Defect groups control

Secondly, it is possible to control the morphology and the crystal size of the MTW by varying the amount of MTEA+ and TEA+ cations in the reaction mixture. The introduction of TEA+ cations leads however to an increased amount of defect groups in the zeolite framework. 

The nature of the reactive centre defines the chemistry of the polymerization, the rate and conditions under which high polymer may form, and particular features of the polymer architecture (such as the tacticity see Section 1.1.2). The nature of the reactive centre and the monomer may also control the side reactions (such as branching) and defect groups that may be introduced, which may affect the subsequent performance of the polymer. In the following, we will consider the most common types of addition polymerization since this may define the properties of the polymer that then control the chemorheology. Certain of these reactions are more important than others in reactive processing, and the particular examples of reactions that occur in forming networks as well as modification of polymers will be considered in more detail. 

Minor (by amount) functionality is introduced into polymers as a consequence of the initiation, termination and chain transfer processes (Chapters 3, 5 and 6 respectively). These groups may either be at the chain ends (as a result of initiation, disproportionation, or chain transfer,) or they may be part of the backbone (as a consequence of termination by combination or the copolymerization of byproducts or impurities). In Section 8.2 wc consider three polymers (PS, PMMA and PVC) and discuss the types of defect structure that may be present, their origin and influence on polymer properties, and the prospects for controlling these properties through appropriate selection of polymerization conditions. 

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