Hyperbranched Polymers: Macromolecules in Between Deterministic Linear Chains and Dendrimer Structures (Rsc Polymer Chemistry, 16, Band 16) - Hardcover

Lederer, Albena; Burchard, Walther

Hardcover

ISBN 10: 1849733945 ISBN 13: 9781849733946

Verlag: Royal Society of Chemistry, 2015

Inhaltsangabe

There is great commercial interest in hyperbranched polymers from manufacturers of polymer formulations, additives and coatings, polymer electronics and pharmaceuticals. However, these polymers are difficult to characterize due to their very complex, multidimensional distribution and there is a great need to understand how to control their synthesis to obtain certain material properties. Hyperbranched Polymers is the first book to examine in detail the recent advances in hyperbranched polymers. Focusing on the structural characterization of hyperbranched polymers, the book summarizes the research in the field and makes a direct correlation between the chemical structure and global molecular properties. This correlation is essential for understanding the structure–properties relation and fills the gap between the synthetic advances and physico-chemical understanding of this polymer class. Written by acknowledged experts in the field, the book will appeal to both scientists working in fundamental research, as well as industrial manufacturers of dendritic polymers.

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Über die Autorinnen und Autoren

Albena Lederer obtained her PhD in 1999 from the University of Mainz following her research in the field of physical chemistry of polymers at the Max-Planck-Institute of Polymer Research in Mainz. Since 2000, she has extensively investigated the physico-chemical properties of branched macromolecules and in 2007 she became leader of the polymer separation group at the Leibniz-Institute of Polymer Research in Dresden. Her main research areas of interest are the characterization of dendritic and multifunctional polymers in solution and the development of new separation methods for branched polymers.

Albena Lederer obtained her PhD in 1999 from the University of Mainz following her research in the field of physical chemistry of polymers at the Max-Planck-Institute of Polymer Research in Mainz. Since 2000, she has extensively investigated the physico-chemical properties of branched macromolecules and in 2007 she became leader of the polymer separation group at the Leibniz-Institute of Polymer Research in Dresden. Her main research areas of interest are the characterization of dendritic and multifunctional polymers in solution and the development of new separation methods for branched polymers.

Von der hinteren Coverseite

There is great commercial interest in hyperbranched polymers from manufacturers of polymer formulations, additives and coatings, polymer electronics and pharmaceuticals. However, these polymers are difficult to characterize due to their very complex, multidimensional distribution and there is a great need to understand how to control their synthesis to obtain certain material properties. Hyperbranched Polymers is the first book to examine in detail the recent advances in hyperbranched polymers. Focusing on the structural characterization of hyperbranched polymers, the book summarizes the research in the field and makes a direct correlation between the chemical structure and global molecular properties. This correlation is essential for understanding the structure properties relation and fills the gap between the synthetic advances and physico-chemical understanding of this polymer class. Written by acknowledged experts in the field, the book will appeal to both scientists working in fundamental research, as well as industrial manufacturers of dendritic polymers.

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Hyperbranched Polymers

Macromolecules in Between Deterministic Linear Chains and Dendrimer Structures

By Albena Lederer, Walther Burchard

The Royal Society of Chemistry

Copyright © 2015 Albena Lederer and Walther Burchard
All rights reserved.

ISBN: 978-1-84973-394-6

Contents

Acknowledgements, xiii, 
Abbreviations, xv, 
Chapter 1 Introduction, 1, 
Chapter 2 Degree of Branching, 20, 
Chapter 3 Control over the Conformation of Dendritic Polymers, 39, 
Chapter 4 Separation and Determination of Molar Mass, 69, 
Chapter 5 Solution Viscosity, 88, 
Chapter 6 Size Determination by Scattering Techniques, 136, 
Chapter 7 Model Calculation of Different Hyperbranched Structures, 193, 
Chapter 8 Scaling Conception and Interpretation of Structural Parameters and Scattering Experiments, 
227, 
Chapter 9 Correlation of Molecular and Bulk Properties, 269, 
Subject Index, 280, 

CHAPTER 1

Introduction

1.1 Overview

Macromolecular branching belongs to nature and is of significant importance for the life functions of organisms. Branching in polymer science has been known since almost the time when first synthesis of linear chains was carried out. No doubt when Staudinger and Schulz carried out the synthesis of styrene they also tried to add divinyl benzene as a second monomer for a co-monomer. The effect was dramatic and rather unexpected. In those days besides the monomer conversion the reaction was also followed by a change in viscosity because the increase of viscosity was a qualitative mean for the increase in molar mass. In the corresponding co-polymerization the increase in the viscosity was significantly lower but after certain time a sudden increase occurred and an non-measurable high value was attained. A highly elastic, gel-like material was obtained whose behaviour greatly resembled that of natural rubber.

The sudden change from a low solution viscosity to an elastic gel remained unclear for some time until, in 1941, Paul J. Flory put forward the mathematically simple expression for the condition of the gelation point:

αc = 1/ ƒ - 1 (1:1)

He described the extent of reaction by the probability α and found a critical conversion αc when gelation takes place. f is the number of functional groups per monomer of the same reactivity, and solubility remains in the pre-gel state of α(f - 1)<1. Branching takes place only if f > 2 and gelation will occur at a connversion beyond the critical point defined by eq (1.1).

Flory intensely tried to derive the molar mass distributions of such randomly branched polymers. It was Walter H. Stockmayer who, in 1943–1944, found the solution and with this distribution he could derive the weight average molar mass expressed in term of the probability of reaction:

Mw/M0 = 1 + αƒ/1 - α(ƒ - 1) = 1 + α/1 - α(ƒ - 1), β = α/2 (1.2)

with M0 the molar mass of the monomer. Flory, as well as other researchers, was excited because this equation now gave a mathematical proof for his derivation of the prediction for the critical point of gelation. A lifelong friendship between the two pioneers, Flory and Stockmayer, began here.

The derivation of the so-simple looking equation was a hard challenge for Stockmayer. He was frustrated that he could not find a solution. It was Maria Goeppert Mayer (the later Nobel Prize winner in 1963 and wife and co-author with Joseph E. Mayer) who gave Stockmayer the decisive hint. She observed Stockmayer's attempt and after a while she said, 'Stocky, why don't you try to use our cluster description when we treated the interparticle interactions between colloidal spheres?'

Flory confirmed the Stockmayer' distribution by applying combinatoral mathematics which will be given in Chapter 7 of this book. In the course of the time Flory also derived a molar mass distribution for the polymerization of AB2 monomers and the corresponding weight average degree of polymerization. No critical conversion for gelation was obtained.

This result surprised even Flory, because he realized that a divergence can be obtained only at full conversion, i.e. α = 1 or in other words, the branching of such AB2samples can never lead to a gel or network. This discovery was the birth date for hyperbranching.

Flory's interest in this type of structure arose from a book by K. H. Meyer in 1950 and from Staudinger. The structure of natural polymers was one of the reasons why Staudinger, with co-workers, turned to chemical synthesis of model polymers in the hope of gaining a deeper understanding of these structures. Amylopectin, the branched component of starch, was one of them.

It took more than 20 years before the subject of AB2 polymers was taken up but the decisive change was made by Kim and Webster by coining the name 'hyperbranching'. These two authors were trying to find a less laborious synthesis for dendrimers, which were known to possess advantageous properties as nano-objects. Although Kim and Webster could not achieve the high accuracy of a perfect structure, so they stated, at least the samples are hyperbranched. This now generally used notation is rather unfortunate because also co-polymers of the A3

1.2 Branched Polymers

In 1935 Staudinger and Schulz observed that the changes in the viscosity of polystyrene solutions depended on the reaction conditions during synthesis. Later, Staudinger and Husemann found a higher number of end groups than expected during their studies on the natural polymers amylopectin and glycogen, which was explained by the existence of branching. Both low viscosity and high number of end groups are typical characteristics of branched polymers. In addition, impeded crystallinity and poor mechanical strength are very common in branched polymers. These properties become more pronounced with branching density and depend on branching topology.

The type of branching can strongly influence polymer properties. Examples include natural polysaccharides, which occur after enzymatic polymerization of glucose, forming different types of branching. Glycogen is formed of glucose monomers and possesses high number of branching points (Figure 1.1). There are up to 50 000 monomer units of glucose on glycogen coupled together. The glucose units are arranged in a tree-like branched structure with a branching point every 8–12 glucose units. Glycogen is an energy supplier for animal cells and is the product of an enzymatic decomposition of starch. Starch is composed of amylose and amylopectin, which are also formed of glucose units, but while amylose possesses linear or very slightly branched chains, in amylopectin branching occurs every 25 units. Starch is the product of photosynthesis in plants. Despite the similar chemical character of the monomer units, the properties of starch and glycogen are different; starch is not soluble in cold water and is semi-crystalline, while glycogen is soluble in water and is not crystalline.

Today the variety of branching in synthetic polymers is manifold and 'branching' becomes a generic term for a huge class of polymer structures. The systematic development in branched polymers started with the discovery of long-chain branched polymers in the 1940s, the synthesis of the first star and graft polymers in the 1960s and the invention of dendrimers in the 1980s and of hyperbranched polymers in the 1990s. Nowadays, the combination of different branched topologies in one...

Details zur Ausgabe

• Verlag: Royal Society of Chemistry
• Erscheinungsdatum: 2015
• Sprache: Englisch
• ISBN 10: 1849733945
• ISBN 13: 9781849733946
• Einband: Gebundene Ausgabe
• Anzahl der Seiten: 286
• Kontakt zum Hersteller: Nicht verfügbar
• Verantwortliche Person: preigu; mail@preigu.de; ; Lengericher Landstr. 19; Osnabrück; 49078; Deutschland