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DSC studies of tactic polypropylenes: The correlation of polymer stereochemistry with thermal properties
Author(s) -
Burfield David R.,
Loi Patrick S. T.,
Doi Yoshiharu,
Mejzík Jir̆í
Publication year - 1990
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/app.1990.070410519
Subject(s) - tacticity , differential scanning calorimetry , crystallization , enthalpy of fusion , enthalpy , materials science , fusion , crystallinity , polypropylene , glass transition , polymer chemistry , polymer , thermodynamics , chemistry , organic chemistry , polymerization , composite material , linguistics , physics , philosophy
A large number of polypropylene samples, of isotacticities spanning the range 0.35 to 1.00 mm, have been examined by differential scanning calorimetry (DSC) in order to establish a calorimetric index for determining stereostructure. Crystallization studies show that the crystallization onset temperature decreases in step with reduced isotacticity. However, samples prepared with supported catalysts show significantly lower crystallization onset temperatures than those from conventional catalysts which is believed to be due to differences in the inter‐ or intramolecular distribution of stereodefects. Furthermore, whole and fractionated samples cannot be fitted by one calibration curve. However, the enthalpy of crystallization is found to be related to the isotacticity by an equation of the form: log Δ H = m log (isotacticity) + c . This relationship is found to be applicable to samples from all types of catalysts examined and to both whole and fractionated samples. Fusion curves have been determined for “as received” as well as conditioned and annealed samples but the melting temperatures are not found to be a reliable guide to isotacticity. The respective enthalpies of fusion are found to follow the same logarithmic relationship stated above and thus can also be used as a basis for a calorimetric isotactic index. Examination of glass transition and related heat capacity data does not provide any clear‐cut alternative index.