Determination of copolymer composition by combustion analysis for carbon and hydrogen

Abstract

A d etailed d esc ription is given of t he method of combustion a na lysis for carbon and hydrogen to determine the co mpos ition of a copoly me r from its carbo ll-hyd roge n ratio. Th e ap paratus a nd procedu res have been d eveloped at the Nationa l Bureau of Stand a rd s over a period o f years. The method has been app lied chiefly to determine what fraction of a styre n e~but adien e co p o l ym~r is d eriv ed [rom styrene. l\1inor in g l·edi nts are r emoved by extraction, with t he exception of the bound mercapta n re idue for whic h correcLion mu t be made. The amo un t of bound mercap tan res idu e is determin ed from measure me nts of t ile sulfur content of t he copolymer by t he Carius method. Meas urement a re made of t he oxygen con Lent a nd Lhe ash co ntent, a lLho ugh the e do not enter in to the calculations. The ~tan dard deviation of a meas urement of carbon-hydrogen ratio is a pproximately 0.001 0 and IS Inde pendent o f sLy rene contenL. This corresponds to a stand ard deviation of about 0.036-percent bound styrene for pol y mers of low styrene co ntent a nd 0.018 percent for polyme rs o f hi g h styre ne conten t. Th e acc uracy of t he meL hod is d emonstrated bv t he fact thaL observ ,tLions o f carbon-hydrogen ratio for fou r out of fiv e samples of po lyb utadiene differed by less Lhan one standard devi ation from t he theoretical valu e.