To what extent should be this polymer sulfonated? I suppose introducing only one sulfonic group per one benzene ring. Right? What is/are the second/ next monomer unit(s)? Maleic anhydride, butadiene, isoprene, ...? Their percentages?

SEPS=(styrene-ethylene-propylene-styrene) monomer unit?

Hello Pavel

yes, i need  introducing only one sulfonic group per one benzene ring of styrene.what does "second/next monomer units" mean?

yes, the monomers of block copolimer SEPS are styrene-ethylene-propylene-styrene

Best Regards.

O. K. it is now clear, pleas know you the value of the average molecular weight of this polymer?

P.

the average molecular weight is 103,000 g/mol

5 g of SEPS x 0.21 = 1.05 g of styrene

1.05 g of styrene / 104 g.mol-1 = about 0.01 mol

so you need 0.01 mol of sulfonating agent

My idea is different from Samer (21 % = w/w %, or mol%?):

Mr (all PS units in SEPS) = 0,21*103000= 21630 g/mol (if 21 % are 21 mol% !!!!!)

5 g (SEPS)= 5/21630=2,311604253351826e-4 mol for all PS Units

ńumber of all PS units in 1 mol of SEPS= 21630/104=208 PS units

mmol of styrene in 5 g SEPS= 2,311604253351826e-4 mol*208*1000=48mmol of PS unit.

You need 48 mmol of your sulfonating agent for 5 g SEPS and introduction of 1 -SO3H per 1 benzene ring(=1 PS unit).

If 21 % = 21 w/w% Samer is right, calculation is simple.

However,

In any case, excess sulfonating agent is not detrimental for the full monosulfonation because more than one SO3 H can not be introduced.

 thank you very much to both,you were of great help