Liquid Crystalline Properties of Polyguanidines

Abstract

Modified polyguanidines were prepared, and their liquid crystalline properties were studied using optical polarizing microscopy and X-ray diffraction. Parameters examined include chirality, the uniformity of the lengths of side chains, and attached side-chain mesogens. If the side chains on the repeat units are identical, then polymer has a more ordered structure in both solution and the solid state. Uniform lengths of the side chains are also important. Poly(N,N′-di-n-hexylguanidine), poly-I, exhibited a lyotropic smectic texture in contrast to a nematic texture of poly(N-(rac)-2-phenylethyl)-N′-methylguanidine) (poly-(rac-II)). Optically pure poly(N-((R)-2-phenylethyl)-N′-methylguanidine) (poly-(R-II)) formed a cholesteric texture, whereas the corresponding racemic polyguanidine, poly-(rac-II), formed a nematic texture. Additionally, poly-(R-II) displayed a mesophase at a lower critical concentration than either poly-I or poly-(rac-II), implying that poly-(R-II) is stiffer than these two other derivatives. Poly(N-6-((4′-methoxyphenylazo)phenyl-4-oxy)hexyl-N′-n-hexylguanidine) (poly-IV), one of combined liquid crystalline structures (liquid crystalline backbone plus liquid crystalline side chains), displayed a lyotropic nematic texture presumably due to the strong dipolar-dipolar interaction between the main chain and side chains that folds the appendages parallel to the molecular axis. Poly(N-12-((4′-methoxybiphenyl-4-oxy)dodecyl-N′-n-dodecylguanidine) (poly-V) and poly(N,N′-di-n-dodecylguanidine) (poly-VI) exhibited thermotropic liquid crystalline behavior.

Facile Synthesis of Rod–Coil Block Copolymers with Chiral, Helical Polycarbodiimide Segments via Postpolymerization CuAAC “Click” Coupling of Functional End Groups

“…41 Additionally, this polymer adopts lyotropic cholesteric mesophases in concentrated CHCl 3 solutions. 35 The use of CuAAC "click" reactions in macromolecular synthesis has expanded tremendously offering new routes in the synthesis of rod−coil block copolymers, core−shell nanoparticles, and rod−coil polymer brushes. 42−45 Our group has successfully demonstrated the ability to efficiently functionalize the side chains of polycarbodiimides using CuAAC "click" chemistry in several reports.…”

Evidence of Entropy-Driven Bistability through 15N NMR Analysis of a Temperature- and Solvent-Induced, Chiroptical Switching Polycarbodiimide

“…18−26 Throughout this time, novel, helical macromolecular scaffolds have emerged including systems such as oligio- 27 and poly(m-phenylene ethynylenes), 28,29 polyisocyanates, 30,31 polyisocyanides, 32−34 poly-(phenyl acetylenes), 35,36 poly(quinaxoline-2,3-dials), 37,38 and polycarbodiimides 39 to name a few. Polycarbodiimides, a relatively young class of helical macromolecules, have been an intense area of interest in the Novak group since the discovery of the controlled "living" Ti(IV)-mediated polymerization of carbodiimides in 1994 due to their attractive properties such as liquid crystallinity, 40,41 high helical inversion barrier, 42 and chiroptical switching. 43 −46 In 2005, Tang et al reported the first polycarbodiimide possessing reversible solvent-and temperature-induced chiroptical switching in toluene.…”

Developments in synthesis, characterization, and self‐assembly of polycarbodiimide systems

“…Helix‐sense selective polymerization can be induced upon polymerization of chiral monomers with achiral initiators. For polycarbodiimide synthesis, chiral N ‐phenethyl‐ N ′‐methylcarbodiimide (PMC) monomers are prime candidates to achieve helix‐sense selective polymerizations due to the resulting polymers (PPMC; poly( N ‐phenethyl‐ N ′‐methylcarbodiimide)) possessing many interesting properties such as cholesteric liquid crystallinity, rigid‐rod backbone structure, and enantiomerically pure helical secondary structure …”

“…Incorporating varied pendant groups has led to the discovery of several interesting properties including lyotropic/thermotropic liquid crystallinity, chiroptical switching, and antimicrobial activity. As mentioned, much of the past research on polycarbodiimides has been outlined in our previous review.…”