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Liquid crystalline segmented and triblock copolymers
Abstract
This thesis describes the synthesis and characterization of segmented and triblock copoplymers with mesogenic hard blocks and flexible spacer soft blocks. Three series of segmented block copolymers, one series of twin liquid crystal (LC) polymers and a variety of model compounds have been prepared. The first series of segmented block copolymers consist of potentially mesogenic dyad hard block and oligomeric flexible spacers. These materials are not liquid crystalline, although chain extended analogs do show elasticity and strength. The second and third series of segmented polymers consists of well defined tetrad and pentad mesogenic blocks. These polymers and their analogous model compounds exhibit liquid crystallinity. The preparation of these materials involved the condensation of a bisphenolic prepolymer of, either poly(tetramethylene ether)glycol, polyTHF, or polypropylene glycol, PPG, of varying molecular weight, with a variety of aromatic diacid chlorides: 4,4$\sp\prime$-azobiphenylene, 4,4$\sp\prime$-azoxybiphenylene, 4,4$\sp\prime$-biphenylene, 2,6-naphthalene and 4,4$\sp\prime$-terephthaloyloxybiphenylene. The resulting polymers are liquid crystalline and exhibit reproducible melt transitions by differential scanning calorimetry, DSC and polarized optical microscopy, POM. The polymer melts are birefringent, and textures for some of the polymers are consistent with either smectic or nematic mesophases. The LC polymers show a convergence of Ti with Tm as the spacer length increases from 40 to $\sim$200 atoms. It is also shown that the type of polymeric soft segment used to prepare tetrad LC polymers has a remarkable effect on the liquid crystallinity and physical properties of the resulting polymer. Finally, variations in the hard block can dramatically effect both the stability and structure of a liquid crystalline phase. In the final section, "twin" or triblock LC polymers are described. These polymers were prepared to compare thermal properties of segmented vs. triblock copolymers with chemically identical blocks. The preparation involved the synthesis of a novel mono functional mesogen. The twins exhibit thermal trends similar to those of the corresponding segmented polymers.
Subject Area
Polymer chemistry
Recommended Citation
Kolb, Eric S, "Liquid crystalline segmented and triblock copolymers" (1991). Doctoral Dissertations Available from Proquest. AAI9120903.
https://scholarworks.umass.edu/dissertations/AAI9120903