常用醇类低温保护剂水溶液的DSC研究

利用差示扫描量热仪(Pyris-Diamond DSC),研究了乙二醇、丙三醇、1,3丙二醇、1,3丁二醇和2,3丁二醇水溶液的过冷行为、水合性质以及玻璃化转变温度,得出了这些性质与溶液浓度的关系.过冷度和未冻水含量在低浓度时没有明显的规律性;而在中高浓度则具有相同的变化规律:随着溶液浓度的增大而增大.各低温保护剂在水合性质上所表现出的差异性,体现了保护剂的官能团(羟基、甲基)所起到的重要作用.保护剂在玻璃化转变温度的明显差异,则反映它们在玻璃化能力方面的强与弱.     

Environmental effects of silicone oil on mechanical properties of low and high molecular weight PMMA

The influence of a silicone oil environment on deformation modes and tensile behaviour of poly(methylmethacrylate) were investigated. Tests were made on samples coated with oils of varying viscosity, ranging from 5 to 1000 cSt. To investigate the effects of polymer molecular weight on environmentally induced craze growth and stability, tests were conducted on an extruded grade of relatively low molecular weight and on a cast grade of high molecular weight. All of the silicone oils acted as crazing agents and tensile strength and ductility were reduced in value as the viscosity of the oil was lowered. The low molecular weight polymer failed in a brittle manner in all environments but developed earlier and more intensive crazing as the liquid viscosity was reduced. The high molecular weight material underwent a ductile-brittle transition when the environment was changed from air to low viscosity silicone oils. The flow of the oil into existing flaws and crazes was sufficiently impeded at 1000 cSt viscosity so that both necking and surface crazing were observed under these conditions. To illustrate the various deformation and fracture modes that were observed, micrographs of free and fracture surfaces are presented and discussed.     

The tensile behaviour of polyethylene terephthalate

Measurements of the load/extension curves of polyethylene terephthalate (PET) over a wide range of temperatures showed four regions of behaviour. These were brittle fracture, ductile, cold-drawing, and uniform extension. A particular study was made of the transitions between brittle fracture and ductile failure, and between ductile and cold-drawing, since these define the limits of the three regimes of failure observed at temperatures below the glass transition and softening range.The effects of molecular weight and crystallinity were examined. The brittle strengths measured in tension at low temperatures showed a very large scatter. There was evidence, in spite of this scatter, that the brittle strength falls with decreasing molecular weight. The yield behaviour was not affected, so that the brittle/ductile transition moves to higher temperatures.Crystallinity affects both brittle strength and yield behaviour. The brittle strength falls with increasing crystallinity, whereas the yield stress rises. Both effects combine to raise the temperature of the brittle/ductile and the ductile/cold-drawing transitions.Stress/temperature curves were also constructed for notched specimens. Notching raises the effective yield stress and reduces the brittle strength so that the brittle/ductile transition is moved to higher temperatures. The observed effects are in qualitative agreement with theoretical predictions of the plastic constraint at the tip of a notch, and thus the latter gives a satisfactory qualitative explanation of notch sensitivity. Notching leads to brittle failure at room temperature, and in notched specimens the brittle strength rises as the temperature is decreased. The brittle strength of the lowest molecular weight sample was again significantly less than that of the higher molecular weight samples.Joint appointment between ICI Ltd and Bristol University.     

冲击韧脆转变曲线数学模型的选择

分别利用Boltzmann函数和双曲正切函数两种数学模型对系列冲击试验中的试验数据进行拟合,得到了材料的冲击韧脆转变曲线,比较了这两种数学模型的优劣和适应性,并对数学模型中各参数的选择进行了讨论。结果表明：Boltzmann函数和双曲正切函数这两种数学模型是同一函数的不同表达式,在拟合冲击韧脆转变曲线过程中都具有同样良好的效果;当曲线上、下平台不明显时,合理地假设上、下平台值,是准确预测韧脆转变温度的前提。     

Thin film and bulk deformation behaviour of poly(ether ether ketone)/poly(ether imide) blends

The deformation behaviour of amorphous thin films of poly(ether ether ketone) (PEEK)/poly(ether imide) (PEI) blends was investigated over a wide temperature range by optical and transmission electron microscopy. All the materials showed localized shear deformation at temperatures well below Tg. In pure PEI and in blends with up to 60 wt% PEEK content, a transition from shear deformation to disentanglement crazing occurred as the temperature was raised. However, this transition was absent in PEEK, which deformed by shear over the whole temperature range, and similar behaviour was found for PEI/80 wt% PEEK. It is argued that at high PEEK content disentanglement crazing is suppressed by strain-induced crystallization and some evidence for crystalline order in deformed regions of initially amorphous PEEK thin films was obtained by electron diffraction. The thin film deformation behaviour of the blends was also shown to be consistent with their bulk deformation behaviour, a high temperature ductile–brittle transition being observed at low PEEK content in tensile tests. This revised version was published online in November 2006 with corrections to the Cover Date.     

Closed-loop phase behaviour in block copolymers

Closed-loop phase diagrams are known in systems with specific intermolecular interactions. In weakly interacting systems, however, such behaviour has never been observed. Here, diblock copolymers formed from polystyrene covalently linked to poly (n-pentylmethacrylate), P(S-b-nPMA), which have only weak segmental interactions, are shown to exhibit a closed-loop phase behaviour over a narrow range of molecular weight. The endothermic transitions from the disordered to ordered and back to the disordered state, as a function of increasing temperature, are dominantly entropic in origin. The morphology and rheological properties of P(S-b-nPMA) undergo characteristic changes at the transitions. Whereas the disorder-to-order transition temperature increases with decreasing molecular weight, the order-to-disorder transition temperature decreases. At a limiting molecular weight, the closed-loop vanishes and no ordering occurs. These findings provide quantitative insight into an elusive transition in weakly interacting multicomponent systems.     

Influence of vitrification on defect formation during curing of epoxies

Defect formation in epoxies due to the chemical shrinkage was observed during isothermal cure over a wide cure temperature range. The observed defects were cohesive cracks and adhesional failures. The influence of the mutual position of the gel and the glass transition points on shrinkage-defect formation was examined. The different types of the cohesive defects can arise in the curing system in both the rubbery and glassy state. The type of defect formed was found to be determined by the relaxational state of the polymer during defect formation. The dependence of the glass transition temperature upon the degree of polymerization is reported for the epoxy/amine polymer system investigated. Experimental parameters of polymer resistance to chemical shrinkage cracking were measured for all investigated cure temperatures.     

一种新的侧链型液晶高分子的合成及表征

分别用基团转移聚合和自由基聚合的方法，合成了一种新的带联苯－西佛碱液晶基元的无间隔段侧链型液晶高分子。运用＾１Ｈ－ＮＭＲ、ＦＴ－ＩＲ、元素分析、ＤＳＣ、ＧＰＣ、ＰＯＭ等方法对单体和聚合物进行了表征。发现相转变温度随分子量的增大而升高，分子量分布对热行为无明显影响，液晶织构不随分子量及其分布的变化而改变。     

Temperature and strain rate dependence of the deformation behaviour of poly(paraphenylene benzobisthiazole)

The mechanical properties of PRT films feature an interesting temperature and strain-rate dependence. The elastic modulus and yield behaviour have been studied over a wide temperature range from 30 to 650° C. The onset of a structural reorganization is observed at about 300° C. The dependence of yield stress on strain rate at different temperatures was examined in terms of the Eyring theory of an activated rate process. It was found that the stress activation volume varies with temperature. The overall elastic-plastic behaviour as a function of temperature and strain rate was interpreted in terms of a previously suggested model that incorporates residual stresses in a rigid rod-like polymer. Enhancement of modulus was also observed due to deformation of the films under elevated temperatures, where better molecular orientation and lateral ordering are achieved.     

Influence of molecular weight on the mechanical performance of a thermoplastic glassy polyimide

Mechanical testing of an advanced thermoplastic polyimide (LaRC^TM-SI) with known variations in molecular weight was performed over a range of temperatures below the glass transition temperature. The physical characterization, elastic properties and notched tensile strength were all determined as a function of molecular weight and test temperature. It was shown that notched tensile strength is a strong function of both temperature and molecular weight, whereas stiffness is only a strong function of temperature. A critical molecular weight (M _c) was observed to occur at a weight-average molecular weight (M _w) of 22000 g/mol below which, the notched tensile strength decreases rapidly. This critical molecular weight transition is temperature-independent. Furthermore, inelastic analysis showed that low molecular weight materials tended to fail in a brittle manner, whereas high molecular weight materials exhibited ductile failure. The microstructural images supported these findings.     

Effects of poly-vinyl alcohol on supercooling phenomena of water

The effects of a polymer additive on the supercooling of water were investigated experimentally. Poly-vinyl alcohols (PVAs) were used as the additives, and samples were prepared by dissolving the PVA in water. Since the characteristics of PVA are decided by its degrees of polymerization and saponification, these were varied along with the concentration as the experimental parameters. Moreover, the effect of purity of the water was also considered. Each sample was cooled and the temperature at the instant when ice appeared was measured. Since the freezing of supercooled water is a statistical phenomenon, many experiments were carried out and the average degree of supercooling was obtained. It was found that PVA affects the nucleation of ice in supercooled water and the degree of supercooling increases with the addition of PVA even for water with low purity. The average degree of supercooling increases with an increase in the degree of saponification of PVA.     

The creep behaviour of ultra-high modulus polypropylene

The creep and recovery behaviour of highly drawn polypropylene monofilaments has been studied over the temperature range 20 to 50° C. A range of samples was examined to identify the influence of draw ratio and molecular weight. It is concluded that the permanent flow creep arises from the presence of two thermally activated processes, one of which relates to the -relaxation process and is associated with the crystalline regions of the polymer, and the second with the molecular network.     

Determination of charpy transition temperature of ferritic steels using miniaturized specimens

Miniaturized specimen technology permits mechanical behaviour to be determined using a minimum volume of material. A method for obtaining the ductile-brittle transition temperature of ferritic steels was developed using a miniaturized notched bar test. Comparisons between conventional and miniaturized specimen ductile-brittle transition temperatures are encouraging. Fracture toughness values were calculated for the miniaturized notched specimens and compared with large-specimen data. The miniaturized specimen values were high, even after appropriate adjustments had been made. Further development may yield valid data when an optimum combination of specimen size, shape, and notch acuity is determined.The work was performed during employment of Battelle.     

Dielectric relaxation of relaxor ferroelectric P(VDF-TrFE-CFE) terpolymer over broad frequency range

Dielectric properties of a relaxor ferroelectric polymer, poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) [P(VDF-TrFE-CFE)] terpolymer, were investigated over a broad range of frequency (from 0.1 kHz to 1 GHz) and a broad range of temperature (-20degC to 76degC). Time-temperature superposition was used to extrapolate the dielectric constant to high frequencies (~1 GHz) from low frequency data (<1 MHz). The consistency between the directly measured and the extrapolated data indicate that the time-temperature superposition can be applied at temperature ranging from the glass transition to the broad ferroelectric-paraelectric transition peak of relaxor, indicating that the glass transition is still the dominating relaxation process at room temperature for the ferroelectric relaxor. Compared with the dielectric properties of poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] copolymer, the terpolymer shows a higher dielectric constant even at 1 GHz, which is considered to originate from the random defects modification converting the long-chain polar-molecular conformation to short-range molecular microstructures and enhancing the molecular motions in both polar and nonpolar nanodomains.     

三水醋酸钠固液相变性能优化实验研究

三水醋酸钠（SAT）在凝固过程中存在着严重的分层和过冷现象,可以利用羧甲基纤维素（CMC）作为增稠剂并添加成核剂来解决过冷问题。本文通过5种成核剂实验得到了效果最好的成核剂配方,其质量配比为SAT∶十二水磷酸氢二纳∶CMC=100∶8∶4。实验过程中还发现加热温度对药品的性质有较大影响,温度过高会导致过冷度变大甚至直接不相变,通过实验得到SAT作为相变材料时加热温度的上限为82℃。     

Time dependent recovery of oriented polyethylene

The recovery behaviour after creep of oriented linear polyethylenes has been studied over the temperature range 20–60 °C. A range of samples was examined to identify the influence of draw ratio and molecular weight. It has been shown that in spite of significant differences in recovery strain level, the recovery kinetics are not affected over a wide range of the structural variations and experimental conditions. It is concluded that the time dependent recovery behaviour is consistent with a model where two thermally activated processes are acting in parallel. More exact values for the activation parameters for both processes of the model have been obtained by taking into account the time dependent distribution of the applied stress between these two processes.     

The synthesis,swelling behaviour and rheological properties of chemically crosslinked thermosensitive copolymers based on <Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide

In this contribution thermosensitive polymer matrices based on N-isopropylacrylamide have been developed. The hydrogels were prepared by photopolymerisation of N-isopropylacrylamide and 1-vinyl-2-pyrrolidinone in appropriate amounts of distilled water. The monomers were cured using a UV-light sensitive initiator called 1-hydroxycyclohexylphenylketone. These copolymers were crosslinked using ethylene glycol dimethacrylate and poly(ethylene glycol) dimethacrylate with molecular weights 600 and 1,000, at 0.1 wt% of the total monomer content. The chemical structure of the xerogels was characterised by means of Fourier transform infrared spectroscopy (FTIR) and the transition temperature of the hydrogels was determined using modulated differential scanning calorimetry (MDSC). By altering the feed ratio, hydrogels were synthesised to have lower critical solution temperatures (LCST) around 37 °C. This ability to shift the phase transition temperature of the gels provides excellent flexibility in tailoring transitions for specific uses. The samples synthesised with PEG1000DMA crosslinking agents absorbed over 18 times their weight in water, while maintaining good gel integrity thus falling marginally short of being characterised as superabsorbent. Each of the samples showed similar deswelling behaviour at 37 °C. Rheological studies showed that increasing the molecular weight of the crosslinking agent caused an increase in hydrogel strength.     

聚对苯二甲酸丁二醇酯的固相缩聚

分子量对聚对苯二甲酸丁二醇酯 (PBT)的性能有直接影响 ,高分子量PBT通常经固相缩聚的方法获得。本文对PBT固相缩聚的机理、影响因素及产物的结晶和熔融性能进行了全面介绍     

Investigation of the aqueous dissolution of semicrystalline poly(ethylene oxide) using infrared chemical imaging: the effects of molecular weight and crystallinity

Fourier transform infrared (FT-IR) imaging was used to successfully explore several factors influencing the dissolution of poly(ethylene oxide). The effect of the degree of crystallinity on the rate of dissolution of mid-range molecular weight PEO was negligible over the temperature ranges studied. The influence of molecular weight on polymer dissolution was found to be much greater than the changes in morphology. An examination of the polymer and solvent images and absorbance profiles, compared with the results of the bulk polymer/solvent boundary movement, confirmed this relationship. An investigation of the bulk polymer/solvent boundary using a crystalline-sensitive polymer band showed the crystalline to amorphous phase change occurred over a short distance. Moreover, solvent diffusion ahead of the bulk polymer/solvent front was minimal, most likely a result of the required phase change, which in turn regulated the degree of solvent ingress. Modeling of the dissolution was performed using the Peppas (power law) model. Physical parameters of the dissolution process were obtained from fitting the release profiles to the power law (fraction released = k x t(n), where k is the dissolution rate constant and n is the release exponent). Results indicated the model worked well to describe dissolution at all molecular weights. By varying the number of data points input to the model and then comparing the generated graphs, it becomes clear that not only does the dissolution slow down over the course of the experiment, but an increase in molecular weight enhances this effect. The effect of different types of drug on the rate of polymer dissolution was also studied. The dissolution of neat polymer was compared to the dissolution of polymer containing 10% (by weight) of theophylline, etophylline, or testosterone. The general trend of all the dissolution curves was the same, with the addition of etophylline and testosterone tracing almost the same route in terms of movement of the bulk polymer/solvent front.     

Thermal and dynamic mechanical properties of blends of bitumen with metallocene catalyzed polyolefins

A high penetration grade bitumen has been blended with up to 50 wt% of two different grades of metallocene catalyzed linear low density polyethylene (m-LLDPE) in order to investigate the potential of these and similar copolymers as a substitute for styrene butadiene styrene triblock copolymers in polymer-modified bitumens (PMB). A continuous polymer-rich phase was observed at m-LLDPE contents as low as 5–10 wt%, along with a significant decrease in the effective glass transition temperature of the PMBs with increasing polymer concentration, suggesting benefits for low temperature flexibility. The m-LLDPE-based PMBs also showed relatively low dynamic shear viscosities up to high polymer contents in the range of temperature and shear rate corresponding to typical PMB processing conditions. However, the presence of bitumen in the m-LLDPE-rich phase led to a significant reduction in the melting points of the m-LLDPE, and softening of the PMBs at temperatures as low as 40–50 °C, depending on the composition and the melting point of the pure polymer. PMBs based on the m-LLDPE with the higher melting point remained fully elastic in this temperature range, but at the expense of increased crystallinity and a higher glass transition temperature, which limit improvements in low temperature flexibility. On the other hand, the potentially broad composition and property windows associated with m-LLDPEs suggest considerable scope for the fine tuning of PMB properties by using combinations of different m-LLDPEs and/or other polyolefins as a means to optimize performance.