Stimuli-responsive polymers. III. Poly(aryl ether ketone amide)s with reversibletrans- ?cis-4,4?-azobenzene and fixed 2,2?-binaphthyl kinking elements in the main chain

Stimuli-Responsive Polymers VI. Azobenzene Modified Copolyaramides with Chiral Helical Geometries: Influence of Rigid, Helix-Disrupting Segments on Physiochemical and Chiroptical Behavior

“…Importantly, cis-isomer half-life values determined at room temperature for all of the polymers exceeded 100 h, allowing for the acquisition of chiroptical data over short time periods that were uncomplicated by rapidly shifting cis-trans isomer populations within the polymer backbones. As observed for other azobenzene modified copolyaramides synthesized in our laboratory, 4,6,8,13 the interconversion of trans-and cisisomeric states within these constructs was completely reversible over numerous isomerization cycles without any apparent hysteresis or photodegradation effects.…”

“…However, all of the polymers were characterized by a prominent exotherm (T azo ) residing within the 428 to 464 • C temperature window (Table III). As we have reported before, 4,6,12 this transition corresponds to the extrusion of molecular nitrogen from the trans-azobenzene mod- ified polymer backbone and serves to ultimately limit the thermal and thermo-oxidative stabilities of these materials beyond 400 • C. A comparison of the data provided in Tables I and III reveals that copolyaramides fitted with higher trans-azobenzene loadings exhibited slightly reduced weight loss onset temperatures under the standard conditions employed in this study.…”

“…3,4 In these systems, the presence of multiple binaphthylene units within the polymer's main chain provides for highly twisted, helical geometries that are unable to pack efficiently or crystallize in the solid state. As the kinked binaphthylene linkages were systematically replaced by more rigid diphenylfluorene moieties to give variants trans-2(R) through trans-6 in this study, polymer solubilities evaluated at room temperature were observed to drop in all but the most aggressive solvent media.…”

“…Polymer residues recovered after heating to 600 • C were severely darkened and were insoluble in all of the organic solvent media listed in Table II. As for other trans-azobenzene modified polyaramides constructed in this laboratory, 4,6,12 melting transitions for these materials were notably absent from their DSC scans. However, all of the polymers were characterized by a prominent exotherm (T azo ) residing within the 428 to 464 • C temperature window (Table III).…”

“…2 Earlier, this laboratory reported the preparation of a number of helical trans-azobenzene modified polyaramides from both (R)-and (S )-1,1 -binaphthyl-2,2 -diamine. 3,4 Some of these materials were specifically designed to undergo reversible helix order ↔ disorder transitions in response to multiple trans ↔ cis azobenzene isomerization reactions triggered within the polymer's main chain. [5][6][7][8] When evaluated in polar solvent media, the helical polyaramides trans-1(R) and trans-1(S) were found to possess specific rotations (sodium D-line) near (−) 500 and (+) 500 deg dm −1 g −1 cm 3 , respectively.…”