[vcx]

 i dissolve about 0.25g of AIBN in HEA, and diferrent mixtures are prepared.The reaction system ratio of AIBN soln:HEA:styrene 1st is 2:8:0 ml, 2nd is 2:7:1, 3rd is 2:6:2, 4th is 2:5:3, 5th is 2:3:5, and the 6th is 2:0:8 in conical flasks.The system flush wih N2 gas.The flasks place in water bath at 60 degree celsius.The question how to determinate the copolymerisation is about or less than 10% conversion?In my trial to do this,the 1st,2nd and 3rd one react very fast,it turn hard in about 10 minutes,4th one become viscous after 1 hour and 5th one become viscous in about 2 hours,and the 6th one become a little viscous after about 2 and a half hours. What i got for the result is the yield of the product is sticky and brownish in colour.It is not dissolve in toluene but dissolve in methanol. Am I get the right product? What do you suggest the steps to do this experiment? Thank you

[DrCMS]

What are you trying to acheive? 

Note that at 60°C the half life of AIBN is ~20 hours.

[vcx]

 The purposes to determine the monomer reactivity ratio, r, are:

•   To predict copolymer composition for the starting feed of styrene-HEA copolymer.
•   To understand some aspects of the kinetic features of the styrene-HEA copolymerization.
 

The inhibitor will decompose at 60 degree celcius.
i only want the reaction occurs below 10% conversion.

[HP]

By kinetic ot steric reasons its also possible the homopolymerization your 2 monomers to be predominant and the yeld of copolymer to be low. Here a link for kinetic of styrene HEMA emulsion copolymerization:
 http://www.ingentaconnect.com/content/jws/pi/2002/00000051/00000008/art00967
Just google: "styrene 2-hydroxyethyl methacrylate" and see the first pdf articles
It's very important in radical polymerizations to free your monomers from the inhibitors they consist...
Whish you success!

[Dude]

Normally, high molar mass polymers are dissolved in a solvent and then precipitated in methanol.  The insoluble material in methanol is filtered, dried and then analyzed by NMR for copolymer composition.  Based upon your descriptions, I would initially guess that you are using too much initiator.  The length of your polymer chain can be estimated by the monomer / initiator ratio (See Young and Lovell, Introduction to Polymers or Odian,Principles of Polymerization).  Brown sticky material suggests a low molar mass oligomer.  Find the molar mass of AIBN - realize it will split into two initiators - take monomer mass and divide

g monomer / 0.25 g AIBN(x g AIBN / 1 mole)(2 active sites / 1 mole) > 10,000 and preferably in the 100,000 g/mol range for non-changing polymer properties.  GPC can be used to see what your molar mass is and if it was consistent with expectation.

Conversion is kept low to negate "consumption" effects upon the initial concentrations.   

[Random Coils]

^ That calculation will be essentially worthless, unfortunately.  While MW is certainly proportional to [M]: ratio, with convetional free radical polymerizations, the ability to estimate MW requires knowlege of many more variables.  The initiator half-life is important (as a previous reply mentioned).  So one would have to calculate the number of radicals that have actually been formed as a function of time.  Also, the initiator efficiency is important.  IIRC, for AIBN at 60 C, the efficiency is around 40%.  These things (among others) would need to be considered in order to estimate the theoretical MW.

If you want to determine conversion, just precipitate your polymer like Dude mentioned (though the polymers with a high composition of HEA will not precipitate into MeOH), and then weight it.  Quick and dirty.  Or use an internal standard to monitor conversion by NMR for aliquots from the polymerization....watch the monomer concentration decrease as a function of time.