Examples of Polymerization with Expansion in Volume

In 1972, Bailey and Sun reported that the cationic polymerzation of 1,4,6-trioxaspiro- 4.4 nonane  

0-1 moves closer to the growing center (covalent bond) and 0-6 closer to C-5 (carbonyl double bond). At the same time the distances between 0-1 and C-5 and between 0-6 and C-7 increase, due to the breaking of single bonds. By this process a compact, dense monomer molecule is transformed into a rather loose polymer segment. 

A number of spiro orthoesters have been synthetized and the volume changes during the cationic ring-opening polymerization have been studied46.  

More recently, Hall reported that in the polymerization of some bicyclic monomers, opening of one ring leads to contraction whereas opening of the second ring is accompanied by expansion47. In the following sections experimental details concerning some typical systems studied to date are are briefly summarized. 

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