Technology & Engineering
Polymer Structures
Polymer structures refer to the arrangement of monomer units in a polymer material. These structures can be linear, branched, or cross-linked, and they greatly influence the properties of the polymer, such as strength, flexibility, and durability. Understanding and controlling polymer structures is essential in designing materials for various applications, from plastics and fibers to adhesives and coatings.
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10 Key excerpts on "Polymer Structures"
eBook - PDFFundamentals of Materials Science and Engineering
An Integrated Approach
- William D. Callister, Jr., David G. Rethwisch(Authors)
- 2021(Publication Date)
- Wiley(Publisher)
Some of these influences are as follows: 1. Degree of crystallinity of semicrystalline polymers—on density, stiffness, strength, and ductility (Sections 4.11 and 8.18). 2. Degree of crosslinking—on the stiffness of rubberlike materials (Section 8.19). 3. Polymer chemistry—on melting and glass-transition temperatures (Section 11.17). WHY STUDY Polymer Structures? Naturally occurring polymers—those derived from plants and animals—have been used for many centuries; these materials include wood, rubber, cotton, wool, leather, and silk. Other natural polymers, such as proteins, enzymes, starches, and cellulose, are important in biological and physiological processes in plants and animals. Modern scientific research tools have made possible the determination of the molecular structures of this group of materials and the development of numerous polymers that are synthesized from small organic molecules. Many of our useful plastics, rubbers, and fiber materials are synthetic polymers. In fact, since the conclusion of World War II, the field of materials has been vir- tually revolutionized by the advent of synthetic polymers. The synthetics can be produced inexpensively, and their properties may be managed to the degree that many are superior to their natural counterparts. In some applications, metal and wood parts have been re- placed by plastics, which have satisfactory properties and can be produced at a lower cost. As with metals and ceramics, the properties of polymers are intricately related to the structural elements of the material. This chapter explores molecular and crystal structures of polymers; Chapter 8 discusses the relationships between structure and some of the mechanical properties. Because most polymers are organic in origin, we briefly review some of the basic concepts relating to the structure of their molecules. First, many organic materials are hydrocarbons—that is, they are composed of hydrogen and carbon.
eBook - PDFFundamentals of Materials Science and Engineering
An Integrated Approach
- William D. Callister, Jr., David G. Rethwisch(Authors)
- 2016(Publication Date)
- Wiley(Publisher)
Some of these influences are as follows: 1. Degree of crystallinity of semicrystalline polymers—on density, stiffness, strength, and ductility (Sections 4.11 and 8.18). 2. Degree of crosslinking—on the stiffness of rubber-like materials (Section 8.19). 3. Polymer chemistry—on melting and glass-transition temperatures (Section 11.17). WHY STUDY Polymer Structures? Naturally occurring polymers—those derived from plants and animals—have been used for many centuries; these materials include wood, rubber, cotton, wool, leather, and silk. Other natural polymers, such as proteins, enzymes, starches, and cellulose, are important in biological and physiological processes in plants and animals. Modern scientific research tools have made possible the determination of the molecular structures of this group of materials and the development of numerous polymers that are synthesized from small organic molecules. Many of our useful plastics, rubbers, and fiber materials are synthetic polymers. In fact, since the conclusion of World War II, the field of materials has been vir- tually revolutionized by the advent of synthetic polymers. The synthetics can be produced inexpensively, and their properties may be managed to the degree that many are superior to their natural counterparts. In some applications, metal and wood parts have been re- placed by plastics, which have satisfactory properties and can be produced at a lower cost. As with metals and ceramics, the properties of polymers are intricately related to the structural elements of the material. This chapter explores molecular and crystal structures of polymers; Chapter 8 discusses the relationships between structure and some of the mechanical properties. Because most polymers are organic in origin, we briefly review some of the basic concepts relating to the structure of their molecules. First, many organic materials are hydrocarbons—that is, they are composed of hydrogen and carbon.
eBook - PDFMaterials Science and Engineering
An Introduction
- William D. Callister, Jr., David G. Rethwisch(Authors)
- 2018(Publication Date)
- Wiley(Publisher)
Other natural polymers, such as proteins, enzymes, starches, and cellulose, are important in biological and physiological processes in plants and animals. Modern scientific research tools have made possible the determination of the molecular structures of this group of materials and the development of numerous polymers that are synthesized from small organic molecules. Many of our useful plastics, rubbers, and fiber materials are synthetic polymers. In fact, since the conclusion of World War II, the field of materials has been vir- tually revolutionized by the advent of synthetic polymers. The synthetics can be produced inexpensively, and their properties may be managed to the degree that many are superior to their natural counterparts. In some applications, metal and wood parts have been re- placed by plastics, which have satisfactory properties and can be produced at a lower cost. As with metals and ceramics, the properties of polymers are intricately related to the structural elements of the material. This chapter explores molecular and crystal structures of polymers; Chapter 15 discusses the relationships between structure and some of the physical and chemical properties, along with typical applications and forming methods. Because most polymers are organic in origin, we briefly review some of the basic concepts relating to the structure of their molecules. First, many organic materials are hydrocarbons —that is, they are composed of hydrogen and carbon. Furthermore, the intramolecular bonds are covalent. Each carbon atom has four electrons that may 14.1 INTRODUCTION 14.2 HYDROCARBON MOLECULES Learning Objectives After studying this chapter, you should be able to do the following: 1. Describe a typical polymer molecule in terms of its chain structure and, in addition, how the molecule may be generated from repeat units. 2. Draw repeat units for polyethylene, poly(vinyl chloride), polytetrafluoroethylene, polypropyl- ene, and polystyrene.
eBook - PDF- Ferdinand Rodriguez, Claude Cohen, Christopher K. Ober, Lynden Archer(Authors)
- 2014(Publication Date)
- CRC Press(Publisher)
21 2 Basic Structures of Polymers 2.1 CLASSIFICATION SCHEMES The study of any subject as vast as and as complex as polymers is simplified by gathering together the many thousands of examples that are known into a few categories about which generalized statements can be made. By speaking about polymers as a special topic, we already are categorizing molecular materials as low-molecular-weight or high-molecular-weight polymers. Within the polymer field, several classifications have been found to be useful. These classifications are based on the following: 1. Molecular structure. We can ask, for example, whether the polymer molecule is linear or branched. Is it made up of identical monomer units (homopolymer) or a mixture of two or more monomer units (copo-lymer, terpolymer). The polymer molecules may exist as separate indi-vidual molecules or they may be covalently linked to a macroscopic network. 2. Physical state. The polymer may be in the molten state with a viscosity characteristic of a liquid or the elasticity associated with a rubbery material. It may also be in a solid state that can have an amorphous glassy structure or a partially ordered crystalline structure. We shall see that the distinctions depend on the temperature, molecular weight, and chemical structure of the polymer. 3. Chemical structure. The elemental composition of a polymer, the chemical groups present (ether, ester, hydroxyl), or the manner of synthesis (chain propagation, transesterification, ring opening) may be used as a means of classifying polymers. A person or company attempting to exploit a unique raw material or process may profitably use such an approach for the devel-opment of a new class of polymers. 4. Response to environment. In the plastics industry, an important factor in economic usage and in end-use stability of a product is the behavior of the material at high temperatures.
eBook - PDFFundamentals of Materials Science and Engineering
An Integrated Approach
- William D. Callister, Jr., David G. Rethwisch(Authors)
- 2022(Publication Date)
- Wiley(Publisher)
2. Degree of crosslinking—on the stiffness of rubberlike materials (Section 9.19). 3. Polymer chemistry—on melting and glass- transition temperatures (Section 12.19). 4.1 | | INTRODUCTION LEARNING OBJECTIVES After studying this chapter, you should be able to do the following: 1. Describe a typical polymer molecule in terms of its chain structure and, in addition, how the molecule may be generated from repeat units. 2. Draw repeat units for polyethylene, poly(vinyl chloride), polytetrafluoroethylene, polypropyl- ene, and polystyrene. 3. Calculate number-average and weight-average molecular weights and degree of polymerization for a specified polymer. 4. Name and briefly describe: (a) the four general types of polymer molecular structures, (b) the three types of stereoisomers, (c) the two kinds of geometric isomers, and (d) the four types of copolymers. 5. Cite the differences in behavior and molecular structure for thermoplastic and thermosetting polymers. 6. Briefly describe the crystalline state in polymeric materials. 7. Briefly describe/diagram the spherulitic structure for a semicrystalline polymer. Naturally occurring polymers—those derived from plants and animals—have been used for many centuries; these materials include wood, rubber, cotton, wool, leather, and silk. Other natural polymers, such as proteins, enzymes, starches, and cellulose, are important in biological and physiological processes in plants and animals. Modern scientific research tools have made possible the determination of the molecular structures of this group of materials and the development of numerous polymers that are synthesized from small organic molecules. Many of our useful plastics, rubbers, and fiber materials are synthetic polymers. In fact, since the conclusion of World War II, the field of materials has been vir- tually revolutionized by the advent of synthetic polymers.
eBook - PDFMaterials Science and Engineering, P-eBK
An Introduction
- William D. Callister, Jr., David G. Rethwisch, Aaron Blicblau, Kiara Bruggeman, Michael Cortie, John Long, Judy Hart, Ross Marceau, Ryan Mitchell, Reza Parvizi, David Rubin De Celis Leal, Steven Babaniaris, Subrat Das, Thomas Dorin, Ajay Mahato, Julius Orwa(Authors)
- 2020(Publication Date)
- Wiley(Publisher)
Many of our useful plastics, rubbers, and fibre materials are synthetic polymers. In fact, since the conclusion of World War Two, the field of materials has been virtually revolutionised by the advent of synthetic polymers. The synthetics can be produced inexpensively, and their properties may be managed to the degree that many are superior to their natural counterparts. In some applications, metal and wood parts have been replaced by plastics, which have satisfactory properties and can be produced at a lower cost. As with metals and ceramics, the properties of polymers are intricately related to the structural elements of the material. This chapter explores molecular and crystal structures of polymers; a later chapter discusses the relationships between structure and some of the physical and chemical properties, along with typical applications and forming methods. 14.2 Hydrocarbon molecules Because most polymers are organic in origin, we briefly review some of the basic concepts relating to the structure of their molecules. First, many organic materials are hydrocarbons — that is, they are composed of hydrogen and carbon. Furthermore, the intramolecular bonds are covalent. Each carbon atom has four electrons that may participate in covalent bonding, whereas every hydrogen atom has only one bonding electron. A single covalent bond exists when each of the two bonding atoms contributes one electron, as represented schematically in an earlier chapter for a molecule of hydrogen (H 2 ). Double and triple bonds between two carbon atoms involve the sharing of two and three pairs of electrons, respectively.
eBook - PDF- Wenceslao González-Viñas, Héctor L. Mancini(Authors)
- 2015(Publication Date)
- Princeton University Press(Publisher)
They melt without decomposing. Due to these properties they are appropriate either for molding when hot, or for injection and lamination, or for reduction into fibers. In this chapter we pay special attention to synthetic polymeric materials and the possi- bilities that advances in synthesis and production offer in terms of properties that can be programmed. 10.1 MOLECULAR STRUCTURE Molecular design has been the most important area that designers of materials have been able to influence. In analyzing the relation between the structure and properties of polymeric materials, we start by enquiring into the macromolecules that form them. Macromolecules that form polymeric material are created by hundreds or thousands of subunits or mers, functional units that are repeated and kept tight by covalent bonds. Each unit comes from a main molecule that can be bonded to other similar units to form a chain. This chain may or may not have lateral ramifications and bond to others through cross-links. The initial molecule is the monomer; it has no free bonds and can convert, under any action, one internal bond to a free link capable of being bonded to other units. This molecule includes one or several functional groups. Ahomopolymer is a polymer formed by only one type of mer. In contrast, a heteropolymer or copolymer is created by more than one type of mer and permits many possibilities for continuously graded and optimized properties, depending on the application we desire. Among the most significant examples of heteropolymers are biopolymers like DNA, which has four types of monomers, and proteins, which can have up to 20 monomers. Homopolymers One simple and paradigmatic example of a homopolymer is polyethylene (PE): · · · − CH 2 − CH 2 − CH 2 − CH 2 − CH 2 − CH 2 − CH 2 − CH 2 − · · · obtained when heating ethylene in the presence of catalysts. This can be represented in this way: n(CH 2 = CH 2 ) −→ (−CH 2 − CH 2 −) n .
eBook - PDFThermoplastic Materials
Properties, Manufacturing Methods, and Applications
- Christopher C. Ibeh(Author)
- 2011(Publication Date)
- CRC Press(Publisher)
43 3 Basic Structures and Characteristics of Polymers and Plastics 3.1 Chemical Bonding in Polymers and Plastics The basic structures and characteristics of polymers and plastics are attribut-able to five main factors such as arrangement, chemical structure, degree of polymerization (size), form, and polymerization method [1,2]. Polymers are composed of recurring monomer units that are essentially organic in nature and are bonded chemically during polymerization. Predominantly, poly-mers and plastics comprise of the elements carbon (C), hydrogen (H), nitro-gen (N), bromine (Br), chlorine (Cl), fluorine (F), oxygen (O), silicon (Si), and sulfur (S). Also, as discussed under Chapter 2, it is typical to fortify polymers with additives. Additives in general, and functional additives in particular are additional sources of chemical bonding in polymers and plastics [3–6]. Popular and currently in-use functional additives include nanomaterials such as nanoclay, carbon nanotubes, carbon nanofibers, nanographenes, etc., powdered metals, metal fibers, compatibilizers, coupling agents, polyhedral oligomeric silsesquioxane (POSS), nanosilica, nanotitanium dioxide, and others [7–10]. Coupling agents and compatibilizers are considered similar but are distinguished by their medium of action. Compatibilizers facilitate adhesion between two immiscible polymers by reducing their interfacial tension, whereas coupling agents accomplish this between a polymer and filler. Carbon nanotubes, carbon nanofibers, nanographenes [11,12], graphite, carbon black, powdered metals, and metal fibers are known for their electri-cal conductivity properties. Chemical bonding in polymers and plastics are further affirmed by some of their inherent adhesive characteristics. In fuse bonding, melting of two, in-contact polymers results in chemical bonding of their molecules and atoms to form essentially one single material.
eBook - PDFIntroduction to Biomaterials
Basic Theory with Engineering Applications
- C. Mauli Agrawal, Joo L. Ong, Mark R. Appleford, Gopinath Mani(Authors)
- 2013(Publication Date)
- Cambridge University Press(Publisher)
6 Polymers Goals After reading this chapter the student will understand the following. Structure of polymers and their common physical states. General properties of polymers. Common types of polymerization techniques used for production. Chemical structure and properties of common biomedical polymers. Structure of hydrogels and their general properties. De fi nition and uses of nanopolymers. In everyday life, we encounter a variety of polymers, some natural and others synthetic. The vast majority of these are carbon-based in nature. They range from synthetic polymers seen in products such as polyethylene grocery bags, polymethylmethacrylate-based window panes, and polystyrene-based eating uten-sils, to natural polymers such as starch, cellulose and rubber. Polymers used as biomaterials are often similar to these common materials. For example, the polymer most extensively used in total joint prostheses is ultrahigh molecular weight polyethylene – chemically identical to the material used for plastic bags, although having a much higher molecular weight. The same is true for bone cement which is used in conjunction with bone surgery and Plexiglass ® , which is used for window panes. Both of these materials are polymethylmethacrylate (PMMA). Of course, any polymer that is used as an implant has to meet strict safety standards as required by governmental and other regulatory agencies and has to be virtually contaminant free. Polymers have the advantage that they can be easily formed into desired shapes using a variety of techniques such as solution casting, melt molding, or machining. Thus, polymer-based implants are relatively inexpensive to manufacture. Poly-mers can also be made reactive so that different chemical molecules can be attached to the surface of implants in order to make them more compatible with the surrounding environment in the body.
eBook - PDF- Jose Asua(Author)
- 2008(Publication Date)
- Wiley-Blackwell(Publisher)
In the linear polymers, the structural units are arranged in a linear sequence. Branched polymers may have short and long branches. Branched polymers include comblike and star polymers. Extensive branching may lead to a dendritic structure. Introduction to Polymerization Processes 5 Table 1.2 Polymer architectures Architecture Examples Comonomers/reactants Polymerization method Linear Ethylene Coordination Branched n-Butyl acrylate Free-radical polymerization Comb Polymethylsiloxane + styrene Atom transfer radical polymerization (ATRP) Star Divinylbenzene + living cationic polyisobutylene Cationic polymerization Dendrimer and hyperbranched Dimethylol propionic acid Step-growth polymerization Crosslinked/network Butadiene Free-radical polymerization Crosslinked polymers are formed by polymer chains linked together forming a three- dimensional network. They are characterized by the crosslinking density (number of junction points per 1000 monomeric units). Unlike linear and branched polymers, crosslinked polymers do not melt upon heating and do not dissolve in solvents (although they are swollen by them). Loose networks (low crosslinking density) have an elastic behavior (rubbers). Dense networks are rigid, inflexible and they do not deform unless temperature is high enough to break the covalent bonds. Gel is often defined as the fraction of the polymer belonging to an infinite three- dimensional network. However, in practice, gel fraction is determined as the fraction of polymer that is not soluble in a given solvent, which may include very large (highly branched) macromolecules. Therefore, the reported gel contents depend on both the solvent and the extraction method used. The macroscopic behavior of the polymer materials caused by the polymer architecture is the basis of the classification of polymers in thermoplastics, elastomers and thermosets. Thermoplastics are linear and branched polymers that melt upon heating.
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