Side group exchange reactions have been studied for linear high polymeric organophosphazenes, [N=P(OR2)]n (n ∼ 15 000). Specifically, the exchange behavior of polymers was examined where OR = OCH 2CF3, OCH2CF2CF2CF 2CF2H, OCH2Cl3, OC6H 4CHO-p, OC6H4CN-p, and OC6H 4NO2-p with sodium trifluoroethoxide. No aryloxy group replacement by trifluoroethoxy was detected, probably due to the well-protected reactive sites of the polyphosphazenes shielded by aryloxy side groups. For the exchange behavior of [N=P(OCH2CF3)2] n and [N=P(OCH2CF2CF2CF 2CF2H)2]n with NaOCH 2CF2CF2CF2CF2H and NaOCH2CF3, partial substituent exchange was achieved for both reactions. Furthermore, under conditions with excess nucleophile these side group exchange reactions are followed by reactions that introduce sodium-oxo groups attached to phosphorus in place of organic substituents, and this is a mechanism for subsequent hydrolysis and molecular weight decline in the presence of water. Thus, the relative instability of high polymeric [N=P(OCH 2CF3)2]n in the presence of excess NaOCH2CF3 emerged as an explanation for problems with the synthesis of [NP(OCH2CF3)2]n and [NP(OCH2CF3)x(OCH2(CF 2)mCF2H)2-x]n, polymers that have attracted wide fundamental and practical interest. However, substituent exchange reactions do appear to be an alternative synthetic approach for the synthesis of some polyphosphazenes, especially mixed-substituted elastomers and the recently reported trichloroethoxy/trifluoroethoxy-containing cosubstituted polyphosphazenes.
All Science Journal Classification (ASJC) codes
- Organic Chemistry
- Polymers and Plastics
- Inorganic Chemistry
- Materials Chemistry