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Crystallization Kinetics of Poly(dimethylsiloxane) Molecular‐Weight Blends—Correlation with Local Chain Order in the Melt?
Author(s) -
Maus Andreas,
Saalwächter Kay
Publication year - 2007
Publication title -
macromolecular chemistry and physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.57
H-Index - 112
eISSN - 1521-3935
pISSN - 1022-1352
DOI - 10.1002/macp.200700051
Subject(s) - crystallization , isothermal process , kinetics , fusion , enthalpy of fusion , polymer chemistry , proton nmr , differential scanning calorimetry , materials science , crystallography , chemistry , thermodynamics , organic chemistry , linguistics , physics , philosophy , quantum mechanics
The crystallization of bimodal PDMS molecular‐weight blends consisting of long (115 kda) and short (5.3 kda) chains is investigated using DSC and proton NMR. In agreement with earlier studies, it is found that the pure long‐chain sample crystallizes more rapidly than the short‐chain sample. Furthermore, the rate passes through a maximum for the 60:40 blend. These observations hold true for non‐isothermal cooling at −5 K · min −1 and isothermal crystallization at 203 K (both DSC) as well as at 218 K (NMR). The samples with 40% long chains or less crystallize to about 75–80% under all conditions, and the crystalline fractions derived from DSC and NMR agree very well, thus also confirming the literature value of 61.3 J · g −1 as the perfect heat of fusion for PDMS, and disproving some earlier studies. A relation of the crystallization kinetics with entanglement‐induced segmental orientation correlations in the melt is postulated. The local chain order is characterized by proton multiple‐quantum NMR, and an attempt is made to correlate this observable with a reduced crystallization rate, corrected for effects of chain transport.