Influence of the longest ethylene and isotactic propylene sequences on crystallization elution fractionation of ethylene/propylene copolymers

Crystallization elution fractionation (CEF) is the newest crystallization-based technique for estimating the chemical composition distribution of ethylene/1-olefin copolymers. Understanding the separation mechanism of CEF for ethylene/propylene copolymers over their full compositional range is challenging because the crystallizabilities of the copolymer chains depend on the longest ethylene sequence and on longest isotactic propylene sequence. We developed a mathematical model to describe the CEF mechanism for ethylene/propylene copolymers over the entire compositional range using population balances for the crystallization and dissolution stages. The joint distribution of longest ethylene and isotactic propylene sequences determines how the copolymer populations crystallize and dissolve. The model was validated with experimental CEF profiles of ethylene/propylene copolymers varying from pure ethylene to propylene homopolymers.     

Comparison of propylene/ethylene copolymers prepared with different catalysts

This study compared a series of experimental propylene/ethylene copolymers synthesized by a transition metal‐based, postmetallocene catalyst (xP/E) with homogeneous propylene/ethylene copolymers synthesized by conventional metallocene catalysts (mP/E). The properties varied from thermoplastic to elastomeric over the broad composition range examined. Copolymers with up to 30 mol % ethylene were characterized by thermal analysis, density, atomic force microscopy, and stress–strain behavior. The xP/Es exhibited noticeably lower crystallinity than mP/Es for the same comonomer content. Correspondingly, an xP/E exhibited a lower melting point, lower glass transition temperature, lower modulus, and lower yield stress than an mP/E of the same comonomer content. The difference was magnified as the comonomer content increased. Homogeneous mP/Es exhibited space‐filling spherulites with sharp boundaries and uniform lamellar texture. Increasing comonomer content served to decrease spherulite size until spherulitic entities were no longer discernable. In contrast, axialites, rather than spherulites, described the irregular morphological entities observed in xP/Es. The lamellar texture was heterogeneous in terms of lamellar density and organization. At higher comonomer content, embryonic axialites were dispersed among individual randomly arrayed lamellae. These features were characteristic of a copolymer with heterogeneous chain composition. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1651–1658, 2006     

Influence of processing on ethylene propylene block copolymers (II): Fracture behavior

The present work investigates the relationships between the microstructural state and fracture properties in commercial polypropylene‐based materials. In this case an isopolypropylene homopolymer and three ethylene propylene block copolymers (EPBC) with different ethylene content (EC) have been studied. A variety of morphologies were obtained by a combination of several processing methods (injection molding, injection molding‐annealing, and compression molding) and thickness. Fracture behavior of deeply double‐edged notched specimens was evaluated by scanning electron microscopy (SEM) and by the essential work of fracture (EWF) method, analyzing the influence of processing, thickness (t), EC, and orientation respect to melt flow direction (MD and TD). The testing direction and EC are the most relevant variables that affect the ability of the crack tip to deform plastically during the crack propagation, determining the final fracture behavior. The fracture parameters obtained with the EWF method, specific EWF, w_e, and plastic item, βw_p, have proved to be very sensitive to the processing induced morphology, finding interesting relationships between such morphologies (characterized by crystallinity index, orientation level, and skin/core ratio) and the fracture parameters of the plaques. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2714–2724, 2006     

Positron annihilation spectroscopic studies of fluorinated ethylene propylene copolymer-g-polystyrene

Polystyrene was grafted onto FEP by simultaneous irradiation using a ⁶⁰Co γ-irradiator. Graft copolymers of different degree of grafting were obtained by varying the irradiation dose. Positron lifetime measurements were carried out on FEP and the grafted samples. A systematic decrease in o-Ps lifetime and intensity with grafting is seen indicating a decrease in pore size as well as total free volume fraction. Temperature dependent (95-250 K) S-parameter measurements in FEP showed saturation of free volume fraction at temperatures corresponding to the β-relaxation, the onset of which is seen at 150 K. Coincidence Doppler broadening results indicate increase in specific volume in the crystalline region of the polymer. Dynamic mechanical analysis (DMA) showed that tan δ value for β-relaxation of the samples decreased with increasing graft percentage. The results are discussed.     

Crystalline characteristics of ethylene/propylene/1,4-hexadiene terpolymers and related ethylene copolymers

An improved differential thermal analytical technique which permits the rapid, convenient characterization of the thermal behavior of crystalline polymers free of any influence of prior thermal history is presented. Characterization of both crystallization and fusion phenomena is described for ethylene/propylene copolymers subjected to well-controlled thermal scanning techniques. Parameters describing these phenomena are derived. While they are nonequilibrium parameters, they are reproducible and capable of correlation with polymer composition. the crystallization onset temperature determined by this cooling technique was found to relate to the molar ethylene content of the copolymers by an equation similar to the one derived by Flory⁵ based on equilibrium melting point. The relationship was found to hold true for a number of ethylene copolymers, including samples of linear and branched polyethylene, commercial EPDM, and ethylene/vinyl acetate copolymers.     

化工工艺中“发泡”现象的消除

发泡现象是化工工艺中普遍存在的一种现象,就比如在造纸工业、石油化工工艺中经常会出现发泡现象,发泡可能会导致所得产品不合格,影响到装置的运行过程,所以需要对发泡现象进行处理,这需要在操作过程中精心操作,合理的使用消泡剂,由此保证操作的正常进行,提高化工产品的纯度。     

共聚聚丙烯注射成型工艺分析

采用差示扫描量热法、热失重及转矩流变仪等分析了共聚聚丙烯(PP)的性能,讨论了注射成型工艺 (如熔体温度、注射压力、注射速率和模具温度等)对共聚PP加工性能及产品性能的影响。结果表明,共聚PP的加工温度在175～325℃,模具温度30～110℃为宜。     

丙烯/1-丁烯无规共聚物与丙烯/乙烯抗冲共聚物的对比研究

对丙烯/1-丁烯无规共聚物(PPB)与丙烯/乙烯抗冲共聚物(PPE)的结晶行为进行对比,在等温结晶时,通过相对结晶度随时间的变化关系、等温结晶曲线等研究,表明丙烯/1-丁烯无规共聚物结晶速率明显低于丙烯/乙烯抗冲共聚物,同时丙烯/乙烯抗冲共聚物的等温结晶速率随乙烯单元含量增加没有明显降低。根据Avrami方程计算了共聚物的结晶活化能,证明丙烯/1-丁烯无规共聚物的结晶能力较丙烯/乙烯抗冲共聚物低。扫描电镜分析丙烯/1-丁烯无规共聚物在丁烯单元摩尔分数2.39%时没有韧性拉伸,而丙烯/乙烯抗冲共聚物在乙烯单元摩尔分数3%时出现韧性拉伸。     

Dynamic mechanical and rheological properties of metallocene-catalyzed long-chain-branched ethylene/propylene copolymers

The dynamic mechanical and rheological properties of five long-chain branched (LCB) and three linear ethylene/propylene (EP) copolymers were investigated and compared using a dynamic mechanical analyzer (DMA) and an oscillatory rheometer. The novel series of LCB EP copolymers were synthesized with a constrained geometry catalyst (CGC), [C₅Me₄(SiMe₂N^tBu)]TiMe₂, and had various propylene molar fractions of 0.01-0.11 and long-chain branch frequencies (LCBF) of 0.05-0.22. The linear EP copolymers were synthesized with an ansa-zirconocene catalyst, rac-Et(Ind)₂ZrCl₂ (EBI), and contained similar levels of propylene incorporation as the CGC copolymers, but no LCB. In dynamic mechanical analysis, the dynamic storage moduli (G′) and loss moduli (G″) of the copolymers decreased with an increase of propylene molar fraction. The α- and β-transitions of the CGC copolymers were overlaid with each other. High damping (tan δ) values were found with the CGC copolymers at temperatures below 0 °C. In oscillatory rheological analysis, compared to the linear EBI counterparts, the LCB CGC copolymer melts showed higher zero shear activation energies, broader plateaus of δ and larger elastic contributions, which are essential characteristics of LCB polymers. It was found that the long chain branching was the determining factor in controlling rheological properties of the polymer melts while the short chain branching from propylene incorporation played a decisive role in affecting dynamic mechanical properties. This work represents the first rheological evidence of LCB in EP copolymers synthesized with CGC.     

Crystallinity and fusion of ethylene oxide/propylene oxide block copolymers: 1. Type PE copolymers

Lamella spacings, specific volumes and melting points have been determined for a series of well characterized poly(propylene oxide)/poly(ethylene oxide) type PE block copolymers with E-block length 40 chain units and P-block lengths 0 to 11 chain units. These properties are interpreted in terms of a stacked lamella model with alternating amorphous and crystalline layers. The crystalline lamella thickness is found to be about 25 E chain units, i.e. the crystals are predominantly of extended-chain type. The specific volume of the polymer in the amorphous lamellae is found to be lower than that of polymer of corresponding composition in the supercooled melt. The melting points are low compared to that of perfectly crystalline poly(ethylene oxide), i.e. 47 to 51°C compared with T⁰_m = 76°C. This is due to the positive free energy of formation from the melt of the amorphous layer (σ₅ 3.5 kJ/mol) and the crystalline/amorphous) interface (σ_o 3 kJ/mol).     

Viscosity characteristics of aqueous solutions of block copolymers of propylene and ethylene oxides

Brookfield viscosity measurements were made on aqueous solutions of surface-active agents composed of block copolymers of propylene and ethylene oxides in which the molecular weights of the polymers varied from 1100 to over 15,000. The hydrophobia bases were polyoxypropylene glycols varying in molecular weight from 940 to 4000. To these were added varying amounts of ethylene oxide so that the polyoxyethylene hydrophil comprised from 15 to 80% of the surfactant total weight. This work has materially expanded previous viscosity studies of aqueous solutions of nonionic surfactants by using a unique type of hydrophobe, two ethylene oxide chains, and far higher molecular weights of hydrophobe and of hydrophil, up to 280 moles of ethylene oxide. The surface-active agents with hydrophobe base molecular weights from 940 to 1100, and in which the polyoxyethylene sections comprised from 15 to 80% of the total weight, did not form gels in aqueous solution. Some surfactants with a hydrophobe base molecular weight of 1750 to 2750, to which varying amounts of polyoxyethylene were added, formed gels in water at a surfactant concentration range of 40% to 80%. With a hydrophobe molecular weight of 3250, gels formed at from 30% to 90% surfactant concentration, while with one nonionic derived from a 4000 molecular weight hydrophobe, a gel formed at only 20% polyol concentration. Two viscosity maxima were found in some cases, as reported occasionally for other systems. An increase in temperature from 0C to 50C generally reduced the viscosity of systems based on hydrophobes of 1175 and lower molecular weights, and increased it in systems based on hydrophobes of 1750 and higher molecular weights. The behavior of these surfactants in forminggels is explained on the basis of hydrogen bonding, micellar aggregation and water entrapment. The moles of water per ethylene oxide group in the adduct varied with the hydrophobe base weight and with the polyoxyethylene hydrophil, and within systems showing maximum viscosities, ranged from 0.3 to 17.1, at 25C, which is much higher than observed in other nonionics.     

Crystallinity and fusion of ethylene oxide/propylene oxide block copolymers: 2. Type PEP copolymers

Lamella spacings, specific volumes and melting points have been determined for a series of well characterized poly(ethylene oxide)/poly(propylene oxide) type PEP block copolymers with E-block length 48 chain units and P-block lengths 0 to 7 chain units. These properties are interpreted in terms of a stacked lamella model with alternating amorphous and crystalline layers. Both extended-chain and once-folded-chain crystalline lamellae are found, the former with thickness about 32 E chain units and the latter with thickness about 21 E chain units. Compared with the specific volume of supercooled melt of the same composition the specific volume of the polymer in the amorphous lamellae is lower in the extended-chain polycrystals and higher in the once-folded-chain polycrystals. The melting points of the copolymers are low compared to that of perfectly crystalline poly(ethylene oxide), i.e. 37 to 55°C compared with T⁰_m = 76°C. This is due to the large positive free energy of formation from the melt of the crystalline/amorphous end interface (σ_o) and the amorphous layer (σ_a). For extended-chain polycrystals we find σ_o 3 kJ/mol and σ_a 3.5 kJ/mol; for once-folded-chain polycrystals we find σ_o 6 kJ/mol and σ_a 2 kJ/mol. We also find σ_o,x = 2.5 kJ/mol for a completely extended-chain end interface and σ_o,f = 10 kJ/mol for a completely folded-chain end interface.     

Lower critical solution temperature behavior of ethylene propylene copolymers in multicomponent solvents

The lower critical solution temperature (LCST) locus for ethylene-propylene copolymers has been determined as a function of pressure in a variety of single and multicomponent solvents. The lower critical end-point temperature (LCEP), which is the intersection of the LCST locus with the vapor-pressure curve, was found to be predictable from the solvent density as previously established for single-component solvents by Charlet and Delmas.¹ Dissolving a low-molecular hydrocarbon gas such as propylene in an alkane has a dramatic effect on lowering the LCEP, and can reduce phase-separation temperatures to levels at which this technique becomes attractive as a practical method for polymer recovery from diluents such as those used in solution polymerizations. Temperatures considerably above the LCEP are needed to minimize the residual polymer concentration in the solvent in the two-liquid-phase region. The solvent critical temperature must be approached for essentially complete elimination of the polymer from the solvent phase. The LCST locus was found to be a linear function of pressure for all of the systems investigated, and the slope of the line, d(LCST)/dP, could be well correlated as a function of solvent density and critical temperature. From the relationship between the LCEP and solvent density and the correlation for d(LCST)/dP, the location of the LCST locus can be readily predicted from a knowledge of solvent properties.     

加工工艺对发泡橡胶结构的影响

通过对不同配方的混炼胶门尼粘度、发泡剂用量与所得发泡橡胶微孔尺寸及微孔间隙关系的分析，讨论了加工工艺对天然及丁腈发泡橡胶结构的影响。其中混炼胶的门尼粘度对发泡橡胶尺寸的影响有较强的规律。发泡橡胶微孔单元内外压差与尺寸的关系和这一规律有很大的相似性。为调节工艺来获得所需结构的发泡橡胶提供了一种可行的方法。     

木质素基复合材料的制备及在乙丙橡胶中的应用

由高沸醇木质素(HBSL)制备得到了HBSL/纳米SiO2复合材料,对产物进行了分析.将木质索/纳米SiO2复合材料作为橡胶的补强剂应用于乙丙橡胶,提高了胶料的硬度和耐老化性能,断裂伸长率从165%提高到 229%,拉伸强度略有降低.木质素纳米复合材料中纳米SiO2的含量是影响胶料性能的主要因素,当含量为5%时橡胶的性能最佳.     

Blends of poly(propylene) and polyacetal compatibilized by ethylene vinyl alcohol copolymers

Polymer blends of poly(propylene) (PP) and polyacetal (polyoxymethylene, POM) with ethylene vinyl alcohol (EVOH) copolymers were investigated by differential scanning calorimetry (DSC), rheological, tensile, and impact measurements, Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The PP–POM–EVOH blends were extruded with a co‐rotating twin‐screw extruder. The ethylene group in the EVOH is partially miscible with PP, whereas the hydroxyl group in the EVOH can form hydrogen bonding with POM. The EVOH tends to reside along the interface, acting as a surfactant to reduce the interfacial tension and to increase the interfacial adhesion between the blends. Results from SEM and mechanical tests indicate that a small quantity of the EVOH copolymer or a smaller vinyl alcohol content in the EVOH copolymer results in a better compatibilized blend in terms of finer phase domains and better mechanical properties. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1471–1477, 2003     

助交联剂对三元乙丙橡胶过氧化物硫化的影响

分别采用三烯丙基异氰脲酸酯(TAIC)、三羟甲基丙烷三甲基丙烯酸酯(TMPTMA)以及高乙烯基聚丁二烯(HVPBd)作为过氧化物硫化三元乙丙橡胶(EPDM)的助交联剂,研究其对EPDM胶料硫化特性及硫化胶力学性能的影响。结果表明,3种助交联剂的添加能明显促进硫化程度,硫化胶的硬度和定伸应力均明显提高,添加TAIC的EPDM混炼胶硫化程度最高,但添加TMPTMA使胶料的焦烧安全性变差,而添加HVPBd的EPDM胶料降解程度最低。通过一级动力学模型及自催化反应模型研究EPDM硫化动力学行为时发现,助交联剂类型影响胶料的硫化反应速率,其中TMPTMA能明显促进硫化反应速率,TAIC次之,而HVPBd几乎没有影响,但硫化反应表观活化能由于助交联剂的添加均出现降低,其中添加TAIC胶料的表观活化能最低。     

Thermodynamics of micellization of poly-styrene-block-poly(ethylene/propylene) copolymers in decane

Light scattering was used to establish the dependence of the critical micelle temperature, CMT, on concentration for solutions of three polystyrene-block-poly(ethylene/propylene) copolymers in decane. Electron microscopy studies of particles isolated from the solutions showed that the micelles had narrow size distributions and micellization could be treated thermodynamically as a closed association. The light scattering results were used to calculate the standard Gibbs energies of micellization, ΔG^φ, and the standard enthalpy, ΔH^φ, and entropy contributions, —TΔS^φ. The values of ΔH^φ were large and negative, and markedly dependent on the molecular weight of the polystyrene block. The values of ΔG^φ for the three samples were on the other hand very similar to each other. The standard entropy contributions were unfavourable to micelle formation.     

Elastomeric properties of ethylene/propylene copolymers prepared by zirconocene/methylaluminoxane catalysts

Ethylene/propylene copolymers (EPM) have been prepared by a liquid propylene suspension process, using homogeneous catalysts based on nonbridged zirconocenes and methylaluminoxane (MAO). When bis(η⁵-cyclopentadienyl)zirconium dichloride (Cp₂ZrCl₂), bis(η⁵-cyclopentadienyl) dimethyl zirconium (Cp₂ZrMe₂) and bis(η⁵-cyclopentadienyl), dibenzyl zirconium (Cp₂ZrBz₂) were used as catalyst components, EPM having low average molecular weight (MW) were in general obtained in low yield. On the contrary, a very large improvement of productivity and MW was observed when bis(η⁵-indenyl)zirconium dichloride (Ind₂ZrCl₂) and bis(η⁵-indenyl) dimethyl zirconium (Ind₂ZrMe₂) as well as bis(η⁵-tetrahydroindenyl)zirconium dichloride [(IndH₄)₂ZrCI₂] were employed in combination with MAO. In particular, this last catalytic system allowed one to obtain EPM with a narrower distribution of MW in addition to the above characteristics. Better performances, in terms of rheological and elastomeric properties, were also found for the crude and vulcanized samples prepared by (IndH₄)₂ZrCl₂/MAO catalyst.     

Polymerization and characterization of ethylene/propylene and ethylene/1-octene copolymers produced with bridged Zr- and Hf-based metallocenes

Ethylene/propylene (E/P) and ethylene/1-octene (E/O) copolymers were polymerized with two bridged metallocene catalyst systems, Et(Ind)₂ZrCl₂/MAO and Et(Ind)₂HfCl₂/MAO, respectively. The copolymers produced and some commercial reference copolymers were characterized by DSC, SEC, DMA and ¹³C NMR. The Hf-catalysed E/P polymerizations showed much lower activities than the corresponding Zr-catalysed polymerizations but gave polymers with high molar mass. The Hf-based copolymers also showed two melting peaks which may be indicative of several active sites of the catalyst. A comparison of E/P copolymers, containing about 20 mol-% propylene and produced with Zr, Hf and homogeneous V-catalysts, respectively, indicated that the Hf and V-catalysts gave material more similar to each other. The E/O copolymers produced with Zr-catalysts gave very low molar masses and the reactivity ratios, calculated from the NMR data, indicated that the Hf-catalyst has a slightly higher reactivity for 1-octene and the Zr-catalyst some better reactivity for ethylene. Segregation fractionation studies by DSC indicated that a lower 1-octene feed gives more heterogeneous copolymers and the DMA measurements reveal the existence of a linear correlation between the 1-octene content and the intensity of the tan δ_max peak.