A large molecule made up of repeating units. Some polymers are naturally occurring, such as xanthan gum, guar gum and starch. Other polymers are modified natural polymers, such as carboxymethylcellulose (CMC) and hydropropyl starch and lignosulfonate. Some are synthetic such as polyacrylates, polyacrylamides and polyalphaolefins. Polymers may be classified by their structure and may be linear, branched or less commonly cyclic. Copolymers contain two or more different monomers that can be arranged randomly or in blocks. In solution, entangled polymer chains can create networks, giving complex viscosity behavior. Polymers that ionize in solution are called polyelectrolytes. Charged groups strongly affect behavior and interactions with colloidal clays, other polymers and solvents. Molecular size (weight) influences how a specific polymer type performs in a given type of mud. A small polymer may be a deflocculant, whereas a large polymer of the same type may be a flocculant. Some are viscosifiers and others are fluid-loss control additives while others are multifunctional.