CHEMICAL PROPERTIES OF FATS AND OILS 303 



Polymerization is now believed to be the essential process which brings 

 about the formation of stable films. This requires the presence of either 

 oxygen or heat. In order for condensation or polymerization to occur, a 

 compound must possess at least two functional groups. It is believed that 

 the phenomena of condensation and poljTnerization represent the same re- 

 action.^^* 



Where a molecule has two such functional groups as the hydroxyl and 

 carboxyl, linear polyrtiers of great length may occur as the result of a com- 

 bination in which a functional group of the second molecule reacts with the 

 third, efc.^" Such a linkage would be akin to a lactone bond, which may be 

 an exceedingly stable linkage. 



Although polymers may arise where only two functional groups are pres- 

 ent per molecule, much more stable products are formed where poly- 

 functional groups occur. Rubber, Bakelite, polyvinyl compounds, and 

 s^Tithetic resins are all substances produced by condensation of such mole- 

 cules. Because the number of reactive groups is too small, the esters of 

 monatomic alcohols, or even of the ethjdene glycol, are ineffective. Tri- 

 glycerides are able to condense because of the large number of functional 

 groups which render possible the formation of stable three-dimensional in- 

 terlocked poljTners of very high molecular weights. Carothers^^^ points 

 out the relationship between the molecular size of the polymer and the per- 

 centage of reacting groups (see Table 46). 



Table 46 



Relationship Between Disappearance of Functional Groups and Resulting 



Molecular Size of Polymer" 



" W. H. Carothers, Chem. Revs., 8, 353-426 (1931); Trans. Faraday Soc, 32, 39-53 

 (1936). 



After the functional groups have acted to the extent of 95% (p = 

 0.95), a very slight increase in the functional groups markedly increases the 

 size of the poljmier. When the value of j) changes from 0.90 to 0.95, the 



»57 W. H. Carothers, Chem. Revs., S, 353-426 (1931); Trans. Faraday Soc., 32, 39-53 

 (1936). 



