POLYMERS IN CHEMICAL SENSORS 3 2. WHAT ARE POLYMERS? In contrast to discrete small molecular compounds, polymers are macromolecules. Except for a few, polymers are organic macromolecules made of carbon and hydrogen atoms in major percentage with some heteroatoms such as nitrogen, oxygen, sulfur, phosphorous, halogens, etc., as minor constituents. A polymer molecule is formed by the repetitive union of a large number of reactive small molecules in a regular sequence (see Figure 1.2). The repeated unit in the backbone of the polymer molecule is known as the mer unit, and the reactive small molecule from which the polymer is formed is called the monomer. The simplest example of a polymer is polyethylene, in which the ethylene moiety is the mer unit. H N n S n N H n Polypyrrole n R Poly(3 alkylthiophene) Polyacetylene Polyaniline S n Polythiophene O n Polyfuran S n n Polyphenylene Polyphenylene sulfide S S n n n Polyisothianapthene Polyphenylenevinylene Polythienylenevinylene n N H n n Polyazulene Polycarbazole Polyfluorene Figure 1.2. Repeating unit structures of some common conducting polymers.