Interest in renewable polymers increased exponentially in the last decade and in this context poly(lactic acid) (PLA) became the leader mainly for practical reasons. Nevertheless, it is outstanding also from a scientific point of view, because its thermal and morphological properties are offering challenging new insights. With regard to dynamic mechanical analysis (DMA), PLA does not have the classical behavior of a thermoplastic polymer. Often, overlapping events (enthalpic relaxation, glass transition and crystallization) that occur as the temperature increases make the DMA result of a PLA look inexplicable even for polymer scientists. This review offers a perspective of the main phenomena that can be revealed in a DMA experiment and systematizes the information that can be obtained for every region (glassy, glass transition, rubbery, cold-crystallization and melting). Also, some unusual patterns registered in some cases will be commented upon. The review intends to offer indices that one should pay attention to in the interpretation of a DMA experiment, even if the investigator has only basic skills with DMA investigations.
Polysiloxanes with polar cyano groups were cross-linked with PDMS by a hydrolysis–condensation process. Materials suitable for transducer applications with improved permittivity, good mechanical properties, and high breakdown fields were obtained.
Abstract. New thermo-reversible networks were obtained from poly(vinyl furfural) and multifunctional maleimide monomers by Diels-Alder (DA) and retro-DA reactions. The poly(vinyl furfural) having acetalization degree of 15 and 25% were obtained by the acid-catalyzed homogenous acetalization of poly(vinyl alcohol) with 2-furfural in a nonaqueous media. The thermal and viscoelastic behaviour of the cross-linked materials have been studied via differential scanning calorimetry, dynamic mechanical analysis and thermogravimetric analysis. The networks exhibit considerable swelling in those organic solvents that dissolve both poly(vinyl furfural) and bismaleimides; by heating in aprotic dipolar solvents at 150°C, they become soluble.
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