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QD251.2 510 Organic Chemistry Solutions Manual 2001 stronger than half a C=C so the gain in enthalpy during polymerization compensates for the loss of entropy at much higher temperatures. Problem 12 Polyvinyl chloride (PVC) is used for rigid structures like window frames and gutters with only small amounts of additives such as pigments. If PVC is used for flexible things like plastic bags, about 20-30% of dialkyl phthalates such as the compound below are incorporated during polymerization. Why is this? 0 0 0 dialkyl phthalate Purpose of the problem One small problem on the composition of plastics rather than just polymers. Suggested solution PVC is a regular polymer with chains that fit together well to form a rigid solid ideal for window frames and gutters but it is inevitably unable to bend far without breaking. Dialkyl phthalates are plasticizers that fit around the rigid chains rather in the way that a solvent fits round solute molecules. The difference here is that the polymer molecules are larger than the 'solvent'. You could also think of the plasticizer as a lubricant to allow the polymer chains to move across each other to make the whole structure flexible. Plasticizers are used in substantial quantities (20-30% suggested in the question). In fact, dialkyl phthalates are made for the plastics industry in amounts greater than those for almost any polymer.