Effect of Plasticizers and Random Copolymers

When a plasticizer is blended into a polymer, the glass transition temperature (Tg) of the polymer decreases. The variation Tg for a mixture of polyfvinyl chloride) (PVC) and dioctyl phthalate 

If the plasticizer is miscible with a polymer, then a mixture of the two substances should yield a homogeneous blend with a single glass transition temperature. Ideally, the resulting can be approximated by a simple relationship such as 

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