Organic Mechanism By: Duyen Vuong 12D

Content Organic Mechanism Vinyl polymers Low density poly(ethene), LDPE –Free radical formation High density poly(ethene), HDPE –Ziegler- Natta catalyst Bibliography

Organic mechanisms To manufacture of poly(ethene) used to make polymers from vinyl monomers Mostly covalent bonds 2 types: –LDPE –HDPE

Vinyl polymers from vinyl monomers (contain double carbon- carbon bonding) largest family of polymers made from the monomer ethylene/ ethene form a long chain of many thousands of carbon atoms containing only single bonds between atoms

Examples of Vinyl Polymers polypropylene Polystyrene poly(vinyl chloride) Polyisobutylene/ type of rubberPolyisobutylene poly(methyl methacrylate) polytetrafluoroethylene

Objective C.9.1 Describe the free- radical mechanism involved in the manufacture of low- density polyethene

Low density poly(ethene) Carried out at very high pressures ( atm) At temperature about 500K (227ºC) Average polymer molecule contains between 4 x 10 ³ to 4 x 10^4 carbon atoms With short branches Has a density of about 0.92g cm^-3 Used mostly for packaging Formed under free radical formation

Free radical formation Definition- molecules with unpaired electrons Highly reactive due to unpaired electrons Biology example- PEROXIDATION (producing ATP inside the body) Elements example- oxygen (ROS- reactive oxygen species), transition metals (Cu- copper, can lose and gain electrons easily) Progress= initiate  propagation  termination

Initiate First step Homolytic fission –when a bond is broken, each of the bonded atoms or groups takes one of the bonding pair of electrons. – Not heterolytic fission –when a bond is broken and two electrons go to one of the element/compound Examples: –Cl2 (UV light)  2Cl· –Br2  2 Br·

Propagation Each step must have odd number of unshared electrons Two compounds containing one unshared electron each never, ever, ever combine Unpaired electrons wanted will swipe one of themselves to pair with Leading us back to the beginning adding of more and more monomer molecules to the growing chains Examples: –Cl · + CH4  · CH3 + HCL –· CH3 + Cl2  CH3Cl + Cl · –Cl · + CH4 -> · CH3 + HCL –· CH3 + Cl2 -> CH3Cl + Cl·

Termination Each of two unpaired compounds form radical–radical combination (coupling) or a disproportionation Examples: –· Cl+ · Cl -> Cl2 –· CH3+ · CL-> CH3Cl –· CH3+ · CH3->C2H6

Examples of the free radical formation

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Objectives C.9.2 Outline the use of Ziegler- Natta catalyst in the manufacture of high- density polyethene

High density poly(ethene) Carried out at pressures (1-50 atm) At low temperature about 350K (77ºC) Using Zieler- Natta catalyst Maily of linear chains with very little branching Higher density 0.96 g cm^-3 More rigid structure Used to make containers and pipes

Ziegler- Natta catalyst  method of vinyl polymerizationvinyl polymerization discovered by two scientists: Ziegler and Natta in the 1950s Can’t make some other kinds of monomers, such as poly(vinyl chloride) Suspension of titanium (III) or titanium (IV) chloride together with an Alkyl- aluminum compound Catalyst and co catalyst: –TiCl3 and Al(C2H5)2Cl –TiCl4 with Al(C2H5)3

Industry process

Chemical process TiCl3 can arrange itself into a number of crystal structures each titanium atom is coordinated to six chlorine atoms= octahedral geometry

 Ti- –transition metal –Have six empty orbitals ( 4s and five 3d- orbitals ) Needs 2 electrons to fill up the orbital Filled 1 up by Al(C2H5)2Cl

Combine with vinyl monomer like propylene  nth(C3H6) two electrons in the π-system of a carbon- carbon double bond fill the left over empty orbital Form a complex

Several pair of electrons shift position The propylene monomer migrates

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