Polymer Synthesis
CHEM 421
• Odian Book
Chapter 3-15, 5-3
Polymer Synthesis
CHEM 421
Living Polymerization (II)
by
Ru-Ke Bai
Department of Polymer Science and Engneering
University of Science and Technology of China
A Brief Review
Polymer Synthesis
CHEM 421
• What is living polymerization?
• No termination
• No chain transfer
• What are the major criteria for living polymerization?
A
B
C
PDI
Mn
PDI
PDI
can be prepared by
ln[M]0/[M]t
Mn
Block copolymers
sequential addition
of monomers.
conversion
Time
Living polymerization is a good tool for the
preparation of block copolymers.
Rankings of Anions…
Polymer Synthesis
CHEM 421
How to characterize the reactivity of a propagating anion?
CH
H
CH
+
CH3
CH3
C
H
C
C
O
C
+
H
O
OR
OR
R
H
R
H
[H
Ka =
][R
]
pKa = - log Ka
[RH]
H
Propagating Anions
pKa of conjugate acid
of prop.chain end
CH
Styrenes, dienes
42
Acrylic esters
25
CH 3
C
C O
O R
CH 3
C
Acrylonitrile
25
C N
CH3
C
C O
R
Vinyl ketones
20
Polymer Synthesis
CHEM 421
Propagating Anions
pKa of conjugate acid
of prop.chain end
CH2CH 2O
Cyclic oxides
16-18
Cyclic siloxanes
Si
O
O
Si
Si
CH3
Si O
O
CH3
CN
Cyano acrylates
C
C
O
OCH3
10-12
11-13
Polymer Synthesis
CHEM 421
Initiators
Useful Initiator
Styrenes.dienes
42
RLi, NH2-, Ar -
Acrylates
25
RMgX, DPHL
Acrylonitriles
25
RO -, C5H5-
Vinyl ketones,
Aldehydes
Cyclic oxides
20
RO -
16-18
RO -
Siloxanes(-D3)
10-12
HO -, RO -
Cyano acrylates
11-13
H2O, HO -, RO -
Super glue
Nitroalkenes
10
KHCO3, H2O
most nucleophilic
pKa
Least nucleophilic
Reactivity
Monomer
Polymer Synthesis
CHEM 421
Microstructure of Dienes
Polymer Synthesis
CHEM 421
Four different microstructures in polyisoprene
cis 1-4 isomer
(natural rubber)
trans 1-4 isomer
1-2 isomer
3-4 isomer
cis-1,4 favored in
hydrocarbon solvents
Can MMA be polymerized via living process ?
Side reactions
1)
2)
3)
Polymer Synthesis
CHEM 421
PMMA via Living Pzn
Polymer Synthesis
CHEM 421
PMMA homopolymer
• Can not use BuLi directly
• Make new initiator (use 1,1-diphenylethylene)
1,1-diphenyl hexyl lithium
Bu
n-BuLi
Li
CH2 C
(DPHL)
• Sterically hindered
• resonant stabilization
CH 3
MMA
Bu
-78 oC, THF
CH 2 C
CH 2
Li
C
C
O
O
CH 3
PMMA via Living Pzn
Polymer Synthesis
CHEM 421
CH 3
CH3
MMA
DPHL
Bu
CH2 C
CH2
-78 oC, THF
CH2
C
C
O
C
O
O
CH3
O
CH 3
CH 3
Methanol
Bu
CH 2 C
CH2
Li
C
H
C
-78 oC, THF
C
O
O
CH 3
Block Copolymers
Polymer Synthesis
CHEM 421
• Definition: Macromolecules
consisting of homogenous
segments made from different
monomers (usually two or three
different monomers).
Ex.
A-A-A-A-A-A-B-B-B-B-B-B
Some Basic Diblock Copolymer
Architectures
• Linear
Polymer Synthesis
CHEM 421
Graft
Ex. PS-b-PI
Ex: PS-g-PI
Star
Microphase Separation
• Most polymers are immiscible
Polymer Synthesis
CHEM 421
Block Copolymer Uses
Thermoplastic Elastomer
Polymer Synthesis
CHEM 421
Common Elastomer
Poly(cis-1,4-butadiene)
SBS (PS-PB-PS)
Physical crosslinking
Thermal reversibility
Can process it repeatedly
heating
cooling
Sulfur
Crosslinking
Chemical rosslinking
Thermal irreversibility
Can’t process it repeatedly
Self-Assembly of Block CopolymerPolymer Synthesis
CHEM 421
Polym. Chem. 2011, 2, 1018–1028.
PB-b-PEO
cryoTEM
micrographs
PS-b-PAA
TEM micrographs
vesicles
Cylindrical
micelles
Spherical
micelles
= packing parameter, v = hydrophobic volume,
area at the hydrophobe-hydrophile/water interface,
length normal to the surface per molecule.
a = interfacial
= the chain
Dispersion of Carbon Nanotubes by Polymer Synthesis
CHEM 421
Block Copolymer
• The study of Single-Walled Carbon Nanotubes (SWNT) composite materials
has been hindered by the poor solubility and processibility of SWNTs.
• PS-b-PAA has been used to stabilize SWNT and prevent their aggregation.
• The micelle-encapsulated SWNTs are compatible with a wide variety of
solvent and polymer matrices, which can be used to produce carbon
nanotube materials.
Kang, Y. and Taton, A. T. J. Am. Chem. Soc. 2003, 125(19) 5650 – 5651.
Synthesis of Block Copolymers
1)
A-B diblock or A-B-A triblock copolymers
same pKa, same reactivity; no problem
any order of addition, can cross over back & forth
x
z
y
2) ethylene oxide/styrene copolymers
•
•
•
styrene pKa= 42
epoxide pKa= 16-18
cross over from ethylene oxide not possible
O
H
x
y
Polymer Synthesis
CHEM 421
Styrene-MMA Block Copolymers
Polymer Synthesis
CHEM 421
3) Styrene & MMA
• Styrene
• Then MMA, but can’t do sequential addition
will attack
so use 1,1-diphenylethylene
C
C O
OCH 3
sterically hindered,
aromatic stablization,
won't propagate itself
Styrene-MMA Block Copolymers
Polymer Synthesis
CHEM 421
1) Styrene
2) cap w/ 1,1-diphenylethylene (DPE)
3) MMA @ -78 oC, THF
C
PS
PMMA
PMMA-PS-PMMA
PMMA
Polymer Synthesis
CHEM 421
PMMA
PS
2 sec-BuLi
55 oC
Li
Li
1) DFI to initiate styrene
2) Diphenyl ethylene to initiate MMA segment
3) Add MMA
DPE
DPE
DFI
PMMA
PS
PS
PMMA
Synthesis of Regular Star PS by Iterative
Methodology Using DPE Functionality
X =
Y
Polymer Synthesis
CHEM 421
=
1st Iteration
Br
1
3
O
1st Iteration
(=
)
1st Iteration
2st Iteration
3st Iteration
4st Iteration
5st Iteration
(=
)
3
O
3
(=
3
)
Synthesis of Asymmetric Star-Branched
Polymers by Iterative Methodology
Br
3
1
Polymer Synthesis
CHEM 421
Synthesis of Asymmetric Star-Branched
Polymers by Iterative Methodology
Br
3
1
Polymer Synthesis
CHEM 421
Synthesis of Star-Branched PS with up to
63 Arms by Iterative Methodology
O
3
O
3
Br
Polymer Synthesis
CHEM 421
5
O
3
O
3
Branched Polymers with Complex Architectures
Macromol. Rapid Commun. 2010, 31,1031-1059.
star-linear-star
(dendrimer)-linear-(dendrimer)
graft-on-graft
star-on-graft
Polymer Synthesis
CHEM 421
star-on-linear
(dendrimer)-on-linear
graft-on-star
star-on-star
Living/Controlled Free Radical
Polymerization
Polymer Synthesis
CHEM 421
 How to perform a living free radical polymerization?
Anionic polymerization
Radical polymerization
kt = 0
kt = 106-108
Ri > Rp
R i < Rp
 Reversible termination
Terminology:
“controlled/living”,
“pseudo-living”,
“quasi-living”, and
“reversible
deactivation radical
polymerization”
Stable Free-Radical Polymerization
(SFRP)
Polymer Synthesis
CHEM 421
TEMPO: 2,2,6,6-tetramethyl-1-piperidinoxyl
• Radical was formed differently
• Reversible chain termination!
M. K. Georges, et al, Macromolecules, 26, 2987( 1993).
Atom Transfer Radical Polymerization
Polymer Synthesis
CHEM 421
(ATRP)
X = Br , Cl
Components:
Monomer: A wide variety of monomers
Initiator: R-X, X = Br and Cl
Catalyst: Cu, Fe, and Ru etc.
• Radical was formed differently
• Reversible chain termination!
Ligand: Bipyridine ect.
Wang, J. S.; Matyjaszewski, K. Macromolecules 1995, 28, 7901-7910.
Reversible Addition-Fragmentation Chain
Polymer Synthesis
CHEM 421
Transfer (RAFT)
• Normal radical initiators (AIBN, etc.)
• Reversible chain transfer!
Rizzardo, E., et al. Macromolecules 1998, 31, 5559-5562.
Advantages of Living Free Radical
Polymerization
Radical polymerization
• A variety of monomers, including
the monomers with OH, COOH groups;
• Perform in bulk, solution, emulsion,
and suspension systems;
Polymer Synthesis
CHEM 421
Anionic polymerization
• Styrenes, dienes, and methacrylates;
• Perform in solution under unaerobic
and anhydrous conditions;
• Complex and expensive.
• Simple and inexpensive.
A powerful platform for preparing a variety of well-defined polymers