Amorphous PP

Fig. 5. Differential scanning calorimetry thermogram. Amorphous PPS is heated from room temperature to 325°C at 20°C/min.

Polypropylenes, and metallocene catalysts amorphous PP, 4, 1052 flexible and elastomeric isotactic PP, 4, 1064 isotactic PP, 4, 1056 syndiotactic PP, 4, 1070 Polypyrroles, with ferrocene groups, 12, 305 Polypyrrole supports, for diphosphine borane complex,... 

Amorphous PP was a byproduct of iPP production in the early slurry processes, and was isolated from the aliphatic solvents in the solvent recycle section. 

This material, often incorrectly referred to as atactic, is actually neither atactic nor fully amorphous, but is a mixture of chains of different stereoregularity and molecular masses, as proved by polymer fractionation.315,374,671,672 The methyl pentad region of the 13C NMR spectrum of such a ZN PP clearly shows both isotactic and syndiotactic stereoblocks. Although the molecular masses of this material are low, amPPs have been used as bitumen additives and in hot-melt adhesives. With the improvement of the stereospecificity of the ZN catalysts for iPP, amPP was no longer available as a byproduct. Fully or largely amorphous PP from ZN has since been produced on purpose, also by adding co-monomers to further reduce crystallinity.673-680... 

A comparison of the physical properties of these polymers with that of fully amorphous PP has been reported.722... 

A modulus value increase upon storage under ambient conditions is also reported for other semi-crystalline polymers like, for instance, polypropylene. Struik [11] measured for PP a continuously increasing dynamic stiffness at 20°C in combination with a decrease of the intensity of the glass-rubber (S) transition of PP (the temperature location of the S-transition did not change). Struik called this phenomenon an amorphous phase ageing effect a densification process of the amorphous PP phase due to a free volume relaxation effect. 

Small and defective PP molecules or amorphous PP chains are partially soluble in the elastomer phase this can lead to a slightly deviating behavior [Martuscelli ef a/., 1983], [Kalfoglou, 1985]... 

Fig. 8.7 Work-equivalent deviatoric shear-strain spikes at individual segments along a PP molecule, in a simulation cell of amorphous PP of Fig. 8.5, during the individual shear transformation events a-h, indicated in Fig. 8.5, plotted as a function of system strain and the backbone carbon number of segments (from Mott et al. (1993) courtesy of Taylor and Francis).

Cyclohexa(p-phenylene sulfide) (CHPS) is a precursor of poly(p-phenylene sulfide) (PPS). The FTIR and Raman spectra of CHPS resemble those of amorphous PPS. Specific modes indicative of the crystal structure and band shifts are reported and a crystal structure change in CHPS which was induced by pressure or heat is identified (84). 

Another important transition detected by DSC is the glass transition. This is the transition that amorphous (noncrystalline) materials undergo in changing from the liquid to rubbery state. In i-PP this is difficult to detect by DSC because the concentration of amorphous PP is small, but detection is easy in a-PP, the glass transition temperature being in the vicinity of -15°C. 

The major conclusion that was deduced from the spectra shown in Figs. 4 and 5 is that the two sites detected for the nitroxides in the heterophasic systems studied can serve as a basis not only for describing the morphology of the system, but also to trace the evolution of the nittoxide signal as a function of treatment time, and the time dependence of the degradation process, in the morphologically different domains in the butadiene-rich and SAN-rich domains in ABS, and in the amorphous PP-rich and EPR-rich domains in HPEC. 

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