超高分子量聚乙烯的研究现状

介绍了超高分子量聚乙烯（UHMWPE)的性能，用途和工艺特点以及国内外关于流动改性UHMWPE的研究现状，阐述了共混改性、润滑剂改性和液晶高分子原位复合材料改性三种加工性能改性方法。     

The synthesis of low molecular weight hydroxy-tipped polyethylene and polypropylene by the intermediacy of Ziegler—Natta catalysts

The use of diethylzinc in conjunction with conventional and supported Ziegler—Natta catalysts permits the synthesis of polypropylene and polyethylene samples with g.p.c. $\text{M}\text{?}{}_{\mathrm{<mtext>n</mtext>}}$ values as low as 4000 and 3000 respectively. At high diethylzinc concentrations the number of metal—polymer bonds appears to be 40% for polypropylene and 50% for polyethylene respectively, as measured by a tritium-quench radiotracer method. The metal-bound macromolecules can be efficiently oxidized with molecular oxygen at 60°C, and subsequently hydrolysed to give hydroxy-tipped polymers. The oxidation efficiency appears to be variable and to be lower at high diethylzinc concentrations.     

Thermal and crystallization behaviors of polyethylene blends synthesized by binary late transition metal catalysts combinations

A series of reactor blends of linear and branched polyethylenes have been prepared, in the presence of modified methylaluminoxane, using a combination of 2,6‐bis[1‐(2,6‐dimethyphenylimino) pyridyl]‐cobalt(II) dichloride ( 1 ), known as an active catalyst for producing linear polyethylene, and [1,4‐bis(2,6‐diidopropylphenyl)] acenaphthene diimine nickel(II) dibromide ( 2 ), which is active for the production of branched polyethylene. The polymerizations were performed at various levels of catalyst feed ratio at 10 bar. The linear correlation between catalyst activity and concentration of catalyst 2 suggested that the catalysts performed independently from each other. The weight‐average molecular weights , crystalline structures, and phase structures of the blends were investigated, using a combination of gel permeation chromatography, differential scanning calorimetry, wide‐angle X‐ray diffraction, and small angle X‐ray scattering techniques. It was found that the polymerization activities and MWs and crystallization rate of the polymers took decreasing tendency with the increase of the catalyst 2 ratios, while melting temperatures (T_m), crystalline temperatures (T_c), and crystalline degrees took decreasing tendency. Long period was distinctly influenced by the amorphous component concentration. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 4188–4198, 2007     

The breaking strength of ultra-high molecular weight polyethylene fibers

Ultimate mechanical properties of polyethylene fibers were measured. Results are in close agreement with the stress-induced melting theory of fracture (for finite molecular weight polymers). The perfect fiber work of rupture W_c, modulus K_c, strength σ_c, and strain _c are found to be W_c=0.084±0.003 GPa; σ_c=7.5 GPa; K_c=335±12 GPa; _c=0.0225±0.0005. The activation energy of fracture is measured as ≈108 kJ/mol—the activation energy of polyethylene fusion and one-third the activation energy of bond scission. Non-uniformity of fibers necessitates averaging properties over several test lengths. Actual stress-strain curves are decomposed into thermodynamic and irreversible components. Fusion theory applies to the thermodynamic component..     

超高分子量聚乙烯纤维的表面处理

综述了超高分子量聚乙烯（UHMWPE）纤维复合材料界面的重要性,总结了表面改性方法对UHMWPE纤维以及UHMWPE／树脂界面的影响。     

低分子量聚乙烯熔融接枝马来酸酐的研究

研究了吉林石化高密度聚乙烯装置副产低分子量聚乙烯与马来酸酐(MAH)的融熔接枝反应,考察了单体、引发剂用量、反应时间、温度对接枝率的影响。马来酸酐接枝低分子量聚乙烯应用于PE/CaCO3体系的性能测试结果表明,接枝物可以起到偶联剂的作用,改善体系的性能。     

宽峰聚乙烯／蒙脱土纳米复合材料的制备

利用2种不同的方法制备了2种氢调敏感性不同的蒙脱土／氯化镁／四氯化钛（MMT／MgCl2／TiCl4）催化剂,利用这2种催化剂及其混配催化剂,通过原位聚合法,制备出一系列宽峰聚乙烯纳米复合材料,采用X_射线衍射仪（XRD）、凝胶色谱测试分析（GPC）及力学性能测试等方法对催化剂及聚合产物进行分析,结果表明,2种催化剂以及按照不同比例混合的混配催化剂均表现出较高的聚合活性,XRD测试结果表明,蒙脱土片层在乙烯聚合过程中发生了插层及剥离,以单片层或几层共存的形式分散于聚乙烯基质中;用混配催化剂可制得宽峰聚乙烯纳米复合材料,Mw／Mn=7．23,并且聚合物的堆积密度达到工业生产的标准,宽峰聚乙烯纳米复合材料的综合力学性能较工业产品5000S及工业上应用的管材料有很大的提高。     

Ethylene polymerization over supported titanium‐magnesium catalysts: Effect of polymerization parameters on the molecular weight distribution of polyethylene

The data on the effects of polymerization duration, cocatalyst, and monomer concentrations upon ethylene polymerization in the absence of hydrogen, and the effect of an additional chain transfer agent (hydrogen) on the molecular weight (MW), molecular weight distribution (MWD), and content of vinyl terminal groups for polyethylene (PE) produced over the supported titanium‐magnesium catalyst (TMC) are obtained. The effects of these parameters on nonuniformity of active sites for different chain transfer reactions are analyzed by deconvolution of the experimental MWD curves into Flory components. It has been shown that the polymer MW grows, the MWD becomes narrower and the content of vinyl terminal groups in PE increases with increasing polymerization duration. It is assumed to occur due to the reduction of the rate of chain transfer with AlEt₃ with increasing polymerization duration. The polydispersity of PE is found to rise with increasing AlEt₃ concentration and decreasing monomer concentration due to the emergence of additional low molecular weight Flory components. The ratios of the individual rate constants of chain transfer with AlEt₃, monomer and hydrogen to the propagation rate constant have been calculated. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

超高分子量聚乙烯改性研究进展

综述了近年来超高分子量聚乙烯（PE?UHMW）改性的最新研究进展,包括采用辐照交联法、填充改性法及共混改性法等进行摩擦性能改性,和采用涂层改性法、等离子体改性法等进行纤维表面性能改性,并讨论了摩擦性能改性与纤维的表面性能改性研究面临的挑战。     

超高分子量聚乙烯溶解均匀性研究

超高分子量聚乙烯纤维生产工艺中,超高分子量聚乙烯溶解设备普遍使用双螺杆挤出机。文章研究了如何使用双螺杆挤出机,具体涉及到螺纹元件的组合、双螺杆挤出机的转速以及各区温度控制等关键技术,制备溶解均匀的超高分子量聚乙烯溶液,以达到纺丝要求。     

Viscous behavior of ultrahigh molecular weight polyethylene solution

The viscous behavior of the decalin solution of ultrahigh molecular weight polyethylene (UHMEPE) was studied. The influence of the concentration of polymer as well as the temperature was investigated. The flow curve can be described by the power-law model. The dependence of the viscosity on the temperature can be described by the Arrhenius–Frenkel–Eyring equation. The dependence of viscosity on the concentration can also be described by a power-law correlation. The addition of aluminum stearate increased the activation energy of flow of the solution. The viscosity of UHMWPE solution was decreased at lower concentration and increased at higher concentration of UHMWPE. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:289–293, 1997     

Effect of aluminoxane on molecular weight and molecular weight distribution of polyethylene prepared by an iron‐based catalyst

A series of aluminoxanes, tetraethylaluminoxane (TEAO), tetraalkylaluminoxane (TAAO), Et₂AlOB(4 ? F ? C₆H₄)OAlEt₂ (BTEAO) and ethyl‐iso‐butylaluminoxane modified with p‐fluorophenylboric acid (BEBAO), were prepared and their effects on molecular weight (MW) and molecular weight distribution (MWD) of polyethylene prepared by the iron‐based catalyst [(ArN?C(Me))₂C₅H₃N]FeCl₂ (Ar?2,6‐dimethylphenyl) ( 1 ) were investigated. It was found that TEAO and BTEAO were highly efficient activators for iron‐based catalysts and introducing the branched bulky group (eg iso‐Bu) into the aluminoxane activator could improve the MW of the resulting polyethylene. The MW of polyethylene produced by activators modified by p‐fluorophenylboric acid was higher than for other aluminoxane activators. The TEAO‐ and TAAO‐based polyethylene exhibited attractive bimodal MWD, and the lower MW fraction of bimodal MWD was shown to be produced in the early stage of polymerization due to chain transfer to the aluminium activator. Copyright © 2004 Society of Chemical Industry     

Ultradrawing behavior of one- and two-stage drawn gel films of ultrahigh molecular weight polyethylene and low molecular weight polyethylene blends

The ultradrawing behavior of gel films of plain ultrahigh molecular weight polyethylene (UHMWPE) and UHMWPE/low molecular weight polyethylene (LMWPE) blends was investigated using one- and two-stage drawing processes. The drawability of these gel films were found to depend significantly on the temperatures used in the one- and two-stage drawing processes. The critical draw ratio (λ_c) of each gel film prepared near its critical concentration was found to approach a maximum value, when the gel film was drawn at an “optimum” temperature ranging from 95 to 105°C. At each drawing temperature, the one-stage drawn gel films exhibited an abrupt change in their birefringence and thermal properties as their draw ratios reached about 40. In contrast, the critical draw ratios of the two-stage drawn gel films can be further improved to be higher than those of the corresponding single-stage drawn gel films, in which the two-stage drawn gel films were drawn at another “optimum” temperature in the second drawing stage after they had been drawn at 95°C to a draw ratio of 40 in the first drawing stage. These interesting phenomena were investigated in terms of the reduced viscosities of the solutions, thermal analysis, birefringence, and tensile properties of the drawn and undrawn gel films. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 149–159, 1998     

超高分子量聚乙烯成型加工及改性

介绍了近些年超高分子量聚乙烯（UHMWPE）的成型加工方法，由于UHMWPE熔体粘度极高，成型加工困难，通常采用模压成型，限制了其应用领域；通过综述中低分子量聚乙烯，聚丙烯，液晶聚合物及无机填料等改性UHMWPE所取得的成绩，指出解开UHMWPE的链缠结是改性最核心的问题。     

Tuning the water permeability of ultra-high molecular weight polyethylene microporous membrane by molecular self-assembly and flow field

We have systematically studied phase separation behavior in ultra-high molecular weight polyethylene/liquid paraffin/dibenzylidene sorbitol (UHMWPE/LP/DBS) ternary blends. The aim of this paper is to investigate the combined effect of DBS and flow field on the structure and water permeability of UHMWPE microporous membrane. The experimental results show that DBS molecules self-assemble into fibrils firstly during cooling and the blends exhibit a gel-like state before liquid–liquid phase transition. The relaxation time of DBS fibrils is quite long, which shows a great sensitivity to flow field as compared to UHMWPE chain. UHMWPE microporous membrane was prepared via thermally induced phase separation method. DBS fibrils, as in situ formed nucleating agent, decrease the pore size and water permeability and enhance mechanical properties of membrane remarkably. Shear flow can result in alignment of DBS fibrils, which facilitates the nucleation of UHMWPE and induces the lamellae aligned perpendicular to flow direction. This feature was used to design thermal and mechanical histories and obtained oriented UHMWPE microporous membrane. In comparison to the isotropic UHMWPE microporous membrane, the oriented UHMWPE microporous membrane provides low tortuous paths across the membrane and produces high water permeability.     

粘度法测定药用聚乙二醇分子量的不确定度评定

粘度法测定了聚乙二醇的相对分子质量,并对测定结果的不确定度进行了分析和评定。通过对测定过程中的各种不确定度分析,得到了测定结果的不确定度主要由溶液配置过程中的容量瓶体积和移液管体积引入的不确定度组成,其他方面的组成较小,在实际评定中可以忽略。     

High molecular weight tail and long-chain branching in SRM 1476 polyethylene

The composition of the high molecular weight tail in the branched polyethylene standard reference material SRM 1476 was studied in detail using size exclusion chromatography coupled with a refractive index, a viscosity, and a light scattering on-line detector. The light scattering determinations of both molecular weight and radius of gyration point at a difference in kind between the molecular species below and above 10⁶ Da. In particular, above 10⁶ Da, increases in molecular weight resulted in a marked “densification” process. This is consistent with a greater concentration of long-chain branching and/or with a change in molecular architecture. Previous literature results for this polymer and a critical comparison of the performance of the different detectors are also discussed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2807–2812, 1999     

Supported titanium–magnesium catalysts with different titanium content: Kinetic peculiarities at ethylene homopolymerization and copolymerization and molecular weight characteristics of polyethylene

The effect of Ti content on the activity of titanium–magnesium catalysts (TMC) and molecular weight distribution (MWD) of polyethylene (PE) produced has been studied. It was found that the activity enhances sharply as Ti content decreases from 0.6 to 0.07 wt %, and shows no significant changes in the Ti content range of 0.6–5.0 wt %. The maximum activity (36 kg PE/mmol Ti × h × bar C₂H₄) was observed for TMC with the lowest Ti content. The catalyst with low titanium content (～ 0.1 wt % of Ti) produced PE with narrower MWD (M_w/M_n = 3.1–3.5) as compared to catalysts with higher titanium content (3–5 wt % of Ti; M_w/M_n = 4.8–5.0). New data on the effect of hydrogen on MWD of PE have been found. Increasing hydrogen concentration results in broadening the MWD of PE, especially in the case of TMC with high titanium content. The data presented indicate the heterogeneity of active centers of TMC in the reaction of chain transfer with hydrogen. The data on the ethylene–hexene‐1 copolymerization over TMC with different titanium content are presented. Comonomer reactivity ratios were shown to be independent of the Ti content in TMC. Presumably the difference in activity of these catalysts is mainly caused by the difference in the number of active centers. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:5436–5442, 2006     

丙酮作为引发体系的第3组分对溶液法合成丁基橡胶的影响

以丙酮作为引发体系的第3组分,采用溶液法合成丁基橡胶,研究了丙酮对聚合的影响。结果表明,丙酮对正离子活性中心具有一定的抑制作用,并能在反应后期减少副反应的发生,进而提高聚合产物的相对分子质量。当乙基倍半铝氯化物、水及丙酮的摩尔比为14.1/1/0.90时,可在较高的温度下制得相对分子质量较高且分子量分布较窄的聚合物。     

Wetting of oriented and etched ultrahigh molecular weight polyethylene

Highly oriented gel‐spun ultrahigh molecular weight polyethylene (UHMWPE) fibers possess many outstanding properties desirable for composite materials but their adhesion to such matrices as epoxy is poor. This article describes the combined effects of drawing and surface modification on the bulk and surface properties of gel‐cast UHMWPE films emphasizing the effects of etching on both undrawn and drawn films. Drawing the films yields a fibrillar structural hierarchy similar to UHMWPE fibers and a significant increase in orientation, melting point, modulus, and strength. The effects of drawing on bulk properties were more significant than those of etching. The poor adhesion of epoxy to the smooth, fibrillar, and relatively nonpolar drawn film surface improves significantly with oxidization and roughening on etching. The interlaminar shear failure occurred cohesively in the UHMWPE, and thus the interlaminar shear failure strength was greater for the drawn UHMWPE with its greater tensile strength. Nitrogen plasma etching yielded the best results, both removing any low molecular weight surface layer and etching the UHMWPE beneath. Oxygen plasma etching enhanced wetting but was too harsh, causing extensive surface degradation and a significant reduction in mechanical properties. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 405–418, 1999