B. Van Mele

Phase separation in miscible polymer blends as detected by modulated temperature differential scanning calorimetry

Phase separation of two partially miscible polymer blends is studied with modulated temperature DSC (MTDSC). The lower critical solution temperature (LCST) demixing behavior of poly(ethylene oxide) (PEO) blended with poly(ether sulphone) (PES) and with poly(3,4 0 diphenylene ether isophtaloyl amide), as determined by cloud point temperatures with optical microscopy, is in excellent agreement with results obtained from non-isothermal MTDSC measurements. The non-isothermal MTDSC apparent heat capacity evolution is time-dependent. It is influenced by the endothermic demixing enthalpy and, in the case of PEO/PES blends, by the vitrification of a high-Tg phase formed. Quasi-isothermal MTDSC measurements contain information on the kinetics of demixing and remixing, emphasizing the added value of MTDSC to follow in situ the diffusion-controlled phase separation processes of partially miscible polymer blends. q 2000 Elsevier Science Ltd. All rights reserved.

Flexibilized styrene-N-substituted maleimide copolymers. I. Multiblock copolymers prepared from styrene-maleimide telechelics and polytetrahydrofuran

Telechelic copolymers of styrene and different N-substituted-maleimides (SMIs) with a molecular weight of 2000–8000 g/mol were synthesized using the starved-feed-reactor technique and were nearly bifunctional when the monomer feed had a high styrene concentration. The COOH-terminated rigid SMI blocks were polycondensated with OH-terminated poly(tetrahydrofuran) (PTHF) blocks, with a molecular weight of 250–1000 g/mol, which are the flexible parts in the generated homogeneous multiblock copolymer. The entanglement density, which is closely related to the toughness of materials, increased in these flexible SMI copolymers (νe = 5.2 · 1025 m−3) compared to the unflexibilized ones (νe = 2.4 · 1025 m−3). The glass transition temperature of these flexibilized, single-phase multiblock copolymers was still high enough to qualify them as engineering plastics.

Physico-Chemical Characterisation of the Influence of Moisture on the Fibre/Matrix Interaction in Epoxy/Anhydride Composites

Abstract The effect of moisture on the fibre/matrix interaction in epoxy/anhydride composites is investigated and explained through the characterisation of the matrix cure in the interphase. The fibre/matrix interaction is inferred from ILSS measurements on the composite, which are compared with a recently-introduced DSC interaction parameter. The matrix cure in the bulk as well as in the interphase is characterised through FT-IR microspectroscopy. Complementary information is gained by measuring the overall Tg value. Moisture is shown to lower the fibre/matrix interaction if the prepreg (= composite precursor) is stored at room temperature or lower prior to final cure. This is due to the reduced crosslink density of the matrix. For PE prepreg stored in ordinary atmospheric conditions, moisture from the surroundings lowers the fibre/matrix interaction sharply. If the prepreg is stored in a dry environment, nearly no effect of the storage is detected on the fibre matrix interaction in PE (polyethylene) fib...

Selective elimination in dialkoxy-PPV precursors yielding polymers with isolated tetraalkoxy-stilbene units

Abstract In the polymerization of 2,5-diethoxy-1,4-phenylenedimethylene-bis(tetrahydrothiophenium chloride) leading to the 2,5-diethoxy-poly(phenylenevinylene) (2,5-diethoxy-PPV) precursor we have varied the NaOH concentration from equimolar to a five-fold excess. Elimination to the conjugated form is observed during polymerization by using concentrations higher than equimolar. Suprisingly, this elimination is very selective, yielding tetraethoxy-stilbene units only. Almost no delocalization over more than two benzene rings, i.e. hexaethoxy-distyrylbenzene units, is observed in polymers with as much as 35% elimination (determined by 1 H NMR spectroscopy). This selectivity is explained by the preference of an E 2 -elimination yielding products with the highest gain in resonance energy at every step: tetraalkoxy-stilbenes. Absorption and emission spectroscopies reveal that significant energy transfer from benzene to stilbene units occurs and that a blue photoluminescence with λ max = 415 nm is present.

Thermal and Infrared Characterization of a Bismaleimide Resin by DSC and TGA/FTIR

The available literature about applications of the combined technique of Thermal Gravimetric Analysis and Fourier Transform Infrared Spectroscopy (TGA/FTIR) is still sparse [1].