Influence of Chemical Structure on Glass Transition Temperature

2 Influence of Chemical Structure on Glass Transition Temperature 

Si-O-Si links, contained in silicones, are extremely flexible, followed by CH2-CH2 and CH2-CH=CH-CH2. The great flexibility of the latter, despite the rigidity of the double bond it contains, stems from the very weak resistance to rotation around the two CH2-CH bonds. Introducing a ring into the main chain considerably increases the value of Tg. 

Short substituents cause steric hindrance to rotation, and all the more so when they are bulky. This also raises Tg. 

Alkyl substituents of increasing length no longer affect flexibility of the main chain. However, they impose a spatial separation of the chains which decreases T 

The glass transition phenomenon is characteristic of the amorphous state and occurs regardless of molecular weight. However, Tg is greatly reduced when the molecular weight M is decreased  

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Influence of chemical structure on glass transition temperature Tg... 

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