Apply this general formula,

Swelling (%) = (Ws - Wd)/Wd × 100

[ Wd= Weight of polymer; Ws= weight of swollen polymer]

Swelling degree :

Extent of swelling in polymers that can be determined via changes in linear dimensions or through volumetric changes.

Most polymers swell by solvent (including water) absorption.

Alain

Dear all;

swelling is the consequence of interaction between a solvent and a matrix. It is the first step before total solvation occuring (if possible). It is an increase in 3D geometry. This expresses the affinity and exchage of enthalpy between the two phase. Sometimes and for partially crosslinked systems, swelling is a tool measure the free volume (average) between knots, in other words to say it measure the crosslink density. For linear polymers, swelling will reflect how good/bad is the solvent for the polymer in question. Regards

When a cross-linked polymer keep in a good solvent, it become swell rather than dissolve. Swelling degree define the change of dimension of polymer. A highly cross-linked polymer shows less degree of swelling.

The swelling value can be calculated by using the following formula:

Swelling (%) = (Ws - Wd)/Wd × 100

Where

Wd= Weight of polymer

Ws= weight of swollen polymer

In this paper there is both, reversible and irreversible swelling study:

http://www.sciencedirect.com/science/article/pii/S0268005X14003452

The formula presented by Hemjyoti Kalita for calculation of swelling degree can be applied to both volume change or weight change due to swelling at the equilibrium of solvent sorption experiment. Another way of expressing swelling degree is to use swelling ratio, Q = Wt (swollen polymer)/ Wt (dry polymer). Based on Flory's theory and equation, the volume fraction of polymer in the swollen gel (V2) is used. The swelling ratio is defined as Q = 1/V2. If you use this equation, the Q value is correlated to the polymer-solvent interaction parameter, x^(3/5). More details about how to determine swelling ratio or swelling degree can be found in the following paper: 

Novel modified starch–xanthan gum hydrogels for controlled drug delivery: Synthesis and characterization. A Shalviri, Q Liu, MJ Abdekhodaie, XY Wu

Carbohydrate Polymers 79 (4), 898-907

Apply this general formula,

Swelling (%) = (Ws - Wd)/Wd × 100

[ Wd= Weight of polymer; Ws= weight of swollen polymer]

Swelling is an usual phenomena of interaction of a Polymer with SOLVENT. Insertion of  such liquid within polymer matrix tend to swell it. This could be either reversible or irreversible. Many a times, some olymer have a tendencey to absorb moisture which tend to change the associted properties. the total moisture insertion is not always reversible. A certain fraction forms a part the polymer matrix. 

Simple way to calculate the % swelling is to consider the difference of weight of the polymer before and after. However, taking dry weight of polymer should be exact to obtained the % swelling.

All disscution is going well but first of all we should answer what for one wants to calculate swelling degree as it is the choice of medium (solvent). To estimate crosslinking or Molecular weight between the junctions-we should choose the proper solvent and I advice to check more solvents taking into account                          interaction between the chains and between the solvent. And here of course Flory theory and modification of it is very important. In the begining of sample analysis it is important to estimate the solubility of the sample in the studied solvent-do not forget about that.

But there are some studies which neeed to calculate the swelling degree for particular application. So it is much simpler. and here the advice of Omkar is good but do not forget as well in this case that part of your polymer can be solved-so check it after the drying of the sample after the swelling test. Otherwice you can missinterpret the results. Of course the temperature is very important and the way of weighting of the swollen sample. Must be very reproducible.

Helena

This is depending on so many factors ; types of oligomers, catalyst, quring agents, Solvents,synthetic temperature and then physical steat of products mostly cross linked polymers two types small chain clp and big chain clp , small chain clp not shows swelling property they are dissolved directly . So if you want to study cross linkages of polymer use comparatively same pure non cross linking polymers make standard analysis reports physical and chemical and then same analysis do on clp thanks