Dear José Domingo Trujillo-Casarreal ,

In your example we talk about a polymer (in this case chitosan). There are numerous types of chitosan polymers that vary in molecular weight (and ‘spread’ in molecular weight), see for example:

http://file.chemscene.com/pdf/DataSheet/DataSheetCS-0130913.pdf and

https://uk.vwr.com/store/product/22162844/chitosan-m-w-190-000-310-000-da-200-800-cp-1-w-w-ch3cooh-1-sigma-aldrich

As indicated in the above links you can describe the polymer in terms of (average) Mw. Since I have no access to the paper you refer to, I urge you to check the following paper:

https://hal.science/hal-03384120/document and in particular Table 1. Here you can see that you can say something about the molecular weight of both the monomer and the polymer (expressed in g/mol). The concentration of monomer units is expressed in monomol/L.

The molecular weight of a polymer can (as you can see in Table 1 for example) be expressed in different ways that all serve their own purpose, see for more info:

https://en.wikipedia.org/wiki/Molar_mass_distribution

Back to your question. For the conversion from monomol/L (or monomol/dL) to for example g/mol you need the information provided by the manufacturer of in this case chitosan (so info like average Mw, Mw of the monomer (or at least the structure so you can calculate yourself), the distribution of the Mw of the polymers (the degree of number of monomers in the various sizes of polymers)) etc.

Hope this clarifies the matter somewhat.

Best regards.