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Polymer SynthesisCHEM 421

Odian Book: Chapter 4

Polymer SynthesisCHEM 421

Emulsion PolymerizationsEconomically importantWestern countries 108 tons/year30% of all polymers made by free radical methodsemulsion polymers accounts for 40-50% of thisFirst employed during WWII for production of synthetic rubberToday: MMA, VC, vinylidene chloride, styrene, fluoropolymers, vinyl acetate, EVA, SA, SBR, chloroprene, etc

Polymer SynthesisCHEM 421

Emulsion Polymerization RecipeWater (continuous phase)Water-insoluble monomerWater-soluble initiatorSurfactant (detergent)

Polymer SynthesisCHEM 421

SurfactantsHydrophobic /Lipophilic core

Polymer SynthesisCHEM 421

SurfactantsTypes- Anionic - Cationic - Amphoterics - Non-ionics

Polymer SynthesisCHEM 421

Emulsion Polymerization Recipe

Polymer SynthesisCHEM 421

Emulsion PolymerizationsPolymzRateSurfactant Concentration

Polymer SynthesisCHEM 421

Kinetics of Emulsion PolymerizationPercentConversionTimeIIIIII

Polymer SynthesisCHEM 421

Kinetics of Emulsion PolymerizationRate% ConversionIIIIII

Polymer SynthesisCHEM 421

Before InitiationIIIIIIIIIMMMMMMMMMMMMMMMMMMMMonomer Dropletca. 1 micron diameterconc = 1011/mLstabilized by soapMicelle Containing Monomerca. 75 diameterconc = 1018/mLRelative surface area1 : 560Initiation of micelles statistically favored

Polymer SynthesisCHEM 421

Interval One: 0 15 % ConversionI IIIIII IIMMMMMMMMMMMMMPPMMMicellesContaining MonomerActivelatex particle

MicellesContaining MonomerMicellesContaining MonomerActivelatex particles

Inactivelatex particles

Inactivelatex particles

Polymer SynthesisCHEM 421

Qualitative Details

ConversionMicellesMonomerDropletsParticleNumberParticleSizeCommentsI0 15%presentpresentincreasesincreasesNucleation period, Increasing RpIIIII

Polymer SynthesisCHEM 421

Interval Two: 15 80% ConversionIIIII IIMMMMMMMMMPPInactivelatex particles

Inactivelatex particles

Inactivelatex particles

Activelatex particles

Activelatex particles

I IMPActivelatex particles

No micellesNumber of particles constant, thereforeRp = constant

Polymer SynthesisCHEM 421

Kinetics of Emulsion PolymerizationNumber ofMicellesTimeIIIIIINumber ofPolymerParticles1018010150

Polymer SynthesisCHEM 421

Qualitative Details

ConversionMicellesMonomerDropletsParticleNumberParticleSizeCommentsI0 15%presentpresentincreasesincreasesNucleation period, Increasing RpII15 80%absentpresentconstantincreasesConstant # of particles,Cp = constantIII

Polymer SynthesisCHEM 421

Interval Three: 80 100% ConversionIIIII IMMMMMMMPPI MPMPI No monomer dropletsNo micelles

Polymer SynthesisCHEM 421

Qualitative Details

ConversionMicellesMonomerDropletsParticleNumberParticleSizeCommentsI0 15%presentpresentincreasesincreasesNucleation period, Increasing RpII15 80%absentpresentconstantincreasesConstant # of particles,Cp = constantIII80 100%absentabsentconstantroughly constantConstant # of particles,Cp = decreasing

Polymer SynthesisCHEM 421

Emulsion Polymerization KineticsOnce inside a particle, radical propagates as rp = kp[M]Overall rate: Rp = kp[M][P.][P.] = N (where N = the sum of micelle and particle concentrations and = average # of radicals per particle)Therefore,Increase N to increase rate!

Polymer SynthesisCHEM 421

Emulsion Kinetics, cont.Smith-Ewart Kinetics:Case 2: = 0.5 (MOST CASES!)1 radical per particleHalf of the particles active, half not activeCase 1: 0.5Termination constant is lowHigh viscosity, initiator; large particles

Polymer SynthesisCHEM 421

Emulsion Polymerization KineticsHow to increase Rp? Increase N to increase rateIncrease surfactant concentration to increase N

Polymer SynthesisCHEM 421

Molecular Weight in Emulsion PolymerizationsMolecular weight determined by rate of growth of a chain divided by rate of radical entry (ri) How to increase molecular weight?DPrp = ri

Polymer SynthesisCHEM 421

Free Radical Solution PolymerizationsRecall To increase molecular weightIncrease monomer concentrationDecrease initiator concentrationTo increase Rate of PolymerizationIncrease monomer concentrationIncrease initiator concentrationCant do both!Rp = kp [M] (kd f [I] / kt)1/2

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