Self-Assembly of Block CopolymerPolymer Synthesis
Polym. Chem. 2011, 2, 1018–1028.
PB-b-PEO
cryoTEM micrographs
CHEM 421
PS-b-PAA
TEM micrographs
vesicles
Cylindrical micelles
)
(=
)
(=
)
1st Iteration
3st Iteration
4st Iteration
5st Iteration
Synthesis of Asymmetric Star-Branched Polymers by Iterative Methodology
Polymer Synthesis CHEM 421
C O OCH3
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
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 ?
R
pKa = - log Ka
H
Propagating Anions
CH Styrenes, dienes
Polymer Synthesis CHEM 421
pKa of conjugate acid of prop.chain end
42
CH3 C C O O R CH3 C C N CH3 C C O R
Polymer Synthesis CHEM 421
Block Copolymer Uses
Thermoplastic Elastomer
SBS (PS-PB-PS)
Physical crosslinking Thermal reversibility
Can process it repeatedly
Polymer Synthesis CHEM 421
Common Elastomer
Poly(cis-1,4-butadiene)
Sulfur
heating
cooling
Crosslinking
Chemical rosslinking Thermal irreversibility
Can’t process it repeatedly
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.
Polymer Synthesis CHEM 421
pKa 42 25 25 20 16-18
Super glue
Useful Initiator
most nucleophilic Least nucleophilic
RLi, NH2-, Ar RMgX, DPHL RO -, C5H5RO RO HO -, RO H2O, HO -, RO KHCO3, H2O
PMMA PS PMMA
Polymer Synthesis CHEM 421
2 sec-BuLi 55 oC Li Li
1) DFI to initiate styrene 2) Diphenyl ethylene to initiate MMA segment 3) Add MMA
DPE DFI PMMA PS PS PMMA DPE
A B C
Block copolymers
PDI
Mn PDI PDI
ln[M]0/[M]t
Mn
can be prepared by sequential addition of monomers.
conversion
Time
Living polymerization is a good tool for the preparation of block copolymers.
Polymer Synthesis CHEM 421
n-BuLi
Bu
CH2 C
Li
1,1-diphenyl hexyl lithium
(DPHL)
• Sterically hindered • resonant stabilization
MMA Bu -78 oC, THF CH2 C CH2
CH3 C C O O CH3 Li
A Brief Review
• What is living polymerization?
• No termination • No chain transfer
Polymer Synthesis CHEM 421
• What are the major criteria for living polymerization?
Rankings of Anions…
Polymer Synthesis CHEM 421
ห้องสมุดไป่ตู้
How to characterize the reactivity of a propagating anion?
CH H CH
+ H
CH3 C H C OR O
CH3 C C OR O
+
H
R
H
Ka = [H ][R ] [RH]
Synthesis of Regular Star PS by Iterative Methodology Using DPE Functionality
X = 1st Iteration Y
=
Polymer Synthesis CHEM 421
Br
O
3
3
1
O
3
3
1st Iteration
(=
2st Iteration
O
x
y
H
Styrene-MMA Block Copolymers
Polymer Synthesis CHEM 421
3) Styrene & MMA
• Styrene • Then MMA, but can’t do sequential addition
will attack C so use 1,1-diphenylethylene sterically hindered, aromatic stablization, won't propagate itself
16-18
Si O Si O O Si
Cyclic siloxanes CH3 Si O CH3
10-12
CN C C O OCH3
Cyano acrylates
11-13
Initiators
Monomer Styrenes.dienes Acrylates Acrylonitriles
Reactivity
Vinyl ketones, Aldehydes Cyclic oxides Siloxanes(-D3) Cyano acrylates Nitroalkenes
10-12 11-13 10
Microstructure of Dienes
Polymer Synthesis CHEM 421
Four different microstructures in polyisoprene
Br
3
1
Synthesis of Asymmetric Star-Branched Polymers by Iterative Methodology
Polymer Synthesis CHEM 421
Br
3
1
Synthesis of Star-Branched PS with up to 63 Arms by Iterative Methodology
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