All issues / Volume 1 (2007) / Issue 8 (August)
Editorial - invited by Prof. Tibor Czigany, no abstract required
A two-photon absorbing polymer has been prepared through radical copolymerization of methyl acrylate and a synthesized monomer containing a two-photon absorbing chromophore (E,E,E)-1,3,5-tristyrylbenzene (1), under conventional radical polymerization conditions. The synthesized polymer was characterized by nuclear magnetic resonance (NMR), infra-red spectroscopy (IR) and gel permeation chromatography (GPC). The linear and nonlinear optical properties were studied by measurement of UV-Vis absorption, fluorescent emission and two-photon cross-section. This synthetic strategy provided a facile approach for synthesis of photonic materials with adjustable chromophore concentration and high molecular weights.
A novel biopolymer-based composite hydrogel was synthesized through chemical crosslinking by graft copolymerization of partially neutralized acrylic acid onto the carboxymethyl cellulose (CMC). The Taguchi method, a robust experimental design, was employed for the optimization of the synthesis based on the swelling capacity of the hydrogels. This method was applied for the experiments and standard L16 orthogonal array with five factors and four levels. In the synthesis of the composite superabsorbent, N,N'-methylene bisacrylamide (MBA) as crosslinker, ammonium persulfate (APS) as initiator, acrylic acid (AA) as monomer, CMC/Celite weight ratio and neutralization percent (NU) were used as important factors. From the analysis of variance of the test results, the most effective factor controlling equilibrium swelling capacity was obtained and maximum water absorbency of the optimized final product was found to be 310 g/g. The surface morphology of the gel was examined using scanning electron microscopy. Furthermore in this research, swelling capacity of composite SAPs was determined under realistic condition (saline solution absorbency under load).
The chemical modifications of poly (vinyl chloride) with aliphatic and aromatic alcohols compounds have been investigated at room temperature and atmospheric pressure, catalysed by a new green basic catalyst, the Maghnite-K+. The presence of ether groups in the products is proven by infra red spectroscopy (IR) as well as by nuclear magnetic resonance spectroscopy (1H NMR), and characterized by intrinsic viscosity as well as by gel permeation chromatography (GPC).
The high molecular weight biphenyl-based polyarylene ether nitrile copolymers were synthesized by nucleophilic substitution reaction of 2,6-dichlorobenzonitrile (DCBN) with varying molar ratios of 4,4’-dihydroxybiphenyl (BP) and hydroquinone (HQ). The BP content of the copolymers has influence on glass transition temperature (Tg), initial decomposition temperature (Tid), mechanical properties and the crystallinity. All the copolymers could be dissolved in NMP, DMF and DMAc on heating, and were stable up to 450°C with a high char yield above 50% at 800°C in nitrogen atmosphere. The glass transition temperature, the melting temperature and tensile strength of copolymers were found to increase with increase in concentration of the BP units in the polymer. The dynamical viscosity and the storage modulus have been influenced by the BP concentration, frequency, temperature and time. This rheological results show that these copolymers have best thermoplastic processability and stability at 300–400°C.
Industrial low-density polyethylene (LDPE) was aged in stagnant distilled water during one year. Two types of this material were studied. The first one was without additives and the second type was doped with 4% of hindered-amine light stabilizers (HALS). Using X-ray photoelectron spectroscopy (XPS), the evidence that an oxidation occurs was demonstrated for the two types of LDPE (with and without HALS). One objective was to observe the chemical groups resulting of the ageing and to propose a mechanism of hydrolytic degradation for LDPE. The analysis of C1s spectra shows that the main oxidation products are C–O and C=O groups. Unlike the hydrolytic degradation of polypropylene, there is no presence of O=C–O groups, which suggests that there is no oxidative chain scission during hydrolytic ageing of the LDPE. The other objective of the study was to observe if the HALS can have an influence in the hydrolytic ageing of the LDPE. The values of the atomic concentration of the oxygen for the two types of samples show that the HALS could slightly slow down the oxidation of the LDPE.
The novel bisphthalonitrile containing benzoxazine (BPNBZ) has been synthesized using bisphenol-A, 4-aminophenoxylphthalonitrile and paraformaldehyde. The structure of the monomer was supported by FTIR spectroscopy, 1H-NMR, and 13C-NMR spectra, which have exhibited that the reactive benzoxazine ring and cyano groups exist in molecular structure of BPNBZ. The cure reaction of BPNBZ was monitored by the disappearance of the nitrile peak and the tri-substituted benzene ring that is attached with oxazine ring peak at 2231, 951 cm–1. The thermal polymerization of the BPNBZ was studied by differential scanning calorimetry (DSC) and dynamic rheometer. It was shown that the bisphthalonitrile containing benzoxazine had completely cured with two-stage polymerization mechanisms according to oxazine ring-opening and phthalonitrile ring-forming. The thermal decomposition behaviors of the polymer were examined by thermogravimetry analysis (TGA) in nitrogen and in air. The materials achieve char yields above 73% under nitrogen at 800°C and above 78% under air at 600°C, which exhibited the cured resin has good thermal stability and thermo-oxidative stability.
All polypropylene (all-PP) composite laminates with unidirectional (UD) and cross-ply (CP) lay-ups were produced by hot consolidation from oriented coextruded PP tapes (PURE®). The consolidation of the tapes, wound on a steel plate, occurred in autoclave vacuum bag molding. The set processing conditions resulted in all-PP laminates of high rigidity as the PP copolymer surface layers of the tapes were molten and thus forming the matrix, while their PP homopolymer core remained unaffected and thus fulfilled its role as reinforcement. Specimens cut off from the laminates were subjected to dynamic mechanical thermal analysis (DMTA) in a broad temperature range (T = –50…120°C) at various frequencies (f = 10–2…101). For the DMTA results the time-temperature superposition principle was adopted and master curves in the form of storage modulus vs. frequency (f = 10–9…1020) and loss factor vs. frequency were created.
Dicumyl peroxide (DCP)-cured thermoplastic vulcanizates (TPVs) based on blends of maleated ethylene propylene rubber (m-EPM) and polypropylene (PP) using maleated-PP as a compatibilizer have been developed. Physical properties of these TPVs change significantly with concentrations of DCP and rubber/plastic blend ratios. Important correlations were obtained from rheometer delta torque values with various physical properties of the TPVs like tension set and crosslink density etc. Wide angle X-ray diffraction study confirms that concentration of DCP has a strong influence on the crystallinity of PP, which might affect the final physical properties of TPVs. The recyclability and ageing characteristics of these TPVs are also found excellent.
The atom transfer radical polymerization (ATRP) of phenoxycarbonylmethyl methacrylate (PCMMA) with styrene (St) were performed in bulk at 110°C in the presence of ethyl 2-bromoacetate, cuprous(I)bromide (CuBr), and N,N,N’,N”,N”-pentamethyldiethyltriamine. Also, a series conventional free-radical polymerization (CFRP) of PCMMA and styrene were carried out in the presence of 2,2’-azobisisobutyronitrile in 1,4-dioxane solvent at 60°C. The structure of homo and copolymers was characterized by IR, 1H and 13C-NMR techniques. The composition of the copolymers was calculated by 1H-NMR spectra. The average-molecular weight of the copolymers were investigated by Gel Permeation Chromatography (GPC). For copolymerization system, their monomer reactivity ratios were obtained by using both Kelen-Tüdõs and Fineman-Ross equations. Thermal analysis measurements of homo- and copolymers prepared CFRP and ATRP methods were measured by TGA-50 and DSC-50. Blends of poly(PCMMA) and poly(St) obtained via ATRP method have been prepared by casting films from dichlorormethane solution. The blends were characterized by differential scanning calorimetry. The initial decomposition temperatures of the resulting copolymers increased with increasing mole fraction of St.