Polymer Chemistry
Controlled/Living Polymerization
Donghui Zhang
Fall 2012
1
Architecture
2
Tacticity
Isotactic
•
•
•
All asymmetric carbons have same configuration
Methylene hydrogens are meso
Polymer forms helix to minimize substituent interaction
Syndiotactic
•
•
•
Asymmetric carbons have alternate configuration
Methylene hydrogens are racemic
Polymer stays in planar zig-zag conformation
Atactic
•
Asymmetric carbons have statistical variation of configuration
3
Statistical description of tacticity
4
Major Developments in the 1950-60's
Living Polymerization (Anionic)
• Mw/Mn  1
• Blocks, telechelics and stars available
(Controlled molecular architecture)
• Statistical Stereochemical Control
• Statistical Compositions and Sequences
• Severe functional group restrictions
5
6
1.
2.
3.
4.
7
Good monomers for anionic polymerizations
labile a-proton
In the polymers
.
steric stabilizing
effect as well
8
Reactivity trend of monomers in
anionic polymerizations
Increasing ease
of initiation
9
Initiators for anionic polymerizations
10
11
Kinetics of Living Polymerizations
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conversion
≈ 1+ 1/n
conversion
conversion (p)
13
Solvent and Counter Ion Effect
1,4 trans content increases crystallinity, Tm > 25oC.
1,4 cis content suppress crystallinity, low Tg (-110oC), Tm ~12oC; used for synthetic rubber
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Solvent characteristics
15
Solvent effect on anionic polymerizations
Ke
[M]
kp
{M-n}
[M-]
propagating
16
Solvent effect on anionic polymerizations
so is the stereoselectivity
17
End functionalization of anionic polymerizations
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End functionalization of anionic polymerizations
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Block copolymers from anionic polymerizations
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Block copolymers from anionic polymerizations
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Block copolymers from anionic polymerizations
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Microphase separation of block copolymers
Sphere
Cylinder
Lamellar
Gyroid
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Application of block copolymers
Hillmyer, 2010 JACS
Russell, 2008 Nano Lett.
24
Industry block copolymers (SBR)
(
)
25
Additional Developments in the 1980's
"Immortal" Polymerization (Cationic)
–
–
–
–
–
Mw/Mn  1.05
Blocks, telechelics, stars
(Controlled molecular architecture)
Statistical Compositions and Sequences
Severe functional group restrictions
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Cationic Polymerization
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Cationic Polymerization
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Monomers for Cationic Polymerization
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Kinetic Steps in Cationic Polymerization
:
of
C+
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31
All these reactions kill the chain growth.
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33
Industry Example of Cationic Polymerization
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(irriversible)
Strategy: prolong the life time of cationic propagating species by reversible formation
of dormant species. (Note: anionic propagating species has a much longer life time).
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36
37
Chain shuffling can increase PDI
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Chain-End Functionalization of Aliphatic Polyether
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Free Radical Initiated Polymerization
•
•
•
•
•
•
•
Controlled Free Radical Polymerization
Broad range of monomers available
Accurate control of molecular weight
Mw/Mn  1.05 --Almost monodisperse
Blocks, telechelics, stars
(Controlled molecular architecture)
Statistical Compositions and Sequences
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Free Radical Polymerizations
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Otsu et al 1982
Iniferter approach
hn
recombination
exhibit living characteristics at low conversion, but PDI is broad as 3 can also
initiate polymerizations.
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The Key Concept in Living Radical Polymerization
PDI= Mw/Mn=1+qM0/Mn = 1+q/n
(Poisson distribution PDI = 1+1/n, slide 25)
(Page 144, Hiemenz and Lodge)
R∙ is a capping agent
and does not initiate
chain growth
formation of dormant
propagating species reduces
the effective polymeric radical
concentration and hence
minimize termination reactions
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Stable Free Radical Polymerization (SFRP)
or Nitroxide Mediated Polymerization (NMP)
SFRP Initiator System (e.g., biomolecular or unimolecular)
+ radical initiator
(BPO, AIBN)
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Stable Free Radical Polymerization (SFRP)
Bimolecular Initiator System
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Stable Free Radical Polymerization (SFRP)
Unimolecular Initiator System
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State of Art for SFRP
•MW > 105, PDI = 1.1-1.2
•High reaction temperature (125-145oC)
•Long reaction time (24-72 hr)
•Low to moderate conversion (<70%)
•Limited scope of monomers: St, MA,
MMA etc.
•functionalized alkoxyamine is required
for block or telechelic polymer synthesis
lower temperature
(60-80oC), shorter
reaction time (several
hrs) and higher
conversion (>99%) are
desired
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Atom Transfer Reversible Polymerization (ATRP)
most common
Example:
Basic components: vinyl monomers, metal catalyst/ligand and initiator
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Atom Transfer Reversible Polymerization (ATRP)
Keq
ki
Keq’
kp
50
State of Art for ATRP
•MW > 105 easily, PDI = 1.1-1.6
•reaction temperature (70-130oC)
•Low to moderate conversion (<80%)
•Tolerant of functional groups, wide scope of monomers: St,
MA, MMA, acrylamide, vinylpyridine (VP), acrylonitrile (AN)
etc. (acrylic acid, vinyl halide, vinyl ether, a-olefin cannot be
polymerized)
•Availability of a variety of initiator and catalysts.
•block polymers and telechelic polymers are readily prepared.
•metal contaminant is sometime less desired
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Reversible Addition-Fragmentation Transfer
Polymerization (RAFT)
SFRP (NMP) and ATRP involves reversible termination
RAFT involves reversible chain transfer
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Reversible Addition-Fragmentation Transfer
Polymerization (RAFT) Mechanism
Stability
can be
controlled
by Z
group
Basic components: vinyl monomers, radical initiator and RAFT chain transfer agent.
The number of growing chain is determined by both CTA and initiator content.53
RAFT Chain Transfer Agent
Design of CTA structures allows for control of the
relative rate of addition and fragmentation steps
RAFT polymerizations are compatible with a variety of activated (St, MMA, MA
etc.) or unactivated vinyl monomers (VAc, NVP). RAFT is versatile and robust as
compared to SFRP and ATRP. But CTA agents need to be individually synthesized.
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Ring Opening Metathesis Polymerization (ROMP)
[Ru] or [Mo] or [W]
catalyst
Schrock’s catalyst
2nd Gen. Grubb’s catalyst
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Ring Opening Metathesis Polymerization (ROMP)
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Ring Opening Metathesis Polymerization (ROMP)
examples of
norbornadiene
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Ring Opening Metathesis Polymerization (ROMP)
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Ring Opening Metathesis Polymerization (ROMP)
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Synthesis of Conjugating Polymers from ROMP
ROMP
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Ring Opening Metathesis Polymerization (ROMP)
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Ring Opening Polymerization (ROP)
Aliphatic Polyester synthesis
metal-mediated reaction
(Coates, Chisholm, Tolman/Hillmyer, Bourissou)
organic-mediated reaction
(Waymouth, Hedrick)
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Ring Opening Polymerization (ROP)
Polypeptide synthesis
Polypeptoid synthesis
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Coordination Polymerization
Ziegler-Natta Polymerization (50-60’s)
•
•
•
•
Stereochemical Control
Polydisperse products
Statistical Compositions and Sequences
Limited set of useful monomers, i.e. olefins
• SINGLE SITE CATALYSTS
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Commodity Polyolefins
Polyethylene
High Density (1954)
HDPE
Bottles, drums, pipe, conduit, sheet, film
Low Density (1939-1945)
LDPE
Packaging Film, wire and cable coating, toys, flexible bottles, house wares, coatings
Linear Low Density (1975)
Shirt bags, high strength films
LLDE
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Polyolefins
• Polypropylene (PP, 1954)
• dishwasher safe plastic ware, carpet yarn,
fibers and ropes, webbing, auto parts
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Ziegler-Natta (Z-N) Polymerization
Radical polymerization is
inefficient due to stable
radicals from chain transfer
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68
isotactic PP
Syndiotactic PP
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Consider polyethylene
% crystallinity: 40-60%
radical process
Z-N process70
Single Site Catalyst 1990
atactic PP
MAO
MAO
isotactic PP
Waymouth 1995
Allows for production of elastomeric polypropylene (PP)
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Single Site Catalyst in 2000
Allows for
production of
thermoplastic
elastomer
CTA
Arriola, Carnahan, Hustad, Kuhlman, Wenzel (Dow Chemical, Freeport, TX)
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Acknowledgement
•MIT OpenCourseWare: Synthesis of Polymers by Dr. Paula Hammond
http://ocw.mit.edu/courses/chemical-engineering/10-569-synthesis-of-polymers-fall-2006/lecture-notes/
•Note by USM Dr. Daniel Savin and Dr. Derek Patton
http://www.usm.edu/polymerkinetics/
•Note by LSU Dr. Daly
•Polymer Chemistry, 2nd edition, Hiemenz and Lodge
•Principle of Polymerization, 4th edition, Odian
•Polymer Chemistry, 4th edition, Pan, Zheijiang University
•“Functional Polymers via Anionic Polymerizations.” Akira Hirao, 1997 ACS Symposium Series.
•“New Polymer Synthesis by Nitroxide Mediated Living Radical Polymerizations.” Craig Hawker, 2001, Chem. Rev.
•“Atom Transfer Radical Polymerization.” Krzysztof Matyjaszewski, 2001, Chem. Rev.
•“Copper(I)-Catalyzed Atom Transfer Radical Polymerization.” Krzysztof Matyjaszewski and Timothy Patten, 1999, Acc.
Chem. Res.
•“Toward Living Radical Polymerization.” Graeme Moad, Ezio Rizzardo, San Thang, 2008, Acc. Chem. Res.
•“Living Radical Polymerization by the RAFT Process.” Graeme Moad, Ezio Rizzardo, San Thang, 2005, Aust. J. Chem.
•“Living ring-opening metathesis polymerization catalyzed by well-characterized transition-metal alkylidene
complexes.” Richard Schrock, 1990, Acc. Chem. Res.
•“The Development of L2X2RuCHR Olefin Metathesis Catalysts: An Organometallic Success Story.” Robert Grubbs, 2001,
Acc. Chem. Soc.
•“Organocatalytic Ring-Opening Polymerization.” Robert Waymouth, James Hedrick, 2007, Chem. Rev.
•“Controlled Ring-Opening Polymerization of Lactide and Glycolide.” Didier Bourissou, 2004, Chem. Rev.
•“Synthesis of Well-Defined Polypeptide-Based Materials via the Ring-Opening Polymerization of α-Amino Acid NCarboxyanhydrides.” Nikos Hadjichristidis, 2009, Chem. Rev.
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