-0 PAINTING MATERIALS

often termed ' macromolecules.' From the work of Staudinger and co-workers,
it is generally agreed that the formation of polystyrene from monomeric styrene
may be represented thus (Ellis, loc. cit.} :

C6H5 C6H6 CeH5 C6H6
This type of polymer is known as a linear polymer. Ellis (loc. cit.) says about it:
' The long chain of polystyrene is, in effect, a single molecule and the properties
of various polymeric styrenes are a function of the size. Relatively short chains
dissolve readily (in solvents) to yield solutions of low viscosity; this low viscosity
is not affected by heat.' Under certain conditions of polymerization, however,
the polymer may form in branched chains or in three-dimensional molecules.
The molecular polymeric structure can be built up to a compact and complex
structure in which the linear chains are fused together at certain points with the
formation of a network design. Such polymers of styrene swell and dissolve little
in organic solvents. The linear molecule, as compared with the three-dimensional
structure, tends to be soluble in all stages of polymerization. For this reason,
resins built from linear macromolecules are more suitable for making lacquers
than are those built from three-dimensional molecules. Ellis (loc. cit.y p. 1131) also
says:
Whatever cohesion there is between the chains of the linear polymer in the forma-
tion of micelles is accomplished by means of secondary valence forces yielding
micelles considered to be elongated. In solution the solvents force themselves
between the linear chains and solubility results. . „ . The thread molecules may
be in random arrangement in solution but they never lose their identity as such.
It is supposed that polymerization plays an important part in the natural forma-
tion of such plant products as cellulose and rubber. Carothers (* Polymers and
Polyfunctionality,' p. 41) has said: ' The most important peculiarity of high
polymers is that they alone among organic materials manifest to a significant
degree such mechanical properties as strength, elasticity, toughness, pliability,
and hardness/
. Polyvinyl Acetate (see Vinyl Resins).
Polyvinyl Alcohol (see Vinyl Resins).
Polyvinyl Chloracetate (see Vinyl Resins).
Polyvinyl Chloride (see Vinyl Resins).
Poppy-Seed Oil is obtained from the seeds of the opium poppy (Papaver
somniferum) which is grown largely in India, Russia, France, and Asia Minor.
The seeds contain 45 to 50 per cent of oil. The cold-drawn oil is pale straw or
light golden yellow in color and is the * white poppy-seed oil ' of commerce; the
hot-pressed oil is reddish in color. It can be sun-bleached to a nearly water-clear