Phase separation of poly(?-benzyl L-glutamate) to liquid crystal and isotropic solution in various helicogenic solvents

Abstract

Solvent effects on the phase separation of poly(y-benzyl L-glutamate) to liquid crystal and isotropic solution have been observed in various helicogenic solvents. The temperature-composition phase diagrams have been determined for each solution. The critical concentrations, v~, at which the phase separation occours have been compared in various solvents. In dimethylformamide in which the polymer is molecularly dispersed, the observed v2 value has agreed with that calculated by Flory's theory. In some solvents in which the polymer aggregates in a head-to-tail mode such as chloroform, the observed v2 values have been considerably small. It is assumed that the polymer aggregates behave as longer particles than the original particles. In dioxane in which the polymer aggregates highly both in a head-to-tail and a side-by-side modes, the v~ value has been a little larger than that in chloroform. In this case the relationship between the aggregation and the liquid crystal formation is so complicated that further investigation is necessary. In aromatic solvents such as m-cresol that dissolves the polymer almost molecularly, the v~ is smaller than that in dimethylformamide. Therefore, the intermolecular interactions between the phenyl groups in the side groups of the polymer and those in solvent molecules must be considered.

Preparation of poly(γ-benzyl-L-glutamate) nanofibers by electrospinning from isotropic and biphasic liquid crystal solutions

“…PBLG was dissolved in CH 2 CI 2 at concentrations of 7.5 and 8 wt%, which are near the critical concentration between the isotropic phase and biphasic phase (mixture of the isotropic and LC phases) that is known as 'point A' . 12,19 Pyridine was added to the solvent at a concentration of 1.0 weight percent to improve the electrospinnability. Figure 2 shows the POM images of the PBLG/CH 2 Cl 2 -pyridine solutions.…”

“…The 7.5 wt% solution exhibited an isotropic phase, whereas the 8 wt% solution exhibited a biphasic structure (mixture of the LC phase and isotropic phase based on the texture of the spherulites). 19 …”

“…[10][11][12]19 A solution in the complete LC phase of PBLG in which a-helices are highly oriented and aggregated is difficult to electrospin because of its high viscosity. The biphase of lyotropic LC appears between the intermediate concentration between critical concentrations for the isotropic and LC phase at a certain temperature, [10][11][12]19 and the biphasic solution can be electrospun. The aims of the present study were (i) to prepare PBLG nanofibers by electrospinning from both isotropic and biphasic solutions and (ii) to investigate the effect of the ordered structure in the spinning solution (that is, the ordered structure in the biphasic solution) on the internal structure and molecular orientation of the electrospun fibers.…”

Fibrillar gels via the self-assembly of poly(l-glutamate)-based statistical copolymers

“…17 None of the aforementioned gels result from the selfassembly of PLGA α-helices. Unlike PLGA, PBLG α-helices can assemble in a head-to-tail and side-by-side fashion 28,43,44 and generate long range order in helicogenic organic solvents. At high concentrations (over 10 wt%), PBLG self-assembly yields lyotropic phases.…”

“…45,46 Although contrasting mechanisms have been proposed for the gelation of PBLG, including (i) phase separation by spinodal decomposition, (ii) nucleation growth, and (iii) a combination of both mechanisms, the result is the formation of a percolated network of fibers. 44,47,48 The stability of PBLG helices and fibers is often attributed to a combination of the following features: intra-molecular hydrogen bonding (especially in aprotic solvents), 11 dipole-dipole interaction of the PBLG helices (especially in non-polar solvents), 43,49,50 and π-π stacking of the outward-pointing pendant benzyl groups. 51 Such organogels present attractive features, including a robust fibrous network and a high porosity, 46 which would be valuable in the context of biomedical hydrogels.…”