Propylene Random Copolymer Research Articles

Miscibility of Isotactic Polypropylene/Ethylene−Propylene Random Copolymer Binary Blends

Miscibility for blends of isotactic polypropylene (PP) and ethylene-d4−propylene random copolymer (EPR)s prepared by copolymerization of propylene and perdeuterated ethylene with metallocene catalyst has been investigated by small-angle neutron scattering (SANS). SANS experiments were conducted for the blends of PP with EPRs containing 19 mol % (D-EPR19) and 47 mol % (D-EPR47) of deuterated ethylene unit at various temperatures. SANS results indicated that most of the blends are in the homogeneous one-phase mixture, and the Flory−Huggins interaction parameter χ analyzed by the random phase approximation is approximately 5.0 × 10-3 for the PP/D-EPR47 blend while it is very small and within the range −1.0 × 10-3 ≤ χ ≤ 1.0 × 10-3 for the PP/D-EPR19 blend. It was also revealed that χ does not change with temperature meaningfully within the temperature range 440 ≤ T ≤ 482 K, while phase separation due to crystallization of PP was observed at 373 K. No domain structure of EPR whose size is in the range of an optical microscope was observed by TEM for the blends quenched from the melt.

Study of a Polymeric Network by Dynamic Fluorescence Quenching Using a Blob Model

The association behavior of a maleic anhydride grafted and pyrene labeled ethylene−propylene random copolymer was studied using fluorescence spectroscopy. The labeling was achieved with 1-pyrenebutanoic acid hydrazide via the grafted anhydride groups. The resulting polar grafts induced intra- and intermolecular associations among the polymer chains in apolar solvents. This association process was studied using steady-state and time-resolved fluorescence spectroscopy as a function of polymer concentration. Due to the high complexity of the polymer system, an improved approach of handling the time-resolved fluorescence data had to be introduced. Thus, the quantitative analysis of the fluorescence decays was carried out using a novel model in which the polymer network is divided into blobs among which the chromophores distribute themselves randomly, according to a Poisson distribution. Results show that, as the polymer concentration is increased, the number of polar group aggregates increases. However, the local concentration of aggregated polar groups in the polymer network does not change. This indicates that as polymer concentration is increased, either that there are only a few polymer aggregates in the solution that increase in size and keep the concentration of polar junctions constant throughout the polymeric network or that more polymer aggregates are formed. This latter process would be reminiscent of micelle formation. This behavior is observed until the overlap concentration (c* = 10−20 g/L), above which newly formed polar aggregates contribute to increasing the local aggregate concentration.

Characterization of microstructure of polypropylene alloys

Two polypropylene (PP) alloys, which have similar composition, molecular weight and molecular weight distribution, but different processing and application properties, were fractionated using a preparative temperature rising elution fractionation (TREF) technique. It was found that PP alloys are mainly composed of four components: ethylene–propylene random copolymer, block-type copolymer, transition copolymer and propylene homopolymer. However, the fractionation data show that the distribution and the composition are different for these two samples. A possible mechanism is proposed for the formation of PP alloys of different compositions. Based on this mechanism, some possible adjustment of the polymerization parameters is suggested to control the microstructure. © 1998 Society of Chemical Industry

Presence of low-melting crystallinity in ethylene-propylene elastomers

The thermal behaviour of some ethylene—propylene random copolymers (EPRs) with 55–70 mol% ethylene content was investigated in the temperature range from − 100 to + 200°C. Irrespective of differences in chemical composition broadness, resulting from different catalytic systems, all samples display a low-melting crystallinity of low degree, developing rapidly when the material is cooled to low temperatures. The poorly crystalline phase, undetectable by X-rays, melts over a broad range of temperature, the lower limit merging with the glass transition and the upper one ending at ∼60°C. The crystal size distribution is affected by isothermal treatments performed below room temperature, but the overall degree of crystallinity is not modified. The low-melting crystalline domains are associated with short ethylene segments comprising < 10 CH 2 sequences. Experimental evidence suggests that 55 mol% is the lower limit of ethylene content in EPR copolymers required to achieve a detectable crystallinity which melts below room temperature.

Crystallization, melting and spherulitic structure of Β-nucleated random propylene copolymers

The characteristics of crystallization, melting and spherulitic growth of a random propylene copolymer (PRC) containing small amount of ethylene were studied in the presence of a selective Β-nucleating agent (calcium pimelate). It was established that the products of isothermal and non-isothermal crystallization are very rich in Β-modification but have mixed polymorphic composition. The formation of α-modification may be attributed to Βα-transition on the surface of growing Β-spherulites resulting in αΒ-twin-spherulites. During melting of PRC of Β-modification, the characteristics observed with Β-nucleated propylene homopolymers, namely, a Βα-recrystallization of recooled samples and separated melting of non-recooled samples (i.e. the melting memory effect), as well as a ΒΒ-recrystallization leading to a perfection of the structure within the Β-modification, are also demonstrated. The disturbance of regularity of the polymer chain highly reduces the tendency to Β-crystallization. In contrast to the observ...

Yielding and impact behaviour of pp/sgf/epr ternary composites with controlled morphology

Dependencies of the yield strength (σyc), yield strain (ɛyc) and Charpy notched impact strength (CNIS) of polypropylene (PP) reinforced with 30 wt% short glass fibres (SGF) and ethylene — propylene random copolymer (EPR) inclusions on EPR volume fraction (ve) were investigated within the interval of ve varying from 0–0.2. Only one limiting phase morphology has been attained reproducibly using a procedure based on chemical modification of PP. Adhesion enhancement between SGF and PP and complete separation between SGF and EPR was achieved by grafting PP with 2wt % maleic anhydride (MAH). Two regions existed on σyc versus ve curves in the case of complete separation of the reinforcement and elastomer. The observed increase of σyc with increasing ve within the interval 0<ve < 0.05 was attributed to the change in the mode of fracture from brittle to quasi-ductile. Such an explanation has been supported by a several fold increase in ɛyc. Above ve=0.05, a monotonic decrease of σyc with increasing ve was observed corresponding well with an explanation based on a reduction of matrix effective cross-section. In this interval of ve the concentration dependence of σyc was described quantitatively using existing composite models and satisfactory agreement between predictions and experimental data was obtained. The CNIS increased monotonically up to ve=0.1 for both homo- and copolymer based composites. Above ve=0.1, CNIS, measured at -20°C using 6 × 4 × 50 mm bars, notched accordingly ASTM D256 standard, increased for copolymer based composites while it remained constant for homopolymer based materials. Physical meaning of these data is, however, obscured by the inability to separate effects of ve from those of specimen geometry using only a single standard impact strength data.

A 13C NMR Determination for Monomer Compositions in Ethylene–Propylene Copolymers, Ethylene–Propylene–Butene-1, and Elthylene–Propylene–Diene Terpolymers

The monomer compositions in a series of propylene heterophasic copolymer, propylene random copolymer, propylene random terpolymer and ethylene–propylene–2-ethylidiene-5-norborane (ENB) terpolymer have been determined from 13C NMR spectra. The simplified and highly resolved 13C NMR spectra made it possible to assign unambiguously and calculate the monomer compositions. A complete sets of NMR chemical shift assignments and the way to measure the quantity of monomer are newly given in diverse polymers. Furthermore, it is shown that complete dyad, triad, tetrad and pentad distributions can be determined by 13C NMR spectra. These NMR quantitative analytical determinations for monomer compositions are consistent with those from Infrared spectroscopic data.

Rules of supermolecular structure formation in sheared isotactic polypropylene melts

Shear-induced crystallization of isotactic polypropylene (iPP) homo-, block, and random copolymers was studied and compared to that in quiescent melt. It was evidenced by means of the thermo-optical technique that melt-shearing, caused by fiber pulling, is associated with the development of α-row-nuclei. The surface of the in situ formed α-row-nuclei may induce the growth of the β-modification of iPP resulting in a cylindrite of polymorphous composition. The polymorphous composition is controlled by the temperature-dependent relative growth rate of the α- and β-iPP for which a model explanation was given. The β-nucleation ability of the α-row-nuclei is lost by melt-shearing at high temperature or remelting. This was attributed to a coverage of the β-nuclei by the α-phase. The structural memory of the supermolecular structures was studied in repeated melting and crystallization cycles and discussed. It was found that the quality of the fiber did not influence the mechanisms concluded. The shear-induced crystallization of propylene block copolymers was highly analogous to the homopolymers. In case of the random copolymers, however, crystallization in sheared melt resulted in an α-cylindritic structure, because for propylene random copolymers the growth rate of the α-modification is always higher than that of the β. It was also demonstrated that the mechanism of shear-induced crystallization was unaffected when the crystallizing PP melt contained selective β-nucleants. © 1996 John Wiley & Sons, Inc.

Sorption, desorption, resorption, redesorption, and diffusion of haloalkanes into polymeric blend of ethylene–propylene random copolymer and isotactic polypropylene

AbstractMolecular transport of haloalkanes into sheets of a polymeric blend of an ethylene–propylene random copolymer and isotactic polypropylene has been studied by a sorption gravimetric technique in the temperature interval of 25–70°C. For all liquids, equilibrium sorption, desorption, resorption, redesorption, and degree of penetrant overshoot have been influenced by the nature of the liquid and the temperature. Diffusion coefficients were calculated from the sorption–desorption kinetic curves using Fick's mathematical relations. The values of diffusion coefficients followed the Arrhenius‐type behavior. The temperature‐dependent sorption data were analyzed using the van't Hoff relation. The activation parameters for diffusion and heat of sorption data were discussed in terms of the molecular interactions between liquids and the polymer chain segments. The experimental and calculated results are discussed on the basis of the chemical nature of liquids. © 1995 John Wiley &amp; Sons, Inc.

Molecular transport of alkanes through thermoplastic miscible blends of ethylene–propylene random copolymer and isotactic polypropylene

AbstractA new experimental protocol based on the measurements of sorption (S), desorption (D), resorption (RS), and redesorption (RD) has been used to study the molecular transport of aliphatic alkanes through the miscible blends of an ethylene–propylene random copolymer and an isotactic polypropylene over the temperature interval 25–70°C. Diffusion and activation parameters are evaluated and their dependencies on solvent size, shape, and nature are discussed. Estimated values of the molar mass between chain entanglements, kinetic rate constants, and overshoot index parameters have been influenced by the polymer–solvent interactions. The sorption–diffusion mechanism is found to be of anomalous type. © 1995 John Wiley &amp; Sons, Inc.

Impact-modified nylon 6/polypropylene blends: 1. Morphology-property relationships

Two types of elastomers grafted with maleic anhydride (MA), an ethylene—propylene random copolymer (EPR) and a styrene—ethylene/butylene—styrene triblock copolymer (SEBS) were found to function both as impact modifiers and compatibilizers for nylon 6/polypropylene blends. The maleic anhydride grafted to the rubber reacts with the amine end-groups of the polyamide, forming a rubber-nylon 6 graft copolymer that locates at the interface between nylon 6 and polypropylene (PP) and thus acts as a compatibilizer. The SEBS- g-MA material appears to be the most effective compatibilizer. The two rubbers were equally effective for increasing room temperature toughness by dispersing in the nylon 6 phase of the blends. Lower ductile-brittle transition temperatures are obtained when EPR- g-MA rubber is used, owing to its lower T g and lower modulus at low temperatures compared to SEBS- g-MA rubber. Blend parameters such as rubber content, nylon 6/PP ratio and molecular weight of the components strongly influence the morphology and toughness of the blends. Low ductile—brittle transition temperatures were obtained for blends in which any combination of the above parameters yielded a morphology where nylon 6 was the matrix phase with polypropylene and rubber finely dispersed in it, provided the component molecular weights were high enough to provide adequate intrinsic ductility.

Solvent Migration and Drying Phbnoubnon of Polymeric Blends of Ethylene-Propylbnb Random Copolymbr and Isotactic Polypropylbnb in the Prbsbncb of Monocyclic Aromatic Liquids at Tbwbraturbs Bbtukbn 25-70°C.

ABSTRACT Solvent sorption and drying performance of engineering polymeric blends of ethylene–propylene random copolymer and isotactic polypropylene in the presence of aromatic liquid: has been studied in the temperature interval 25–70°C. The drying of the polymer is studied from the desorption and redesorption experiments. The present results indicate that the rate of solvent migration and the drying phenomenon is controlled by internal mass transfer of solvent molecules within the polymer matrix. A technique is developed to study the sorption (S) –desorption (D) – resorption (RS)–redesorption (RD) i.e., S–D–RS–RD of the polymer sheets. The S–D–RS–RD experiments are a convenient measure of knowing the continuous weight loss of the polymer during long–term solvent exposure.

Morphology and mechanical properties of biaxially oriented films of polypropylene and HDPE blends

AbstractBiaxially oriented films of blends of high‐density polyethylene (HDPE) with polypropylene (PP) homopolymer and PP copolymers prepared by twin‐screw extrusion and lab‐stretcher have been investigated by scanning electron microscopy (SEM), polarized microscopy, differential‐scanning calorimeter, and universal testing machine. Three different kinds of PP copolymers were used: (i) ethylene–propylene (EP) random copolymer; (ii) ethylene–propylene (EP) block copolymer; (iii) ethylene–propylene–buttylene (EPB) terpolymer. In the SEM study of the morphology of films of HDPE with various PP blends, phase separation is observed between the PP phase and the HDPE phase for all blends and compositions. In all blends, HDPE serves to reduce the average spherulites size, probably acting as a nucleating agent for PP. The reduction of spherulite size appeared most significantly in the blend of EPB terpolymer and HDPE. A large increase of crystallization temperature was found in the blend of EPB terpolymer and HDPE compared with the unblended EPB terpolymer. For the blend of EPB terpolymer and HDPE, the improvement of tensile strength and modulus is observed with an increase of HDPE content, and this can be considered as a result of the role of HDPE in reducing average spherulite size. © 1994 John Wiley &amp; Sons, Inc.

Study of Polyolefin Gel in Organic Solvents IX. Ethylene Sequence Distribution of Ethylene–Propylene Random Copolymer and Crystalline Junction Size in Its Thermoreversible Gel

The crystalline junction size ζ, which is the number of consecutive ethylene units per crystalline sequence such as –[–CH2–CH2–]–, in an ethylene–propylene (EP) copolymer gel was determined from gel-melting temperatures using the Takahashi theory. In order to examine the correlation between the size ζ and number-average length of ethylene sequences estimated from NMR measurements, an ethylene sequence distribution curve of the copolymer was established from 13C NMR data assuming 1st-order Markov statistics and number-average length in number of ethylene units (L[EE···E]) was calculated from its distribution curve. The average length L[EE···E] determined from this curve was in good agreement with that calculated directly from E/P triad data of NMR. Moreover, number-average length (L[EE···E≥5]) of ethylene sequences greater than or equal to 5, whose value is the crystallizable minimum number of consecutive ethylene units in an EP copolymer, approximately agreed with the junction size ζ in gel, i.e., ζ≃L[EE···E≥5].

Thermoplastic elastomers from iPP/EPR blends: Crystallization and phase structure development

AbstractThe phase morphology and structure of thermoplastic elastomers obtained from isotactic polypropylene (iPP) and ethylene—propylene random copolymer (EPR) blends by means of the dynamic curing of EPR rubbery component carried out during its melt mixing with iPP in a Banbury mixer at 180°C were investigated. Samples obtained by compression molding and by using isothermal crystallization conditions of the iPP phase were analyzed by means of differential scanning calorimetry, of optical, scanning, and transmission electron microscopy, and of wide‐angle and small‐angle X‐ray diffraction. The influence of cooling below the melting point and of EPR molecular structure on the kinetic and thermodynamic parameters related to crystallization process of the iPP phase was also studied. It was found that the process of dynamic curing of the EPR component dramatically affects the development of the phase morphology and structure in the material. As a matter of fact, the blend containing the uncured EPR is characterized by the presence of iPP domains randomly distributed in the EPR rubbery matrix, whereas in the blend containing the cured EPR the iPP phase becomes the continuous phase crystallizing in a structure that resembles a cobweb tending to surround the EPR cured particles; moreover such an iPP cobweb appears to be contituted by row structures of stacked lamellae. It was found that the addition of EPR phase interferes dramatically with the crystallization process of the iPP, thus inducing drastic modification in its intrinsic morphology (size, neatness, regularity of spherulites, inner structure of spherulites, etc.). Such interference was found to be comparatively stronger when the iPP phase crystallizes in presence of cured EPR. The elastic behavior of the thermoplastic elastomer material was accounted for by applying the “leaf spring model” to the morphology and structure of the iPP phase crystallized in presence of cured EPR. © 1994 John Wiley &amp; Sons, Inc.

Characterization of propylene‐ethylene block copolymers using solid state 13C‐NMR spectroscopy

AbstractCommercial block copolymers of propylene with ethylene (PEBC) are multiphase systems comprising block and random copolymers as well as small amounts of homopolymers. At present, no satisfactory method exists for characterizing the “blocky” structure of these copolymers. This article aims to fulfill this need. Accordingly, the block and random copolymers of propylene with ethylene have been investigated using 13C CP/MAS NMR with high‐power dipolar decoupling. Comparisons have been made between the spectra of block and random copolymers and it is shown possible to distinguish between them by means of an additional signal, appearing at 32.5δ, in block copolymers (attributable to block junctions). © 1992 John Wiley &amp; Sons, Inc.

Radiation-induced structural changes in poly(propylene-ran-ethylene) film: Effect of antioxidant 2,2,6,6-tetramethylpiperidine derivatives

The isotactic random copolymer of propylene and 2.3 wt% ethylene in films with and without bis(2,2,6,6-tetramethyl-4-piperidinyl)sebacate (LS-770) or bis( N-chloro-2,2,6,6-tetramethyl-4-piperidinyl)-sebacate (LS-770-Cl) was γ-irridiated up to 20 Mrad in air at room temperature. Progressive oxidation proceeded to form hydroperoxide and carbonyl groups, which were depressed by the antioxidizing action of the additives. The apparent antioxidizing activity of LS-770 was higher than of LS-770-Cl. From differential scanning calorimetry, to evaluate the melting temperature and heat of fusion, main-chain scission and subsequent recrystallization were suggested to occur in the interlamellar amorphous regions. In association with recrystallization, the helical regularity in the isotactic sequence of the propylene units increased with increasing radiation dose, as evaluated from the sequence-sensitive i.r. absorption bands. X-Ray diffraction analysis indicated a transformation of disordered crystallines to the closest packed monoclinic structure during the irradiation. A density rise was also observed, which was probably due to the combined effects of the recrystallization and the oxygen uptake. These physical-structural changes were effectively depressed by the additives, for which the LS-770-Cl was more active than the LS-770.

New elastomeric networks based on functionalized ethylene–propylene rubbers and hydroxyl terminated polybutadiene. I. A kinetic study on the monoesterification

AbstractEthylene–propylene random copolymers bearing grafted succinic anhydride functions have been reacted with an α,ω‐hydroxyl telechelic polybutadiene to obtain elastomeric interpolymer complexes. A kinetic study has been carried out by infrared techniques to study the influence of the addition of catalyst, stoichiometry, and temperature on the degree of monoesterification reaction.

Structure-properties relationships in some random copolymers of propylene

Correlations have been investigated between the content of short isotactic segments and thermal properties in some propylene/olefin random copolymers. Polypropylene copolymers modified by ethylene show variations different from those for copolymers modified by ethylene and butene. However, in both cases, the weldability temperature decreases on increasing the comonomer concentration.

Radial Distribution Function Study for Ethylene–Propylene Random Copolymer by X-Ray Diffraction Method

The local chain conformation and packing in the amorphous solid of a polymer were determined for ethylene–propylene random copolymer (EPRC) by the analysis of the radial distribution function (RDF) obtained from X-ray diffraction measurement at room temperature. A new method was devised for removing the contribution of H atoms to the observed RDF in such a polyatomic system consisting of C and H atoms, and the C-C pair RDF for EPRC was derived. From the C-C pair RDF, the number of intrachain and interchain atoms were obtained. From this result, it was found that the amorphous bulk state and the isolated state in θ-solvent are nearly equal in the conformational probabilities for trans and gauche states in the EPRC chain.