The origin of a dramatic loss of tensile strength in poly(4-methyl-1-pentene) [PMP] above a major dynamic mechanical transition that occurs around 45 °C is explored. The usual mechanisms associated with loss of strength in polymers are shown to be absent in this case. Viscous dissipation disappears almost completely during deformation of PMP above the transition of interest here. A thermodynamic analysis of reversible deformation is shown to provide remarkably good predictions of the work of rupture under such conditions. The thermorheological responses of PMP suggest that the transition of concern here is not accompanied by the onset of rapid backbone motions but by pendant group motions. Indeed, 2D wideline separation (WISE) NMR, which correlates dynamics (via 1 H widelines) with structure (via 13 C chemical shifts), clearly reveals that this transition is primarily accompanied by the onset of rapid pendant group motions. Such motions, coupled with the relatively large inter-backbone distances in PMP, provide the conditions necessary for elimination of viscous dissipation. These findings require refinement of the previously held view that the transition around 45 °C in PMP denotes a glass transition associated with the onset of rapid backbone segmental motions.
SynopsisThe infrared spectra of alkaline jute stick have been discussed and compared to that of untreated and control sample. A higher shift in the 0 -H and lower shift in the C-H stretching frequencies were observed in alkaline sample. The presence of a strong band at 1440-1430 cm-' may be due to the coupling of COO-frequency with CH2 deformation frequency. The C -0 stretching mode at 1240 cm-' disappears on alkaline treatment with the formation of new peaks at 1265 and 1225 cm-'. The P-glucosidic band at 895 cm-' is shifted to 880 cm-' with doubled intensity in alkaline jute stick.
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