Potential Barrier Heights and Phase Transition in Polyphenyls and Poly(p-Phenylene)

Abstract

The analysis from X-ray or neutron diffraction data, of the unusually high librational motion around the long molecular axis of the p-terphenyl central ring, reveals a doubly-peaked probability density function (p.d.f.), associated with a double-well potential function between two twisted conformations (φ = ± 13.3° on either side of the average molecular plane). This p.d.f. is the pretransitional effect of an order-disorder transition which takes place at low-temperature. With a simple model averaging the intermolecular interactions, it is possible to separate in the overall libration on each site, at the bottoms of the double well, the contribution of the torsional g mode (θ²) = 35 deg², responsible for the jumps above the barrier, from the contribution of the other modes (θ²) = 17.5 deg². Thus it becomes possible to determine the parameters of the model describing the intermolecular, as well as the intramolecular interactions and to specify the non-sinusoidal shape of the intramolecular potential between two adjacent phenyl rings. It is straightforward to extend the model to any p-polyphenyl molecule with any number of phenyl rings, by considering that the molecular packings are the same in all the family. The model gives an estimate of the reorientational potential barrier heights V = 4.57 kJ mol^?1 in p-terphenyl, V = 7.91 kJ mol^?1 in p-quaterphenyl, in good agreement with NMR results; the calculated p.d.f. are doubly peaked and V < kT at room temperature, which characterizes order-disorder transitions. On the other hand, the model gives a singly peaked p.d.f. and V = 1.25 kJ mol^?1 < kT in crystalline biphenyl, which agrees with the displacive nature of the phase transition. Combined with the features of the incommensurate phase of biphenyl at T = 20K, it gives an estimate of the interactions involved in the modulated phase, predicting a large increase of intermolecular interactions in biphenyl at low-temperature. Finally it is applied to poly(p-phenylene), predicting a twisted conformation in agreement with recent diffraction results and high reorientational barrier potentials.     

聚氯乙烯/木粉复合材料的研究进展

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金属基复合材料的摩擦学性能及结合强度试验研究

以聚酰胺66（PA66）、聚苯硫醚(PPS) 及65Mn钢板为主要原料,制备了一系列不同配比的金属基复合材料,并对这些材料进行不同条件下的摩擦学性能试验,最后通过结合强度试验来分析材料间的结合强度。结果表明,复合材料的摩擦因数及磨损速率随着聚酰胺66的增加而降低;同种材料的摩擦系数及磨损速率随着载荷和对摩速度的增加而先增大后减小;结合强度试验表明金属基复合材料的结合强度随着聚苯硫醚的增加而逐渐增大。     

ASA树脂制备方法的新进展

探讨了ASA树脂制备过程中,工艺上的一些关键问题和解决的方法,包括制备大粒径丙烯酸丁酯胶乳的各种附聚方法、共聚过程中活性单体的选择以及对接枝率的影响等。     

太阳能电池生产项目污染产生与处理措施

太阳能电池是使用硅片经过表面处理、扩散、硅沉积、电极印刷、焊接等工序制备。该过程中产生一定的酸性废气、有机废气、氨气,以及酸碱废水、有机废水等;文章介绍了太阳能电池的生产工艺流程,论述了大气、水污染物产生情况及其处理措施;并对太阳能电池生产中废气、废水污染物特点及相应的污染处理工艺进行了探讨并提出相关建议。     

气固相法生产氯化聚氯乙烯树脂的研究进展

着重介绍了气固相法制备氯化聚氯乙烯（CPVC）树脂的研究进展,对该法制备CPVC的生产工艺、反应机理以及反应动力学进行了阐述,其中生产工艺主要包括热引发氯化、光引发氯化和等离子体引发氯化等。     

载铜蒙脱土对聚氯乙烯材料阻燃性能的研究

通过离子交换反应将铜离子负载在无机层状蒙脱土上,采用十六烷基三甲基溴化铵对载铜蒙脱土进行有机改性,并将其作为阻燃剂添加到软质聚氯乙烯(PVC)材料中。利用X射线衍射对PVC/有机改性载铜蒙脱土的结构进行表征。结果表明,PVC分子链插层进入有机改性载铜蒙脱土层间形成插层型结构,且蒙脱土的层间距达到3.69 nm。热重分析、极限氧指数、垂直燃烧和烟密度测试结果表明,有机改性载铜蒙脱土有效改善了PVC的热稳定性,大幅提高了其阻燃性能。载铜蒙脱土的用量仅为PVC用量的3 %时,垂直燃烧即可达到V0级。     

Peptide-Mimicking Poly(2-oxazoline)s Displaying Potent Antimicrobial Properties

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Effect of silane treated fly ash on physico-mechanical,morphological, and thermal properties of recycled poly(vinyl chloride) composites

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