Condensation polymerization is a form of step-growth polymerization, is a process by which two molecules join together, resulting in loss of small molecules which are often water. The type of end product resulting from a condensation polymerization is dependent on Monomers with only one reactive group do not padlock a growing chain, and thus give end products with a lower molecular weight. Linear polymers are created using monomers with two reactive end groups and monomers with more than two end groups give three-dimensional polymers which are cross linked.