极低密度聚乙烯与其它聚乙烯的共混

从结构角度，用ＤＳＣ，ＷＡＸＤ，ＳＡＸＳ研究了聚乙烯（ＰＥ）家族中极低密度聚乙烯（ＶＬＤＰＥ）与其它ＰＥ的互容性．ＨＤＰＥ／ＶＬＤＰＥ是共晶互容的，以其大量无规部分“溶解”了ＨＤＰＥ的结晶缺陷部分，提高了ＨＤＰＥ的Ｔｃ，Ｔｍ，Ｘｃ，结晶峰半高宽变窄，晶胞参数随组成而有最低值．ＶＬＤＰＥ与ＬＬＤＰＥ结构极为相似，ＤＳＣ及ＷＡＸＤ证明其共混物是共晶相容体系．ＬＤＰＥ／ＶＬＤＰＥ的结晶度符合按组成的计算值，但晶胞参数ａ，ｂ以及晶粒尺寸增大，ＤＳＣ上有分别相应于两组份的两个Ｔｍ；ＶＬＤＰＥ的Ｔｃ，Ｔｍ峰高之和高于按组份的计算值，ＬＤＰＥ的Ｔｍ，Ｔｃ则低于计算值．认为是正如ＬＬＤＰＥ／ＬＤＰＥ，ＬＤＰＥ向充满整个体积的ＶＬＤＰＥ中不断填入，以ＶＬＤＰＥ为晶核而结晶，形成相分离的不相容体系．     

Temperature dependence of radiation effects in polyethylene: Cross‐linking and gas evolution

High‐density polyethylene (HDPE) and low‐density polyethylene (LDPE) were irradiated in vacuo at 30–220 and 30–360°C, respectively, with γ‐rays at doses of 10–400 kGy. Temperature dependence of cross‐linking and gas evolution was investigated. It was found that cross‐linking was the predominant process up to 300°C and the gel point decreased smoothly with temperature. The increase of G(x) with temperature was likely attributed to the temperature effect on addition of radicals to the double bonds present in the polymer. Above 300°C, the gel fraction at a given dose decreased remarkably with temperature and turned to zero at 360°C. The molecular weight variation determined with gel permeation chromatography (GPC) indicated the enhanced degradation at 360°C by radiation. G‐values of H₂ increased with temperature and varied with dose. The compositions of the C₁–C₄ hydrocarbons evolved depended on the structures of side branches. Raising the temperature favored the formation of unsaturated hydrocarbons, and the yield of unsaturated relative to saturated hydrocarbons decreased with dose. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1541–1548, 1999     

Adiabatic Calorimetry of a Very Low Density Polyethylene Copolymer

The heat capacity of a very low-density polyethylene copolymer (VLDPE) was measured between 10 and 410 K. Using two sets of literature data for the fully crystalline and the fully amorphous states, crystallinities were calculated as a function of temperature. During the stabilisation periods in the melting process no equilibrium is reached, because of an exothermic process, which is attributed to (re)crystallization. Values for the enthalpy of melting and for the heat capacity of the liquid are given. This revised version was published online in August 2006 with corrections to the Cover Date.     

Random copolymer of butadiene and propylene prepared with TiCl4–Et3Al–phosgene catalyst

The copolymerization of butadiene and propylene was investigated. It was found that the catalyst system of TiCl₄–Et₃Al–COCl₂ yields a random copolymer of high molecular weight with a small amount of gel polymer above room temperature. Tetrachloroethylene was a good solvent for the production of high polymer containing a high proportion of propylene units in high yield. The fractionation and the analysis of degradation experiments of copolymer indicate that the copolymer is of random distribution of propylene units in the copolymer. However, the monomer reactivity ratios, r_BD = 6.36 and r_Pr = 0.42, suggest some degree of blocked character. The properties of the copolymer were superior to those of cis-1,4–polybutadiene, especially in resistance to thermal aging.     

Chain scission efficiency and reactive-ion etch resistance of alternating copolymers of styrene and olefins trisubstituted or tetrasubstituted with electron-withdrawing groups

Alternating copolymers of styrene (St) with electron-deficient olefins trisubstituted or tetrasubstituted with cyano and carboalkoxy groups have been subjected to ⁶⁰Co γ-radiolysis together with a series of copolymers of methyl methacrylate (MMA) and St. The chain scission susceptibility G_s—G_x determined by membrane osmometry drastically decreases as St is incorporated in poly(methyl methacrylate) (PMMA). Whereas the alternating St-MMA copolymer is slightly crosslinked upon irradiation, an alternating copolymer of St with diethyl 2-cyano-1,1-ethylenedicarboxylate maintains a fairly high degradation sensitivity (G_s—G_x = 1.2). The reactive-ion etch rates were determined for the series of polymers in CF₄/O₂ (92/8). The etch resistance is significantly increased by introduction of St units in PMMA, and the highly substituted alternating copolymer etches as slowly as the MMA(50)—St(50) copolymers. Thus the alternating copolymer of NCCH=C(CO₂Et)₂ with St behaves like PMMA when exposed to high-energy radiation but is comparable to PSt in plasma environments.     

TIME-DEPENDENT MORPHOLOGY OF POLYETHYLENE-POLYPROPYLENE BLENDS

The effect of time-temperature treatment on morphology of polyethylene-polypropylene (PE-PP) blends wasstudied to establish a relationship between thermal history, morphology and mechanical properties. Polypropylene (PP)homopolymers were used to blend with various polyethylenes (PE), including high density polyethylene (HDPE), lowdensity polyethylene (LDPE), linear low density polyethylene (LLDPE), and very and ultra low density polyethylene(VLDPE and ULDPE). The majority of the blends were prepared at a ratio of PE:PP = 80:20, while blends of PP and LLDPEwere prepared at various compositions. Thermal treatment was carried out at temperatures between the crystallizationtemperatures of PP and PEs to allow PP to crystallize first from the blends. On cooling further, PE crystallized too. A verydiffuse PP spherulite morphology in the PE matrix was formed in some partially miscible blends when PP was less than 20%by mass. Droplet-matrix structures were developed in other blends with either PP or PE as dispersed domains in a continuousmatrix, depending on the composition ratio. The scanning electron microscopy (SEM) images displayed a fibrillar structureof PP spherulite in the LLDPE-PP (80:20) and large droplets of PP in the HDPE-PP (80:20) blend, providing larger surfacearea and better bonding in the LLDPE-PP (80:20) blends. This explains why the blends with diffuse spherulite morphologyshowed greater improvement in tensile properties than droplet-matrix morphology blends after time-temperature treatment.     

Reactions of polyolefins with strong lewis acids

Treatment of a cyclohexane solution of low density polyethylene and polystyrene with anhydrous aluminum chloride causes chemical reaction between the two polymers which results in the formation of a graft copolymer. The initial copolymer-forming reaction is very rapid, and prolonged contact of the polymers with aluminum chloride causes subsequent degradation in molecular weight. Treatment of separate solutions of polyethylene, isotactic polypropylene, and ethylene–propylene copolymers with aluminum chloride was studied as a function of time. The intrinsic viscosities of the polymers dropped from initial values of 2.4–6.5 to 0.55–0.85 in 5 min, followed by a slower decline over the next 2 hr. In the case of polypropylene, the low molecular weight fragments largely retained the isotactic structure, which demonstrates that stereochemical isomerization is not a major reaction.     

Analytical scale supercritical fluid fractionation of a low molecular weight,high density polyethylene wax with carbon dioxide

This paper reports on the use of supercritical carbon dioxide to fractionate a low molecular weight, high density polyethylene into very narrow molecular weight distributions (MWDs). A simple extraction system was developed that allowed relatively trouble free extractions of the polyethylene samples. Fractions were collected at successively higher densities of CO₂ at constant temperature and then analyzed by capillary supercritical fluid chromatography (SFC), or high temperature gel permeation chromatography (GPC) and/or differential scanning calorimetry (DSC). Fractionations were performed at three different temperatures (60,80, and 100°C). Higher temperatures were found to yield greater recoveries and higher MWDs at any given density. Reducing the increment between successive extraction steps resulted in polydispersities being reduced to nearly “monodisperse” levels. Total recoveries ranged from 12 to 33% depending on the temperature, and the highest molecular weight fraction extracted by the CO₂ was centered around 1500.     

Structure and property relationships in ethylene–vinyl acetate copolymers

The effects of vinyl acetate content on crystallinity of ethylene–vinyl acetate (E/VA) copolymers were investigated by x-ray diffraction and differential thermal analysis (DTA). The values of these parameters obtained from DTA were found to agree quantitatively with data calculated from x-ray, probability equations, and copolymer theory. The melting points of the crystalline copolymers, and the molar amounts of vinyl acetate to produce a completely amorphous rubber corresponds exactly to that predicted by the Flory theory. The random character expected in E/VA copolymers is thereby confirmed. The physical properties of E/VA copolymers of all ranges of compositions and crystallinity were determined. Depending directly upon vinyl acetate content, the copolymers changed progressively from highly crystalline polyethylene to semicrystalline polyethylene, a completely amorphous rubber, a soft plastic with a glass transition near room temperature. Properties which were correlated with copolymer composition include: crystallinity, melting point, density, modulus, tensile strength, glass transition, and solubility. Finally, the effect on crystallinity and physical properties of replacing the acetoxy group in E/VA with the smaller, highly polar hydroxyl group (ethylene—vinyl alcohol copolymer) was also investigated.     

Heat shrinkability of electron-beam-modified thermoplastic elastomeric films from blends of ethylene-vinylacetate copolymer and polyethylene

The heat shrinkability of electron-beam-irradiated thermoplastic elastomeric films from blends of ethylene–vinylacetate copolymer (EVA) and low-density polyethylene (LDPE) has been investigated in this paper. The effects of temperature, time and extent of stretching and shrinkage temperature and time have been reported. Based on the above data, the optimized conditions in terms of high heat shrinkage and low amnesia rating have been evaluated. Influence of radiation doses (0–500 kGy), multifunctional sensitizer levels (ditrimethylol propane tetraacrylate, DTMPTA), and blend proportions on heat shrinkability has been explained with the help of gel fraction and X-ray data. With the increase in radiation dose, gel fraction increases, which in turn gives rise to low values of heat shrinkage and amnesia rating. At a constant radiation dose and blend ratio, percent heat shrinkage is found to decrease with increase in DTMPTA level. Gel content increases with the increase in EVA content of the blend at a constant radiation dose and monomer level, giving rise to decrease in heat shrinkability. Heat shrinkage increases with the increase in percent crystallinity, although the amnesia rating follows the reverse trend.     

Rheological investigation of the influence of molecular structure on natural and accelerated UV degradation of linear low density polyethylene

Metallocene and Ziegler-Natta (ZN) linear low density polyethylenes (LLDPEs) of different branch types and contents as well as linear high density polyethylene (HDPE) were exposed to natural and accelerated weather conditions. The degree of UV degradation of exposed samples was measured by rheological techniques and results were compared with unexposed polymers. Dynamic shear measurements were performed in an ARES rheometer in the linear viscoelastic range. The degree of enhancement or reduction in viscosity and elasticity was used as a measure of the degree of cross-linking or chain scission, respectively. The degradation results of LLDPE suggest that both cross-linking and chain scission are taking place. Chain scission dominated the degradation at high levels of short chain branching (SCB) and long exposure times. The degradation mechanism of m-LLDPE and ZN-LLDPE is similar; however, m-LLDPE showed a higher degradation rate than ZN-LLDPE of similar M_w and average SCB. ZN-LLDPE was found to be more stable than a similar m-LLDPE. Comonomer type had little influence on degradation. Dynamic shear rheology was very useful in revealing the influence of different molecular parameters and it exposed the degradation mechanism.     

Preparation and characterization of polyethylene based graft copolymers. Applications in the immobilization of enzymes

In the last few years new copolymeric supports for the immobilization of biological compounds have been developed. The graft copolymer polyethylene-g.co-hydroxyethyl methacrylate, partially hydrolyzed, has shown to be a very promising support for this purpose.

The more recent work in the preparation and characterization of this copolymer, as well as the immobilization of a lipase, is reported in this paper. Branches of poly(hydroxyethyl methacrylate) were grafted onto low density polyethylene by using gamma radiation. The influence of the presence and absence of air, as well as the monomer concentration on the yield of grafting were evaluated.

The obtained copolymers were characterized by DSC and FTIR. The influence of the support properties on the synthesis biocatalytic activity was detected.     

MMA/MAh共聚物的合成及其凝胶聚合物电解质性能

从聚甲基丙烯酸甲酯型凝胶聚合物电解质存在的问题出发,设计制备一种甲基丙烯酸甲酯/共聚马来酸酐型凝胶聚合物电解质.采用溶液聚合法,以偶氮二异丁腈(AIBN)为引发剂,甲基丙烯酸甲酯(MMA)、顺丁烯二酸酐(MAh)为单体,其MMA与MAh单体摩尔配比为1∶1,合成了P(MMA-co-MAh)共聚物;采用凝胶色谱(GPC)、傅立叶红外光谱(FTIR)、核磁共振(MNR)、示差扫描量热法(DSC)、热失重分析(TGA)、X-射线衍射分析(XRD)对所合成共聚物的结构进行了表征.结果表明,合成的共聚物为无规非晶型聚合物,其数均分子量Mn为6.40×104,共聚物中MMA与MAh链段摩尔比大约为8∶1,热分解温度为300℃,玻璃化转变温度(Tg)为121.3℃.以P(MMA-co-MAh)共聚物为树脂基体,环状碳酸1,2-丙二酯(PC)为增塑剂,LiClO4为电解质盐,制备了凝胶聚合物电解质(GPE),当共聚物含量为45 wt%时,GPE具有好的成膜性,其室温离子电导率为3.0×10-5S/cm.     

强紫外光作用下PVC/增韧剂体系结构与性能的演变

通过UV, FTIR, DSC及力学性能和色差的测试分析, 实时追踪了在紫外光老化过程中, 聚氯乙烯/氯化聚乙烯(PVC/CPE), 聚氯乙烯/丙烯酸酯类共聚物(PVC/ACR)及聚氯乙烯/丙烯腈-丁二烯苯乙烯共聚物(PVC/ABS)体系的微观结构和宏观性能的演变过程. 结果表明, 在光老化过程中, ACR和CPE对PVC脱HCl生成共轭双键反应、氧化降解反应、交联反应及玻璃化转变温度(T_g)的变化等均有抑制作用, 而ABS则对这些反应起促进作用. 在宏观上表现为ACR和CPE的加入能提高体系的色泽稳定性, 体系的力学性能保持率较高. 而ABS的作用相反.     

Nuclear magnetic relaxation in polyolefin resins

Nuclear magnetic resonance (NMR) spin–lattice relaxation times (T₁) in various polyethylene and polypropylene resins were measured at 20 MHz and at temperatures of 130–490 K. At each temperature and for all resins, only a single value of T₁ was found, which was consistent with the occurrence of rapid spin diffusion throughout the protons attached to the polymer chains. The data were analyzed for the estimation of activation energies corresponding to molecular motion causing spin–lattice relaxation. Two well‐defined minima were found for log_e(T₁) plotted as a function of temperature for all of the polypropylene resins. Single very broad minima were found for all of the polyethylene samples. In contrast, the free induction decay signals from all of the resins following single radio‐frequency pulses were observed to contain a rapidly decaying component followed by a much more slowly decaying signal. These components were used to estimate the amount of rigid component present in the solid resins at room temperature. Samples of one high‐density polyethylene and one low‐density polyethylene were irradiated with γ radiation up to a 500‐kGy dose to examine the effects of crosslinking on the NMR relaxation. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 572–584, 2002; DOI 10.1002/polb.10116     

Macromolecular scission and crosslinking rate changes during polyolefin photo-oxidation

Chain scission and crosslinking rates have been derived from molecular mass distributions obtained by gel permeation chromatography at different stages during photodegradation of various thermoplastics exposed to ultraviolet irradiation (UV). Results are given for a high density polyethylene (HDPE); a low density polyethylene (LDPE); a linear low density polyethylene (LLDPE); a polypropylene homopolymer (PPHO); and a polypropylene copolymer (PPCO). As the oxidation progressed, it was observed that the scission rate for HDPE, LLDPE, PPHO and PPCO increased near to the exposed surface whereas for LDPE the rate remained almost unchanged. The crosslink rate fell near to the surface with HDPE and LDPE but increased with PPHO and PPCO. The reaction rates near to the bar centre (∼1.5 mm from the exposed surface) were low for HDPE, PPHO and PPCO; this is attributed to oxygen starvation, caused by consumption of oxygen by rapid reaction near the surface. Reaction was observed in the interior with LDPE and LLDPE, presumably because of a combination of a higher oxygen diffusion rate than for HDPE and a lower rate of consumption of oxygen near the surface than with the polypropylenes.     

结晶聚合物的辐射效应——多官能团单体对LDPE的结晶成核作用

根据x射线、电镜、DSC和凝胶分数的测试结果,讨论了多官能团单体结构对低密度聚乙烯聚集态结构的影响以及结晶度与辐射交联(或剂量)的关系。发现由于单体的存在导致低密度聚乙烯结晶度增加而结晶尺寸变小(即结晶成核效应);成核效应越大,增强辐射交联的效果也越大。添加具有高结晶成核作用的单体有利于低密度聚乙烯的辐射交联,同时也加速其结晶结构的破坏。     

Some investigations on the post radiation grafting of acrylamide onto polyethylene films

A study has been made on the post radiation grafting of aqueous acrylamide onto low density polyethylene film. It was found that the addition of 0.05 wt % Mohr's salt reduced effectively the homopolymerization of acrylamide and the grafting process was successfully achieved. The dependence of the grafting rate on the preirradiation dose and monomer concentration was found to be of 1.43 and 1.4 order, respectively. The overall activation energy for the graft polymerization was found to be 13.5 and 1.95 Kcal/mol below and above 45°C, respectively. Some properties of the graft copolymer such as swelling behaviour, electrical conductivity, and reverse osmosis desalination of saline water (water flux and salt rejection), were also investigated and the possibility of its uses in the practical applications was discussed.     

Thermal degradation of high density polyethylene in a reactive extruder

The thermal degradation of high density polyethylene was conducted in a reactive extruder at various screw speeds with reaction temperatures of 400 °C and 425 °C. The residence time of the extruder was estimated and the molecular weight distribution of the fed plastic and reaction products was analysed using gel permeation chromatography. A continuous kinetic model was used to describe the degradation of the high density polyethylene in the reactive extruder. The breakage kernel and the scission rate model parameters were estimated from the experimental data for a variety of cases. It was found that purely random breakage and a scission rate which had a power law dependence on molecular size of 0.474 best described the experimental data.     

Adhesive effect of linear low-density polyethylene gels on polyethylene moldings

Adhesive effect of linear low density polyethylene (LLDPE) gels in organic solvents such as decalin, tetralin, and o-dichlorobenzene on high density polyethylene (HDPE) moldings has been investigated by shearing tests, and DSC measurements. For all of the gels the temperature at which the heated gel starts to exhibit the adhesive effect was about 70 °C, which is similar to the result of LDPE gel. In particular, when heated at 110 °C, LLDPE gel in tetralin showed such a strong bond strength that polyethylene plates of 3 mm in thickness and 20 mm in width gave rise to necking. It was found that LLDPE gel behaved as though it added LDPE gel to HDPE gel namely LDPE-like components in LLDPE resin exerted the adhesive effect at lower heating temperature, HDPE-like components exerted the strong adhesive effect at higher heating temperature.