Morphology of solution crystallized trans-1,4-polyisoprene

The film formation method has been successfully used to grow single crystals and other complex morphological features of low melting form (LMF) and high melting form (HMF) of trans-1,4-polyisoprene (TPIP). Below 40 °C dilute amyl acetate solution gave hexagonal shaped LMF crystals. Thick and elongated hexagonal shaped morphology was shown by HMF crystals at temperatures above 40 °C. Straight faces and sharp corners of the single crystals, and also of complex crystals, acquired round shapes when highly polydispersed TPIP was used for crystallization.     

Growth of polyethylene single crystals from the melt: change in lateral habit and regime I–II transition

Using the technique of extraction, single crystals have been obtained from polyethylene fractions isothermally crystallized from the melt at atmospheric pressure. It has been found that the lateral habit of single crystals changes in the vicinity of the transition temperature of growth regime (regime I–II): lenticular shape elongated in the direction of theb axis (type A) in the range of regime I and truncated lozenge with curved edges of {200} and {110} growth faces (type B) in that of regime II. The transition of lateral habit causes a drastic change in the width of {110} growth faces; {110} growth faces are well developed in type B crystals while they cannot be observed and must be very small in type-A crystals. It has been shown that the growth regime of the small {110} growth face of type-A crystals must be in regime I; hence the regime I–II transition can be explained as the result of this change in lateral habit (width of the {110} growth face).     

New aspects of yielding in semicrystalline polymers related to microstructure: Branched polyethylene

The application of thermodynamics of eutectoid copolymers and a generalized Tabor-relation to relationships between mechanical properties (microhardness, yield stress) and microstructure in semicrystalline polymers is considered. The approach is illustrated by results on melt-crystallized low density polyethylene, investigated near the yield point at different temperatures. The success of the approach emphasizes that semicrystalline polymers, despite being viscoelastic hetereogeneous systems, give rise to a yielding process entailing the irreversible deformation of a larger number of crystals within cooperative super-structure units. Microhardness provides, within this context, a unique measure of the crystal size average. Comparison of calculated and experimental data favors the view of deformed crystals containing basal defective surface boundaries (meso-crystals) which yield cooperatively.Dedicated to Professor Dr. Dr. h. c. Armin Weiss on the occasion of his 60th birthday.     

Photochemically induced phase transitions in the system cetyltrimethyl-ammonium bromide-water containing N-methyl-N,N-diphenylamine

Phase transition temperatures from lyotropic liquid crystals to the isotropic micellar solution of the system cetyltrimethylammonium bromide-water (CTAB-H₂O) were measured in the presence of 0.1-0.9 weight % of N-methyl-N,N-diphenylamine (MPA). They were determined by optical and viscometric methods and were found to increase as a function of MPA concentration in solutions containing 21 and 23 weight % of CTAB. This effect was reversed when MPA was in situ photochemically converted to N-methylcarbazole, allowing photochemically induced phase transitions.     

Equilibrium and non-equilibrium melting of branched polyethylene relating to defect incorporation within crystals

New equilibrium melting point data, for polyethylene containing chain defects, are tested in the light of random copolymer predictions. A simplified expression for the melting point depression of random copolymers containing small amounts of non-crystallizable units is derived. Non-equilibrium melting data for rapidly quenched polyethylene samples are also reported. The fusion enthalpyH(X), and the surface free energy _e for crystals containing defects are evaluated using crystallinity, equilibrium meltingtemperatures and X-ray long period data. It is shown that increasing defect penetration within crystals induces a decrease ofH(X) withX in accordance with theoretical predictions. Finally _e is, similarly, shown to decrease with increasing number of chain defects attached to the crystal surface.     

Adhesion of a pair of polyethylene moldings by polyethylene gels

It was found that polyethylene gels in solvents such as benzene, toluene, xylene, decalin, tetralin, tetrachloroethylene, 1,1,2,2-tetrachloroethane, and chlorobenzene are effective for adhesion of a pair of polyethylene plates. In particular, the adhesion strength of polyethylene gels in decalin, tetralin and tetrachloroethylene was strong enough for practical use.Adhesive effect appears due to local dissolution of the surface of polyethylene plate in contact with the gel with increasing temperature, and subsequent recrystallization.     

Thermo-optical analysis as a complementary method in the study of phase transitions of thermotropic liquid crystalline polymer and its blends with polycarbonate

Differential scanning calorimetry (DSC) and thermo-optical analysis (TOA) were applied to study the phase transitions phenomena of thermotropic liquid crystalline polymer and its blends with polycarbonate. It was found that both methods are complementary. Glass transition temperatures of the blends of polycarbonate with liquid crystalline polymer were measured and discussed.     

Adhesion of molded polyethylene using polyethylene gels by microwave heating

Adhesive effect of polyethylene gels on the molded polyethylene by heating with microwaves has been investigated. Polyethylene gels in polar organic solvents such aso-xylene, chlorobenzene,o-dichlorobenzene,m-dichlorobenzene, 1,1,1,2-tetrachloroethane, and 1,1,2,2-tetrachloroethane were used as adhesives. All of these gels showed adhesive effect when heated with microwaves. In particular, the gels in 1,1,2,2-tetrachloroethane showed such strong adhesion that polyethylene plates of 3 mm in thickness and 20 mm in width gave rise to necking by heating for 8 min in a 500 W (2450 MHz) microwave oven.     

Van der Waals networks in the compressive deformation of polyethylene

The compressive stress-strain behavior of biaxially oriented polyethylene (PE), obtained by pressing uniaxially oriented samples, is described with the aid of the van der Waals equation of state. Results are discussed in terms of two parameters: the biaxiality (B) and the biaxial draw ratio (), which offer a measure of the strain along the two principal directions and of the average draw ratio on the film plane, respectively. Comparison of experimental and calculated data indicates that after compression up to very large deformations the maximum average strain ( _m ), which is proportional to the square root of the chain length of the network, remains constant. This result supports the view that the network of entanglements is not destroyed after compression. Experiments carried out on isotropic melt crystallized PE show the presence of a network having a not very different chain length. Finally, it is shown that the segment length of this network is close to the X-ray long period of the initial structure. This result implies the existence of a high density of entanglements (two entanglements every three adjacent lamellae), which are rejected into the defective layer of the crystals.     

Extreme swelling of a lyotropic lamellar liquid crystal

The evolution of the OBS/water/decane/pentanol lyotropic lamellar crystal is followed from 0% to more than 90% decane content. The lamellar spacing (d) varies then from 35 Å to 11000 Å. The swelling is followed with small angle x-ray scattering and the Bragg divergence in the intensity is found to disappear in moderately swollen lamellar crystal (d from 200 Å up to 800 Å) while the central scattering increases. More striking is the reappearance of the Bragg divergences observed by SAXS (d from 800 Å to 1100 Å) and for extremely swollen lamellar crystals in the angular distribution of scattered light (d from 2 000 Å to 10 000 Å). We discuss these observations along the lines of the recent models of swollen lamellar liquid crystals and in particular the apparent evolution of the dilute lamellae.     

The effect of segment length and concentration on dielectric properties of polypropyleneoxide-based polyurethanes

Three series of segmented polyurethanes based on MDI, variable chain extender, and polypropylene oxide of MW=1000, 2000, and 3000 were synthesized and their dielectric behavior examined.Dielectric relaxations in the segmented polyurethanes were investigated between –150°C and +150°C in the 100 Hz to 10 kHz range. In general, three transitions, designated as, , and were observed, and ascribed in accordance with calorimetric relaxations to glass transitions of the hard and soft segments, and Shatzki-type motions, respectively. The effect of structure variables such as soft segment size, type of chain extender (ethylene glycol, butane diol, and hexane diol) and soft segment concentration, as well as the effect of interaction of the phases on dielectric properties was discussed. It was found that a certain degree of phase mixing exists in all series, detected by the variation of theT _g of the soft segment with soft segment concentration, contrary to DSC results, which was ascribed to thermal treatment prior to the dielectric measurements. It appears that interfacial polarization becomes important only above the transition temperature.     

Packing of long-chain cycloalkanes in various crystalline modifications: an electron diffraction investigation

The structure and thermal behavior of long-chain cycloalkanes (CH₂)_n with n= 48, 72, 96, 144 and 288 have been investigated by electron diffraction, WAXS and SAXS analysis. Five different modifications have been characterized by their subcells as a function of ring size, crystallization conditions and temperature. The rings adopt, in all modifications, a conformation with two straight stems connected by folds. Similarity with the polyethylene lattice is achieved only for n144. In this case, the stems are perpendicular to the layer surface and pack in the well-known orthorhombic subcell regardless of whether the rings are crystallized from solution or melt. (CH₂)₉₆ forms the same type of subcell when crystallized from the melt, but the stems are oblique to the layer surface. Rings of all sizes undergo a transition into a phase in which the stems are arranged similarly as in the rotator phase of linear paraffins. (CH₂)₇₂ and (CH₂)₉₆ exhibit additional transitions at lower temperatures. One significant feature of some transitions is the change of conformation and length of the folds.     

Adhesive effect of high density polyethylene gels on polyethylene moldings

Adhesive effect of polyethylene moldings by use of high density polyethylene gels in organic solvents such as decalin, tetralin, ando-dichlorobenzene was investigated by shearing tests, electron microscope, and DSC measurements. All of the gels showed such a strong adhesive strength over 36 kg/cm² that polyethylene plates of 3 mm in thickness gave rise to necking sufficient for practical use, when heated at 120 °C for 2 h. In particular, the gel in tetralin showed a strong adhesive strength when heated at 110 °C. It was found that adhesive strength increases with the heating temperature; the temperatures at which adhesive strength begins to increase differ depending on the type of polyethylene sample and solvent. It is apparent that polyethylene gels exhibit an adhesive effect when they are heated at higher temperatures than the gel melting temperatures, and that the closer the SP values of solvents used for the gelation are to the molded polyethylene, the stronger the adhesion of the polyethylene molding.     

Electrolytic conductivity of poly(1,3-propylene phosphate) solutions containing mono- and divalent-counterions

The results of conductivity measurements for aqueous solutions of poly(1,3-propylene phosphate) (PPP), which can be considered as a synthetic analogue of naturally occurring teichoic acids, are reported. Experiments were carried out with oligomeric fractions of a polymer in acidic, sodium, potassium, magnesium and calcium forms. The concentration and molecular weight dependence of the equivalent conductivity of PPP was analysed and the limiting equivalent conductivity determined. From the conductivity data, the polyion-counterion interaction parameter F and the equivalent conductivity of a polyion _p were calculated. It was shown that both F and _p depend on polyelectrolyte solution concentration and molecular weight of PPP. Conclusions concerning mono- and divalent metal ions binding to PPP are drawn.     

Temperature-dependent fracture mechanisms in ultra-high strength polyethylene fibers

The influence of the temperature on the mechanical properties of gel-spun hot-drawn ultra-high molecular weight polyethylene fibers has been investigated.From these experiments two different fracture mechanisms could be distinguished. The results indicate that above 20C a stress-induced orthorhombic-hexagonal phase transition is responsible for fiber failure. In the hexagonal or rotator phase the chains can easily slip past one another and fiber fracture is initiated by creep. Below 20C the phase transition cannot be introduced because the stress needed for the phase transition would exceed the covalent-bond strength in the polyethylene chain. The strength temperature data of the low temperature region was treated with Zhurkov's kinetic concept, leading to a bond-fracture activation energy of 160 kj/mol and an activation volume of 0.01 nm³. These values, together with the data from irradiation and shrinkage experiments, indicated that in the low temperature region fiber failure might be initiated by the fracture of trapped entanglements instead of that by overstressed, taut tie molecules.     

Further electron microscope observations on polyethylene III. Smectic intermediate state during melting and crystallization

While it was possible to demonstrate in the first part of this paper [1] that the granular structure in an LPE melt created by short-time staining with chlorosulfonic acid is an artifact, it was demonstrated in the second part [2] that an artifact can actually be useful. It makes it possible to differentiate between the mobile melt and a very thin layer of fixed melt on the crystalline lamellae which corresponds to the switchboard model.This third part reports the discovery of a smectic type of liquid crystal intermediate state both in the melting and in the crystallization processes, which many authors regarded as impossible because of the flexibility of the molecules in polyethylene.Extracts presented at the 32nd Hauptversammlung der Kolloid-Gesellschaft und Berliner Polymeren Tage 1985, 2–4 October 1985 in Berlin     

DC dielectric study of polyethylene/CaCO3 composites

The dielectric properties of composite samples prepared by polymerizing ethylene on the surface of filler are compared to those of mechanical mixtures consisting of CaCO₃ and ultra high molecular weight polyethylene. After presenting the normalized master curves of AC dispersion and loss measured at different relative humidities, the field strength dependence of the 50 Hz AC and DC responses were studied. With one exception, the effect is small. Thermally stimulated polarization (TSP) and depolarization (TSD) curves are presented; the peak appearing on the TSP curves of the samples stored under ambient conditions is interpreted as a result of water desorption. The high temperature DC conductivity and the depolarization current density are higher in the composites and mechanical mixtures than in the matrix. The dielectric properties of the wet filler particles were calculated from the measured composite and matrix data using various mixture formulae. The results can be understood and interpreted if the dielectric properties of adsorbed water are described by the cluster theory of dielectric relaxation.     

Dielectric properties of moist CaCO3 filled polyethylene composites

The capacitance and the dielectric loss tangents of CaCO₃ filled polyethylene composites were studied. Composite samples, prepared by polymerizing ethylene on the surfaces of fillers, pre-treated by polymerization catalysts, were compared to normal mechanical mixtures. Dielectric dispersion,, and loss, , proved to be sensitive to heating or vacuum treatment. Investigation of samples under conditions of different relative humidities showed that the dielectric dispersion is due to adsorbed water. Both and increased with decreasing frequency and the ratio of loss and dispersion was nearly constant. Dielectric data measured at different relative humidities could be represented by a single Cole-Cole plot. Samples soaked in water for different periods yielded qualitatively similar but quantitatively different Cole-Cole plots. Composite samples showed higher losses at similar humidities.Possible interpretations in terms of a molecular relaxation model, an interfacial relaxation model, including a charged double layer mechanism, percolation theory and the universal response theory were examined, but none was able to fully explain the observed phenomena.     

Microhardness and surface free energy in linear polyethylene: The role of entanglements

The microhardness of a series of melt crystallized samples of linear polyehtylene was investigated in a wide range of molecular weights. The x-ray long period was analyzed to study the variation of the hardness-derived constantb as a function of molecular weight (M ). It is pointed out thatb offers a measure of the hardness depression due to the finite thickness of the lamellar crystals. The data obtained show that the increase and final leveling-off (forM 200 000) ofb withM parallels the concurrent increase of the surface free energy, as derived from DSC experiments. Results are discussed using the concept og chain folded lamellae as thermodynamically stable non-homogeneous microphases. Comparison of experimental and calculated data supports the view that the number of molecular entanglements, segregated onto the defective surface boundary of the heterogeneous crystals influence the shearing mechanism within the mesocrystals and thereby control the yield behavior of the material.     

Chain-structure-superstructure relations in eutectoid copolymers

It will be shown that low-density polyethylene is a eutectoid copolymer with non-random distribution of branchings along the chains. From a line-profile analysis it is deduced that the crystal-size-distribution is uniquely related with the distribution of branchings thus yielding that basic features of the colloid-structure are controlled by the chemical structure of the macromolecules.