Phase structure and polymorphism of highly syndiotactic polypropylene

Abstract

Polymorphs of higbly syndiotactic polypropylene were studied by magic angle spinning 13C NMR. The conversion of one crystalline form into another was observed by the formation of different conformers of the polymer chain. The reversion of the metastable forms t9, the conventional crystalline phase was followed directly by variabletemperature experiments and the addition of plasticizers. The multiplicity of signals associated with these structures were fully assigned in terms of trans,gauche conformations, by taking into account a sequence of four bonds in the main chain. Additional signals due to the packing of helical chains of opposite chirality are discussed in terms of the packing disorder present in the structure. The spectral pattern due to the amorphous region depends on temperature and thermal history, because the chain sequences can be observed under conditions of static and dynamic disorder as compared with the NMR time-scale. The chains are fairly elongated, because they contain a considerable amount of trans sequences. Phase distribution and interfaces were characterized :by hydrogen relaxation times in the rotating frame T1pH.Phase specificity was retained by recovering the magnetization on the 13C nucleus under high-resolution conditions. Apparently spin diffusion cannot average out the T1pH value over the whole material when the thickness of the crystalline lemellae is increased by the annealing treatment. In the stretched material crystalline and amorphous phases are intimate and the chains in the amorphous phase also appear to be partly extended.KEY WORDS 13C CP/MAS NMR TIP experiments Syndiotactic polypropylene Phase domains

Structural and Thermal Behavior of Poly (3-octylthiophene): a DSC,13C MAS NMR, XRD, Photoluminescence, and Raman Scattering Study

“…[16 -19] The trans conformations, that give rise to a better chain packing, belong to a crystalline phase. [20,21] Inner methylenes generate a signal at 33.9 ppm due to purely trans conformations and an upfield peak at 31.6 ppm that can be assigned to chains experiencing gauche conformations. In the NMR spectra performed at 60 8C only the upfield signals for methyls, C-79, and inner methylenes survive indicating that a conversion from trans to gauche conformations occurs already at that temperature.…”

Mechanically and thermally induced chain conformational transformations between helical form I and trans-planar form III in syndiotactic polypropylene using FT-IR and Raman spectroscopic techniques

“…It has been shown [38,39] by high-resolution solid-state 13 C NMR spectroscopy that annealing of the trans-planar form III at about 50 8C it results in a transformation to the helical conformation. Bonnet et al [31] mention that when a highly strained sample of sPP in trans-planar form III is annealed, a transformation of the trans-planar chains into the helical chain conformation takes place above 80 8C.…”

Spontaneous Crystallization of the Planar Zigzag Form of Syndiotactic Polypropylene at 0 °C

“…including a noncrystalline one, a line forming a doublet with the upfield line at 39.1 ppm is evidently included in the line at 47.7 ppm. 21,22 Such doublet splitting is induced by the so-called γ-gauche effect 7 for the methylene carbons with different environments in the t 2 g 2 helical structure in the crystalline region. The spectral profile begins to change progressively when specimens are soaked in ice-water for a few hours.…”