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

Abstract

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...

Oriented crystallization in fiber formation: Inferences from the structure and properties of melt spun syndiotactic polypropylene filaments

“…The spectra of all the sPP fibers show peaks at 19, 27, and 48 ppm, along with a shoulder at 21 ppm on the methyl peak. Such a spectrum with a single distinct methylene peak (48 ppm) arises from a mostly (TTTT) conformation 18, 19, 21, 22, 37. The methylene carbons do not receive any γ‐ gauche effect in the trans planar conformation and exhibit only a single peak.…”

“…For example, although syndiotactic polypropylene (sPP) was first synthesized in 1960s by Natta et al,1 significant interest in the polymer did not result until the work of Ewen et al in 1988,2 which facilitated the production of highly syndiospecific polypropylene. Renewed research interest in sPP has produced several reports3–23 on processing, structure, and properties of this polymer, and also on comparisons with its isotactic analog (iPP), a polymer that has been in large‐scale production for approximately four decades. Among the various aspects of sPP, the most significant with regard to its applications pertains to its crystallization characteristics.…”

“…An important aspect in this regard is the set of three distinctly different chain conformations in these structures (Fig. 1), namely (1) a highly coiled (T 2 G 2 ) 2  conformational sequence,3–5, 11–13, 20, 24 (2) a (T 6 G 2 T 2 G 2 ) conformational sequence,8, 18, 19, 21, 22 and (3) an all‐ trans fully extended structure 6, 9, 18, 25, 26. The various crystal forms of sPP, along with the corresponding conformational sequences, are summarized in Table I.…”

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

“…A large number of investigations on the molecular chain conformation and molecular packing in crystals have also been reported for sPP. As for the polymorphs, four crystalline forms are known: the planar zigzag, − t 2 g 2 t 6 g 2 , − and two forms with the t 2 g 2 conformation. − Of these, the crystals with the planar zigzag conformation have been believed to be formed only by cold drawing after quenching from the melt into an ice−water mixture. − Very recently, we have found that the crystallization of the planar zigzag form is spontaneously induced at 0 °C without any mechanical stress, although the growth rate is very slow. In this communication, we report briefly the first results to confirm such spontaneous crystallization of the form at 0 °C, which have been obtained by CP/MAS 13 C NMR and wide-angle X-ray scattering methods.…”