Polymer Synthesis

Modern Methods and Technologies

Guojian Wang, Junjie Yuan

• Publisher: De Gruyter
• Year: 2020
• Print ISBN: 9783110596342
• eBook ISBN: 9783110597141
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Organic Chemistry

The book systematically presents fundamental principles, properties, implementation methodologies, technologies and applications of polymer synthesis. Ring opening metathesis polymerization, click chemistry, macromolecular self-assembly, carbon nanomaterials and their modification with polymers are discussed in detail. With abundant illustrations, it is an essential reference for polymer chemists, material scientists, and graduate students.

Chapter 1 Ionic living polymerization

1.1 Introduction

The addition polymerization of vinyl monomer under the action of foreign force is usually chain polymerization. The basic characteristics of chain polymerization are that the reaction needs active center, for example, free radical, negative ion, and positive ion; and the whole process could be divided into three elementary reactions. The activation energy of each step has a large difference. Time has little effects on molecular weight, mainly affecting the conversion rate. So far, the most widely used method in chain polymerization is free radical polymerization, which is mainly due to the wide range of monomers for free radical polymerization, various synthesis methods, simple preparation process, and low cost of industrialization. At present, about 70% of the polymer materials are products of radical polymerization.

Free radical polymerization process can be divided into chain initiation, chain growth, chain termination, chain transfer, and other elementary reactions. The activation energy is 105–150 kJ/mol, propagation activation energy is 16–33 kJ/mol, and termination activation energy is 8–21 kJ/mol. Therefore, slow initiation, fast growth, and rapid termination are basic characteristics of free radical polymerization dynamics.

In addition, radical polymerization has the following characteristics: The initiator concentration is very low, usually 10⁻⁷–10⁻⁹ mol/L. The initiator concentration varies greatly with the conversion rate, and it is a first-order kinetic process. The time has little effect on the molecular weight. Prolonging the polymerization time is mainly to increase the conversion rate. There are a large number of chain transfer reactions and chain termination reactions during the polymerization process, including termination of coupling and termination of disproportionation. Therefore, the molecular weight and molecular weight distribution cannot be controlled.

Like radical polymerization, ionic polymerization can be divided into three steps: chain initiation, chain growth, and chain termination. The fundamental difference between ionic polymerization and free radical polymerization is that the reactive species of the polymers are different. The reactive species of ionic polymerization are charged ions, usually carbon cations or carbon anions. Therefore, ionic polymerization can be divided into two major categories of cationic polymerization and anionic polymerization. The stability and reactivity of ions depends not only on the structure and properties of the ions themselves, but also on their environment, such as temperature, pressure, and solvent properties. The same ions can show completely different properties in different environments. In addition, the requirements of experimental conditions for ionic polymerization are very harsh, and traces of water, air, or impurities will have a strong influence on the polymerization process. Therefore, the experimental repeatability is poor. These factors make ionic polymerization much more complex than radical polymerization.

Cationic polymerization is characterized by rapid initiation, rapid growth, easy transfer, and difficult termination. Its industrial implementation is relatively difficult, so there are few practical applications. Anionic polymerization has developed rapidly in recent years. The basic characteristics of its dynamics are rapid initiation, slow growth, and no termination. The so-called slow growth is relative to initiation. In fact, its growth rate is much faster than radical polymerization. The most striking feature of anionic polymerization is the absence of termination, which leads to the concept of living polymerization. Living polymerization is one of the greatest discoveries in the history of polymer development. The concept is proposed to create a new era in polymer design, making it develop from the realm of freedom to the realm of necessity.

It has been nearly 50 years since the discovery of living polymerization. It has already become one of the most academic and industrially valuable research directions in the field of polymer chemistry. According to Szwarc’s initial definition of living polymerization, the so-called living polymerization refers to those polymerization reactions that do not cause any stoppage of the chain extension reaction or irreversible side reactions. However, few reaction systems fully satisfy such conditions. Since the group transfer reaction was discovered in the early 1980s, it was found that, although such polymerizations have chain transfer and chain termination reactions, they are negligible relative to the chain growth reaction, and thus various expected structures can still be obtained. The polymer and the relative molecular mass can be designed within a certain range, the relative molecular mass distribution index is less than 1.1 and has the characteristics of obvious living polymerization. This greatly expands the concept of living polymerization. In order to distinguish them from real living polymerizations, these macroscopic effects are similar to th...

Table of contents

• Title Page
• Copyright
• Contents
• Chapter 1 Ionic living polymerization
• Chapter 2 Group transfer polymerization
• Chapter 3 Living controlled polymerization of free radical
• Chapter 4 Synthesis of dendrimers and hyperbranched polymers
• Chapter 5 Open-loop disproportionation polymerization
• Chapter 6 Click chemistry
• Chapter 7 Macromolecular self-assembly
• Chapter 8 Carbon nanomaterials and their polymer modifications
• Index