Relationship between glass transition temperature and melting point of polymers

RELATIONSHIP BETWEEN GLASS TRANSITION TEMPERATURE AND MELTING POINT OF POLYMERS 

It has been observed that the ratio of glass transition temperature to melting point (both of course expressed in K) has about the same value for many polymers Tg/Tm 2/3. This feature was first reported by Boyer (1952) and, independently, by Beaman (1953) and Bunn (1953). In later work Boyer (1954,1963) discussed the subject more fully (Fig. 6.8) and gave the following rules  

Unsymmetrical polymers were defined as those containing a main-chain atom that does not have two identical substituents. Other polymers are regarded as symmetrical. Since then many workers have used this relationship as a rule of thumb. 

The truth probably lies between these two opinions the two phenomena show both points of correspondence and points of difference. Thus a constant Tg/Tm ratio may be 

In conformity with these considerations, the following general rules for the Tg/Tm ratio may be formulated  

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