Viscoelastic Properties of Poly(γ-benzyl glutamate)

Abstract

The effect of solvents on the structure and preperties of cast films of poly(r-benzyl glutamate) (PBLG) were studied. From X-ray diffraction measurements, it was found that films cast from dichloroethane, chloroform, and dichloromethane (called film A) had a well-ordered structure consisting of helices packed on a regular hexagonal lattice, while films cast from benzene and tetrahydrofuran (called film B) showed less crystallinity than film A. As for viscoelastic properties, film A showed peaks of tan iJ at 38 and 105°C (110 Hz). In the case of film B, the lower-temperature peak was shifted to a higher temperature and the peak was broadened. Film B further exhibited a remarkable decrease of modulus at about 135°C, which was accompanied with a small peak of tan iJ at this temperature. After being annealed at 140°C, film B showed a remarkable increase in its tan iJ peak at 105°C and simultaneously the lowertemperature peak shifted to 40°C and the peak at 135°C vanished. To elucidate these changes, differential thermal analysis (DT A) was performed. The DT A thermogram on film B showed an endothermic peak at 135°C, which was not observed after the film was annealed at 140°C. From the fact that the aggregates of superhelices of PBLG, which were precipitated from dimethylformamide solution by adding propionic acid, also showed an endothermic peak at 135°C, it is argued that the superhelical structure exists in the solid state of film B and stacks of benzene ring in the side chain are responsible for the characteristic behaviors of film B.

Influence of Casting Conditions on the Structure of Poly(γ-benzyl-L-glutamate)

“…B-80% and B-100% exhibited an endothermic peak at 135°C, while no peak was observed for the others. As reported previously, 6 the endothermic peak is related to a breakdown of stacks of the benzene rings in the side chain of PBG. The stack of the benzene ring, which is formed in poor solvents and considered to be retained in cast films and precipitates, is broken at 135°C.…”

“…Films cast from EDC have a difierent structure from those cast from benzene, as reported by Fukuzawa, et al: 6 films cast from EDC are form C or film A and films from benzene are form A or film B. It is interesting to study the structures and properties of films cast from EDC-benzene mixed solution.…”

“…Forms A and B have a higher modulus than form C in the lower temperature region (20-90°C). Fukuzawa, et al, 6 reported that cast films could be classified into two types of structures and properties: the first group was cast films from 1,2-dichloroethane (EDC), chloroform, or dichloromethane solution (film A) and the second was from benzene or tetrahydrofuran solution (film B). It was found that the viscoelastic behaviors of films A and B were respectively similar to those of forms C and A proposed by McKinnon and Tobolsky.…”

Molecular Aggregation and Gelation in Poly(y-benzyl L-glutamate) Solutions

“…The complex involves the stacking of side chain benzene rings.U The transition of more concentrated gels ( C> 80 wt%) is accompanied by the collapse of this stacking structure. 29 The dependence of melting points on molecular weight is remarkable below 10 5 in molecular weight, as shown in Figure 3. The data given in Figure 1 and 2 were obtained for a polymer with a molecular weight of 1.5 x 10 5 , which is high enough to be free from any appreciable molecular weight dependence.…”

Stiff Chain Polymer Lyotropic Liquid Crystals

“…Several wide line NMR studies indicate the presence of side chain motion in the solid polymer at room temperature (1 10-114). A variety of other studies sup port this in some cases, contradict it in others (115)(116)(117)(118)(119)(120)(121)(122)(123)(124)(125)(126)(127)(128)(129)(130). A major conclusion is that the method of preparing a solid PBLG film may have a significant effect on Annu.…”