Linbo Wu

High Molecular Weight Poly(butylene succinate-co-butylene furandicarboxylate) Copolyesters: From Catalyzed Polycondensation Reaction to Thermomechanical Properties

Novel potentially biobased aliphatic-aromatic copolyesters poly(butylene succinate-co-butylene furandicarboxylate) (PBSFs) in full composition range were successfully synthesized from 2,5-furandicarboxylic acid (FA), succinic acid (SA), and 1,4-butanediol (BDO) via an esterification and polycondensation process using tetrabutyl titanate (TBT) or TBT/La(acac)(3) as catalyst. The copolyesters were characterized by size exclusion chromatography (SEC), Fourier transform infrared (FTIR), (1)H NMR, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), and their tensile properties were also evaluated. The weight average molecular weight (M(w)) ranges from 39,000 to 89,000 g/mol. The copolyesters are random copolymers whose composition is well controlled by the feed ratio of the diacid monomers. PBSFs have excellent thermal stability. The glass transition temperature (T(g)) increases continuously with φ(BF) and agrees well with the Fox equation. The crystallizability and T(m) decrease with increasing butylene furandicarboxylate (BF) unit content (φ(BF)) from 0 to 40 mol %, but rise again at φ(BF) of 50-100 mol %. Consequently, the tensile modulus and strength decrease, and the elongation at break increases with φ(BF) in the range of 0-40 mol %. At higher φ(BF), the modulus and strength increase and the ultimate elongation decreases. Thus, depending on φ(BF), the structure and properties of PBSFs can be tuned ranging from crystalline polymers possessing good tensile modulus (360-1800 MPa) and strength (20-35 MPa) to nearly amorphous polymer of low T(g) and high elongation (~600%), and therefore they may find applications in thermoplastics as well as elastomers or impact modifiers.

Styrene polymerization with ternary neodymium-based catalyst system: effects of catalyst preparation procedures

Abstract The ternary catalyst system neodymium phosphate/di-n-butyl magnesium triethyl aluminum complex/hexamethyl phosphoramide (Nd(P204)3/MgBu2·AlEt3/HMPA) for the polymerization of styrene was examined. The effects of the addition order of each component, the aging time and temperature and the presence of a small amount of styrene during the preparation of the catalyst system on the activity of the catalyst system and the molecular weight of the resultant polymers were investigated. A stable and homogeneous catalyst system which produces polystyrene with narrow molecular weight distributions can be prepared by an alkylation reaction of Nd(P204)3 with MgBu2·AlEt3 at ambient temperature followed by the addition of HMPA. An introduction of a small amount of styrene during the preparation of the catalysts can further improve their stability.

DBU-catalyzed biobased poly(ethylene 2,5-furandicarboxylate)polyester with rapid melt crystallization : synthesis, crystallization kinetics and melting behavior

Poly(ethylene 2,5-furandicarboxylate) (PEF) is in the spotlight as a new emerging biobased polyester. Usually, PEF exhibits very slow and weak melt crystallization behavior. In this study, PEF synthesis via a transesterification polycondensation method catalyzed by 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as an organic nonmetallic catalyst was attempted. PEF with a moderate molecular weight (intrinsic viscosity 0.54 dL g−1) and low diethylene glycol furandicarboxylate unit content (DEGF 1.7%) was successfully synthesized and the melt crystallization kinetics and melting behavior were investigated. The DBU-catalyzed PEF exhibited rapid melt crystallization in both nonisothermal and isothermal manners. At cooling rate of 10 °C min−1, a melt crystallization peak appeared around 158 °C with a crystallization enthalpy of 29 J g−1. DSC and WAXD results indicated a crystallinity of 27–34% after sufficient isothermal melt crystallization at 160–210 °C. A minimum of melt crystallization half time, 1.6 min, appeared at 160 °C. The equilibrium melting point of PEF was estimated to be 243 °C.

Synthesis and characterization of altaicadispirolactone

Abstract Altaicadispirolactone was synthesized via a simple route. In this route, levulinic acid was used as a starting material, and bromination followed by hydrolysis and BF3 · OEt2‐catalyzed cyclization were carried out. A single‐crystal ORTEP drawing has been created and more detailed crystallographic data of the compound has been obtained from X‐ray analysis.

Bursty magnetic reconnection under slow shock‐generated whistler waves

Nonlinear dynamics of magnetic reconnection with an external sub-Alfvenic parallel shear flow is investigated by using two-dimensional compressible Hall MHD simulation. Two pairs of slow shocks in the inflow region are generated by the sub-Alfvenic shear flow in the MHD simulation. With inclusion of Hall effects, it is found that whistler waves are generated in the downstream region of slow shocks. The whistler waves propagating toward the reconnection region drive a large bursty enhancement in magnetic reconnection during its decaying phase.

Effect of Monomer Structure on Crystallization and Glass Transition of Flexible Copolyesters

Amorphous flexible (co)polyesters with low glass transition temperature (Tg) are very desirable in impact modification of biodegradable brittle polymers and synthesis of biodegradable elastomers. However, most flexible polyesters and binary copolyesters made from linear diacid(s) and diol(s) are crystalline polymers. In order to investigate the effect of monomer structure on the crystallization and Tg of such copolyesters, novel ternary or multiple flexible copolyesters containing various structural units were designed and synthesized in this study, and characterized with 1HNMR, GPC, DSC, WAXD, TGA and tensile testing. Introducing aromatic diacid (especially asymmetric one) or short-chain branched diol is favorable to depress copolyester crystallization, and leads to higher Tg at the same time. From easily crystallized to fully amorphous copolyesters with low Tg were successfully synthesized by adopting different combination of structural units. In addition, the existence of aromatic structural unit in copolyesters is helpful to improve their tensile properties.Graphical AbstractFlexible copolyesters containing various structural units were designed and synthesized. Introducing asymmetric, rigid aromatic or short-chain branched unit is favorable to depress copolyester crystallization, and leads to higher Tg at the same time. Crystalline to fully amorphous copolyesters with low enough Tg have been successfully synthesized by adjusting the structural units.