凝胶色谱法在聚丙烯分子量及分子量分布测定中的应用

根据聚丙烯在凝胶色谱柱上的淋洗特点,确定了测定其分子量及分子量分布试验条件;采用示差和黏度双检测凝胶色谱系统,利用普适校正方法,不需要Mark常数K、α值,可直接测定聚丙烯分子量分布并给出分子量分布曲线;采用统计方法计算数均分子量、重均分子量、黏均分子量,可以为课题研究提供一定的依据和指导。     

高分子分子量、分子量分布与熔体指数(MI)关系的研究(Ⅱ)──聚丙烯的分子量、分子量分布及熔体指数(MI)的实验考察

本文采用凝胶渗透色谱法（ＧＰＣ：ＷＡＴＥＲＳ－１５０Ｃ），对不同分子量、分子量分布和熔体指数的聚丙烯进行了测定，测定ＭＩ的样品近５０种，为验证本文第Ｉ部分提出的理论方程提供了相当充分的基础数据。从中发现齐格勒一纳塔催化剂的工业级聚丙烯的熔体指数范围可以很宽（０．５—１６ｇ／１０ｍｉｎ）。而重均分子量的范围大体上为２．５×１０５一３．５×１０５，数均分子量范围为２×１０４一６×１０４，从而使分子量分布分散系数（Ｍｗ／Ｍｎ）范围为４—１６。     

采用色谱柱和激光光散射联用的方法表征胶原蛋白肽的分子量

分子量分布是胶原蛋白肽(collagen polypeptide,简写为CP)的重要指标,与它的物理化学性质及生物学活性密切相关。本文较为详细地阐述了采用色谱柱和激光光散射联用(SEC-MALLS)的方法表征胶原蛋白肽分子量的原理和方法,采用SEC-MALLS方法对蛋白酶水解明胶制备的胶原蛋白肽进行检测,得到了产品的分子量分布范围、平均分子量、尖峰分子量及各段分子量内组分含量等信息。     

超高分子量聚乙烯分子量及分子量分布的测定

超高分子量聚乙烯UHMWPE的分子量和分子量分布直接影响其加工性能和机械性能,然而传统的凝胶色谱法(GPC)存在一定的局限性,粘均分子量难以全面反映UHMWPE的结构特点。为了开发出一种精度高、重复性好的UHMWPE分子量和分子量分布测试方法,本研究在常规高温GPC设备的基础上,基于溶液流动分级机理,选取了合适凝胶孔径的凝胶色谱柱,改善了普通GPC测试结果分子量分布偏宽的问题。并通过对UHMWPE/三氯苯溶解方法的深入研究,解决了普通GPC测试结果重复性差的问题。对UHMWPE新产品的研发和后期的加工有着重要的实际意义。     

聚合工艺条件对超高分子量聚乙烯性能的影响

通过在不同工艺条件下超高分子量聚乙烯聚合的小试试验,探讨了聚合压力、温度、催化剂浓度、助催化剂浓度以及搅拌速度等因素对超高分子量聚乙烯的影响。实验表明,各种工艺条件对超高分子量聚乙烯的分子量和机械性能有着不同程度的影响,其中以温度对分子量的影响最大;另外超高分子量聚乙烯的分子量和机械性能也存在着一定的关系。     

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。     

PE-UHMW分子量及其分布表征技术进展

针对常规分子量表征手段很难用于超高分子量聚乙烯(PE–UHMW)的分子量测试现状,综述了PE–UHMW分子量分布及其大小测试方法。PE–UHMW分子量分布可以通过以下方式实现:利用不同温度时溶解性不同实现分离,利用凝胶色谱柱实现分离,利用运动速度与分子量之间的关系实现分离。PE–UHMW分子量测试目前主要有黏度法、凝胶色谱连用技术、流变仪法等,其中黏度法在实际生产中得到了广泛应用,但这种方法重复性差,其可靠性和准确性还不稳定。     

超高分子量聚乙烯分子量测试方法研究进展

聚合物材料的性能与其分子量及其分布有较强的相关性,对分子量及其分布准确测量具有重要意义。文章介绍了基于分析化学的端基分析法,基于热力学原理的沸点上升法/冰点下降法、渗透压法,基于物理性能的光散射法,基于机械性价的黏度法、流变法等分子量测试方法的研究进展。通过对比不同测试方法的特点,为超高分子量聚乙烯分子量及其分布的测试提供技术支撑。流变法、GPC法和检测联用技术有望成为PE-UHMW分子量测试方法研究重点。     

聚丙烯分子量及分子量分布的化学和机械降解的影响

本文研究了化学和机械降解对聚丙烯分子量和分子量分布的影响。原始聚丙烯树脂的分子量,分子量分布与聚合过程中氢调量、催化剂类型有密切的关系。随着氢调量增加,原始树脂的分子量变小、分子量分布变宽。但是,由原始聚丙烯树脂降解的产物在熔体流动指数(MFI)相同的条件下,氢调量多则降解树脂的分子量大、分子量分布宽,从高效催化聚丙烯得到的降解树脂的分子量、分子量分布都明显低于用普通催化剂产生的降解树脂。通过调节聚合过程中的氢调量、催化剂及聚合后的化学降解程度,可以在较大的范围内选择适合于纺制优质聚丙烯纤维的分子量和分子量分布。     

窄分子量分布端羟基环氧乙烷-四氢呋喃共聚醚的合成及表征

用三氟化硼乙醚络合物(BF3.OEt2)为催化剂,乙二醇(EG)为起始剂,甲苯作溶剂,通过阳离子开环聚合制备出了窄分子量分布(w/n<1.3)的端羟基环氧乙烷-四氢呋喃(TEO)共聚醚,探讨了聚合温度、时间、反应介质、加料方式、起始剂及单体配比对分子量及其分布的影响,采用凝胶渗透色谱-多角度激光散射联用仪(SEC-MALLS)对其分子量及分布进行准确的测定,并用IR和1HNMR对共聚醚结构进行了表征。研究表明:有EG存在时,采用一次加料的方式,以甲苯为溶剂,温度为0℃,单体配比为11,∶反应时间为5 h的条件下制得的共聚醚具有分子量分布较窄的特点。     

半芳香尼龙PA12T的微波辅助聚合与表征

半芳香尼龙具有优异的力学强度、耐热性能和耐溶剂性能,在电子电器、汽车、轨道交通、特种装备中具有重要应用,受到了国内外学者和产业界的广泛关注。然而,传统聚合方法存在的制备周期长、分子量分布宽等技术难题长期得不到有效解决。本文利用微波能够使吸波材料快速、均匀升温的特点,首次在微波辅助条件下制备了耐高温半芳香尼龙PA12T,研究了在密闭条件下,以水作为吸波介质,水的用量、反应温度以及反应时间等条件对聚合产物特性黏数的影响,并对产物结构及热性能进行了表征。结果表明,微波辅助聚合与传统聚合方法相比,反应时间缩短三分之一以上,且产物分子量分布较窄,为解决传统半芳香尼龙聚合方法存在的问题进行了有价值的探索。     

Thermal pyrolysis of polypropylene: effect of reflux-condenser on the molecular weight distribution of products

When polypropylene is heated in an inert atmosphere and the volatile products are condensed, the molecular weight distribution (MWD) of the product obtained is very wide. In addition, this product is very waxy, has poor flow properties, and is unusable as a liquid fuel. To improve the product quality, ZSM-5 and other catalysts are usually used in the recycling process. However, these catalysts are costly. On the other hand, if the higher boiling fractions of the volatiles evolved due to degradation are not allowed to escape, then the MWD of the final product can be improved. This paper compares the effects of degradation with and without a reflux on the MWD of the product. Initial MWD of the polypropylene determined by GPC was used for all the simulations. In solving the governing population balance equation for the polymer degradation process, the rate constant for degradation has been fitted to the total weight loss of the polypropylene at a given temperature. The problems arising from the use of moment method with an assumed gamma-distribution are also discussed. A fixed-pivot discretization technique has been adopted for solving the governing equations.     

Preparation of oligochitosan via In situ enzymatic hydrolysis of chitosan by amylase in [Gly]BF4 ionic liquid/water homogeneous system

The preparation of oligochitosan with excellent performance via in situ enzymatic hydrolysis of chitosan by amylase in ionic liquid system is reported. It has been found that [Gly]BF₄ ionic liquid leads to the good solubility and assistant degradation for chitosan, as well as good biocompatibility for amylase. In the homogeneous system that contained 1.0 g chitosan (degree of deacetylation = 88.5%) and 99.0 g 2 wt % [Gly]BF₄ aqueous solution, oligochitosan with 2200 viscosity‐average molecular weight has been obtained after 0.12 g amylase being used for 3 h at 50°C and pH 5.0. This result is superior to that conducted in acetic acid system. Moreover, [Gly]BF₄ can be easily separated from the product and reused with only slight performance loss (oligochitosan product with 2700 viscosity‐average molecular weight has been obtained after [Gly]BF₄ being reused for five times). In addition, the mechanism for enzymatic hydrolysis of chitosan in [Gly]BF₄ ionic liquid has been described. The research on the moisture‐absorption, ‐retention, and antibacterial activity of oligochitosan product shows that the smaller molecular weight would bring the better moisture‐absorption and antibacterial properties. The oligochitosan product with 2200 viscosity‐average molecular weight exhibits preferable antibacterial properties to S. aureus and E. coli. At the same time, the moisture‐absorption and ‐retention capacity of the above product can reach 32% (relative humidity (RH) = 43%), 62% (RH = 81%), and 150% (RH = 43%), 35% (dry silica gel) respectively. The enzymatic preparation of oligochitosan through [Gly]BF₄ ionic liquid/water homogeneous system can be an efficient and environment‐friendly method for academics and industry. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41152.     

Molecular weight distribution of products of free radical nonisothermal polymerization with gel effect. Simulation for polymerization of poly(methyl methacrylate)

A gel effect model for the free radical polymerization of PMMA under nonisothermal conditions has been used to simulate the profiles of various system parameters, such as temperature, initiator concentration and conversion. Cumulative molecular weight and instantaneous radical molecular weight profiles for processes with greatly different histories have been computed using the method of moments. Continuous approximation of the discrete variable, degree of polymerization, renders the transformation of a large set of ordinary equations for species conservation into partial differential equations. The resulting radical and dead polymer molecular weight distributions give averages consistent with those found by the method of moments. Basic rules of thumb correlating the product molecular weights with the governing process parameters have been established based on simulations applicable to either plug flow or well-stirred batch reactors.     

宽峰高相对分子质量高密度聚乙烯专用料的研制

通过淤浆法小试聚合装置合成了不同相对分子质量的高密度聚乙烯粉末,对聚合工艺条件对产物物性的影响进行了研究.同时.考察了不同相对分子质量的聚乙烯共混合成宽峰聚乙烯专用料的规律.结果表明:通过调整聚合工艺条件.在淤浆法小试聚合装置聚合产物的相对分子质量可调;不同相对分子质量的聚乙烯粉末共混可以制备宽峰HDPE:合成的宽峰HDPE专用料的综合力学性能优良,在树脂研究院进行加工,性能良好.     

宽峰高相对分子质量高密度聚乙烯专用料的研制

通过淤浆法小试聚合装置合成了不同相对分子质量的高密度聚乙烯粉末,对聚合工艺条件对产物物性的影响进行了研究。同时,考察了不同相对分子质量的聚乙烯共混合成宽峰聚乙烯专用料的规律。结果表明:通过调整聚合工艺条件,在淤浆法小试聚合装置聚合产物的相对分子质量可调;不同相对分子质量的聚乙烯粉末共混可以制备宽峰HDPE;合成的宽峰HDPE专用料的综合力学性能优良,在树脂研究院进行加工,性能良好。     

Thermal and kinetic study of radical polymerization I. Melt state bulk polymerization of acrylamide by DSC

Radical‐initiated bulk polymerization of acrylamide in the presence of potassium persulfate in the melt phase has been investigated by differential scanning calorimetry (DSC). The method presented here has been carried out in isothermal condition. This not only saves energy and time but also has some less probable side effects. Side effects such as evaporation and imidization could affect the final yield and properties of the obtained product. Different temperatures have been examined for isothermal polymerization to find out the optimum temperature with complete conversion of acrylamide to its corresponding polymer. During the polymerization process, high‐molecular‐weight polyacrylamide is being produced without any significant loss in total yield. The molecular weight was determined by inherent viscosity measurement. Also, no side reaction such as imidization resulting in partial insolubility or crosslinked product was being observed. It is noteworthy that we believe DSC studies show the existence of living radicals that has not been reported before. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2335–2340, 2003     

高效分散剂聚丙烯酸钠的合成及应用

研究了低相对分子质量的聚丙烯酸钠合成及其作为分散剂在矾土基低水泥浇注料上的应用。该合成的特点是采用了过硫酸盐与还原剂硫代硫酸钠组成的复合引发剂体系,并且使用次磷酸钠作为新型链转移剂,代替了传统的异丙醇,最终得到所需分子量的产品。同时研究了其产品作为高效分散剂在矾土基低水泥浇注料的耐火材料上的应用,结果表明,合成的产品具有良好的分散效果。     

Synthesis,separation and characterization of knotted ring polymers

Knotted ring polystyrene (PS) with molecular weight of 380 k was successfully synthesized by intramolecular cyclization reaction in cyclohexane under extremely diluted condition. Crude product was confirmed to include linear precursor molecule, single ring molecules, and various intermolecular-reacted byproducts by SEC and interaction chromatography characterizations. The crude product was fractionated repeatedly several times by high performance interaction chromatography and finally highly-purified knotted ring molecules were obtained. It has been found by SEC-MALS that the chain dimension of the knotted ring polymers is evidently smaller than those of linear and the trivial ring polymer, while knotted polymer molecules have the same absolute molecular weight as the corresponding counterparts.     

淀粉接枝丙烯酰胺的合成及其絮凝性能的研究

以玉米淀粉(St)和丙烯酰胺(AM)单体为原料,采用过硫酸钾引发剂合成了淀粉接枝丙烯酰胺共聚物(St-g-AM)。用红外光谱对接枝共聚物进行了结构表征,用粘度法测定了分子量。讨论了聚合反应的各个因素对接枝共聚反应的影响,考察了接枝共聚物的絮凝性能。结果表明,以接枝效率为考察目标,其最佳的合成工艺为:引发剂的浓度为0.07 g/100 mL,淀粉与丙烯酰胺的质量比为1∶2.2,反应温度为65℃,反应时间3 h。淀粉接枝丙烯酰胺共聚物比430万分子量的聚丙烯酰胺(PAM)对高岭土水样的絮凝性能更好,当接枝共聚物的投加量为6 mg/L时,对高岭土水样的浊度去除率达到81.77%。最佳条件所合成出的淀粉接枝丙烯酰胺的分子量为75万。