Effect of carrier nature and monomer pressure on polymerization of ethylene with high activity catalyst system

Velikova, M.; Damyanov, D.

doi:10.1007/s002890050593

Cited by 4 publications

(9 citation statements)

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“…This fact induces inner stresses in the crystals, which provoke the occurrence of the monoclinic phase. This is the most probable explanation, reported by Velikova and Damianov, 19 for clearing up the reason that a bigger quantity of physical entanglements and therefore monoclinic phase occurs in the samples prepared with Ti catalytic systems. 19 Moreover, the vanadium catalyst give also the monoclinic phase together with the orthorhombic phase.…”

Section: Waxs Measurementsmentioning

confidence: 75%

“…The kind and the structure of catalyst system used, polymerization conditions and kinetics is described in. 18,19 Table I shows the catalyst used and the molecular weight, M η , determined viscometrically in decalin at 135 • C and degree of crystallinity obtained from WAXS. Samples were prepared by pressing the polymer powder at 180 • C and 10 MPa during 10 min and then cooling to room temperature.…”

Section: Methodsmentioning

confidence: 99%

“…The study of the polymerization kinetics shows a relatively higher activity of the titanium catalytic systems. 19 These catalysts have not good mechanical stability and during polymerization show a tendency to mechanical destruction. It was established that under the condition of heterogeneous ionic coordinated polymerization, with highly activated catalytic systems, the tie molecules enter into the lamella and physical entanglements in the amorphous areas are higher.…”

Section: Waxs Measurementsmentioning

confidence: 99%

“…18,19 At low activity and high stability of the catalytic particle and relatively high crystallization rate it is possible to build crystals with longer chains and small quantity of entanglements 18 (vanadium catalytic systems, sample 1). In the case of the UHMWPE obtained with titanium catalytic system (samples 2 and 3) having a low mechanical stability, polymerization rate exceeds the crystallization one and the structure of the UHMWPE is predominately lamellar with a high concentration of tie molecules and entanglements in amorphous areas.…”

Section: Microhardness Measurementsmentioning

confidence: 99%

“…In the case of the UHMWPE obtained with titanium catalytic system (samples 2 and 3) having a low mechanical stability, polymerization rate exceeds the crystallization one and the structure of the UHMWPE is predominately lamellar with a high concentration of tie molecules and entanglements in amorphous areas. 19 The decreasing of the macromolecular segments in the amorphous phase leads to an additional stretching of tie molecules and tightening of entanglements, therefore the resistance of the amorphous phase against the penetration increases. That is why MHT of samples 2 and 3, with many physical entanglements, increases.…”

Section: Microhardness Measurementsmentioning

confidence: 99%

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Mechanical Properties of Ultra High Molecular Weight Polyethylene Obtained with Different Cocatalyst Systems

Zamfirova

Pereña

Benavente

et al. 2002

Polym J

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ABSTRACT:Three types of semicrystalline ultra high molecular weight polyethylene, obtained with amorphous SiO 2 -supported Ziegler-Natta catalyst systems modified by vanadium and titanium, have been studied by wide angle XRay scattering, dynamic mechanical thermal analysis and microhardness methods. In all the cases a significant amount of monoclinic modification is observed, which is estimated to be of the order of 10%. With increasing the degree of crystallinity and quantity of entanglements, storage modulus and α relaxation increase and γ relaxation decreases. A weak β relaxation occurs only in the sample obtained with vanadium catalytic systems. Microhardness measurements give the possibility of distinguishing the effect of crystallinity from the effect of entanglements: Vickers microhardness is sensitive predominately to crystalline phase, while total microhardness is sensitive also to the structural peculiarities in the amorphous phase.KEY WORDS Ultrahigh Molecular Weight Polyethylene (UHMWPE) / Dynamic Mechanical Thermal Analysis (DMTA) / Wide-Angle X-Ray Diffraction (WAXS) / Microhardness / Ultrahigh Molecular Weight Polyethylene (UHMWPE) (M>10 6 ) possesses excellent mechanical properties and some advantages over conventional polyolefins as a high level of durability, excellent creep characteristics and abrasion resistance. [1][2][3][4][5] For this reason it is used in demanding applications such as artificial hip and knee joints, machine parts, fibres, polymer coating on metal surface, separators, acoustic diaphragms, etc.It is established that this semicrystallyne polymer has a specific morphology. There are many reports concerning the structure of nascent 6 and differently processed UHMWPE samples. 3,[7][8][9] The occurrence of polymorphism 3, 7, 10-12 is characteristic for crystal part, the orthorhombic crystals lattice being the most typical. It was established that the crystal lamellae in both nascent and processed unoriented UHMWPE have similar dimensions, close to 20 nm on average. 6 This thickness could be varied from 10 nm after necking 13 up to 100 nm in highly oriented fibres. 8 There are reported some cases where a part of the typical, stable and prevailing orthorhombic crystals could be transformed into a monoclinic or transient hexagonal phase. 3, 7-11, 14, 15 Thus, monoclinic crystals are observed in highly deformed samples (fibers) 7-10 or in the samples crystallized under stress. 16 Moreover, there are experimental results showing that polyethylene crystals transform from the stable orthorhombic crystal into a transient hexagonal phase, observed when the polymer is subjected to the action of fast electrons 14 or at high pressure and temperature. 3,15 Since the chain mobility is rather high in the hexagonal phase, sintering has been achieved via this transient phase. 3 There were found reports concerning to the study of the amorphous phase by NMR 8 and by positron annihilation lifetime spectroscopy. 17 It was reported a 5% of disordered all-trans interfacial material and/or tie molecu...

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Section: Waxs Measurementsmentioning

confidence: 75%

Section: Methodsmentioning

confidence: 99%

Section: Waxs Measurementsmentioning

confidence: 99%

Section: Microhardness Measurementsmentioning

confidence: 99%

Section: Microhardness Measurementsmentioning

confidence: 99%

See 3 more Smart Citations

Mechanical Properties of Ultra High Molecular Weight Polyethylene Obtained with Different Cocatalyst Systems

Zamfirova

Pereña

Benavente

et al. 2002

Polym J

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A supported titanium postmetallocene catalyst: Effect of selected conditions on ethylene polymerization

Pietruszka

Białek

Czaja

2011

J of Applied Polymer Sci

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Ethylene polymerization with a titanium complex [N,N-ethylenebis(3-methoxysalicylideneiminato)titanium dichloride] immobilized on the magnesium support with the formula MgCl 2 (THF) 0.32 (Et 2 AlCl) 0.36 was studied. In particular, the effects of polymerization temperature, monomer pressure, and polymerization time on the activity of the catalyst and on the polyethylene properties (molecular weight and its distribution, melting point, crystallinity, and bulk density) were evaluated. The findings of investigations prove that the studied supported titanium catalyst is highly active in ethylene polymerization, and its activity increases with increasing temperature and monomer pressure. Moreover, stability of the catalytic systems is dependent on the activator type used. Me 3 Al, when employed as an activator, makes the catalytic system undergo no deactivation in practice. The catalyst coupled with MAO turned out less stable.

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Effect of silica-type sol–gel carrier’s structure and morphology on a supported Ziegler–Natta catalyst for ethylene polymerization

Korach

Czaja

Mrowiec-Białoń

et al. 2006

European Polymer Journal

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Effect of carrier nature and monomer pressure on polymerization of ethylene with high activity catalyst system

Cited by 4 publications

References 0 publications

Mechanical Properties of Ultra High Molecular Weight Polyethylene Obtained with Different Cocatalyst Systems

Mechanical Properties of Ultra High Molecular Weight Polyethylene Obtained with Different Cocatalyst Systems

A supported titanium postmetallocene catalyst: Effect of selected conditions on ethylene polymerization

Effect of silica-type sol–gel carrier’s structure and morphology on a supported Ziegler–Natta catalyst for ethylene polymerization

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