FUNCTIONAL POLYMERS AND SEQUENTIAL COPOLYMERS BY PHASE-TRANSFER CATALYSIS .24. THE INFLUENCE OF MOLECULAR-WEIGHT ON THE THERMOTROPIC PROPERTIES OF A RANDOM COPOLYETHER BASED ON 1,5-DIBROMOPENTANE,1,7-DIBROMOHEPTANE, AND 4,4'-DIHYDROXY-ALPHA-METHYLSTILBENE

The influence of molecular weight on thermal transitions and on their thermodynamic parameters is discussed for a random thermotropic liquid crystalline copolyether based on the reaction of a 1:1 molar mixture of 1,5-dibromopentane and 1,7-dibromoheptane with 4,4 prime -dihydroxy- alpha -methylstilbene. Optimum phase transfer catalyzed polyetherification reaction conditions were established for the synthesis of polymers containing bromoalkane chain ends only over a wide variety of molecular weights. All these copolyethers present a crystalline and an enantiotropic nematic mesophase over the entire range of molecular weights studied. Both the thermal transitions and their thermodynamic parameters are strongly molecular weight-dependent up to M OVER BAR //n equals 10,000-12,000, after which they remain constant.