Solution Properties of Synthetic Polypeptides. IV. Trimethylenediamine-Initiated Poly-γ-Benzyl-L-Glutamate

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Abstract
A polypeptide was synthesized by polymerization of N‐carboxy‐γ‐benzyl‐L‐glutamate anhydride in dioxane containing trimethylenediamine (TMDA) as initiator. When dissolved in a helicogenic solvent, such as dimethylformamide (DMF), this polypeptide molecule is expected to take a gross conformation which may be pictured as two rigid rods linked by a flexible joint, since the TMDA residue is intolerant of intrachain hydrogen bonding. Light scattering, osmotic pressure, viscosity, and sedimentation rate were measured on seven samples of this polypeptide in DMF at 25°C, and the results were compared with the corresponding data on triethylamine (TEA)‐ or sodium methoxide (SMO)‐initiated PBLG, which presumably assumes the form of a straight rod in DMF, as can be argued from various existing evidences. It was found from this comparison that the introduction of one freely bending portion into a rigid‐rod macro‐molecule hardly affects the dependence on molecular weight (and slightly the absolute magnitude as well) of [η] and s0 characteristic of rigid rods. Thus, for M̄w larger than 105, the values of s0 of TMDA‐initiated PBLG samples were only 0.15 (in Svedberg units) higher than those of TEA‐ or SMO‐initiated PBLG samples of equal molecular weight, almost independently of M̄w. Likewise, the [η] values of the former were lower by a constant factor of about 14% than those of the latter when M̄w was above 105. The accuracy of these numerical results, however, should be taken with some reservation, because a possibility that the TMDA‐initiated PBLG is a mixture of straight and once‐broken rod polypeptides was also suggested.