C. Yang et al., A PHENOMENOLOGICAL MODEL FOR PREDICTING THERMOCHROMISM OF REGIOREGULAR AND NONREGIOREGULAR POLY(3-ALKYLTHIOPHENES), Macromolecules, 29(20), 1996, pp. 6510-6517
Thermochromism of a series of cast films of poly(3-alkylthiophenes) (P
3ATs, A = hexyl, octyl, dodecyl, and hexadecyl) with different head-to
-tail(HT) diad content (70-100%) was studied. The thermochromic behavi
or is found to be controlled by the HT diad content and the side chain
length. P3ATs with moderate HT diad content give rise to a clear ther
mochromic isosbestic point irrespective of the length of the alkyl sid
e chain. Regioregular polymers possessing a >90% HT diad content exhib
it either a continuous thermochromic blue shift or an isosbestic point
, depending on the alkyl side chain length. The different thermochromi
c characteristics are attributed to subtle morphological differences b
etween the polymers. DSC and X-ray diffraction studies indicate that P
3AT samples with moderate HT regularity are formally amorphous with a
quasi-ordered phase dispersed in continuous disordered domains. P3ATs
with high HT regularity consist of crystalline, quasi-ordered, and dis
ordered phases. For polymers with short alkyl side chains, these phase
s equilibrate with each other and destroy the thermochromic isosbestic
point. Polymers with long alkyl side chains melt at much lower temper
ature and are converted directly between the crystalline and disordere
d phases.