Influence of annealing and chain defects on the melting behaviour of poly(vinylidene fluoride)

The melting behaviour of poly(vinylidene fluoride) (PVDF) was investigated by differential scanning calorimetry (DSC) and small- and wide-angle X-ray scattering in order to study the influence of the chain defects content and of the temperature of annealing on the crystallization and melting behaviour.All the DSC scans show a double endotherm and the analysis of the data suggests that the low temperature endotherm is due to the melting of a population of thin lamellae, whose thickness increases during the annealing, but a high content of chain defects prevents the lamellar thickening and the main effect in this case is the crystallization of thin lamellae from a portion of polymer which did not crystallize during the quenching from the melt. Furthermore, the two melting endotherms, which are observed, can be partially ascribed to a melting-recrystallization process.Furthermore, stepwise isothermal cooling was performed in a differential scanning calorimeter followed by melting scans of fractionated PVDF samples to point out the possible presence of a series of endothermic peaks.     

1,2-二乙炔基四苯基乙硅烷与1,2-二乙炔基四甲基乙硅烷的共聚及其光解

1,2-二乙炔基四苯基乙硅烷与1,2-二乙炔基四甲基乙硅烷在催化剂铑(Ⅰ)络合物[氯化三-(三苯基膦)铑]的作用下得到一种新的含硅共聚物。实验证明此共聚物的主链是有规交替结构。研究了固体薄膜及其溶液的光解作用,并测定了SbF_5蒸气处理后的共聚物薄膜的导电性。     

A competitive (dual) simplex method for the assignment problem

Where there is abundance of mystery and confusion in every direction, the truth seldom remains hidden for long. It's a matter of having plenty of angles to go at it from. Only the utterly simple crimes - the simplex crimes, you may say - have the trick of remaining baffling. - Sir John (from Michael Innes,The Open House (A Sir John Appleby Mystery), Penguin Books, 1974).A dual simplex method for the assignment problem leaves open to choice the activity (i,j) of rowi and columnj that is to be dropped in pivoting so long asx _ij < 0. A choice (i,j) over columnsj having at least 3 basic activities that minimizesx _ij is shown to converge in at most ( ₂ ^n-1 ) pivots, and at most O(n ³) time, and it is argued that on average the number of pivots is at mostn logn. Dedicated with affection to George B. Dantzig on the occasion of his seventieth birthday.     

γ-射线辐照对尼龙6纤维结构的影响

<正> 过去的大多数研究表明,高能射线辐照会引起聚乙烯及聚丙烯等稀烃类聚合物分子链交联及降解,而且会导致结晶度下降。张利华等人最近的研究表明,对于尼龙1010塑料,仅当辐照剂量高到一定程度后,辐照才会破坏结晶。此外,Stowe等人曾经研究过近紫外线对尼龙66纤维结构的影响,结果表明,在空气气氛中的近紫外辐照主要导致尼龙66纤维降解,并使纤维结晶度提高。有关高能射线辐照对高度取向的合成纤维结构及性能的影响的研究尚不多见。本工作将讨论γ-射线对于尼龙6纤维结构的影响。     

含间苯基聚芳醚酮的合成与性能研究

含间苯基聚芳醚酮的合成与性能研究林权，张万金，吴忠文，尹玖梅（吉林大学化学系，长春，１３００２１）（中国科学院长春应用化学研究所）关键词聚芳醚酮，间苯基，熔点，结晶度聚芳醚酮作为一类耐高温特种工程塑料，由于具有优异的热、电、机械性能，已被广泛应用于电...     

涤纶织物热定型后动态力学行为

利用Rhcovibron DDV-II-EA型动态粘弹谱仪测试了PET平纹布在不同温度热定型后的布样及其经、纬纱的动态力学性质。发现布及其纱的动态力学-温度谱与原纤维的截然不同。在[Ε]-T 曲线上出现[Ε]峰,[Ε]_max值随织物热定型温度的增高呈指数下降,峰位向高温移动。同时在Ε’’-T曲线上出现双损耗模量峰,相应的松弛转变活化能相差半个数量级。初步分析认为,与织布过程及随后的织物热定型有关。     

咪唑类离子液体结构与熔点的构效关系及其基本规律

熔点是界定、研究离子液体及其使用过程的一个重要参考指标,因此研究离子液体分子结构与熔点之间的构效关系及其基本规律有特别重要的意义。本文以从近两百遍文献及Beilstein Gmelin网络数据库中收集的约900种咪唑类离子液体中的384种咪唑类离子液体的熔点数据为依据,考察了离子液体分子结构与熔点之间的构效关系及其基本规律,这对离子液体的设计合成及应用有指导作用。     

Poly(butylene terephthalate)/poly(ε-caprolactone) blends: Influence of PCL molecular mass on PBT melting and crystallization behavior

The isothermal crystallization kinetics and melting behavior of poly(butylene terephthalate) (PBT) in binary blends with poly(ε-caprolactone) (PCL) was investigated as a function of PCL molecular mass by differential scanning calorimetry and optical microscopy. The components are miscible in the melt when oligomeric PCL (M_w = 1250) is blended with PBT, whereas only partial miscibility was found in mixtures with higher molecular mass (M_w = 10,000 and 50,000). The equilibrium melting point of PBT in the homopolymer and in blends with PCL was determined through a non-linear extrapolation of the T_m = f(T_c) curve. The PBT spherulitic growth rate and bulk crystallization rate were found to increase with respect to plain PBT in blends with PCL1250 and PCL10000, whereas addition of PCL50000 causes a reduction of PBT solidification rate. The crystallization induction times were determined by differential scanning calorimetry for all the mixtures through a blank subtraction procedure that allows precise estimation of the crystallization kinetics of fast crystallizing polymers. The results have been discussed on the basis of the Hoffman-Lauritzen crystallization theory and considerations on both the transport of chains towards the crystalline growth front and the energy barrier for the formation of critical nuclei in miscible and partially miscible PBT/PCL mixtures are widely debated.     

Thermal transitions of DODAB vesicular dispersions

Two endothermic transitions, at 36°C and 44°C, were observed with differential scanning calorimetry (DSC) upon heating dioctadecyldimethylammonium bromide vesicle dispersions that were equilibrated below 15°C while in samples kept at 25°C there was only the transition at 44°C, which was shown to be the gel to liquid–crystalline transition by ¹H-NMR measurements. The transition at 36°C was reversed in an exothermic transition around 13°C upon cooling. The slowness of this transition at ambient temperatures suggests that the presence of the transition at 36°C in a DSC upscan depends strongly on the sample history.