Polymer Chemistry Controlled/Living Polymerization Donghui Zhang Fall 2012 1.

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Polymer Chemistry

Controlled/Living Polymerization

Donghui ZhangFall 2012

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Architecture

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Tacticity

• Asymmetric carbons have alternate configuration• Methylene hydrogens are racemic• Polymer stays in planar zig-zag conformation

R R R R R R R R

R R R R R R R R

R R R R R R R R

Isotactic

• All asymmetric carbons have same configuration • Methylene hydrogens are meso• Polymer forms helix to minimize substituent interaction

Syndiotactic

Atactic

• Asymmetric carbons have statistical variation of configuration

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Statistical description of tacticity

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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

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7

1.

2.

3.

4.

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Good monomers for anionic polymerizations

. labile a-protonIn the polymers

steric stabilizing effect as well

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Reactivity trend of monomers in anionic polymerizations

Increasing ease of initiation

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Initiators for anionic polymerizations

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Kinetics of Living Polymerizations

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≈ 1+ 1/n

conversion (p)

conversion

conversion

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1,4 trans content increases crystallinity, Tm > 25oC.1,4 cis content suppress crystallinity, low Tg (-110oC), Tm ~12oC; used for synthetic rubber

Solvent and Counter Ion Effect

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Solvent characteristics

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Solvent effect on anionic polymerizations

[M-]{M-n}

[M]propagating

Ke

kp

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Solvent effect on anionic polymerizations

so is the stereoselectivity

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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.

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( )

Industry block copolymers (SBR)

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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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32All these reactions kill the chain growth.

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Industry Example of Cationic Polymerization

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OR

+HI

OR

IZnI

OR

IOR

OR

ZnI

+

-

OR

I

ZnI

OR

dormantspecies

OR

IOR

ZnI

ORreactivespecies

(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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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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Iniferter approach

Otsu et al 1982

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

formation of dormant propagating species reduces

the effective polymeric radical concentration and hence

minimize termination reactions

R is a capping agent ∙and does not initiate

chain growth

PDI= Mw/Mn=1+qM0/Mn = 1+q/n(Poisson distribution PDI = 1+1/n, slide 25)

(Page 144, Hiemenz and Lodge)

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Stable Free Radical Polymerization (SFRP)or Nitroxide Mediated Polymerization (NMP)

+ radical initiator (BPO, AIBN)

N

O

SFRP Initiator System (e.g., biomolecular or unimolecular)

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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)

Basic components: vinyl monomers, metal catalyst/ligand and initiator

Example:

most common

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Atom Transfer Reversible Polymerization (ATRP)

Keq’

R'

kp

ki

Keq

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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

Basic components: vinyl monomers, radical initiator and RAFT chain transfer agent.The number of growing chain is determined by both CTA and initiator content.

Stability can be

controlled by Z

group

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RAFT Chain Transfer Agent

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.

Design of CTA structures allows for control of the relative rate of addition and fragmentation steps

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Ring Opening Metathesis Polymerization (ROMP)

[Ru] or [Mo] or [W]catalyst

2nd Gen. Grubb’s catalystSchrock’s catalyst

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Ring Opening Metathesis Polymerization (ROMP)

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Ring Opening Metathesis Polymerization (ROMP)

examples ofnorbornadiene

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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)

metal-mediated reaction

organic-mediated reaction

Aliphatic Polyester synthesis

(Waymouth, Hedrick)

(Coates, Chisholm, Tolman/Hillmyer, Bourissou)

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Polypeptide synthesis

Ring Opening Polymerization (ROP)

Polypeptoid synthesis

HN

O

nHN

O

O

O

R Initiators

initiators: RNH2 HNTMS2 (Cheng, 2007) Ni(bipy)(COD) (Deming, 1997)

-nCO2

NO

O

OR -nCO2

RNH2 N

O R

n

N

NN

O

O

O

R R

Rn-2

-nCO2

NHC NN

iPr

iPr iPr

iPrNHC

Zhang, 2010

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Coordination Polymerization

• Stereochemical Control• Polydisperse products• Statistical Compositions and Sequences• Limited set of useful monomers, i.e. olefins

• SINGLE SITE CATALYSTS

Ziegler-Natta Polymerization (50-60’s)

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Commodity Polyolefins

Polyethylene

Low Density (1939-1945)LDPE

Packaging Film, wire and cable coating, toys, flexible bottles, house wares, coatings

High Density (1954) HDPE

Bottles, drums, pipe, conduit, sheet, film

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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TiCl

Cl Cl

Cl

CH2 CH

CH3

CH2

CH2=CHCH3

Syndiotactic PP

isotactic PP

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Consider polyethylene

radical process

Z-N process

% crystallinity: 40-60%

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Single Site Catalyst 1990

Allows for production of elastomeric polypropylene (PP)

Waymouth 1995

atactic PP isotactic PPMAOMAO

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Single Site Catalyst in 2000-olefinethylene

+

CTA

Allows for production of thermoplastic

elastomer

Arriola, Carnahan, Hustad, Kuhlman, Wenzel (Dow Chemical, Freeport, TX)

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Acknowledgement•MIT OpenCourseWare: Synthesis of Polymers by Dr. Paula Hammondhttp://ocw.mit.edu/courses/chemical-engineering/10-569-synthesis-of-polymers-fall-2006/lecture-notes/•Note by USM Dr. Daniel Savin and Dr. Derek Pattonhttp://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 N-Carboxyanhydrides.” Nikos Hadjichristidis, 2009, Chem. Rev.