4. a) A rectangular polymer bar of length 40mm fits exactly into a steel mold cavity and the entire assembly was heated from 20 to 100C. The linear thermal expansion coefficients of the polymer and steel are 80106C1 and 10106C1, respectively. What percent the strain encountered by the polymer sample along the length ? b) Briefly explain how porosity affects the thermal conductivity of polymeric materials. c) Briefly explain how the degree of crystallinity affects the thermal conductivity of polymeric materials. d) Briefly explain how the indicated property changes for the polymers given below. (Hint: consider the crystallinity) (10 pts) CH2CH2+ i) Thermal conductivity ii) Transparency