Iterative Methodology with Regeneration of DPE Function

All living anionic polymers herein used were adjusted to be around 10 000 g/mol in M value. The two reaction steps, (1) and (2), were carried out in THE at —78 °C for 1 h and 10 min, respectively. The linking reaction and the regeneration of the DPE function in each iterative process were confirmed by SEC and H NMR analysis to be essentially quantitative. Therefore, the targeted polymers were always obtained in nearly 100% yields and isolated in 80% yields by fractional precipitation. The isolated polymers, that is, AB diblock, 3-arm ABC, 4-arm ABCD, and 5-arm ABCDE stars, exhibited sharp monomodal SEC peaks without shoulders and/or tailings. 

As can be seen from the results summarized in Table 4.3, the molecular weights of the resulting polymers were in good agreement with those observed by SLS and H NMR. 

The compositions observed by H NMR were consistent with those calculated from the feed ratios. Accordingly, these results clearly indicate that well-defined 3-arm ABC, 4-arm ABCD, and 5-arm ABCDE p-star polymers are successfully synthesized by repeating the processes with five different tiving polymers. Thus, the first proposed iterative methodology with the regeneration of DPE reaction sites works very well. 

The 5-arm ABCDE star synthesized by this method is the first successful p-star polymer with five different arm segments. Furthermore, the E segment of the resulting star was readily and quantitatively converted to a poly(4-vinylphenol) segment by treatment with BU4NF, resulting in a new functional 5-arm ABCDE star with an acidic and ionic segment. Since the final 5-arm star still possesses a DPE function at the core, this procedure enables further synthetic sequence of stars with more arms and components. 

The advantage of this procedure is that, in essence, any monomer that undergoes living anionic polymerization from a DPE anion can be used. On the other hand, the successive synthesis of star-branched polymers can no longer be continued. 

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