物理老化对聚苯基单醚喹啉薄膜银纹化的影响

物理老化实质上是聚合物材料在 Tg 以下存放过程中 ,其凝聚态结构通过链段或更小运动单元的运动 ,从热力学非平衡态向平衡态过渡的一个结构弛豫过程[1] .在这一过程中 ,聚合物的密度、自由体积、焓、熵和力学性质随温度和时间产生变化 .因为银纹化是聚合物的特性 ,所以银纹化也将随结构回复过程而产生变化 .有关物理老化对聚合物银纹化的影响尚未得出一致的结论 [2～ 4 ] .聚苯基单醚喹啉 (结构见 Scheme1 )是一种高性能的芳杂环聚合物 [5] ,它可以在比较苛刻的条件下作为绝缘材料和膜材料使用 .有关这类高性能的芳杂环聚合物的物理老化…     

几种芳杂环高分子膜对气体分离性能的研究

聚苯基-1,2,4-三嗪(PPT)、聚苯基单醚喹嗯啉(PPQ(E))、聚苯基喹哑心啉(PPQ(B))、聚酰亚胺(PI)和聚苯并咪唑吡咯酮(PY)均是耐高温高分子。本文制备了这些高聚物的均质膜(除PI外),研完了它们对O_2、N_2和H_2、N_2、CO、CH_4的分离性。     

N-苯基苯二甲酰亚胺和2-苯基喹噁啉晶态分子动力学行为研究

本文在晶体结构分析的基础上, 对二个芳香杂环高聚物模型化合物N-苯基苯二甲酰亚胺和2-苯基喹噁啉分子的原子热振动参数进行分析, 结果表明N-苯基苯二甲酰亚胺晶态分子基本上为刚性分子, 而2-苯基喹噁啉分子的热振动应包含分子内取代苯基的内旋转运动, 其平均平方振幅为53(25) deg~2。     

N-苯基苯二甲酰亚胺和2-苯基喹噁啉晶态分子动力学行为研究

本文在晶体结构分析的基础上,对二个芳香杂环高聚物模型化合物N-苯基苯二甲酰亚胺和2-苯基喹噁啉分子的原子热振动参数进行分析,结果表明N-苯基苯二甲酰亚胺晶态分子基本上为刚性分子,而2-苯基喹噁啉分子的热振动应包含分子内取代苯基的内旋转运动,其平均平方振幅为53(25)deg~2。     

单轴取向PET薄膜的α松弛与力学行为的相关性

本文用动态力学方法研究了在不同温度和速度下单轴自由辐拉伸的聚对苯二甲酸乙二酯薄膜的非晶区状态,表明从熔体骤冷的非晶态试片在不同热拉伸条件下拉伸,可以得到非晶状态有显著差别的单轴取向薄膜。它们的非晶状态可以用动态力学温度谱的α峰的高度,形状和位置来表征。具有不同非晶状态的试样的储能模量E′(25℃)、屈服应力、负荷-伸长曲线与α松弛的参数以及其他结构参数间有很好的相关性。在一定的条件下热拉伸温度和速度存在Arrhenius型的速度-温度变换关系。     

含喹噁啉环的化合物改性聚己内酰胺

合成了14种由三种含喹(哑心)啉环的芳香化合物改性的聚己内酰胺(MC尼龙),并对其形态、抗冲击强度、吸水性及熔融行为等进行了表征。聚苯基单醚喹(哑心)啉(PPQ)单模型化合物对MC尼龙结晶部分几乎没有影响。少量(0.005—5.0％)吩嗪的引入使MC尼龙的颜色、形态及性能等发生巨大变化,改性体系被认为是氢键相互作用,PPQ双模型化合物的改性作用介于二者之间。     

含喹噁啉环的化合物改性聚己内酰胺

 合成了14种由三种含喹(哑心)啉环的芳香化合物改性的聚己内酰胺(MC尼龙),并对其形态、抗冲击强度、吸水性及熔融行为等进行了表征。聚苯基单醚喹(哑心)啉(PPQ)单模型化合物对MC尼龙结晶部分几乎没有影响。少量(0.005—5.0％)吩嗪的引入使MC尼龙的颜色、形态及性能等发生巨大变化,改性体系被认为是氢键相互作用,PPQ双模型化合物的改性作用介于二者之间。     

非晶态聚对苯二甲酸乙二酯膜应力屈服机制的示差扫描量热研究

采用示差扫描量热法、应力应变测量研究了物理老化对非晶态聚对苯二甲酸乙二酯（ＰＥＴ）膜单轴拉伸过程中应力屈服行为的影响．结果表明，非晶高聚物经物理老化后屈服应力，应力屈服峰及热焓吸热峰均增大；屈服前后的ＤＳＣ结果表明，经过屈服点后试样热焓吸热峰消失，屈服后的试样经物理老化后，应力屈服峰又再现．从凝聚缠结的观点解释了非晶高聚物物理老化和应力屈服的本质．     

半晶聚对苯二甲酸乙二酯中的受限非晶相

当半晶聚对苯二甲酸乙二酯 (PET)的结晶度 (Xwc)处于一定范围内时 ,其物理老化后在差示扫描量热(DSC)曲线上的玻璃化转变区有吸热双峰出现 .通过对此吸热双峰分别与完全非晶试样和具有相当高Xwc 的半晶试样物理老化后在DSC曲线上出现的吸热单峰的比较 ,表明半晶PET中存在两种性质极为不同的非晶区 ,即自由非晶区和受限非晶区 .动态力学热分析 (DMTA)曲线上显示的损耗正切 (tanδ)双峰进一步证实了这两种不同非晶区的存在 .这两种不同非晶区的产生是由于试样中晶粒对非晶相中高分子链段活动性的不同限制作用所致 .研究发现 ,对于由冷结晶得到的半晶试样来说 ,出现两种不同非晶区所需的Xwc 上下限都随结晶温度 (Tc)的升高而增高 .还发现 ,在物理老化过程中 ,虽然非晶相的总量基本保持不变 ,但部分自由非晶区却逐渐转变为受限非晶区 .上述实验结果很好地符合Struik的“扩展玻璃化转变”模型 .     

PP/EPDM共混物热氧稳定性研究

通过热氧加速老化的方法研究了不同的EPDM含量和抗氧剂对聚丙烯和三元乙丙橡胶共混物(PP/EPDM)热氧稳定性的影响.通过对老化前后试样的力学性能变化分析,热失重(TG)分析和扫描电镜(SEM)分析,结果表明:在热氧加速老化的初期,PP/EPDM共混物的拉伸强度随着时间的增长呈逐渐上升的趋势;在老化中期,共混物的拉伸强度变化不大;在老化后期,共混物的拉伸强度逐渐下降.在整个老化过程中,断裂伸长率都呈逐渐下降的趋势.而随着EPDM含量的增加,相应共混物的拉伸强度和断裂伸长率的下降减缓;相应共混物的分解温度得到较大的提高;抗氧剂的加入,能进一步提高共混物的热氧稳定性.     

An investigation of the yield and postyield behavior and corresponding structure of poly(methyl methacrylate)

The mechanical behavior of glassy polymers is time and temperature dependent as evidenced by their viscoelastic and viscoplastic response to loading. The behavior is also known to depend strongly on the prior history of the material, changing with time and temperature without chemical intervention. In this investigation, we examine the effects of this process of physical aging on the yield and postyield behavior and corresponding evolution in the structural state of glassy polymers. This has been achieved through a systematic program of uniaxial, isothermal, constant strain–rate tests on poly(methyl methacrylate) (PMMA) specimens of different thermal histories and by performing positron annihilation lifetime spectroscopy (PALS) measurements prior to and after mechanical deformation. PALS is an indicator of the free volume content, probing size and density of free volume sites and can be considered to be a measurement of structural state. The results of the mechanical tests show that aging acts to increase both the initial yield stress and the amount of strain softening which occurs subsequent to yield. Moreover, the amount of strain softening was found to be independent of strain rate indicating that softening is related to an evolution in structure as opposed to deformation kinetics. Furthermore, after sufficient inelastic straining, the initial thermal history is completely erased as evidenced by identical values of flow stress following strain softening, for both annealed and quenched polymer. Strong confirmation of the structural state or free volume related nature of the strain softening process is obtained by our companion PALS measurements. PALS detects an increase in the size of free volume sites following inelastic deformation and finds the initially annealed and quenched specimens to posses the same post-deformation distribution. The size of sites is found to evolve steadily with inelastic strain until it attains a steady-state value. This evolution of free volume with strain follows the observed softening of the flow stress to a steady-state value. These results provide experimental evidence that an increase in free volume with inelastic straining accompanies the strain softening phenomenon in glassy polymers and that strain softening is indeed a de-aging process. Based on our experimental results a mechanistically based constitutive model has been formulated to describe the effects of thermal history on the yield and postyield deformation behavior of glassy polymers up to moderate strains. The model is found to successfully capture the effects of physical aging, strain softening, strain rate, and temperature on the inelastic behavior of glassy polymers when compared with experimental results. © 1993 John Wiley & Sons, Inc.     

Study of the size and numerical concentration of the free volume of carbon filled HDPE composites by the positron annihilation method

In this paper, the size and numerical concentration of free volume of high density polyethylene/carbon black (HDPE/CB) composite were investigated by positron annihilation lifetime spectroscopy (PALS). The PALS were measured in two series of samples, one with various CB contents in the composites and the other with changing the temperature of HDPE/CB composite containing 25 phr CB. It was found that the important parameters of PALS show their fluctuation around the percolation threshold. The conductivity of HDPE/CB is controlled by CB contribution, and that can be reflected in o-Ps lifetime. The temperature dependence of positron lifetimes reveals that the existence of glass transition temperatures and the size of free volume holes increases when temperature increases above glass transition. The results observed from the second set of samples suggest that positive temperature coefficient is in some way related with free volume expansion. The experiment facts implied that the conductivity of HDPE/CB was related with not only the size of free volume holes but also the number of free volume holes. The Doppler-broadening of HDPE/CB was also investigated.     

Molecular simulations of physical aging in polymer membrane materials

Poly(1-trimethylsilyl-1-propyne) (PTMSP), the most permeable polymer known, undergoes rapid physical aging. The permeability of PTMSP to gases and vapors decreases dramatically with physical aging. Cavity size (free volume) distributions were calculated in as-cast and aged PTMSP, using an energetic based cavity-sizing algorithm. The large cavities found in as-cast PTMSP disappear in aged PTMSP, which is consistent with the positron annihilation lifetime spectroscopy (PALS) measurements. We also characterized the connectivity of cavities in both as-cast and aged PTMSP membranes. Cavities are more connected in as-cast PTMSP than in aged PTMSP. The average cavity sizes calculated from computer simulation are in good agreement with PALS measurements. The transport and sorption properties of gases in as-cast and aged PTMSP are also measured by molecular simulation. Computer simulations showed the decrease of permeability and the increase of permeability selectivity in PTMSP membranes with physical aging, which agrees with experimental observations. The reduction in gas permeability with physical aging results mainly from the decrease of diffusion coefficients. Solubility coefficients show no significant changes with physical aging.     

The effects of physical aging in polycarbonate

The effects of physical aging below the glass transition temperature on selected properties of polycarbonate have been studied. Changes in tensile yield strength, post yield stress drop, and fracture toughness as a result of annealing at 120°C for 240 h have been measured and are related to changes in free volume as measured by positron annihilation lifetime spectroscopy. The free volume concentration remains constant during the aging heat treatment at 120°C but decreases after cooling due to aging. The relationship between free volume changes and physical property changes is discussed in terms of molecular conformations and fracture mode. The effect of aging on fracture morphology is presented to aid interpretations of fracture mode.     

不同后处理条件下聚萘二甲酸乙二酯纤维的结构变化

对不同纺速下制得的聚萘二甲酸乙二酯 (PEN)初生纤维进行了冷拉伸、定长热处理和热拉伸等后处理 .通过WAXS、DSC等测试研究了纤维中结构变化与后处理条件之间的关系 .结果表明 ,较低纺速下所制得的无定形初生纤维在低于Tg 温度下的冷拉伸时发生了应力诱导结晶 ,纤维中生成了α晶体 .同样的初生纤维在定长热处理过程中直至 2 0 0℃仍保持无定形结构 .这些结果说明施加应力相对于升高温度对于α晶体的生成更为重要 .而热拉伸样品中结晶结构的形成与初生纤维的结构有很大关系 ,低纺速下无定形初生纤维在热拉伸后形成α晶体 ,而高纺速下主要含有 β晶体的初生纤维经热拉伸后 β晶体会部分转变为α晶体 ,且 β晶转变为α晶的难易程度取决于初生纤维中 β晶的完善程度 ,初生纤维中 β晶越完善 ,热拉伸时 β晶体越不易转变为α晶体     

Aging and cold crystallization of melt‐extruded poly(trimethylene terephthalate) films

We analyzed the thermal crystallization, glass‐transition behavior, and mechanical properties of melt‐extruded poly(trimethylene terephthalate) (PTT) films to investigate their physical aging and annealing effects. The physical aging and annealing of PTT films had an influence on the glass‐transition temperature, recrystallization behavior, and mechanical properties. When samples were aged at an ambient temperature, the crystallization temperature decreased largely within 5 h, the heat of crystallization increased, and the breaking stress and breaking elongation increased. The glass‐transition temperature of annealed samples, which was obtained from differential scanning calorimetry and dynamic mechanical measurements, increased with increasing annealing temperature below 80 °C but decreased above that temperature. In addition, the glass‐transition temperature and modulus of annealed samples were largely affected by the annealing time; in particular, they increased sharply within 1 h on annealing at 50 °C. Consequently, the change in the glass‐transition temperature on annealing was ascribed to the fact that the molecular constraint due to recrystallization and the mobility of rigid amorphous PTT chains competed with each other, being dependent on the annealing temperature. The mechanical properties of aged samples were closely related to their cold‐crystallization behavior. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1920–1927, 2001     

Effect of physical aging of poly(1‐trimethylsilyl‐1‐propyne) films synthesized with TaCl5 and NbCl5 on gas permeability,fractional free volume,and positron annihilation lifetime spectroscopy parameters

The effect of physical aging on the gas permeability, fractional free volume (FFV), and positron annihilation lifetime spectroscopy (PALS) parameters of dense, isotropic poly(1‐trimethylsilyl‐1‐propyne) (PTMSP) films synthesized with TaCl₅ and NbCl₅ was characterized. As‐cast films were soaked in methanol until an equilibrium amount of methanol was absorbed by the polymer. When the films were removed from methanol, film thickness initially decreased rapidly and was almost constant after 70 h in air for both catalysts. This timescale was much longer than the timescale for complete methanol desorption (ca. 5 h). From the film‐thickness data, the reduction in FFV with time was estimated. For samples prepared with either catalyst, the kinetics of FFV reduction were well‐described by a simple model based on the notion either that free‐volume elements diffuse to the surface of the polymer film and are subsequently eliminated from the sample or that lattice contraction controls polymer densification. Methane permeability decreased rapidly during the first 70 h, which was the same timescale for the thickness change. The decrease in methane permeability was smaller in films prepared with NbCl₅ than with TaCl₅. The logarithm of methane permeability decreased linearly as reciprocal FFV increased, in accordance with free‐volume theory. The PALS results indicate that the concentration of larger free‐volume elements (as indicated by the intensity I₄) decreased with aging time and that the other PALS parameters were not strongly influenced by aging. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1222–1239, 2000     

Free volume quantities and viscoelasticity of polymer glasses

We have investigated, in terms of the Cohen-Turnbull theory, a relationship for polycarbonate (PC) glasses between average stress relaxation times, <to, and average free volume sizes, 〈v_f〉, obtained from positron annihilation lifetime spectroscopy. This examination suggests that the minimum free volume required for stress relaxation, v*, decreases with decreasing temperature and that, near the glass transition temperature, only a subset of extremely large free volume elements contributes to the stress relaxation of PC glasses. This suggestion is consistent with the idea that near the glass transition temperature, the viscoelastic response is dominated by large-scale, main-chain motion, whereas at lower temperature it is controlled by local motion. Moreover, comparison with the v* value estimated from gas diffusivity through various PC species at room temperature shows that the required free volume size for stress relaxation in the glass transition region is much larger than that for gas diffusion. Previously we showed that the Doolittle equation fails to correlate viscoelastic relaxation times of polymer glasses with changing temperature; determining the free volume fraction, h, from theoretical analysis of volume recovery data and theory, the Doolittle equation is shown to be valid in PC above 135°C (T_g - 14°C) irrespective of temperature and physical aging times. This result supports the idea suggested in the previous article that, as glassy polymers approach the transition region, viscoelastic properties increasingly tend to be controlled by free volume. © 1996 John Wiley & Sons, Inc.     

Effect of conductive fillers on the cyclic stress-strain and nano-scale free volume properties of silicone rubber

The effect of carbon black(CB) and graphite(G) powders on the macroscopic and nano-scale free volume properties of silicone rubber based on poly(di-methylsiloxane)(PDMS) was studied through thermal and cyclic mechanical measurements, as well as with positron annihilation lifetime spectroscopy(PALS). The melting temperature of the composites(Tm) and the endothermic enthalpy of melting(?Hm) were estimated by differential scanning calorimetry(DSC). Tm and the degree of crystallinity(χc) of PDMS composites were found to decrease with increasing the CB content. This can be explained due to the increase in physical cross-linking which results in a decrease in the crystallite thickness. Besides, χc was found to be dependent on the filler type. Cyclic stress-strain behavior of PDMS loaded with different contents of filler has been studied. Mullins ratio(RM) was found to be dependent on the filler type and content. It was found that, RM increases with increasing the filler content due to the increase in physical cross-linking which results in a decrease in the size of free volume, as observed through a decrease of the o-Ps lifetime τ3 measured by PALS. Moreover, the hysteresis in PDMS-CB composites was more pronounced than in PDMS-G composites. Furthermore, a correlation was established between the free volume Vf and the mechanical properties of PDMS composites containing different fillers. A negative correlation was observed between Vf and RM.