Iranian Polymer Journal
Year:2006 | Volume:15 | Issue:7 (73)|Papers Count:6

This paper deals with preparation of PE clay nanocomposite specimen for transmission electron microscopy (TEM) and studying the difference between dispersion of clay in low density polyethylene using poly(hydrogen methyl siloxane) (PHMS) as coupling agent and untreated one. Argon ion milling is the conventional means by which film sections are thinned to electron transparency for TEM analysis, but this technique exhibits significant problems. In particular, selective thinning and imaging of sub-micrometer inclusions during sample milling are highly problematic. We have achieved successful results using the focused ion beam (FIB) lift-out technique, which utilizes a 30 kV Ga+ ion beam to extract electron transparent specimens with nanometer scale precision. Using this procedure, we have prepared a number of thin film materials representing a range of structures and compositions for TEM analysis. We believe that FIB milling will create major new opportunities in the field of thin film nanocomposite materials microanalysis. FIB Cutting technique has been successfully applied to prepare TEM specimens of nano-sized clay in low density polyethylene film. In order to see the effect of dispersion and adhesion of clay to matrix using coupling agent a series of PE clay nanocomposite containing clay encapsulated by PHMS, untreated clay were prepared by melt blending. The effects of coating on clays and dispersion of clay in low density polyethylene were studied by TEM.

4,4'-Hexafluoroisopropylidene-2,2'-bis-(phthalic acid anhydride) (1) was reacted with L-isoleucine (2) in acetic acid and the resulting N,N'-(4,4'-Hexafluoroisopropylidendiphthaloyl)- bis-L-isoleucine (3) was obtained in high yield. The direct polycondensation reaction of this diacid with several aromatic diols such as bisphenol A (4a), phenolphthalein (4b), 1,4-dihydroxybenzene (4c), 4,4'-dihydroxydiphenyl sulphide (4d), bisphenyl-2,2'-diol (4e) and 4,4'-dihydroxydiphenyl sulphone (4f) and 2,6 dihydroxy toluene (4g) was carried out in a system of tosyl chloride (TsCl), pyridine (Py) and N,N-dimethylformamide (DMF). The reactions with TsCl were significantly promoted by controlling alcoholysis with diols in the presence of the catalytic amounts of DMF to give a series of optically active poly(ester-imide)s (PEI)s with good yield and moderate to high inherent viscosity ranging 0.35-0.66 dL/g. The polycondensation reactions were significantly affected by the amounts of DMF, molar concentration of monomers, TsCl and Py, aging time, temperature and the reaction time. Some of the above polymers were fully characterized by 1H NMR, FTIR, elemental analysis and specific rotation. Some structural characterization and physical properties of these optically active PEIs are reported.

Microcellular foams are foamed plastics characterized by a cell density typically greater than 109 cells/cm3 and cell sizes on the order of 10 μm. As the blowing agent, an inert gas such as CO2 or N2 is usually used. Because of very tiny cells, these foams exhibit improved mechanical and physical properties, for instance, strength-to-density, toughness, thermal and electrical properties are highly improved. In this paper, structural and mechanical properties of microcellular foams of ABS and its composites (glass fibre and mineral filled) are studied and compared. Gas absorption, gas desorption, density, size and number of microcells, and most importantly, ultimate tensile strength and ultimate strain are compared. The results show that a sound microcellular structure and a high strength-to-density can be obtained by regulating temperature and time at the vicinity of glass transition temperature. The results also revealed that although mechanical properties are improved, the enhancement is not as it has been widely asserted.

Gas phase copolymerization of ethylene/1-butene was performed in a semibatch reactor using MgCl2 supported Ziegler-Natta catalyst. Prepolymerized catalysts with different Al/Ti ratios were prepared by slurry polymerization of ethylene and the resulting polymers were dried in-situ. DSC and FTIR were used to identify 1-butene incorporation in the copolymerization. DSC Measurements showed that by copolymerization of ethylene with 1-butene, Tm and the crystallinity decrease. This decrease is more pronounced in lower Al/Ti ratios. By increasing Al/Ti ratio, the crystallinity of copolymers increases. FTIR showed that with introducing 1-butene in the polymerization and formation of ethylene/1-butene copolymer, the A1378/A1368 ratio increases considerably. Polymerization rates were affected by Al/Ti ratio showing two regions of different slopes. The slopes in the first region in the polymerization rate curves are similar while the slopes in the second region vary depending on the Al/Ti ratio. The decay constant (kd) of catalyst deactivation was calculated and it was concluded that Al/Ti with value of 8 has a lower kd indicating lesser temperature variation during polymerization which is probably preferred in industrial production of ethylene- 1-butene copolymers.

Aredox system of potassium diperiodatocuprate (III) (DPC)/poly(diethylene glycol phthalic anhydride) (PPAG) was employed to initiate block copolymers of methyl acrylate (MA) and PPAG in alkaline medium. Block copolymers with high total conversion were obtained, which indicated that potassium diperiodatocuprate (III)/poly(diethylene glycol phthalic anhydride) redox pair is an efficient initiator for this blocking. The kinetics of block copolymerization and total conversion at different conditions (concentration of reactants, temperature, and concentration of potassium diperiodatocuprate (III), reaction time) were investigated. The results indicated that the best reaction conditions were as follows: reaction time=40 min, reaction temperature =35ºC, concentration of potassium diperiodatocuprate (III)=3.12×10-3 mol/L and the reactants concentration=2.45 mol/L, and the equation of the polymerization rate (Rp) was as follows: Rp=k[methyl acrylate]1.63[potassium diperiodatocuprate (III)/ poly(diethylene glycol phthalic anhydride)]0.67, that the overall activation energy of block polymerization was 44.57 kJ/mol. 1H NMR Spectral analysis and infrared spectra proved that the block copolymers were synthesized successfully, and the molecular weight of the block copolymer was obtained to be 33,000. SEM Micrographs show that there are some interstices and two distinct phases in PMMA-nylon 6 (A), and on the contrary, the interstices and two phases have disappeared in PMMA-block copolymer- nylon 6 (B). The above features suggest that the block copolymer showed greatly improved compatibility of the components between PMMA and nylon 6.

This review covers the current status of living free radical polymerization (LFRP) methods and assesses recent advances made especially in the recently years. Three LFRP methods, nitroxide mediated polymerization (NMP), atom transfer radical polymerization (ATRP), and reversible-addition fragmentation chain transfer (RAFT), are described and the validity of each method is compared on the basis of the range of polymerizable monomers, reaction conditions, and the ease of chain end group transformation. Living radical graft polymerization of monomers such as styrene onto SBR, ABS, PVC and polystyrene formed by NMP and ATRP will be discussed. Also, the synthesis of block, graft, and hyperbranched copolymers by NMP is covered. Studies using ATRP to synthesize block copolymers, bottle brush copolymers, and hydrogels are assessed. Also, the synthesis of star copolymers with alternating hydrophobic and hydrophilic arms is described. For RAFT, the utility of difunctionalized initiators and trithiocarbonates as RAFT agents for ABA block copolymer formation are described.