De‐tert‐butylation of poly(N‐tert‐butyl‐N‐n‐propylacrylamide): Stereochemical analysis at the triad level

The stereochemical analysis of polymers derived from N,N‐disubstituted acrylamides is usually difficult. The diad tacticity can be determined from the 1H nuclear magnetic resonance (NMR) signals of the main‐chain methylene groups. However, the splitting because of the configurational sequences is poor, even in 13C NMR, which does not allow determination of the tacticity at the triad level. In contrast, the stereochemical analysis of polymers derived from N‐monosubstituted acrylamides is easily conducted and the triad tacticity can be determined from the 13C signals of the main‐chain methine groups. Thus, stereochemical analysis of N,N‐disubstituted polymers should be able to be conducted if the polymers are transformed into N‐monosubstituted polymers with retention of the configurational sequence. Poly(N‐tert‐butyl‐N‐n‐propylacrylamide) was radically prepared, and de‐tert‐butylation was conducted by treatment with scandium triflate in a mixed solvent of CH3CN and 1,4‐dioxane at 50, 80, and 110°C. 1H NMR analysis of the resulting polymers indicated quantitative conversion after 72 hr, regardless of the temperature. 13C NMR analysis of the transformed polymers confirmed that the configurational sequences were retained during the reaction. Thus, the triad stereochemical analysis of N,N‐disubstituted polymers was successfully conducted by de‐tert‐butylation as a polymer reaction, followed by 13C NMR analysis of the transformed polymers. The stereochemical analysis of N,N‐disubstituted polyacrylamides is usually difficult because the splitting caused by configurational sequences in the NMR spectra is poor. This work reports the de‐tert‐butylation of poly(N‐tert‐butyl‐N‐n‐propylacrylamide) [poly(TBNPAAm)]. The 13C NMR signals of the resulting poly(N‐n‐propylacrylamide) [poly(NNPAAm)] exhibit splitting caused by the triad stereosequences. De‐tert‐butylation followed by 13C NMR analysis successfully reveals that a heterotactic‐rich polymer is prepared by the radical polymerization of TBNPAAm. It should be noted that the characterization of heterotactic polymers requires stereochemical analysis at the triad level.