Which of the two substances, propene or polypropylene, would have the higher melting point? Why?

polypropane, its molecules are way bigger than proprane's, and bigger molecules attract eachother with a larger force (vanderwaalspower), so there is more power needed to rip the molecules away from eachother. That means there is more heat needed to melt the substance, because when you melt a substance you destroy the vanderwaalspower between molecules.