Entropy effect of alkyl tails on phase behaviors of side-chain-jacketed polyacetylenes: Columnar phase and isotropic phase reentry
writer：Xiaoqing Liu, Jun Wang, Shuang Yang, Yongfeng Men , Pingchuan Sun,* Er-Qiang Chen*
keywords：columnar liquid crystalline phase,reentrant isotropic phase,entropy effect
source：期刊
specific source：Polymer 2016, 87, 260-267
Issue time：2016年
We have investigated phase behaviors of a series of polyphenylacetylene derivatives, poly[di(n-alkyl)ethynylterephthalates] (Pn, n is the number of carbon atoms of n-alkyl group, from 2 to 14), which are largely influenced by the length of n-alkyl tails on 2,5-position of the phenyl group. With short alkyl groups (n <=6), Pns form columnar liquid crystalline (Col) phases due to the “jacketing effect” of sidechains. As the alkyl tails become longer (n >=8), an isotropic phase, which can be considered as a reentrant one (Ire), is identified between lamellar phase (Lam) at low temperatures and Col phase at high temperatures. This unusual phase behavior is determined by the motional state of the side-chains. Thanks to in-situ variable temperature solid-state NMR experiments, the motion of main- and sidechains in different phases were distinguished, providing strong evidence for the entropy effect of sidechains which drives Ire and then Col phase in Pns (n >=8) upon heating.