Diels–Alder Condensations
Crotonic acid esters of cellulose undergo addition reaction with cycloaliphatic amines, like morpholine or piperidine and with aliphatic primary amines [79]. Unsaturated polymers can also undergo Diels–Alder reactions. One example is a reaction of hexachlorocyclopentadiene with polycyclopentadiene [80]:
The addition takes place in an inert atmosphere at 140–150C. Over 90 mol.% conversion is achieved in 6 h. Diels–Alder condensations of fumaric and maleic acids polyesters with various dienes [81] can serve as another example. These reactions require 20 h at room temperature. Diels–Alder condensations can also be carried out on polymers of 1,3,5 hexatriene, 1,3,5-heptatriene, and 2,4,6-octatriene [82]. Sulfonate-substituted maleic anhydride adds to low functionality hydrocarbon elastomers, like EPDM, presumably via an Alder-ene type reaction [83]:
Thiols add to diene rubbers by a free-radical mechanism [84]. Thus, antioxidants, like 4-(mercaptoacetamido)-diphenylamine, add–SH groups to the double bonds of cis-polyisoprene and polybutadiene in the presence of free-radical initiators [84]. Thiol compounds also add photochemically to polymers containing double bonds. For instance, unsaturation can be introduced into polyepichlorohydrin by a partial elimination reaction. The product then reacts with mercaptans, aided by a photosensitizer (like benzophenone) and ultraviolet light [85]:
