The preparation of polystyrene/MCM-41 nanocomposites was carried out by grafting from and grafting through approaches and in the presence of unmodified MCM-41, using reversible addition-fragmentation chain transfer (RAFT) polymerization. The MCM-41 was modified by attaching S-dodecyl-S-(,-dimethylacetic acid)trithiocarbonate (DDMAT) as the RAFT agent and methacrylate group using 3-methacryloxypropyldimethylchlorosilane. The kinetics of styrene RAFT polymerization by different approaches was compared with the model polymerization mediated by free DDMAT. The quantity of the grafted chain grown from the surface and inside of the pores of MCM-41 and free polymer chains in bulk was determined by thermogravimetric analysis. The molecular weight of the produced polymer chains increased linearly with the monomer conversion for three methods. The gel permeation chromatography showed that the molecular weight of grafted and free polymer chains in the grafting from approach is higher than other methods, and molecular weight distributions were relatively narrower whereas the rate of polymerization for grafting from was higher. (c) 2013 Wiley Periodicals, Inc. Adv Polym Technol 2013, 32, 21372; View this article online at wileyonlinelibrary.com. DOI 10.1002/adv.21372
Electrospinning is a versatile method for spinning various polymers into nanoscale fibers. Nanofibers produced by electrospinning or other methods show enhanced properties such as high surface area to volume ratio, flexibility in surface functionalities, and mechanical properties. To increase their practical usage and opening new windows for their innovative applications, theses nanofibers can be assembled into an ordered structure like yarn. Besides their intrinsic-based polymer characteristics, these nanofiber yarns have an exceptional high specific surface area as a heritage of their forming nanofibers. This unique property together with the increased number of fibers in an unit area of cross section will improve their some properties such as water and chemical absorbency and flexibility in comparison with conventional yarns. So far, miscellaneous methods are established for fabricating electrospun nanofibers into yarn and the effects of processing factors on the characteristics of produced nanofiber yarns are studied by many researchers. In this review, the achievements in nanofibers bundles and yarn production and different established methods including twisted, hybrid, and core types are discussed. It also reviews the reinforced yarns by carbon nanotubes and the mechanical properties of nanoyarns. (C) 2013 Wiley Periodicals, Inc.
Magnetoelectric polymer nanocomposite is synthesized using conducting polyindole and nano-sized magnetite (Fe3O4) particles through the in situ polymerization method. The effect of nanoparticles content on the polyindole matrix is studied by Fourier transform infrared (FTIR) and ultraviolet (UV) spectroscopy, scanning electron microscopy, X-ray diffraction, differential scanning calorimetry (DSC), and DC conductivity measurements. FTIR and UV spectra of the composite show the intermolecular interaction between the polymer and magnetite nanoparticles. Morphological observation and crystal structure studies reveal that nanoparticles are uniformly dispersed in the polymer with well-shaped spheres, and their average sizes are in the nano region. DSC studies, showing an increase in glass-transition temperature with an increase in the content of Fe3O4, reveal the ordered arrangement of the polymer chain in the nanocomposite than pure polyindole. DC conductivity of the nanocomposites increases with an increase in the content of nanoparticles, and the conductivity of the nanocomposite is higher than that of polyindole. The dependence of magnetization on the applied magnetic field for the nanocomposites is studied using the vibration sample magnetometer technique. It has been found that the saturated magnetism linearly increases with increasing the Fe3O4 content in the polymer composite. (C) 2013 Wiley Periodicals, Inc.
This paper addresses the preparation of polyaniline (PANI) via a rapid mixing method in which a nanosheet (nanoflake) structure was observed by scanning electron microscopy. The microstructures of acid-and ammonia-dedoped PANI samples were studied by Fourier transform infrared spectroscopy. The effects of polymerization conditions (time and temperature of reaction, monomer/oxidant ratio, and acid type) on the polymerization yield, electrical conductivity, and ammonia-sensing performance of PANI-based sensors were investigated using a Taguchi experimental design. It was found that acid type has the most significant effect on polymerization yield and ammonia-sensing property of PANI. The conductivity of PANI films was mostly influenced by reaction time, reaction temperature, and acid type, respectively. Some interesting behaviors were observed for influential factors that have been comprehensively justified. (C) 2013 Wiley Periodicals, Inc.
Nanoporous or mesoporous structures and hence a decrease in dielectric constant can always be induced with the introduction of air into polymeric materials. It is therefore achievable to prepare ultra-large-scale integrated circuit (ULSIC) on ultralow dielectric constant (i.e., low-k) materials. The research on nano/mesoporous polymer based low-k materials, including the past decade advances, the introduction of principles and methods of nano/mesopores, characterization, commonly used raw materials, typical products, and corresponding dielectric properties, is extensively reviewed and summarized in this paper. The nano/mesopores can be introduced into the polymers by more than five methods such as reprecipitation, sol-gel, thermolysis, supercritical foaming, and electrochemical etch. The pore size, morphologies, porosities, and film thicknesses of the products can be controlled by raw materials and processing conditions in these methods. The low-k dielectric materials based on nano/mesoporous polymers have great potential application in ULSIC in light of their special dielectric, optical, thermal, and mechanical properties. (C) 2013 Wiley Periodicals, Inc.
A new polymeric ligand, 4,7-dihydroxy-1,10-phenanthroline/formaldehyde polymeric ligand [poly-(DHPF)], was synthesized via the polycondensation of 4,7-dihydroxy-1,10-phenanthroline and formaldehyde in an acidic medium. Polymer metal complexes, poly-[DHPF-M(II)Cl-2], were subsequently prepared with Co(II) and Ni(II) ions. The synthesized polymers were characterized by elemental and spectral analyses. The polymer metal complexes were evaluated as catalyst precursors for ethylene oligomerization, using methylaluminoxane as an activator. Different Al/M [M = Co(II) and Ni(II)] ratios were investigated at two different ethylene pressures. Poly-[DHPF-Co(II)Cl-2] (C-1) and poly-([DHPF-Ni(II)Cl-2] (C-2) were isolated as blue and green solids, respectively. Complex C-2 was found to be a more effective precatalyst than C-1 in the presence of a cocatalyst. Thus, C-2 exhibited the maximum activity of 1.92 x 10(6) g mol(-1) (Ni) h(-1) bar(-1) with an Al/Ni ratio of 3000: 1 at room temperature, whereas C-1 exhibited a maximum activity of 1.87 x 10(6) g mol(-1)(Co) h(-1) bar(-1) with a 5-atm pressure of ethylene. Upon increasing the Al/Co ratio at 1 atm pressure of ethylene, the catalytic activity of precatalyst increased and the process became more selective for higher oligomers. The catalytic activity and selectivity with 1-decene using C-1 were 3.16 x 10(5) g mol(-1)(Co) h(-1) bar(-1) and 72%, respectively, with 5 atm ethylene and an Al/Co ratio of 300:1. (C) 2013 Wiley Periodicals, Inc.