Syndiotactic polypropylene after drawing: The effect of stretching polymer chains on magic angle spinning NMR

Sozzani, Piero; Galimberti, Maurizio Stefano; Balbontin, Giulio

doi:10.1002/marc.1992.030130602

Cited by 43 publications

(43 citation statements)

References 13 publications

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“…The signals were assigned on the basis of a rotational isomeric state model applying the same procedure followed in Ref. 16. Complete conversion to the helix form was observed after heating to above 50°C, as for the stretched phase.…”

Section: Metastable Crystalline Formsmentioning

confidence: 99%

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Phase structure and polymorphism of highly syndiotactic polypropylene

Sozzani

Simonutti

Comotti

1994

Magnetic Reson in Chemistry

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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

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Section: Metastable Crystalline Formsmentioning

confidence: 99%

“…The results for three samples will be described and compared: (A) the polymer obtained from polymerization was hot washed with toluene, precipitated with methanol, dried under vacuum, melted and annealed at 140°C for 12 h; (B) sample obtained by quickly cooling from the melt; (C) stretched as described in Ref. 16.…”

Section: Phase Domain Extensionmentioning

confidence: 99%

Phase structure and polymorphism of highly syndiotactic polypropylene

Sozzani

Simonutti

Comotti

1994

Magnetic Reson in Chemistry

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“…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.…”

Section: Introduction and Literaturementioning

confidence: 99%

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

Sura

Desai

Abhiraman

2001

J of Applied Polymer Sci

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ABSTRACT:In processes, such as melt spinning, the crystallization behavior of syndiotactic polypropylene (sPP) is found to be substantially different from that of most other linear polymers. The anisotropic stress field in such processes leads invariably to extension as well as alignment (orientation) of the chains in the melt, both of which contribute usually to dramatic enhancement in the rate of crystallization. However, since the primary structure of the sPP chain in its most preferred crystal form is comprised of a "coiled helical," O(T 2 G 2 ) 2 O, sequence, stress-induced chain extension can lead to conformational sequences that are not favorable for crystallization in this form. As a consequence, process conditions that generate higher stress levels can cause a diminution in the rate of crystallization of this polymer. Such conformation-related aspects of oriented crystallization of sPP have been addressed through an analysis of the structure and properties of melt-spun fibers, produced over a range of spinning speeds. The results serve to identify a refinement that is needed in current models of oriented crystallization and also a mechanism to promote the nucleation of crystallization of sPP.

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“…As st-polypropylene chains became oriented on stretching, Sozzani et al (35) found that the trans-gauche ratio of bond placements shifted in favor of the trans. This was especially noticeable in the necking region; see Figure 2.12 (36), where the switch from tggt and gttg to nearly all tttt placements was observed.…”

Section: Analysis Of Polymers During Mechanical Strainmentioning

confidence: 99%

Chain Structure and Configuration

Sperling

2005

Introduction to Physical Polymer Science

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Syndiotactic polypropylene after drawing: The effect of stretching polymer chains on magic angle spinning NMR

Cited by 43 publications

References 13 publications

Phase structure and polymorphism of highly syndiotactic polypropylene

Phase structure and polymorphism of highly syndiotactic polypropylene

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

Chain Structure and Configuration

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