High-resolution solid-state NMR study of isotactic polypropylenes

Abstract

Since the commercialization of Ziegler-Natta process of polypropylene synthesis, this technology was for decades almost the only source of all grades of polypropylene (PP). Only at the end of the last century a new process was developed, based on metallocene catalysis. This process provides new types of metallocene PP (m-PP) different from previous Ziegler Natta PP types (ZN-PP), the main difference consisting in the production of grades with different stereoregularity (isotactic, syndiotactic, hemi-isotactic, atactic) [1] or narrow polydispersity of the polymer chains, compared to Ziegler-Natta catalysts, which produces only highly polydisperse isotactic polymers. The tacticity of isotactic (i) m-PP and ZN-PP is virtually the same (98% of isotactic diads), though the configurational defects are more frequent in m-iPP [2]; this might be reflected in a lower melting temperature of m-iPP in comparison with ZN-iPP. Comparing to ZN-iPP, m-iPP offers a unique balance of stiffness, transparency, and organoleptic properties which is not achievable with ZN-iPP. On the other hand, m-iPP is usually less rigid than ZNiPP homopolymers. Thus, any additional information on similarity or differences in m-iPP vs. ZNiPP behaviour seems to be of scientific as well as Abstract. The high-resolution solid-state 13 C NMR spectra were recorded for metallocene (m) and Ziegler-Natta (ZN) isotactic polypropylenes (iPP) in pelletized form using cross polarization (CP) and magic angle spinning (MAS) techniques within the temperature range of 20-160°C. Besides the CP MAS experiments also the MAS 13 C NMR spectra (without CP), MAS 1 H NMR spectra and rotating frame spin-lattice relaxation times T 1" ( 13 C) were measured at elevated temperatures. With the rise of temperature the splitting of CH 2 , CH and CH 3 signals into two components was detected in 13 C NMR spectra and assigned to amorphous and crystalline phases. The temperature dependences of chemical shifts and integral intensities obtained from the deconvoluted spectra provided information on the main chain and CH 3 groups motions in amorphous and crystalline regions of studied samples. While T 1" ( 13 C) values show that the rate of segmental motion in amorphous regions in m-iPP and ZN-iPP is virtually the same, larger linewidths in 13 Vol.6, No.3 (2012) 204-212 Available online at www.expresspolymlett.com DOI: 10.3144/expresspolymlett.2012.23 * Corresponding author, e-mail: olga.fricova@tuke.sk © BME-PT commercial importance. NMR investigation is considered to be one of the basic relevant methods. The high-resolution solid-state 13 C NMR studies of iPP reported NMR spectra recorded with combination of magic angle spinning (MAS), cross polarisation (CP) and dipolar decoupling (DD) techniques [3][4][5][6][7][8][9][10][11][12][13][14]. Since iPP can crystallize in several crystalline forms, depending on the crystallization temperature and on the presence of specific nucleating agents, the shape of the spectra was found to depend strongly on the physical treatment of the sa...

Estimation of the Degree of Crystallinity of Partially Crystalline Polypropylenes Using ^{13}C NMR

“…These parameters can be then used for deconvolution of the CH 2 line in a quantitative 13 C NMR spectrum, obtained in an experiment with a long delay time, and then for the calculation of the degree of crystallinity of these samples with comparable accuracy. This procedure was veried * corresponding author; e-mail: viktor.hronsky@tuke.sk on pelletized m-iPP and ZN-iPP samples characterized in [1] and the values of degree of crystallinity 54% and 58%, respectively, are in good agreement with those reported there.…”

“…The results of the calculations of degrees of crystallinity are summarized in the Table. The values obtained from NMR and DSC experiments dier more than those obtained for iPP samples with hexagonal structure [1], which could result from the fact that the structure of foils studied was not pure monoclinic (the ratio of the components in CH 2 and CH 3 lines in Fig. 1A is 1.6:1 which diers from theoretically expected 2:1).…”

“…The evaluation of the degree of crystallinity using 13 C NMR is based on the fact that magnetic moments of the nuclei of the same functional group within crystalline and amorphous domains experience dierent internal magnetic elds and produce dierent lines in the 13 C NMR spectra. The relative number of 13 C nuclei within crystalline domains, which is the degree of crystallinity, can be estimated in i-PP samples by the deconvolution of CH 2 and CH lines in quantitative 13 C NMR spectra, as was reported in [1] for i-PP with hexagonal structure. The deconvolution of sucient accuracy of these lines was achieved using two components assigned to 13 C nuclei in amorphous and crystalline domains.…”

Origin of toughness in β-polypropylene: The effect of molecular mobility in the amorphous phase

“…With increasing temperature, however, a more vigorous molecular motion is activated in the r.c. amorphous phase, and new well-resolved CH 2 and CH resonance lines appear in the high-frequency region [21]. Therefore, ss-NMR experiments at elevated temperatures are important for understanding the molecular origin of the physicochemical and mechanical properties of i-PP systems.…”

Characterization of the morphology of iPP/sPP blends with various compositions

“…Those splits have a theoretical ratio of 2 to 1 Figure 7. CP-DD MAS 13 C NMR spectra of the blends iPP/sPP compared to virgin iPP and sPP corresponding to the presence of two sites in the % crystalline form of iPP [27]. This crystalline form was expected since it is that obtained in usual crystallization conditions.…”