Polypropylene chain mobility

Several of the described eondis phases are CD glasses (Sect. 4.2-4 ami 4.6) with different paths into the glassy states. Some of these CD glasses seem to have no corresponding, stabte eondis phase, but are produced as intermediates in the path from melt to stabte erystal [polypropylene]. The ferroelectric effect of poly(vinylidene fluoride), polytrifluOToethylene and its copolymers seems coimected to eondis glass and disorder transitions (Curie temperatures). Condis states seem also to have enhanced chain mobility on mechanical (teformation. 

On the other hand, the incorporation of a small content of ethylene units in the polypropylene chains has an influence on the regularity of the molecular structure. In fact, a change in tacticity induced by the shortening of isotactic sequences was observed (Zimmermann, 1993). Although this has a negative influence on crystallisation kinetics, an opposite effect should come from the enhanced mobility due to the presence of the ethylene sequences. As a result of these counteracting effects, a relatively narrow window of cooling rates exists in which an enhancement of crystallization kinetics sets in (Foresta et al., 2001). 

Degrees of functionalization of up to 10-18 % and 20-22 % by wt respectively, were achieved by reacting ethylene-propylene copolymers (EP) and polyethylene (PE) at 200"C in bulk with diethylmaleate in the presence of dicumylperoxide. Apparently, in the case of ethylene-propylene copolymer, the reactive tertiary C-H bonds are less sterically hindered than in polypropylene. In the case of polyethylene, despite the lack of tertiary hydrogens, the higher chain mobility causes a high degree of functionalization which is, however, negatively offset by the crystallinity of polyethylene. 

In this study, the modified Kissinger method was applied to polypropylene crystallization in the presence of inorganic additives. Minerals such as talc in fine powder format could influence the crystallization behavior of polypropylene as reported [19,20]. With the use of the modified Kissinger method, chain mobility due to the additive effect in crystallization could be revealed. Avrami and Ozawa methods were also applied to analyze the crystallization kinetics and used in conjunction with the apparent energy to better characterize the crystallization behavior. This method could facilitate resin and additive selection and provide simulation of the crystallization behavior of polypropylene in melt processing. 

The glass transition temperature rises with the polarity of the polymer chain. It is assumed that the decrease in the mobility of the chain in this case is due to an increase in intermolecular forces. Table 2.4 shows how the presence of polar groups such as —Cl, —OH, or —CN tends to increase Tg more than do nonpolar groups of equivalent size. Polar interactions considerably restrict rotation hence poly(vinyl chloride), (—CH2 CHC1—) , has a Tg. higher than that of polypropylene, (—CH2 — CH(CH3)—) . 

The conformation and molecular mobility of the noncrystalline chains for syndiotactic polypropylene (sPP) samples well crystallized have been characterized at different temperatures by high-resolution solid-state NMR. The purposes are to investigate the cause inducing the high trans fraction of sPP chains in the noncrystalline state just after quenching at 0 °C from the melt and to know some correlation with the crystallization of form III with the planar zigzag conformation around 0 °C. 

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