| Bisphenol-A Polycarbonate (BPAPC) is known for its superior mechanical properties which makes this material an attractive alternative for many applications. Over time however, the mechanical integrity of this polycarbonate deteriorates, leaving a brittle, low strength material, though no observable chemical change has taken place. This phenomena is observed in most glassy polymers and is termed physical aging. The physical aging mechanism is examined by two phases of work in this study. The first phase entails analysis of physically aged, high molecular weight BPAPC plaques using Wide Angle X-ray Scattering (WAXS). Using a high temperature stage on the WAXS Diffractometer, it is possible to anneal, or physically age BPAPC samples while in the x-ray beam, following the aging mechanism first hand. Through this technique the morphological changes of the polymer are followed as a sample is aged for 100 hrs. The second phase entails examination of conformational changes on a more segmental level. Applying Raman Spectroscopic techniques developed in the Laane and Letton laboratories, it is possible to directly monitor conformational changes of aged samples by observing vibrational frequency shifts as small as 0.2 cm;Through the above research, it was confirmed that physical aging enhances the over all order of the BPAPC polymer chains through a decrease in the amorphous nature of the sample. Moreover, mechanisms which impose orientation in the sample effect the inter-molecular vibrations more significantly than the intra- or lateral vibrational modes. Ultimately, the information derived from above will be used to enhance the current understanding of the structure/property relationships of materials. |
