Homopolymer and copolymer PAN precusors can be used in the cartoon fiber manufacture process. These two kinds of precusors have different machanism during oxi-dation reaction.The phenomena which take place in the oxidation process for two kinds of precusors are investigated by means of DTA

thermal mechanical measurement

ESR which measures the concertration of free redicals and acoustic propagation method which measures the variation of Young's modulus. It was observed that homopolymer PAN precu-sor is mainly cyclized by free radical process

but since this sample has already partly hydrolyzed

so that it also can be induced by ion transfer process. Meanwhile for copolymer precusor

it seems that ion transfer process is the main one.