Y. Zhao et al., MELTING BEHAVIOR OF POLY(3-ALKYLTHIOPHENE)S WITH LONG ALKYL SIDE-CHAINS, Macromolecular chemistry and physics, 198(4), 1997, pp. 1035-1049
The melting behavior of two non-oriented poly(3-alkylthiophene)s (P3AT
s) containing 12 and 14 carbon atoms, respectively, in the alkyl side
chain was investigated by means of differential scanning calorimetry.
We show that the two P3ATs display three melting endotherms after an i
sothermal annealing from the melt. Two of the melting peaks arise from
the ordered structures which are completed in the course of the quenc
hing of the sample from the melt, and judging from the essentially con
stant melting temperatures and heats of fusion, they are not influence
d by the subsequent isothermal annealing conditions. On the other hand
, a much slower crystallization induced by the annealing, which occurs
over a wide range of temperatures, is responsible for the appearance
of a third melting endotherm which is strongly dependent on the crysta
llization condition. We show that this secondary crystallization is no
t a perfection of the existing ordered structures, rather it results i
n distinct crystals which melt at a temperature T-m slightly above the
crystallization temperature T-c. Moreover, it is shown that the plot
of T-m versus T-c parallels the line of T-m = T-c, and that the differ
ence T-m - T-c increases linearly as the number of carbon atoms in the
side chain decreases. On the basis of the calorimetric and X-ray diff
raction measurements, it is suggested that the secondary crystallizati
on originates from the alkyl side chains.