Polymers are organic compounds having a unit cell called monomers. It has carbon as a basic element. they can be complex in nature depending on the number of monomers. The process by which polymers are joined is known as polymerization. Polymerization can be by addition or condensation method.
Addition polymerization has initial stage, chain propagation and termination stage.
Condensation is a process by which two unlike polymers are joined using a catalyst. Example is ethylene.
classification of polymers
the classification is based on the following:
Physical structure: this is accounted on the elasticity and viscosity of the compound. Polymers can exist in solid state with a glassy structure of crystalline and non-crystalline. The physical state depends on the temperature, molecular mass and chemical structure.
Chemical structure: this is based on the type of chemical group it possesses. Chemical groups such as; esters, carboxylic, Amines, Amides and hydroxyl groups. The consideration is made on the type of ring, such as open, close and trans-esterification arrangement.
Molecular structure: the linearity and branching of the monomers of a consideration. Polymers are covalently linked and interlinked.
Environmental response: this is the sensitivity of the polymeric material to external forces. External forces are temperature, heat and pressure. Thermoplastic and thermosetting nature is considered also.
Properties of Polymers
The properties of polymer vary with molecular structure and they include:
- Specific gravity: they have low thermal conductivity; low electrical properties; corrosion resistance; and low rigidity.
- Solubility: the solubility of polymeric material increases with temperature. Dissolving a low monomer causes an increase in volume due to expansion of the coil. The degree of viscosity depends on degree of expansion of coil. It should be noted that polymers under both permanent and plastic deformation. The permanence is caused by slipping of between adjacent molecules due to attractive forces.
- Thermoplastic: thermoplastics include materials that are softened on the application of heat. They are cooled in order in order to form a desired shape. The heating temperature should be above the decomposition temperature. They include: polythene, PVC and polystyrene. Some characteristics of thermoplastics are: resale value, low temperature and easily molded into shape. They have long chains.
- Thermosetting: thermosetting are re-softened once they are set and hardened. They are required in high structures with high rigidity strength value. At high temperature and rate of reaction; they lose strength. They have three dimensional arrangements. Examples includes; phenolic and expoxides.
- Fibres: these are filament like materials. Fibres can be found in animals, plants and vegetable.
- Rubber: rubber is elastomers. It is a petroleum product. It has high elasticity and good resistance to corrosion. It can be used in thermal insulation, adhesives and flexible tubing.
- Adhesives: they are designed to serve as bonding agents such as glue.
- Coating: polymers can be used as decorative and protective agents. it is use in conjunction with unsaturated oil. Examples are: stryrenenutandiene latexes
Er.R.K.Rajput, material science and engineering. S.K. katara and sons publishers, fourth edition 2013
Ferdinand .R and etel al. principles of polymer system. Taylors’s and plans pulishers. Fifth edition 2003.