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