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er reading toggle the table of contents ziegler natta catalyst 22 languages العربية azərbaycanca català čeština deutsch ελληνικά español euskara فارسی suomi français हिन्दी bahasa indonesia italiano 日本語 한국어 nederlands polski português русский türkçe 中文 edit links article talk english read edit view history tools tools move to sidebar hide actions read edit view history general what links here related changes upload file permanent link page information cite this page get shortened url switch to legacy parser print export download as pdf printable version in other projects wikimedia commons wikidata item appearance move to sidebar hide from wikipedia the free encyclopedia catalyst for synthesis of polymers of 1 alkenes a ziegler natta catalyst named after karl ziegler and giulio natta is a catalyst used in the synthesis of polymers of 1 alkenes alpha olefins two broad classes of ziegler natta catalysts are employed distinguished by their solubility heterogeneous supported catalysts based on titanium compounds are used in polymerization reactions in combination with cocatalysts organoaluminum compounds such as triethylaluminium al c 2 h 5 3 this class of catalyst dominates the industry 1 homogeneous catalysts usually based on complexes of the group 4 metals titanium zirconium or hafnium they are usually used in combination with a different organoaluminum cocatalyst methylaluminoxane or methylalumoxane mao these catalysts traditionally contain metallocenes but also feature multidentate oxygen and nitrogen based ligands 2 ziegler natta catalysts are used to polymerize terminal alkenes ethylene and alkenes with the vinyl double bond n ch 2 chr ch 2 chr n history edit the 1963 nobel prize in chemistry was awarded to german karl ziegler for his discovery of first titanium based catalysts and italian giulio natta for using them to prepare stereoregular polymers from propylene ziegler natta catalysts have been used in the commercial manufacture of various polyolefins since 1956 as of 2010 the total volume of plastics elastomers and rubbers produced from alkenes with these and related especially phillips catalysts worldwide exceeds 100 million tonnes together these polymers represent the largest volume commodity plastics as well as the largest volume commodity chemicals in the world in the early 1950s workers at phillips petroleum discovered that chromium catalysts are highly effective for the low temperature polymerization of ethylene which launched major industrial technologies culminating in the phillips catalyst a few years later ziegler discovered that a combination of titanium tetrachloride ticl 4 and diethylaluminium chloride al c 2 h 5 2 cl gave comparable activities for the production of polyethylene natta used crystalline α ticl 3 in combination with al c 2 h 5 3 to produce first isotactic polypropylene 3 usually ziegler catalysts refer to titanium based systems for conversions of ethylene and ziegler natta catalysts refer to systems for conversions of propylene also in the 1960s basf developed a gas phase mechanically stirred polymerization process for making polypropylene in that process the particle bed in the reactor was either not fluidized or not fully fluidized in 1968 the first gas phase fluidized bed polymerization process the unipol process was commercialized by union carbide to produce polyethylene in the mid 1980s the unipol process was further extended to produce polypropylene in the 1970s magnesium chloride mgcl 2 was discovered to greatly enhance the activity of the titanium based catalysts these catalysts were so active that the removal of unwanted amorphous polymer and residual titanium from the product so called deashing was no longer necessary enabling the commercialization of linear low density polyethylene lldpe resins and allowed the development of fully amorphous copolymers 4 the fluidized bed process remains one of the two most widely used processes for producing polypropylene 5 stereochemistry of poly 1 alkenes edit natta first used polymerization catalysts based on titanium chlorides to polymerize propylene and other 1 alkenes he discovered that these polymers are crystalline materials and ascribed their crystallinity to a special feature of the polymer structure called stereoregularity short segments of polypropylene showing examples of isotactic above and syndiotactic below tacticity the concept of stereoregularity in polymer chains is illustrated in the picture on the left with polypropylene stereoregular poly 1 alkene can be isotactic or syndiotactic depending on the relative orientation of the alkyl groups in polymer chains consisting of units ch 2 chr like the ch 3 groups in the figure in the isotactic polymers all stereogenic centers chr share the same configuration the stereogenic centers in syndiotactic polymers alternate their relative configuration a polymer that lacks any regular arrangement in the position of its alkyl substituents r is called atactic both isotactic and syndiotactic polypropylene are crystalline whereas atactic polypropylene which can also be prepared with special ziegler natta catalysts is amorphous ultimately the stereoregularity of the polymer is determined by the catalyst used to prepare it most polymers produced with a ziegler natta catalyst are enantioselective site controlled meaning the stereochemistry of each added monomer is dependent primarily on the stereochemistry of the catalyst barring stereo errors rather than the stereochemistry of the previous monomer thus the chirality of the catalyst greatly influences tacticity for example achiral bis 2 phenylindenyl zirconium dichloride produces isotactic polymers whereas its chiral variant produces syndiotactic polymers the attachment of bulky ligands to the metal center results in steric hindrance designed to restrict the orientation from which the incoming alkene can attack the metal center 6 7 unique behaviors of the catalyst can also strongly impact tacticity for example the open site of vcl 4 al c 2 h 5 2 cl alternates between the axial and equatorial site with every monomer addition as a result each successive propylene monomer will insert into the vanadium carbon bond from opposite sides the alternating active site geometry thus produces a polymer chain with alternating enantiomeric configurations producing syndiotactic polypropylene see mechanism of ziegler natta polymerization for the detailed mechanism 8 heterogeneous catalysts edit the first and dominant class of titanium based catalysts and some vanadium based catalysts for alkene polymerization can be roughly subdivided into two subclasses both heterogeneous catalysts catalysts suitable for homopolymerization of ethylene and for ethylene 1 alkene copolymerization reactions leading to copolymers with a low 1 alkene content 2 4 mol lldpe resins and catalysts suitable for the synthesis of isotactic 1 alkenes the overlap between these two subclasses is relatively small because the requirements to the respective catalysts differ widely commercial catalysts are supported by being bound to a solid with a high surface area both ticl 4 and ticl 3 give active catalysts 9 10 the support in the majority of the catalysts is mgcl 2 a third component of most catalysts is a carrier a material that determines the size and the shape of catalyst particles the preferred carrier is microporous spheres of amorphous silica with a diameter of 30 40 mm during the catalyst synthesis both the titanium compounds and mgcl 2 are packed into the silica pores all these catalysts are activated with organoaluminum compounds such as al c 2 h 5 3 10 all modern supported ziegler natta catalysts designed for polymerization of propylene and higher 1 alkenes are prepared with ticl 4 as the active ingredient and mgcl 2 as a support another component of all such catalysts is an organic modifier usually an ester of an aromatic diacid or a diether the modifiers react both with inorganic ingredients of the solid catalysts as well as with organoaluminum cocatalysts 10 these catalysts polymerize propylene and other 1 alkenes to highly crystalline isotactic polymers 9 10 homogeneous catalysts edit a second class of ziegler natta catalysts are soluble in the reaction medium traditionally such homogeneous catalysts were derived from metallocenes but the structures of active catalysts have been significantly broadened to include nitrogen based ligands a post metallocene catalyst developed at dow chemical 11 metallocene catalysts edit main article kaminsky catalyst these catalysts are metallocenes together with a cocatalyst typically mao o al ch 3 n the idealized metallocene catalysts have the composition cp 2 mcl 2 m ti zr hf such as titanocene dichloride typically the organic ligands are derivatives of cyclopentadienyl in some complexes the two cyclopentadiene cp rings are linked with bridges like ch 2 ch 2 or siph 2 depending on the type of their cyclopentadienyl ligands for example by using an ansa bridge metallocene catalysts can produce either isotactic or syndiotactic polymers of propylene and other 1 alkenes 9 10 12 13 metallocenes are referred to as single site catalysts where the active site across each metallocene complex is structurally identical the surface of a heterogeneous catalyst is not uniform so there are many different active sites with differing electronic environments as the structure of the active site directly affects the stereoregularity and tacticity heterogeneous catalysts may produce polymers with a broader range of tacticities metallocenes do not suffer from this weakness and so often result in polymers with greater stereoregularity and narrower molecular weight distributions the chirality of the metallocene is a major determinant in whether the polymer is isotactic or syndiotactic 7 non metallocene catalysts edit main article post metallocene catalyst ziegler natta catalysts of the third class non metallocene catalysts use a variety of complexes of various metals ranging from scandium to lanthanoid and actinoid metals and a large variety of ligands containing oxygen o 2 nitrogen n 2 phosphorus p and sulfur s the complexes are activated using mao as is done for metallocene catalysts most ziegler natta catalysts and all the alkylaluminium cocatalysts are unstable in air and the alkylaluminium compounds are pyrophoric the catalysts therefore are always prepared and handled under an inert atmosphere mechanism of ziegler natta polymerization edit the structure of active centers in ziegler natta catalysts is well established only for metallocene catalysts an idealized and simplified metallocene complex cp 2 zrcl 2 represents a typical precatalyst it is unreactive toward alkenes the dihalide reacts with mao and is transformed into a metallocenium ion cp 2 zr ch 3 which is ion paired to some derivative s of mao a polymer molecule grows by numerous insertion reactions of c c bonds of 1 alkene molecules into the zr c bond in the ion simplified mechanism for zr catalyzed ethylene polymerization many thousands of alkene insertion reactions occur at each active center resulting in the formation of long polymer chains attached to the center the cossee arlman mechanism describes the growth of stereospecific polymers 3 14 this mechanism states that the polymer grows through alkene coordination at a vacant site at the titanium atom which is followed by insertion of the c c bond into the ti c bond at the active center orbital interactions of initial coordination edit the electrons in the filled pi orbital white of the alkene are donated to the empty d orbital grey of the titanium the electrons in one of the filled d orbitals white of titanium are accepted by the antibonding pi orbital grey of the alkene upon coordination of the alkene to the catalyst the alkene donates electrons from its pi bonding orbital into the metal center s empty d orbital while also accepting electrons from the metal s filled d orbitals into its empty pi anti bonding orbital the synergy of these interactions stabilize the overall bond between the alkene and metal center and thus facilitates initial coordination 15 8 termination processes edit on occasion the polymer chain is disengaged from the active centers in the chain termination reaction several pathways exist for termination cp 2 zr ch 2 chr n ch 3 ch 2 chr cp 2 zr ch 2 ch 2 r ch 2 cr polymer another type of chain termination reaction called a β hydride elimination reaction also occurs periodically cp 2 zr ch 2 chr n ch 3 cp 2 zr h ch 2 cr polymer polymerization reactions of alkenes with solid titanium based catalysts occur at special titanium centers located on the exterior of the catalyst crystallites some titanium atoms in these crystallites react with organoaluminum cocatalysts with the formation of ti c bonds the polymerization reaction of alkenes occurs similarly to the reactions in metallocene catalysts l n ti ch 2 chr polymer ch 2 chr l n ti ch 2 chr ch 2 chr polymer the two chain termination reactions occur quite rarely in ziegler natta catalysis and the formed polymers have a too high molecular weight to be of commercial use to reduce the molecular weight hydrogen is added to the polymerization reaction l n ti ch 2 chr polymer h 2 l n ti h ch 3 chr polymer another termination process involves the action of protic acidic reagents which can be intentionally added or adventitious commercial polymers prepared with ziegler natta catalysts edit polyethylene polypropylene copolymers of ethylene and 1 alkenes polybutene 1 polymethylpentene polycycloolefins polybutadiene polyisoprene amorphous poly alpha olefins apao polyacetylene references edit giuliano cecchin giampiero morini fabrizio piemontesi 2003 ziegler natta catalysts kirk othmer encyclopedia of chemical technology wiley vch doi 10 1002 0471238961 2609050703050303 a01 isbn 0 471 23896 1 hoff ray mathers robert t eds 2010 handbook of transition metal polymerization catalysts online ed john wiley sons doi 10 1002 9780470504437 isbn 978 0 470 50443 7 1 2 natta g danusso f eds 1967 stereoregular polymers and stereospecific polymerizations pergamon press nowlin t e mink r i kissin y v 2010 supported magnesium titanium based ziegler catalysts for production of polyethylene in hoff ray mathers robert t eds handbook of transition metal polymerization catalysts online ed john wiley sons pp 131 155 doi 10 1002 9780470504437 ch6 isbn 978 0 470 50443 7 polypropylene production via gas phase process technology economics program intratec 2012 isbn 978 0 615 66694 5 housecroft catherine sharpe alan 2018 inorganic chemistry 5th ed pearson pp 991 992 1 2 stevens malcolm 1999 polymer chemistry an introduction 3rd ed oxford university press p 248 1 2 ziegler natta polymerization pslc ws retrieved 2026 04 29 1 2 3 hill a f 2002 organotransition metal chemistry new york wiley interscience pp 136 139 1 2 3 4 5 kissin y v 2008 chapter 4 alkene polymerization reactions with transition metal catalysts amsterdam...