On the tacticity of polynorbornenes with 5,6-endo pendant groups that contain substituted aryl chromophores.
Two dimers and a series of polymers with 5,6-endo pendant aryl groups that contain different substituents at the para positions were synthesized. The conformation and stereochemistry of the dimers and polymers were determined by nonlinear optical analysis (EFISH) as well as UV/Vis and 13C NMR spectroscopy. The chemical shifts of C7 for the polymers appeared as two peaks in the 13C NMR spectra when the substituents are electron-withdrawing groups. The percentage decrease in the relative extinction coefficient of the polymers, epsilon(d), was linearly related to the Hammett constant sigma. Polynorbornenes with electron-withdrawing substituents may adopt isotactic stereochemistry with all pendant groups aligned in one direction. The nature of the interactions between neighboring chromophores may be one of the most important factors in directing the stereoregularity and conformation of these polymers. The corresponding polymers derived from the exo isomers appeared to be less stereoregular.
Lin
Wei-Yu
WY
Department of Chemistry, National Taiwan University, Taipei 106, Taiwan.
Wang
Hsian-Wen
HW
Liu
Zhi-Chang
ZC
Xu
Jun
J
Chen
Chih-Wei
CW
Yang
Yun-Chin
YC
Huang
Shou-Ling
SL
Yang
Hsiao-Ching
HC
Luh
Tien-Yau
TY
D019281:Dimerization; D006841:Hydrocarbons, Aromatic / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D009636:Norbornanes / Q000737:chemistry*; D011108:Polymers; D013057:Spectrum Analysis; D013237:Stereoisomerism
D006841:Hydrocarbons, Aromatic; D009636:Norbornanes; D011108:Polymers