Molecular motions in crystalline and mesomorphic forms of poly(diethylsiloxane)

✍ Scribed by V. M. Litvinov; V. Macho; H. W. Spiess

• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 661 KB
• Volume: 48
• Category: Article
• ISSN: 0323-7648
• DOI: 10.1002/actp.1997.010481102

✦ Synopsis

Molecular motions in low molar mass (46200 g mol-') poly(diethylsi1oxane) (PDES) are studied by 2H NMR. From DSC measurements the existence of the crystalline phases a,, B, and a2, /I2, as well as a pronounced mesogenic phase a, , is clearly established. Based upon calculations of averaged field gradient tensors based on cone models a detailed motional analysis in the different phases has been conducted. At low temperatures the only motion present besides methyl rotation are librations of the ethyl groups with amplitudes below 25". The motion in the conformational disordered phase is characterized by conformational changes within the side chains, accompanied by occasional rotations through angles larger than 70" within the backbone. The flexibility of the ethyl groups, however, is limited by steric hindrance, prohibiting a full rotation. This situation is observed also in the meso phase where there is an additional rotational degree of freedom around the main chain axis.