In 1920, after systematically studying the structural properties of many polymers, the German scientist audinger (1881-1965) put forward the macromolecular hypothesis, and in his epoch-making article "on polymerization", he proposed that polystyrene, polyformaldehyde, natural rubber and other polymers have linear long-chain structure, This is still true today. Almost at the same time, scientists first reported X-ray evidence of polymer crystallization. At that time, the polymers studied were cellulose and its derivatives. The first crystalline polymer determined by X-ray diffraction is polysaccharide cellulose, whose crystalline unit is cellobiose. However, the cell size of polymer crystal obtained from these evidences is much smaller than the length of polymer chain, which is the normal cell size. So people asked stodinger, the polymer long chain should be expressed in the polymer cell. The polymer is composed of long chains. How does it discharge into this "small cell"? The density of this polymer crystal should be 50 times that of the normal cell
at the academic conference held in Duesseldorf, Germany, in 1926, on one side was stodinger, the initiator of the polymer concept, and on the other side were many famous scientists. They still opposed the existence of polymers and adhered to the so-called "micelle association theory", believing that substances such as cellulose, wool and rubber were the result of small molecules gathering together through strong interactions, such as hydrogen bonds. In his speech, stodinger told the audience that hundreds of organic chemists have confirmed the existence of polymer compounds, which are thousands of times larger than the organic compounds they are studying. Some scientists present commented: "Mr. Staudinger, we are so shocked, just as zoologists found an elephant 1500 feet long and 300 feet tall when traveling in Africa". The "macromolecule theory" was under intense siege at that time. This meeting is more like a celebration of the victory of low molecular theory, with only stodinger fighting alone. However, he insisted on the viewpoint of macromolecule discovered by himself, insisted on the viewpoint that the size of polymer has nothing to do with its cell size, and continued to carry out a lot of basic work with the adherents of polymer theory. In 1927, stodinger measured the molecular weight of polyoxymethylene by end group method, and determined that the crystal structure of polyoxymethylene belongs to orthogonal crystal system by X-ray diffraction. The fact that there are only 4 (CH2O) units in each cell indicates that there are only partial chain segments of polyoxymethylene in the cell. In 1930, stodinger derived the relationship between viscosity and molecular weight of polymer dilute solution, which gave people a powerful tool to observe macromolecules. During this period, stodinger worked with nger to design a simple device to measure the shape of macromolecules - the approximate length width ratio of long-chain molecules using flow birefringence technology. At the same time, X-ray crystallographers confirmed that along the stretching direction of the fiber axis, the crystal length of cellulose, that is, the long cycle, is much larger than the size of a single crystal cell, or even larger than the size of a single microcrystalline region, which further supports stodinger's view that the size of polymers has nothing to do with the size of crystal cells. At this time, American rothers obtained polymers with molecular weight of 20000 through condensation reaction, so the concept and existence of polymers have been indisputably demonstrated by experimental facts. In 1930, at the annual meeting of organic chemistry and colloidal chemistry in Frankfurt, Germany, stodinger's polymer theory was widely accepted, and people who insisted that cellulose and other low molecules became lonely. In 1932, stodinger published his first monograph, organic polymer rubber and cellulose. In the same year, stodinger's theory was widely recognized at the Faraday society. Stodinger is the founder of polymer science. In recognition of his outstanding contributions, stodinger, 72, was awarded the Nobel Prize in chemistry in 1953
polymer science has been established for nearly a hundred years, but how polymer crystallizes, its crystallization and structure are often puzzling. The polymer chain is very long. In the case of melt (or glass state), the chains are often entangled and curled. At first glance, the crystallization of such a system is quite difficult or impossible, even if the crystallization is quite irregular. However, this is not the case. Most polymers have a solid regular crystal structure inside the crystal. What is more surprising is that the crystallization rate of some polymers is often faster than that of low molecular materials. Until the end of the 20th century, people seemed to have some consensus on polymer crystallization and structure: ① when the melt was cooled below the equilibrium melting point (or heated to above Tg by glassy heating), the polymer chains with linear or regular structure were orderly arranged to the crystal surface one by one through the chain segments during crystallization. At this time, all sub chain segments with high scores developed for many years chose the same helical conformation, and all spirals were arranged and oriented in parallel, Then the polymer chain segments are regularly arranged from the side and stacked into crystals. At this time, thermodynamics is a driving force, and dynamic factors play a decisive role. At a specific temperature, it has the maximum development rate and forms a folded chain lamellar crystal structure. At this time, the crystal will not be able to untie the entangled chain in time, and the defects at the end of the chain will be excluded to the amorphous region. ② In the crystalline state, the molecular segments are arranged in parallel with each other. ③ Unit cell repeat units are chemical repeat units (monomers) or crystal structure repeat units that make up molecular chains. ④ When the polymer crystallizes from the melt or concentrated solution, the product has crystalline and amorphous micro areas, and the crystalline and amorphous micro areas have the same components. ⑤ Because the length of polymer chain is much larger than the size of microcrystalline, the revolutionary concept of chain folding in this field has been proposed: ortho regular folding chain model and non ortho irregular folding chain model (or the switchboard model). The latter polymer chain can enter and leave the crystalline and amorphous regions several times, so the classical knotted micelle model can still explain this phenomenon well. ⑥ The crystallization of polymer from melt or concentrated solution often produces spherulite structure, and the molecular chain is tangent to the spherulite, rather than along the radial direction. Polymer single crystals are generally formed in dilute solution. At present, lauritze Hoffman (LH) classical theory, which dominates the crystallization and nucleation of polymers, has been questioned. Several new crystallization theories and concepts have been proposed and have attracted widespread attention, but the debate is still in progress, and it will take time for it to be widely accepted. There is still a lack of quantitative description of how polymer processing conditions (temperature, pressure, stress deformation, etc.) affect the structural properties of products from the perspective of process theory design
polymer crystallization and structure points out that crystallization includes the crystallization process of polymer from different initial states, which can include thermodynamic and kinetic processes such as nucleation, growth and termination of polymer crystallization. Structures or structures of crystal emphasize more on studying the coordinate position, periodicity and symmetry of stacking of atoms, molecules, ions, etc. (for polymers, that is, chain segments or crystalline units) in the crystal, so as to obtain the shape, size and spatial structure information of polymer cell
polymer crystallization and structure is a monograph that comprehensively and systematically expounds polymer crystallization and structure. The whole book is divided into 16 chapters except "Overview". This paper briefly reviews the arduous process of the establishment of polymer science. At that time, because most scientists did not understand and misunderstood polymer, they almost strangled Polymer Science in the cradle. Therefore, Chapter 1 of this book focuses on the definition and characteristics of crystalline polymers and melting thermodynamics. Chapter 2 briefly introduces the basic theories and concepts of X-ray diffraction and geometric crystallography, and expounds the steps and methods of determining the crystal structure of small molecules and polymers. In Chapter 3 ~ 5, the applications of modern physical methods and means such as infrared spectroscopy, NMR and thermal analysis in polymer crystallization and structure are introduced respectively. Chapter 6 describes the structural morphology of crystalline polymers. Chapter 7 introduces the formation of polymer spherulites, an important form of polymer crystallization from melt and concentrated solution, and the mechanism of the formation of different spherulites. Chapter 8 discusses polymer isomerism in detail, which is divided into two categories: structural isomerism (or isomerism) and stereoisomerism. The two categories include four basic isomers, namely structural isomers (isomers), optical isomers, geometric isomers and conformational isomers. Structural isomerism (isomerism) refers to the fact that polymers have exactly the same chemical group, which should be adjusted and tightened; (2) The wear of the blade and fulcrum of the force point will increase the load error to varying degrees into isomerism (the molecular formula is the same), but its atoms or groups are connected (arranged) in different ways; Optical isomerization is due to asymmetric carbon atoms; Geometrically isomeric molecules have non rotatable double bonds or blocked non rotatable C-C single bonds; Conformational isomerism is formed by free rotation around C-C single bond. Configuration is not the case. The conversion of their atoms or substituents must be the destruction or re formation of chemical bonds. Configuration isomerism includes optical isomerism (enantiomer isomerism) and CIS trans (geometric) isomerism. Chapter 9 and 10 focus on the crystallization kinetics of polymers and the formation and structure of polymer crystals under the influence of different external field properties. Chapter 11 and 12 summarize the theory and Simulation of polymer crystallization, as well as polymer crystallization in confined systems. Chapter 13 and 14 describe the crystallization and structure of some important natural polymers and biodegradable polymers. In Chapter 15 and 16, the crystal structures of polyamide and crystalline conjugated polymers are reviewed. Relevant in the above areas "The Monographs on raw materials entering the factory and the monographs contributed by famous scholars Strobl, Schultz, geil, Wunderlich, tadokoro, Bassett and mandelkern provide very valuable knowledge and innovative concepts, which encourage us to write this book well. We sincerely hope that this book can help high score scientists and young students studying in this major to broaden their horizons in this field.
this article is excerpted from Mo Zhishen and other works Overview of polymer crystallization and structure (Beijing: Science Press, 2017.3)
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