Modification of Polymer Properties

Carlos Federico Jasso-Gastinel, José M. Kenny

• Publisher: William Andrew
• Year: 2016
• Print ISBN: 9780323443531
• eBook ISBN: 9780323443982
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

Modification of Polymer Properties provides, for the first time, in one title, the latest information on gradient IPNs and gradient copolymers. The book covers the broad range of polymer modification routes in a fresh, current view representing a timely addition to the technical literature of this important area. Historically, blends, copolymers, or filled polymers have been developed to meet specific properties, or to optimize the cost/properties relationship. Using the gradient structure approach with conventional radical polymerization, it has been shown that it is possible to optimize properties if appropriate gradients in the composition of copolymer chains are obtained. An overview of the gradient structure approach for designing polymers has not appeared in the recent literature and this title covers the different methods used to modify properties, offering the whole range of ways to modify polymers in just one volume and making this an attractive option for a wide audience of practitioners. The approach for each chapter is to explain the fundamental principles of preparation, cover properties modification, describe future research and applications as examples of materials that may be prepared for specific applications, or that are already in use, in present day applications. The book is for readers that have a basic background in polymer science, as well as those interested in the different ways to combine or modify polymer properties. - Provides an integrated view on how to modify polymer properties - Presents the entire panorama of polymer properties modification in one reference, covering the essential information in each topic - Includes the optimization of properties using gradients in polymers composition or structure

1

Introduction

Modifiable Characteristics and Applications

C.F. Jasso-Gastinel, J.F.A. Soltero-Martínez and E. Mendizábal, University of Guadalajara, Guadalajara, Jalisco, México

Abstract

For the introductory chapter, an overview of the science and technology panorama of polymers is presented, focusing on the elements that have an influence on their properties. In that way, it starts by highlighting the importance of primary and secondary bonds on the structure and properties of polymers, and continues with some classifications of polymers that allow the understanding of the parameters that are related to their properties, including type and number of components, chemical and spatial structure, as well as polymer response to temperature after a polymer is formed; the different types of applications are also included before polymer morphology is explained and the relevance of polymer molecular weight is examined. Polymer recyclability and degradability are also discussed along with the relationship between chemical structure and properties, as well as the theoretical estimation of polymer properties with respect to structure, and finally the factors to be considered for polymer selection are presented.

Keywords

Bonds; classifications; molecular weight; structure-properties; morphology; properties estimation; polymer selection

1.1 Development of Polymers

The development of humankind since the first half of the 20th century has been closely related to the application of polymers from natural or synthetic origin. The studies to understand the relationship between structure and properties of those polymers have contributed significantly to the advancement in the field. From there, considerable research has also been done to expand the available properties by the combination or modification of polymers to make products.

The word “polymer” (from Greek roots) stands for a molecule that contains many (poly) parts (mers); i.e., it has a high number of equal parts or units (e.g., 1000–5000 for hydrocarbons), and with that size it acquires properties that are useful for different applications in solution, dispersion, or as a solid material. If the number of units is small (around 12–20), the molecule is known as an oligomer (a few units); those molecules find their use in the oil field (Wu, 1989), in electronics (Murphy and Fréchet, 2007), etc., while smaller molecules like telomers (2–5 units) have no practical use as materials. The reactant to make a polymer consists of a single molecule (monomer) that can react and rapidly grow unit by unit as a chain; alternatively, two molecules containing different functional groups may react (comers) to form polymer chains by means of stepwise reactions (Odian, 2004a).

Monomers and comers are commonly simple small (gaseous or liquid) molecules. For small molecules, chemical structure, molecular weight (MW), and isomerism play an essential role in their behavior at environmental conditions. For instance, in Table 1.1, it can be observed that sulfhydric acid is a gas, while water is a liquid at room temperature, even though the former has higher MW than the latter. In that case, the main difference between them relies on their chemical structure, because of the high forces of attraction that occur between water molecules. In the same table, it can be seen that hydrocarbons like methane or butene are gases at room temperature, while decane is a liquid, and as the MW of hydrocarbons increases, they convert into brittle or hard solids at room temperature. It is clear that in this case, the main difference between those molecules is the MW rather than the chemical structure. Additionally, in Table 1.1, pentane isomers show different boiling points due to their different spatial configuration. The parameters that affect small molecules also affect the behavior of big molecules, including natural macromolecules like proteins and cellulose or synthetic polymers.

Table 1.1

Properties of Some Common Substances

Substance	Boiling Temperature (P=1 atm; C°)	Molecular Weight (g/mol)	Physical State at 25°C
Water	100	18.01	Liquid
Sulfhydric acid	−60	34.08	Gas
Methane	−161.5	16.04	Gas
Butene	−6.26	56.11	Gas
n-Pentane	36.1	72.15	Liquid
Isopentane	27.7	72.15	Liquid
n-Decane	174.1	142.29	Liquid
C300H602	–	4209.816	Solid (brittle)
C700H1402	–	9820.216	Solid (hard)

In addition to the above-mentioned parameters that affect polymer behavior, the technological potential of polymeric materials broadens because they can be synthesized with more than one monomer in a reactor, be mixed with additives and/or blended with other polymers, and even be modified after they are formed (Carraher and Moore, 1983; Swift et al., 1997). Moreover, since the properties of a polymer article also depend on the processing method and the article geometry, plenty of methods to prepare polymers and processes to make products have been developed and applied with success since decades ago (Cheremisinoff, 1998; Lenz and Ciardelli, 1979; Matyjaszewski and Davis, 2002), and processing equipment is also in constant development.

To visualize the advances and potential of the polymer field, some classifications and schemes are presented in Section 1.3. Detailed nomenclature and basic definitions can be seen in the compendium prepared by the IUPAC (Jones et al., 2008).

1.2 Bonding in Polymers

The electrostatic forces that hold together or attract atoms and molecules apply also to polymers. Depending on the force magnitude, they have been classified as primary and secondary bonds. Primary bonds (ionic, covalent, coordinated covalent, and metallic) vary approximately from 35 kcal/mol to 213 kcal/mol depending on the electronegativity of the atoms involved. The force of primary bonds is big enough to hold together the atoms to form a molecule (e.g., O₂, H₂O, C₂H₄, polyethylene, etc.). The most common bond of this type in polymer structure is the covalent bond, while the coordinated covalent appears seldom. Ionic bonds are present in polymer with ionic charge, and the metallic bond became of interest in this field with the appearance of conductive polymers (Wudl et al., 1980).

The dissociation of primary bonds can only happen by chemical reaction. That is, the spatial configuration formed with such bonds during a synthesis reaction is fixed, giving the capability to obtain stable isomers (e.g., cis, trans, or isotactic polymers). As a consequence, primary bonds are responsible for the thermal and photochemical stability of polymers. Secondary bonds (dispersion, polar, induced polar, and hydrogen bond) that stand for forces of attraction between molecules are much weaker than primary bonds, normally ranging from 3 kcal/mol to 7 kcal/mol, and can be dissociated by the application of energy that promotes physical changes with no modification in chemical structure. That is, they are related to physical properties like fusion, evaporation, dissolution, flow, elastic deformation, etc. The dispersion forces which are present in all compounds are the weakest forces of attraction between molecules; the presence of polarity in molecules causes an increase in molecular cohesion, promoting an increase in their mechanical and thermal resistance. A stronger force of attraction appears if a bridge or link between a hydrogen atom and one of oxygen, nitrogen, or fluorine is formed (hydrogen bond); that kind of attraction may occur inter- or intramolecularly contributing to cohesion and chain alignment, magnifying mechanical and solvent resistance in polymers. The importance of hydrogen bonding is so great that water is a liquid at ambient conditions due to the bridges generated between the oxygen and hydrogen of different molecules. In polymeric materials it is of great importance for processing conditions and the final properties of polymers like polyamides, polyesters, polyurethanes, polyur...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Dedication
• Contributors
• About the Editors
• Preface
• 1. Introduction: Modifiable Characteristics and Applications
• 2. Filled Polymer Composites
• 3. Nanofillers in Polymers
• 4. Additives in Polymers
• 5. Surface Modification of Polymers: Chemical, Physical, and Biological Routes
• 6. Smart Polymers
• 7. Blends and Alloys
• 8. Gradients in Homopolymers, Blends, and Copolymers
• Index