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Aliphatic liquid crystal copolymers with long flexible spacers
Abstract
The goal of this project was to produce a series of well-defined copolymers that could be classified as aliphatic liquid crystal thermoplastic elastomers. The copolymers that were produced consisted of hard and soft segments, linked through ester bonds. The hard segments were 3 and 5-ring all aliphatic mesogens containing trans-1,4-cyclohexylene (CH) and/or 1,4-bicyclo (2.2.2) octylene (BCO) units. The soft segment consisted of flexible polyglycols, either polytetrahydrofuran (PTHF) or polypropylene glycol (PPG), of varying number average molecular weight (650 to 2900 g/mole). Model compounds were synthesized to find mesogenic hard segments to incorporate into copolymers. When compared to analogous aromatic mesogens the B3 and BCB tetraester mesogens behaved as expected. The B3 and BCB samples all exhibited very broad mesophase ranges, as a consequence of low $\rm{\bf T\sb{m}}$ and high ${\bf T\sb{i}}$. Branched chain end 3-ring model compounds were also synthesized to model the effects of branching in the soft segment, similar to the copolymers containing PPG. The copolymers displayed many of the trends that are described in the literature for semiflexible MCLCP's with aromatic mesogens. Increasing soft segment length caused a decrease in transition temperatures. Increasing hard segment length increased the transition temperatures and phase separation and also produces a material considered to be a liquid crystal thermoplastic elastomer. Branching on the soft segment, also caused a decrease in the transition temperatures and changes the type of mesophase observed. Branching did not eliminate the mesophase as is the case in aromatic mesogens, but instead produced a material that may be classified as a liquid crystal thermoplastic elastomer. This work demonstrates the importance of structure property relationships in liquid crystalline behavior. The behavior of aliphatic 3 and 5 ring mesogens both in small molecules and polymers showed that the aromatic system is not as important to liquid crystalline behavior as is mesogen geometry and rigidity; and in the case of copolymers, the soft segment.
Subject Area
Organic chemistry|Polymers
Recommended Citation
Thomas, Rebecca Mae, "Aliphatic liquid crystal copolymers with long flexible spacers" (1996). Doctoral Dissertations Available from Proquest. AAI9639041.
https://scholarworks.umass.edu/dissertations/AAI9639041