When addition polymers are formed, no by-products result. Formation of a condensation polymerA polymer formed by condensation reactions between monomers and the growing polymer chain; in a condensation polymerization a small molecule each time a monomer becomes bonded to the polymer chain., on the other hand, produces H2O, HCl, or some other simple moleculeA set of atoms joined by covalent bonds and having no net charge. which escapes as a gasA state of matter in which a substance occupies the full volume of its container and changes shape to match the shape of the container. In a gas the distance between particles is much greater than the diameters of the particles themselves; hence the distances between particles can change as necessary so that the matter uniformly occupies its container.. A familiar example of a condensationThe process in which a liquid forms from gas or vapor of the same substance. A chemical reaction in which two molecules combine to form a very small molecule and a larger molecule than either of the two reactants. polymer is nylonAny of several human-made polyamide fibers; polyamides are formed by condensation of an amine group with a carboxylic acid group., which is obtained from the reaction of two monomers
These two molecules can link up with each other because each contains a reactive functional group, either an amineAn organic compound formally derived from ammonia by the replacement of one or more hydrogen atoms by alkyl groups. Examples are primary amine: RNH2; secondary amine: R2NH; tertiary amine: R3N. or a carboxylic acidAn organic compound containing the functional group -C(=O)OH. which react to form an amide linkageA chemical bond linkage formed when a carboxylic acid reacts with an amine, often found in polymers such as nylon and proteins; in proteins also called a peptide bond.. They combine as follows:
Below is a video of the reaction to form nylon. This reaction is slightly modified from the one described above, as adipoyl chloride, not adipic acid, is used as a reactantA substance consumed by a chemical reaction.. Thus HCl, not H2O is produced. This also means that the chain terminates in an acid chloride, rather than the carboxylic acid shown above. Note that an amideAn organic compound formally derived from a carboxylic acid by the replacement of the hydroxyl group by -NH2, -NHR, or -NR2. linkage is still formed.
A solutionA mixture of one or more substances dissolved in a solvent to give a homogeneous mixture. of adipoyl chloride in cyclohexane is poured on top of an aqueousDescribing a solution in which the solvent is water. solution of 1,6-diaminohexane in a beaker. Nylon (6,6) polyamide is formed at the interface of the two immiscibleDescribes two liquids that cannot be dissolved in one another in all proportions. liquids and is carefully drawn from the solution and placed on a glassA solid material that does not have the long-range order of a crystal lattice; an amorphous solid. A glass melts over a range of temperatures instead of having the definite melting temperature characteristic of crystalline solids. rod. The rod is then spun, and the Nylon (6,6) polyamide is spun onto the rod.
Well-known condensation polymers other than nylon are Dacron, Bakelite, melamine, and Mylar.
Nylon makes extremely strong threads and fibers because its long-chain molecules have stronger intermolecular forces than the London forces of polyethylene. Each N—H group in a nylon chain can hydrogen bondAn attractive force, either intramolecular or intermolecular, between an electronegative atom and a hydrogen atom attached to another electronegative atom. to the O of a C=O group in a neighboring chain, as shown below. Therefore the chains cannot slide past one another easily.
If you pull on both ends of a nylon thread, for example, it will only stretch slightly. After that it will strongly resist breaking because a large number of hydrogen bonds are holding overlapping chains together. The same is not true of a polyethylene thread in which only London forces attract overlapping chains together, and this is one reason that polyethylene is not used to make thread.