Polymer Technology Of Chemical Engineering

CONTENT Polymer Thermoplastic polymer Thermosetting polymer Rubber Fibbers Molecular Weight Distribution

CONTENT Number Average Molecular Weight Random Alternating Block and Graft

Introduction Polymer: it is derived from Greek word poly means many and mar means parts of a polymer is substance which is obtained from the combination of many monomers

Thermosetting polymer & Thermoplastic polymer They can be softened or plasticized repeatedly on applicator of thermol energy without which change in properties of treated with certain preacaution. E.G polystrene , nylons, pvc etc. Thermosetting Polymer: They can be obtained in soluble and fusible forms in early or intermidate stages of their synthesis . But they get set or cured and become insoluble and infusible when further heated or thermolly treated the curing or setting process involves chemically reaction leading to further growth and cross linking of the polymer chain molecules and producing gaint molecule. E.G urea, diens resins etc.

RUBBER RUBBER: These polymers are chracterized by long range elasticity. They are rather weak

Plastic Plastic: These are usually much stronger then Rubber some of them are hard , horny, rigid, stiff and dimensionaly stable, while other may be soft and flexible. Plastic exhibits tensile strength ranging b/w 4000-15000 –psi. and elongation at break ranging usually from 20 to 200% of even highers. E.G= POL;YTHENE PVC POLYSTETR Etc.

FIBERS Fibers: Strongest of three types polymers metrial here among the natural polymer of industrial importance the fore most place is occupied by fibers, which may be either plant or animal orgin. Tensile strength (20,000 to 1,50,000 psi) Length diameter is 100:1. E.G = cotton , cellulose, silk etc.

Molecular Weight Distribution Molecular weight of polymer sample can be number average molecular weight, weight average, molecular weight viscosity average molecular weight. Let us consider we have polymer sample having total number of molecular =n there are various type of molecule present in the polymer sample and total weight of sample =w n=n1+n2+n3……+ni=Eni n1 of them have m1 molecular weight in sec.a n2 of them have m2 molecular weight in section b. ni molecules have Mi molecular weight in every section.

Random Alternating Block And Graft Random Alternating Block and Graft: when two different repeat unit in co-polymer are distributed at random throughout the chain the polmer is called co-polymer . In certain co-polymer a more ordered sequence of repeat unit is seen and than these co-polymer are termed alternating block or graft co-polymer. when two repeated unit are distributed alternatly throughout the chain, the polymer is term and alternating co-polymer. when sequence or block of an one repeats unit is followed by a block of another repeat unit whichn in turn is followed by a block ofv the first repeat unit and soon, the polymer is called a block co-polymer. Block co-polymer are,therefor linear molecules in which both repeat unit Are consicutivily distributted inj fairly long sequence. Graft co-polymer on the other hand, are branched molecules where the man chain is made entirely of the branch chain are made of yet another unit

Free Radicals Free Radicals: free radical are atom ions or molecule that contain an unpaired electron. make them unstable and highly reactive in a process called oxidation. Free radical steel e –s from other molecules structure of the affected molecule structure of the affected molecules may sets off a chain reaction by damaging the structure.

D

DEGREE OF POLYMERIZATION The degree of polymerization is the on. of repeat unit present in a polymer molecule the size and the molecular weight of the polymer molecular depend on the no. of repeat unit on the degree of polymerization For Exes : 5 molecules of ethylene (-CH2-CH2-) add on to each other to form a single molecule of polythene [- CH2-CH2-] 5 here the repeat unit are (-CH2-CH2) so the degree of polymerization in 5.

Chain growth polymerization or addition polymerization Chain-growth polymerization or chain polymerization is a polymerization technique where unsaturated monomer molecules add onto the active site of a growing polymer chain one at a time. Growth of the polymer occurs only at one (or possibly more) ends.

Diagrame

Effect of molecular weight on polymer properties Almost all properties of a polymer depend on the molecular weight and its distribution, that is, low and high molecular weight polymers will have vastly different mechanical and thermo-physical properties. For example, polymeric materials consisting of a rather small number of repeat units (often called oligomers1) will be rather soft or even liquid and will possess little or no strength whereas polymeric materials of high molecular weight will be solid, and have much improved mechanical properties. One usually observes a steep rise in the mechanical and visco-elastic properties with increasing molecular weight until a certain molecular weight is reached, beyond which the properties are nearly independent of the chain length, that is, all properties will eventually reach an asymptotic value. It was found, that the molecular weight dependence of many properties can be described by an expression of the form

Bulk Polymerisation Bulk polymerization or mass polymerization is carried out by adding a soluble radical initiator to pure monomer in liquid state. The initiator should dissolve in the monomer. The reaction is initiated by heating or exposing to radiation. As the reaction proceeds the mixture becomes more viscous. The reaction is exothermic and a wide range of molecular masses are produced. Bulk polymerization is carried out in the absence of any solvent or dispersant and is thus the simplest in terms of formulation. It is used for most step-growth polymers and many types of chain-growth polymers. In the case of chain-growth reactions, which are generally exothermic, the heat evolved may cause the reaction to become too vigorous and difficult to control unless efficient cooling... Bulk polymerization has several advantages over other methods, these advantages are[citation needed]: The system is simple and requires thermal insulation. The polymer obtained is pure. Large castings may be prepared directly. Molecular weight distribution can be easily changed The product obtained has high optical clarity Disadvantages[citation needed]: Heat transfer and mixing become difficult as the viscosity of reaction mass increases. The problem of heat transfer is compounded by the highly exothermic nature of free radical addition polymerization. The polymerization is obtained with a broad molecular weight distribution due to the high viscosity and lack of good heat transfer. Very low molecular weights are obtained. Gel effect. For reducing the disadvantages of bulk polymerization, the process can be carried out in a solution. This is known as solution polymerization. [1]

Bulk Polymerisation

Amit Kr. Kashish kumar JaiDev