Importance of Tg || Tg-Molecular Weight and Melting Point || Glass Transition Temperature (Part-2)
Channel: PaathShaaala
Date: 2021-05-16

Importance of Glass Transition Temperature 
Glass transition temperature (Tg) is an important property of the polymer. 
It is useful for the evolution of the flexibility of polymer at a particular temperature. 
The value of Tg decides whether a polymer will behave like a rubbery state (plastic) at the use temperature. 
Tg is an important parameter for the industrial preparation of different articles of polymer material. 

Glass Transition Temperature and molecular weight  
In general, as the molecular weight of polymer increases, glass transition temperature also increases. 
At first, there is a rapid increase in glass transition temperature, then it increases slowly and finally reaches a constant value. 
The glass transition temperature is influenced by molecular weight up to about 20,000. 
After this, the glass transition temperature is almost unaffected.
More the segmental motion - lower Tg
At the end of the polymer chain has more segmental motion because one end is free therefore segmental motion is more in low molecular weight polymer. 
Hence low molecular weight polymer has low Tg. 
After molecular weight 20000, the proportion of chain end to chain segment is almost constant. 
Hence the glass transition temperature also remains constant. 

Glass Transition Temperature and melting point  
The temperature at which liquid-solid transition of a crystalline polymer occurs is called the melting point (Tm) or freezing point(Tf) of the polymer.
An amorphous polymer stays amorphous at any temperature however the mobility of its molecules changes sharply when the temperature reaches to a certain temperature (glass transition temperature).
Most polymers are composed of both crystalline and amorphous portions (domains) which behave differently according to their structures.