Abstract
Undrawn and drawn poly-γ-methyl-L-glutamate (PMLG) fibers having different secondary structures were treated with 18N sulfuric acid, and the apparent weight loss was measured. From quantitative analysis by infrared spectra of the hydrolysis degree of side chain ester groups in insoluble residue, the apparent weight loss was devided into the weight loss due to hydrolysis of main chain and that of side chain. Besides, the density and intrinsic viscosity of insoluble residue were measured, and the accessibility of PMLG fibers to sulfuric acid is discussed in connection with secondary structures. The results were as follows;
(1) In both PMLG fibers, the weight loss due to hydrolysis of main chain proceeds at two stages, the early stage of higher rate and the later one of lower and constant rate. The former is considered to be due to the dissolution of more accessible amorphous region from the decreasing behavior of intrinsic viscosity of insoluble residue. The weight loss due to hydrolysis of main chain in the first stage is larger in undrawn fiber and therefore it is considered that undrawn fiber has larger accessibility than drawn fiber.
(2) Density of insoluble residue supports quantitative analysis of the hydrolysis degree of side chain by infrared spectra.
(3) The difference of accessibility to sulfuric acid between undrawn and drawn fibers was concluded to be caused by the following facts. Since random-coil structure is difficult to be recognized in both fibers, the region where α-helix dose not stand side by side but stand random situation in undrawn fiber decrease during the α→β transformation by drawing.
