Reactions, Acids and Bases, Energy of Chemical Changes and Nuclear Changes. Appearance of real linear polymer chains as recorded using an atomic force microscope on a polymer chemistry an introduction pdf, under liquid medium. Because of their broad range of properties, both synthetic and natural polymers play essential and ubiquitous roles in everyday life.
Polymers range from familiar synthetic plastics such as polystyrene to natural biopolymers such as DNA and proteins that are fundamental to biological structure and function. Polymers, both natural and synthetic, are created via polymerization of many small molecules, known as monomers. Their consequently large molecular mass relative to small molecule compounds produces unique physical properties, including toughness, viscoelasticity, and a tendency to form glasses and semicrystalline structures rather than crystals. The units composing polymers derive, actually or conceptually, from molecules of low relative molecular mass.
The term was coined in 1833 by Jöns Jacob Berzelius, though with a definition distinct from the modern IUPAC definition. The modern concept of polymers as covalently bonded macromolecular structures was proposed in 1920 by Hermann Staudinger, who spent the next decade finding experimental evidence for this hypothesis.
In biological contexts, essentially all biological macromolecules—i. The simplest theoretical models for polymers are ideal chains.
Natural polymeric materials such as shellac, amber, wool, silk and natural rubber have been used for centuries. A variety of other natural polymers exist, such as cellulose, which is the main constituent of wood and paper. PVB, silicone, and many more.
Most commonly, the continuously linked backbone of a polymer used for the preparation of plastics consists mainly of carbon atoms. Silly Putty and waterproof plumbing sealant. Polymerization is the process of combining many small molecules known as monomers into a covalently bonded chain or network. During the polymerization process, some chemical groups may be lost from each monomer.
This is the case, for example, in the polymerization of PET polyester. OC-C6H4-COO-CH2-CH2-O-, which corresponds to the combination of the two monomers with the loss of two water molecules. The distinct piece of each monomer that is incorporated into the polymer is known as a repeat unit or monomer residue. Laboratory synthetic methods are generally divided into two categories, step-growth polymerization and chain-growth polymerization.
The essential difference between the two is that in chain growth polymerization, monomers are added to the chain one at a time only, such as in polyethylene, whereas in step-growth polymerization chains of monomers may combine with one another directly, such as in polyester. However, some newer methods such as plasma polymerization do not fit neatly into either category. Synthetic polymerization reactions may be carried out with or without a catalyst.
Laboratory synthesis of biopolymers, especially of proteins, is an area of intensive research. There are three main classes of biopolymers: polysaccharides, polypeptides, and polynucleotides.