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Thermostable nanocomposites based on densely cross-linked Cyanate Ester Resins (CER), derived from bisphenol E and doped by 0.01–10 wt.% epoxycyclohexyl-functionalized polyhedral oligomeric silsesquioxane (ECH-POSS), were synthesized and characterized in detail by means of TEM, SAXS, EDXS, FTIR, DSC, DMA, TGA, far-IR and creep rate spectroscopy techniques. It was revealed that ultra-low POSS contents (≪1 wt.%), covalently embedded into CER network, substantially changed its nanostructure and properties. This resulted in changing network dynamics; increasing glass transition temperatures by 20–50 °C; enhancing high temperature elastic and creep resistance properties, and increasing thermal stability under inert atmosphere at T

Thermal analyzes have been performed on poly( l -lactide acid) (PLLA) annealed at 353 K for different durations in order to obtain a crystallinity degree varying between 0% and 42%. From temperature modulated differential scanning calorimetry investigations, we have calculated the average volume of a cooperative rearranging region (CRR) at the glass transition temperature ξ T g 3 , according to the method developed by Donth. The results show that the presence of crystalline phase in PLLA amorphous matrix implies modifications on structural relaxation phenomena, in particular on the average number of monomer units relaxing in the same time at the glass transition temperature.

The dipole dynamics and α-relaxation behaviour of polyvinyl chloride PVC, poly(ethylene-co-vinyl-acetate) EVA70 and blend of them EVA70/PVC have been investigated by differential scanning calorimetry (DSC) and dielectric relaxation spectroscopy (DRS). The differential scanning calorimetry (DSC) thermograms measured on samples show a single glass transition in the analysed temperature range. These three polymers are wholly amorphous and pure PVC and pure EVA70 are miscible in the ratio 1:1. The glass transition temperature Tg decreases significantly with presence of EVA70. Furthermore, the values of apparent activation energies for molecular motions at the α-relaxation and the values of fragility index have also been determined for each sample using Moynihan expression for DSC results and Vogel–Fulcher–Tammann–Hesse (VFTH) form for DRS results. It is shown a large dependence of all the values of these parameters with the content of EVA70. Comparing these three polymers, we found that the more fragile glass forming liquid is the PVC. Fragility decreases drastically with EVA70 content. EVA70 and EVA70/PVC blend exhibit practically the same behaviour. The effect of inter- and intra-molecular interactions on fragility is discussed to explain these variations.

Unsaturated polyester resins cured with varying styrene content (20–50% (w/w)) has been studied by calorimetry (DSC). We have evaluated the values of the heat capacity at the glass transition ΔCp=[Cp,l−Cp,g]T=Tg, the values of apparent activation energy Δh*, and the values of the fragility index m for each sample. It is found a constant value of ΔC p =0.29 J g −1 K−1 for all the samples while Δh* and m increase with the styrene content. These results discussed in regard with the strong fragile glass-formers concept indicate a character becoming more fragile when the amount of styrene increases. Introducing the “bead concept” proposed by Wunderlich, we show that the average elementary energy barrier that the molecular species (or relaxing units) must overstep during their relaxation process is unchanged whatever the content of styrene. The origin of the variations with the styrene content of the fragility behavior is understood by the increase of the bead number.

The variations of the heat capacity ΔC p =[ C p l − C p g ] T = T g at the glass transition, and the value of the fragility index m were determined for two melamine formaldehyde resins by calorimetric investigations. These values characterise respectively the thermodynamic aspect and the kinetic aspect of the Angell “Strong–Fragile” concept. For resins cured with a neutral pH, the 3D network formed is made of massive molecular units connected together by small length chains, and the values are ΔC p =0.13 J K −1 g −1 and m =143. For acid pH curing conditions, the 3D network is made of only massive molecular units connected together and we obtain ΔC p =0.12 J K −1 g −1 and m =35. By comparing our results with the results of the literature concerning three-dimensional networks and inorganic polymers, we are able to conclude that the relaxation occurs in these systems mainly by movements involving triazine rings.

The diffusion and permeation properties of liquid water through an isophthalic-maleic acid-propanediol-based copolyester resin were studied with a highly sensitive permeameter. The value of the parameters of the exponential dependence of the diffusion coefficient on the water concentration decreases with the curing extent, except that of the plasticization coefficient, which decreases after a post-curing at 120°C. Infrared-spectrophotometric and calorimetric data show that the curing involves mainly a polymerization of styrene during the curing at 25°C, and a crosslinking by the opening of the double bonds on the polyester chains in the subsequent curing step at 80°C. The water sorption by the resin results in a 20°C-decrease in the glass transition temperature of the water saturated resin, leading to the diffusivity enhancement by the plasticization effect.

The objective of this experimental study is to obtain some new information on the plasticization of thermoplastic polymers by water. The effect of moisture on the poly(ethylene terephtalate) (PET) thermal properties has been investigated using differential scanning calorimetry. By heating PET film samples at different rates, thermokinetic parameters such as the apparent activation energy for glass transition, the apparent activation energy, Avrami exponent and heating function for crystallization, have been determined in relation to the polymer water content.

International audience; In this work, the variations of the relaxation times are investigated above and below the glass transition temperature of a model amorphous polymer, the polycarbonate. Three different techniques (calorimetric, dielectric and thermostimulated currents) are used to achieve this goal. The relaxation time at the glass transition temperature was determined at the temperature dependence convergence of the relaxation times calculated with dynamic dielectric spectroscopy (DDS) for the liquid state and thermostimulated depolarisation currents (TSDC) for the vitreous state. We find a value of s(Tg) = 110 s for PC samples. The knowledge of the temperature dependence, s(T), and the value s(Tg) enables to determine the glass-forming liquid fragility index, m. We find m = 178 ± 5.