6
Polymers
Almost all foods contain macromolecules and almost all of these
macromolecules are polymers. Polymers have specific properties, warranting
a separate treatment; some aspects of them are discussed in this chapter.
6.1 INTRODUCTION
A polymer molecule in its simplest form is a linear chain of covalently
bonded identical monomers. A very simple synthetic polymer is poly-
ethylene, which is obtained by linear polymerization of ethylene, CH 2 CH 2 ,
yielding ½ 22 CH 222 n; i.e., a very long paraffin chain. Another simple
example is poly(oxyethylene), ½ 22 O 22 CH 222 CH 222 n.n is the degree of
polymerization, and it can be very high, up to about a million. The
monomers may have one or more reactive side groups.
Such molecules have very specific properties, due to their size and
flexibility. A linear molecule withn¼ 104 , built of monomers with a molar
mass of 30 Da, will be taken as an example. The molecule is thus very large,
molar mass 300 kDa. Its length-to-diameter ratio is like that of a 10 m string
of about 1 mm thickness. If it were tightly coiled up in a sphere, it would
assume a diameter of about 10 nm. In other words, it would be of colloidal
rather than molecular size, and many polymer molecules are even far larger.