Ziqing Wang

One-pot synthesis of high-molecular-weight aliphatic polycarbonates via melt transesterification of diphenyl carbonate and diols using Zn(OAc)2 as a catalyst

A simple and efficient route for one-pot synthesis of high-molecular-weight aliphatic polycarbonates (APCs) by direct melt transesterification of diphenyl carbonate (DPC) with aliphatic diols at equimolar amounts was developed. Zn(OAc)2 was found to be the best catalyst for this reaction among the screened transition metal acetates. The effects of reaction conditions on Mw and yield of the poly(1,4-butylene carbonate) (PBC) were investigated, where the highest Mw of 156200 g mol−1 with a yield of 83% was obtained under suitable reaction conditions. In addition, based on the results of thermogravimetric and differential thermal analysis (TG-DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR), a plausible reaction mechanism over Zn(OAc)2 was proposed for APC synthesis.

Magnesium acetate used as an effective catalyst for synthesizing aliphatic polycarbonates via melt transesterification process

High-molecular-weight aliphatic polycarbonates(APCs) were synthesized through a two-step transesterification process under solvent-free conditions. Oligomers with equal numbers of hydroxyl and phenyl carbonate terminal groups could be easily controlled by using equimolar amounts of diphenyl carbonate(DPC) and aliphatic diols as feedstocks in the first step. In the second step, the high-molecular-weight APCs can be obtained by connecting ―OH with OC(O)OC6H5 end-group upon removing the generated phenol at reduced pressure. Mg(OAc)2 was found to be the best catalyst for this process among the screened catalysts, which gave the poly(1,4-butylene carbonate)(PBC) a weight-average molecular weight(Mw) of 148600 and a yield of 84.8% under its suitable reaction conditions. In addition, based on the results of X-ray diffraction(XRD), scanning electron microscopy(SEM) and fourier transform infrared spectroscopy(FTIR), a possible reaction mechanism over Mg(OAc)2 was proposed for APCs synthesis.

Thermoelectric anisotropy of n-type Bi2Te3−xSex prepared by spark plasma sintering

The anisotropy of the thermoelectric properties of Bi2Te3−xSex (0.3 ≤ x ≤ 0.9) is investigated at temperatures from 300 to 523 K. The results indicate that due to the anisotropic microstructures, the anisotropic resistivity ρ and thermal conductivity κ of Bi2Te3−xSex are obtained. For example, the resistivity ratio ρp/ρn (here subscript n and p denote the directions normal and parallel to the pressing direction, respectively) and thermal conductivity ratio κp/κn for Bi2Te3−xSex are around 1.55–2.25 and 0.53–0.79, respectively. As a result, a highly anisotropic figure of merit (ZT) is obtained. A maximum ZTn of ∼0.7 is obtained in the temperature range of 440–470 K for Bi2Te2.1Se0.9. Moreover, the maximum ZTp for Bi2Te2.6Se0.4 is ∼0.6 in the temperature range from 400 to 470 K.

Structure-activity correlations of calcined Mg-Al hydrocalcites for aliphatic polycarbonate synthesis via transesterification process

Mg-Al mixed oxides with different Mg/Al molar ratio were prepared by thermal decomposition of hydrotalcitelike precursors at 500 °C for 5.0 h and used as catalysts for the transesterification of diphenyl carbonate with 1,4-butanediol to synthesize high-molecular-weight poly(butylene carbonate) (PBC). The structure-activity correlations of these catalysts in this transesterification process were discussed by means of various characterization techniques. It was found that the chain growth for the formation of PBC can only be obtained through connecting ―OH and ―OC(C)OC6H5 end-group upon removing the generated phenol, and the sample with Mg/Al molar ratio of 4.0 exhibited the best catalytic performance, giving PBC with Mw of 1.64 × 105 g/mol at 210 °C for 3.0 h. This excellent activity depended mainly on the specific surface area and basicity rather than pore structure or crystallite size of MgO.

Synthesis of Poly(isosorbide carbonate) via Melt Polycondensation Catalyzed by Ca/SBA-15 Solid Base

Ca/SBA-15 solid bases with different Ca/Si atomic ratios were prepared by a one-pot route and employed as catalysts for the production of poly(isosorbide carbonate) (PIC) from diphenyl carbonate and isosorbide via a transesterification polymerization process. The relationship between physicochemical properties and catalytic performance for Ca/SBA-15 in this melt process was investigated by means of various characterization techniques. It was found that basic site amount and strength were responsible for this transesterification process; the weak and medium basic sites inclined to promote polycondensation reaction. It was worth noting that strong basic sites could favor the decomposition of the resultant PIC, resulting in the decrease of weight-average molecular weight (Mw) and yield, and the sample with Ca/Si atomic ratio of 0.4 exhibited the best catalytic performance, giving PIC with Mw of 4.88 × 104 g/mol and Tg of 169 °C at the optimal conditions. This excellent activity can be ascribed to the presence of rich basic sites and specific basic strength on the surface of 0.4Ca/SBA-15.