Carbon-13 Nuclear Magnetic Resonance of Atactic Polypropylene

ABSTRACT:The high resolution solid state 13 C NMR spectra were observed for highly syndiotactic polypropylene samples with three kinds of crystalline forms, forms I, II, and III. The forms I and II are the most stable helical conformation, (-TTGG-), and all trans planar zigzag conformation, respectively. The sample with the third new crystalline form, form Ill, was prepared by soaking the sample with form II in toluene at room temperature for two days. The conformation was proposed to be (-T 6 G2 T2 G2-). This is based on the comparison of the observed spectrum with the calculated ones with 13 C NMR y-effect for the candidates of the conformation. There are form I (23%) and amorphous component (I 1 %) other than form III (66%) in the sample at 20°C. From the variable temperature NMR experiments of these three samples with predominantly forms I, II, and III, respectively, the transitions among different crystalline forms and amorphous component were discussed.KEY WORDS Highly Syndiotactic Polypropylene/ High Resolution Solid State 13 C NM R Spectroscopy/ 13 C y Shielding Effect/ Crystalline and Amorphous Components/ (-T6 G2 T 2 G2-) Form of Syndiotactic Polypropylene / Contrary to isotactic polypropylene (i-PP), syndiotactic polypropylene (s-PP) has recieved very little attention. This is due to the poor syndiospecificity of the earlier catalysts. However, in the last few years, new metallocene catalysts have been developed, which allow very high syndiospecificity. 1 • 2 Thus, a detailed structural study of such a highly stereoregular s-PP will be necessary.Two different crystalline forms 3 -7 of the chains have been reported for s-PP obtained by changing the preparations of s-PP samples. One form is called form I which consists of chains with (-TTGG-)i conformation, and another is form II with planar zigzag conformation. Form I is the most stable structure in s-PP, while form II undergoes a transition to form I above 50°C with increasing temperature. 6 The structures of form I and of the sample after drawing have already been studied by Bunn et al. 7 and Sozzani et al. 8 • 9 by using solid-state 13 C NMR. These NMR spectra were interpreted in terms of preferred conformations and the y-effect on the 13 C NMR chemical shift. 10 • 11 In this study, a sample with predominantly new crystalline form, form III, was obtained by special sample preparation. The 13 C CP/MAS NMR spectrum was significantly different from those of other forms, forms I and II. The differences in the spectra among three forms, I, II, and III were interpreted by taking into account of the preferred conformations and the 13 C NMR y-effect. Then the conformation of the new crystalline form, form III, was proposed. Moreover, the transition among three crystalline forms and amorphous component was examined from the temperaturedependent 13 C CP/MAS NMR spectra of three samples and then the determination of the fraction of each form t To whom correspondence should be addressed. tt Present address: Plastic Laboratory, Tokuyama Co., 1-1 Harumicho, To...

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confidence: 97%

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confidence: 97%

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High Resolution Solid State 13C NMR Spectroscopy of Polypropylene with Very High Syndiospecificity

Asakura

Aoki

Date

et al. 1996

“…4 lation. 3 Similarly, Zhu and coworkers investigated the methine carbon signals of highly isotactic polypropylene. 5 Since only five isolated peaks were obtained, they did not make complete assignment.…”

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confidence: 99%

13C NMR Assignments of the Methine Carbons in Polypropylene Using Two-Dimensional 13C-13C INADEQUATE NMR Spectroscopy

Miyatake

Kawai

Seki

et al. 1989

ABSTRACT:The methine carbon resonances for atactic polypropylene were assigned based on methyl carbon resonances by two-dimensional 13 C-13 C INADEQUATE NMR spectroscopy. In combination with the analysis of 1 H decoupled 13 C NMR spectra of isotactic, syndiotactic and atactic polypropylenes, nine peaks observed were assigned to three heptad resonances (mmmmmm, mmmmmr, and rmmmmr), and six pentad resonances (mmmr, rmmr, mmrr, rmrr, mmrm, and mrmr and rr). KEY WORDSPolypropylene / Tacticity / 13 C NMR / Two-Dimensional INADEQUATE NMR / 13 C NMR spectroscopy is a powerful tool for the study of stereochemical structure of polypropylene. Zambelli and coworkers made assignments of the methyl pentad stereosequences on the basis of the spectra of model compounds of polypropylene. 1 Subsequently, Zambelli and coworkers 2 and Schilling and Tonelli 3 analyzed the methylene hexad stereosequences on the basis of the calculation using rotational isomeric states (RIS) and ygauche parameters. Both assignments, however, showed notable disagreement. Recently, Chen and Lee indicated that the assignment by Schilling and Tonelli was correct from the examination of the 13 C NMR spectra of atactic polypropylene. 4 lation. 3 Similarly, Zhu and coworkers investigated the methine carbon signals of highly isotactic polypropylene. 5 Since only five isolated peaks were obtained, they did not make complete assignment. Thus, only limited experimental evidence for the assignment of the methine carbon resonances has been presented.In addition to the methylene hexad, Schilling and Tonelli made assignments of the methine pentad stereosequences in atactic polypropylene on the basis of a similar calcut To whom correspondence should be addressed.The objective of this work is to establish the assignment of the methine carbon resonances. For this purpose, we used the two-dimensional (2D) 13 C-13 C INADEQUATE NMR method which gives information about the methine carbon resonances through the firmly assigned methyl carbon resonances. EXPERIMENT AL MaterialsIsotactic polypropylene (IPP) was prepared 809

“…20, No. 2,1988 gamma-effect of 13 C chemical shift and Mark's RIS model of E-P copolymer can well predict 13 C chemical shift differences for carbons included in definite units, which are surrounded by different comonomer sequences. These predicted 13 C chemical shifts depend on differences of comonomer sequences, and are comparable to stereosequence dependence.…”

Section: Discussionmentioning

confidence: 92%

13C NMR Chemical Shifts Calculation for Model Compounds of Ethylene–Propylene Copolymer with a Low Ethylene Content

Hayashi

Inoue

Chûjô

et al. 1988

ABSTRACT:13 C NMR chemical shifts of the model compounds for ethylene-propylene (E-P) copolymer with a low ethylene content were calculated using the gamma-effect of 13 C chemical shift and Mark's rotational isomeric state matrices of E-P copolymer. The carbons of interest in the model compounds are included in the same monomer unit surrounded by different comonomer sequences due to the substitution of monomer unit between ethylene and propylene. Observed 13 C chemical shift differences for the carbons of interest were reasonably explained by the calculation. The magnitude of the gamma-effect was found to be sensitive to the change of the comonomer sequences. These estimated chemical shift differences are comparable to the stereosequence dependence of 13 C chemical shifts. The calculated 13 C NMR chemical shifts of stereoregular E-P copolymer with a low ethylene content allow the assignments of complicated tactic and comonomer sequence dependent resonances in the methyl resonance region. This calculation method also predicted the 13 C NMR chemical shift differences for the methylene carbons included in ethylene unit situated in two different comonomer sequences, namely, (I) the ethylene unit surrounded by the isotactic polypropylene chain, and (II) the ethylene unit which is the structural element of the isotactic poly(l-methyltetramethylene) as a model of regularly alternating ethylene-propylene copolymer.KEY WORDS Ethylene-Propylene Copolymer/ 13 C NMR / Chemical Shift Calculation / Ethylene-propylene (E-P) copolymers are industrially important materials, since some of their properties, such as impact strength, flexibility, and transparency of polypropylene products are modified by the copolymerization with ethylene. For example, the impact strength of E-P copolymer is two or three times larger than that of polypropylene with a relatively small decrease (30--40%) of the rigidity. Tacticity and comonomer sequence distributions are important factors dominating the mechanical properties of E-P copolymers. 13 C NMR is the most powerful analytical method to determine these two factors. In recent years, by improvement of sensitivity and resolution of NMR spectra, we can observe tactic-and comonomer-sequence dependent hexad or heptad resonances. Further, the calculation methods of 13 C NMR chemical shifts have been also improved to allow assignments of hexad or heptad resonances of polypropylene and related polymers.Chemical shift calculation based on the 13 C NMR gamma-effect and the rotational iso-107