Comparison of Gas and Liquid Propylene Polymerization Technique – Hydrogen Effect on Thermal, Rheological, and Morphological Properties of PP

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 (TiCl4/phthalate/MgCl2 + 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 Rp‐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 · gcat−1 · h−1, in contrast to GP with a maximum of Rp,0 = 45 kg · gcat−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).

New application for metallocene catalysts in olefin polymerization

“…13 The higher melt strength of these copolymers is required for industrial processes such as foaming, thermoforming, or blowmoulding. 49 Poon et al 50 have analyzed the microstructure, morphology, and mechanical properties of propene/hexene copolymers. Furthermore, Arnold et al 51 reported the copolymerization of propene with higher a-olefins up to hexadecene in the presence of the Et(Ind) 2 HfCl 2 /MAO catalyst, and detected the effect of the side chain length on melting points and isotacticities.…”

Processing, Morphology, and Mechanical Properties of Liquid Pool Polypropylene with Different Molecular Weights

“…[39] Before the system was adjusted to the appropriate polymerisation temperature of 70 8C and pressure of about 60 bar, hydrogen was added as a chain transfer agent for controlling the molecular weight. The hydrogen concentration was varied from 0 to 1 500 mg of H 2 to achieve a wide variation of average molecular weight in a range from 101 000 to 1 600 000 g Á mol À1 .…”

“…Therefore, thermal and rheological data of the LP-PP samples (reported in a previous paper [39] ) were imported into the database. A Cross-WLF viscosity model (Equation (1) and (2)) was used to characterise the temperature and shear rate dependence of viscosity.…”

Synthesis and Characterization of Defined Branched Poly(propylene)s with Different Microstructures by Copolymerization of Propylene and Linear Ethylene Oligomers (Cn = 26–28) with Metallocenes/MAO Catalysts

“…Besides the variation of the stereoregularity to change the macromolecular profile of poly(propylene), it is interesting to focus on branched poly(propylene)s. Low melt strength is required for industrial processes, such as foaming, thermoforming, or blowmelting. [10] However, Poon et al have analyzed the microstructure, morphology, and mechanical properties of propylene/hexene copolymers. [11] Furthermore, Henschke et al…”