Chemistry
Crystalline Polymer
Crystalline polymers are a type of polymer with a highly ordered molecular structure, resulting in a regular and repeating pattern. This arrangement gives them a distinct crystalline appearance and properties such as stiffness, strength, and high melting points. The ordered structure of crystalline polymers makes them more resistant to deformation and provides them with unique mechanical and thermal characteristics.
Written by Perlego with AI-assistance
Related key terms
1 of 5
9 Key excerpts on "Crystalline Polymer"
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)
We think of polymer crys- tallinity as the packing of molecular chains to produce an ordered atomic array. Crys- tal structures may be specified in terms of unit cells, which are often quite complex. For example, figure 14.10 shows the unit cell for polyethylene and its relationship to the molecular chain structure; this unit cell has orthorhombic geometry. Of course, the chain molecules also extend beyond the unit cell shown in the figure. Molecular substances having small molecules (e.g. water and methane) are normally either totally crystalline (as solids) or totally amorphous (as liquids). As a consequence of their size and often complexity, polymer molecules are often only partially crystalline (or semicrystalline), having crystalline regions dispersed within the remaining amorphous material. Any chain disorder or misalignment will result in an amorphous region, a condition that is fairly common, because twisting, kinking, and coiling of the chains prevent the strict ordering of every segment of every chain. Other structural effects are also influential in determining the extent of crystallinity, as discussed shortly. The degree of crystallinity may range from completely amorphous to almost entirely (up to about 95%) crystalline; in contrast, metal specimens are almost always entirely crystalline, whereas many ceramics are either totally crystalline or totally noncrystalline. SemiCrystalline Polymers are, in a sense, analogous to two‐phase metal alloys, discussed previously. The density of a Crystalline Polymer will be greater than an amorphous one of the same material and molecular weight because the chains are more closely packed together for the crystalline structure.
eBook - PDF- J. W. S. Hearle, R. H. Peters, J. W. S. Hearle, R. H. Peters(Authors)
- 2013(Publication Date)
- Butterworth-Heinemann(Publisher)
The present chapter is concerned with the crys-tallinity of polymeric substances that have been synthesized in the laboratory or manufactured industrially, but many of the same general principles should be applicable also to naturally occurring polymers. In many ways, however, man-made polymers are more suited to the types of investigation to be reviewed here, since they are chemically better defined and more homogeneous and their physical state can be more readily altered or controlled. Most of the material to be described refers primarily to unoriented systems, since an understanding of these is a prior requisite for a better insight into the structure of fibres. Nevertheless, in the final section, a few guiding principles will be outlined to show how our present knowledge about crystalline structural elements in unoriented systems might be linked up with effects observed when such systems are oriented. A Crystalline Polymer consists of entities belonging to a variety of dimensional levels. Much misunderstanding and, in the past, often 332 THE CRYSTALLINITY OF HIGH POLYMERS futile controversy has been due to the fact that this stratification into different dimensional levels has not been clearly appreciated. Results obtained on structures at different levels are not necessarily directly comparable. In order to establish the proper perspective from the beginning, this stratification is laid out in Table 10.1. This is the framework on which the whole treatment of the subject will be built. It should be appreciated that the dimensions quoted in the table are merely indicative of actual magnitudes. There is a considerable overlap between the sizes of entities adjacent in the sequence; nevertheless, within one and the same specimen, the sequence is expected to be preserved. The range of entities covered by Table 10.1 includes both the structure and the texture of Crystalline Polymers in the usual crys-tallographic sense of these terms.
eBook - PDF- David I. Bower(Author)
- 2002(Publication Date)
- Cambridge University Press(Publisher)
Chapter 4 Regular chains and crystallinity Ideal crystals are regularly repeating three-dimensional arrays of atoms. It follows that, if a polymer is to be able to crystallise, even if only to a limited extent, the minimum requirement is that its chains must themselves have regularly repeating units along their lengths and must be able to take up a straight conformation. This chapter is concerned with the types of regu-larity and irregularity that polymer chains can have, with how regular chains pack together and with the experimental study of the crystal struc-ture at the level of the unit cell, the smallest unit from which the crystal may be imagined to be built by regular repetition of its structure in space, as described in section 2.5.1. 4.1 Regular and irregular chains 4.1.1 Introduction It is a geometrical requirement that if a polymer is to be potentially capable of crystallising, its chains must be able, by undergoing suitable rotations around single bonds, to take up an arrangement with translational symme-try . If a polymer is actually to crystallise there is also a physical require-ment: the crystal structure must usually have a lower Gibbs free energy than that of the non-crystalline structure at the same temperature. Consideration of this physical requirement is deferred to later sections; the present section deals only with the geometrical requirement. Geometrical regularity can be considered to require (i) chemical regularity of the chain and (ii) stereoregularity of the chain. The second requirement cannot be met unless the first is met, but chemical regularity does not guarantee that the second requirement can be met. Chemical regularity means that the chain must be made up of identical chemical repeat units , i.e. units with the same chemical and structural for-87 mula, and the units must be connected together in the same way.
eBook - PDFPolymer Structure Characterization
From Nano To Macro Organization
- Richard A Pethrick(Author)
- 2007(Publication Date)
- Royal Society of Chemistry(Publisher)
26. B.M. Ocko, E.B. Sirota, M. Deutsch, E. DiMasi, C.S. Coburn, J. Strzalka, S.Y. Zheng, A. Tronin, T. Gog and C. Venkataraman, Phys. Rev. E , 2001, 63 , 33. 27. C.S. Yoon, J.N. Sherwood and R.A. Pethrick, J. Chem. Soc., Faraday Trans.1 , 1989, 85 (10), 3221–3232. 28. M. Maroncelli, S.P. Qi, H.L. Strauss and R.G. Snyder, J. Am. Chem. Soc. , 1982, 104 , 6237. 29. T. Yamamoto, H. Aoki, S. Miyaji and K. Nozaki, Polymer , 1997, 38 (11), 2643–2647. 30. H. Yamakawa, S. Matsukawa, H. Kurosu, S. Kuroki and I. Ando, J. Chem. Phys. , 1999, 111 (15), 7110–7115. 31. H. Honda, S. Tasaki, A. Chiba and H. Ogura, Phys. Rev. B , 2002, 65 (10), 104112. 32. F. Mina, T. Asano, D. Mondieig, A. Wurflinger and C. Josefiak, J. Phys. IV , 2004, 113 , 35–38. 33. S.L. Wang, K. Tozaki, H. Hayashi, S. Hosaka and H. Inaba, Thermochim. Acta , 2003, 408 , 1–2. 34. K. Kato and T. Seto, Jpn. J. Appl. Phys. Part 1 , 2002, 41 (4A), 2139–2145. 35. K. Nozaki, T. Yamamoto, T. Hara and M. Hikosaka, Jpn. J. Appl. Phys. Part 2 , 1997, 36 (2A), L146–L149. 36. H. Honda, S. Tasaki, A. Chiba and H. Ogura, Phys. Rev. B , 2002, 65 (10), 104112. 106 Chapter 4 CHAPTER 5 Morphology of Crystalline Polymers and Methods for Its Investigation 5.1 Introduction Polymers when they solidify will form a crystalline, partially ordered or totally disordered structure, depending on the regularity of the polymer backbone and the strength of the polymer–polymer interactions. In the melt, the flexible chain will normally contain a number of higher energy gauche conformations and adopts a random coiled form consistent with its inherent entropic disorder. On cooling, the lower energy trans form becomes predominant and chains prefer a more extended structure. The all-trans sequences produce linear sections of chain that are able to interact with other chains and initiate crystal growth. The extent to which the molecule eliminates the higher energy conformations on cooling will dictate its ability to crystallize.
eBook - PDF- Alexandre Blumstein(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
1 Scattering in Liquid Crystalline Polymer Systems J. H. Wendorff Deutsches Kunststoff Institut Darmstadt, West Germany IV. VI. I. Introduction Introduction Characteristic Properties of Liquid Crystalline Phases A. Physical Properties B. Structural Properties Structural Analysis by Scattering Methods A. Basic Features of Structural Analysis B. Determination of the Molecular Structure C. Determination of the Supermolecular Structure D. Structural Analysis in Liquid Crystalline Systems Liquid Crystalline Order of the Main Chain in Polymers A. Polymers with Flexible and Semiflexible Chains B. Polymers with Rigid Chains Liquid Crystalline Order of the Side Groups in Polymers A. General Survey B. Polymers with Side Groups Containing the Cholesterol Moiety C. Polymers with Various Side Groups Liquid Crystalline Structures Displayed by Block Copolymers References 1 3 3 4 7 7 7 13 13 16 16 21 26 26 29 31 37 37 Polymers that display structures that are intermediate between the three-dimensionally ordered crystalline state and the disordered isotropic 1 2 J. H. Wendorff fluid state have been given considerable interest in the last few years for the following reasons : (i) These polymers can be considered as model systems for isotropic amorphous polymers, where semiordered regions have been proposed to exist, and for drawn amorphous polymers, where by the drawing process a high degree of orientational order can be introduced. (ii) Polymers that form partially ordered melts or partially ordered solutions can be processed in such a way that fibers with a very high degree of orientational order and chain extension are obtained. This specific struc-ture leads to superior mechanical properties of the material. (iii) Polymers with ordered melts are of technological importance for the same reasons that low molecular weight systems with anisotropic melts are used widely today in technical products such as electrooptical displays.
eBook - PDFThermoplastic Materials
Properties, Manufacturing Methods, and Applications
- Christopher C. Ibeh(Author)
- 2011(Publication Date)
- CRC Press(Publisher)
499 21 Liquid Crystalline Polymers 21.1 LCP Overview Liquid Crystalline Polymers (LCPs) are a unique group of polymers that have an ordered structure in the molten (and solution) phase comparable to that found in low molecular weight nonpolymeric liquid crystals (LCs) in the liq-uid phase [1–3]. LCPs exist in a state in which the molecules are ordered and mutually aligned but the material can still flow; flow is “typically” a liquid or fluid characteristic. This alignment is characterized as “self-reinforcing,” and gives LCPs a high degree of orientation and exceptional mechanical proper-ties. In addition, LCPs exhibit very low viscosity in the melt and solution phases, and have ease of processability. The ordered nature of LCPs is attrib-utable to their unique combination of high aspect ratio (length to diameter ratio) and rigid molecular structure. This combination favors a high strength to weight (or specific strength) property. LCPs are specialty-engineering thermoplastic resins that are characterized by a unique combination of out-standing properties and attributes such as • Dimensional stability • High specific strength • Chemical resistance • Flammability/heat resistance • Self-reinforcing • Ease of processing LCs, often referred to as mesophases, were first identified more than a cen-tury ago. They are low molecular weight (liquid) compounds with unique electro-optical properties. LCs exist at the inter-phase of the conventional iso-tropic fluid and that of the solid state and tend to exhibit both fluid and solid state characteristics. Figure 21.1 is a schematic of the molecular arrangement in LCPs compared to those of their amorphous and semicrystalline thermo-plastic counterparts. LCPs, unlike their thermoplastic counterparts, exhibit 500 Thermoplastic Materials ordered molecular arrangement in the liquid state. This ordered molecular arrangement or crystallinity persists and is enhanced in the solid state.
eBook - PDF- Wenceslao González-Viñas, Héctor L. Mancini(Authors)
- 2015(Publication Date)
- Princeton University Press(Publisher)
The term “plastic” means able to deform in a permanent way and thus able to be shaped under pressure and appropriate temperature. Here strong bonds are not formed between polymeric chains, although they can interact among themselves. Upon cooling the material stays amorphous as it takes on the aspects of a glass. The entanglement that gives stiffness to thermosets (albeit with definite differences) is shared by synthetic and natural rubbers. But this time it is induced to obtain more elasticity. This disposition to entangle is exploited to enhance the material’s resistance to temperature and to enable it to bear repetitive elastic deformations without being deformed irreversibly. These materials are known as elastomers or rubbers. Many properties of polymeric materials depend on the molecular weight and the degree of crystallization. Figure 10.25 shows the separate regions typical of oils, waxes, and polymeric materials in the solid state. POLYMERIC MATERIALS 145 10 3 100 50 0 10 4 10 5 Crystallinity (%) Molecular weight Liquids Greases Brittle waxes Tough waxes Hard plastics Soft plastics Soft waxes Figure 10.25 Sketch of a phase diagram for oligomers and polymers of ethylene. Thermal Properties Thermal properties are clearly affected by the structure of polymeric materials: polymeric bonds are much more dispersed than are bonds in other solids. This makes the thermal conductivity small, because there is little transmission of vibrations, and the specific heat is huge, because the molecular vibrations are independent, in contrast to other materials. They are, therefore, classified as thermal insulators. The more densely packed or crystalline the material, the higher is the conductivity and the lower the specific heat becomes. In the vibrations of the material, both whole molecules and pieces of molecules have mobility— an important difference compared to other thermal insulators. The two kinds of mobility determine macro-Brownian and micro-Brownian movement.
eBook - PDF- Xin-Jiu Wang, Qi-Feng Zhou;;;(Authors)
- 2004(Publication Date)
- WSPC(Publisher)
Chapter 5 Liquid Crystalline Polymers as High Performance Fiber and Structural Materials 5.1. INTRODUCTION Organic polymers can be used as structural materials because they may be as strong as inorganic materials such as iron and steel. Polyethylene is a well-known example. Polyethylene with the simple chemical structure of — (CH 2 CH 2 ) n —, has been found to show mechanical properties dependent on processing and morphology. In certain diluted (say 0.001 to 0.01 percent in xylene) conditions PE may form single crystals (Keller, 1957) from which a strong mat can be prepared. In most cases PE is melt-processed resulting in the very complex semicrystalline morphology of spherulites with chain-folded lamellae and interlamellar links (Hoffman et al ., 1976). Such PE samples often show moderate mechanical properties useful in applications such as film, foil, bottles, tubing, and coatings. With vigorous stirring of a high molecular weight PE solution (0.1 to 1 percent), “shish kebabs” are formed. They are very strong (stronger than steel based on weight) because the “shish” is formed of extended chains along the length of the shish (Pennings and Kiel, 1965; Pennings et al ., 1970). The more recently developed “gel-spinning” (Smith and Lemstra, 1979) of PE has resulted in fibers ( e.g. , “Spectra”) with extended-chains and very high tensile strength (up to ∼ 5 GPa) and modulus (up to ∼ 220 GPa). With a polymer the condition of processing and thus the morphology has a remarkable effect on the properties of polymeric materials as shown by the above examples. However, the highest tensile strength and modulus are possible only when the polymer molecules are the most extended and assembled in fibril form, and when the chains are aligned along the long 245 246 Liquid Crystalline Polymers axis of the fibril. In such conditions the molecular response to stretching will be bond extension and bond angle distortion. Both the processes have very high activation energy.
eBook - PDFPolymer Viscoelasticity
Stress and Strain in Practice
- Evaristo Riande, Ricardo Diaz-Calleja, Margarita Prolongo, Rosa Masegosa, Catalina Salom(Authors)
- 1999(Publication Date)
- CRC Press(Publisher)
states in concentrated solutions or in the molten state. Polymers with aro matic rings in the main chain connected by ester or amide groups take on the conformation of a rigid linear chain, giving rise to highly crystalline solids. When they are melted or dissolved, they partly maintain their order, passing through liquid crystal states before reaching the isotropic disordered liquid state. Typical examples of polymers with a rigid chain structure (main-chain LC polymers) are shown in Figure 2.17. Liquid crystals are classified into two groups known as thermotropics and lyotropics. Thermotropics are those that are formed in the melting of crystalline solids, and they can remain in the liquid crystal mesophase without decomposition, passing to the isotropic liquid state when subse quently heated. As their mesophases are turbid, the temperature at which the transition to the isotropic liquid phase takes place is called the clearing temperature. Lyotropic LCs form mesophases in concentrated solution when the concentration exceeds a critical value. Not all Crystalline Polymers pass through liquid crystal states. Flexible polymers, which adopt statistical coil conformations in the dissolved and molten states, pass directly to the isotropic liquid when dissolved or melted. Only if they are modified by introducing side mesogen groups could they form liquid crystal phases (side-chain LC polymers). The mesogen groups confer the liquid crystal characteristic; they have the form of rigid rods or discs, like those illustrated in Figure 2.18a. Figure 2.18b shows the possible 0 (c) Crystalline and Amorphous States 53 R ~ © -< 0 > -R r -@ < o _ @ . r R -@ -CH=CH-@ ~ R (a) R R R Side-chain LCP Main-chain LCP Figure 2.18 (a) Some typical mesogen groups, (b) Schematic representation of types of liquid crystal polymers according to the location of the mesogen groups: in the main chain (right) or as side substituents (left).
Index pages curate the most relevant extracts from our library of academic textbooks. They’ve been created using an in-house natural language model (NLM), each adding context and meaning to key research topics.
