Volume 42, Issue 3

Abstract: The organic coatings made with powder dyes constitute an alternative solution to liquid dyes, for thez ensure a proper equilibrium between performance, price and work protection. Depending on the utilization field, this kind of organic coatings may be realized with different degrees of shine, from dull to glossy. In practice there are preferred the dull coatings because the surface defects of the cover films (needle shots, craters, scratches) are less visible on this type of surfaces. In this paper it was analyzed the possiblity of using as a splice agent a carboxyfunctional polyester and it was emphasized the influence of this splice agent on some characteristics of the epoxy-polyesteric powder dyes of white signal type and of cover films made with them. Keywords:organic coatings, powder dyes, splice agent, cover films

Abstract: In this paper the numerical simulation of the injection moulding of the total hip prosthesis (acetabular) cup made of UHMWE is carried out in order to determine the optimal conditions for injection process parameter. The numerical simulation was performed using finite element Moldflow Plastic Insight software especially designed for injection molding. Keywords: injection moulding, acetabular cup, hip prosthesis, plastic material, finite element

Abstract: This paper describes the general concept on structure – liquid crystalline properties relationship for main chain polymers which contain rigid rod – like mesogens. The influence of the mesogenic group, flexible spacers, molecular weight and molecular weight distribution, and of stereospecifical effects on the nature and stability of the mesophases are discussed. Keywords: chain polymers, mesogenic group, stereospecifical effects

Abstract: Turpentine from pine trees is a renewable source of materials used as feedstock by the chemical industry. The paper presents some ways to use turpentine in the polymer chemistry for preparation of polyterpenes, adhesives, copolymers based on the main components of turpentine, a- and b- pinene respectively, as well as polymeric networks obtained by chemical reactions between turpentine components and a vinyl ester resin. Keywords: turpentine, pinene, polyterpene, copolymerization

Abstract: The Wittig-Horner reaction is one of the most important reactions in organic chemistry for obtaining alkene. Phase transfer catalyzed reactions are often more easily and cheaply carried out than conventional methods. The copolymer functionalized with diethyl or dibutyl phosphonate were reacted with benzalaldehyde or propionaldehyde to give olefin groups grafted on macromolecular support. The reactions were carried out in benzene or dichloromethane. By using benzaldehyde, higher degree of double bond were obtained. Keywords: polymer-suported Wittig-Horner reagent, phase transfer catalysed, styrene-divinylbenzene copolymers

Abstract: This paper deals with the multiobjective optimization problem, applied to the free radical polymerization of styrene. The objectives taken into account and proportionally combined into a scalar objective function are: maximization of the monomer conversion or achievement of a desired value for conversion, minimization of the polydispersity index, minimization of the reaction time, obtaining of a polymer with desired polymerization degree. Using different values of the weights, the objectives which have to be reached and, also, their importance within the polymerization problem are established. The decision variables are the initial concentrations of the two initiators (benzoyl peroxide and tertbutylperbenzoate) and temperature represented by two or three isothermal steps. For solving the optimization problem, several methods are used and compared: sequential quadratic programming, genetic algorithm and a hybrid method obtained by successive use of the two above methods. This last solving alternative improves the results of the optimization procedure. The possibility of changing the weight values of the proposed objectives is a favorable opportunity to consider technological criteria for the optimization problem. Keywords: optimization, free radical polymerization, polydispersity index

Abstract: There were obtained simple thin films of polypyrrole (PPy) and polythiophene (PTh) and double layer films polypyrrole / polythiophene (PPy/PTh) on silicon substrate from deposition in DC plasma reactor. The films obtained were characterized by FT-IR spectroscopy. The influence of thermal treatment on the structure of the films and of interactions at the interface PPy/PTh in 100-400 ºC domain temperatures in argon atmosphere was studied. It was observed that the PPy film processed in plasma is more stable in environmental air that PTh film. It was found that thermal treatment in the range 250-300 ºC in argon atmosphere release interaction between PPy/PTh films. The principal phenomenon observed in the double layer was one of protection of the more reactive PTh film counter oxidation process by coating with PPy layer. Keywords: plasma polymerization, thin films, interfaces phenomena

Abstract: Photochromic compounds are able to change their absorption spectra when exposed to light or dark condition. This process is reversible when the photochromic moieties exist, as usually occurs, in two different forms, whose relative concentration depends on the wavelength of incident light. Polymers with side-chain photochromic groups have recently attracted a great deal of interest because the photoisomerisation of the chromophores can induce reversible variation of the macromolecular structure and hence their physical properties. Keywords: photochromic, polymeric materials

Abstract: The oxidability of low density polyethylene stabilized with several antioxidants was investigated by oxygen uptake. The radiosterilization doses (5, 10 and 20 kGy) were applied for characterization of antioxidant activity of calix[4]arene, Santonox R, Ionox 220, Irganox 1076, Irganox 1081, tri-t-butylphenol and elementary selenium. Their contribution to the radiostability of LDPE is discussed in comparison with control sample. The order of increasing the oxidation induction time was established for depicting the evolution of oxidative degradation in stabilized polyethylene. Keywords: low density polyethylene, stabilization, radiosterilization

Abstract: Controlled/living radical polymerization (CLRP) is a field that has been expanding continuously during the last 15 years, as the method allows for the synthesis of well-defined polymers under mild conditions. Many CLRP systems have been developed, all of them relying on an equilibrium between a minute concentration of radicals and a large amount of dormant species. Among them, atom transfer radical polymerization (ATRP) has evolved as one of the most versatile techniques for the production of well-defined materials. This paper briefly reviews the fundamentals of ATRP, while a future paper will be discussing the applications. Keywords: controlled/living radical polymerization, atom transfer radical polymerization, transition metal catalysis

Abstract: By replacing polystyrene hard blocks with poly-á-methylstyrene ones, the service temperature of thermoplastic elastomers can be considerably enhanced, because the glass transition temperature of the latter is about 170°C. The thermodynamics of polymerization of á-methylstyrene is well-known (ÄH and ÄS are -35.1 kJ.mol-1 and -104 J.mol-1 K-1, respectively) so that the “ceiling” (equilibrium) concentration of AMS at various temperatures may be calculated. The living polymer molecules can attain a state of dynamic chemical equilibrium with the monomer molecules. If the temperature is subsequently raised above the ceiling temperature, the Gibbs free energy again favors the monomer. The higher the á-methylstyrene concentration and the lower the polymerization temperature, the higher is the achievable monomer conversion, but never hundred percent. Using n-butyllithium initiator alone, at low reaction temperature, when the maximum achievable theoretical conversion is the highest, the polymerization of á-methylstyrene occurs very slowly in hydrocarbon reaction media. Sasol Germany GmbH developed a high performance living anionic polymerization active center modifier, the purity of which is in agreement with those imposed by the highly sever conditions imposed by these reactions: 2-(2-ethoxyethoxy)-2-methylpropane. The purpose of this paper is to establish a regression model in order to determine the optimal conditions (temperature, reaction time, active center modifier concentration) of á-methylstyrene anionic polymerization in toluene (melting point – 93°C), initiated by n-butyllithium – 2-(2-ethoxyethoxy)-2-methylpropane system, using the factorial design of experiments. Keywords: polystyrene, poly-á-methylstyrene, n-butyllithium

Abstract: The samples of type EPDM (ethylene-propylene-dienmonomer) rubber and elastoplastic mixtures obtained with either polyethylene or polypropylene in various weight percentages were studied using IR spectroscopy, thermal analysis as well as optical microscopy. The analyses proved the compatibility between EPDM elastomers and investigated plastic materials. The results could be used for choosing the suitable compositions, processing and fields for application of these composites. Keywords: EPDM (ethylene-propylene-dienmonomer) rubber, polyethylene, polypropylene, IR spectroscopy, thermal analysis

Abstract: The possibility of obtaining thermally stable epoxy compositions by modifying composition of epoxy resins at 100-130°C with 6-20 phr 1,1’-(methylene-1,4-phenylene)bismaleimide and using 9-10 phr 4,4’-diaminodiphenylmethane as curing agent was studied. The cure behavior of these systems was studied using differential scanning calorimetry (DSC) and the thermograms indicated a unimodal exothermic peak for blends. The thermal stability as studied by thermogravimetric analysis (TGA) of the cured DGEBA resin was found to improve with polyaminobismaleimide blending. Keywords: epoxy resins, differential scanning calorimetry, polyaminobismaleimide

Abstract: New polyesters with maleimide pendent groups have been synthesized by direct solution polycondensation reaction between 4-42 - dihydroxy- biphenyl and two functional bismaleimides containing carboxylic functionalities. The products were characterized by infrared and proton nuclear magnetic resonance spectroscopy. Thermal properties of the new synthesized copolymers were studied by thermogravimetric analyses and differential scanning calorimetry. Keywords: bismaleimides, polyesters, thermal stability

Abstract: The ways leading to the increase of the flowrate of an extruder of a given geometry are examined, while considering the real situation: screw is rotating and the barrel is stationary; the granules slide onto the surface of the screw; in the granules’ relatively thick layers, relative motion takes place, equivalent to a velocity gradient. Reference was made to the granular material in the feeding zone, to the parameters specific to the feeding zone and their influence on the flowrate, through the values of the friction coefficients onto the barrel and screw (flowrate is proportional with the term , hence an increase in this term in a given case will lead to an increase in the flowrate value). The influence of both the grooves in the feeding zone and of the angle between the direction of movement of the granules and the position of grooves onto the interior surface of the barrel was analysed. There was also considered the posibility of increasing the flowrate through the increase in the bulk density of the granules in the feeding zone, while considering the influence of pressure as well as the ratio between the depth of the screw channel in the feeding zone (adjustable using grooves) and the granules’ diameter. Keywords: extruder floerate, friction coefficient, bulk density, pressure

Abstract: This paper investigates the rheological properties of some o-sec-butyl-phenoxyacetic esters as a function of temperature, shear rate, and type of the polyol used to prepare the ester. The curves viscosity-temperature and viscosity-shear rate in loop tests at 20, 40, 60, 80oC were obtained and interpreted, and the activation energies of viscous flow and the creep curves were determined. Also, physical and phase changes were analyzed using differential scanning calorimetry (DSC) and correlations between the rheological and thermal behavior were established. Keywords: ester, rheology, DSC