Macromolecules, Vol.30, No.25, 7701-7720, 1997
Monodisperse linear liquid crystalline polyethers via a repetitive 2(n) geometric growth algorithm
A simple and general stepwise procedure for the synthesis of linear monodisperse liquid crystalline (LC) polyethers with degrees of polymerization (DPs) up to 33 (M-n = 15 090) is presented. The particular examples used for this demonstration are based on the conformationally flexible mesogen 1-(4-hydroxy-4'-biphenylyl)-2-(4-hydroxyphenyl)butane (TPB) and flexible spacers containing 10 methylenic units. The synthetic algorithm employed is exemplified by two synthetic pathways and is based on the repetition of a synthetic cycle consisting of either five or three synthetic steps. After each cycle the molecular weight is doubled. The method is very versatile, as it allows the synthesis of a large library of compounds. Linear monodisperse oligomers with DP = 1, 2, 4, 16, 17, and 33 and with a variety of chain ends were synthesized. The dependence of the phase behavior of these oligomers on the nature of their chain ends and on their DP was investigated. The mesophase stability and range increase continuously with DP. The effect of chain ends on the phase behavior decreases with DP with the following trend on the stabilization on the nematic phase of these polyethers: Bn (i.e., benzyl) > (CH2)(10)OH > (CH2)10Br similar to (CH2)(10)OMs > (CH2)(8)CH=CH2 similar to (CH2)(9)CH3 > THP (i.e., tetrahydropyranyl) > OH.