Chain structure thermal behaviour

Structurally related )S-diketonato metal complexes with lateral chains have also been synthesised. The first complex of this type, 31a, was not mesomorphic [63], nor was the analogous copper complex, 31b [64], essentially due to the small anisotropy of the complexes. However, more rod-like complexes, such as 32, showed monotropic nematic phases [65]. Only a few members have been synthesised, and thus it is rather difficult to rationalise the thermal behaviour of these compounds. Anyway, melting points were found to decrease very steeply with rising m, suggesting again that the lateral chains disrupt the efficient molecular packing of the complexes in the crystal state. The crystal structures of two homologues (32 n=3 and m=l and... 

Figure 6.30 presents a summary of the different possible structures existing in different temperature regions. The phase transitions are dominantly of first-order type. A relatively common thermal behaviour of semiflexible main-chain and side-chain polymers with long spacers is that a smectic structure is formed directly from the isotropic melt without the appearance of any intermediate nematic phase. The development of a smectic phase requires some axial order of the chain. Statistical main-chain copolymers generally do not possess a smectic mesomorphicity. On cooling, they transform into a nematic glass. 

The thermal behaviour of materials can also provide important information about the structure and morphology of a material. For example, while most synthetic polymers have a glass transition temperature (Tg) associated with amorphous structure in the material, only polymers with regular chain architecture can crystalhse and so have a melting temperature (IJn). These in turn can have a direct effect on the mechanical performance of the materials since below Tg polymers tend to be glassy and become more rubbery above 7. These thermal properties can also be used to identify or verify the nature of the composition. For example, random copolymers will only exhibit one Tg that will be somewhere in between the 7 s of the individual homopolymers, whereas block copolymers will exhibit 7 s characteristic of each homopolymer but will be slightly shifted due to imperfect phase separations. Similarly this can be applied to polymeric blends, which are essentially two polymeric systems mixed together. 

This work investigates the behaviour of elastomeric chains (polybutadienes of identical molecular weight but different microstructures) in the close vicinity of carbon black surfaces in order to attain a better understanding of the structure and properties of interphases. Elastomer-filler interactions are assessed through the study of the thermal properties and NMR relaxation characteristics of the corresponding materials. MAS solid-state NMR provides information on the effect exerted by polymer-filler interactions on the mobility of the various constitutive species of the macromolecular backbone. 

The thermal volatilization analysis of a mixture of polyvinylchloride and polystyrene is given in Fig. 81. The first peak corresponds to the elimination of HC1 and the second to that of styrene. Dehydrochlorination is retarded in the mixture. The production of styrene is also retarded styrene evolution, in fact, does not occur below 350°C. This contrasts with the behaviour of polyvinylchloride-polymethylmethacrylate mixtures for which methacrylate formation accompanies dehydrochlorination. The observed behaviour implies that, if chlorine radical attack on polystyrene occurs, the polystyrene radicals produced are unable to undergo depolymerization at 300° C. According to McNeill et al. [323], structural changes leading to increased stability in the polystyrene must take place. This could also occur by addition of Cl to the aromatic ring, yielding a cyclohexadienyl-type radical which is unable to induce depolymerization of the styrene chain. 

---