Synthetic Polymer Chemistry

Innovations and Outlook

Zheng Zhao, Rong Hu, Anjun Qin, Ben Zhong Tang, Zheng Zhao, Rong Hu, Anjun Qin, Ben Zhong Tang

• Publisher: Royal Society of Chemistry
• Year: 2019
• eBook ISBN: 9781788018913
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Organic Chemistry

Polymeric materials form the basis of daily life. Despite the great contribution of traditional methodologies such as anionic and radical polymerizations in preparing various functional polymers, the increasing demand for polymers with new structures and functions has inspired the development of new synthetic techniques. Many new polymerizations including click polymerization, controlled/living radical polymerization, multicomponent polymerization have been well developed. Focusing on breakthroughs and recent progress, Synthetic Polymer Chemistry provides efficient tools for the synthesis of linear and topological polymers. Chapters cover topics including fabrication of supramolecular polymers, organocatalytic synthesis and olefin co(polymerization). This title will be a valuable reference for those working in polymer chemistry, as well as students and researchers interested in opto-electronic, biological and materials sciences.

CHAPTER 1

New Polymers From SuFEx Click Chemistry: Syntheses and Perspectives

Long Xu ^a , Peng Wu^*b and Jiajia Dong^*a

^a Key Laboratory of Organofluorine Chemistry, Center for Excellence in Molecular Synthesis, Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences, Chinese Academy of Sciences, 345 Ling-Ling Road, Shanghai 200032, PR China,

^b Department of Chemical Physiology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA,
^*E-mail: [email protected], [email protected]

Sulfur(vi) Fluoride Exchange (SuFEx) click chemistry was reported by Sharpless et al. in 2014. The applications of SuFEx click chemistry have been demonstrated in various disciplines since then, including the development of synthetic methods and the preparation of polymers. Fluorosulfates have also been found to be unique warheads for covalent capture of protein side chains in a highly selective, context-dependent manner. A review of the story of discovering SuFEx will be included in this chapter. We will also focus on the details demonstrating the whole process to synthesize new polysulfonate and polysulfate polymers, especially the evolution of the catalysts involved. Aside from leading to the discovery of new polymers, SuFEx click chemistry as a powerful tool in polymer modification will also be discussed herein.

1.1 Introduction

1.1.1 Reactivity isn't Everything, It is the Only Thing

Vince Lombardi, Coach of the Green Bay Packers

“Winning isn't everything,
It is the only thing.”

“Reactivity isn’t everything,
It is the only thing.”

K. Barry Sharpless at the 15th national fluorine conference of the Chinese Chemical Society

Polymers are powerful tools for exploring nature. Condensation polymers, such as polyesters, polyurethanes, polycarbonates, and polyamides, appear in almost every corner of our daily life. From apparel to cell phones, from medical apparatus to aerospace crafts, they have evolved our approaches to discover the mystery of nature and are essential components of our modern society. Taking a close look at the polycondensation process to generate those polymers, functional groups (normally hydroxyl or amino groups) and other functional groups (normally carbonyl groups) are buckled together by reliable and robust reactions to form carbon-heteroatom linkages as shown in Scheme 1.1. Not surprisingly, Mother Nature is an expert synthesizer of polymers. She generates the backbones of proteins from the polycondensation of amino-carboxylic acids, and nucleic acids from the polycondensation of nucleotides.

Scheme 1.1 Industrial routes to access polyesters, polyurethanes, polycarbonates and polyamides.

Generally speaking, polycondensation may be regarded as the stepwise ligation of different functional groups with loss of water or an equivalent. Therefore, the reactivity of the functional groups in the building blocks is crucial for the construction of condensation polymers. Amidation and esterification are well adapted as polymer-forming chemical reactions, and the reactivity of carbonyl group towards O, N-nucleophiles has been well investigated and elucidated in the past century. For instance, the amidation process happens rapidly above 180 °C to 200 °C without catalysts and is usually free from side reactions to deliver the desired amides in very high yields. This is very important for the formation of high-molecular-weight polyamides as the principle of equal reactivity of all functional groups during polycondensations determines that the loss of one functional group through side reactions may significantly limit the molecular weight and yield that can be reached. From this perspective, the outcome of polycondensations highly depends on the reactivity of the functional groups of the monomers. Only those chemical reactions possessing an ideal efficiency (higher yield in shorter reaction time) and selectivity (fewer side reactions) are chosen by polymer scientists to create various useful materials.

Imagine a polycondensation between monomer A-A with B-B and define the yield of the chemical reaction A-A + B-B → A-A-B-B (assuming that the ratio of A-A : B-B is exactly 1 : 1) as Y. Figure 1.1 gives the cumulative yield Y _n of the reaction as a function of {2X _n − 1} in a linear stepwise sequence.

Figure 1.1 Overall yield (Y _n ) as a function of {2X _n − 1} in a successive fashion.

From Figure 1.1, we can tell that with Y = 90%, Y _n reached almost 0 when 2X _n − 1 = 40, which means that the degree of polymerization (X _n ) is limited to around 20, thus constraining the size of the polymer. Pushing Y up to 97%, the yield of the polymers with X _n ∼ 50 (2X _n − 1 = 100) does not even exceed 10%. Elevating Y to 99% only improves the overall yield of condensation polymer with X _n ∼ 50 to 40%. One comment here is that for a chemical reaction yielding 99% desired product, it is already a near-perfect one for a synthetic chemist, but it is still not good enough for producing those big fellows. To achieve an overall yield of condensation polymer with X _n ∼ 50 above 90%, each step needs to proceed with a yield of 99.95% or even higher!

The calculations above illuminate the extraordinary dependence of those processes on yield per step. In short, the yields can never be too high! Carothers

equation (where r is the stoichiometric ratio of reactants) determines that the ratio of the two functional groups involved in polycondensation will also influence the degree of polymerization (X _n ), thus requiring the high purity and stability of monomers. Searching for reactions with strong thermodynamic driving forces and well-controlled, selective, efficient pathways is a permanent pursuit in polymer chemistry and its allied disciplines.

1.1.2 Accessibility and Capacity: Who is the Boss in the Market?

Discovering ideal reactivity is not enough for the polymer industry because producing polymers is unlike the syntheses of fine-scale chemicals in grams or kilograms, polymers require grand industrial plants to generate millions of tons of products per annum. Table 1.1 lists the world production of polyesters, polyurethanes polycarbonates, and polyamides in recent years. ¹

Table 1.1 World production of polyesters, polyamides, polycarbonates, and polyurethanes.

Polymers	World production (million tons)
Polyesters	71 in 2016
Polyamides	3.9 in 2011
Polycarbonates	5.1 in 2016
Polyurethanes	20 in 2015

In the polymer industry, the power of a company rests upon its access to monomers and their related polymers. After all, you can't change the world, or even the single market, with several kilograms of something in your hand. Most of the monomers for polycondensation are streamed from the portal of the petrochemical industry that provides the most basic raw materials for organic syntheses. For instance, MDI (methylene diphenyl diisocyanate) is an important monomer (world production in 2015: 7.5 million tons) for the production of polyurethanes (world production in 2015: 20 million tons). ¹ The 4,4′ isomer (4,4′-diphenylmethane diisocyanate) is most widely used and is also known as Pure MDI. The synthetic route of MDI is depi...

Table of contents

• Cover
• Halftitle
• Series Editor
• Title
• Copyright
• Preface
• Contents
• Chapter 1 New Polymers From SuFEx Click Chemistry: Syntheses and Perspectives 1
• Chapter 2 Thiol Chemistry for Precision Polymer Synthesis 32
• Chapter 3 Precise Synthesis of Polyethylene-based Star Polymers: From Anionic Polymerization to Polyhomologation 65
• Chapter 4 Fabrication of Supramolecular Polymers 89
• Chapter 5 Olefin (Co)polymerizations Enabled by Catalyst Design Based on Sidearm Strategy 129
• Chapter 6 Bimetallic Complex Mediated Meso-epoxide Desymmetrization Copolymerization 167
• Chapter 7 Carbon Dioxide Copolymer From Delicate Metal Catalyst: New Structure Leading to Practical Performance 197
• Chapter 8 Chemosynthesis of Poly(ε-Lysine) via Ring-opening Polymerization of Cyclic Lysine 243
• Chapter 9 Fused (Hetero)Cyclic Polymers Synthesized by Alkyne-Based Polymerizations 264
• Chapter 10 Organocatalytic Synthesis of CO2(COS)-basedCopolymers 307
• Subject Index