Polymer high molecular weight, exercises

Arylene ether/imide copolymers were prepared by the reaction of various amounts 4,4 -carbonylbis[Ar-(4 -hydroxyphenyl)phthalimide] and 4,4 -biphenoi with a stoichiometric portion of 4,4 -dichlorodiphenyl sulfone in the presence of potassium carbonate in NMP/CHP [55]. To obtain high molecular weight polymer, the temperature of the reaction was kept below 155 °C for several hours before heating to >155°C in an attempt to avoid undesirable side reactions such as opening of the imide ring. The imide ring is not stable to conditions of normal aromatic nucleophilic polymerizations unless extreme care is exercised to remove water. Special conditions must be used to avoid hydrolysis of the imide as previously mentioned in the section on Other PAE Containing Heterocyclic Units and as practiced in the synthesis of Ultem mentioned in the Historical Perspective section. 

Exercise 29-2 Suppose a bottle of 1,3-cyclopentadiene were held at a temperature at which polymerization is rapid, but depolymerization is insignificant. Would the polymerization result in conversion of all of the 1,3-cyclopentadiene into essentially one gigantic molecule Why or why not How would you carry on the polymerization so as to favor formation of polymer molecules with high molecular weights ... 

Exercise 29-21 The rate of radical polymerization of ethenylbenzene, induced by benzoyl peroxide in mixtures of tetrachloromethane and benzene, is independent of the concentration of tetrachloromethane. At high concentrations of tetrachloromethane, the average molecular weight of the polymer is greatly reduced and chlorine is found in the polymer. Explain. 

However, since these properties are also influenced by factors such as copolymer composition, solvent type and overall molecular weight, solution polymers made by both the all-in and drip-feed processes find use in surface coating applications. The latter process allows stricter control to be exercised over the process conditions, and this is often desirable when dealing with highly exothermic chemical reactions and where product consistency is required. 

Besides these low-molecular weight molecules, high-molecular mass polymers have been investigated as new conjugating moieties able to endow the bound molecules with their peculiar features. In this way it is possible for example to add more hydrophobic character to the antisense derivative, to increase their cellular penetration. Besides, the presence of larger molecules will reduce their clearance from the body, increasing the time life useful to exercise a therapeutic action. 

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