Growth Polymerization

Chain-growth polymerization has been used to prepare a number of olefin-functionalized metal-containing monomers. For example, a munber of articles have detailed the polymerization of organometaUic olefinic monomers such as 82-84. Depending on the nature of the double bond and the metallic group, radical, cationic, and anionic initiators can be used to polymerize these monomers. 

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It is the third of these criteria that offers the most powerful insight into the nature of the polymerization process for this important class of materials. We shall frequently use the terms step-growth and condensation polymers as synonyms, although by the end of the chapter it will be apparent that step-growth polymerization encompasses a wider range of reactions and products than either criteria (1) or (2) above would indicate. 

Table 5.1 Hypothetical Step-Growth Polymerization of 10 AB Molecules ...

We shall have considerably more to say about this type of kinetic analysis when we discuss chain-growth polymerizations in Chap. 6. 

The preceding discussions of the kinetics and molecular weight distributions in the step-growth polymerization of AB monomers are clearly exemplified by the esterification reactions of such monomers as glycolic acid or co-hydroxydecanoic acid. Therefore one method for polyester synthesis is the following ... 

Source M. F. Drumm and J. R. LeBlanc, Step-Growth Polymerizations, D. H. Solomon (Ed.), Marcel Dekker, New York, 1972, p. 196. 

The fact that both AH and AS are expected to be positive for reaction (5. EE) means that AG tends to be negative at higher temperatures and positive at lower temperatures. Thus linear molecules tend to be favored over rings at higher temperatures. We have seen elsewhere in this chapter that step-growth polymerizations are usually conducted at elevated temperatures. 

AA and BB monomers and also AB monomers invariably react to form predominantly linear structures in all but the rather special case where the ring structure in reaction (5.CC) has a value of 1 = 5 or 6. This explains why so many of the monomers in step-growth polymerizations are tetra-, hexa-, and decamethylene compounds. 

Discussion of ladder polymers also enables us to introduce a step-growth polymerization that deviates from the simple condensation reactions which we have described almost exclusively in this chapter. The Diels-Alder reaction is widely used in the synthesis of both ladder and semiladder polymers. In general, the Diels-Alder reaction occurs between a diene [XVI] and a dienophile [XVll] and yields an adduct with a ring structure [XVlll] ... 

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