Lesson 11 Polymer Chemistry (1).pptx

Lesson 11 Polymer Chemistry (1).pptx

1. Welcome to World University Of Bangladesh Department of Civil, EEE & Textile Course title: Chemistry Course Code: CHEM 105, 305 & 103 Presented by Md. Shahidul Islam Lecturer in Chemistry Basic Science Division

2. Topics: Polymer Chemistry Definition of Polymer, Mer , Monomer Basic criteria that monomers generally fulfill in products high polymers- Classification of Polymer- Addition polymer & Condensation polymer Distinguish between addition and condensation polymerization Crystalline melting point (Tm ) Glass Transition Temperature ( T g ) Application of polymers

3. Polymer Definition: Polymer is a large molecule built up by the repetition of small and simple chemical units and contains high molecular Weight. For example: CH 2 - CH 2 - CH 2 - CH 2 -Polyethylene Mer : The repeating unit in a polymer chain is known as mer. It is a simple chemical entity and does not exist in normal condition.   For example : I n polyethylene the repeating unit is -CH 2 -CH 2 -, which is not existence in normal condition. Thus, -CH 2 -CH 2 - is a mer . Monomer: The simple compounds from which polymers are obtained are called monomers . For Example: n CH2=CH2 → [- CH2-CH2-CH2-CH2-]n Monomer Polymer

4. Basic criteria that monomers generally fulfill in products high polymers- -   1 ) The monomers which undergo polymerization reaction must have poly functional groups. 2 ) Small polymeric unit must have stability. 3 ) The small unit containing cyclic structure does not give polymerization reaction. So they must have non cyclic existence.    

5. Classification of Polym er Classify polymers according to their physical properties---   Polymers are classified on the basis of their physical properties or on the action of heat are on three categories- i . Thermoplastics ii. Elastomers iii. Thermosetting   Classify polymers on the basis of structural units---   Polymers are classified on the basis of structural units are two categories- i . Homo polymers ii. Copolymers Classify polymers on the basis of mode of synthesis---   Classify polymers on the basis of mode of synthesis are two categories- i . Addition polymers ii. Condensation polymers

6. Addition polymer & Condensation polymer Addition polymers: The polymerization process in which the formation of polymers from monomers without the loss of Small molecules, i.e.; in which molecules of monomers are simply added together is called additional polymerization and such polymers are known as addition polymer . For example-- The molecules of ethylene monomer can add on two form polyethylene , in which, the structural identity of ethylene is retained. n CH2=CH2 → [-CH2-CH2-CH2-CH2-]n Condensation polymers: The polymerization process in which the formation of polymers from the poly functional monomers of organic molecules with the elimination of some small molecules such as, water, HCl , NH 3 , etc. is called condensation polymerization and the product is called condensation polymer . For Example: n HO-CH 2 -CH 2 -OH + n HO-C-CH 2 -C-OH → HO-(- CH 2 -CH 2 -O-C-CH 2 -C-O- ) n -H + (n-1)H 2 O Ethylene glycol Malonic acid

7. Distinguish between addition and condensation polymerization-   Addition polymerization Condensation polymerization   1 Polymers are formed by addition reaction without elimination of any species. 1 Polymers are formed by the indentation of two or more monomers with the elimination of small molecules such as –H­ 2 O,NH 3 ,HCL etc. 2 It is a rapid process. 2 It is very slow process. 3 Addition polymerization proceeds by chain mechanism. 3 Condensation polymerization proceed by stepwise inter molecular condensation. 4 Polymers of high molecular weight obtained by additional polymerization. 4 Low molecular weights polymers are obtained by condensation polymerization. 5 Chain length is independent of time. 5 Chain length is dependent on time. 6 The rate of addition polymerization reaction is controlled by the addition of inhibitor or retarder. 6 The rate of condensation polymerization reaction is not controlled by such chemicals.

8. Crystalline melting point (Tm ): If we take a sample of a crystalline solid and measure its volume change with temperature , we will get a plot as shown in the following fig . It can be see from the plot that at the melting point (Tm) there is an abrupt jump in the volume change of the material. This melting temperature is known as crystalline melting point . A crystalline substance can exist as a crystalline or as a molten liquid with solid to liquid transition occurring at a temperature known as the crystalline melting point (T m ).

9. Glass Transition Temperature ( T g ): The highly disordered solids often show rubber-like properties if the temperature is high enough for a large amount of segmental motion to exist. On the other hand, if the melt of a non- crystallizable (amorphous) polymer is cooled it becomes more viscous and flows less readily. If the temperature is reduced low enough it becomes rubbery and as the temperature is reduced further it becomes a relatively hard and elastic polymer glass. The temperature at which the polymers undergoes the transformation from a rubber to a glass is known as the glass transition temperature ( T g )   Below the T g , the polymeric states as glassy and above the T g , the polymeric states as rubbery. Any material which can be cooled sufficiently below its melting temperature without crystallizing will undergo a glass transition.

10. Application of polymers: Medicine : Many biomaterials, especially heart valve replacements and blood vessels are made of polymers like Dacron, Teflon and polyurethane . Consumer Science: Plastic containers of all shapes and sizes are light weight and economically expensive than the more traditional containers. Clothing, floor coverings , garbage disposal bags and packaging are other polymer application . Industry: Automobile parts, windshield for fighter planes, pipes, tanks, packing materials , insulation, wood substitutes, adhesive, matrix for composites and elastomers are all polymer application used in the industrial market . Sports: Playground equipment, various balls, golf clubs, swimming pools and protective helmets.

11. Thank you