Handbook of Fluoropolymer Science and Technology

Dennis W. Smith, Scott T. Iacono, Suresh S. Iyer, Dennis W. Smith, Scott T. Iacono, Suresh S. Iyer

• Publisher: Wiley
• Year: 2014
• Print ISBN: 9780470079935
• eBook ISBN: 9781118850084
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Industrial & Technical Chemistry

Handbook of Fluoropolymer Science and Technology

A comprehensive handbook on fluoropolymer synthesis, characterization, and processing

Fluoropolymers, one of the more durable classes of polymer materials, are known to enable novel technologies as a result of their remarkable properties. As key components in industry applications, fluoropolymers have established commercial interest and scientists have discovered more efficient approaches of handling them. This book reviews up-to-date fluoropolymer platforms as well as recently discovered methods for the preparation of fluorinated materials. It focuses on synthesis, characterization, and processing aspects, providing guidelines for practicing scientists and engineers. In addition, the book covers:

• Concepts and studies from leading international laboratories, including academia, government, and industrial institutions
• Emerging technologies and applications in energy, optics, space exploration, fuel cells, microelectronics, gas separation membranes, biomedical instrumentation, and more
• Current environmental concerns associated with fluoropolymers, relevant regulations, and growth opportunities

Overall, the chapters provide coverage of chemical methods and help the reader further understand how fluoropolymer research provides solutions for material challenges. The concepts in this book also inspire professionals to identify new markets and funding sources for fluoropolymer research and development.

1
FLUORINATED POLYPHOSPHAZENES

HARRY R. ALLCOCK

The Pennsylvania State University

1.1 BACKGROUND

Polyphosphazenes (Structure 1.1) are a broad class of macromolecules with a backbone of alternating phosphorus and nitrogen atoms and with two side groups (R) attached to each phosphorus atom.

STRUCTURE 1.1

The skeletal architecture may be linear, branched, star, or dendritic, or it may be part of a di- or triblock copolymer in conjunction with organic macromolecules or poly(organosiloxanes) (silicones). However, it is in the wide variety of side groups that this system differs from many other polymer platforms. More than 250 different organic, organometallic, or inorganic side groups have been utilized in single-substituent arrays or in di-, tri-, or higher mixed-substituent patterns. Thus, hundreds of different polyphosphazenes are known with a corresponding diversity of properties and potential uses [1]. These can be divided into different “families” of polymers such as inert biomaterials, bioerodible polymers, optical materials, membranes, ionic conductors, and so on. One of the most important and most interesting families consists of polyphosphazenes that bear fluorinated organic side groups. Examples of polymers within this group are shown in Figure 1.1.

FIGURE 1.1 Examples of fluorinated organophosphazene polymers.

1.2 SYNTHESIS METHODS AND PROPERTY DEVELOPMENT

A number of different access routes have been developed to poly (organophosphazenes) [1]. We have focused on a two-stage sequence that involves first the preparation of a linear polymeric reaction intermediate, poly(dichlorophosphazene), (NPCl₂)_n, followed in a second step by replacement of the chlorine atoms in this polymer by organic side groups (Figure 1.2) [2–4]. The reactive intermediate is accessible either by a ring-opening polymerization of a cyclic trimer, (NPCl₂)₃, or via a living cationic condensation polymerization of a phosphoranimine (Figure 1.2) [5–15]. Another route to poly(dichlorophosphazene) is via the condensation reactions of Cl₃P

N-POCl₂ [16], a method that yields lower molecular weight polymers than the ring-opening route. Replacement of the chlorine atoms in (NPCl₂)_n is accomplished by reactions with nucleophiles such as alkoxides, aryloxides, amines, or organometallic reagents.

FIGURE 1.2 Two-stage synthesis of poly(organophosphazenes).

This is a very different protocol than that exists for most classical polymers, where the side groups destined for the final polymer must be in place on the monomer before polymerization [17]. Modification of the side groups in conventional macromolecules after polymerization is restricted to simple reactions such as hydrolysis of esters or partial sulfonation. It is the high reactivity of poly(dichlorophosphazene) that allows the broad diversity of structure and properties that are a characteristic of poly(organophosphazenes). Other valuable methods have been developed to prepare poly(organophosphazenes) that involve the condensation reactions of organic-substituted phosphoranimines [18–21], but the range of side groups used in that process is more restricted than in the macromolecular substitution method, and the molecular weights tend to be lower.

Use of these synthetic techniques has led to the development of numerous different classes of phosphazene materials, many of which contain fluorine, but others that do not [1]. For example, a versatile class of hydrogel polyphosphazenes and ion conductive materials possesses nonfluorinated oligoethyleneoxy side chains. Nonfluorinated aryloxy substituents give fire-retardant polymers. Amino acid ester side groups or nonfluorinated alkoxy groups generate bioerodible properties that have been developed extensively for tissue engineering applications. Nevertheless, the presence of fluorine in the side group structure has led to some of the most intriguing developments, and this is the focus of the rest of this article. Using the two-step synthesis protocol, molecular diversity is accomplished in several different ways.

Method 1. Different nucleophiles give polymers with different side groups and diverse properties [1–4]. For example, oligoethyleneoxy side groups give water-soluble, water-stable polymers [22]. Aryloxy side units generate hydrophobic, water-insoluble polymers. Amino acid ester side groups or oligopeptide units linked to the polymer skeleton through the amino terminus generate bioerodible characteristics [23]. Fluoroalkoxy or fluoroaryloxy side groups generate hydrophobic, water- and radiation-stable polymers [24].

Method 2. A second method for structural and property tuning involves the introduction of two or more different side groups along the same polymer chain. For example, amphiphilic character is accessible by the use of fluoroalkoxy groups and oligoethyleneoxy side chains, with the exact properties being controlled by the ratios of the two. Two different fluoroalkoxy side groups on the same chain have a striking effect on the polymer morphology. A polyphosphazene with only trifluoroethoxy side groups is a film- or fiber-forming microcrystalline material, similar to poly(tetrafluoroethylene) in surface properties but, unlike Teflon, soluble in ordinary organic solvents such as acetone or methylethylketone. By contrast, the related polymer with both trifluoroethoxy and longer chain telomer fluoroalkoxy groups is an amorphous elastomer, prized for its low glass transition temperature (approximately −60°C), solvent and oil resistance, and impact-absorbing character.

For polyphosphazene molecules that bear two or more different side...

Table of contents

• Cover
• Titlepage
• Copyright
• Foreword
• In Memoriam
• Preface
• Contributors
• About the Editors
• 1 Fluorinated Polyphosphazenes
• 2 Mn2(CO)10-Visible Light Photomediated, Controlled Radical Polymerization of Main Chain Fluorinated Monomers and Synthesis of Block Copolymers Thereof
• 3 Interfacial Response of Semifluorinated Multi-Block Copolymers
• 4 Fluoropolymer Nanocomposites
• 5 Thermal Degradation and Pyrolysis of Polytetrafluoroethylene
• 6 Molecular Simulation of Fluoropolymers
• 7 Vapor Deposition of Fluoropolymer Surfaces
• 8 Functionalized and Functionalizable Fluoropolymer Membranes
• 9 Poly[Methyl(3,3,3-Trifluoropropyl)Siloxane]
• 10 Functional Fluorous Copolyoxetane Polymer Surface Modifiers
• 11 Self-Organizing Semifluorinated Methacrylate Copolymers
• 12 Synthesis of Fluoropolymers Using Borane-Mediated Control Radical Polymerization for Energy Storage Applications
• 13 Fluoropolymers in Supercritical Carbon Dioxide: Phase Behavior, Self-Assembly, and Stabilization of Water/Co2 Emulsions
• 14 Semifluorinated Polymers from Trifluorovinyl Aromatic Ether Monomers
• 15 Combustion Characterization of Energetic Fluoropolymer Composites
• 16 Amorphous Perfluoropolymers
• 17 Fluoropolymers for Sustainable Energy
• 18 Evolution of Academic Barricades for the use of Tetrafluoroethylene (TFE) in the Preparation of Fluoropolymers
• 19 Fluoropolymer Surfaces/Interfaces
• 20 Fluoropolymer Dielectrics
• 21 Fluoropolymers—Environmental Aspects
• 22 Fluorinated Ionomers and Ionomer Membranes Containing the bis[(perfluoroalkyl) sulfonyl]imide Protogenic Group
• 23 Fluorinated Silsesquioxanes
• 24 Multidimensional NMR of Fluoropolymers
• 25 Melt Processible Perfluoroplastics for Demanding Applications
• Index
• End User License Agreement