Browse Articles

The paper presents, in a general and sugestive manner, some basic knowledge about nomenclature and concepts usually encontered in the field of liquid crystalline materials (both low molecular compounds and polymers). There are briefly presented: definitions, mesophase types, textures and defects and a short description of liquid crystalline polymers. Keywords: liquid crystalline materials, low molecular compounds, polymers

This paper presents the main aspects of an experimental study concerning the reactions of a bifunctional photostabilizator of benzophenonic type (2,4-dihydroxy-benzophenone) with monoisocyanate (phenylisocyanate) and two diisocyanates (2,4-toluylen diisocyanate and 4,4’-diphenylmethanediisocyanate). The conditions for the synthesis of urethane compounds and alophanat are presented as well as the existing ways (with a support of IR spectroscopy, UV-VIS spectroscopy, HPLC – reverse phase and thermal analyses) of these compounds from the numerous of possible theoretical structures. The study of these reactions is useful for revealing some aspects on the way of binding of photostabilizators of this type in polyurethanes macromolecules. Keywords: photostabilizators, isocyanates, urethane compounds, alophanat compounds

Interpenetrating polymer networks (IPNs) are a special type of polymer blends, constituted by combination of two or more network polymers, synthesized in juxtaposition. The synthesized IPNs were carried out in order to improve the material properties of many widely used polymers. Although several papers on IPNs have already described the use of polyurethane (PU) based compositions, the importance of PU-epoxy IPNs needs special emphasis. This paper is a review with some results regarding PU-epoxy IPNs, pointing out own studies on synthesis and characterization of PU-modified epoxy resin semi-IPNs. Keywords: epoxy resins, networks, vinyl ester resins, unsaturated resins, graft, morphology

The paper presents results concerning the synthesis and characterization, as polymer processing aids, plasticizers and/or lubricants, of some diesters of unsymmetrical structure of phtalic anhydride, by taking into account aliphatic alcohols such as C3, C4, C6, C2-6, izo C10 and izo C13, along with complex alcohols of aliphatic-aromatic nature, such as phenoxy-ethanols. Three series of unsymmetrical diesters were performed considering as special alcohols the 2-phenoxyethanol, 2-[(o-sec butyl)phenoxy]ethanol and 2-[(p-nonyl)phenoxy]ethanol, respectively. The variation of the representative plasticizing and/or lubricating properties as a function of both the length of the aliphatic chain introduced by the aliphatic alcohol and the length and position of the alkyl pendant group existent on the aryl ring of the complex alcohol, was studied. Considering these alternatives, it was possible to obtain either plasticizing or lubricating properties as a function of the structural features. Thus, on the basis of the results recorded it was fully proved the valability and the consistency of the polyfunctionality and assimetry principles. Keywords: unsymmetrical phtalic diesters, plasticizers, lubricants, phenoxy-ethanols

The Wittig-Horner reaction is the most general method for regiospecific introduction of carbon-carbon double bounds in organic synthesis. Phase transfer catalyzed reactions are often more easily and cheaply carried out than conventional methods. The paper deals with the synthesis of copolymers functionalized with olefin groups by Wittig-Horner type polymer-analogous reactions in phase transfer catalysis. The copolymer bond aldehyde was reacted with phosphonates to obtain olefin groups grafted on macromolecular support. Keywords: polymer-suported Wittig-Horner reagent, phase transfer catalysed, styrene-divinylbenzene copolymers

In this study, a series of three different thermoplastic poly(ether-urethane-urea)s were synthesized from hexamethylene diisocyanate (HDI), polypropylene glycol (PPG) as macrodiols and hexamethylene diamine (HMDA) as chain extender. The molecular weights of the macrodiols were in the range 400 - 2000 g/mol. The polymers have been characterized by means of 1H-NMR, IR spectroscopy and other techniques. Tensile testing was performed on dumbbell-shaped specimens cut from thin films at room temperature on a TIRAtest 2161 tensile tester (Germany). The hard segment contents were calculated on the basis of urea content, as described by Flory, which represents the best method of the evaluation of the material residing in the hard phases. Keywords: poly(ether-urethane-urea), macrodiols, hard segment contents (HSC)

Segmented poly (ester-urethanes) elastomers based on poly (ethylene diethylene adipate) diols as a soft segment and aromatic diisocyanates in the hard segment were synthesized by a conventional method. The precipitated polyurethane films have been degraded after a limited exposure to reactive agents: 4,4’-methylenebis(phenyl isocyanate) epichlorohydrin and propylene oxide in benzene. The effects on mechanical properties of precipitated polyurethane films were found to be a measure of the degradation due to reactive agents. 4,4’-methylenebis(phenyl isocyanate) and propylene oxide had an increase in the hard segment content which was associated with increased hard domain crystallinity, hardness and improvement in mechanical properties. It is suggested that the superior mechanical performance may be related to interconnecting hard domain texture by cross-linking process. Theis study attempts to correlate the mechanical properties of the precipitated polyurethane films with the nature of the reactive agents. In all cases, the effect of reactive agents was to increase the ultimate tensile strain, except epichlorohydrin. Keywords: poly (ester urethanes) films, reactive agents, mechanical properties

The paper presents two plastic materials from epoxidic resins and compounded polymers families which have properties to visualize stress field produced by mechanical loadings. Using these properties two experimental techniques, photoelasticity and cromoplasticity, were developed for mechanical behaviour investigation of engineering structures. To illustrate the potential of these experimental techniques, in the paper are presented results of a combined analysis undertaken on the state stress in the fastening elements of a hidroagregate, loaded both in elastic and elastoplastic field. Keywords: epoxidic resins, compounded polymers, photoelasticity, cromoplasticity

A series of five new aromatic polyhydrazides containing pendent acetyloxybenzamide groups has been synthesized by low-temperature solution polycondensation of 5-(4-acetyloxybenzamido)-isophthaloyl chloride with dihydrazides of terephthalic, isophthalic, 2,5- or 2,6-pyridin dicarboxylic acids, or with p-aminobenzhydrazide in N-methyl-2-pyrrolidinone (NMP). These polyhydrazides were gradually thermally treated up to 280°C in order to be converted in corresponding poly(1,3,4-oxadiazole)s. The inherent viscosity of polyhydrazides is in the range of 0.31-0.69 dL/g. The polymer structures were confirmed by infrared spectra. The polymers were characterized from solubility and thermal properties point of view. Keywords: polyhydrazides, poly(1,3,4-oxadiazole)s, 5-(4-acetyloxybenzamido) group, thermal stability

Hyperbranched poly (e-caprolactone) copolyesters (hb-PCL) have been prepared by combination of ring opening polymerization (ROP) of e-caprolactone (e-CL) as cyclic AB monomer and concurrent polyconden­sation of 2,2´-bis(hydroxymethyl)butyric acid (BHB) as branching AB2 comonomer unit, using a supported lipase (Candida Antarctica Lipase B, CALB; Novozym 435) as catalyst. By systematic variation of the BHB fraction, hyperbranched copolyester samples with systematically varied degrees of branching (DB) have been obtained. 1H-NMR and 13C-NMR spectra provided detailed information on the DBs. Molecular weights for the hb-PCLs were determined by means of SEC and VPO and exhibited a decreasing tendency with increasing fraction of branching comonomer. Thermal properties of the hb-PCL samples were investigated with respect to the DB. As expected, Tm and DHm were found to decrease with increasing content of BHB (DSC). The crystalline morphology of the samples was investigated by WAXS, revealing the DB-dependent existence of two crystalline polymorphs with different density and chain packing. Light microscopy studies demonstrated both a different crystal habitus for the hyperbranched copolymers, as well as a decrease of the crystalline fraction for the hb-PCL samples in comparison to the linear analogue. With increasing DB, the crystallites became small and irregularly shaped, indicating phase segregation in crystallizable and non-crystallizable material during crystallization. Solution viscosimetry showed low specific and intrinsic viscosity for the branched materials and demonstrated that the hyperbranched samples assume an increasingly compact solution structure with increasing extent of branching. For both CHCl3 and THF solutions, an increase of the temperature from 20 to 50oC results in a decrease of [h] for all analyzed hb-PCLs. Keywords: copolyesters, hyperbranched polymers, degree of branching, polymer morphology