[RyanG]

Can you make a polymer with just dicarboxylic acids or must you also have a dialcohol/diamide?

[DrCMS]

If the dicarboxylic acid contains a double bond, such as maleic or fumaric acids, you can do a free radical polymerisation to form polydicarboxylic acids.

[Organishe]

PTA (polyterephthalic acid) is a condensation polymer formed from terephthalic acid, which would be just as you describe. I am unsure of what it is used for, but I am reasonably sure its a relatively common plastic used in various packaging and a multitude of other things, I'm sure.

[HP]

If talking for polymerisation only by COOH groups then its possible to make polymer with some dicarboxylic acid by polycondensation reaction of it dihalogenanhydride with it disalt to obtain polyanhydridic polymer:
ClCOR-COCl + NaOOC-R-COONa -->-..OCOR-COOO-...

[wereworm73]

Like HP, I was thinking of a polyanhydide when I first read this, though water can break it back down to carboxylic acids again. 

You might want to try using dicarboxylic acids that can't form stable cyclic anhydrides (for instance, I'd avoid butanedioic & pentanedioic acid since they can respectively form 5- & 6-membered anhydride rings).  Otherwise, you'll have another unwanted side reaction going on.  One time in Ochem, I was supposed to identify an unknown compound (pentanedioic acid) with IR & NMR spectra, but because it was in equilibrium with cyclic pentanedioic anhydride, I was getting pretty confused from the results.

[HP]

It seems hard to obtain polyanhydride only from diacid especially if R not very long...Cyclic anhydride formation in heating is classical reaction for obtaining maleic, succinic, buthandioic and so on anhydrides. If wont obtain polyanhydride the most relative reaction is as i described in my last post.