content of the polymer main chain. Both ΔH and ΔS for the conformational transition from random coil to helix assumed negative values, which also greatly depended on the length of the pendent groups. Whereas the helical conformation of poly(5) and poly(6) was readily generated in chloroform, neither THF nor toluene was favorable for helix formation.
Ñ -Propargylamides具有侧链基团与不同的长度(HC⋮CCH 2 NHCOR,R =(CH 2)Ñ H,Ñ = 1-8)在负载Rh催化剂的存在下进行聚合[(NBD)的Rh +乙-(C 6 H 5)4 ; nbd =
2,5-降冰片二烯]以高收率获得具有中等分子量和高立构规整度的聚合物[poly(1)-poly(8)]。通过在不同温度下在
氯仿溶液中测量UV-vis光谱,研究了所得聚合物的构象转变行为。在检查的聚合物中,聚(5)和聚(6)在相对较高的温度下具有稳定的螺旋构象,并且其螺旋含量最高。由于缺乏链柔韧性和分子间氢键,具有较短烷基悬垂链的Poly(2)-poly(4)不存在稳定的螺旋构象。聚(1)不完全溶于任何溶剂。含有较长侧链的Poly(7)和poly(8)由于聚合物主链的顺式含量较低,因此仅在低温下呈螺旋构象。两个Δ ħ和Δ小号从随机线圈到螺旋的构象转变假定为负值,这也