- Overview of polymeriza1on catalysis

Transcription

1 - verview of polymeriza1on catalysis Different coordina-on polymeriza-on mechanisms: RP, RMP, (meth)acrylate polymeriza6on, olefin polymeriza6on. Different catalysts: Metal- based catalysts, organic catalysts and enzymes. 1

2 Ring pening Polymeriza1on (RP) Ring opening polymeriza6on is a versa6le process to polymerize a wide range of cyclic monomers. For example: Why would such polyesters be formed? Enthalpy or entropy driven? 2

3 Ring pening Polymeriza1on (RP) ot only for cyclic esters, also for example for cyclic ethers and the combina6on of different cyclic molecules can be ring opened. For example: 3

4 RP of cyclic esters. What are the requirements of the catalyst? Ancillary ligand Metal δ + δ - Me n! Robust and tunable ancillary ligand system! Electrophilic metal center (can be ca6onic)! Polarized metal- polymer bond! Vacant coordina6on site to bind monomer 4

5 Catalysts for RP of cyclic esters. Examples of catalysts for ring opening polymeriza1on of cyclic esters. i Pr Al i Pr i Pr Sn H Zn H u M t-bu M = Al, Cr, Mn, Co u M t-bu t-bu Cocat: [Ph 2 PPPh 2 ] + Cl -, Et 4+ Br -, t-bu M i Pr t-bu THF X t-bu M Me t-bu t-bu Me Ph Ph Ph Ph M M M = Mg, Ca, Zn M = Y, La M = Mg, Zn 5

6 Ring pening Polymeriza1on mechanism RP of ε- caprolactone. n Al n! + Al! "! "! + Al! "! "! + Al! "! + Al! "! +! +! "! " 6

7 Ring pening Polymeriza1on mechanism RP of ε- caprolactone.! + Al! "! +! "! "! + Al! "! + Al! " n H Al n H + n n xs Al 7

8 Polyhydroxybutyrates Catalyst requirements:! Lewis acidic metal.! Free coordina6on site.! Some6mes a cocatalyst is required. 8

9 Ring pening Polymeriza1on mechanism 9

10 xirane- based (co- )polymers 10

11 xirane carbon monoxide copolymers C R R R [catalyst] R [catalyst] n yields an AB- polymer R + R [catalyst] R R n [catalyst] 2 C yields an AABB- polymer R Two similar but different synthe1c polymers. 11

12 Step growth versus chain growth M w % m o n o m er c o n s u m p t i on = step growth polymeriza6on = chain growth polymeriza6on 12

13 xirane carbon monoxide copolymers Inversion of configura6on 13

14 xirane carbon monoxide copolymers Inversion of configura6on 14

15 xirane anhydride copolymers 15

16 xirane- carbon dioxide copolymers 16

17 xirane- carbon dioxide copolymers Bimetallic mechanism. 17

18 RP cocatalyst assisted X t-bu Cr t-bu t-bu t-bu X Cr t-bu X Cr t-bu t-bu t-bu X Cr 18

19 Enzyma1c polymeriza1on Bacteria (Alcaligenes latus). Up to 90% polymer poly(r- 3- hydroxybutyrate) - PHB n n poly(r- 2- hydroxypropionate) - PLA lipase Pseudomonas cepacia 19

20 Enzyma1c ring opening polymeriza1on Enzyma1c polymeriza1on of ε- caprolactone. Monomer ac1va1on: Lipase H + Lipase C(CH 2 ) 5 H (EAM) Ini1a1on: Lipase C(CH 2 ) 5 H + H 2 HC(CH 2 ) 5 H + Lipase H (EAM) Propaga1on: Lipase (EAM) C(CH 2 ) 5 H + H C(CH 2 ) 5 H H C(CH 2 ) 5 H n n+1 + Lipase H 20

21 RP polymeriza1on using organic catalysts - heterocyclic carbenes are effec6ve nucleophilic catalysts for the RP of cyclic ethers and esters. Chain transfer agents such as alcohols can be added to control the molecular weight and produce end- func6onalized polymers. 21

22 RP polymeriza1on using organic catalysts ucleophilic catalyst + n-1 n 2 n 22

23 RP polymeriza1on using organic catalysts ucleophilic catalyst R 2 n H RH! n + R 2 n H 2 n 23

24 lefin metathesis polymeriza1on Acyclic Diene Metathesis (ADMET) Ring pening Metathesis Polymeriza1on (RMP) Ancillary ligand Metal δ + R 2 δ - C(H)R 1 R2 24

25 lefin metathesis polymeriza1on Schrock type Grubbs type 25

26 lefin metathesis polymeriza1on ADMET Cross metathesis polymeriza1on Polyolefins by step growth polymeriza6on (polycondensa6on). 26

27 lefin metathesis polymeriza1on Ring opening metathesis polymeriza1on 27

28 RMP 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. 28

29 Coordina1on polymeriza1on acrylates Metal δ + δ -! Metal mediated Michael addi6on! Migratory reac6on Ancillary ligand Me! MMA is prochiral which leads to tac6city Me Cp 2 Zr Me Me P n Me Cp 2 Zr Cp 2 Zr P n Me Me * Chirality P n Coordina6on intermediate Me Res6ng state 29

30 Coordina1on polymeriza1on olefins Metal δ + δ - CH3! Migratory inser6on! propylene is prochiral which leads to tac6city Ancillary ligand Chirality Cp 2 Zr Cp 2 Zr Cp 2 Zr H Cp 2 Zr * P n+1 P n P n P n 30

31 Coordina1on polymeriza1on olefins - MMA 31

32 Coordina1on polymeriza1on catalysts n n n Ancillary ligand Metal δ + δ - Me n Ancillary ligand Metal δ + R 2 δ - C(H)R 1 R2 Me Me Me Metal δ + δ - Metal δ + δ - CH3 Ancillary ligand Me Ancillary ligand 32

33 rganometallics the requirements for catalysis In catalysis, we want to ac6vate a substrate so it can react with another reagent already bonded to the catalyst site. In cataly6c coordina6on polymeriza6on, the monomer coordinates to the metal site and is thereby ac6vated, which allows it to react with the growing chain. Characteris1cs of a metal- based catalyst: Cocat.! Electrophilic metal center (can be ca6onic)! Vacant coordina6on site Metal δ + δ- Polymer! Polarized metal- polymer bond! Robust and tunable ancillary ligand system Monomer! Some6mes a cocatalyst is required Ancillary ligand! o easily accessible side reac6ons! Low costs 33