The most significant property of poly-p-xylylene is its thermal stability.
The crystalline melting point is 375-425°C and in an inert atmosphere the material is claimed to have a useful life of 10 years at 220°C. The thermal
stability in air is not exceptional. Poly-p-xylylene also maintains useful
properties at temperatures as low as - 200°C. The polymer has outstandingly
good electrical insulation characteristics and is used as a dielectric in special
capacitors.
It may be noted that poly-p-xylylene is considerably less stable than polyp-
phenylene owing to the presence of the relatively weak dibenzyllinkages. It
may also be noted that the isomeric polyxylylenes have been prepared but
poly-o-xylylene has a polymer melt temperature of 110°C whilst poly-mxylylene
has a softening temperature of only 60°C; these polymers are
therefore of no immediate interest.
제조 방법
When di-p-xylylene is pyrolysed, both methylene bridges are homolytically
cleaved to give the reactive intermediate p-xylylene which spontaneously
forms the linear polymer on cooling. Generally, the polymer is deposited (in
the polymerization chamber) on to a cold condenser and then removed as
film; alternatively, the polymer is deposited directly on to an object which is
required to be coated. Typically, an average molecular weight of about
500000 is attained.
