Abstract: The molar ratio of ethylene to vinylaeetate in ethylene-vinylacetate copolymers (EVA) was greater than 3:1, sothe side chains were deemed consisted mainly of ethyl and butyl branches. In this work, the 1378cm^-1 band of CH₃ side group in ataetie polypropylene was selected as key band for determination of the amount of branched chains in eopolymers, the 780cm^-1 band of C₂H₅ group in 2-ethylhexane for ethyl branche, the 730cm¹ band of C₄H₉ side group in poly-a-hexane for butyl branches, respectively. A reasonable estimation of branched chain distribution has been carried our by following equations. nCH₃/1000C=(0.50546 A₁₃₇₈/dt)-1.01966 nC₂H₅/1000C=(1.27161 A₇₈₀/dt)-7.67873 nC₄H₉/1000C=(0.09113 A₇₃₀/dt)-6.41352 nL.B/1000C=(0.50564 A₁₃₇₈/dt)-(1.27161 A₇₈₀/dt) -(0.09113 A₇₃₀/dt)+13.07259The interference from CH₃ in acetoxyl of VA is eliminated using band substraetion manipulation in FTIR and then the number average degree of branching has been determined by above equations. The results obtained were in good agreement with those obtained by ¹H NMR technique.

Key words: EVA copolymer, FTIR. branched chain, degree of branching, distribution, determination