Why is stereoregular polyacrylonitrile obtained by polymerization in urea canals isotactic?

摘要

Because stereoregular i-PAN is obtained from the constrained polymerization of acrylonitrile monomer in expandable urea clathrates, we studied the inclusion compounds formed between guest AN and PANs and host cyclodextrins whose rigid channel diameters are in the range of the canals in urea clathrates. ICs of AN were successfully formed with alpha- and gamma-CDs but did not yield PANs, and only ICs between gamma-CD, and a- and i-PANs were formed in solution. Modeling of AN and s- and i-PAN-CD-ICs were performed using PM3 parameters to estimate their stabilities. We conclude that the polymerization of AN in urea clathrate channels produces predominantly i-PAN as a consequence of its improved fit compared with s-PAN.