Polymer Chemistry Controlled/Living Polymerization Donghui Zhang Fall 2012

Architecture

Tacticity Isotactic Syndiotactic Atactic 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

Statistical description of tacticity

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

1. 2. 3. 4.

. Good monomers for anionic polymerizations labile a-proton In the polymers steric stabilizing effect as well

Reactivity trend of monomers in anionic polymerizations Increasing ease of initiation

Initiators for anionic polymerizations

Kinetics of Living Polymerizations

conversion ≈ 1+ 1/n conversion conversion (p)

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

Solvent characteristics

Solvent effect on anionic polymerizations Ke [M] propagating kp {M-n} [M-]

Solvent effect on anionic polymerizations so is the stereoselectivity

End functionalization of anionic polymerizations

End functionalization of anionic polymerizations

Block copolymers from anionic polymerizations

Block copolymers from anionic polymerizations

Block copolymers from anionic polymerizations

Microphase separation of block copolymers Sphere Cylinder Lamellar Gyroid

Application of block copolymers Hillmyer, 2010 JACS Russell, 2008 Nano Lett.

Industry block copolymers (SBR) ( )

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

Cationic Polymerization

Cationic Polymerization

Monomers for Cationic Polymerization

Kinetic Steps in Cationic Polymerization : of C+

All these reactions kill the chain growth.

Industry Example of Cationic Polymerization

(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).

Chain shuffling can increase PDI

Chain-End Functionalization of Aliphatic Polyether

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

Free Radical Polymerizations

Otsu et al 1982 Iniferter approach hn recombination exhibit living characteristics at low conversion, but PDI is broad as 3 can also initiate polymerizations.

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

Stable Free Radical Polymerization (SFRP) or Nitroxide Mediated Polymerization (NMP) SFRP Initiator System (e.g., biomolecular or unimolecular) + radical initiator (BPO, AIBN)

Stable Free Radical Polymerization (SFRP) Bimolecular Initiator System

Stable Free Radical Polymerization (SFRP) Unimolecular Initiator System

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

Atom Transfer Reversible Polymerization (ATRP) most common Example: Basic components: vinyl monomers, metal catalyst/ligand and initiator

Atom Transfer Reversible Polymerization (ATRP) kp ki Keq Keq’

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

Reversible Addition-Fragmentation Transfer Polymerization (RAFT) SFRP (NMP) and ATRP involves reversible termination RAFT involves reversible chain transfer

Stability can be controlled by Z group 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.

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.

Ring Opening Metathesis Polymerization (ROMP) [Ru] or [Mo] or [W] catalyst Schrock’s catalyst 2nd Gen. Grubb’s catalyst

Ring Opening Metathesis Polymerization (ROMP)

Ring Opening Metathesis Polymerization (ROMP) examples of norbornadiene

Ring Opening Metathesis Polymerization (ROMP)

Ring Opening Metathesis Polymerization (ROMP)

Synthesis of Conjugating Polymers from ROMP

Ring Opening Metathesis Polymerization (ROMP)

Ring Opening Polymerization (ROP) Aliphatic Polyester synthesis metal-mediated reaction (Coates, Chisholm, Tolman/Hillmyer, Bourissou) organic-mediated reaction (Waymouth, Hedrick)

Ring Opening Polymerization (ROP) Polypeptide synthesis Polypeptoid synthesis

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

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

Polyolefins Polypropylene (PP, 1954) dishwasher safe plastic ware, carpet yarn, fibers and ropes, webbing, auto parts

Ziegler-Natta (Z-N) Polymerization Radical polymerization is inefficient due to stable radicals from chain transfer

isotactic PP Syndiotactic PP

Consider polyethylene % crystallinity: 40-60% radical process Z-N process

Single Site Catalyst 1990 Waymouth 1995 MAO MAO atactic PP isotactic PP Waymouth 1995 Allows for production of elastomeric polypropylene (PP)

Allows for production of thermoplastic elastomer Single Site Catalyst in 2000 CTA Allows for production of thermoplastic elastomer Arriola, Carnahan, Hustad, Kuhlman, Wenzel (Dow Chemical, Freeport, TX)

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 N-Carboxyanhydrides.” Nikos Hadjichristidis, 2009, Chem. Rev.