" . .

.:, .r: ,7: # '!

c.kC\~ VI ..., ...., '

E~(\\ ~ fO~~v{l ••.4iA.

( U-e1uojtr. •• ' ~y~.)

----

· .:

r-,",".r,"".~ "'.

HETEROGENEOUS," .',- .'~. -

:;. "," "~.' . ? r

POL YMERIZATION

.. SYSTEMS:

EMULSION .POLYMERIZATION

PROBLEMS ASSOCIATED WITHEACH PROCESS·

Mass (bJlk') High viscosity; Difficult', "convective heat transfer' .I pt\.... .'

, .\

. ? r

Solution Moderate viscosity; Lessdifficult convective heattransfer; Solvent recovery .'r".14 ( .L(tt~ )

Suspension Difficult stabilitycharacteristics; impurities~ rh.SA.~

Emulsion Less difficult stabilitycharacteristics; markedincrease in impurities2..fh •.~r

Emulsion.4

, \ ,

EMULSION POLYMERIZATION(LATEX) PROCESSES

e.g. poly vinyl chloridevinyl acetatestyrenestyrene-butadiene

. ..'

-,

~. .\

'7' I

lL.w~"••.•. Il.&,t,c,i It

r> Typical recipe: . ~ - .

Monomer 50-100 parts . 10c)

Water 100 .parts ,';0

Emulsifier 2-6 parts ~4t(soap)

Initiator 0.5-1.5 parts fJ If

Emulsion.5

ion Polymerization

[aqueous phase initiation]

xM+SO~ ---.. oMxSO;

:aqueous phase polymerization][micelles formed by in situ surfactant]

/-,",'ri~',," '0 micelle]primary particle (unstable)

1 [coagulation]

stable mature particle

[polymerization in particle]

final latex particle

FIg. 8-3. Schematic of the general mechanism of surfactant-free emulsion polymerization.

_Iacroradicals are isolated from each other in emulsion polymerizations be-se they grow in particles, which can accommodate either one or zero radicals at

_ instant. The distinguishing feature of the kinetics of such reactions is that the_merization rate and polymer molecular weight are proportional to the num-

oer of particles, as distinct from free-radical polymerizations in bulk, solution orspension. An interesting consequence is that the rate of polymerization will be·ersely proportional to the particle size. This holds at fixed final polymer content,.eh is the way such reactions are usually performed. Polymer molecular weighty also be affected by particle size under the same conditions.When a mixed monomer feed is used, the course of the copolymerization.. be sensitive to the volume ratio between the monomer and water phases,

291

WATER/SOAP "'SOLUTIONS"

e.g. sodium dodecyl sulphatesodium stearate

'~ r r

__-----0micelles'

~50-106 A'

Wticelleso

~So.,'oo A

--0 -0'

.......... '

,:' ':. I.... ........

. . .'., - .. - .. j

J~)!~'', .'.

iI

WATERlSOAPIMONOMERMIXTURES

..,r....~ .'.

. ...

-; . .... -;

/

emulsified monomer dropletsN-~f5-- " 10,000 - 30,000 A .

~ ~1012_1013 droplets/lit Hjf

• Total volume inemulsified droplets x .micelles x/65

, • Total surface area ofemulsified droplets . ymicelles 63y

EmuIsion.7