Hi Seyed, why do you think that methacrylamide will bind to Au particles?

The only cheap functional group that really bind tightly to Au are -SH compounds.

Hi Steingrimur and thanks for your answer.

I dont think so. We use a CTA for HPMA polymerization which has thiol groups. Thus we use the thiol part of the polymer for conjugation to AuNPs.

Common chain transfer agents include thiols and halocarbons.

OK, you didn't mention that you had free thiols as a part of your AuNP synthesis in your original question.

As for size selection, I think you have 2 choices: 1) gel filiation of the de novo NPs. 2) ultrasonication of the mixture followed by gel filtration. To block any -SH binding to Au after the ultrasonication, you could add 1 mM iodoacetamide or maleimide. 

Spin columns with defined MW cutoffs will be quicker than gel filtration if you are in a hurry. 

Thanks for your nice comments.