Talking about polymer chemistry and its learning

Talk about polymer chemistry and its learning> Xiao Weidong (College of Chemistry and Materials Science, Hubei University, Wuhan, Hubei 430062, China) provides an effective method to learn polymer chemistry - migration method.

Polymer chemistry is the basis of polymer science. Polymer chemistry studies molecular design, synthesis, and modification of macromolecular compounds, provides new compounds for macromolecular scientific research, and provides new materials for the national economy. In recent years, with the development of interdisciplinary development, distant subjects such as mathematics, physics, biology, and related disciplines such as organic chemistry, analytical chemistry, physical chemistry, chemical engineering, and inorganic chemistry have involved the study of polymer science from the perspective of the discipline. The work has made the content of polymer chemistry more extensive and has become a new scientific field with multiple functions and interdisciplinary areas.

1 The main research areas of polymer chemistry Polymerization and polymerization methods are one of the main areas of polymer chemistry research, and their research results are directly related to the polymer polymerization industry. The study of the free radical polymerization mechanism and initiation system and the reaction kinetics of the whole polymerization process has promoted the synthesis of new polymer materials and the enhancement of industrial polymerization techniques. The research on coordination polymerization, especially the work of rare earth catalysts on synthetic rubber, has promoted the formation of synthetic rubber industrial technology and improved the production technology of large-scale polymer industrial production. Cationic living polymerization, anionic ring-opening polymerization and block and star polymer synthesis methods and new polymerization reactions such as "group transfer polymerization", molecular chemistry show a new posture. Synthesis of polyimides, liquid crystalline polymers, and compounds such as polyaryl ketones, polyaryl ethers, and polyaryl sulfones, which have been studied in polycondensation reactions, has provided new materials for the electronics industry and aerospace industry.

Functional polymers are another important area of ​​polymer chemistry. It studies the molecular design and synthesis of various new functional compounds, the relationship between structure and function, and the application technology as a new material. It involves reactive polymers, ion exchange resins, polymer catalysts, solid electrolytes, liquid crystal polymers, reaction separation membranes, medical macromolecules and a variety of optical (high transmittance, high refractive index, nonlinear optical properties, etc. ) Electro-active polymers (electrical conductivity, piezoelectricity, electromagnetic wave absorption, etc.), magnetic (organic polymer magnetics), etc. The research work in this field is mainly for the society to seek out special new materials, study the relationship between the molecular structure and the formation of various special macroscopical properties, and it has strong multidisciplinary characteristics in the discipline.

The study of natural polymers is another branch of polymer chemistry. At present, the research on natural polymers in the world is far less than the research scale of synthetic polymers. However, natural polymers are natural and inexhaustible macromolecular resources given by us. Under the threat that petroleum resources will be depleted in the future, The formation, modification and use of natural polymers are necessary. Our work in this area mainly includes studies on cellulose, lignin, chitin, starch, silk, eucommia gum, animal skins and hairs, and studies on the chemical modification of cellulose and the research on the liquid crystal phase of cellulose. Research on medical chitin material research, leather research, sheep and rabbit hair modification research, and research on gutta percha material. The separation, extraction and chemical modification of natural resources from different natural resources, as well as the application of various materials, will enable various natural polymers to be used as raw material for the next generation of synthetic polymers.

2 The current most active research field in polymer chemistry The current most active work in polymer chemistry is the study of polymerization and polymerization methods, which are mainly embodied in the polymerization reaction, polycondensation reaction, polymerization method and process of vinyl monomers and cyclic monomers. And other fields.

The living polymerization of vinyl monomers and cyclic monomers can control the molecular weight and molecular weight distribution, and can also be used to prepare block copolymers, telechelic polymers and star polymers having various properties, as well as to study the structure and properties thereof. The relationship between them provides convenience and is a type of polymerization reaction that should be considered. Living polymerization includes anionic living polymerization, cationic living polymerization, coordinated anion living polymerization, radical living polymerization and active ring-opening polymerization and the like. Coordination polymerization is one of the main methods currently used in the industry to produce high molecular polymers. In order to cooperate with the development of the polymer industry and to provide high-quality macromolecular polymers with excellent properties, attention should be paid to the research of new polymerization catalysts and copolymerization catalysts. In recent years, internationally, “the production of high-performance polymers with different properties and different uses, such as plastics and rubbers, has been transformed from different catalysts by using the same polymerization process line with several basic vinyl monomers as raw materials”. The new process concept of flexible production line should actively carry out exploration in this area.

Group transfer polymerization is a new kind of polymerization reaction, which is also a kind of living polymerization. It is characterized by mild conditions, polymerization at room temperature, easy control, and great flexibility. It is an important research topic for the development of polymer cutting technology. Ring-opening displacement polymerization is another new type of active coordination polymerization reaction, and attention should be paid to the follow-up study of this polymerization reaction.

Monomerization and ordering of the polymerization reaction will be one of the means to obtain a high-performance village material, including alternating copolymerization, template polymerization and crystal polymerization. The main method for achieving this polymerization is to form a charge transfer complex or ion pair between monomers or monomer and template polymer. Template polymerization has strong biomimetic features and is an important research area for obtaining homopolymers and copolymers. The initiation of the system is the core of the polymerization study. The new initiation system not only improves the polymerization conditions, controls the polymerization process, but also allows the development of new polymer varieties. Important chemical initiation systems include oxidation-reduction and charge-transfer complexation initiation systems, coordination initiation systems for metal center atoms, ion initiation systems, and photosensitive initiation systems. There are also physical initiation methods such as radiation initiation, plasma initiation, and microwave initiation. It is necessary to pay attention to the study of different initiation methods and their best suitable application occasions, so as to search for new production methods, new polymer compounds and new production processes for new polymer materials.

The focus of basic research on polycondensation reactions is to control the polymerization reaction, improve the polymerization conditions, develop new polycondensation reactions, and prepare high-performance or special-function polymers. Important topics in this field include the active polycondensation reaction, which is to improve the polymerization conditions by increasing the activity of the reactants, such as the activation of carboxylic acid, the silanization of nucleophilic monomers, the use of phase transfer catalysts, etc., and the latent catalysts in the polycondensation reaction. And closed monomer research is an important means to control the cross-link curing speed, widely used in coatings, adhesives and strong plastics and other fields.

In order to overcome the problem of environmental pollution, some solvent-free polymerization methods have become a research hotspot. Among them, emulsion polymerization is one of the research focuses. Through emulsion polymerization, monodispersed latex, various polymer microspheres, functionalized latex and compounded latex can be prepared. Emulsifier-free emulsion polymerization is also an important method. Solid phase polymerization, gas phase polymerization, and LB film polymerization (monolayer polymerization) are also noteworthy. In particular, the polymerization of LB films has broad application prospects in molecular electronics, microelectronics, integrated optics, and lithography. In addition, in order to promote the development of the polymer industry and meet the requirements of various special processes, attention should also be paid to exploring other new polymerization methods. In recent years, due to the penetration of the biosphere into the polymer chemical industry, "microbial polymerization" and natural enzyme-catalyzed "enzyme-catalyzed polymerization" have emerged. This is a new sign of polymerization research and should be noted.

3 The use of migration theory for good interactions between macromolecular chemistry learning in psychology is called migration, the promotion of the role of the transfer is called positive migration, seize the low molecular chemistry on the positive migration of polymer chemistry, it is easy to learn polymer Chemistry. Like low-molecular compounds, high-molecular compounds are also linked by atoms through chemical bonds, and the chemical nature of substances is the movement behavior of bonding or bondable electrons. It can be seen that the causes and research methods of chemical properties of high and low molecular compounds should be consistent. For example, a polyethylene with a molecular weight of up to 300,000 can be oxidized, halogenated, and cracked, with similar chemical properties to only thirty ethane. The polymer compound also has properties that some low-molecular compounds do not have at all, such as the elasticity, swelling properties of the linear polymer, and abnormality in the dilute solution. These problems can be solved by further in-depth analysis and understanding of the relationship between the nature of the compound and the structure, and to find out the specificity under the new conditions. For example, a linear polymer chain with a large aspect ratio cannot be densely arranged as a fine lattice like a low-molecular compound, and inevitably generates some loose segments, so that a reversible deformation occurs under the action of an external force (elasticity). The definition of basic concepts in molecular chemistry, the nomenclature, composition, structure, and preparation reactions of macromolecular compounds are ubiquitous.

3.1 The relevant content of the introduction part of the introduction is “Basic knowledge of polymer chemistry, which is the key content to grasp. From the formation process of polymer compounds, the principle of formation and the law of the evolution of low-molecular to high-molecular properties, it is important to understand the important concepts in polymer chemistry, such as the interrelationship between chain segments and monomer segments and segmental motion. The main chain structure is used to classify the composition and structure of the polymer compound, and then classified according to the process performance in order to understand the application of the polymer compound. While classifying, it is also required to compare the materials such as fibers, rubbers, and plastics in terms of the molecular weight size, mechanical strength (tensile strength and elasticity), physical structure, polymer generics, and application properties. Higher understanding and understanding of application performance relationships. Controlling low-molecular-weight compounds, according to the structure, configuration and conformational levels, the order of bonding, the bonding method, the spatial status of the substituents, and the conformational relationship between monomers were studied in detail to further deepen the understanding of the relationship between the structure and properties of macromolecular compounds. The formation process of the polymer, the relationship between the physical state and the physical and mechanical properties are carefully discussed.

3.2 Free Radical Polymerization Free radical polymerization is one of the most clearly studied types of polymerization reactions, and it is also a key content to grasp. It is required to carefully analyze the motion of the double bond electrons in each monomer molecule, and analyze the various types of monomers according to their electronic properties and steric hindrance to find out the suitable type of polymerization reaction. From the knowledge of the reaction process of hydrocarbon radicals, analyze the polymerization of monomers, translate the radical reaction of radical polymerization, and discuss the speed determination step, type of chain transfer reaction, chain length reaction and chain termination. Reactions and the termination of deuteration and the termination of the deuteration of the competition, reaction trends, the ability to compete with the monomer structure and reaction conditions, etc., in order to deepen the understanding of the principle of free radical polymerization. Since the chain initiation reaction is a speed determination step of radical polymerization, it is required to clarify the types, activities, efficiency, and influencing factors of the common initiator, the relationship between the activity of the peroxide initiator and the molecular structure, and the like.

The thermodynamics and kinetics of free radical polymerization determine the possibility of polymerization of monomers, the rate of polymerization, the effect of the constituent elements of the polymerization system on the composition, structure, and properties of the polymerization products. From the research methods of kinetic thermodynamic phenomena of low-molecular-weight compounds, the basic knowledge of the dynamics of the basic assumptions of dynamic research, dynamic equations and their significance, macroscopic dynamic phenomena, and the causes of natural kinetics are naturally understood. ,self-taught. Correctly understand the significance of the kinetic chain length and degree of polymerization, the difference and the relation, the influence of the chain transfer reaction on the degree of polymerization (including the phenomenon of inhibition and induction) and the influence of reaction temperature on the degree of polymerization. From the basic concept of thermodynamics, the basic theory and the basic relationship 3.3 Analysis of free radical copolymerization application Transfer thinking from the relative rate of monomer into the polymer (copolymer) deduces the composition of the copolymer, the composition of the type and the ideal copolymer , Alternating copolymerization, non-ideal point of non-ideal copolymerization monomer composition, activity of the composition of the copolymer, and based on this understanding of several common copolymers and their polymerization. The relative activity of homopolymerization and copolymerization of monomers is used to interpret the concept of susceptibility rate, discuss its physical and chemical significance, and further discuss the influence of external conditions such as temperature and pressure on its qualitative and quantitative relationship between chemical structure and chemical activity. The relationship discusses the relative activity of monomers and free radicals, and thus discusses in detail the possibility of copolymerization of monomers and the effect on the composition of the copolymer. 3.4 Free Radical Polymerization Polymerization Methods Free radical polymerization methods are briefly described in general textbooks. Pang Zuren has more to say in polymer chemistry, especially the rapid development of emulsion polymerization, learners can not be ignored. The method of synthesizing low-molecular-weight compounds is used to carry out the migration of the polymerization method against the migration phenomenon of the composition, structure and properties of the polymer compound. From the free radical polymerization mechanism, the phase state of the polymerization system, the polymerization process, and the structure and properties of the polymer, a comparative discussion was made. From the main components of the emulsion polymerization system and its effects, the characteristics of the elementary reaction of the emulsion polymerization, the composition change rules in each reaction stage, and the polymerization site, the nucleation mechanism and other aspects are discussed. The rules, characteristics, and application prospects of emulsion polymerization are studied, and the most important features, such as high polymerization rate, high polymer molecular weight, and relatively concentrated distribution, are reasonably explained.

3.5 Ionic Polymerization There are two kinds of large positive migrations, namely the migration of low molecular synthesis to macromolecular synthesis and the migration of free radical polymerization to ionic polymerization. The relationship between the monomer structure and the polymerization reaction is discussed from the activity relationship of the active center (ion), and the types and characteristics of the ionic polymerization monomer and the initiator are analyzed to prepare for studying the mechanism of ion polymerization and ion polymerization. A comprehensive comparison of the properties of free radical polymerization, cationic polymerization, and anionic polymerization of the monomer active intermediates yields the types, characteristics, and effects on the structure and properties of the polymerization products. Changes, and explain the formation of reactive polymers and stoichiometric polymerization in anionic polymerization. The influence factors of ion polymerization were summarized from the aspects of solvent polarity, polymerization temperature and the nature of counter ions, and were compared with the results of free radical polymerization. The situation of ring-opening polymerization is more complicated, and the mechanism of ring-opening polymerization under different conditions of different monomers or the same kind of monomer is often not the same, so it needs to be studied one by one.

3.6 Coordination Polymerization Coordination polymerization is not mature enough to understand the content, but only requires basic understanding of its basic reactions and basic concepts. From the complex coordination between monomer and catalyst, the coordination process, the catalytic mechanism, the stereochemistry of coordination catalysis and the influence of monomer catalyst structure on the polymerization were studied. The composition, type, nature, and mode of action of the Ziegler-Nyta initiator. Taking the coordination polymerization of a typical monomer propylene as an example, the type of coordination polymerization initiation system, the influence of the ratio on the polymerization rate, the average molecular weight, and the three-dimensional structure of the product were studied, and the mechanism of coordination polymerization was further understood.

3.7 Gradual polymerization Gradual polymerization is a non-linked ion polymerization process that can be gradually improved from the following aspects.

From the discussion of the migration of condensation reaction to polycondensation reaction, the discussion of the control of free radical polymerization reaction, and consciously entering into the characteristics of polycondensation reaction, mechanism, degree, equilibrium constant and its effect on the degree of polymerization of polycondensation polymer, can raise the awareness of polycondensation reaction. Understanding the structural reasons of the polycondensation reaction from the influence of the functionalities on the polymer structure, and proceeding from the production, processing, and application of polymers, understanding the important role of the bulk polycondensation prepolymers and the influence and control of the gelation on the polymerization reactions method. From the stepwise polymerization kinetics and thermodynamic characteristics, we must understand the necessary basic conditions to design some specific preparation methods, and in turn deepen the understanding of the stepwise polymerization reaction from the specific implementation of the design preparation method. 3.8 Chemical Reaction of Polymers From the chemical composition and structure of polymers, the relationship between low-molecular organic compounds and chemical properties is checked, and the chemical reactions that the polymers may undergo and the ease with which the reactions are carried out are evaluated, and reasonable methods are proposed for further analysis. Promote the scope of application of polymer materials and the development of new polymer materials, broaden the thinking of learners to research and apply polymer materials.