高性能Ｍg-RE基合金研究进展

采用铸造或压铸的方法制备了系列Mg-RE 基合金,研究了合金的组织、时效过程和力学性能.结果表明,各种Mg-RE合金的微观组织、相组成以及力学性能既有相似之处也有明显差别,合金的相组成由a-Mg 以及Mg-Gd 基合金中加入其它稀土元素,可有效改善合金的时效硬化特性和提高合金的力学性能.合金性能的提高主要与时效过程中生成的镁稀土化合物强化相有关.

PP-g-AA接枝共聚物的制备及表征

以部分预辐照聚丙烯(rPP)作为聚丙烯反应挤出接枝丙烯酸(AA)的引发剂,制备了PP-g-AA接枝共聚物。考察了预辐照剂量、预辐照聚丙烯用量以及单体浓度等因素对接枝反应的影响。采用红外光谱、差热扫描量热仪和偏光显微镜等测试技术对接枝产物的形态、结构及性能进行了研究。结果表明,这种新的PP-g-AA共聚物制备方法能有效抑制聚丙烯的降解并获得较高力学性能的接枝产物。研究发现,当rPP的预辐照剂量为4 kGy,反应原料的组成为m(PP)∶m(rPP)∶m(AA)=90∶10∶0.8时,得到的产物有较高的接枝率(0.19%),并且具有相对最佳的力学性能;这种接枝产物与铝板有很强的粘接效果,其剥离强度达4.88 kN/m。

A novel approach to synthesis of functional CPVC and CPE or graft copolymers - in situ chlorinating graft

A new process of graft copolymerization of poly(vinyl chloride) (PVC) and polyethylene (PE) with other monomers was developed. The grafted chlorinated poly(vinyl chloride) (CPVC) and chlorinated polyethylene (CPE) were synthesized by in situ chlorinating graft copolymerization (ISCGC) and were characterized. Convincing evidence for grafting and the structure of graft copolymers was obtained using FT-IR, H-1-NMR, gel permeation chromatography (GPC), and the vulcanized curves. Their mechanical properties were also measured. The results show that the products have different molecular structure from those prepared by other conventional graft processes. Their graft chains are short, being highly branched and chlorinated. The graft copolymers have no crosslinking structure. The unique molecular structure will make the materials equipped with special properties.

Properties of complex of Tb(III) and poly(N-isopropylacrylamide)-g-poly(N-isopropylacrylamide-co-styrene) core-shell nanoparticles

We successfully prepared a new kind of thermoresponsive and fluorescent complex of Tb(III) and PNIPAM-g-P(NIPAM-co-St) (PNNS) core-shell nanoparticle. It was found that Tb(III) mainly bonded to 0 of the carbonyl groups of PNNS, forming the novel (PNIPAM-g-P(NIPAM-co-St))-Tb(III) (PNNS-Tb(III)) complex. The maximum emission intensity of the complex at 545 nm is enhanced about 223 times comparing to that of the pure Tb(III). The intramolecular energy transfer efficiency from PNNS to Tb(III) reaches 50%. When the weight ratio of Tb(III) and the PNNS-Tb(III) complex is 1.2 wt.%, the enhancement of the emission fluorescence intensity at 545 nm is highest.

Preparation of fully cross-linked CNBR/PP-g-GMA and CNBR/PP/PP-g-GMA thermoplastic elastomers and their morphology, structure and properties

Binary CNBR/PP-g-GMA and ternary CNBR/PP/PP-g-GMA thermoplastic elastomers were prepared by reactive blending carboxy nitrile rubber (CNBR) powder with nanometer dimension and polypropylene functionalized with glycidyl methacrylate (PP-g-GMA). Morphology observation by using an atomic force microscope (AFM) and TEM revealed that the size of CNBR dispersed phase in CNBR/PP-g-GMA binary blends was much smaller than that of the corresponding CNBR/PP binary blends. Thermal behavior of CNBR/PP-g-GMA and CNBR/PP blends was studied by DSC. Comparing with the plain PP-g-GMA, T, of PP-g-GMA in CNBR/PP-g-GMA blends increased about 10degreesC. Both thermodynamic and kinetic effects would influence the crystallization behavior of PP-g-GMA in CNBR/PP-g-GMA blends. At a fixed content of CNBR, the apparent viscosity of the blending system increased with increasing the content of PP-g-GMA. FTIR spectrum verified that the improvement of miscibility of CNBR and PP-g-GMA was originated from the reaction between carboxy end groups of CNBR and epoxy groups of GMA grafted onto PP molecular chains. Comparing with CNBR/PP blends, the tensile strength, stress at 100% strain, and elongation at break of CNBR/PP-g-GMA blends were greatly improved.

Fractionated crystallization of dispersed PA6 phase of PP/PP-g-MAH/PA6 blends

Fractionated crystallization behavior of dispersed PA6 phase in PP/PA6 blends compatibilized with PP-g-MAH was investigated by scanning electron microscopy (SEM), differential scanning calorimeter (DSC), polarized light microscopy (PLM), and wide-angle X-ray diffraction (WAXD) in this work. The lack of usual active heterogeneities in the dispersed droplet was the key factor for the fractionated crystallization of PA6. The crystals formed with less efficient nuclei might contain more defects in the crystal structures than those crystallized with the usual active nuclei. The lower the crystallization temperature, the lesser the perfection of the crystals and the lower crystallinity would be. The fractionated crystallization of PP droplets encapsulated by PA6 domains was also observed. The effect of existing PP-g-MAH-g-PA6 copolymer located at the interface on the fractionated crystallization could not be detected in this work.

Room-temperature strategy for networked nonspherical gold nanostructures from Au(III)-[G-2]-CO2H dendrimer complex

The present work describes a convenient approach to fabricate networked nonspherical gold nanostructures by using [G-2]-CO2H dendrimer and toluene as capping and bridging agents in a CH2Cl2 and H2O biphasic system. A controlled linear assembly is achieved without the use of any catalyst at room temperature. UV-vis spectrum, transmission electron microscopy (TEM), selected area electron diffraction (SAED), and X-ray diffraction (XRD) analysis show that the product is well networked nanostructures with diameter of 4-10 nm and consists of coalesced face-centered cubic gold nanocrystals. Extended experiments reveal that both benzene and dimethylbenzene can also inhabit the gold ions to make them crosslinked, prolong the nucleation points and eventually facilitate the formation of the networks.

Poly(L-lactide)/starch blends compatibilized with poly(L-lactide)-g-starch copolymer

The poly(L-lactide) (PLLA)/starch blends were prepared by the PLLA grafting starch (PLLA-g-St) copolymers as a compatibilizer, and their thermal, mechanical and morphological characterizations were performed to show the better performance of these blends compared to the virgin PLLA/starch blend without the compatibilizer, including PLLA crystallinity, interfacial adhesion between the PLLA matrix and starch dispersive phases, mechanical test, medium resistance, and contact angle. The 50/50 composite of PLLA/starch compatibilized by 10% PLLA-g-St gave a tensile strength of 24.7 MPa and an elongation at break of 8.7%, respectively, vs. 11.3 MPa and 1.5%, respectively, for the simple 50/50 blend of PLLA/starch.

PB-g-PMMA核壳粒子的合成及其在PVC中的分散

聚丁二烯(PB)橡胶粒子与聚氯乙烯(PVC)不相容。采用乳液聚合手段,在聚丁二烯乳胶粒表层接枝与聚氯乙烯相容的聚甲基丙烯酸甲酯(PMMA)充当增容剂制备了聚丁二烯接枝聚甲基丙烯酸甲酯(PB g PMMA ,MB)核壳粒子。用熔融共混法制备了PVC/MB共混物。SEM照片表明,这种核壳结构的粒子在聚氯乙烯中的分散情况随着核壳比的不同而改变,当核壳质量比小于93/7时能够完全均匀地分散在PVC基体中,核壳质量比大于94/6时根本不能分散在PVC基体中,核壳质量比为93/7是粒子能否分散开的转折点。共混物的力学性能数据表明,当MB加入量改变时,共混物也存在脆韧转变点,但受MB粒子的核壳比影响。

ABS树脂合成中影响PB-g-SAN接枝共聚物接枝率的因素

采用种子乳液聚合方式 ,以 K2 S2 O8为引发剂引发聚合 ,合成了一系列 PB- g- SAN接枝共聚物。考察了引发剂用量、分子量调节剂 (TDDM)用量和橡胶 (PB)含量对 PB- g- SAN接枝共聚物接枝率的影响。并将 K2 S2 O8引发剂与氧化 -还原引发体系做了比较。结果表明 ,随着引发剂 K2 S2 O8用量逐渐增加 ,PB- g- SAN接枝共聚物的接枝率逐渐降低。引发剂用量太少时 ,不能满足聚合要求 ,PB- g- SAN接枝共聚物的接枝率也会降低。随着分子量调节剂 (TDDM)用量的增加 ,PB- g- SAN接枝共聚物的接枝率逐渐降低。随胶含量的增加 ,PB- g- SAN接枝共聚物的接枝率逐渐降低。采用氧化 -还原引发体系引发聚合有利于接枝反应的进行 ,在 PB含量相同时 ,采用氧化 -还原引发体系合成的 PB- g- SAN接枝共聚物的接枝率比采用 K2 S2 O8合成的接枝共聚物接枝率高。

Temperature dependence of the distribution of the first passage time: Results from discontinuous molecular dynamics simulations of an all-atom model of the second beta-hairpin fragment of protein G

More than 22 000 folding kinetic simulations were performed to study the temperature dependence of the distribution of first passage time (FPT) for the folding of an all-atom Go-like model of the second beta-hairpin fragment of protein G. We find that the mean FPT (MFPT) for folding has a U (or V)-shaped dependence on the temperature with a minimum at a characteristic optimal folding temperature T-opt*. The optimal folding temperature T-opt* is located between the thermodynamic folding transition temperature and the solidification temperature based on the Lindemann criterion for the solid. Both the T-opt* and the MFPT decrease when the energy bias gap against nonnative contacts increases. The high-order moments are nearly constant when the temperature is higher than T-opt* and start to diverge when the temperature is lower than T-opt*. The distribution of FPT is close to a log-normal-like distribution at T* greater than or equal to T-opt*. At even lower temperatures, the distribution starts to develop long power-law-like tails, indicating the non-self-averaging intermittent behavior of the folding dynamics. It is demonstrated that the distribution of FPT can also be calculated reliably from the derivative of the fraction not folded (or fraction folded), a measurable quantity by routine ensemble-averaged experimental techniques at dilute protein concentrations.

Morphology and thermal and mechanical properties of PBT/HIPS and PBT/HIPS-g-GMA blends

The modification of high-impact polystyrene (HIPS) was accomplished by melt-grafting glycidyl methacrylate (GMA) on its molecular chains. Fourier transform infrared spectroscopy and electron spectroscopy for chemical analysis were used to characterize the formation of HIPS-g-GMA copolymers. The content of GMA in HIPS-g-GMA copolymer was determined by using the titration method. The effect of the concentrations of GMA and dicumyl peroxide on the degree of grafting was studied. A total of 1.9% of GMA can be grafted on HIPS. HIPS-g-GNU was used to prepare binary blends with poly(buthylene terephthalate) (PBT), and the evidence of reactions between the grafting copolymer and PBT in the blends was confirmed by scanning electron microscopy (SEM), dynamic mechanical analysis, and its mechanical properties. The SEM result showed that the domain size in PBT/HIPS-g-GMA blends was reduced significantly compared with that in PBT/HIPS blends; moreover, the improved strength was measured in PBT/HIPS-g-GMA blends and results from good interfacial adhesion. The reaction between ester groups of PBT and epoxy groups of HIPS-g-GMA can depress crystallinity and the crystal perfection of PBT.

Effect of the compatibilization of linear low-density polyethylene-g-acrylic acid on the morphology and mechanical properties of poly(butylene terephthalate)/linear low-density polyethylene blends

A poly(butylene terephthalate) (PBT)/linear low-density polyethylene (LLDPE) alloy was prepared with a reactive extrusion method, For improved compatibility of the blending system, LLDPE grafted with acrylic acid (LLDPE-g-AA) by radiation was adopted in place of plain LLDPE. The toughness and extensibility of the PBT/LLDPE-g-AA blends, as characterized by the impact strengths and elongations at break, were much improved in comparison with the toughness and extensibility of the PBT/LLDPE blends at the same compositions. However, there was not much difference in their tensile (or flexural) strengths and moduli. Scanning electron microscopy photographs showed that the domains of PBT/LLDPE-g-AA were much smaller and their dispersions were more homogeneous than the domains and dispersions of the PBT/ T,T PE blends. Compared with the related values of the PBT/LLDPE blends, the contents and melting temperatures of the usual spherulites of PBT in PBT/LLDPE-g-AA decreased.

HIPS-g-MA共聚物对HIPS/PC共混物相容性、形态和拉伸性能的影响

研究了 HIPS/ PC共混物的相容性及 HIPS- MA对 HIPS( 30 ) / PC( 70 )共混物的相容性、形态和拉伸性能的影响。DSC研究结果表明 ,HIPS/ PC共混物中 PS的玻璃化转变温度 ( Tg)不随组成而变化 ,而PC的 Tg 随其质量分数的降低逐渐向低温移动 ,说明 HIPS/ PC是部分相容体系。通过 DSC、扫描电镜形态观察和拉伸性能测试结果发现 ,当 HIPS- g- MA的含量低于 7.5 %时 ,共混物的相容性改善不明显 ,当其含量达到 7.5 %时 ,对共混物有明显的乳化作用 ,说明饱和的界面浓度在 7.5 %左右。HIPS- g- MA接枝共聚物在 HIPS( 30 ) / PC( 70 )共混物中的增容作用可能是酯交换反应原位生成的嵌段共聚物所致

Morphology, crystallization behaviors, and mechanical properties of PA1010/HIPS and PA1010/HIPS-g-MA blends

The binary blends of polyamide 1010 (PA1010) with the high-impact polystyrene (HIPS)/maleic anhydride (MA) graft copolymer (HIPS-g-MA) and with HIPS were prepared using a wide composition range. Different blend morphologies were observed by scanning electron microscopy according to the nature and content of PA1010 used. Compared with the PA1010/HIPS binary blends, the domain sizes of dispersed-phase particles in PA1010/HIPS-g-MA blends were much smaller than that in PA1010/HIPS blends at the same compositions. It was found that the tensile properties of PA1010/HIPS-g-MA blends were obviously better than that of PA 1010/HIPS blends. Wide-angle xray diffraction analyses were performed to confirm that the number of hydrogen bonds in the PA1010 phase decreased in the blends of PA1010/HIPS-g-MA. These behaviors could be attributed to the chemical interactions between the two components and good dispersion in PA1010/HIPS-g-MA blends.