Polymer Synthesis CHEM 421 Odian Book Chapter 3

Polymer Synthesis CHEM 421 • Odian Book Chapter 3 -15, 5 -3

Polymer Synthesis CHEM 421 Living Polymerization (II) by Ru-Ke Bai Department of Polymer Science and Engneering University of Science and Technology of China

A Brief Review Polymer Synthesis CHEM 421 • What is living polymerization? • No termination • No chain transfer • What are the major criteria for living polymerization? A B C Block copolymers PDI ln[M]0/[M]t Mn can be prepared by sequential addition of monomers. Time Living polymerization is a good tool for the preparation of block copolymers.

Rankings of Anions… Polymer Synthesis CHEM 421 How to characterize the reactivity of a propagating anion?

Propagating Anions p. Ka of conjugate acid of prop. chain end 42 25 25 20 Polymer Synthesis CHEM 421

Propagating Anions p. Ka of conjugate acid of prop. chain end 16 -18 10 -12 11 -13 Polymer Synthesis CHEM 421

Initiators Useful Initiator Styrenes. dienes 42 RLi, NH 2 -, Ar - Acrylates 25 RMg. X, DPHL Acrylonitriles 25 RO -, C 5 H 5 - Vinyl ketones, Aldehydes Cyclic oxides 20 RO - 16 -18 RO - 10 -12 HO -, RO - 11 -13 H 2 O, HO -, RO - Siloxanes(-D 3) Super glue Cyano acrylates Nitroalkenes 10 KHCO 3, H 2 O most nucleophilic p. Ka Least nucleophilic Reactivity Monomer Polymer Synthesis CHEM 421

Microstructure of Dienes Polymer Synthesis CHEM 421 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) Polymer Synthesis CHEM 421

PMMA via Living Pzn Polymer Synthesis CHEM 421 PMMA homopolymer • Can not use Bu. Li directly • Make new initiator (use 1, 1 -diphenylethylene) 1, 1 -diphenyl hexyl lithium (DPHL) • Sterically hindered • resonant stabilization

PMMA via Living Pzn Polymer Synthesis CHEM 421

Block Copolymers Polymer Synthesis CHEM 421 • Definition: Macromolecules consisting of homogenous segments made from different monomers (usually two or three different monomers). Ex. A-A-A-B-B-B-B

Some Basic Diblock Copolymer Architectures • Linear Ex. PS-b-PI Polymer Synthesis CHEM 421 Graft Star Ex: PS-g-PI

Microphase Separation • Most polymers are immiscible Polymer Synthesis CHEM 421

Block Copolymer Uses Thermoplastic Elastomer Polymer Synthesis CHEM 421 Common Elastomer Poly(cis-1, 4 -butadiene) SBS (PS-PB-PS) Physical crosslinking Thermal reversibility Can process it repeatedly heating cooling Sulfur Crosslinking Chemical rosslinking Thermal irreversibility Can’t process it repeatedly

Self-Assembly of Block Copolymer. Polymer Synthesis CHEM 421 Polym. Chem. 2011, 2, 1018– 1028. PB-b-PEO cryo. TEM micrographs PS-b-PAA TEM micrographs vesicles Cylindrical micelles Spherical micelles = packing parameter, v = hydrophobic volume, area at the hydrophobe-hydrophile/water interface, length normal to the surface per molecule. 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. 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 p. Ka, same reactivity; no problem any order of addition, can cross over back & forth 2) ethylene oxide/styrene copolymers • • • styrene p. Ka= 42 epoxide p. Ka= 16 -18 cross over from ethylene oxide not possible Polymer Synthesis CHEM 421

Styrene-MMA Block Copolymers Polymer Synthesis CHEM 421 3) Styrene & MMA • Styrene • Then MMA, but can’t do sequential addition

Styrene-MMA Block Copolymers Polymer Synthesis CHEM 421 1) Styrene 2) cap w/ 1, 1 -diphenylethylene (DPE) 3) MMA @ -78 o. C, THF

PMMA-PS-PMMA Polymer Synthesis CHEM 421 1) DFI to initiate styrene 2) Diphenyl ethylene to initiate MMA segment 3) Add MMA

Synthesis of Regular Star PS by Iterative Methodology Using DPE Functionality X = Y Polymer Synthesis CHEM 421 = 1 st Iteration 1 1 st Iteration (= ) 1 st Iteration 2 st Iteration 3 st Iteration 4 st Iteration 5 st Iteration (= )

Synthesis of Asymmetric Star-Branched Polymers Polymer Synthesis CHEM 421 by Iterative Methodology 1

Synthesis of Asymmetric Star-Branched Polymers by Iterative Methodology 1 Polymer Synthesis CHEM 421

Synthesis of Star-Branched PS with up to 63 Arms by Iterative Methodology 5 Polymer Synthesis CHEM 421

Branched Polymers with Complex Architectures Macromol. Rapid Commun. 2010, 31, 1031 -1059. star-linear-star (dendrimer)-linear-(dendrimer) graft-on-graft star-on-graft Polymer Synthesis CHEM 421 star-on-linear (dendrimer)-on-linear graft-on-star-on-star

Living/Controlled Free Radical Polymerization Polymer Synthesis CHEM 421 u How to perform a living free radical polymerization? Anionic polymerization Radical polymerization kt = 0 k t = 106 -108 R i > Rp R i < Rp u Reversible termination Terminology: “controlled/living”, “pseudo-living”, “quasi-living”, and “reversible deactivation radical polymerization”

Stable Free-Radical Polymerization (SFRP) Polymer Synthesis CHEM 421 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 Polymer Synthesis CHEM 421 (ATRP) X = Br , Cl Components: Monomer: A wide variety of monomers Initiator: R-X, X = Br and Cl Catalyst: Cu, Fe, and Ru etc. • Radical was formed differently • Reversible chain termination! Ligand: Bipyridine ect. Wang, J. S. ; Matyjaszewski, K. Macromolecules 1995, 28, 7901 -7910.

Reversible Addition-Fragmentation Chain Polymer Synthesis CHEM 421 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 • A variety of monomers, including the monomers with OH, COOH groups; • Perform in bulk, solution, emulsion, and suspension systems; Polymer Synthesis CHEM 421 Anionic polymerization • Styrenes, dienes, and methacrylates; • Perform in solution under unaerobic and anhydrous conditions; • Complex and expensive. • Simple and inexpensive. A powerful platform for preparing a variety of well-defined polymers