1. Polyolefins: Catalysis and dedicated analysis
6BM56, ( )

2. Scope & objectives
Providing a comprehensive fundamental introduction into the chemical aspects of catalytic olefin polymerization.
Get insight into several aspects of the macromolecular science of polyolefins by following the course of a polyolefin molecule from its origin at the catalyst site to its application in the end product.
Generate the ability to rationally design a catalytic system, a production process and a processing methodology to produce a polyolefin end-product with certain predefined properties.
6BM56, ( )

3. Scope & objectives
Providing a comprehensive fundamental introduction into the chemical aspects of catalytic olefin polymerization.
Get insight into several aspects of the macromolecular science of polyolefins by following the course of a polyolefin molecule from its origin at the catalyst site to its application in the end product.
Generate the ability to rationally design a catalytic system, a production process and a processing methodology to produce a polyolefin end-product with certain predefined properties.

4. Polyolefins: Catalysis and dedicated analysis
Introduction - overview of polymerization catalysis
Generally, catalysts are (transition) metal coordination complexes.
Generally, the complexes contain a reactive group that forms the initiating group of the growing chain. This group is often a halide or alkoxide (ROP), an alkylidene (ROMP), enolate (acrylate polymerization) or an alkyl or hydride (olefin polymerization).
But what are the characteristics of a good catalyst?
Before that, some basics…

5. Organometallics – basics
18 electron rule.
The valence shell of transition metals can accommodate 18 electrons (1 S + 3 p + 5 d orbitals). Filling the valence shell will result in a noble gas configuration.
Steric reasons often prevent the metal
to fulfill the 18 electron rule.
Transition metal complexes with less than
18 valence electrons show enhanced reactivity.
18 VE
16 VE

6. Organometallics – basics
A nucleophile is a reagent that is “nucleus-loving”.
It has an electron-rich side and can form a bond by donating an electron pair to an electron-poor substrate, the electrophile.
An electrophile is a reagent that is “electron-loving”.
It has an electron-poor side and can form a bond by accepting an electron pair from an electron-rich substrate, the nucleophile.
Closely related to nucleophiles and electrophiles are acids and bases.

7. Organometallics – basics
Some hydrocarbons can be acidic.
Which of the following are Brønsted acids?
Going from sp ➞ sp2 ➞ sp3: the e- is more distant from the positively charged nucleus which makes it less stable.
Some reagents have different functions (Lewis/Brønsted acids/bases or electrophiles/nucleophiles?
Lewis acid Lewis base Brønsted acid Brønsted base Brønsted base

8. Organometallics – basics
Nucleophiles electrophiles, Brønsted and Lewis acids and bases.

9. Organometallics – basics
Hardness and softness.
The difference in the ionization energy of a neutral atom to its ion is a measure for the so-called hardness of an element (the hardest atoms are those with high ionization energies and low electron affinity).
Simple rule of thumb: the hardness of an atom is related to the charge of the atom divided by the ionic radius.
For example, AlF3 is a very hard molecule, while SnI2 is a soft molecule.
Polarizability.
The harder the atom/molecule, the less polarizable it will be. Clearly, the more diffuse orbitals of heavier elements in a group are more easily to polarize than the orbitals of the lighter elements, and hence the heavier elements are softer (e.g. fluorine is hard, iodine is soft).

10. Organometallics – basics
Relative bond strength.
M = Ti, Zr, Hf;
R =
Ti-Np = 185
Zr-Np = 221
Hf-Np = 240
Ti-Bz = 217
Zr-Bz = 263
Ti-NEt2 = 307
Zr-NEt2 = 337
Hf-NEt2 = 364
Ti-OiPr = 447
Zr-OiPr = 517
Hf-OiPr = 535

11. Mechanism – termination
For late transition metals, the
DE(M-H – MC) is significantly larger than for early transition metals.
Consequently, late transition metals undergo b-H elimination more rapidly.

12. Organometallics – basics
Summarizing.
Transition metal complexes with less than 18 VE are reactive
the metal in such complexes – are Lewis acids/electrophiles
the metal in such complexes – form polar bonds
the metal in such complexes – tend to bind Lewis bases d- d+ X
Metal
Lewis base
Ancillary ligand

13. Organometallics – the requirements for catalysis
In catalysis, we want to activate a substrate so it can react with another reagent already bonded to the catalyst site.
In catalytic coordination polymerization, the monomer coordinates to the metal site and is thereby activated, which allows it to react with the growing chain.
Electrophilic metal center (can be cationic)
Vacant coordination site
Polarized metal-polymer bond
Robust and tunable ancillary ligand system
Sometimes a cocatalyst is required
No easily accessible side reactions
Low costs
Polymer
Monomer
Metal
Ancillary ligand d+ d-
Cocat.
Characteristics of a metal-based catalyst:

14. Chain growth polymerization
Coordination polymerization is generally a chain growth process. n
kpropagation n
kinitiation
kpropagation
ktermination or
kchain transfer +
The word chain is used in a statistical sense and has no relationship with the actual growing polymer chain.
─ = step growth polymerization
─ = chain growth polymerization

15. Step growth polymerization
Polycondensation is a step growth process. …
During step growth reactions all monomers are reactive at the same time.
High conversion is required in order to obtain high molecular weight polymers.
─ = step growth polymerization
─ = chain growth polymerization

16. -Overview of polymerization catalysis
Different coordination polymerization mechanisms:
ROP, ROMP, (meth)acrylate polymerization, olefin polymerization.
Different catalysts:
Metal-based catalysts, organic catalysts and enzymes.

17. Ring Opening Polymerization (ROP)
Ring opening polymerization is a versatile process to polymerize a wide range of cyclic monomers. For example:
Why would such polyesters
be formed?
Enthalpy or entropy driven?

18. Ring Opening Polymerization (ROP)
Not only for cyclic esters, also for example for cyclic ethers and the combination of different cyclic molecules can be ring opened. For example:

19. ROP of cyclic esters. What are the requirements of the catalyst?d- d+
OMe
Metal
Ancillary ligand
Robust and tunable ancillary ligand system
Electrophilic metal center (can be cationic)
Polarized metal-polymer bond
Vacant coordination site to bind monomer

20. Catalysts for ROP of cyclic esters.
Examples of catalysts for ring opening polymerization of cyclic esters.
M = Al, Cr, Mn, Co
Cocat: [Ph2PNPPh2]+Cl-, NEt4+Br-,
M = Mg, Ca, Zn
M = Y, La
M = Mg, Zn

21. Ring Opening Polymerization – mechanism
ROP of e-caprolactone.

22. Ring Opening Polymerization – mechanism
ROP of e-caprolactone. xs H+

23. Polyhydroxybutyrates
Catalyst requirements:
Lewis acidic metal.
Free coordination site.
Sometimes a cocatalyst is required.

24. Polylactide and poly(lactide-co-glycolide)
Chirality plays an important role in polylactide
and poly(lactide-co-glycolide).
DL-lactide L-lactide D-lactide

25. Ring Opening Polymerization – mechanism

26. Oxirane-based (co-)polymers

27. Oxirane – carbon monoxide copolymers
Two similar but different synthetic polymers.

28. Step growth versus chain growth
─ = step growth polymerization
─ = chain growth polymerization 1 % M w m o n er c s u p t i on

29. Inversion of configuration
Oxirane – carbon monoxide copolymers
Inversion of configuration

30. Inversion of configuration
Oxirane – carbon monoxide copolymers
Inversion of configuration

31. Oxirane – anhydride copolymers

32. Oxirane-carbon dioxide copolymers

33. Oxirane-carbon dioxide copolymers
Bimetallic mechanism.

34. ROP – cocatalyst assisted

35. Enzymatic polymerization
poly(R-3-hydroxybutyrate) - PHB
Bacteria (Alcaligenes latus).
Up to 90% polymer
poly(R-2-hydroxypropionate) - PLA
lipase Pseudomonas cepacia

36. Enzymatic ring opening polymerization
Enzymatic polymerization of e-caprolactone.
Monomer activation:
Initiation:
Propagation:

37. ROP polymerization using organic catalysts
N-heterocyclic carbenes are effective nucleophilic catalysts for the ROP of cyclic ethers and esters.
Chain transfer agents such as alcohols can be added to control the molecular weight and produce end-functionalized polymers.

38. ROP polymerization using organic catalysts
Nucleophilic catalyst +

39. ROP polymerization using organic catalysts
Nucleophilic catalyst
ROH +

40. Olefin metathesis polymerization
Acyclic Diene Metathesis (ADMET)
Ring Opening Metathesis Polymerization (ROMP) d- d+
C(H)R1
Metal
Ancillary ligand

41. Olefin metathesis polymerization
Schrock type Grubbs type

42. ADMET – Cross metathesis polymerization
Olefin metathesis polymerization
ADMET – Cross metathesis polymerization
Polyolefins by step growth polymerization (polycondensation).

43. Ring opening metathesis polymerization
Olefin metathesis polymerization
Ring opening metathesis polymerization

44. ROMP – an example
3 homopolymerizes norbornene but does not homopolymerize cyclooctene.
However, 3 does copolymerize norbornene and cyclooctene.
Why does 3 copolymerize these monomers and what is the structure of the copolymer?
A is sterically less hindered than D.
A➝B➝C➝D will only occur when severe ring strain is released since finally a sterically more hindered species is formed.
D➝E➝F➝A will occur also for non-strained cyclic olefins since finally a sterically less hindered species is formed.

45. Coordination polymerization – acrylates
Metal mediated Michael addition
Migratory reaction
MMA is prochiral which leads to tacticity
Metal
Ancillary ligand * ➘
Chirality
Coordination intermediate
Resting state

46. Coordination polymerization – olefins
CH3
Migratory insertion
propylene is prochiral which leads to tacticity
Metal
Ancillary ligand
Chirality ➘ *

47. Coordination polymerization – olefins - MMA

48. Coordination polymerization – catalysts
Metal
Ancillary ligand d+ d-
OMe d- d+
C(H)R1
Metal
Ancillary ligand d- d- d+ d+
CH3
Metal
Metal
Ancillary ligand
Ancillary ligand

49. Organometallics – the requirements for catalysis
In catalysis, we want to activate a substrate so it can react with another reagent already bonded to the catalyst site.
In catalytic coordination polymerization, the monomer coordinates to the metal site and is thereby activated, which allows it to react with the growing chain.
Electrophilic metal center (can be cationic)
Vacant coordination site
Polarized metal-polymer bond
Robust and tunable ancillary ligand system
Sometimes a cocatalyst is required
No easily accessible side reactions
Low costs
Polymer
Monomer
Metal
Ancillary ligand d+ d-
Cocat.
Characteristics of a metal-based catalyst: