问答题
Predict which polymer in each pair listed can have higher degree of crystallinity, and justify your answers. (1) PE or Polystyrene (PS) (2) LDPE or HDPE (3) PE or Nylon (4) Atactic [C2H3(CH3)]n orisotactic [C2H3(CH3)]m (5) isotactic (C2H3Cl)n, orisotactic [C2H3(CH3)]n (6) Cooling molten PP to form solid PP under high cooling rate or under low cooling rate
【正确答案】Predict which polymer in each pair listed can have higher degree of crystallinity, and justify your answer. (12) (1) PE Polymers with large, bulky side groups cannot be packed efficiently, and therefore have difficulty forming crystals (2)HDPE Polymers with branched chains cannot be packed efficiently, and hence it is far more difficult to form crystals (3)PE Polymers with long repeat units require more extensive chain segment motion to establish Long range order, and hence it will crystallize slowly, and can be easily formed into glasses using modest quench rates. (4) isotactic [C2H3(CH3]n Symmetrical structures that permit close packing of chains favour crystallinity. (5) isotactic (C2H3Cl)n Stronger secondary forces allow greater compacting. The existence of small, regularly spaced polar side groups can aid in the formation of polymer crystals by providing a driving force for the necessary alignment of adjacent chain segments. low cooling rate Polymers are long chain structures. The movement of polymer chains needs time. Slow cooling means giving Polymer chains more time to allow them to align.