Odian Book Chapter 3-15, 5-3

Living Polymerization (II) by Ru-Ke Bai Department of Polymer Science and Engneering University of Science and Technology of China

A Brief Review What are the major criteria for living polymerization? What is living polymerization? No termination No chain transfer What are the major criteria for living polymerization? Mn A PDI Block copolymers can be prepared by sequential addition of monomers. C B Time ln[M]0/[M]t Living polymerization is a good tool for the preparation of block copolymers.

Rankings of Anions… How to characterize the reactivity of a propagating anion?

Propagating Anions pKa of conjugate acid of prop.chain end 42 25 25 20

Propagating Anions 16-18 10-12 11-13 pKa of conjugate acid of prop.chain end 16-18 10-12 11-13

Initiators Monomer pKa Useful Initiator Styrenes.dienes 42 RLi, NH2-, Ar - Acrylates 25 RMgX, DPHL Acrylonitriles RO -, C5H5- Vinyl ketones, Aldehydes 20 RO - Cyclic oxides 16-18 Siloxanes(-D3) 10-12 HO -, RO - Cyano acrylates 11-13 H2O, HO -, RO - Nitroalkenes 10 KHCO3, H2O most nucleophilic Super glue Reactivity Least nucleophilic

Microstructure of Dienes 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)

PMMA via Living Pzn PMMA homopolymer Can not use BuLi directly Make new initiator (use 1,1-diphenylethylene) 1,1-diphenyl hexyl lithium (DPHL) Sterically hindered resonant stabilization

PMMA via Living Pzn

Block Copolymers 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 Graft Ex: PS-g-PI Ex. PS-b-PI Star

Microphase Separation Most polymers are immiscible

Block Copolymer Uses Thermoplastic Elastomer Common Elastomer Poly(cis-1,4-butadiene) SBS (PS-PB-PS) Physical crosslinking Thermal reversibility Can process it repeatedly Sulfur Crosslinking heating cooling Chemical rosslinking Thermal irreversibility Can’t process it repeatedly

Self-Assembly of Block Copolymer Polym. Chem. 2011, 2, 1018–1028. PB-b-PEO PS-b-PAA cryoTEM micrographs TEM micrographs vesicles Cylindrical micelles Spherical micelles = packing parameter, v = hydrophobic volume, a = interfacial area at the hydrophobe-hydrophile/water interface, = the chain length normal to the surface per molecule.

Dispersion of Carbon Nanotubes by 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 A-B diblock or A-B-A triblock copolymers same pKa, same reactivity; no problem any order of addition, can cross over back & forth 2) ethylene oxide/styrene copolymers styrene pKa= 42 epoxide pKa= 16-18 cross over from ethylene oxide not possible

3) Styrene & MMA Styrene-MMA Block Copolymers Styrene Then MMA, but can’t do sequential addition Styrene

Styrene-MMA Block Copolymers cap w/ 1,1-diphenylethylene (DPE) MMA @ -78 oC, THF

PMMA-PS-PMMA DFI to initiate styrene Diphenyl ethylene to initiate MMA segment Add MMA

Synthesis of Regular Star PS by Iterative Methodology Using DPE Functionality X = Y 1st Iteration 1 1st Iteration ( = ) (= ) ( = ) 1st Iteration 2st Iteration 3st Iteration 4st Iteration 5st Iteration

Synthesis of Asymmetric Star-Branched Polymers by Iterative Methodology 1

Synthesis of Asymmetric Star-Branched Polymers by Iterative Methodology 1

Synthesis of Star-Branched PS with up to 63 Arms by Iterative Methodology 5

Branched Polymers with Complex Architectures Macromol. Rapid Commun. 2010, 31,1031-1059. star-linear-star star-on-linear (dendrimer)-linear-(dendrimer) (dendrimer)-on-linear graft-on-graft graft-on-star star-on-graft star-on-star

Living/Controlled Free Radical Polymerization How to perform a living free radical polymerization? Anionic polymerization Radical polymerization kt = 0 kt = 106-108 Ri > Rp Ri < Rp Reversible termination Terminology: “controlled/living”, “pseudo-living”, “quasi-living”, and “reversible deactivation radical polymerization”

Stable Free-Radical Polymerization (SFRP) 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 (ATRP) X = Br , Cl Components: Monomer: A wide variety of monomers Initiator: R-X, X = Br and Cl Catalyst: Cu, Fe, and Ru etc. Ligand: Bipyridine ect. Radical was formed differently Reversible chain termination! Wang, J. S.; Matyjaszewski, K. Macromolecules 1995, 28, 7901-7910.

Reversible Addition-Fragmentation Chain 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 Anionic polymerization A variety of monomers, including the monomers with OH, COOH groups; Perform in bulk, solution, emulsion, and suspension systems; Simple and inexpensive. Styrenes, dienes, and methacrylates; Perform in solution under unaerobic and anhydrous conditions; Complex and expensive. A powerful platform for preparing a variety of well-defined polymers