Quantitative Correlation between Steric Defects and Thermal Behavior in Highly Syndiotactic Polystyrene: A Study Based on DSC and 13C NMR Spectroscopy
✍ Scribed by Luigi Abbondanza; Luigi Abis; Nicoletta Cardi; Fabio Garbassi; Riccardo Po
- Publisher
- John Wiley and Sons
- Year
- 2003
- Tongue
- English
- Weight
- 180 KB
- Volume
- 204
- Category
- Article
- ISSN
- 1022-1352
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✦ Synopsis
Abstract
Several syndiotactic polystyrene (sPS) samples have been synthesized by using different catalytic systems. Their stereochemistry has been determined by ^13^C NMR spectra in both the aliphatic CH~2~ and aromatic C~1~ resonance regions. The observed peaks have been unambiguously assigned to specific hexads and heptads, respectively, and their intensities have been used to draw the percent of defects (meso dyads) in the polymer chains. On the hypothesis that chain defects are at the origin of chain folding and thus determine the thickness of crystalline lamellae, we performed differential scanning calorimetry (DSC) analysis on the same samples, and their thermal parameters were measured. A model was developed to determine the amount of steric defects from the DSC melting‐peak profiles, and the results obtained were compared with the NMR results. A satisfactory agreement was found (correlation factor 0.96) in the explored range of defect concentrations (up to 2.5% of meso dyads). The possible influence of the extraction procedure of the amorphous fraction was found to be negligible. Thus, information on stereochemistry can be obtained from DSC experiments starting from as‐prepared (not extracted) samples.
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