Broadband Dielectric Spectroscopic Characterization of the Hydrolytic Degradation of Hydroxyl-Terminated Poly (D,L-lactide) Materials

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Polymers and High Performance Materials


Broadband dielectric spectroscopy was used to examine hydroxyl-terminated poly(D,L-lactide) samples that were hydrolytically degraded in 7.4pH phosphate buffer solutions at 37° C. The dielectric spectral signatures of degraded samples were considerably more distinct than those of undegraded samples and a Tg - related relaxation associated with long range chain segmental mobility was seen. For both degraded and undegraded samples, a relaxation peak beneath Tg was observed, which shifts to higher frequency with increasing temperature. Linear segments on log-log plots of loss permittivity vs. frequency, in the low frequency regime, are attributed to d.c. conductivity. An upward shift in peak frequency maximum was observed after 95 days of immersion in buffer solution. This behavior implies a decrease in the time scale of long range chain segmental motions. Permittivity data for degraded and undegraded materials were fitted to the Havriliak-Negami equation with subtraction of the d.c. conductivity contribution to uncover pure relaxation peaks. Parameters extracted from these fits were used to construct Vogel-Fulcher-Tammann-Hesse (VFTH) and distribution of relaxation time, G(τ), curves. The relaxation time for this αtransition in both degraded and undegraded samples showed VFTH temperature behavior. G(τ) curves showed a general broadening and shift to lower τ with degradation, which can be explained in terms of a broadening of molecular weight within degraded samples and faster chain motions.

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ACS Symposium Series



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