Abstract
Summary: A comparison of PP qualities, which are produced with two different polymerization techniques–gas phase(GP) and liquid pool (LP)–under precise control of the polymerization temperature (70 °C) and pressure (GP = 25 bar, LP < 60 bar) using identical Ziegler‐Natta catalyst (TiCl~4~/phthalate/MgCl~2~ + TEA/silane), is presented. A series of homopolymer PP in a wide MW range from 100 000 to 1 600 000 g · mol^−1^ was polymerized. During polymerization all samples were characterized exactly by their __R__p‐profil. The effect of hydrogen on the initial reaction rate and on MW and MWD was analyzed on the basis of this so‐called kinetic fingerprint. The results showed that the polymerization rate reached a maximum for LP, of about 150 kg · g~cat~^−1^ · h^−1^, in contrast to GP with a maximum of R~p~,~0~ = 45 kg · g~cat~^−1^ · h^−1^. Analysis was carried out by means of GPC, SEM, DSC, platte‐platte rheometer, and WAXS. The results first showed that the MWD of LP PP is narrower (PD ∼ 6.8) than for the GP PP (PD ∼ 8), polymerized in two steps. An SEM study of the powder particle shows the typical dent surface morphology of polymers using Ziegler‐Natta catalysts for polymerization. WAXS and DSC analysis demonstrated that almost only the α‐modification of crystalline structure exists and that the crystallinity becomes considerably higher after solidification from melt. Furthermore, it was found that the crystallite size distribution depends on the polymerization technique. Rheological studies indicate that GP PP behaves more elastically. To summarize, it is shown that PP produced with the LP polymerization technique is more homogenous and of high quality.
Particle geometry of gas phase and liquid pool polymerized PP powder observed by SEM (PP‐L0).
magnified imageParticle geometry of gas phase and liquid pool polymerized PP powder observed by SEM (PP‐L0).