Analysis of branched poly(ethylene terephthalate)

Poly(ethylene terephthalate) modified with 1,1,1‐trishydroxymethyl propane (THP) and pentaerythritol was analyzed with respect to branching by combined GPC/viscometry measurements. The average effective functionality of the branching molecules was calculated and compared with the theoretically attainable functionality, thus permitting one to distinguish between different branching theories. Maximum effectiveness was achieved only at low concentrations of the modifiers added. Pentaerythritol and THP were found equivalent in the ratio 1 : 3, estimated from their influence on the polydispersities of the branched polyester. It was shown that apparent molecular weights obtained from GPC calibration with linear standards can be converted by correction factors. The resulting molecular weight averages of the branched PET samples were in a good agreement with those from the GPC/viscometry iteration procedure.