Polymer

Polymer

1. 1. What is Polymer

   • It is a macro-molecule consists of repeated chemical units called Monomer, joined together to form a chain, Polymer usually contain more than five monomers,some contain 100 or 1000 of monomers in each chain, monomers are bonded together by Covalent-bond. Polymer can be classified as plastic(resin), Elastomers(rubber) and Fibers(nylon)
   • Monomer: the small individual repeating units/molecule are known as monomer A-A-A-A-A-A A: is the monomer
   • Polymerization: The process in which the monomer molecules are linked together to form a big polymer molecule  As ethylene to poly-ethylene 

2. 4. Classification of Polymer

   • Monomer
     • Homopolymer : consists of monomer of the same type
     • Copolymer: have different repetitive unit 1. Random A,B 2. Alternating A,B 3. Block A then Block B 4. Graft: chain of B grafted onto "A" backbone
     • Homo-polymer
     • Co-polymer
   • Structure
     • 1. Linear 2. Branched 3. Cross-linked  4. Network
     • Linear
     • Branched
     • Cross-Linked
     • Network
   • Arrangement
     • Isomerism: Two compounds with same chemical formula have quite different structure 
     • Tacticity: is the position of the side group (-R) in the polymer chain 1. Isotactic: R group on the same side 2. Syndiotactic: R group on different sides 3. Atactic R group Random
     • Isomers
     • Tacticity
   • Origin
     • 1. Natural polymer: obtained from nature as silk,wool,natural rubber 2. Semi-synthetic: obtained by simple chemical treatment of natural polymer to improve their physical properties (ex tensile strength) as cellulose acetate  3. Synthetic polymer: polymers synthesized in laboratory from low molecular weight compound as nylon,PVC,synthetic rubber,polyethylene, polystyrene
     • Natural
     • Semi-synthetic
     • synthetic
   • Thermal Response Tm & Tg
     • 1. Thermoplastic: linear or branched polymers that turn to liquid (soft) when heated and when cooled they freeze to glassy(hard) state. They can remelted and reformed.Ex: polyethylene, PVC, Teflon, Polypropylene(PP), Polystyrene (PS) . They Never achieve 100% crystallinity, they are semi-crystalline with both Crystalline and Amorphus
     • 2. Thermosetting: Cross linked polymers when heated they are chemically decomposed, so they can't be recycled. They can't be remelted or reformed . They are stronger than thermoplastic polymers. Ex: Bakelite, phenolics (adhesion,coating), Amines ( electric molding).
     • Elastomers: They are themosets or thermoplastic Ex: Natural rubber can be thermoplastic or themoset depending on the structure.
     • Tm: melting temperature Tg : glass transition temperature Tg: is the temperature at which the polymer transform from glass state(hard) to rubbery state(soft). below Tg polymer is hard. As Tm,Tg inc. ,the stiffness inc., and intermolecular force inc. Crystalline phase characterized by Tm Amorphus phase characterized by Tg Crystalline - Semi-crystalline - Amorphus - Liquid Amorphus polymer : higher viscosity than semi-crystalline and less chemical resistance and better for weather resistance Ex: PVC, PS (Polystyrene) Semi-crystalline: lower viscosity and more brittle than amorphus Ex: PE,PP,PET
     • Thermoplastic
     • Thermoset
     • Elastomers
   • Mode of Formation
     • Chain-Growth(Addition):  Polymers formed by the addition of monomers repeatedly without  removal of by-product.Ex: Teflon(PTFE), PE,PP, PVC.Reaction Mechanism:1. Initiation: broke the double or triple bond by addition of heat,then it reacts with another repeat unit to form chain.2. Propagation: the growing of the chain, maybe forming branches on the polymer chain.3. Termination:end of the reaction by combination or disproportion.Combination: involves the coupling of two growing polymer chain radical.Disproportion: the two chains coming together, one chain gain "H" from the second chain and double bond is formed in the second chain.
     • Step-Growth (Condensation): after adding of monomers a small molecule( like water,alcohol,ammonia) is condensed(formed) as by product. Ex: Polyamides(Nylons), Polyesters(PET). Step-growth reactions are slower than Chain-growth
     • Chain-Growth (Addition)
       • Polymerization Techniques
         • 1. Bulk Polymerization  2. Solution Polymerization 3. Suspension Polymerization 4. Emulsion Polymerization 5. precipitation Polymerization
     • Step-Growth (Condensation)
       • Polymerization Techniques
         • 1. Melt Poly-condensation  2. Solution Poly-condensation 
   • Molecular Weight
     • Molecular weight used as indication for many characteristics in the polymer as toughness,melting and freezing point,shape of distribution,solubility and chemical resistance.

3. 3. Adv. & Disadv. of Polymers

   • Advantages  1. cheap 2. lightweight 3 tough 4.easily to shape 5.chemical resistance 6. Thermal & electrical insulation
   • Disadvantages 1. Low stiffness/Strength 2. Limited temperature range 3. High thermal expansion coefficient 

4. 5. Polymer Synthesis (Process)

   • Extrusion: the polymer enters in the hooper in solid state and by the motion of the screw and compression, the polymer is melted and then the molten polymer transfer to molding to become the final product. Blow Molding as in plastic bottles 
   • Extrusion
   • Molding
     • Injection Molding
     • Blow Molding
     • Compression Molding

5. 2. Raw Materials

   • From crude oil and natural gas we can obtain ethylene, propylene, styrene and then transform them to PP,PE,PS,...