New catalysts for poly(butylene terephthalate) synthesis 1. Titanium-lanthanides and titanium-hafnium systems

A complete study of the catalytic activity of lanthanide-, and hafnium acet ylacetonate catalysts in PET synthesis was conducted in order to investigat e any improvement in the process and/or in the properties of the final poly mer with respect to the industrially used titanium tetrabutoxide (TBT) cata lyst. Small scale polymerization and subsequent scale up in higher capacity reactors showed that TBT-Hf(acac)(4) and TBT-La(acac)(3) mixed catalysts w ere more active with respect to TBT as single catalyst. Decreases in polyme rization time and THF formation were also observed, which in turn can impro ve the productivity of the whole process. Furthermore, for similar values o f molecular weight, a lower melt viscosity (and thus better processability and crystallizability) was obtained by using mixed catalysts, presumably du e to weaker interactions of the polymer terminal groups to lanthanum and ha fnium metals with respect to titanium. (C) 2001 Elsevier Science Ltd. All r ights reserved.