5. polymerisation practice tepe

*Chapter 5:Polymerization Techniques

Bulk polymerization

Solution polymerization

Suspension polymerization

Emulsion polymerization

Interfacial condensation polymerization

Etc.

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*1. Bulk Polymerization : Liquid monomer Initiator Inhibitors Chain transfer agents

Homogeneous : polymer remains dissolved in monomers. Ex. PMMAHeterogeneous : aka. Precipitation polymerization polymer is insoluble in its monomers. Ex. Polyacrylonitrile, PVCProblem : heat transfer not good

Make objects with a desirable shape by polymerization in a mold.In the reactor:-

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*

MonomerModel of Batch Polymerization

*Pros & Cons of Bulk PolymerizationAdvantageDisadvantage Obtain purest possible polymer

Conveniently cast to shape

Obtain highest polymer yield per

reactor volume Difficult to control

Reaction has to be run slowly

Cannot get high rate and high

MW at the same time

Difficult to remove last traces

of unreacted monomer

*

*Ex. 1 The maximum possible temperature rise in a polymerizing batch may be calculated by assuming that no heat is transferred from the system. Estimate the adiabatic temperature rise for the bulk polymerization of styrene, Hp = -16.4 kcal/mol, molecular weight = 104Solution Hp for polymerization of styrene = 16,400 cal/mol (assuming complete conversion) meaning that polymerization of 1 mol styrene release heat in the amount of 16,400 calories.In the absense of heat transfer, all this energy heats up the reaction mass. To a reasonable approximation, the heat capacity of most liquid organic systems may be taken as 0.5 cal/g-oC

From Q = mc T(Note that- Boiling point of styrene = 146 oC)

*Solution Polymerization : Monomer dissolved into inert- solvent / inhibitor Monomer Initiator CTA Inert solvent

Use for :Solvent helps controlling heat transfer from reaction. Thermosetting condensation polymer (stop before gel point)

Ionic polymerization

Ziegler-Natta solution process

2. Solution Polymerization

*Model of Solution PolymerizationIIIIIMonomerSolventInitiator

*The effect of solvent solubility on the molecular weight of polyurethane produced by solution methodViscosity of polymer MWpolymer High viscosity = high molecular weight !

SolventViscosity of polymer solutionPrecipitation of polymer out of the solutionXyleneChlorobenzeneNitrobenzeneDimethyl sulfoxide0.060.170.360.69Precipitate immediately

Precipitate immediately

Precipitate within 0.5 hr.

Polymer remain dissolved in solution

* Rate [M] reduce rate,

chain length xn Solvent waste Need solvent separation &

recovery Have traces of solvent, monomer Lower yieldSolvent may not be really inert

(May interfere w/ rxn.-act as CTA)AdvantageDisadvantagesolvent Reduces the tendency toward

autoacceleration

Increases heat capacity/heat-

transfer

Reduces viscosity

Minimize runaway reaction

Pros & Cons of Solution Polymerization

*Ref: S.L. Rosen, John Wiley & Sons 1993

*Ex. 2 Estimate the adiabatic temperature rise for the polymerization of a 20% (by weight) solution of styrene in an inert organic solventSolution In 100 g of the reaction mass, there are 20 g of styrene, so the energy liberated on its complete conversion to polymer is

Temperature rise is calculated fromQ = mc T

Therefore, the adiabatic temperature rise is then

*Ref: S.L. Rosen, John Wiley & Sons 1993

*Ref: S.L. Rosen, John Wiley & Sons 1993

*3. Suspension Polymerization :

Monomer into water, suspending agents (Ex.Ionic detergent, barium sulfate)- Ex. Polyvinyl alcohol- Beads of polymer ( 10-1000 m)Model of suspension polymerization

*

Typical Composition:

*Pros & Cons of Suspension Polymerization Advantage1. Easy heat removaland control2. Obtain polymer in a directly useful from DisadvantageLow yield / reactor volumeTraces of suspending agent on particle surfacesCannot run continuouslyCannot be used for

-condensation polymers-ionic or Ziegler-Natta polymerization

*Ref: S.L. Rosen, John Wiley & Sons 1993

*Reaction occurs in water phase until polymer gets very

hydrophobic and then dissolve back in the monomer region.Ex. Latex - very very small particle stable in solution - particle size

*

*growing polymer particleMonomers inside the micelle decrease

Unreacted monomers in other micelles and in droplets diffuse through water to the growing particlesReaction terminates when 2nd radical gets in reaction starts again for the 2nd chain when 3rd particle gets in.Steps in Emulsion PolymeriztionWater-soluble initiatorPolymer born in waterMonomer swollen micellePolymer moves to micelle

*Ref: S.L. Rosen, John Wiley & Sons 1993

*Ref: S.L. Rosen, John Wiley & Sons 1993

*Interfacial Polycondensation of Nylon 6/115. Interfacial Polycondensation

*

Experiment onInterfacial Polycondensation of Nylon 6/11

*Pros & Cons of some polymerization techniques

ProsConsBulk- easy- No contamination- Difficult to control temp. and heat transfer- High viscositySolution-good heat transfer-easy to control reaction temp.-low viscosity-polymer produced may be used directly in the solution form- Need to use solvent adding cost Difficult to eliminate solvent entirely Solvents sometimes act as chain transfer agent leading to lower MW polymerSuspension- Good heat transfer- easy to control reaction temp.- low viscosity- polymer produced may be used directly as polymeric suspension-Need extra process in washing out suspending agent/contaminants and drying the polymer beads-Polymer beads may stick together and maybe contaminated with suspending agent -Good only for addition polymerization using hydrophobic free radical initiator.Emulsion-- Good heat transfer- easy to control reaction temp.- low viscosity- polymer produced may be used directly as polymer latex-Need extra process in washing out emulsifier/ contaminants and drying-Good only for addition polymerization using hydrophilic initiator.

InterfacialReaction is fast at room temp. and pressure. No need for high temp. like in normal polycondensation.Can produce polymer in fiber form - Good heat transfer- low viscosityLimited to polycondensation where the two reactants are insoluble in each other ex. Acid chloride (quite expensive) Need extra process in recovering solvent and excess reactants

*Comparing different techniques for Polycondensation

conditions(bulk)(solution) (interfacial)TempHeat stabilizationKinetic of Reaction Reaction time1 1 1ProductivityEquality of reactantsPurity of reactantsEquipment Pressure,

*6. Gas-Phase Olefin Polymerization : Use Zieler-Natta catalyst

Moderate P (7-20 atm)

Low temperature ( < 100 oC)

Use fluidized bed reactor

Good Point : No solvent

Monomer separation is easy

Low capital + operating cost

*Ref: S.L. Rosen, John Wiley & Sons 1993

*Ref: S.L. Rosen, John Wiley & Sons 1993

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