Hi Samahir, Have a look at this comprehensive paper on Polymer dissolution, you might find your answer here.

Article A review of polymer dissolution. Prog Polym Sci (Oxford)

Regards, Hendrik

Dear all, how solubility is achieved without complete dissolution since the shape is kept constant ? Solubility is the destruction of cohesion that maintains molecules in a given form. Swelling is the first step to reach solubilization (if the material is soluble), it is a diffusion process function of concentration, temperature (or say any energy input such as mixing), and time. If you want only swelling play on concentration, i.e., less solvent or high compound mass. My Regards

Unlike small molecules which dissolve almost instantly in suitable solvents, dissolving polymeric molecules (macro molecules) will occur gradually because disentanglement of the long chains will take time & diffusion of the solvent molecules into the matrix of the polymer requires time also. The polymer needs to swell first before dissolution. At the start of my postgraduate studies, my distinguished professors taught me how test the solubility properly of polymer in various liquids: the polymer sample, say 0.1 gram , is placed in a test tube which can be stoppered & the liquid solvent , say 10 ml., is added and then the tube is closed & shaken for a while. The tube is left on a rack for 24 hours and after that one can judge if it is soluble, insoluble, or partially soluble. Sometimes, a beginner will mistake formation of dispersion or colloid as solubility. A true solution has to be clear one phase; colorless or colored !

Please see this good review of polymer dissolution mechanism:

Hi;

A polymer is a set of macromolecules entangled and interacting with each other. When a solvent is introduced, its molecules gradually penetrate the polymer to interact with the macromolecules. The macromolecular chains move apart, their mutual interactions decrease, and eventually become independent and free to move. Several phenomena occur during the dissolution process: swelling of the solid particles, formation of a gel, and then obtaining a translucent solution.

With my best regards

Dear Samahir Sheikh Idris , as clearly stated by the authors above swelling and solubility of polymers is counterintuitive at first glance, and your observations of highest solubility and swelling make even harder explaining what is actually happening in your experiments.

It would be useful to know what kind of polymer you have, particularly if your polymer is just a mass of entangled chains or if it is a crosslinked polymer. Also the polydispersity value would be helpful as it would be the kind of polymer you have (linear, branched, kind of funtional groups...) and possible crystalline domains.

Entangled polymers (chains not bonded each other) can swell initially to favour the untangling process before dissolution. In this case, if your polymer shows a strong polydispersity it could be that some short chains become soluble before the long chains, which could keep the shape while the fraction of small chains are dissolved. In this case, adding more solvent would remove the medium sized chains and therefore the volume and shape of the original mass would be affected.

Crosslinked polymers have their chains bonded making a kind of network that could be considered as a single giant molecule with the size and volume of the original object. In this case the material could only be swelled by the solvent, but not dissolved. Dissolution in this case would mean some chemical reaction that breaks some of the covalent bonds that form the network, which is not properly a dissolution process but a digestion.

In many cases when you get a crosslinked polymer, it is possible that some chains or monomers remain just trapped and entangled in the main network and therefore in this case the solvent could first swell the network, allowing the trapped and non-bonded molecules be more movable and by adding more solvent and with time these molecules could be removed (dissolved) from the main network, which mean that the mass keeps the shape and at the same time a portion of the original mass is transfered to the solvent. This amount would be larger when the amount of non bonded molecules is higher in the initial polymer.

This last option could be the situation which fits better to your observations. This is something you should be able to assess by analyzing the composition of your solute.

If your polymer includes some kind of charges (not chemically bonded to the crosslinked network) these charges could be what you have in your dissolution. Often these charges could be large (in industrial polymers) and that could explain the simultaneous swelling and high solubility.

If you made your polymer, you should know if you added some charges, additives, dyes, etc.

Hope it helps.