Soluções e Polímeros Modernos

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12 Modern Materials Solutions to Exercises Check. From Solution 12.73, an E₈ of 1.85 V corresponds to = 0.5. E₈ =1.88 eV should have a very similar composition, and = 0.54 is very close to = 0.5. The P/As composition is very sensitive to wavelength, and provides a useful mechanism to precisely tune the wavelength of the diode. Polymeric Solids (section 12.8) 12.75 Monomers are small molecules with low molecular mass that are joined together to form polymers. They are the repeating units of a polymer. Three (of the many) monomers mentioned in this chapter are CH₃ H CH₂ CH C C CH₂ CH₂ CH₃ propylene styrene isoprene (propene) (phenyl ethene) (2-methyl-1,3-butadiene) 12.76 n-decane does not have a sufficiently high chain length or molecular mass to be considered a polymer. 12.77 Analyze. Given two types of reactant molecules, we are asked to write a condensation reaction with an ester product. Plan. A condensation reaction occurs when two smaller molecules combine to form a larger molecule and a small molecule, often water. Consider the structures of the two reactants and how they could combine to join the larger fragments and split water. Solve. A carboxylic acid contains the OH functional group; an alcohol contains the -OH functional group. These can be arranged to form the C ester functional group and Condensation reaction to form an ester: CH₃ C CH₂ CH₃ CH₃ acetic acid ethanol ethyl acetate If a dicarboxylic acid (two -COOH groups, usually at opposite ends of the molecule) and a dialcohol (two -OH groups, usually at opposite ends of the molecule) are combined, there is the potential for propagation of the polymer chain at both ends of both monomers. Polyethylene terephthalate (Table 12.5) is an example of a polyester formed from the monomers ethylene glycol and terephthalic acid. 352