Chapter 1
Basic Issues of Functionalized Polymers
In organic chemistry, functionality is often used as a synonym for a functional group. Functionalization means the introduction of functional groups. According to IUPAC (1), the functionality of a monomer is defined as the number of bonds that a repeating unit of a monomer forms in a polymer with other monomers. Thus, in the case of a functionality of f = 2, a linear polymer is formed by polymerizing a thermoplastic material.
Monomers with a functionality of > 3 lead to a branching point, which can result in crosslinked polymers, i.e., a thermosetting polymer (2).
Functional polymers are also sometimes called smart polymers (3). Here, the basic issues of functionalized polymers are discussed.
Functional polymers are polymers with advanced optic and/or electronic properties. The advantages of functional polymers include their low cost, the ease in which they can be processed and a range of attractive mechanical characteristics for functional organic molecules.
These properties can be adjusted whilst material usage is kept low, consequently opening interesting environmental perspectives. Polymer-bound substances can spread their activity without endangering people or the environment. Examples of functional polymers are (4):
- Semiconducting conjugated polymers.
- Stimuli-responsive polymers,
- Thermally responsive polymers,
- pH-sensitive polymers,
- Toner materials,
- Supercapacitors,
- Ion exchange resins,
- Biomimetic materials, and
- Supramolecular metallopolymers.
Functional polymers are macromolecules to which chemically bound functional groups are attached which can be utilized as reagents, catalysts, protecting groups, and others. Functional polymers are low cost, easy to process and have a range of attractive mechanical characteristics for functional organic molecules.
The polymer support can be either a linear species, which is soluble, or a crosslinked species which is insoluble. A polymer that can be used as support should have significant mechanical stability under the reaction conditions. Such properties of the support play an important role in the functionalization reactions of polymers. So, the polymer properties can be modified either by chemical reactions on pendant groups or by changing the physical nature of the polymers. Special uses of functional polymers are shown in Table 1.1.
Table 1.1 Uses of functional polymers (5).
Field of Application Use Analytical chemistry Polymers as stationary-phase (chromatography/extraction) Catalysis engineering Polymers as a catalyst Medicine, agriculture, washing agents Controlled release from polymer matrices, design and synthesis of functional polymers, polymer-bound dyes, reactive and functional polymers Polymer modification Surface and functional coatings
There are monographs dealing with functional polymers (6-14).
A comprehensive and authoritative overview of functional polymers and polymeric materials has been presented (14). This ranges from their synthesis and characterization, to their properties, actual applications and future perspectives.
Functional polymers and smart polymeric materials play a decisive role in new innovations in all areas where new materials are needed. Optoelectronics, catalysis, biomaterials, medicine, building materials, water treatment, coatings, and many more applications rely on functional polymers.
Functional polymers are polymers that respond to different stimuli or changes in the environment. The types of polymers, including temperature-, pH-, photo-, and enzyme-responsive polymers, have been assessed (10). These issues include shape-memory polymers, smart polymer hydrogels, and self-healing polymer systems.
Applications of functional polymers include smart instructive polymer substrates for tissue engineering, smart polymer nanocarriers for drug delivery, the use of smart polymers in medical devices for minimally invasive surgery, diagnosis, and other applications, and smart polymers for bioseparation and other biotechnology applications. Functional polymers are also used for textile and packaging applications, and for optical data storage.
Adaptive polymers are those which are responsive to different stimuli, namely physical, mechanical, chemical and biological stimuli, with a controlled and/or predicable behavior. They can be used in textiles, skin care, medicine and other related areas. Some versatile functional polymers, such as chitosan, cylodextrin and dendrimer, and hyperbranched polymers have also been reviewed (8).
Functional polymers are also important materials for coatings (11). For example, superhydrophobic surfaces can be produced.
Also, functional biopolymers have been reviewed (15). A comprehensive overview of the synthesis, properties and biomedical applications of functional biopolymers has been presented. A lot of topics are covered, such as synthetic biopolymers, blood-compatible polymers, ophthalmic polymers and stimuli-responsive polymers. An up-to-date review of cell encapsulation strategies and cell surface and tissue engineering has also been included in this work.
1.0.1 Standards
Actually, standards specifically designed for functional polymers are rare. No standard with the term functional polymer in the title could be found. However, in the scientific literature, in the context of functional polymers, some standards for measuring the properties of these polymers have been mentioned. These standards are collected in Table 1.2.
Table 1.2 Standards in the context of functional polymers.
Number Title Reference ASTM D3643-15 Standard Test Method for Acid Number of Certain Alkali-Soluble Resins (16) ASTM D790-17 Standard Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials (17) ASTM D785-08 Standard Test Method for Rockwell Hardness of Plastics and Electrical Insulating Materials (18) ASTM D638-14 Standard Test Method for Tensile Properties of Plastics (19) ASTM D570-98 Standard Test Method for Water Absorption of Plastics (20) ASTM F813-07 Standard Practice for Direct Contact Cell Culture Evaluation of Materials for Medical Devices (21) ASTM F619-14 Standard Practice for Extraction of Medical Plastics (22) ASTM D5229 Standard Test Method for Moisture Absorption Properties and Equilibrium Conditioning of Polymer Matrix Composite Materials (23) ASTM D2872-12e1 Standard Test Method for Effect of Heat and Air on a Moving Film of Asphalt (Rolling Thin-Film Oven Test) (24) ISO 17736 Workplace air quality - Determination of isocyanate in air using a double-filter sampling device and analysis by high pressure liquid chromatography (25) ISO 8986-1 Plastics - Polybutene-1 (PB-1) moulding and extrusion materials - Part 1: Designation system and basis for specifications (26)
The Functional Polymers Group of the National Institute of Standards and Technology in Gaithersburg, MD, develops directives, measurement methods, data, standards, and science for the functional properties (e.g., electronic, ion transport) of polymeric materials within functional devices and applications in forms that include thin films, interfaces, nanostructures, and membranes (27). The projects and programs of this group are summarized in the following sections.
1.0.1.1 Polymers for Next-Generation Lithography
Here, measurements were developed and applied with high-spatial and chemically specific resolution to elucidate the properties and process kinetics of critical materials at nanometer scales that are needed to advance next-generation photolithography, including both the 193 nm (deep ultraviolet) and 13.5 nm (extreme ultraviolet) lithography platforms.
This provides the foundation for a rational design of materials and processing strategies for the fabrication of sub-32 nm structures. The measurement platform integrates specular and off-specular X-ray and neutron reflectivity, near-edge X-ray absorption fine structure spectroscopy, quartz crystal microbalance, solid-state nuclear magnetic resonance, polarization-modulation infrared reflectance absorption spectroscopy, and infrared variable angle spectroscopic ellipsometry. These measurements relate the fundamentals of polymer interfaces to high-resolution lithographic patterning.
1.0.1.2 Templated Assembly of Block Copolymer Films
Block copolymers are materials that naturally self-assemble into monodisperse, chemically distinct domains, however, their placement and orientation are difficult...
