| 摘要 |
<p>The dielectric of a capacitor (see Division H1) comprises a branched copolymer of at least one aromatic vinyl compound and at least one polyunsaturated ketone containing a crossed conjugated double bond group of the formula <FORM:1068839/C3/1> e.g. of the formula <FORM:1068839/C3/2> wherein R1 and R5 are aromatic, aliphatic or heterocyclic residues, R2 and R6 are hydrogen atoms or aliphatic residues, R3 and R4 are hydrogen atoms or together form a trimethylene group. Examples of such ketones are dibenzal acetone, benzal mesityl oxide, phorone and dibenzal cyclohexanone. The ketone may constitute up to 15% of the polymer. The aromatic vinyl compound may be styrene or vinyl naphthalene and the copolymer may also include between 15 and 25% by weight of an a -substituted aromatic vinyl compound such as a -methyl styrene or a -methyl vinyl naphthalene. Known methods of polymerization such as bulk, suspension and emulsion polymerization are employed, and the copolymer is freed of saltlike impurities by water washing, and of unreacted monomers by spray drying or solvent extraction.</p> |
