Zhanxin Jing

Synthesis and properties of polyimide foams containing benzimidazole units

In this research paper, a series of novel polyimide (PI) foams containing benzimidazole units were prepared derived from polyester ammonium salt (PEAS) precursor powders, which were synthesized by co-polymerization of benzophenone-3,3′,4,4′-tetracarboxylic dianhydride (BTDA) with two diamines of 2-(4-aminophenyl)-5-aminobenzimidazole (BIA) and 4,4′-diaminodiphenyl ether (ODA) with various molar ratios. The effects of incorporation of BIA on the morphology, thermal and mechanical properties of co-polyimide (co-PI) foams were explored. The results show that the BIA has a significant influence on foaming degree of PEAS precursor powders. The density of co-polyimide foams increases with increasing the BIA content in the polymer chains. Moreover, the thermal stability of the resultant co-polyimide foams presents a remarkable upward trend with incorporating more BIA units into the polymer chains. As the BIA loading up to 30 mol%, the glass transition temperature of co-polyimide foams increases around 50 °C in comparison with the pristine polyimide foam. Furthermore, the compressive strength of the co-polyimide foams is in the range of 0.30–0.75 MPa, which is superior to their of commercial polyimide foams with the same density. The co-polyimide foams with higher thermal and mechanical properties expand their potential application in many high-tech fields such as aerospace and aviation industries.

Synthesis and characterization of porous polyimide films containing benzimidazole moieties

In this study, a series of porous polyimide films containing benzimidazole units were prepared through a phase separation process. The dibutyl phthalate was selected as porogen. The copolyimides were prepared by the reaction of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride with two diamines of 2-(4-aminophenyl)-5-aminobenzimidazole (BIA) and 4,4′-diaminodiphenyl ether with various molar ratios. The resultant porous polyimide films exhibit optimum cell-size distributions. The effects of BIA on morphology, mechanical, and thermal properties of the porous films were explored. It was found that as the BIA content reached up to 30 mol%, the porous copolyimide film demonstrates remarkable thermal stability and admirable mechanical properties with the glass transition temperature of 294°C, 5% weight loss temperature in argon flow up to 545°C, and a tensile strength of 48 MPa. The incorporation of BIA into the polyimide chains brought the highly rigid structures and strong intermolecular interactions, resulting in the enhancement in the thermal stability and the mechanical properties.

Influence of PLA stereocomplex crystals and thermal treatment temperature on the rheology and crystallization behavior of asymmetric poly(L-Lactide)/poly(D-lactide) blends

Asymmetric poly(L-lactide)/poly(D-Lactide) (PLLA/PDLA) blends were prepared by adding small amounts of PDLA into the PLLA matrix with the formation of stereocomplex crystallites (sc-crystallites). Rheological results indicated that the PLLA/PDLA melt at lower temperatures (<Tm,sc, the melting temperature of the formed stereocomplex crystallites) underwent the transition from liquid-like to solid-like viscoelastic behaviors with increasing of the PDLA concentration, which was related to the sc-crystallites reserved in the melt of asymmetric PLLA/PDLA blends. Dissolution experiment indicated the presence of sc-crystallites network structure in the PLLA/PDLA blends, and the size of the sc-crystallite junction particles network increased with increasing of the PDLA concentration. DSC and POM studies indicated that the PDLA concentration and the thermal treatment temperature had a significant influence on the PLLA crystallizability behavior. At low thermal treatment temperature (<Tm,sc), reserved sc-crystallites showed an obvious promoting effect for PLLA crystallization. With increasing of the thermal treatment temperature, its promoting effect decreased due to melting of the sc-crystallites. This result suggests the sc-crystallites played two roles: nucleation sites and cross-linking points, and the two roles had a competitive relationship with change of the thermal treatment temperature and the PDLA concentration.

Synergistic Effects of Polyethylene Glycol and Polyhedral Oligomeric Silsesquioxanes on Crystallization Behavior of Poly(L-lactide)

ABSTRACT The synergistic effects of poly(ethylene glycol) (PEG) and polyhedral oligomeric silsesquioxanes (POSS) on the crystallization behavior of semicrystalline poly(L-lactide) (PLLA) were systemically investigated using differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). Initially, the influences of PEG and POSS, individually, on PLLA crystallization were studied. The results indicated that PEG, as an efficient plasticizer, enhanced the mobility of the PLLA chains, resulting in decreasing of the glass transition temperature. The enhanced crystallization capacity of PLLA was strongly dependent on the molecular weight and content of the PEG, increasing with decreasing of the molecular weight and increasing of the PEG content. The experimental results also indicated that POSS was a heterogeneous nucleating agent, promoting the crystallization of PLLA. The synergistic effects of PEG and POSS on PLLA crystallization were then analyzed. The results showed that in the presence of PEG and POSS the crystallinity of PLLA was further enhanced due to their synergistic effects.