Fundamentals of Polymer Synthesis

Many new developments in cationic polymerizations and in polymer synthesis in general are due to the synthesis of new monomers and therefore new polymers with novel properties. However, the most significant developments are in more controlled polymerizations that enable the synthesis of materials with well-defined properties. After a brief introduction to polymer synthesis, we will focus on syntheses involving only cationic intermediates. Much of the basis of this chapter is covered in general 

The less ambiguous classification is based on the polymerization mechanism, which can be either chain growth or step (nonchain) growth. In the latter case, a given functional group has similar if not identical reactivity, whether it is in the monomer or at the polymer chain end. In a chain growth mechanism, only monomer adds to the active species at the growing chain end i.e., two monomer molecules will not react with each other. 

Propagation is the only elementary reaction in a step polymerization [Eq. (1)]. 

Although a low molecular weight by-product such as water or alcohol is usually generated by each propagation reaction, polyadditions may also proceed by a step mechanism. For example, no by-product is generated by the reaction of diols and diisocyanates to form polyurethane. Because the product always contains reactive end groups, unless one of the reac- 

A step polymerization yields high molecular weight polymer only after very high conversion is reached (Fig. 1) as described by Carother s equation [Eq. (2)] relating the number average degree of polymerization (DP ) to conversion (p). 

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