Carboxylic acid-and anhydride-terminated polystyrenes of different molecular weights from 4500 to 672 000 were grafted from melt onto silicon substrates modified with epoxysilane monolayer. The grafted chains are densely packed with a density close to the known value for the bulk material. The tethered polymer layers are very smooth, uniform, mechanically stable, and cover homogeneously the modified silicon. At the degree of polymerization (N) close to the critical molecular weight, the grafting process is the most effective, resulting in the grafted unperturbed macromolecules. We suggest that the grafting from the reactive polymer melt is controlled by steric constraints through the minimum available free volume between the grafted macromolecules, which is reachable by another reactive end. This volume correlates with the size of monomeric unit and varies very little with the molecular weight.

Dense and homogeneous grafted polymer layers were anchored from the melt onto a silicon wafer modified with a macromolecular anchoring layer rich in epoxy functional groups. A monolayer of poly(glycidyl methacrylate) (PGMA), attached to silicon wafers, served as the macromolecular anchoring layer. Carboxylic acid- and anhydride-terminated polystyrenes (PS) of different molecular weights were used for the grafting. The grafted layers did not dewet at elevated temperatures and did not desorb in a good solvent under ultrasonic treatment. Comparison of the results for the grafting to the PGMA primary layer with literature data obtained for the grafting to the epoxysilane monolayer suggested that there were many similarities between these grafting processes. The same major trends were observed. However, the grafting to the PGMA layer was much more effective. We attribute the high efficiency of the PGMA anchoring layer in the grafting reactions to the high mobility of the epoxy reactive groups and formation of an interpenetrating zone at the PS/PGMA interface.

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The microstructure of the free volume and its temperature dependence in fluoroelastomeric copolymers of tetrafluoroethylene (TFE) and perfluoro(methyl vinyl ether) (PMVE), PFE, as well as vinylidene fluoride (VDF) and hexafluoropropylene (HFP), VDF78/HFP22, were studied by pressure−volume−temperature experiments (PVT, T = 300−485 K, P = 0−200 MPa) and positron annihilation lifetime spectroscopy (PALS, T = 100−473 K, P = 0 MPa). Employing the Simha−Somcynsky equation of state (S−S eos), the excess free (hole) volume fraction h and the specific free and occupied volumes, V f = hV and V occ = (1 − h)V, were estimated from the specific total volume V. The temperature and pressure variation of these volumes and their expansivity and compressibility will be discussed. The PALS spectra were analyzed using the routine LT9.0 assuming a dispersion in both the positron (τ 2) and orthopositronium (o-Ps) lifetime (τ 3). From the lifetime parameters the hole size distribution, its mean value 〈v h〉 and dispersion σ h were calculated. From a comparison of 〈v h〉 with V and V f the specific hole number N h‘ was estimated. N h‘ was determined to be independent of the temperature. Indications were found that o-Ps may prefer larger holes with a weight approximately proportional to the hole volume. Apparent discrepancies between S−S modeling and the conclusions from PALS are discussed. From the comparison of the hole size distribution with the theory of thermal fluctuation a fluctuation volume 〈V〉 is estimated which decreases above T g with increasing temperature. Attempts are made to interpret the PALS results in terms of the theory of structural and dynamic heterogeneity of glass-forming liquids.

To cite this version:E. Logakis, Ch. Pandis, P. Pissis, J. Pionteck, P. Pötschke. Highly conducting poly(methyl methacrylate) / carbon nanotubes composites: Investigation on their thermal, dynamic-mechanical, electrical and dielectric properties. Composites Science and Technology, Elsevier, 2011, 71 (6) This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. AbstractNanocomposites of poly(methyl methacrylate) (PMMA) containing various multi-walled carbon nanotubes (MWCNT) contents were prepared using melt mixing. Several techniques were employed to study the influence of the MWCNT addition on the thermal, mechanical, electrical and dielectric properties of the PMMA matrix. The electrical percolation threshold (p c ) was found to be 0.5 vol.% by performing AC and DC conductivity measurements. Significantly high conductivity levels (σ dc ) were achieved: σ dc exceeds 10 -2 S/cm already at 1.1 vol.%, the criterion for EMI shielding (σ dc > 10 -1 S/cm) is fulfilled at 2.9 vol.%, and the highest loaded sample (5.2 vol.%) gave a maximum value of 0.5 S/cm. Dielectric relaxation spectroscopy measurements in broad frequency (10 -1 −10 6 Hz) and temperature ranges (-150 to 170 ºC) indicated weak polymer-filler interactions, in consistency with differential scanning calorimetry and dynamic mechanical analysis findings. Weak polymer-filler interactions and absence of crystallinity facilitate the achievement of high conductivity levels in the nanocomposites.

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Multifunctional sensing abilities of cellulose/in situreduced graphene oxide composites prepared by a simple and “green” approach are presented.

Polyamide 6 (PA6)/multi‐walled carbon nanotubes (MWCNT) nanocomposites were produced by diluting a masterbach containing 20 wt % nanotubes using melt mixing. The influence of the addition of well dispersed MWCNT (as indicated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM)) on the thermal transitions, and crystallization behavior of the PA6 matrix is investigated. Differential scanning calorimetry (DSC) results show a reduction in heat capacity jump at the glass transition which is interpreted by an immobilized interfacial layer near the nanotubes. Furthermore, both DSC and X‐ray diffraction (XRD) measurements indicate that nanotubes favor the formation of the α crystalline form of PA6. These findings are correlated with the observed improvement of the storage modulus as revealed by dynamic mechanical thermal analysis (DMTA). Additionally, a new crystallization peak appears when MWCNT are added, and is attributed to the formation of a different morphology of the same type crystallite around the nanotubes walls (trans‐crystallinity). Finally, water sorption measurements show an increase of water content, normalized to the amorphous polymer fraction, in the nanocomposites. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 764–774, 2009