Poly-y-benzylglutamate

When we determine values of 7 for benzene rings attached to polymers, we find that they are much shorter than for benzene itself they are in fact at the lower limit of usefulness of the direct method. We have found (3) that for the phenyl resonance of a low molecular weight polystyrene in carbon disulfide 7 is only about 0.4 0.1 sec. at 25°. For the backbone protons, 7 is even shorter and cannot be measured by the direct method. For the phenyl groups of poly-y-benzylglutamate in trifluoroacetic acid, 7 is 0.7 0.1 sec. Recently, more reliable values have been obtained for polystyrene by the spin echo method (72). For a polymer of molecular weight 63000 in tetrachloroethylene, three 7 X values could be resolved. At 25°, these were 0.033 sec. for the aliphatic protons, 0.076 sec. for the ortho protons and 0.20 sec. for the meta-para protons. The temperature coefficients for all three Tt values correspond to a heat of activation of about 3 kcal/mole. The differences in the absolute Tx values at the aromatic positions can be explained in terms of of differences in the sums of r e in equation (56). The shorter aliphatic Tj value probably reflects also a longer correlation time for backbone... 

Fig. 26. Viscosity plot for poly-y-benzylglutamates. Dashed curve through filled circles is for helical polymers...

When the most common spiropyran SP-4 was mixed in poly(y-benzylglutamate) to prepare a film, a reversible change in optical rotation was observed upon 365 nm light irradiation and visible light irradiation [49], The largest Aa before and after UV irradiation at sodium D-line (589 nm) was 1.225° for 4 mol% concentration. It was supposed that the change might have arisen from the chiral interaction between the chiral polypeptide environment and the colored merocyanine. Indeed, an induced CD was observed. 

Fellers and Lewis, Gilbert et.al., Ambrosio and Sixou) such as cellulose derivatives, poly-y -benzylglutamate and aromatic polyester and polyam.ides (8-11). 

Fig. 15. The polarizing micrograph (left) and the electron micrograph (right) of electrically oriented films of poly(-y-benzylglutamate)s. Left PBLG cast and dried from a CH2Br2 solution (84 V/cm). Right an equimolar mixture of PBLG and PBDG cast and dried from a CHCI3 solution (180 V/cm), O replica...

According to (5.10), the equilibrium azimuthal angle at the upper surface can be nonzero (Figure 5.2). This implies twist and hence optical activity of the sessile droplet. The twist angle increases as the ratio K2/K decreases so that the effect might be strongly pronounced for nematic polymers such as poly-y-benzylglutamate (PBG), where the ratio K2/K can be as small as 0.1 or even smaller [14],... 

Finally we must know how ordered or disordered the polymer is. If the forces between residues are not strong compared to the solvent-residue interactions, or if different helical conformations have nearly the same stability, then there may be different conformations present in solution. We usually expect a polymer to become more ordered as the temperature is decreased, but this is not necessarily true. If solvent—residue attractions dominate at low temperature, a polymer may change from an ordered helix at high temperature to a disordered coil at low temperature. Poly-y-benzylglutamate in ethylene dichloride-dichloro-acetic acid shows this behavior [1]. 

Degee, P., Dubois, P., Jerome, R., and Teyssie, P. (1993) Synthesis and characterization of biocompatible and biodegradable poly( -caprolactone-b-Y-benzylglutamate) diblock copolymers. Journal of Polymer Science Part A Polymer Chemistry, 31,275-278. 

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