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.     

Morphology and optical properties of liquid crystals embedded in polyester resin matrix

This paper reports on morphological, thermo-optical, and electro-optical results of UV-cured polyester resin film containing liquid-crystal nematic and cholesteric domains. Electro-optic measurements were performed in an applied d.c. electric field. The morphological structure of PDLC film is modified by the various methods of their preparation. Size-distribution curves drawn vs the duration of the initial cooling obtained for cholesteric liquid crystal domains are presented.     

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.     

Broadband dielectric spectroscopy on a discotic liquid crystalline polymer

Broadband dielectric spectroscopy is employed for the first time to study the molecular dynamics in discotic liquid crystalline polymers. One dielectric relaxation process is found which is strongly broadened and asymmetric. It is assigned a local hindered rotation of the ester groups attaching the spacer to the discotic mesogen. This assignment is supported by NMR measurements on the identical substance.Dedicated to Prof. E. W. Fischer on the occasion of his 60th birthday.     

Preparation of micron-size monodisperse polymer microspheres having cationic groups

Micron-size monodisperse crosslinked polymer microspheres having chloromethyl groups were prepared by seeded copolymerization of styrene, divinylbenzene, and chloromethylstyrene in the presence of 2.1- monodisperse polystyrene seed particles produced by dispersion polymerization. The modification reaction of chloromethyl groups on the surfaces with polyamines such as triethylenetetramine and ethylenediamine was carried out. From the measurements of potential and the amount of chloride ion released, the introduction of a large number of cationic groups at the surfaces was confirmed.Part CXXXI of the series Studies on suspension and Emulsion.     

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).     

Calorimetric and diffractometric study of the lowest room-temperature transition of polytetrafluoroethylene

Through differential scanning calorimetry and wide angle x-ray scattering, the room-temperature transitions of native (never melted) polytetrafluoroethylene have been investigated. The independence of the transitions, and in particular of the lowest one, on the heating kinetics, seems to suggest that also this transition is a true crystal-crystal transition.     

Dynamic shear compliance of polymer melts and networks in dependence on crosslinking density

Mechanical relaxation processes in polymer melts and networks are discussed. This is performed by decomposing master curves of the dynamic shear compliance into i) glass relaxation with its plateau complianceJ _eN ; ii) shearband process with its relaxation strengthJ _B , which is reciprocal to the total crosslink densityp _c ; and iii) flow relaxationJ _F and viscous flow (for uncrosslinked melts only). Plateau complianceJ _eN > is exponentially reduced only by effective crosslinks (p _c ^* p _c /30). This behavior is understood on the level of a meander superstructure, which includes shearbands. The observed saturation inJ _eN at higher dicumylperoxide (DCUP) crosslinking-which doesn't appear with radiation-can be explained by the lack of chemically induced effective crosslinks across the interfaces among meander cubes. This lack may be a consequence of DCUP molecules concentrating at the interfaces and thereby preventing the contact and radical recombination between chains at adjacent meander faces.Crosslink densitiesp _c (per monomer), determined from the reduction of shearband relaxation strength, vary linearly with the crosslinking agent and read: p_c2.4 · 10^–2 Dose/MGy andp _c 0.97 · 10^–2 DCUP/phr for radiation and DCUP crosslinking, respectively. This implies, e.g., that a dose of 0.4 MGy (40 Mrad) is equivalent to 1 part DCUP phr in a crosslinking polyisoprene. From activation-curve analysis it follows that3 r/d stays constant, and _s - _so (free energy of formation of a segment-dislocation) andQ _y -Q _yo (activation energy for segmental jumps) vary with the square ofP _c , as does the glass temperaturT _g -T _go from DSC measurements.     

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     

The theory of flexoelectric effect of polymer glasses

Electric polarization induced by a nonhomogenous deformation flied — flexo-electricity — has has been studied on a model of polymer in the glassy state. The results are expressed in terms of phenomenological coefficients, which are analogical to the electric polarizability. It is found that a gradient of the tensor of small rotation, and not just that of small deformation contributes to the polarization. Dedicated to Prof. Dr. W. Pechhold on the occasion of his 60th birthday     

Phase transition of polycarbonate in blends with liquid crystal

Phase transition temperatures of polycarbonate film consisting of micron-sized liquid crystalline droplets were investigated using differential scanning calorimetry (DSC) and thermo-optical analysis (TOA) methods. Both a decrease in (T _g ) and (T _m ) of the polycarbonate with an increase of liquid crystal (LC) content in the sample were observed. The decrease ofT _g is related to the plastifying effect of a low molecular weight LC substance remaining soluble in the polycarbonate matrix. A fraction of the liquid crystal contained in the droplets was estimated on the basis of theT _g decrease.     

Dynamics of phase separation and critical phenomena in polymer mixtures

The phenomenological mean-field theory for statics and dynamics of polymer mixtures is described, generalizing the approaches of Flory-Huggins, Cahn-Hilliard and de Gennes. Predictions are made for critical behavior, spinodal decomposition and homogeneous nucleation. The validity of the mean-field approximations is discussed with Ginzburg criteria. The results of the theory are compared to computer simulations and recent experiments.Invited talk delivered at the Tagung der Deutschen Physikalischen Gesellschaft, Fachausschu\ Polymerphysik, Kaiserslautern, 12–14 March 1986, and at the Gordon Research Conference on Polymer Physics, Andover, New Hampshire, 14–18 July 1986.The author is grateful to Dieter W. Heermann, Alla Sariban, Harry L. Frisch, Josef JÄckie and Thomas Schichtel for their fruitful collaboration on this research described in this review. He thanks them and Arthur BaumgÄrtner for allowing to present partially unpublished material, and for stimulating discussions. Furthermore the author has benefitted from discussions with P. G. de Gennes, P. Pincus, H. Sillescu and G. R. Strobl. This research is supported in part by the Deutsche Forschungsgemeinschaft, Sonderforschungsbereich 41.     

Estimation of distribution of vinyl groups in micron-sized monodisperse polymer microspheres by bromine titration method

The distribution of vinyl groups in polystyrene/poly(styrene-divinylbenzene) (PS/P(S-DVB)) composite microspheres produced by seeded copolymerization of S and DVB in the presence of 2.1-m monodisperse PS seed particles was estimated from the amount detected with bromine titration method as a function of the reaction time under various conditions.Part CXXIII of the series Studies on Suspension and Emulsion.     

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.     

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.     

Study of the polymer latex coalescence by dielectric measurements at microwave frequency—feasibility of the method

The measurement of the complex dielectric constant ( ^*=–j) in the dipolar absorption domain of the free water molecule (microwave region) permits us to follow quasi-specifically and precisely the water circulation during the coalescence process of a latex. Weight losses and dielectric constants variations have been simultaneously recorded upon latex drying, in a resonant cavity at 5 and 9 GHz and under controlled atmosphere and temperature. Two different latexes were studied (polybutylacrylate (PBuA) and polystyrene (PS)) from which the glass transition temperature effect was investigated. It is found that the harder the polymer particles, the more clearly evidenced the flocculation and packing points are. This method appears to be quite reliable for discriminating the various steps in the film formation process of latexes.     

Eigenvectors of the polyethylene chain with conformational defects calculated semianalytically by Green's function

Eigenvectors of vibrating polyethylene chains with (200) and (110) folds have been calculated by solving the phonon-scattering problem exactly with the method of Green's function. The results are applied to analyze the resonance modes of the (200) fold (ggtgg: 1353, 1356, 1374 cm^–1) and the (110) fold (approximately ggggtg: 820, 1288, 1342, 1348, 1372, 1374 cm^–1) in terms of the characteristic vibrations of smaller subunits of the (200) fold (gg, gtg) and the (110) fold (ggggtg, gggg, gtg) which can be identified spectroscopcally.Dedicated to Prof. Dr. W. Pechhold on the occasion of his 60th birthday     

Phase behavior and elastic properties of a slightly crosslinked liquid crystalline main-chain polymer

A liquid crystalline main-chain polymer was slightly crosslinked by a reaction with, -difunctionalized oligo-siloxanes. Crosslinking does not disturb the liquid crystalline phases, which are identified by x-ray measurements as smecticB and smecticA phases. Measurements of the elastic properties of the crosslinked sample show rubber-like elasticity, even in the liquid crystalline phases. A difference of 7 K was found between cooling and heating for the smecticA/isotropic transition from DSC and mechanical measurements.     

Localization of carboxyl groups at surface layer of carboxylated polymer emulsion particles by alkali treatment

For the purpose of localizing carboxyl groups from inside to particle surface, styrene — butyl acrylate — methacrylic acid (74.3/17.0/8.7, mol ratio) terpolymer emulsion was kept under pH 9 at different temperatures. The amount of carboxyl groups at the particle surface, As, was remarkably increased by the alkali-treatment above 35 °C. On the other hand, As value of the alkalitreated emulsion was decreased by keeping under ph 3 above 45 °C, although in the case of the original emulsion without the alkalitreatment, it was not changed by the acid-treatment. These results suggest that a part of polymer segments which have ionized carboxyl groups is dragged out at the surface by an increase in the affinity of the groups against water, and the dragged segments turn back into the inside again when the carboxyl groups are deionized.Part 97 of the series Studies on Suspension and Emulsion.     

Use of porous biodegradable polymer implants in meniscus reconstruction. 2) Biological evaluation of porous biodegradable polymer implants in menisci

Several series of porous, biodegradable PU/PLLA foams were used for meniscus reconstruction in dogs. PLLA-fiber reinforced PU/PLLA composites, PU/PLLA, and PU foams were implanted in severe meniscus lesions. The healing process was initiated as a result of blood vessels and other cells ingrowth into these porous materials. To accomplish good ingrowth of fibrocartilaginous tissue, the materials should have interconnected macropores of 200–300n with a high total pore volume. PLLA fibers were used to reinforce the materials, but seem to retard the degradation process and the ingrowth of fibrocartilaginous tissue.