Polyethylene terephtalate (Mylar, Dacron) is cooled rapidly from 300 C (state 1) to room temperature. The resulting material is rigid and perfectly transparent (state 2). The sample is then heated to 100 C (state 3) and maintained at that temperature, during which time it gradually becomes translucent (state 4). It is then cooled down to room temperature and is again found to be rigid, but is now translucent rather than transparent (state 5). For this polymer, Tm= 267 C and Tg = 69 C. Sketch a general specific-volume vs. temperature curve for a crystallizable polymer, illustrating Tg and Tm, and show the locations of states 1-5 for the sample above. Why does it become translucent? Think about our scattering discussion. A rubber band, made of a styrene-butadiene random copolymer, is swollen to equilibrium in toluene; the volume increases by a factor of 5. Taking x = 0.4, estimate the number of strands per unit volume, and therefore the extent of cross-linking. Estimate Young's modulus for both the dry and swollen rubber bands. Polyethylene terephtalate (Mylar, Dacron) is cooled rapidly from 300 C (state 1) to room temperature. The resulting material is rigid and perfectly transparent (state 2). The sample is then heated to 100 C (state 3) and maintained at that temperature, during which time it gradually becomes translucent (state 4). It is then cooled down to room temperature and is again found to be rigid, but is now translucent rather than transparent (state 5). For this polymer, Tm= 267 C and Tg = 69 C. Sketch a general specific-volume vs. temperature curve for a crystallizable polymer, illustrating Tg and Tm, and show the locations of states 1-5 for the sample above. Why does it become translucent? Think about our scattering discussion. A rubber band, made of a styrene-butadiene random copolymer, is swollen to equilibrium in toluene; the volume increases by a factor of 5. Taking x = 0.4, estimate the number of strands per unit volume, and therefore the extent of cross-linking. Estimate Young's modulus for both the dry and swollen rubber bands.