Chain extenders are multifunctional molecules that link the end groups of polymer segments (e.g., COOH end groups in PET) together which results in a high molecular polymer.
As 1,3-PBO reacts with the COOH end groups of PET, less hydrogen bonds and, as a result.
The amount of COOH end groups in PET extruded without chain extenders was about 38.9 [+ or -] 0.4 mmol [kg.sup.-1].
This nonrelaxing behavior at long times is found for 1-PET, although 1PET possesses the lowest concentration of COOH end groups, which is the preferred end group for TGDDM reaction.
The authors explain that interactions of polar groups such as the OH and COOH end groups of the PET grades considered here can cause a more pronounced viscosity decrease at higher temperatures.