Exercise 4 a) PS (Polystyrene), PMMA (Poly Methyl Methacrylate Acryl) (Plexiglass), and PC (polycarbonate) are transparent polymers, unless they are mixed with pigments etc. PE (polyethylene), PP (polypropylene), and PA 6.6 (nylon 6.6) on the other hand are mist and milky white. What is the cause? Explain why. b) Why do not crosslinked polymers have crystalline structures? c) Vis v.h.a. diagrams of how mechanical properties vary as a function of temperature for the 4 different polymeric materials. d) Describe the temperature range in which the following polymeric materials should be used: PS (Polystyrene), PP (polypropylene), PMMA (Poly Methyl Methaacrylate Acrylic) (Plexiglass) and PA6.6 (nylon 6.6).