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An attempt is made to describe mutual truncation between two coinciding spherulites. It is shown that if in a sample the borderlines between spherulites are not straight lines, the spherulites did not arise simultaneously. Using. a mathematical approach it is possible to determine the time distribution of primary nucleation from the shapes of truncated spherulites. This was done for polyoxymethylene samples at two different crystallization temperatures. The superiority of thermal over athermal type of nucleation depends on the crystallization temperature which lead to different spherulite size distributions.

Temperature dependences of shrinkage forces appearing in oriented polymer samples when heated at constant length were recorded for polycarbonate, polyethylene terephthalate, polyethylene and polypropylene. The influence of various processing conditions on thermally stimulated shrinkage forces is demonstrated. A four-state model is proposed which qualitatively describes the temperature dependences of shrinkage forces in amorphous polymers.

A new model is presented that generates amorphous structures with linear chains filling up the space completely. The model is based on a simple concept that the space is filled up with elements containing chain segments that can be connected into chains according to the ‘domino’ game rules. Examples of model applications are shown.

The construction and principle of operation of small-angle light scattering apparatus for studies of supermolecular structure in thin polymer films is described. The apparatus can be used to study changes in spherulite structure during crystallization and changes in films subjected to steady or sinusoidal strain. Typical results with polyethylene films are given.

The relationship between drawing rate and drawing stress was studied for amorphous poly(ethylene terephthalate) (PET) under various experimental conditions. Three types of expriments were performed: simple drawing with necking at constant rate, drawing through a conical die, and drawing at constant stress. Under constant stress conditions a transition between two stable regimes of drawing can be observed. The transition occurs at a critical stress σc at which the rate of neck propagation changes by some orders of magnitude. Such a transition was found both below and above the glass transition of PET. With constant drawing rates instabilities of neck propagation were observed under certain experimental conditions. Such self-oscillations, described by other authors, are not due to heat effects as has been proposed, but are related to the existence of the critical stres σc. Stress-induced transitions in deformation behavior as in PET were observed for polypropylene and nylon 6 but not for polycarbonate. The results obtained by various methods including morphological studies do not support the assumption that the instabilities are caused by thermal effects due to the dissipation of deformation energy. Rather, a model is proposed which is based on the existence of a “spinodal transition” from the isotropic into the highly oriented state.

A version of DSC technique is proposed which ensures good accuracy in comparing the melting behaviour of two apparently similar samples. The information is obtained in the form of comparative thermograms recorded during simulataneous melting of both samples. The method is applied to observe the influence of cooling conditions and annealing on melting behaviour of low-density polyethylene.

The four-state model proposed in a previous paper to describe thermal shrinkage in oriented polymers is solved to describe the time dependences of shrinkage forces under constant temperature conditions. The time dependences of shrinkage forces have been recorded for polycarbonate and polyethylene terephthalate at temperatures below the glass transition. It is shown that experimentally recorded time dependences of shrinkage forces can be satisfactorily fitted by dependences predicted by the model, and the comparison leads to reasonable values of activation energy and activation volume for the shrinkage process.

A model is proposed which considers various cases of arrangement of crystallizable chain elements of branched polyethylene in lamellar crystalline elements. On the bases of statistical calculations, relationships between crystallinity and long spacing of the lamellar structure are derived. Calculated relations are compared with experimental crystallinity and long spacing values determined for polyethylene samples crystallized under various cooling conditions.

Viscoelastic loss spectra and differential scanning calorimetry (d.s.c.) traces of oriented and aged glassy polycarbonate and poly(ethylene terephthalate) were recorded and compared with the results of shrinkage and shrinkage force measurements. It was shown that ageing effects such as ‘intermediate relaxation’ (in damping test) and the development of sub-Tg endotherm (on d.s.c. traces) coincide well with dimensional instabilities of oriented samples. Observed correlations are explained on the basis of internal stress relaxation, which seems to be an important feature of physical ageing of oriented glassy polymers.

A solution of equations describing the mechanical properties of two-component, three-dimensional model suitable to represent local properties of materials with different structures is presented. The model is applied as a unit element in “series” and “parallel” aggregate models. As examples numerical calculations have been performed for aggregates of randomly oriented unit elements built up of elastic and viscoelastic components arranged in lamellar, fibrillar and droplet-like structures. It has been shown that the “series” and “parallel” models do not describe uniquely mechanical properties of the aggregate and that the range of uncertainity is very large. Therefore, a new “packet” model is proposed for averaging the mechanical properties of an three-dimensional aggregate.

Two new mechanical models for the description of mechanical properties of two-component polymer blends are proposed. On the basis of these models the dependence of the dynamic complex moduli on the blend content is theoretically calculated. Results obtained theoretically are compared with experimental data for polyethylene and polypropylene blends.

Dynamic birefringence and dynamic light scattering techniques have been used to characterize the morphological changes in low-density polyethylene during sinusoidal deformation with various frequencies at constant temperature. Measurements have been conducted on samples with various morphologies. Two separate relaxation processes in the frequency range from 0.003 to 20 cps have been found to be strongly dependent on the morphology (i.e. spherulite perfection, degree of orientation correlation and sizes of crystalline elements) and less dependent on crystallinity of samples. By comparison of the results with calculated stress distribution inside spherulite mechanical model, the locations of distinguished relaxation processes in particular morphology elements have been discussed.

The renormalization group technique, developed in the mean field theory, is applied here as a method for calculating of elastic or viscoelastic properties of heterogeneous materials with complex structures. The method consists in averageing of properties of small volume elements of the heterogeneous system by step-wise application of a recurrence relation which renormalizes properties of the group of neighbouring cells to properties of a new cell of larger dimensions. The recurrence relations are derived on the basis of the “packet” model — a group of eight elemental cells.

The spontaneous break-up of long threads of polymer melt suspended in the melt of the other polymer has been observed. The kinetics of this process was studied for several pairs of polymers. The possibility of description of this process by the theory of development of stationary capillary waves is demonstrated.

The theoretical backgrounds of the method of spherulite size distribution determination, on the basis of the small-angle light scattering technique, are presented. Special corrections of experimental data are introduced to achieve great accuracy of the determination of scattered light intensity distribution. Experiments have been done on low-density polyethylene samples obtained in various crystallization conditions. For these samples, the stepwise distributions of spherulite size have been determined.

Plasma-polymerized thin films of hexamethylcyclotrisilazane were pyrolysed in vacuum and studied by transmission electron microscopy. Examination of the polymer film after various durations of pyrolysis revealed significant changes in their surface structure and a distinct difference in the thermal stability powder and film phases. The number of powder particles in the surface layer and their size increased with pyrolysis time. The observations showed that powder particles embedded in the film matrix were gradually exposed in the surface layer owing to a decrease in the film thickness during pyrolysis. Good agreement was obtained between the experimental and theoretical distribution curves of particle size. The identical properties of powder particles exposed in the surface of the pyrolysed film and those taken from the interelectrode region indicates that they are primarily formed in the gas phase.

Etude par mesure de birefringence et diffusion RX aux petits angles, a temperature ambiante

Small-angle light scattering technique has been used to record changes in spherulite size during non-isothermal crystallization of low-density polyethylene under different cooling conditions. From these changes, the spherulite growth rates at various temperatures in the range 72–91° have been determined. The results are discussed on the basis of the Hoffman Lauritzen theory.

The physical structure of semicrystalline polymers influences many of their properties. It has been shown that thermal treatment (rate of cooling and annealing) as well as the action of mechanical forces (drawing) of isotactic polypropylene (PP) resulted in materials with different mechanical properties. In the case of isotropic films the crystallization temperature or annealing temperature from the glass and consequently morphological structure which has been formed, determine the values of modulae, yield stress and viscoelastic properties. Reoptical behaviour has been found to be sensitive to structural differences too. The structure and mechanical properties of highly oriented PP samples which have been obtained by drawing through a flat die have been found to be dependent on parameters characterizing this process (drawing rate, apex angle of die and elongation ratio).

The surface morphology of the PP fibres with internal helical texture were studied. The studies were carried out by the direct observation of the untreated fibre surface, and by the ‘marked deformation’ method of microscopical objects using a ‘JEOL’ scanning electron microscope. The results showed the helical internal texture of these fibres.

The theoretical description of mechanical properties of heterogeneous materials has been a subject of investigation of several authors in last few years. The interest in this field is involved by technological importance of composite polymeric materials like polymer blends, filled polymers and block copolymers. Blending of polymers is usually used to improve properties and processability of materials. On the other hand most of polymers that are considered to be chemically homogeneous become physically heterogeneous when considered on a microscopic scale. An example is the coexistence of crystalline and amorphous regions in most crystallizing polymers.

The aim of this paper is to present a polymeric material showing anisotropy of electrical conductivity obtained by a modified version of a new method of preparing conductive polymeric films.

The dynamics of the fragile glass-forming liquid diglycidyl ether of bisphenol-A was studied by depolarized Rayleigh-Brillouin light-scattering and photon correlation spectroscopy above the glass transition, in the temperature range from 261 to 473 K and in the frequency range from 1 Hz to 300 GHz. The structural (alpha-) relaxation process was revealed and no signature of the secondary relaxation previously evidenced by dielectric spectroscopy at about 0.1 GHz was observed. The characteristic time of the alpha process differs from that determined by dielectric spectroscopy of an amount, which increases with increasing temperature. The relaxation times were compared with viscosity data to test the predictions of the classic Stokes-Einstein-Debye model. The tau proportional, variant eta behavior was verified for dielectric data, while a fractional power law of viscosity tau proportional, variant eta(0.89) was obtained for light-scattering relaxation times, extending over more than seven decades in viscosity and time. This deviation of light scattering from viscosity data could be interpreted in terms of cooperative motion in the supercooled liquid with a characteristic length xi(a) proportional, variant(T-T0)(-v) where T(0)=229 K is the Vogel temperature and v is close to 2 / 3 which is consistent with the prediction of the fluctuation theory of glass transition.

Mixing or blending of polymers is one of the most important processes in plastics technology. In this way it is possible, as has been found in various investigations (e.g., 1), to obtain materials characterized by properties which are not only highly desirable in many ways, permitting a wide range of applicability of the products, but also significantly different from the components making up the blend. I t is generally known that properties of polyblends depend not only on the kind and weight ratio of the blended polymers but also on the phase structure of the blend, the latter being determined by the parameters of the blending process. The phase structure of the blends can be well defined only in two extreme cases: when the polymers are completely miscible and form a single phase and when they are completely immiscible and form a two-phase system, where the phase structure corresponds to the componential structure of the blend. So far, however, the picture of phase structure of the blends of partly miscible pol2Tners is not completely clear. In earlier studies of blend polymer blending in our laboratories, polypropylene (PP) and polyethylene (PE) were selected as a pair of polymers generally held to be incompatible (2). However, in a recent paper concerned with blends of the same polymers, we have suggested the possibility of interdiffusion of the two components in the melt. In other words, these two polymers may in fact be at least partially miscible. The adoption of the hypothesis of polymer diffusion in the melt enabled us to interpret the phenomena observed during the crystalization of the polymer blends under investigation. The aim of the present study is to examine the phenomena taking place on the border between the components and to furnish confirmation of the previously adopted hypothesis.

Purpose To measure the endotoxin concentration (EC) of 25 commercially available, hyaluronic acid- and hydroxypropylmethylcellulose-based (HPMC) ophthalmic viscosurgical devices (OVDs). Methods The in vitro Limulus amebocyte lysate (LAL) assay, which indicates the presence of endotoxins originating from gram-negative bacteria, was used to determine the EC. The procedure was performed according to the European Pharmacopoeia/USP. EC including duplicate determinations, negative controls, dilution series with control standard endotoxin, dilution series with sample extract and positive sample control. Results 16 OVDs (Amvisc®, Amvisc® Plus, Biolon®, Coatel®, Healon®, Healon® GV, Healon®5, HPMC Ophtal® L, Microvisc®, Microvisc® Plus, Ocucoat®, Provisc®, Rayvisc®, Viscoat®, Visco Shield® 2%, Visko® 1.4%) had an EC under 1.2 endotoxin units/mL, five (Adatocel®, HPMC Ophtal® H, LA Gel®, Viscorneal®, Viscorneal® Plus) had an EC ≥ 1.2 and ≤ 24 EU/ml, and four (Biocorneal®, Dispasan® also named Ophthalin, Dispasan® Plus, Visko® 1%) had an EC of > 24 EU/ml. Discussion To avoid viscoelastic-related inflammatory or immunological reactions, the use of pure OVDs is recommended, especially for surgical procedures with an inherent possibility of leaving viscoelastic remnants in the eye (e.g., cataract surgery, viscocanalostomy or penetrating keratoplasty).

X ABSTRACT: Monte Carlo simulations, using the cooperative motion algorithm (CMA), have been employed to investigate the statics and dynamics of both symmetric and asymmetric diblock copolymer melts near the order-disorder transition. Investigation of the static properties has revealed the existence of two characteristic temperatures in the system: the ODT expressed as a peak in the heat capacity and a higher temperature T1 at the crossover between the homogeneous state and the state with considerably increased concentration fluctuations. As T1 is crossed, the increased amplitude of concentration fluctuations is accompanied by a significant increase of the average end-to-end distance of chains and the local chain orientation correlation. The dynamic properties of these systems have been observed by means of the relaxation of the single-bond, the chain end-to-end vector, and the block end-to-end vector, as well as by the single point concentration autocorrelation function. Corresponding relaxation times have been determined as a function of temperature. Below the ODT, a splitting of both the chain and the block end-to-end vector orientation correlation function is observed, while the relaxation of composition fluctuations becomes slower than that of the block orientation. The slow process is attributed to the conformal relaxation of the coherent interfaces formed in the ordered state.

Conducting in situ composites made by two-step reticulate doping of polymers with ET polyiodides show several exceptional characteristics like high conductivity at low dopant amount, transparency and easiness of production in a form of large-area, flexible films. The most interesting finding is that the ET polyiodides forming the crystalline network can be transformed into the superconducting β-phase of ET 2 I 3 , yielding polymer composites showing the transitions to superconducting state at low temperatures. Systematic studies on the phase structure of the as-obtained films and on conditions controlling the transformation into the superconducting form were performed allowing optimization of the key parameters like composition, temperature, time and atmosphere of annealing.