constitutePolymer chainThe combination of atoms that determine the polymer structure to be connected in a certain way is called structural unit.When the structural unit is composed of single elementidentical, but when the electronic structure is changed, the structural unit can be calledMonomer unit、Repeat unit(Repeating unit), orChain link（Chain element）。
Structural Unit: compositionPolymer chainThe combination of atoms that determine the polymer structure to be connected in a certain way is called structural unit.The basic unit of a monomer molecule entering a macromolecular chain through polymerization.The element composition of the structural unit can be the same as or different from that of the monomer.[1]
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Repeat structural unitThe smallest basic unit on the macromolecular chain that can be repeated in chemical composition and structure, which can be referred to as repeating unit or chain link for short.It is based on unit structure and appears repeatedly in the polymer chain.
Monomer unit: the structural unit with identical composition of elements formed by monomer molecules through polymerization.
When the structural unit is composed of single elementidentical, but when the electronic structure is changed, the structural unit can be calledMonomer unit、Duplicate unit(Repeating unit), orChain link（Chain element）。
Degree of polymerization: Degree of polymerization is an index to measure the size of polymer.There are two representations: 1) expressed by the number of structural units in the macromolecular chain;2) Expressed as the number of repeating units in the macromolecular chain.
The degree of polymerization is also a parameter to characterize the size of the polymer. It refers to the number of repeating units contained in the polymer, and its value is proportional to the molecular weight.The degree of polymerization also has statistical average significance.Molecular weight and molecular weight distribution are important factors affecting material properties.Experiments show that only when the molecular weight or degree of polymerization of the polymer reaches a certain value can it show a useful mechanical strength, which is called the critical degree of polymerization.The degree of polymerization of different polar polymers has different effects on the mechanical strength. The critical degree of polymerization of strong polar polymers is 40,Non-polar polymer80, and the weak polar polymer is between the two.It can also be seen from the figure thatMolecular weight of high polymerThe use and processing properties of polymers should be comprehensively considered for the control of.Because the higher the molecular weight of the polymer, the higher the mechanical strength.However, with the increase of molecular weight, the interaction force between molecules also increases, leading to the increase of high-temperature flow viscosity, which makes processing and molding difficult.The molecular weight distribution also has a significant impact on the processing and use of polymer materials. Generally speaking, a narrower molecular weight distribution is conducive to the improvement of processing control and use performance, such as synthetic fibers and plastics.But some polymers are just the opposite, such asNatural rubberAfter plasticating, the molecular weight is reduced and the distribution is widened to overcome the original processing difficulties and facilitate processing and molding.
N represents the number of repeat units, also known as the number of links, equal to the degree of polymerization.[1]
Polymer materials
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Polymer materials are made ofrelative molecular massMuch higher than ordinary organic compoundsPolymer compoundA substance made from the main ingredients.Generally, the relative molecular weight of organic compounds is only tens to hundreds. High molecular compounds are polymers with a relative molecular weight of tens of thousands or even millions through polymerization of small monomers.The huge molecular weight endows these organic polymers with new physical and chemical properties: they can be rolled into films;It can be spun into fiber;Components that can be extruded or molded into various shapes;It can produce strong bonding ability;It can produce huge elastic deformation;It has many unique properties such as light weight, insulation, high strength, heat resistance, corrosion resistance, self lubrication, etc.So people make it into a series of excellent and colorful products such as plastics, rubber, fiber, composite materials, adhesives, coatings, etc., making it an indispensable and irreplaceable material for all sectors of industrial and agricultural production, scientific research, and all links of human life.
The properties of polymer materials are the concrete reflection of their internal structure and molecular motion.Master the relationship between the structure and performance of polymer materials, and provide reliable basis for correct selection and rational use of polymer materials, improving the performance of existing polymer materials, and synthesizing polymer materials with specified properties.
The polymer chain of polymer materials is usually more than 10000,Polymer chain structureWith many polymer chainsAggregate structureIt forms a special structure of polymer materials.Therefore, polymer materials haveLow molecular compoundIn addition to its structural characteristics (such as isomers, geometric structures, rotational isomers), it also has many special structural characteristics.Polymer structure is usually divided into two parts: chain structure and aggregate structure.Chain structure refers to singlePolymer compoundMolecular structure and morphology, so the chain structure can be divided into short range and remote structure.The short-range structure belongs to the chemical structure, also known as the primary structure, including the type and arrangement of atoms in the chain, the types of substituents and end groups, the arrangement order of structural units, the type and length of branch chains, etc.Remote structure refers to the size and shape of molecules, the flexibility of chains and the conformation of molecules in the environment, also known as secondary structure.Aggregated structure refers to the overall internal structure of polymer materials, including crystal structure, amorphous structure, oriented structure, liquid crystal structure and other related molecular stacking in polymer materials, collectively referred to as tertiary structure.[2]
