chemical review 2000, issue 4 “frontiers in metal-catalyzed polymerization” also
DESCRIPTION
Chemical Review 2000, Issue 4 “FRONTIERS IN METAL-CATALYZED POLYMERIZATION” Also Angew. Chem. Int. Ed. 1999, 38, 428 ± 447. Soluble Metallocene Cataysts. Used a mixture of meso and racemic ansa -titanocenes Stereo-rigid Ethylene-bridged Rac: chiral with C 2 -symmetric axis - PowerPoint PPT PresentationTRANSCRIPT
Polymer SynthesisCHEM 421
Chemical Review 2000, Issue 4“FRONTIERS IN METAL-CATALYZED
POLYMERIZATION”
Also
Angew. Chem. Int. Ed. 1999, 38, 428 ± 447
Polymer SynthesisCHEM 421
Soluble Metallocene Cataysts
• Used a mixture of meso and racemic ansa-titanocenes– Stereo-rigid– Ethylene-bridged– Rac: chiral with C2-symmetric axis– Meso: achiral
Polymer SynthesisCHEM 421
Polymer SynthesisCHEM 421
Polymer SynthesisCHEM 421
• Unbridged metallocene catalysts• Rapid isomerization, low barriers• What kind of polymer is produced?
–Atactic Polymer
Polymer SynthesisCHEM 421
• Unbridged metallocene catalysts
• Added phenyl group to indene– Inhibits rate of ligand rotation
Polymer SynthesisCHEM 421
Polymer SynthesisCHEM 421
• Unbridged metallocene catalysts
• Added phenyl group to indene
Polymer SynthesisCHEM 421
Polymer SynthesisCHEM 421
Physical Properties of Polypropylene
Polymer SynthesisCHEM 421
Olefin Polymerizations with Early Metal Catalysts
Metallocene Catalysts:Technological advance
A) Incremental
B) Major:
1) New Materials
2) Detailed mechanistic understanding
Not a black box anymore…
~ 2 × 1011 lbs/year polyethylenes(PE), polypropylenes(PP) produced worldwide!
Polymer SynthesisCHEM 421
Olefin Polymerizations with Early Metal Catalysts
Metallocene Catalysts:Incremental technological advance
● Increased activities/productivities
● Many different grades of ethylene/ α-olefin copolymers ● Control of MW, MWD
bimodal, unimodal, PDI < 5.0!
Existing markets are being extended into new applications
Polymer SynthesisCHEM 421Metallocene Catalysts
• Major Technological Advance–New Materials
» Syndiotactic polystyrene
»Tm = 270 °C, 40-50% X-tal w/ good rate of x-tallization
» Syndiotactic and elastomeric PP
» Cyclic Olefin Copolymers
»Hoechst’s TopazTM (Tg = 140 – 200 °C)
CH2 CH2
Polymer SynthesisCHEM 421
Late vs Early Transition Metal Catalysts
1. Less oxophilic ― improved functional group tolerance
2. Rapid β-elimination ― chain transfer competitive with
propagation dimers, oligomers
3. Generally, lower activities
MP -elim.
propagation M P
M H + P
Polymer SynthesisCHEM 421
Late Metal Catalysts
• Not useful…β-elimination
MN
N
R
MN
N
R
MN
N
R
H
RM
N
N H+
RM
N
N H+
Propagation
Β-Elimination
Dissociation
Displacement
Polymer SynthesisCHEM 421Chain Transfer Mechanisms
NNR R
HR
R+NNR R
HM M
Associative Displacement at axial postion
Polymer SynthesisCHEM 421
Chain Transfer Mechanisms
NN
HR
R+NN
HM M
Associative Displacement (retarded by blocking axial postions)
Polymer SynthesisCHEM 421Blocking of Axial Coordination Sites
Polymer SynthesisCHEM 421α–Diimine Based Catalysts
■ High molecular weight polymers with unique microstructures from:
● ethylene
● α – olefins
● cyclopentene
● trans-1,2-disubstituted olefins
■ Copolymers of ethylene with certain polar vinyl monomers
N N
RR
H3C solv.
R'
R'R'
R' M
R = H, Me, acenaphthyl
R' = -iPr, -Me, aryl, halogen
A
M = Ni, PdA =
CF3
CF3
B4
Polymer SynthesisCHEM 421
Mechanistic Model
MN
N
RM
N
N
R
MN
N
R
MN
N
R
H
MN
NR
insertion
methyl branchresting state
MN
N
R'
turnover-limiting
"chain running"
MN
N
insertion
ethyl branch
R'
Polymer SynthesisCHEM 421Polyethylene
N N
R' SolvR
RR
R Pd
+
N N
Br BrR
RR
R Ni
/ Et2AlCl
30 °C~500 TO/hr
30 °C~1-3 x 106 TO/hr
Mn > 105
amorphous PEhyperbranched,
~100 branches / 1000 C's
Mn 105 - 106
Tm: 25° - 135° C5 - 80 branches / 1000 C's
increasing [C2H4] decreases branchingincreasing T increases branching
Early Metal CatalystsTi (IV), Zr (IV), Cr/SiO2 n
linear PEsemicrystalline
Tm ~ 136 °C
Polymer SynthesisCHEM 421
Poly (α–Olefins)
N N ArArM
+R R
Early Metal CatalystsR
R RRR
"chain-straightened" (1, 3 enchainment)
chain-straightened, primarily C1, C4 branches
1,2-insertion
Polymer SynthesisCHEM 421
Commercial Copolymers of Ethylene and Polar Vinyl Monomers
CO2Me
CO2Bu
CO2H
CO2H
OAc
CN
Si(OMe)3
● Radical Initiation
● High temperatures, very high ethylene pressure