Abstract: | Samples of poly(ethylene terephthalate) (PET) modified with small amounts of trimesic acid groups and hence containing long chain branching have been prepared. From the content of trifunctional modifier and from the experimental value of the extent of reaction, the weight-average molecular weight and branching density have been calculated, assuming that all the end-groups are equally reactive and intramolecular reactions are absent. The values of and have been correlated with the experimental values of intrinsic viscosity η] and the Newtonian melt viscosity η0. General relations of the following type have been obtained: In particular, η] and η0 increase on increasing and decrease on increasing , but, at equal η] values, η0 increases with . Through the last relation, the reliability limits of which should be experimentally checked, and from measurements of η] and η0, it is possible to calculate of a branched PET. |