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All issues / Volume 7 (2013) / Issue 12 (December)

Hard challenge with soft materials: Understanding large deformation and fracture behavior
P. M. Frontini
Vol. 7., No.12., Pages 959-959, 2013
DOI: 10.3144/expresspolymlett.2013.93
This is an editorial article. It has no abstract.
Self-standing chitosan films as dielectrics in organic thin-film transistors
J. Morgado, A. T. Pereira, A. M. Braganca, Q. Ferreira, S. C. M. Fernandes, C. S. R. Freire, A. J. D. Silvestre, C. Pascoal Neto, L. Alcacer
Vol. 7., No.12., Pages 960-965, 2013
DOI: 10.3144/expresspolymlett.2013.94
Organic thin film transistors, using self-standing 50 µm thick chitosan films as dielectric, are fabricated using sublimed pentacene or two conjugated polymers deposited by spin coating as semiconductors. Field-effect mobilities are found to be similar to values obtained with other dielectrics and, in the case of pentacene, a value (0.13 cm2/(V•s) comparable to high performing transistors was determined. In spite of the low On/Off ratios (a maximum value of 600 was obtained for the pentacene-based transistors), these are promising results for the area of sustainable organic electronics in general and for biocompatible electronics in particular.
On a novel method to synthesize POSS-based hybrids: An example of the preparation of TPU based system
O. Monticelli, A. Fina, D. Cavallo, E. Gioffredi, G. Delprato
Vol. 7., No.12., Pages 966-973, 2013
DOI: 10.3144/expresspolymlett.2013.95
A novel method to prepare polymer/polyhedral oligomeric silsesquioxanes (POSS) hybrids by melt reactive blending is proposed in this paper, by the controlled polymer chain scission and reaction of chain ends with functional silsesquioxanes. Application to thermoplastic polyurethanes (TPU) is addressed, taking advantage of the polyurethane chain scission equilibrium reaction, leading to the formation of highly reactive isocyanate and hydroxyl chain ends. Despite the isocyanate chemistry has been widely studied for the preparation of polymer/POSS hybrids by in situ copolymerisation, the exploitation of similar chemical processes in an industrially viable and environmental friendly melt blending process is currently an open research field. In this work, the reaction in the molten state of dihydroxyl-functionalised POSS with the polyurethane chain is demonstrated to produce a TPU/POSS hybrids. The effect of POSS concentration on nanomorphology, thermal properties and surface properties is studied, showing significant changes compared to pristine TPU. In particular, an increase of glass transition temperature is observed in the presence of reactive POSS (ΔT up to about 10°C in the presence of 10 wt% loading). Furthermore, an increase of surface water wettability, evidenced by the decrease of water contact angle from 95° for pristine TPU to 70° in TPU containing 10"wt% of reactive POSS, is found.
Preparation and characterization of a stereocomplex of poly(lactide-co-ε-caprolactone)/tricalcium phosphate biocomposite using supercritical fluid technology
R. I. Nurqadar, P. Purnama, S. H. Kim
Vol. 7., No.12., Pages 974-983, 2013
DOI: 10.3144/expresspolymlett.2013.96
A novel biocomposite material from a stereocomplex of poly (L-lactide-co-ε-caprolactone) (PLLCL) and poly (D-lactide-co-ε-caprolactone) (PDLCL) and inorganic tricalcium phosphate (TCP) was prepared by supercritical fluid method. Both pristine and poly (L-lactide)-grafted-TCP (PLLA-g-TCP) were used. PLLA-g-TCP was produced by ringopening polymerization of L-lactide in the presence of surface-activated TCP. Infrared (IR) spectroscopy and scanning electron microscopic (SEM) images confirm the attachment of PLLA onto the activated TCP surface. The stereocomplex formation of biocomposite was confirmed by differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD). The biocomposite containing PLLA-g-TCP has higher stereocomplex degree and more homogeneous TCP distribution compared to the biocomposite containing pristine TCP. The presence of PLLA-g-TCP in the stereocomplex PLLCLPDLCL (s-PDLCL) enhance the stereocomplex degree up to a certain content and also supports the homogeneous TCP dispersion in the stereocomplex matrix. These phenomena support the improvement in mechanical properties of the s-PDLCL composite the optimum content of PLLA-g-TCP being 10%. The biocomposites containing TCP materials are promising materials for biomedical application, especially for bone tissue engineering.
Active diluents effects of 4-nonylphenoxy-1, 2-dinitrilbenzene on phthalonitrile containing benzoxazine and their copolymerization behaviors
M. Z. Xu, M. D. Liu, S. H. Dong, G. Y. Qiu, X. B. Liu
Vol. 7., No.12., Pages 984-995, 2013
DOI: 10.3144/expresspolymlett.2013.97
4-nonylphenoxy-1, 2-dinitrilbenzene (NP-ph), a novel kind of phthalonitrile containing flexible hydrocarbyl chains, has been synthesized. The structures of NP-ph were investigated by Nuclear Magnetic Resonance Spectroscopy (1H-NMR) and Fourier Transform Infrared Spectroscopy (FTIR). Low viscosity NP-ph/phthalonitrile containing benzoxazine (BA-ph) blends were achieved by melt blending BA-ph with various content of NP-ph. Copolymerization behaviors and processability of NP-ph/BA-ph have been investigated by Differential Scanning Calorimetry (DSC) and Dynamic Rheological Analysis. Results indicated that NP-ph/BA-ph blends processability was improved and can be controlled by varying NP-ph contents, processing temperature and time. NP-ph/BA-ph polymers were prepared from the thermal polymerization with short curing time and low curing temperatures without addition of any other curing agents, which displayed high glass transition temperature (>360°C) and attractive thermal decomposition temperature (>420°C). The outstanding glass transition temperature and desirable thermo-oxidative stabilities, together with good processability and sound process conditions could enable the NP-ph/BA-ph polymers to be further explored in the fields under some practical critical circumstances with requirements of high wears and temperatures.
Phase behavior of UCST blends: Effects of pristine nanoclay as an effective or ineffective compatibilizer
F. Hemmati, H. Garmabi, H. Modarress
Vol. 7., No.12., Pages 996-1011, 2013
DOI: 10.3144/expresspolymlett.2013.98
The effects of unmodified nanoclay (natural montmorillonite) on the miscibility, phase behavior and phase separation kinetics of polyethylene (PE)/ethylene vinyl acetate copolymer (EVA) blends have been investigated. Depending on the blend composition, it was observed that the intercalated pristine nanoclay influences the biphasic morphology either as an effective compatibilizer or just as an ineffectual modifier. In spite of the presence of micrometer-sized agglomerated tactoids, natural nanoclay can play a thermodynamic role in reducing the interfacial tension of polymer components. The addition of clay nanoparticles was found to change the phase diagram slightly and diminishes the composition dependency of the binodal temperatures. Moreover, it was observed that a small amount of unmodified layered silicate slows down the phase separation process considerably and enhances the solubility of each polymer in the domains of its counterpart. The findings of this study verify that even poorly dispersed nanoclay with high surface tension can act as a conventional compatibilizer and change the immiscible PE/EVA blends to the partially miscible ones.
Effect of an organoclay on the reaction-induced phase-separation in a dynamically asymmetric epoxy/PCL system
J. Rotrekl, A. Sikora, L. Kapralkova, J. Dybal, I. Kelnar
Vol. 7., No.12., Pages 1012-1019, 2013
DOI: 10.3144/expresspolymlett.2013.99
The addition of layered silicates can significantly affect the phase behaviour of both immiscible thermoplastic blends and partially miscible thermoset systems that undergo reaction-induced phase separation (RIPS) during curing. This study focuses on the phase behaviour of polycaprolactone (PCL)/epoxy in the presence of organically modified montmorillonite (oMMT). Due to the high dynamic asymmetry caused by the differences in the molecular weights and viscosities of the PCL and the uncured epoxy, the critical point is localised at low PCL concentrations, as indicated by the pseudophase diagram. The addition of oMMT to the system led to the marked shift of the critical point towards higher concentrations of PCL, with an increase in the oMMT content occurring as a consequence of the preferential localisation of the clay in the epoxy phase, making this phase more dynamically slow. Significant changes in morphology, including phase inversion of the PCL/epoxy systems caused by the presence of oMMT, were recorded for PCL concentrations ranging from 10 to 30%.
Thermo-responsive, UV-active poly(phenyl acrylate)-b-poly(diethyl acrylamide) block copolymers
Z. J. Wang, B. H. Lessard, M. Maric
Vol. 7., No.12., Pages 1020-1029, 2013
DOI: 10.3144/expresspolymlett.2013.100
The homopolymerization of phenyl acrylate (PA) was investigated for the first time by nitroxide mediated polymerization (NMP) with the succinimidyl form of the SG1-based unimolecular initiator 2-[N-tert-butyl-2,2-(dimethylpropyl)-aminooxy]propionic acid (BlocBuilder MA). The control of PPA homopolymerization was improved by the use of 15 mol% additional free nitroxide SG1 ([tert-butyl[1-(diethoxyphosphoryl)-2,2-dimethylpropyl]amino]oxidanyl) and dispersities, Mw/Mn, of around 1.2 were achieved. A PPA homopolymer was then successfully chain-extended with diethyl acrylamide (DEAAm) to form a block copolymer of PPA-b-PDEAAm where the PDEAAm segment is thermo-responsive, while the PPA block is potentially UV-active. The thermo-responsive behavior of the block copolymer in 0.5 wt% aqueous solution was studied by UV-Vis spectrometry and dynamic light scattering (DLS), indicating cloud point temperatures of 26–30°C, close to that reported for PDEAAm homopolymers.
Published by:

Budapest University of Technology and Economics,
Faculty of Mechanical Engineering, Department of Polymer Engineering