Catalytic action of calcium acetate and the manganese acetate–sodium acetate mixture in the pre-esterification of dimethyl terephthalate with ethylene glycol

Products of pre-esterification of dimethyl terephthalate with ethylene glycol at various times carried out with two catalysts, i.e., calcium acetate and a mixture of manganese and sodium acetates, were studied. Thin-layer chromatography was used to follow the fundamental reaction and determine the type and degree of oligomerization. It was established that the manganese–sodium acetate mixed catalyst is more efficient both with regard to pre-esterification and oligomerization.     

Ageing of Conductive Polyaniline/Poly(Ethylene-co-Vinylacetate) Composites Studied by Thermal Methods

The long-term environmental ageing of conductive composite films containing ethylene-co-vinyl-acetate (EVA) copolymer and a complex of polyaniline (PANI) and dodecylbenzenesulfonic acid (DBSA) was studied by using differential scanning calorimetry (DSC). We assume that both phase separation and crosslinking of PANI main chains occur in the systems. On the other hand, the competition between PANI–DBSA complex self-organization and crystallization of EVA matrix result in structural changes and formation of continuous conductive network, responsible for significantly increased (ca five orders of magnitude) electrical conductivity of the aged films. This revised version was published online in August 2006 with corrections to the Cover Date.     

Electrophysical Properties and Thermal-Deformation Stability of Composites Containing Polyaniline Layers Deposited on Porous Polyethylene Films

The conducting properties of composites prepared by deposition of polyaniline layers on the surface of porous polyethylene films from dispersions and by polymerization in situ were studied.__________Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 3, 2005, pp. 484–489.Original Russian Text Copyright © 2005 by Kuryndin, Mokreva, Terlemezyan, Sidorovich, Praslova, Elyashevich.     

Thermal behavior and characterization of solid-state chlorinated polyethylenes

The melting behavior of solid-state chlorinated polyethylene samples of various average molar mass has been studied by employing the differential scanning calorimetry method. Both the thermal and thermodynamic characteristics of the as-prepared chlorinated powdery polymer samples were found to be essentially different, compared to those of the melt-crystallized ones. The changes in the corresponding values depended mainly on the content of the comonomer units such as chloromethylene and dichloromethylene groups and their distribution along the polymer chains. Therefore, it can be assumed that the order of the polymer crystals arrangement is disturbed in the course of both the chlorination process and the subsequent melt crystallization.     

Colloidal aqueous dispersion of polyaniline nanotubes grafted non-covalently with poly(ethylene oxide)-block-poly(acrylic acid) copolymer

Polyaniline (PANI) nanotubes were prepared by oxidative polymerization of aniline in the presence of two structure-directing agents—salicylic acid (SA) and sodium dodecyl sulfate (SDS). When using only SA, mainly aggregated nanotube dendrites or coral-like structures have been obtained. Addition of a very small amount of the surfactant SDS, much less than the critical micelle concentration, results in substantial reduction of the aggregated nanotube morphology on the account of isolated PANI nanotubes, which is the favorable structure from the point of view of further modification. In order to make the isolated nanotubes water dispersible, their surface was modified by complex formation (non-covalent grafting) with hydrophilic poly(ethylene oxide)-block-poly(acrylic acid) copolymer. These water-dispersible PANI nanotubes might be good candidates for some biochemical and biomedical applications.     

Calorimetric investigations of high density polyethylene/polyaniline composites

Summary Electrically conductive composites containing high density polyethylene (HDPE) and polyaniline (PANI) - dodecylbenzenesulfonic acid (DBSA) complex were prepared in situ by bulk oxidative polymerization of aniline (ANI) in presence of DBSA. Their thermal behaviour and crystallinity parameters were studied for the first time by using differential scanning calorimetry (DSC). It was found that the presence of the conductive complex does not affect the crystalline structure of the matrix polymer neither during in situ polymerization of ANI in powdered HDPE nor upon heating of HDPE/PANI·DBSA composite up to 180°C followed by fast cooling.     

Dependence of the conformation of nascent poly(oxymethylene) on the conditions of cationic polymerization of trioxane in solution

The conformational structure of nascent poly(oxymethylene) (POM) obtained by cationic polymerization of trioxane in nitrobenzene was investigated by i.r. spectroscopy. It was found that the conformational order of this POM depends considerably on the conditions of preparation. Under conditions of simultaneous polymerization and crystallization, “A” polymer, with long sequences of monomer units in regular G conformation, is obtained. Under conditions of successive polymerization and crystallization, the formation of conformational defects in the helical POM chains is favoured. Then, depending on the supersaturation, we obtained either (a) POM of “B” form with short sequences of monomer units in G conformation, or (b) POM of a mixed type, the i.r. spectrum being describable as a superposition of “A” and “B” spectra. The results indicate that, at comparatively high catalyst concentration, the thermodynamical approach for regulation of supermolecular structure of polymers can be applied successfully for regulation of the conformational order of nascent POM also. At lower concentration of active centres in the polymerizing system, kinetic factors affect considerably the conformational structure of nascent POM.     

Structural Investigations of Polyaniline Prepared in the Presence of Dodecylbenzenesulfonic Acid

Structural studies of powdered polyaniline (PANI) prepared in aqueous medium by the oxidative polymerization of aniline in the presence of dodecylbenzenesulfonic acid(DBSA) were performed by means of DSC and WAXS. The influence of the alkyl side-chains on the structure and crystallinity of the as-synthesized PANI—DBSA and on the structural transitions taking place in PANI upon washing and heating were investigated. It was found that DBSA induces crystallinity in the rigid matrix of PANI, and residual crystalline phases were also observed after the deprotonation of PANI—DBSA. For the first time, a melting peak and a relaxation transition of non-cross-linked PANI were registered.This revised version was published online in November 2005 with corrections to the Cover Date.