Analysis of the fractionation of ethylene–propylene copolymerization products

The solution fractionation of ethylene–propylene copolymerization products was simulated by assuming an appropriate partition relationship for the polymer distribution between the two liquid phases and by using data for the molecular weight dependence of the solubility. Bivariate and log normal distribution functions were assumed for the polydispersities of the copolymer and the homopolymers, respectively. The products can be classified into five types: copolymer (EP), polyethylene–polypropylene (PE–PP), polypropylene–copolymer (PP–EP), polypropylene–copolymer–polyethylene(PP–EP–PE), and copolymer–polyethylene (EP–PE). The present work is mainly concerned with the latter three types. The experimental results, which could not be explained earlier in terms of pure EP or PE–PP blends, could be explained by the present computer analysis. Thus, even though the distribution curves vary in a complicated way with the component types and the ratios of amounts present, analysis of this kind should be useful for understanding the nature of unknown samples. Finally, the possibility of isolating pure components by solution fractionation is discussed.     

Fractionation of ethylene–propylene copolymers

Ethylene–propylene (EP) copolymers were fractionated according to chemical composition, molecular weight, or monomer sequence length, which are fundamental distribution factors. Cloud points of polyethylene (PE), polypropylene (PP), and EP copolymer were determined prior to the fractionation. From the results, it was estimated that xylene–butyl cellosolve and tetralin–ethyl carbitol systems were suitable for the fractionations according to chemical composition and molecular weight, respectively. EP random-type copolymers were fractionated using a xylene–butyl cellosolve system. Separations according to chemical composition were obtained as expected. Then, the above polymer fractions were further fractionated in a tetralin–ethyl carbitol system. and the dependence on molecular weight was observed fairly well. Furthermore, fractionation according to monomer sequence length was satisfactorily achieved by solvent extraction using ethyl ether, n-hexane, cyclohexane, and n-heptane. Therefore, it is concluded that the more detailed characterizations of EP copolymers are made possible by a combination of these techniques.     

Photodegradation of ethylene–propylene copolymer and ethylene–propylene–ethylidenenorbornene terpolymer

Significant progress has been made in recent years regarding the photooxidation of olefin copolymers, but questions still remain. This paper reviews the progress and probes the photooxidative chemistry of ethylene–propylene (EP) and ethylene/propylene/diene monomer (EPDM) copolymers. Both stabilized and unstabilized polymer plaques were irradiated in a xenon are and the surface chemistry followed using infra-red spectroscopy. Model compounds were used to help elucidate the chemistry caused by unique structural features present in the copolymers. Volatile products evolved during photooxidation were determined giving valuable insight into the degradation chemistry.     

Characterization of ethylene–propylene rubber and ethylene–propylene–diene rubber networks

The stress–strain (S/S) and the swelling equilibrium behavior in a series of ethylene propylene rubber (EPR) and ethylene propylene diene monomer (EPDM) networks were investigated and the results were employed to evaluate the effects of varying the cure conditions on the crosslinking efficiency in these networks. The S/S curve of completely swollen vulcanizates is in agreement with the predictions of rubber elasticity theory, while that of dry or partially swollen vulcanizates is fully described by the Mooney-Rivlin equation. ? values determined in benzene were found to vary linearly with v_r (v_r = equilibrium volume fraction of rubber in swollen sample). Crosslinking efficiency, moles of crosslinks produced per moles of crosslinking agent used, ranges from 3.7 in peroxide-cured EPDM (55% wt ethylene and 2.6% unsaturation) to 0.15 in similarly cured EPR (43% ethylene). Efficiency in the latter system improves to 0.6 by addition of a coagent (sulfur) to the cure formula. Crosslinking efficiency in EPDM (55% ethylene) was found to increase in the order: peroxide- > resin- > sulfur-cured. In the EPDM sulfur vulcanizates, changing the terpolymer in the cure formula resulted in significant changes in the crosslinking efficiency.     

Morphology of photodegraded heterophasic ethylene–propylene copolymers

The morphology of photooxidative degraded films of heterophasic ethylene–propylene copolymer (EPQ‐30R) was investigated and compared with isotactic polypropylene and linear low‐density polyethylene by scanning electron microscopy. Surface damage caused by polychromatic ultraviolet irradiation (λ ≥ 290 nm) at 55°C in air is presented in different micrographs. Changes occurring due to the formation of polar groups during photooxidative degradation are discussed. Morphological study of these photodegraded polymer samples show very good correlation with the photodegradation results. The rate of photooxidation is very fast in case of isotactic polypropylene, compared with polyethylene and ethylene–propylene copolymers. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 215–225, 1999     

Properties and microstructures of ethylene–propylene terpolymers

The properties of raw polymer and gum vulcanizates of several ethylene–propylene terpolymers with respect to thermal transitions, stress relaxation, and swelling behavior are discussed in relation to the influence of ethylene content and microstructure. It is shown that at high ethylene contents, the presence of associated regions, perhaps microcrystallites, in low concentration produces polymers having thermoplastic behavior. The degree of crystallinity is apparently very low, and polymers of nominally similar ethylene contents can exhibit disparate behavior reflecting differences in heterogeneity of molecular composition.     

Thermal analysis of ethylene–propylene copolymer-grafted-glycidyl methacrylate

The thermal properties of ethylene–propylene copolymer grafted with glycidyl methacrylate (EP-g-GMA) were investigated by using differential scanning calorimetry (DSC). Compared to the plain ethylene–propylene copolymer (EP), peak values of melting temperature (T_m) of the propylene sequences in the grafted EP changed a little, crystallization temperature (T_c) increased about 8–12°C, and melting enthalpy (ΔH_m) increased about 4–6 J/g. The isothermal and nonisothermal crystallization kinetics of grafted and ungrafted samples was carried out by DSC. Within the scope of the researched crystallization temperature, the Avrami exponent (n) of ungrafted sample is 1.6–1.8, and those of grafted samples are all above 2. The crystallization rates of propylene sequence in EP-g-GMA were faster than that in the plain EP and increased with increasing of grafted monomer content. It might be attributed to the results of rapid nucleation rate. © 1996 John Wiley & Sons, Inc.     

Properties of ethylene–propylene copolymer/PA-1010 blends using ethylene–propylene copolymer-graft-acrylic acid as a compatibilizing agent

The modification of ethylene–propylene copolymer (EP) has been accomplished by radical initiators. The resulting EP-graft-acrylic acid (EP-g-AA) has been used to obtain ternary PA/EP/EP-g-AA blends by melt mixing. Different blend morphologies were observed by scanning electron microscopy: the domain size of the EP-dispersed phase in the polyamide 1010 matrix of compatibilized blends decreased compared with that of uncompatibilized blends. It is found that EP-g-AA used as the third component has a profound effect on the mechanical properties of the resulting blends. This behavior has been attributed to serious chemical interactions taking place between the two components. Thermal analysis shows that some thermal properties of PA in compatibilized PA/EP/EP-g-AA changed because of chemical reactions taken place during the blending process. Wide angle x-ray diffraction measurements also confirmed this result. © 1996 John Wiley & Sons, Inc.     

Photoinitiated oxidation of heterophasic ethylene–propylene copolymers. I. Comparison of oxidation products

Detailed photoproducts from photoirradiation of heterophasic ethylene-propylene copolymers and their fractions have been compared by infrared spectroscopy combined with chemical derivatization. The oxidized films were treated with gaseous NH₃, SF₄, and NO for the rapid identification and resolution of the various carbonyl species, alcohols, and hydroperoxides. The photoproduct formation depends upon the composition of the sample. The heterogeneities in thin films were also determined by micro FTIR spectroscopy. © 1993 John Wiley & Sons, Inc.     

Gel permeation chromatography of polyoxymethylene

Gel permeation chromatography of polyoxymethylene has been studied using N,N-dimethylformamide as the solvent. Polyoxymethylene samples used here are a copolymer of tetraoxane with 1,3-dioxolane and a commercial polyoxymethylene whose molecular weight distributions are moderately broad. Their intrinsic viscosities [η] range from 1.4 to 2.8 dl/g. Factors affecting chromatograms are discussed, and the operating conditions were determined by using the analytical scale GPC. On the basis of these operating conditions, the molecular weight fractionation of polyoxymethylene was carried out by using the preparative scale GPC. It was found that polyoxymethylene can be effectively fractionated to give seven to ten fractions each of them containing the fractionated polymer ranging in weight from 0.2 to 8 mg when 40 mg polymer sample was used for a run of the measurement. The fractionated polymers were also found to have a narrow molecular weight distribution within a single peak, and their M_w/M_n values decrease with increasing molecular weight.     

Elastic and viscoelastic behavior of ethylene–propylene copolymers

The viscoelastic behavior of an ethylene–propylene copolymer is analyzed. Two different vulcanization procedures were followed; in the first a binary mixture of initiator-polymer was used, while in the second the polymer was diluted by a solvent. The networks thus obtained show a different viscoelastic behavior depending on the different vulcanization procedure used. Results, analyzed in terms of supramolecular organization being present in the amorphous material, give some important information about the molecular nature of the C₂ coefficient of the Mooney-Rivlin equation, and therefore about the well-known deviations from the Gaussian theory shown by all rubber-like networks.     

Gel permeation chromatography of isotactic polypropylene using the cyclohexane–decalin solvent system

The molecular weight distribution of iPP and its copolymers with ethylene have been studied using cyclohexane/decalin as eluent at 333 K. The fractionation of the polymers using the same solvent system was also investigated. Reproducible and reliable molecular weight distribution and averages have been obtained.     

Gel permeation chromatography using controlled-porosity glass. I. Polyacrylamide–formamide solution

The process of characterizing polyacrylamide and its partially hydrolyzed materials by gel permeation chromatography was examined. The use of controlled-porosity glass and formamide as the stationary phase and the eluent, respectively, resulted in chromatographic behavior in accord with the hydrodynamic volume concept for polyacrylamide fractions. The addition of a salt (KCl) to the eluent was found to retard the elution of the hydrolyzed polyacrylamide.     

Morphology–toughness correlation of polypropylene/ethylene–propylene rubber blends

A polypropylene homopolymer was blended with ethylene–propylene rubber in different mixing ratios. The influence of the ethylene–propylene rubber content on the toughness behavior was investigated. According to the results of instrumented impact tests, brittle‐to‐tough transition temperatures were found for different ethylene–propylene rubber contents. Critical transition temperatures could be determined not only in the region of predominantly unstable crack propagation but also in the region of stable crack initiation. In situ measurements provided information on the deformation processes on the crack tip. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3364–3371, 2006     

Gel permeation chromatography of heated fats

The high and low molecular weight components of heated fats have been separated with gel permeation chromatography. With Sephadex LH-20, as well as with Biobeads SX-1, the high molecular weight components of heated fats may be directly separated when chloroform, acetone, chloroform-methanol or tetrahydrofuran are employed as swelling agents and eluting solvents. Presented at the AOCS Meeting, Ottawa, September 1972.     

Gel permeation chromatography on branched polymers

In gel permeation chromatography on long-chain branched polymers, calibration with linear samples leads to incorrect results. There are, however, several ways in which the data can be treated correctly. All of them call for the use of extra experimental information, such as viscosity or light scattering data of the whole polymer or the GPC eluent. The Drott—Mendelson method, using [η] of the whole polymer and GPC data, has been employed for analysing three low density polyethylene samples. The potentialities of viscometry and light-scattering measurements in the GPC effluent have also been examined. From [η], M_w and GPC data the long-chain branching index g′ can be derived in three ways, although it should be stated that the average g′-values so found for polydisperse samples are different.     

Gel permeation chromatography: Differential operation

Operation of gel permeation chromatographs in the differential mode provides a sensitive method for detecting small differences in molecular weight distribution between similar samples. The solvent used in this case is a dilute solution of the reference polymer in an organic solvent. This solution is used in both the reference and the separation column. Samples of the material to be compared are injected in the normal manner. Only differences between the samples are reflected in the resulting chromatogram. For process control, this offers a simplified data presentation and should lead to easier detection of changes in operating conditions.     

Fracture behaviour of controlled‐rheology ethylene–propylene block copolymers

The evolution of the molecular weight distribution and the thermal, mechanical and fracture behaviour of controlled‐rheology ethylene‐propylene block copolymers (ca 8 wt% ethylene content) has been analysed. Various concentrations of di‐tert‐butylperoxide were utilized. The melt flow index increased with the peroxide content due to the reduction of the molecular weight and the narrowing of the molecular weight distribution. However, the thermal behaviour and degree of crystallinity were not improved and some mechanical properties, such as the tensile strength and elongation at break, presented an anomalous behaviour. This trend can be explained by the presence of the elastomeric phase. The addition of peroxide influenced strongly the J–R curves obtained via the elastic–plastic fracture mechanics approach. The slope of these curves was markedly reduced with addition of peroxide to almost being flat for the highest concentration. This loss of ductility and the sudden decrease of the fracture toughness values with an increasing amount of peroxide were mainly due to the reduction in the molecular weight. Copyright © 2011 Society of Chemical Industry     

Stress–strain optical study of styrene–butadiene and ethylene–propylene rubbery copolymers

Birefringence–temperature behavior at constant stress during cooling and heating of styrene–butadiene and ethylene–propylene copolymers between ?120°C and +60°C was investigated. Copolymer composition, thermal treatment, and stress levels were shown to have a pronounced effect on the photoelastic properties.