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The morphology and thermomechanical properties of well-defined polyethylene-graft-poly(n-butyl acrylate) (PE-g-PBA) copolymers prepared via atom transfer radical polymerization were investigated. Differential scanning calorimetry (DSC), small angle X-ray scattering (SAXS), wide angle X-ray scattering (WAXS), dynamic mechanical measurement and large deformation tensile tests were performed on the graft copolymers and the results were compared with the behavior of the polyethylene macroinitiator. The existence of both crystalline polyethylene segments and amorphous poly(n-butyl acrylate) segments in the copolymers leads to microphase separation and unique thermomechanical behavior. Strong microphase separation was observed by DSC and X-ray diffraction studies. Correlation of morphology and thermomechanical properties was also studied using dynamic mechanical measurement and large deformation tensile tests.

New aromatic poly(ether-ketone)s containing hexafluoroisopropylidene groups have been prepared by aromatic nucleophylic displacement reaction of the potassium salts of aromatic dihydroxy compounds containing fluoren, 1,3,4-oxadiazole or phenylquinoxaline rings with 2,2-bis[4-(4-fluorobenzoylphenyl)hexafluoropropane. These polymers were readily soluble in various organic solvents such as N,N-dimethylformamide, pyridine, tetrahydrofuran and chloroform and gave flexible films by casting such solutions. Their glass transition temperatures (Tg) were in the range of 189–222°C and they were thermally stable up to 480°C. The polymer films displayed low dielectric constants, in the range of 2.8 – 3.2, and good mecanical properties, with tensile strength in the range of 46 – 61 MPa and elastic modulus of 1.4 – 1.6 GPa.

Photon correlation spectroscopy in the polarized geometry has been used to systematically investigate the complex dynamics of a highly concentrated entangled polymer solution in a nominally good solvent, poly(butylacrylate) in dioxane. In addition to the well known fast cooperative diffusion process, a slow virtuallyq-independent mode is detected, whereq is the scattering wavevector, in agreement with previous experimental works on semidilute solutions. This mode is attributed to the viscoelastic nature of the transient physical network, formed by the entanglements, which relaxes its elastic stress induced by the concentration fluctuations, as confirmed by small amplitude oscillatory shear measurements; the latter reveal a terminal relaxation time comparable to the characteristic time of the slow relaxation process. Results, especially in terms of concentration and temperature dependence, are evaluated and discussed in view of the existing theoretical treatments in the field, predicting the existence of the slow viscoelastic relaxation. The relationship between dynamic light scattering and mechanical spectroscopy is established.

Correlation of molecular details with macroscopic properties of complex polymer systems requires application of various simulation methods corresponding to various size scales. Two problems related to simulations on the mesoscopic size scale are discussed. The first one concerns the mechanism of molecular rearrangements in coarse-grained molecular simulations and the second one concerns numerical renormalization of properties on the supramolecular scale, where various properties of microphases organized in various ways over a broad size range contribute to macroscopic properties.

Dynamic behavior of various polymer melts is studied on the basis of a comparison of viscoelastic properties with the information obtained from dielectric spectroscopy. The experimental observations are compared with results of computer simulation of corresponding systems. The studies include simple melts of linear chains, block copolymer systems of miscible components, as well as the behavior of melts with molecular objects of complex topology-like stars or microgels. In the case of polyisoprene linear chain melts an equivalence of terminal relaxation times determined from mechanical and dielectric measurements is demonstrated. Using linear block copolymers of isoprene and butadiene, relaxation times of chain fragments (isoprene blocks) in relation to relaxation times of whole copolymer chains are determined and compared with theory and simulation. Both the experimentally determined block relaxation times and relaxation times of chain fragments in simulated linear chain melts show a disagreement with predictions of the reptation theory. In the case of multiarm star polymers and microgel melts, the slow relaxation modes observed in viscoelastic spectra are assigned to cooperative translational motions detected in corresponding simulated systems in which an ordering of such molecules is demonstrated. This suggests that the terminal relaxation in multiarm star or microgel melts is governed by another relaxation mechanism than in linear chain melts. High efficiency of the Cooperative Motion Algorithm in simulation of dense systems of complex molecules is demonstrated.

Dielectric spectroscopy (10−1 Hz to 107 Hz) has been employed to study the molecular dynamics of a series of cyclic and linear polydimethylsiloxanes (PDMS) of various molecular weights ranging from 300 to 10 000 g/mol in the temperature range above the glass transition (from 130 K to 190 K). The observed α-relaxation depends strongly on both molecular weight and structure of the samples. For linear PDMS oligomers, the α-relaxation shifts towards lower temperatures with decreasing molecular weight in good accordance with the Fox-Flory-model. Cyclic PDMS reveals a qualitatively different molecular weight dependence: for a given temperature the α-relaxation time increases with decreasing ring length, but has a maximum for small oligomers (degree of polymerizationn≈6). The shape of relaxation curves and, with it, the relaxation time distribution is independent from length and architecture of the chains The observed experimental findings are in qualitative agreement with dynamic Monte-Carlo simulations.

A new model for molecular rearrangements in liquids is proposed. The liquids are regarded as dense ensembles of vibrating molecules satisfying the excluded volume condition. A continuity condition is applied on the molecular scale of such systems and is regarded as controlling rearrangements leading to translations of molecules beyond the range of their vibration amplitude. It results in cooperative rearrangements which are considered as taking place in systems with fluctuating density. Rates of rearrangements are considered as being controlled by thermal activation with activation energy barriers dependent on local density. Various dependencies of the activation energy barriers on local density are examined. It is shown, that the model is able to reproduce the extremal cases of temperature dependencies of relaxation times represented on one edge by the Arrhenius relation and on the other edge by the Vogel-Fulcher-Tamman relation. The model can, however, provide a broad spectrum of other dependencies filling the gap between these extremes. All cases are based on the uniform microscopic picture of cooperative molecular rearrangements resulting from system continuity. The model is implemented as a simulation algorithm (Dynamic Lattice Liquid - DLL algorithm) which is used to simulate dynamic properties of liquids and polymer melts. Simulation results obtained for polymers are compared with experimental results obtained by means of the dynamic mechanical measurements on polyisobutylene samples with various molecular weights.

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.

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.

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.