Dear Mr. Kumar,

The explanation of this effect  includes the important role of terminal polymeric groups which are hydrophilic. The mole ratio between terminal and backbone  polymeric groups determines predominantly the solubility of single molecule (or macromolecule) in water. In your case the monomer is maximally hydrophilic but with the MM increase the water solubility will be drop.

Sincerely,

Prof. Iordanskii

Dear Mr. Kumar,

The explanation of this effect  includes the important role of terminal polymeric groups which are hydrophilic. The mole ratio between terminal and backbone  polymeric groups determines predominantly the solubility of single molecule (or macromolecule) in water. In your case the monomer is maximally hydrophilic but with the MM increase the water solubility will be drop.

Sincerely,

Prof. Iordanskii

Another aspect is that in the case of a polymer/solvent mixture the mixing enthropy is much smaller than in the case of a monomer/solvent mixture, thus the free enthalpy change is less negative

Reduced entropy (∆S) of mixing is a good answer (Prof. Banhegyi) for decreasing solubility of a monomer upon polymerisation or a polymer, such as poly(N-hydroxymethyl acrylamide) as molar mass increases. Free energy of mixing (∆G) must be negative for solubility. Enthalpy of mixing is another part of the equation, ∆G = ∆H - T∆S, since ∆H is related to interactions and there will be polymer(monomer)–solvent interactions, polymer–polymer interactions and solvent–solvent interactions. The latter can be considered constant because there are many more moles os solvent. Polymer–polymer interactions are likely to increase with polymerisation as monomer units will be linked and held in proximity and solvent molecules can be excluded from the randomly coiled polymer, partly an entropy (randomness) consideration, but partly an interaction contribution.