I want to make a polymer that alternates units of maleic acid and styrene; this is possible using maleic anhydride but I have not seen it tried using the diacid. I'm not even sure how to query the search because most sources containing "styrene-maleic acid copolymers" have either used commercially available reagent or used anyhydride in their polymerization and then they hydrolyzed it.
Simply follow the well known method and obtain your product unless you would like to surprise your colleagues :)
My guess is that the anhydride is preferred for a very good reason. It may be due to stability, or reactivity of the vinyl group, or solubility or even cost. But using the diacid sounds like fun, and you will never know if you don't give it a go...
You can check the Polymer Handbook or many polymer texts for this data.
Maleic acid and styrene may not be that easily soluble in the same suitable solvents - maleic acid may also have some chain transfer agent character that limits MW. Generally 1,2-disubstituted ethenes (vinyls) are poor monomers for steric reasons. Tying it back into the ring for maleic anhydride may limit this liability. We have copolymerized N-substituted maleimides with styrene - appears to alternate like maleic anhydride.
Note that the maleic anhydride is the controlling monomer in this alternating copolymerization. Styrene will polymerize to make a homopolymer and random copolymers with other monomers, but maleic anhydride will NOT homopolymerize or make random copolymers. The rate of reaction of a maleic anhydride with a maleic anhydride sourced radical end of a polymer chain is zero.
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