Construction Of The Full Phase Diagram For The System Of Poly(γ-benzyl-l-glutamate)/dimethylformamide On The Basis Of The Complex Of Literature Data

Abstract

The system poly-γ-benzyl-l-glutamate—dimethylformamide (PBG/DMF) is the most-studied of the rodlike polymer-solvent systems. However, up to now there is no satisfactory experimental phase diagram (PD) for this system in the entire range of concentrations. For all studied systems only fragments of the PD are known. Some regions of these fragments agree qualitatively with the theoretical PD for an ensemble of rodlike particles in an isotropic solvent. However, most parts of the PD do not agree with the theoretical ones. A critical analysis of the corresponding experimental data was carried out and on the basis of this analysis a new PD was constructed in the enti re range of concentration. The obtained PD differs essentially from the known theoretical diagram and is very close to the diagram predicted by Papkov taking into account the formation of crystallosolvates. The peculiarities of the phase transitions in the various regions of the PD are considered. It is shown that the so-named lyotropic liquid crystals (LC), on the basis of solved rodlike polymers, are thermotropic LCs diluted by the isotropic solvent. A specific role in the PD are played by the crystallosolvates (CS), which are identified with the phase defined by Luzzati as the “complex phase.” In particular, the phase region LC-CS exists instead of the LC-LC region in the theoretical PDs. Some new concepts of the crystallosolvate defects and on the “limiting” LC phase are discussed. Consideration of the liquidus lines CS/LC and CS/(isotropic liquid) permits us to propose some explanations of the PDs at low polymer concentrations. Most parts of the real PD represent the superposition of different phase equilibria and are complicated by the processes of gelation, crystallization and crystallosolvate formation that cannot be described by the modern theories. The fragments of the PDs in the literature for some rodlike polymers in solution agree well with the general PD for PBG/DMF. Special features of the phase transitions in the different areas of the PD are discussed. On the basis of the principles used in this work for construction of the PD, critical consideration of the PDs published in the literature have been carried out; our understanding of results obtained by other authors are presented. The perspectives of further investigations are considered.

Keywords:

• Polymer
• Liquid crystal
• Phase diagram
• Gel
• Crystallosolvate
• Poly(γ-benzyl-l-glutamate)

Acknowledgments

Notes

^†Dedicated to Paul Flory's memory.

a We note that in Refs. 64-98 and other of our works PBG synthesized by the known scheme41,107,108 of polycondensation of corresponding N-carboxy-anhydride in benzene, with tri-ethylamine as initiator was used. This technique leads to narrow molecular mass distributions.109,110 The synthesis was carried out during many years for our works by a chemical laboratory headed by Prof. T. A. Sokolova and then by Prof. G. P. Vlasov. We are very grateful to them and to their colleagues.