Moorsheads empirical approach

Moorshead proposed an empirical approach to explain the action of the plasticizers, which is found qnite nseful to predict as to what sort of plasticizer is needed to perform a particular function. Moorshead tried to justify why some polymers can be plasticized so efficiently as PVC does while others are not, why some chemicals are good plasticizers, and why some stractnres in plasticizers confer such interesting properties. In some ways Moorhead s approach compiles the concepts of both theories discussed above. This approach was developed for PVC but could be applied to other polar polymers. 

Plasticization theories discussed above agree that plasticizers penetrate into the polymer mass, separating chains and thus reducing intermolecular forces between them. Having this in mind, Moorshead analyzed prerequisites for a polymer to be plasticized  

In order to introduce a liquid into the mass of such polymers, cohesion forces in the liquid molecules must be of the same type as the cohesion forces acting in the polymer mass If the liquid has the same order of cohesion energy as the polymer it will remain stable between the polymer chains. Neither the polymer nor the liquid molecules tends to associate with themselves preferentially. It is not surprising therefore that liquids which have a suitable dipole structure are just those which are most compatible with PVC polymers. 

Polar groups in a plasticizer are essential for good compatibility. When plasticizer molecules are introduced into the polymer mass, polymer chains are separated by the small liquid molecules, which are able to line up their dipoles with the polymer dipoles. Dipoles aligned in this way are quite strong points of attraction. Liquid molecules may have polarizable ring stractures forming points of mutual attraction. Polymer chains separated in this way are more easily moved relative to one another than they are when bonded very closely. This is illnstrated in Fignre 5.3. 

The stmcture of the plasticizer molecnle as a whole has a profound effect on the properties of the plasticized componnd. Polar and polarizable gronps in a plasticizer 

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