Chemically Initiated Solid-state Polymerization of TXN

These processes are carried out with crystals of TXN. An alternative is polymerization of crystals suspended in nonsolvent. Typical cationic initiators like BF3 130,131) or SnCl4 132,133) are most frequently used. 

In suspension polymerization, initiator (e.g. BF3 OEt2) is dissolved in the suspending medium. In the polymerization of crystals alone, gaseous BF3 (usually diluted with N2) is used. 

The characteristic feature of chemically initiated solid-state polymerization of TXN is the decrease of molecular weight with conversion. This is illustrated by the data in Table 7.13. It was concluded that high-molecular-weight polymer may be produced only on the surface of a crystal. At a later stage, when polymer is formed in the inner part of the crystal, lower-molecular-weight polymer results. The molecular weight increases with increasing temperature (cf. Table 7.13), and depends also on 

Essentially the same results were obtained for SnCl4-initiated suspension polymerization 132). The molecular weight decreased with increasing conversion and as in the BF3 initiated polymerization increased after addition of a small amount of a good solvent131). 

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