Free Volume, Glass Transition and Degree of Branching in Ethylene/α-Olefin Copolymers: Positron Lifetime, Differential Scanning Calorimetry, Wide-Angle X-Ray Scattering, and Density Studies
✍ Scribed by David Bamford; Günter Dlubek; Thomas Lüpke; Duncan Kilburn; Jarda Stejny; Tammo J. Menke; M. Ashraf Alam
- Publisher
- John Wiley and Sons
- Year
- 2006
- Tongue
- English
- Weight
- 197 KB
- Volume
- 207
- Category
- Article
- ISSN
- 1022-1352
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✦ Synopsis
Abstract
Summary: Positron annihilation lifetime spectroscopy, differential scanning calorimetry, wide‐angle X‐ray scattering, and density measurements were used to systematically study the variation of the glass transition temperature T~g~ and the mean size v~h~ of holes (local free volumes) in n‐alkyl branched polyethylenes. The samples were commercial ethylene‐rich copolymers with 1‐propene, 1‐butene, and 1‐octene comonomers. From the total specific volume V and the crystallinity X~c~ the specific volume of the amorphous phase V~a~ was estimated and used to calculate the specific hole‐free volume V~f~. It was found that T~g~ and X~c~ decrease and V, V~a~, V~f~, and v~h~ increase with increasing weight fraction of comonomers. Both the real crystalline and amorphous specific volumes decrease with increasing crystallinity X~c~. For not too high contents of comonomers, T~g~ decreases and v~h~ increases linearly with the number and with the length of n‐alkyl branches. This behavior was attributed to an increased segmental mobility caused by branching. Both T~g~ and v~h~ follow linear master curves as a function of the degree of branching if this is defined as the fractional number of carbon atoms in the side chains compared with the total number of carbon atoms. A method for estimating T~g~ from v~h~ measured at room temperature is shown. The number density of holes N~h~ shows a slight variation from 0.6 to 0.8 (±0.1) nm^−3^ with increasing branching.
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