Acta Polymerica最新文献

Under the conditions of “normal growth” on rough surfaces, crystallization rates follow from the balance between the attachment and detachment of the chain sequences building up the layer-like crystallites. In the proposed model, detachment rates are related to the change in the mean-field potentials experienced in the crystal and the melt; attachment rates are associated with the population number of straight sequences in the melt. Both rates show an exponential dependence on the sequence length. Combination of this picture with the basic kinetic criterion that the crystallite thickness found at a chosen crystallization temperature maximizes the growth rate yields equations that agree with the general observations. A detailed check of the model predictions is carried out in a discussion of data recently obtained for syndiotactic polypropylene. Attachment rates calculated using an RIS treatment are in fair agreement with those derived from the experimental data on the basis of the model.

We have determined by forced Rayleigh scattering the diffusion coefficients of photo-labeled polystyrene micronetwork spheres (radii ≤ 10 nm) in melts of linear polyvinylmethylether (M_w ≤ 40 000 g/mol) at temperatures of 20−80°C. An expected slippage of the spheres through the meshes of the entanglement network appears possible but is still within the experimental uncertainty of our results.

The interest in block copolymers containing liquid crystalline (LC) segments is due to the resulting interplay between mesophase formation and the microphase structure which creates opportunities in tailoring their nanostructure. This review summarizes recent literature reporting LC-coil block copolymers with well controlled microphase morphologies produced using living methods. Developing applications are also described and include LC displays and low energy surfaces.

Negative thixotropic behavior in aqueous glycerol solutions of partially hydrolyzed polyacrylamide was studied at various concentrations of Na⁺, Ca²⁺ and Al³⁺ chlorides. A decrease in critical shear stresses and more intensive negative thixotropic behavior observed in the presence of multivalent cations were explained in terms of their stronger charge screening effect. This effect suppresses intermolecular electrostatic repulsions, which act against association of polymer molecules and, thus, against the occurrence of negative thixotropy.

The individual impact of different degradation mechanisms occurring during composting on the degradation of poly(3-hydroxybutyrate-co-6%-3-hydroxyvalerate) [poly(3HB-co-6%-3HV)] have been assessed in simulated tests. Biotic hydrolysis with Aspergillus fumigatus had the largest impact on the breakdown of poly(3HB-co-6%-3HV) during composting conditions, with small changes in molecular weight and large weight loss. The major degradation products in the biotic environment were 3-hydroxy butyric acid and 3-hydroxy valeric acid. Abiotic hydrolysis during composting conditions (sterile water pH 7 at 60°C) has minor or no effect during such short times as 21 days. During abiotic hydrolysis both monomers and dimers were idientified while the abiotic thermo-oxidation of poly(3HB-co-6%-3HV) showed no degradation at all. The quantitation of degradation products and copolymer composition analysis by ¹H NMR indicate that the abiotic hydrolysis is not random. Crotonic and 2-pentenoic acid which is produced at 100°C in air was not produced at 60°C during 298 days. We propose that this temperature is too low to promote the well-known six-member transition that produces crotonic acid, 2-pentenoic acid and oligomers with crotonyl or pentenoyl end groups.

Surface eruptions that are approximately 0.5 μm in diameter at the base and about 700 Å in height have been observed by atomic force microscopy on single crystals and films of polydiacetylenes of the alkylurethanes of 5,7-dodecadiyn-1,12-diol when the polymerization is performed using ⁶⁰Co gamma radiation in the presence of air. The eruption process is associated with monomer polymerization and is anisotropic, as the eruptions are found only on the (100) face of single crystal specimens. Crystals having surface eruptions are irreversibly converted from blue to red at room temperature on exposure to a single pulse of 532 nm laser light while crystals lacking eruptions do not undergo this change.

This article summarizes rheological features of moderately concentrated, diblock copolymer micellar solutions in selective solvents. In solvents of monomeric sizes, spherical micelles (with glassy cores) are arranged on cubic lattices to exhibit elasto-plastic responses. These lattices are formed due to an osmotic constraint for the conformation of solvated corona blocks of the micelles. In polymeric solvents (homopolymers) chemically identical to the corona blocks, this constraint is screened and the micelles are randomly dispersed in the systems. In this type of blends (micellar dispersions) in short, nonentangling matrices the micelles have no plasticity but exhibit two-step viscoelastic relaxation: The fast relaxation process corresponds to relaxation of individual corona blocks while the slow process is attributable to diffusion of the micelles. Corresponding to these molecular mechanisms, the fast process exhibits modest damping of the nonlinear relaxation modulus against large step strains while the slow process exhibits much stronger damping. Under steady flow, the micellar dispersion exhibits two-step shear-thinning with the molecular origin identical to that for the nonlinear damping. All these rheological features of the micellar lattices and dispersions are strikingly similar, in many aspects, to the features of colloidal crystals and hard-sphere suspensions of solid particles.

The vinylic polymerization of 5-norbornene-2-carboxylic esters with different palladium catalysts to polymers of high molecular weights is reported. Computer simulations based on a force field approach show that these polymers display a rigid statistical chain conformation and are thus a further example of rotationally strongly constrained polymers. The polymers are soluble in a variety of solvents despite their rigidity, they are amorphous, possess glass transition temperatures well above 250°C, and have a high packing density. The dipoles located in the lateral groups perform a secondary relaxation process similar to the case of flexible or rigid rod-like polymers containing ester groups.

This paper reviews electrospray ionization mass spectrometry (ESI-MS) as an analytical tool for the investigation of non-biological materials. The fundamentals of the method are briefly described and principles of the interpretation of ESI mass spectra are explained. Differences in comparison to biochemical applications of ESI-MS are discussed. Selected examples show how ESI-MS can be used for the investigation of synthetic monomers, oligomers, and polymers, especially in cases where other analytical methods fail.

The morphology and electron diffraction patterns of sheared films of a series of aliphatic-aromatic poly(azomethine ethers) with n = 1,4 and 7–10 CH₂ units in the aliphatic segment have been characterized by transmission electron microscopy. The films were prepared by shearing in the liquid crystalline (nematic) state. In all cases, lamellae ca. 400 Å thick and more or less perpendicular to the shear direction and perpendicular to the substrate were obtained. Annealing increases the lamellar thickness and overall order. Redrawing of annealed, sheared samples of n = 10 suggests they consist of chain folded lamellae. Electron diffraction (ED) yielded h0l single crystal patterns in all cases, except for n = 1, which yielded orthorhombic, fiber-like patterns. The h0l patterns suggest a planar, single crystal orientation over the entire sample. Annealing sheared samples above the crystal-liquid crystal transition temperature resulted in reorientation of the molecules (from parallel to perpendicular) with respect to the substrate. ED patterns changed accordingly from h0l to hk0. Sheared samples with n = 4 gave both orthorhombic and monoclinic diffraction patterns.