Studies On Polydiacetylene/Common Polymer Blends With Reversible Thermochromism Via Synergetic Effect

When properly packed in the solid state,diacetylene monomers can be topochemically polymerized into polydiacetylene by UV,γ- or strong X-ray irradiation.Usually,colorless diacetylene crystals turn into blue polydiacetylene crystals,which often undergo an irreversible "blue-to-red" colorimetric transition when environmental stimuli are applied.This unique transition has found many applications as colorimetric sensors;and the polydiacetylenes with reversibility have attracted great interest for they can be repeatedly used.Despite the fact that reversible thermochromism has been reported for polydiacetylenes,the fundamental physics for the reversibility and how to achieve the reversibility still desire further investigation. In addition,no reversible thennochromism has been realized for irreversible polydiacetylenes in polymer blends so far.In this thesis,we have studied the feasibility of reversible thermochromism through a hierarchical self-assembly in poly(vinyl pyrrolidone)(PVP) and poly(10,12-pentacosadiynoic acid)(PDA,an irreversible polydiacetylene in the pure form) blend or poly(vinyl alcohol)(PVA) and PDA blend via synergetic effect.In detail,a method for preparing non-covalently connected micelles(NCCM) was used to fabricate PVP/DA(the monomer of PDA) or PVA/DA nano-suspension in aqueous solution,followed by drying at different temperatures.In this first step self-assembly,water-soluble PVP/DA or PVA/DA nanoaggregates were obtained because of PVP stabilization at the outer surfaces via hydrogen bonding.In the second step self-assembly,the "bricks and mortar" structure(crystallized DA bilayers being the bricks and PVP or PVA chains being the mortar) or pure DA nanocrystals were formed in the blend films,depending on whether the suspension solution was dried slightly above or far away from the DA crystal melting point at 63℃.Intriguingly, after topochemical polymerization,the film with the "bricks and mortar" structure exhibited reversible thermochromism,while pure PDA nanocrystals did not. Dissolving the film with the reversible thermochromism leads to the water soluble nanoaggregates showing the reversibility.From these results,we conclude that the physical constraint exerted on every PDA bilayers by the PVP or PVA mortar substantially helped reversible conformational changes in the PDA main chain.This synergetic effect was believed to be one of the important reasons for the reversible thermochromism.