A survey has been made of spherulites formed by the isothermal crystallization of polypropylene from the melt in the temperature range 110°–148°C. Four types of spherulite have been distinguished and their structural morphology, optical properties, melting behavior, and growth rates have been examined.

Spherulitic Crystallization in Polypropylene

Structure and morphology of poly(propylenes): a molecular analysis

The crystalline structure, spherulitic crystallization and melting behaviour of isotactic polypropylene (iPP) is comprehensively reviewed, illustrated and discussed. It is demonstrated and summarized how the nucleation, development and growth of the different spherulites depend on the crystallization and melting conditions both in quiescent and sheared melt. Based on the results the microtexture development during real processing conditions is elucidated for selected examples. Several subjects of intense debate on the above topics are clarified using evidence from polarized optical micrography and differential scanning calorimetry.

Supermolecular structure of isotactic polypropylene

Infrared spectra of polyethylene terephthalate and three of its deuterated analogs have been obtained in the region of 70 to 3600 cm-i, polarized spect,ra having been obtained down to 330 cm-l On the basis of analysis of the predicted spectrum, and with the aid of data from benzene and substituted benzenes, a complete assignment of the spectrum has been made This assignment suggests a modification of the proposed chain structure of this polymer It also leads to the conclusion that the changes in the spectrum which occur upon crystallization of the polymer are not associated with different isomeric forms of the -OCH2CH20portion of the chain, but rather with changes in the symmetry and resonance characteristics of the substituted benzenoid ring framework

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Infrared spectra of high polymers

The spherulitic and lamellar morphology of melt-crystallized isotactic polypropylene

An attempt is made to account for the observed birefringence of the various types of polypropylene spherulite in terms of preferred crystalline orientation. Evidence is also presented showing that some of these spherulites crystallize with a new metastable crystal structure, not previously described.

H. D. Keith

Papers

Evidence for a Second Crystal Form of Polypropylene