In the synthesis of tricomponent poly(ethylene terephthalate) copolyesters through the direct esterification route

in order to control process of production to obtain the desired molecular weights of polymers

the simplified and nonsimplified calculation equations for the number average degree of polymerization n and the number average molecular weights n of oligomers and polycondensates were given

respectively. The calculation equations

derived on the basis of reaction mechanism and technological characteristics

relate Xn and Mn to the extent of reaction of carboxyl groups and the amounts of small molecules produced.The various main reactions and important side reactions were all considered for the nonsimplified calculation equations

but for the simplified calculation equations

the various side reactions were neglected.The simplified Xn calculation equations were compared with carothers wquation by calculation

the results are the same.Applied to the dicomponent polyester systems

the simplified Xn equations are the same as that used conventionally for the dicomponent linear polycondensates.The simolified and nonsimplified calculation wquations for An and Mn of tricomponent poly(ethylene terephthalate) copolyesters can be extended and applied to the dicomponent polyester systems and multicomponent copolyester systems over three components.