, ▁and ▁sh aped ▁into ▁the ▁final ▁product ▁form ▁by ▁mel ting , ▁pressing , ▁or ▁injection ▁m old ing . ▁ ▁Chem ical ▁process ▁C uring ▁a ▁therm os et ting ▁res in ▁transform s ▁it ▁into ▁a ▁pl astic , ▁or ▁el ast omer ▁( r ub ber ) ▁by ▁cross link ing ▁or ▁chain ▁extension ▁through ▁the ▁formation ▁of ▁c oval ent ▁b onds ▁between ▁individual ▁ch ains ▁of ▁the ▁polym er . ▁Cross link ▁density ▁var ies ▁depending ▁on ▁the ▁mon omer ▁or ▁pre pol ym er ▁mix , ▁and ▁the ▁mechanism ▁of ▁cross link ing : ▁ ▁Ac ry lic ▁res ins , ▁poly esters ▁and ▁vin yl ▁est ers ▁with ▁uns atur ated ▁sites ▁at ▁the ▁ends ▁or ▁on ▁the ▁back bone ▁are ▁generally ▁linked ▁by ▁cop ol ym er isation ▁with ▁uns atur ated ▁mon omer ▁dil u ents , ▁with ▁c ure ▁initi ated ▁by ▁free ▁radical s ▁generated ▁from ▁ion izing ▁radiation ▁or ▁by ▁the ▁phot ol yt ic ▁or ▁thermal ▁decomposition ▁of ▁a ▁radical ▁initi ator ▁– ▁the ▁intensity ▁of ▁cross link ing ▁is ▁influenced ▁by ▁the ▁degree ▁of ▁back bone ▁uns atur ation ▁in ▁the ▁pre pol ym er ; ▁▁ ▁E po xy ▁functional ▁res ins ▁can ▁be ▁hom o - pol ym er ized ▁with ▁an ionic ▁or ▁c ation ic ▁catal yst s ▁and ▁heat , ▁or ▁cop ol ym er ised ▁through ▁nucle oph il ic ▁addition ▁re actions ▁with ▁mult if unction al ▁cross link ing ▁agents