Acta Polymerica最新文献

Comb-like polymers (CP) based on modified alternating methyl vinyl ether/maleic anhydride copolymer with oligo-oxyethylene side chains of the type O(CH₂CH₂O)_nCH₃ have been synthesized and characterized, and complexed with LiNO₃ to form an amorphous polymer electrolyte. CP/salt complexes showed conductivity up to 10⁻⁵ S/cm at room temperature. The temperature dependence of ionic conductivity suggests that the ion transport is controlled by segmental motion of the polymer, shown by linear curves obtained in Vogel–Trammann–Fulcher plots. The ionic conductivity maximum moves to a higher salt concentration as the temperature increases. IR results also indicate that the ester in CP might decompose at 140°C and reproduce the maleic anhydride ring.

The evidence for biphasic morphology in lightly sulfonated polystyrene (PS-SSA) ionomers neutralized by bifunctional organic cations (namely, 1,6-hexanediamine or HDA) is established by comparing their dynamic mechanical behavior, as a function of ion content and degree of neutralization, with that for metal-neutralized biphasic ionomers. The trends as a function of ion content regarding the transition temperatures and intensities of the HDA-neutralized ionomers parallel what is observed for metal-neutralized ionomers, in particular polystyrene-based ones. A small-angle X-ray scattering peak, identified as an “ionomer peak”, is observed in the PS-SSA-HDA ionomer of the highest ion content studied. Furthermore, it was observed that partial neutralization affects the cluster phase more strongly than the matrix phase. This can be explained by the contribution of the acid groups to the matrix T_g, and their ability, when present in large amounts, to affect the ionic interaction strength or facilitate ion hopping, which influences primarily the cluster T_g.

Topological considerations concerning the ratio of linear, imperfectly branched, dendritic and terminal units in hyperbranched polymers based on AB₂, AB₃ and AB_m (m≥2) type monomers are summarized. The reaction of AB₂ monomers with a core molecule of the structure B_f is also treated. For larger hyperbranched polymers based on AB₂ monomers the fraction of terminal units has to be equal to the number of dendritic units. A general expression for the degree of branching (DB) is derived for AB₂ systems, which is based on the number of dendritic and linear units. The expression is valid for low molecular weight as well as high molecular weight hyperbranched polymers in contrast to the commonly used expression based on dendritic, linear and terminal units. DB may not exceed 0.5 in hyperbranched polymers based on AB₂ systems (0.44 in AB₃ systems). Furthermore, a general expression for DB in hyperbranched polymers based on AB_m monomers is derived. Consequences for signal ratios in NMR-spectra of hyperbranched polymers are discussed. The expressions presented allow verification of NMR-integration ratios obtained experimentally on the basis of model compounds.

The X-ray long periods from high molecular weight injection molded polyethylene (PE) with a shish-kebab structure have been compared with values derived from electron micrographs. It is shown that while small angle X-ray scattering (SAXS) presents two long periods, the direct measurements from transmission electron microscopy (TEM) furnish only the lower SAXS periodicity. In an attempt to clarify this discrepancy of results, laser light diffraction and Fourier transformation of electron micrographs have been undertaken. Using this method two long periods are found in all regions investigated. Results are discussed in terms of the role played by the structured or “weakly crystalline” interlamellar parts, containing a lower electron density, which are neglected by the small angle scattering of X-rays and which give rise in particular regions to larger scattering periodicities.

This paper describes the preparation of new alkynes bearing furanic substituents and their polymerization by catalytic systems based on transition metal halides in order to obtain novel materials with original properties because of the presence of both furan moieties and alternate single and double bonds. However, difficulties arising from the specific reactivity of the heterocycle in our experimental conditions led us to envisage an indirect way to obtain well-defined products, using an aromatic polymer as the precursor.

A critical overview of different synthetic approaches to poly(p-xylylene)s (PPXs) is coupled with perspectives on particular structure–property relationships and challenging applications. An attempt is made to emphasize the potential of different synthetic approaches to PPXs focused on different applications. Additionally, the synthesis and polymer analogous reactions of PPXs without leaving groups and functionalized PPXs (with leaving groups in the a-position) serving as processable precursors for non-processable polymers are evaluated.

The viscoelastic properties of fourteen syndio- and isotactic polypropylenes (PPs) were measured in the molten state at several temperatures by means of oscillatory rheometry. Metallocene catalysis allows the control of molecular mass of both PP families and provides narrow molecular mass distributions (MMD) with a polydispersity of about 2. The validity of the Arrhenius and WLF equations for PP was checked. Syndio- and isotactic PP follow Arrhenius behavior but exhibit different activation energies of flow. From the dynamic shear moduli, viscoelastic parameters were determined and correlated with molecular mass. The dependence of the zero shear viscosity on the weight average molar mass exhibits the well-known scaling relation. Stereoregularity has an important effect on the viscoelestic behavior of PP melts.

A bipolar membrane (BM) is a layered structure composed of one cation and one anion ion-exchange layers joined together in series. Polymer BMs offer promising applications for many industrial processes (e. g., the use of bipolar electrodialysis for environmentally clean technologies and the treatment of salt-water effluents) because of their unique electrochemical properties. The most important of these properties is the electric field enhanced (EFE) water dissociation which arises when an electric current is forced through the membrane. This phenomenon occurs at the bipolar junction of the BM, and its coupling with ion transport, though still poorly understood, is the basis of most of the potential applications of BMs. In this review, we will focus on recent work concerning the physical chemistry of BMs and give a general overview of their electrochemical properties, emphasizing both theoretical and experimental aspects. We will model first the electric double layer at the bipolar junction between the two ion-exchange layers, and describe then the EFE water dissociation occurring in this junction. Later, we will present in detail a complete theoretical model for the coupling of ion transport and water dissociation in BMs, and show that this model is able to explain the experimental trends observed in the electrochemical characterization of polymer BMs by means of membrane potential, current–voltage curve, and impedance measurements.

Samples of alkyloxy derivatives of phthalocyaninato-poly(siloxane) (PCPS) with various patterns of substitution were prepared by solution casting. After this history of treatment they form lyotropic hexagonal columnar mesophases. Textures and defects were analyzed in the “frozen” state (with the solvent evaporated) by optical and electron microscopy. With the exception of the space occupied by a single molecule, significant differences of the behavior in the liquid crystalline state were not found among the PCPS derivatives. The side chains of the samples under investigation are too short to be ordered but in the frozen liquid crystalline state the main chains are in register. Both optical and electron microscopy provide evidence for undulations of the molecular trajectories with preferential orientation. Defects typical of hexagonal columnar phases, e.g. walls of various origin and developable domains, where observed. Together with the undulations, transversal edge dislocations occur, as can be demonstrated by high resolution electron microscopy. Inserted lattice half-planes enable the system to minimize the elastic energy of the highly persistent molecules in the bent director field.

The size of glass transition cooperativity for 11 polymers and glycerol is determined from heat capacity spectroscopy (HCS) and differential scanning calorimetry (DSC) by using a calorimetric fluctuation formula. The data cover in total the 0.25 ≤ x ≤ 0.95 part of the reduced temperature interval between the Vogel temperature and a cooperativity onset temperature. A steep cooperativity increase at lower temperature is observed. The data are consistent with the hypothesis that the temperature dependence can be described by the enlargement of a minimal cooperativity at the onset.