Stable helical polyguanidines: poly[N-(1-anthryl)-N'-[(R)- and/or (S)-3,7-dimethyloctyl]guanidines].
Using chiral catalysts of (R)- and/or (S)-BINOL-Ti, the asymmetrical polymerization of achiral monomer, N-(1-anthryl)-N'-n-octadecylcarbodiimide, yielded soluble nonregioregular polyguanidines of Poly-R1 and Poly-S1. A racemization process occurred when the toluene solution of Poly-R1 was annealed at elevated temperatures (70-80 degrees C). Kinetic studies reveal this to be a slow process with an activation energy of ca. 36 kcal/mol. On the other hand, using titanium(IV) trifluoroethoxide catalyst, the polymerization of N-(1-anthryl)-N'-[(R)- and/or (S)-3,7-dimethyloctyl]carbodiimides afforded highly regioregular polyguanidines of Poly-R2 and Poly-S2. These polymers adopt stable helices in various solvents and elevated temperatures, whose kinetically controlled conformations and thermodynamically controlled conformations are essentially the same.
Tang
Hong-Zhi
HZ
Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695, USA.
Lu
Yujie
Y
Tian
Gonglu
G
Capracotta
Michael D
MD
Novak
Bruce M
BM