Study On Thermotropic Spiralization Of Polyphenylacetylene With Bis-hydroxyl Groups

A series of substituted achiral phenylacetylenes having hydroxyl groups,M1,M2,M3,were synthesized and polymerized to produce the corresponding homopolymers,P1,P2,P3.Chiral substituted phenylacetylenes M4 and M5 were copolymerized with achiral M1 to produce copoly-(17/43)and copoly-(17/53),respectively.P1 having a dodecyl substituent in the system of Pl/chiral phenylethyl amine showed intense circular dichroism signals at the absorption region of the main chain in the UV-vis region in toluene,hexane and THF at a rather high temperature.However,P1 did not show any CD signal at low temperature in the system.This result suggested P1 could be induced into one-handed helix along with transformation of main chain conformation from cis-transoidal to cis-cisoidal by heating.This unique thermotropic chiral induction phenomenon may be caused by the competition of H-bonds in the system at different temperature.P2 also showed weaker CD signal at low temperature in n-hexane,THF,toluene and chloroform containing R-phenylethylamine without heating.A slight CD signal of P3 also was induced with the existence of R-phenylethylamine produced.Copoly-(17/43)in the n-hexane/achiral alkylamine system also showed the thermotropic one handed helicity induction phenomenon having critical temperature.The critical temperature decreases with the increase of the chain length of the achiral amine because the higher the compatibility between the amine molecule and the solvent.Because of the lack of hydroxyl groups,copoly-(17/53)is difficult to form intramolecular hydrogen bonds between the polymer units,which makes it difficult to be induced to be one-handed helical structure.It is shown that the hydroxyl groups acted key roles for the thermotropic helical induction of the polyphenylacetylenes.