Effect of -C(CF3)2- on the surface energy of main-chain liquid crystalline and crystalline polymers

Novel fluorinated main-chain liquid crystalline/crystalline polymers were prepared through thin film polymerization. Two polymer systems were studied: one from 2,6-acetoxynaphthoic acid (ANA): acetoxy acetanilide (AAA), and 4,4'-(hexafluoroisopropylidene)bis(benzoic acid) (6F acid) and the other from ANA, hydroquinone diacetate (HQAT), and 6F acid. The surface energy was estimated using contact angles of water, glycerol, and diiodomethane. A small amount of -C(CF3)(2)- in the main chain lowered the surface energy, and the fluorocarbons were preferentially enriched at the air-polymer interface, causing low surface energy and large water contact angles. These results agreed with XPS data. Since the -O-Ar-O- unit in the HQAT moiety is more rigid than the -O-Ar-N- unit in the AAA moiety, LC texture formed more easily in the ANA/HQAT/6F acid system than in the ANA/AAA/6F acid system. Contrarily, the fluorocarbons enriched more preferentially at the surface in the ANA/AAA/6F acid system than in the ANA/HQAT/6F acid system. Moreover, the hydrogen bonding originating from the amide group hindered further decrease of surface energy with an increase in 6F acid content in the ANA/AAA/6F acid system.