聚丙烯熔体流动指数与分子量及其分布的关系

研究了聚丙烯(PP)的熔体流动指数(MI)与聚合物不同分子量之间的关联性,对于分子量分布较窄的PP,数均分子量(Mn)、重均分子量(Mw)和粘均分子量(Mv)均能较好的关联;反之,MI与Mn关联性下降,而MI与Mn和Mv的关联性仍很好,尤其是MI与Mv的关联性受分子量分布的影响很小;MI与Z均分子量的关联性很差。同时．确定了MI与各种分子量之间的关联式,该式用于本体PP工艺反应器内氢气浓度的计算和MI的预测,与实验测量结果吻合良好。     

新型高流动聚丙烯注塑专用料分子量及流变性能研究

对由聚合得到的新型高流动聚丙烯注塑专用料M#的热稳定性、分子量及流动性进行了系统的表征,井与国外样品AP03B和M1600进行了比较.结果表明;M#和AP03B、M1600的热稳定性相似,起始分解温度304℃,最大热失重温度458℃.重均分子量及分子量分布的大小顺序为:M#＞AP03B＞M1600.熔体流动速军(MFR)大小顺序为AP03B＞M1600＞M#.在高温下,剪切速率(γ)将对M#的加工性能有较大影响.     

Effects of physical ageing on creep in polypropylene

Creep data have been obtained for polypropylene at 23°C over an extensive time range (10⁻⁸–10⁶ s) as a function of the elapsed time t_e between quenching from 80°C and the start of the creep experiment. The creep curves have been fitted with empirical functions capable of describing the behaviour across the entire β- and -relaxation regions. Analyses of results from both short-term (t0.1 t_e) and long-term tests suggest that physical ageing produces a decrease in relaxed compliance for the β-(glass-rubber) relaxation together with an increase in average retardation time and broadening of the -process. Some decrease in magnitude of the -relaxation also seems to be significant. It is proposed that ageing in polypropylene at room temperature could involve decreases in contour length of amorphous tie-molecules (yielding more extended conformations) through coupled motions in the crystalline and amorphous regions associated with the -mechanism.     

Effect of molecular weight and branch content on the creep behavior of oriented polyethylene

Creep studies were carried out on a range of homopolymers and copolymers of polyethylene with well‐defined molecular weight and branch content. The creep data were analyzed in terms of two thermally activated processes acting in parallel and the effects of molecular weight and branch content are discussed. It is shown that increasing either the number‐average molecular weight or the weight‐average molecular weight gives improved creep behavior at all stress levels. The introduction of butyl branches leads to lower creep at low‐stress levels but can give rise to higher creep at high stress. Plots of the equilibrium log₁₀(strain rate) versus stress at fixed draw ratio (strain) can be used to define sections through a unique true stress/true strain/strain rate surface for each material. These creep results have an additional value in terms of the link between slow crack propagation (SCG) in polyethylene and fibril creep, confirming the proposal made elsewhere that SCG can be quantified in terms of creep to failure across the true stress/true strain/strain rate surface. © 2003 Wiley Periodicals, J Appl Polym Sci 89: 1663–1670, 2003     

Correlations of single-point parameters of linear rheology and molecular weight distribution of polypropylene homo- and copolymers

For various purposes, it is required to compress the shape of the molecular weight distribution (MWD) of polymers into a limited set of parameters. With increasing molecular weight and polydispersity, the MWD data obtained from chromatography become increasingly unreliable due to deficiencies in the high molecular weight region, making estimation via melt rheology more preferable. A number of empirical parameters obtained from melt rheology can be related back to MWD parameters. The target of this study is to establish the reliability of such relations for polypropylene homo- and copolymers. It is found that correlations between polydispersity from rheological crossover modulus and polydispersity via chromatography are not always valid. Therefore, the range of applicability must be kept in mind when attempting predictions based on these correlations because rheological measurements are sensitive to molecular characteristics in ways different from chromatography. The use of a modified polydispersity index is shown to be more reliable.     

High molecular weight polypropylene nanospheres: Synthesis and characterization

The high molecular weight (MW) polypropylene with average particle size of 60 nm was synthesized by controlled growth mechanism using Ziegler–Natta catalyst. The atomic force microscopy (AFM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) studies showed that PP nanoparticles were spherical in shape. Structure and crystallinity were concomitantly studied through Fourier transform infrared spectroscopy and X‐ray diffraction, respectively. It shows nanospherical PP particles with more crystallinity (～ 75%) compared with macrosized PP (～ 59%). In addition, differential scanning calorimetry studies revealed the finite particle size effect on T_g and the scale dependence T_g followed a first order exponential trend. As particle size goes down to nano‐ scale from macrosize, continuous elevation of T_g's were observed from ?25 to ?11°C. This phenomenon was directed to configuration entropy of single spherical nanoparticles of PP. The mechanical properties and surface roughness were also evaluated through AFM. At last, the properties of nanosized PP were compared with micron and macrosized particles. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Studies on the influence of molecular weight and isotacticity of polypropylene on the formation of mesomorphic phase

Polypropylene (PP) blends with various molecular weight and isotacticity were prepared through solution blending and subjected to rapid melt quenching. Structural changes in the PP matrix during mesomorphic phase formation were measured by FTIR spectroscopy and wide‐angle X‐ray diffraction measurements. The blends with different molecular weight and isotacticity provided the pathway to understand their influence on mesomorphic phase formation. It is observed that low molecular weight PP with low isotacticity forms mesomorphic phase, whereas high molecular weight and low isotactic PP does not lead to the formation of mesomorphic phase. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Compatibilization of recycled poly(ethylene terephthalate) and polypropylene blends: Effect of polypropylene molecular weight on homogeneity and compatibility

The effectiveness of compatibilizers in enhancing the dispersion of polypropylene (PP) at various molecular weights in recycled polyethylene terephthalate (RPET) was elucidated. The idea of incorporating PP of different molecular weights evolved from the intention of simultaneously recycling the PET bottles together with the PP‐based bottle caps, which are often of low molecular weight (M_w). Three grades of PP with known molecular weights were blended with RPET at various loadings of compatibilizers. Morphological analyses suggest that the dispersion of the PP particles was more homogeneous, and the average particle size was smaller when low M_w PP was incorporated. This indicates that the interaction between the compatibilizer and PP particles was more intense with the presence of a large number but shorter PP molecular chains. Moreover, specimens containing low M_w PP were found to remain homogeneous regardless of compatibilizer and PP content in the RPET/PP blends. The homogeneity of the blends significantly affected their mechanical performance as well. Higher stiffness, yield strength, deformability, and toughness were observed when low M_w PP was incorporated, regardless of PP and compatibilizer loadings. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Determining molecular weight scale and molecular weight distribution of ethylene-tetrafluoroethylene alternating copolymer via a rheological technique

A self-scaling rheology-based technique was developed to determine the molecular weight (MW) and molecular weight distribution (MWD) of ethylene-tetrafluoroethylene alternating copolymer (ETFE). The self-scaling technique makes determining MW and MWD with isolated completely rheological method possible. Moreover, the two key parameters (the plateau modulus and zero-shear viscosity) were obtained by more robust numerical technique, which let determining MW and MWD via rheological method initiated by Tuminello [Macromolecules 1993, 26, 499] being building on more robust and rigid basis. Our case overcomes the shortage of Tuminello's method and gives more practical and simply mean to analyze the MW scale and MWD in the production and application of ETFE. It is found that the peak MW of a ETFE (commercial grade: EP541) is 1.73 × 10⁵ g/mol, the MWD curve is a pattern with a slightly raised “shoulder” at high-molecular mass end, and a high peak on the median and the polydispersity is broad (the polydispersity index is near to 10.3). The wide polydispersity indicates the commercial ETFE combining good processability of relative lower MW molecules with physical properties of high MW ones. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Rheological properties of polypropylenes with different molecular weight distribution characteristics

Relationships between the rheological properties and the molecular weight distribution of two polypropylene series with different molecular weight distribution characteristics were studied. The end correction coefficient in capillary flow is determined by the molecular weight M_w and the molecular weight distribution M_w/M_n, and is higher as both characteristic values are larger. The die swell ratio at a constant shear rate depends on M_w, M_w/M_n, and M_z/M_w, and is higher as the three characteristic values are larger. The critical shear rate at which a melt fracture begins to occurs depends on the molecular weight M_w and the molecular weight distribution M_z/M_w, and is proportional to M_z/M_w² in a log–log plot. The critical shear stress does not depend on the molecular weight, and is higher as M_z/M_w is higher. The zero‐shear viscosity is determined by a molecular weight of slightly higher order than M_w, and the characteristic relaxation time is determined by M_z. The storage modulus at a constant loss modulus scarcely depends on the molecular weight, and is higher as the molecular weight distribution M_w/M_n is higher. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2128–2141, 2002     

分子量分布对低密度聚乙烯光氧老化特性的影响

采用衰减全反射红外光谱技术（ATR-FTIR）、热重分析法（TG）、凝胶渗透色谱（GPC）、扫描电子显微镜（SEM）和力学试验比较研究了不同分子量分布指数低密度聚乙烯（LDPE）的光氧老化特性,分析了分子量分布对LDPE化学结构、热稳定性、平均分子量、表面微观形貌和力学性能的影响规律。结果表明分子量分布越宽,LDPE不饱和度增长越剧烈,支化作用增长越显著;分子量分布越窄,羰基指数增长越快;分子量分布对于分子结构的断链行为并无影响。分子量分布指数越大,LDPE起始热分解温度和失重5%对应温度下降更快,热稳定性更容易变差,平均分子量下降更多,表面微观形貌老化现象越严重;弯曲强度和冲击强度受影响更显著,指数为6.0的LDPE老化24 d冲击强度就已丧失。分析认为,分子量越大、分布越窄表明分子链越长、短分子链越少,与氧接触而产生自由基的概率也越小,因此聚乙烯分子量分布越宽,材料越容易老化。     

The molecular weight distribution of oligomers

It is shown that the relation $\text{P}{}_{\mathrm{w}}\text{P}{}_{\mathrm{n}}\text{= 2}$ or the nonuniformity U = 1 is only a limiting case for high degrees of polymerization, is no more valid for oligomers. Two new relations are derived, one including and one excluding monomers. For the oligomer part of cationically produced polystyrenes the second relation is in good agreement with experiments.     

Effect of recovery methods and conditions on the yield,solubility, molecular weight,and creep compliance of regenerated chitosan

The objective of this study is to explore the effect of using different recovery methods and conditions on the yield, solubility, molecular weight, and creep compliance of the regenerated chitosan. The results show that yields obtained by dialysis were higher than those using recovery medium of alkali solutions, organic solvents, or alkali–alcohol–water mixtures. For those chitosans employing alkali solutions as the recovery medium, the higher the alkali concentration used, the higher the yields obtained, although the total quantity of alkali in the solution were the same. Solubilities of regenerated chitosans were similar and independent at the methods of using alkali solution, organic solvent or alkali–alcohol–water mixture or at different concentrations of alkali solution. The molecular weight of regenerated chitosan decreased from 2.37 × 10⁷ to 1.68 × 10⁷ Da proportionally with the concentration of the alkali solution of the recovery medium from 1N to 8N. Creep compliance of regenerated chitosan gel obtained from 65% degree of deacetylation (DD) chitosan was lower than that of either 72 or 89% DD chitosan gel. Of the same DD chitosan, compliance of regenerated chitosan gels obtained by using a higher concentration of alkali solution was lower than that of a lower concentration ones. Hydrogels regenerated from different DD chitosans and/or different recovery mediums have different structure and tactile properties. Therefore, they can be used as wound dressings suited to different applications. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 193–202, 2002; DOI 10.1002/app.10296     

Influence of molecular weight distribution on flow properties of commercial polyolefins

The aim of this work is to investigate the effects of molecular weight distribution on some conventional flow properties of polyolefins like melt flow index, melt flow ratio, and power law index. The study is designed in two steps. First, the statistical correlation analysis was carried out for proper choice of input variables for each output property and to find the most relevant mathematical forms of the considered parameters for the modeling section. Then the considered property was correlated to the entire molecular weight distribution using spline functions. The best fit was achieved by variation of the number of spline nodes and their values. The proposed methodology is able to be coupled with a polymerization model to correlate the polymerization conditions to the final properties of the product and design a polymerization control loop. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

窄分布低分子质量端羟基聚四氢呋喃的合成与研究

以三氟化硼乙醚配合物(BF3·OEt2)为催化剂,环氧丙烷(PO)为起始剂,二氯甲烷(CH2 Cl2)作溶剂,通过四氢呋喃的阳离子开环聚合合成了窄分子质量分布(Mw/Mn＜1.3)的端羟基聚四氧呋喃(PTHF).研究了三氟化硼乙醚配合物用量、溶剂用量、起始剂用量、反应时间对PTHF分子质量(Mn)及其分布(Mw/Mn)...     

利用分子量分布探讨粉末活性炭对膜生物反应器的影响

采用空间排阻液相色谱法监测了不同粉末活性炭（PAC）投加量下膜生物反应器混合液分子量分布情况,发现当PAC投加量从1 g·L^-1增加到2 g·L^-1时,混合液中分子量大于10×10³的物质会增加;分子量小于0.5×10³及介于3×10³～10×10³的物质含量相当;分子量介于0.5×10³～3×10³的物质显著减少。膜污染速率分别为2.74、3.10 kPa·m^-1,证实了混合液中分子量大于10×10³的有机物是引起膜污染的主要物质。     

Effects of molecular weight distribution on the spinodal temperature of polymer mixtures

The effects of molecular weight distribution on the phase stability of polymer mixtures were explored theoretically and experimentally. Based on the lattice‐fluid theory and volume‐fluctuation thermodynamics, the spinodal conditions for a lattice‐fluid mixture of two polymers with molecular weight distribution were derived. The results indicated that the phase stability of a polymer mixture decreases by increasing the molecular weight distribution of polymers in the blend. To confirm the theoretical results with experiments, the changes in the spinodal temperatures of poly(ethyl methacrylate)/polystyrene (PEMA/PS) blends and tetramethyl polycarbonate/polystyrene (TMPC/PS) blends were examined when each component has a different molecular weight distribution. When the weight‐average molecular weight of each component is the same, a blend composed of polymers having broad molecular weight distribution always exhibited lower phase separation than that composed of polymers having narrow molecular weight distribution at the same blend composition. Copyright © 2004 Society of Chemical Industry     

基于聚合物分子量分布的乙烯淤浆聚合工艺优化

分子量及分布是聚合物生产过程中极其重要的质量指标,但目前的技术水平并不能实现分子量及其分布的实时测量,基于反应机理的动态建模是实现其软测量的重要方法。以乙烯淤浆聚合工艺为研究对象,基于聚合机理,分别以聚合物的平均分子量和分子量分布为目标,以循环气中氢气乙烯比为决定变量,采用稳态优化方法求取聚合物生产的工艺条件。结果表明:以平均分子量为优化目标所得的结果与分析值的偏差较大,虽然聚合物的平均分子量符合要求,但聚合物的分子量分布曲线与所需产品的分子量分布曲线之间的最大误差可达0.092;而以分子量分布曲线为目标所得的最大误差只有0.069。因此,以分子量分布曲线作为目标的优化方法明显比常规的以平均分子量为目标的优化方法优越。     

Evolution of molecular weight and molecular weight distribution in ab initio styrene emulsion polymerizations using series of rigid rodlike cationic amphiphiles as surfactants

The emulsion polymerization of styrene is carried out using a series of unconventional rigid rodlike cationic surfactants (1‐[ω‐(4′‐methoxy‐4‐biphenylyloxy)alkyl]pyridinium bromides, PCX) of different lengths. The evolution of the molecular weight (M) and molecular weight distribution of the polymers is analyzed to obtain information about the chain stopping mechanism. Our results indicate that the M is strongly dependent on the initial surfactant concentration and is not dependent on the alkyl chain length. The Clay and Gilbert model [ln P(M) versus M plots] yields a concave‐up region at low molecular weights and a linear region that extends to high values. The slope of the linear region, which is related to the rate coefficient of the chain transfer to the monomer versus the propagation rate coefficient ratio, decreases as the PCX concentration increases. This behavior indicates that as the PCX concentration increases the chain transfer to monomer becomes the dominant chain stopping mechanism. On the other hand, the ln P(M) versus M plots of polymer samples taken at low and high conversions show differences in slope, particularly at low PCX concentration. It is likely that at low conversion the chain transfer to monomer competes with other chain stopping mechanisms that could be associated with a coagulative nucleation process. The formation of a high molecular weight fraction at low conversion supports this explanation. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1513–1523, 2002; DOI 10.1002/app.10489     

Controlled rheology of polypropylene: Modeling of molecular weight distributions

A mathematical model for the controlled degradation of polypropylene is presented in this article. A previous model of this process was extended to predict the whole molecular weight distribution of the modified resin. Probability generating functions were applied to transform the infinite set of mass balance equations of both polymer and radicals. The integration of the transformed set of equations yielded the probability generating function transforms. These transforms were then inverted with two different inversion algorithms, recovering the molecular weight distributions of the polymer. The model predictions were compared with our experimental data and other information taken from the literature. Good agreement was obtained. The approach presented here is also useful for other polymerization and postpolymerization processes. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1676–1685, 2003