Introduction to Organic Construction Materials

Macromolecules are very large molecules with atoms linked together by covalent bonds. They may be linear chains, branched, or three-dimensional networks.Some natural macromolecules, such as those present in biological construction materials, have avery complex structure. 

However, many synthetic macromolecules have a relatively simple structure being formed by a chemical process called polymerization, which consists in joining together repeating poly) small units mers) to form a macromolecule called a polymer. 

Network polymers, e.g., silicones, epoxies, and urethane foams 

According to Kravelen,( l the fundamental characteristics of a polymer are the chemical structure and the molecular mass distribution pattern. The former includes the nature of the repeating units, end groups, composition of possible branches and cross-links, and defects in the structural sequence. The molecular mass distribution, which depends upon the synthesis method, provides information about the average molecular size and its irregularities. These characteristics are responsible, directly or indirectly, forthe polymer properties. They are directly responsible forthe cohesive force, packing density and potential crystallinity, and molecular mobility (with phase transitions). Indirectly, these properties control the morphology and relaxation phenomena (behavior of the polymer). 

Semi-organic polymers include materials with heteroatoms directly bonded to the carbon backbone of the pol5mier, but do not contain nitrogen, sulfur, oxygen, or a halogen. One example is poly(dimethyl siloxane) 

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