Towards high molecular weight poly(bisphenol a carbonate) with excellent thermal stability and mechanical properties by solid-state polymerization

Poly(bisphenol A carbonate) (BPA-PC) was post-polymerized by solid-state polymerization (SSP) after supercritical CO₂-induced crystallization in low molecular weight particles prepolymerized via melt transesterification reaction. The effects of the crystallization conditions on melting behavior and SSP of BPA-PC were investigated with differential scanning calorimetry (DSC), Ubbelohde viscosity method and gel permeation chromatography (GPC). The reaction kinetics of the SSP of crystallized prepolymers was studied as a function of reaction temperatures for various reaction periods. As a result, the viscosity average molecular weight of BPA-PC particles (2 mm) increased from 1.9 × 10⁴ g/mol to 2.8 × 10⁴ g/mol after SSP. More importantly, the significantly enhanced thermal stability and mechanical properties of solid-state polymerized BPA-PC, compared with those of melt transesterification polymerized BPA-PC with the same molecular weight, can be ascribed to the substantial avoidance of undergoing high temperature during polymerization. Our work provides a useful method to obtain practical product of BPA-PC with high quality and high molecular weight.     

Fabrication of electrospun PVDF nanofibers with higher content of polar <Emphasis Type="Italic">β</Emphasis> phase and smaller diameter by adding a small amount of dioctadecyl dimethyl ammonium chloride

In this work, the effect of dioctadecyl dimethyl ammonium chloride (DDAC, a kind of alkyl ammonium salt) on polar β phase content and the diameter of electrospun PVDF nanofibers was investigated for the first time. Our experimental results show that the diameter of the electrospun PVDF nanofiber could be largely reduced and the content of polar β phase also become dominant immediately by just adding a little amount of DDAC. When the mass fraction of DDAC reached 4%, the content of polar β phase increased by about 39.1% compared with PVDF nanofibers without DDAC. Besides, the crystallinity of PVDF nanofibers also increased with the addition of DDAC. Based on the results, the possible mechanism of cooperative effect between electrospinning and DDAC on fiber diameter and formation of β phase in PVDF was discussed.     

Preparation of nylon MXD6/EG/CNTs ternary composites with excellent thermal conductivity and electromagnetic interference shielding effectiveness

In this article,hybrid fillers with different dimensions,namely,2-dimensional (2-D) expanded graphite (EG) and 1-dimensional (1-D) multi-walled carbon nanotubes (CNTs),were added to aromatic nylon MXD6 matrix via melt-blending,to enhance its thermal and electrical conductivity as well as electromagnetic interference shielding effectiveness (EMI SE).For ternary composites of MXD6/EG/CNTs,the electrical conductivity reaches up nine orders of magnitude higher compared to that of the neat MXD6 sample,which tumed the polymer-based composites from an insulator to a conductor,and the thermal conductivity has been enhanced by 477％ compared with that of neat MXD6 sample.Meanwhile,the EMI SE of ternary composite reaches ～50 dB at the overall filler loading of only 18 wt％.This work can provide guidance for the preparation of polymer composites with excellent thermal and electrical conductivity via using hybrid filler.     

基于有延展反射面的挡光板的多曲面前照灯的光学设计

挡光板是近代投射式汽车前照灯用于调节近光灯配光性能的重要部件。采用聚焦法调整挡光板拐点的位置可以有效地抑制投射式前照灯近光照射时光型截止线上的色差和梯度问题,具有提高驾驶员视觉舒适度和行车安全指标的功能。采用一种基于有延展反射面的挡光板的多曲面LED前照灯的光学设计,使用NX10.0建立结构模型,LucidShape软件进行仿真,配光屏幕最大照度值为51.9 lx。研究基于有延展反射面的挡光板的光学设计与常规挡光板的光学设计的配光差异,以及两者在吉利汽车2017年提出的近光路照标准下两者数据对比情况。结果表明:具有延展反射面的挡光板可以有效提高配光Ⅲ区各点的基础数值,进一步提高行车时道路前方40 m～50 m处的视觉亮度,利于辨清道路前方及行人情况。     

聚晶金刚石复合片热残余应力分布规律实验研究

利用改进的应力释放法、X射线衍射法以及Raman光谱,对平面界面结构金刚石复合片表面热残余应力分别进行了实验研究,得到了金刚石层表面热残余应力值及其分布规律,同时得到了基体厚度与热残余应力的相关关系.研究结果表明,采用应力释放法、X射线衍射法及Raman光谱法测试PDC表面热残余应力,其测试结果均与有限元分析结果相吻合,证明了这三种方法的有效性.其中,X射线衍射法测试结果的误差最大,应力释放法其次,Raman光谱法最为精确.由于应力释放法应变片尺寸及X射线衍射法光斑照射范围的限制,无法在试样表面上取较多的测试点,因此难以得到理想的热残余应力分布曲线.而Raman光谱法中所采用的激光光斑仅5μm,可以取更多的测试点,因此其结果更能真实的反映金刚石层表面热残余应力的分布规律.本文的研究结果为精确测试PDC热残余应力,从而为优化PDC界面结构、提高PDC使用性能提供了理论和实验依据.     

树枝状大分子PAMAM合成及对蒙脱土插层改性和应用研究

有机阳离子改性蒙脱土已广泛应用于聚合物改性制备高性能聚合物。本文合成了不同代数G0(零代)、G2(二代)的树枝状大分子聚酰胺-胺(PAMAM),同时对G0、G2代PAMAM进行了季铵化改性,得到了PAMAM季铵盐,进一步用PAMAM季铵盐插层改性钠基蒙脱土(Na+-MMT)得到了PAMAM季铵盐改性蒙脱土(PAMAM/MMT)。XRD分析表明,PAMAM季铵盐己与Na+-MMT中的Na+进行了离子交换,同时提出了G0、G2代PAMAM季铵盐对MMT的双分子和单分子插层模型。进一步研究了PAMAM/MMT对聚碳酸酯(PC)的流变性能的影响规律,结果表明PAMAM/MMT可明显降低聚碳酸酯熔融剪切粘度,有利于提高其加工性能。     

岩体不连续间距数学模型的一个修正函数

不连续间距对岩体性质具有十分重要的意义。基于无限长测量线得到的岩体不连续间距的负幂指数分布是最重要的一种概率分布密度, 为纠正因用有限长测量线而带来的不连续间距的分布误差, 本文提出了一个封闭形式的修正函数。结果表明, 该法可显著减少不连续间距的相对误差, 从而可以采用较短的测量线来测量岩体的不连续间距。     

腺病毒(adenovirus)DNA的转录活性与宿主细胞核骨架(nuclear matrix)的关系

本文用温和的选择性细胞抽提技术,提取腺病毒(adenovirus)感染6h的Hela细胞核内各种DNA组分,分别以腺病毒DNA的早期转录区(El_a,El_b)与晚期转录区(L_2)作探针进行Southern杂交,结果表明只有正在活跃转录着的腺病毒DNA片段才与宿主细胞核骨架紧密结合,从而说明宿主细胞核骨架可能对病毒DNA的转录有重要作用。     

上游边界层对向上散热的水平热板自然对流换热影响的研究

论文对具有上游边界层场合的水平加热表面向上对流换热的自然对流进行了实验研究,采用全息干涉法测定温度场,对侧壁高度为50,100,150毫米三种情况进行了实验测定,发现其边缘效应与无侧壁时的水平板情况不同,在6×10~3相似文献