reduce the dispersed phase droplet size and provide sufficient adhesion between the matrix and dispersed phase. In addition, a polyalkylene glycol liquid (PAG) was added to the blend (4 wt%) to serve as a PLA plasticizer and interfacial modifier. The multicomponent blends exhibited significant increases in strain at break as compared to neat PLA and were subjected to a range of uniaxial strains (10-90%) at room temperature. These cold drawn materials exhibited nearly constant cross-sectional area and fine micro-cellular structures, as revealed by scanning electron microscopy. Distinct different voiding mechanisms observed for the PBE-and PP-containing blends were ascribed to the differences in the dispersed phase elastic moduli and deformability. The material density of cold drawn blends was reduced by up to 34% when compared to the precursor blends without a noticeable change in cross-sectional area. The novel low-density microcellular PLA blends demonstrated outstanding mechanical properties such as high strength, high modulus, substantial ductility, and a 14-fold increase in impact resistance as compared to PLA homopolymer.