8.1 Introduction 8.2 Heterogeneous Ziegler-Natta polymerization 8.3 Homogeneous Ziegler-Natta polymerization 8.4 Ziegler-Natta copolymerization 8.5 Supported metal oxide catalysts 8.6 Alfin catalysts 8.7 Metathesis polymerization

8.1 Introduction + Karl Ziegler’s discovery ( in Germany-1950s) at low temperatures and pressures transition metal compound (Ti, V, Cr) + ethylene을 중합 Organometallic compound (AlR3) linear polyethylene (HDPE) – denser, tougher, higher melting because the more regular structure allows closer chain packing and a high degree of crystallinity. HDPE (high-density polyethylene) – bottle, pipe LDPE (low-density polyethylene) – lap, film, coating LLDPE (linear low-density polyethylene) - copolymer of ethylene and 1-butene (Ziegler-type catalysts) - less energy to produce than LDPE

8.1 Introduction Giulio Natta’s discovery ( in Italy) polymerizing  - olefins (1-alkenes) + catalysts of the type described by Ziegler Stereoregularity polymer 생성. (Ziegler & Natta - 1963년 Nobel Prize) Reduced Metal Oxides Alfin catalyst Other complex catalysts.

Principal Stereochemistry TABLE 8.1 Commercially Available Polymers Synthesized with Complex coordination Catalysts Polymer Principal Stereochemistry Typical Uses Plastics Polyethylene, high density (HDPE) Polyethylene, ultrahigh molecular weight (UHMWPE) Polypropylene Poly(1-butene) Poly(4-methyl-1- pentene)a Polystyrene 1,4-Polybutadiene 1,4-Polyisoprene Ethylene-1-alkeneb copolymer (linear low- density polyethylene, LLDPE) Ethylene-propylene block copolymers (polyallomers) Polydicyclopentadienec Bottles, drums, pipe, conduit, sheet, film, wire and cable insulation Surgical prostheses, machine parts, heavy, heavy-duty liners Automobile and appliance parts, rope, cordage, webbing, carpeting film Film, pipe Packaging, medical supplies, lighting Specialty plastics Metal cam coatings, potting compounds for transformers Golf ball covers, orthopedic devices Blending with LDPE, packaging film, Bottles Food packaging, automotive trim, toys, bottles, film, heat-sterilizable containers Reaction injection molding (RIM) structural plastics - Isotactic Syndiotactic trans

Principal Stereochemistry cis trans - TABLE 8.1 Commercially Available Polymers Synthesized with Complex coordination Catalysts Polymer Principal Stereochemistry Typical Uses Tires, conveyer belts, wire and cable insulation, footware Tires, footware, adhesives, coated fabrics Blending with other elastomers Molding compounds, engine mounts, car bumper guards Asphalt blends, sealants, adhesives, cable coatings Impact modifier for polypropylene, Wire and cable insulation, weather stripping, tire side walls, hose, seals cis trans - Elastomers 1,4-Polybutadiene 1,4-Polyisoprene Poly(1-octenylene) (polyoctenamer)c Poly(1,3-cyclo- pentenylene polymer)c Polypropylene (amorphous) Ethylene-propylene copolymer (EPM, EPR) Ethylene-propylene- diene copolymer (EPDM) aUsully copolymerized with small amounts of 1-pentene. b1-Butene, 1-hexene, and 1-octene. cSynthesized by ring-opening metathesis polymerization of the corresponding cycloaldene.

8.2 Heterogenous Ziegler-Natta Polymerization 8.2.1 Heterogeneous Catalysts Definition (1) transition metal compound ( an element from groups Ⅳ to Ⅷ ) - catalyst - halides or oxyhalides of Ti, V, Cr, Mo, Zr (2) organometallic compound ( a metal from groups Ⅰ to Ⅲ ) - cocatalyst - hydrides, alkyls, or aryls of metals (such as Al, Li, Zn, Sn, Cd, Be, Mg) Most important from the commercial standpoint TiCl3 TiCl4 + R3Al combination of

8.2 Heterogenous Ziegler-Natta Polymerization 8.2.1 Heterogeneous Catalysts Catalyst preparation mixing the components in a dry inert solvent in the absence of oxygen usually at a low temperature. Character of Catalysts having high reactivity toward many nonpolar monomers. high degree of stereoregularity.

8.2 Heterogenous Ziegler-Natta Polymerization 8.2.1 Heterogeneous Catalysts TiCl4-AlR3 (R = alkyl) system – initially exchange reactions (8.1) (8.2) (8.3) then reduction via homolytic bond cleavage (8.4) (8.5)

8.2 Heterogenous Ziegler-Natta Polymerization 8.2.1 Heterogeneous Catalysts Remove of radicals formed in these reactions by combination, disproportionation, or reaction with solvent. TiCl3 – formation by the equilibrium (8.8)

8.2 Heterogenous Ziegler-Natta Polymerization 8.2.1 Heterogeneous Catalysts Stereochemistry에 영향을 미치는 요인 Better activity is by using TiCl3 TiCl3의 , , ,  form , ,  : high degree of stereoregularity  : 40%-50% stereoregularity, 50%-60% – linear structure (atactic polymer) close-packed layered crystal structures. stereoregularity is very much dependent on surface characteristics of the catalyst. The nature of the transition metal The alkyl groups of the cocatalyst The presence of additives.

TABLE 8.2. Variation of Polypropylene Isotacticity with Catalysta Catalystb Stereoregularity (%) AlEt3 + TiCl4 AlEt3 + -TiCl3 AlEt3 + -TiCl3 AlEt3 + ZrCl4 AlEt3 + VCl3 AlEt3 + TiCl4 + P, As, or SB compounds AlEt2X + TiCl3 AlEtX2 + -TiCl3 + amine 35 45 85 55 73 90-99 99 a Data from Jordan6 and Dawans and Teyssié.7 b Et = ethyl; X = halogen.

8.2 Heterogenous Ziegler-Natta Polymerization 8.2.1 Heterogeneous Catalysts Problem of Ziegler-Natta catalysts low efficiency difficult of catalyst remove improvement of low efficiency (high-mileage catalysts) Impregnating the catalyst on a solid support (MgCl2, MgO) Ex) typical TiCl3-AlR3 catalyst yields about 50-200g/atm,h,g(catalyst) of polyethylene using a MaCl2-supported catalyst – 7000g/atm,h,g(catalyst) Activity

8.2.2 Mechanism and Reactivity in Hetrerogeneous Polymerization A. Two mechanism a) monometallic mechanism ① Monomer is complexed at a titanium atom exposed on the catalyst surface by a missing chlorine atom. ② Shifting the vacant octahedral position ③ Insertion reaction ④ Migration of the chain occurs to reestablish the vacant site on the surface. SCHEME 8.1

SCHEME 8.1. Monometallic mechanism of Ziegler-Natta polymerization.

8.2.2 Mechanism and Reactivity in Heterogeneous Polymerization A. Two mechanism a) Bimetallic mechanism Ti 와 monomer가 -complex를 이룬다. Cyclic transition state가 존재한다. Ionization Original form 두 mechanism의 공통점 ① Ti atom과 monomer가 -complex를 이룬다. ② Cyclic transition state가 존재한다. ③ Insertion에 의해 중합반응이 진행된다. (stereoregularity 결점)

SCHEME 8.2. Bimetallic mechanism of Ziegler-Natta polymerization.

8.2.2 Mechanism and Reactivity in Heterogeneous Polymerization Ziegler-Natta polymerization – nonpolar monomers사용 monomer activity – decreases with increasing steric hindrance about the double bond. reactivity

8.2.2 Mechanism and Reactivity in Heterogeneous Polymerization Termination transfer to monomer (8.9 and 8.10) internal hydride transfer (8.11) transfer to cocatalyst or to an added alkylmetal compound (8.12) transfer to added hydrogen (8.13) (8.9) (8.10) (8.11) (8.12) (8.13)

8.2.2 Mechanism and Reactivity in Heterogeneous Polymerization (8.14) Hydrogen – the preferred transfer agent because it reacts cleanly, leaves no residue low in cost Molecular weight distributions insoluble catalyst - broad soluble catalyst - narrower

8.2.2 Mechanism and Reactivity in Heterogeneous Polymerization FIGURE 8.1 Types of rate curves observed in Ziegler-Natta polymerization: (A) constant; (B) decay- ing; and (C) decaying to constant. Polymerization rate Time A B C

8.2.3 Stereochemistry of Heterogeneous Polymerization insoluble catalysts Isotactic polymers level of stereoregularity – depending, to a degree, on how exposed the active site is on the catalyst surface. 1-alkenes – approaches from the same side, giving rise to isotactic placement. double bond of the monomer undergoes cis opening exclusively cis addition to the double bond occurs

8.2.3 Stereochemistry of Heterogeneous Polymerization erythro-Diisotactic threo-Diisotactic (8.15) (8.16) Similar behavior : 1,2-disubstituted olefins.

8.2.4 Polymerization of Dienes 1,3-butadiene : the four possible structures cis-1,4 ; trans-1,4 ; isotatic 1,2 ; syndiotactic 1,2 TABLE 8.3. Catalysts for the Stereospecific Polymerization of Butadiene Catalysta Yield (%) Polymer structureb Ref. no. R3Al + VCl4 R3Al + VCl3 R3Al + VOCl3 R3Al + TiI4 R2AlCl + CoCl2 R3Al + Ti(OC6H9)4 Et3Al + Cr(C6H5CN)6 Al/Cr = 2 Al/Cr = 10 97-98 99 93-94 96-97 90-100 ~100 trans-1,4 cis-1,4 1,2 st-1,2 it-1,2 2 13 14 a Et = ethyl b st = syndiotactic, it = isotactic.

8.2.4 Polymerization of Dienes Isoprene cis- and trans-1,4, 1,2, and 3,4 polymerization TABLE 8.4. Catalysts for the Stereospecific Polymerization of Isoprene Catalysta Yield (%) Polymer Structure Ref. No. R3Al + -TiClB3 Et3Al + VCl3 Et3Al + TiCl4 Al/Ti < 1 Al/Ti > 1 Et3Al + Ti(OR)4 91 99 95 96 trans-1,4 cis-1,4 3,4 15 14 a Et = ethyl

8.2.4 Polymerization of Dienes Definition of mechanism whether the catalyst coordinates one(1,2 polymerization) or both(1,4 polymerization) double bonds of the diene. 2. that coordination of a -allylic structure occurs and that the direction of approach of monomer determines the structure. (8.17) (8.18)

8.2.4 Polymerization of Dienes (8.19) (8.20) Conjugated cyclic dienes : Ziegler-Natta polymerization Nonconjugated dienes : coordination catalysts 1 2

8.3 Homogeneous Ziegler-Natta Polymerization 8.3.1 Metallocene Catalysts Cp2TiCl2 3 R2AlCl 4 5 6 The earliest metallocene catalysts MAO – used in conjunction with metallocene catalysts

8.3 Homogeneous Ziegler-Natta Polymerization 8.3.1 Metallocene Catalysts General structure Examples of catalysts 7 M : Zr, Ti, Hf X : Cl, alkyl Z : C(CH3)2, Si(CH3)2, CH2CH2 R : H, alkyl 9 8 Me2Si(Ind)2ZrCl2 Me2C(Flu)(Cp)ZrCl2 form isotactic and syndiotactic polypropylene usually written in condensed form

8.3 Homogeneous Ziegler-Natta Polymerization 8.3.2 Mechanism and Reactivity with Metallocene Catalysts Difference between metallocene and heterogeneous Ziegler-Natta catalysts ① the former have well-defined molecular structure ② polymerization occurs at one position in the molecule ③ the transition metal atom. SCHEME 8. 3. Formation of the active site in a zirconocene catalyst. 10 3

8.3 Homogeneous Ziegler-Natta Polymerization 8.3.2 Mechanism and Reactivity with Metallocene Catalysts SCHEME 8.4. Possible polymerization mechanism for ethylene.

8.3 Homogeneous Ziegler-Natta Polymerization 8.3.2 Mechanism and Reactivity with Metallocene Catalysts Character of polymers prepared with metallocene catalysts ① Narrower molecular weight distributions than those prepared with heterogeneous catalysts. Better mechanical properties. ③ Polydispersities (Mw/Mn) range from 2to 2.5 for the former, compared with 5 to 6 for the latter. ④ The molecular weight of the metallocene-based polymers decreases with increasing polymerization temperature, increasing catalyst concentration, and addition of hydrogen to the monomer feed.

8.3 Homogeneous Ziegler-Natta Polymerization 8.3.2 Mechanism and Reactivity with Metallocene Catalysts Activities of metallocene catalysts from 10 to 100 times higher than those of conventional Ziegler-Natta catalysts. While it is often difficult to correlate structural variables with activity, the following generalizations can be made : For the group 4B metals, the order of activity is Zr>Ti>Hf. Alkyl groups on the cyclopentadiene rings increase catalyst activity if they are not too bulky. Large, bulky alkyl groups and electron-withdrawing groups decrease the activity. Increasing the size of the groups attached to the atom bridging the cyclopentadiene rings (C or Si) reduces the activity. MAO affords much higher catalyst activities than ethyl- or higher alkylalumoxane cocatalysts.

8.3 Homogeneous Ziegler-Natta Polymerization 8.3.2 Mechanism and Reactivity with Metallocene Catalysts Another way that metallocene catalysts differ from eterogeneous catalysts 11 (8.21) norbornene high-melting stereoregular polymers

8.3 Homogeneous Ziegler-Natta Polymerization 8.3.3 Stereochemistry of Metallocene-Catalyzed Polymerization Metallocene catalysts exhibit a remarkable ability to control polymer stereochemistry. Structural variations synthesis of atactic polypropylene and higher poly(1-alkenes) isotactic syndiotatic type CpZrCl2 atactic polymer isotactic and syndiotactic polymer 8 9 chiral achiral

8.3 Homogeneous Ziegler-Natta Polymerization 8.3.3 Stereochemistry of Metallocene-Catalyzed Polymerization The much different sizes of the two pi ligands of 8 assumed to play a role in the formation of symdiotactic polymer substitution of a methyl group on the cyclopentadiene ring of 9 hemiisotactic polypropylene (alternate methyls isotactic, the others atactic)

8.3 Homogeneous Ziegler-Natta Polymerization 8.3.3 Stereochemistry of Metallocene-Catalyzed Polymerization Producing polypropylene having alternating atactic and isotactic blocks Ex) The zirconium catalyst can rotate between chiral and achiral geometries 12 (8.22) Thermoplastic elastomers having a range of properties from a single monomer in a one-pot synthesis

8.3 Homogeneous Ziegler-Natta Polymerization 8.3.3 Stereochemistry of Metallocene-Catalyzed Polymerization SCHEME 8.5. A mechanism for isotactic placement with a metallocene catalyst. Optically active isotactic polymer would form from a pure enantiomer of 8

8.4 Ziegler-Natta Copolymerization (R:aliphatic) CnH2n+1 n=2일 경우 LLDPE n=1일 경우 EPDM(EPM) TABLE 8.5 ethylene is much more reactive than higher alkenes with both heterogeneous and homogeneous catalysts. EPDM is prepared with small amounts of a nonconjugated diene to facilitate crosslinking. 13 14 15 Typical dienes ethylidenenorborene dicyclopentadiene 1,4-hexadiene

TABLE 8.5. Representative Reactivity Ratios in Ziegler-Natta Copolymerizationa Monomer 1 Monomer 2 Catalystb r1 r2 Heterogeneous Ethylene Propylene Homogeneous 1-Butene 1-Hexene TiCl3/AlR3 VCl3/AlR3 Cp2ZrMe2 [Z(Ind)2]ZrCl2c 15.72 5.61 26.90 4.04 31 6.6 55 69 0.110 0.145 0.043 0.252 0.005 0.06 0.017 0.02 a Data from Boor3 and Kamisky.22 b R = C6H13; Cp = cyclopentadiene; Me = methyl; Z = bridging group; Ind = indene. c Z = CH2CH2.

8.5 Supported Metal Oxide Catalysts Typical supports : Alumina, silica, charcoal (숯) metals : Cr, V, Mo, Ni, Co, W, Ti etc Prepare of Catalysts ① The support material is impregnated with the metal ion, then heated in air at a high temperature to form the metal oxide. ② when the support material is an oxide such as alumina, the two oxides are coprecipitated and dried in air. Catalyst is activated treatment with a reducing agent (hydrogen, metal hydride, carbon monoxide) Poisoning of the catalyst in the presence of water, oxygen, acetylene.

8.5 Supported Metal Oxide Catalysts (8.23) Character of the supported metal oxides ① yield polyethylene with approximately equal amounts of saturated and unsaturated chain ends. ② not as active as Ziegler-Natta catalysts, and they do not give rise to a high degree of steroregularety.

8.6 Alfin Catalysts alcohol + olefin effective in polymerizing butadiene and isoprene to very-high-molecular-weight polymer The most effective catalyst for diene polymerization - allylsodium, sodium isopropoxide, sodium chlofide (8.24) (8.25) (8.26) polymerize butadiene within minutes to a polymer having a molecular weight of several million

8.7 Metathesis Polymerization Alkenes undergo a double bond redistribution reaction (8.27) (8.28) 16 17

8.7 Metathesis Polymerization Synthesis of polymers by olefin metathesis (8.29) (8.30) acylic dienes

8.7.1 Ring-Opening Metathesis Polymerization Propagation steps (8.31) That certain group Ⅷ metal compounds (8.32) 18 7-oxanorbornene derivatives

Examples of three metathesis polymerizations (8.33) 19 (8.34) 20 (8.35) 21 polyoctenamer norbornene polymer

with cyclic polyenes 22 (8.36) (8.38) 24 23 1—methyl-1,5-cyclooctadiene cis,trans-cyclodeca-1,5-diene 1,3,5,7-cyclooctatetraene

8.7.2 Acyclic Diene Metathesis Polymerization ADMET(Acyclic diene metathesis) polymerization of 1,9-decadiene (8.39) ADMET is also useful for the synthesis of functionalized polymers. the symthesis of an unsaturated polymer containing ester functionality. (8.40)

byproduct of ADMET polymerization 8.7.2 Acyclic Diene Metathesis Polymerization addition of ethylene to an unsaturated polymer can effect depolymerization byproduct of ADMET polymerization (8.41)