¹³C CP/MAS NMR studies of morphological changes in polypropylene: 1—Annealing of quenched films

Abstract

High-resolution l3C cross-polarization/magic angle spinning (CP/MAS) spectra of the crystalline component of quench-cooled isotactic polypropylene (iPP) were obtained by using a pulse sequence that incorporates a delay period with a reduced spin locking field prior to cross-polarization, thus exploiting the differences inlH TIp relaxation times between the various phases. The spectra of samples annealed at high temperature have resolved splitting, ranging between 0.2 and 1.1 ppm, for all carbon resonances. The methyl resonance is composed of three resolved peaks whose relative areas, as obtained through peak deconvolution, depend on the anneal temperature. Large changes in these peak areas coincide with an exothermic transition observed by differential scanning calorimetry. The spectra of the interfacial and amorphous phases, obtained by subtraction, indicate a reduction in the amorphous content at anneal temperatures> 100°C while the interfacial component appears to increase owing to recrystallization and the formation of more amorphous/crystal interfaces.

13C CP/MAS NMR studies of morphological changes in polypropylene: 2. The double melting endotherm of spunbonded fabrics

“…For both, the methyl resonance is composed of three peaks while the methine resonance consists of only two. The intensity distributions and the splitting patterns are very similar to those reported previously for quench-cooled films annealed for 1 h at temperatures between 100 and 115"C. 26 As noted in that case, the midfield methyl (MFM) peak is most sensitive to the level of order in the crystalline phase of iPP in that it increases in intensity as higher levels of order are attained. CP/MAS NMR spectra of the purely crystalline phase of the spunbonded fabrics annealed for 0 min at temperatures between 120 and 163°C are presented in Figure 7.…”

“…26 As a result of the relaxation of the spins of the amorphous and interfacial phases during this period with reduced field-spin locking, only the signal from the material with the highest crystalline order, which possesses the longest relaxation times, was accumulated. The spectra of the more mobile phases, with the shorter relaxation times, were obtained separately by subtracting the above mentioned spectra from those having contributions from all phases, obtained with r = 10 ps.…”

Molecular Structure of Isotactic Polypropylene Formed from Homogeneous Solution. Gelation and Crystallization

“…7,16,17,21 Caldas et al investigated the relationship between the crystalline form and the intensity ratio of doublet, and established the origin of different intensity ratio for the lower crystalline order form (α 1 ) with C2/c and the higher crystalline order form (α 2 ) with P2 1 /c space group. [16][17][18] Two different environments giving doublet exist in the crystal cell depending on the arrangement of left-and right-handed helices at the interlayer region.A gelation as well as crystallization is another recent topic. Generally the gelation accompanies the formation of three dimensional network structure consisted of crystalline as a cross-linking point.…”

Morphological reorganization and mechanical enhancement in multilayered polyethylene/polypropylene films by layer multiplication or mild annealing

“…Another point of view is provided by the study of proton relaxation times in the rotating frame T 1ρ ( 1 H), a mainstay of NMR crystallography . This observable can vary up to a factor of 5 (from 20 to 100 ms) during the annealing of iPP, with larger values associated to the development of a more rigid matrix and larger crystalline regions . For annealed samples containing sindio stereosequences it levels at 50 ms even after long annealing time .…”