| 摘要 |
Expandable synthetic resins are manufactured by a process which includes the polymerization, preferably suspension polymerization, under pressure of an a -ethylenically unsaturated compound in the presence of a normally gaseous expanding agent and a nitrite. Suitable monomers are styrene, methylmethacrylate, alpha-methyl styrene and acrylonitrile and mixtures thereof. Examples of expanding agents are hydrocarbon gases such as butane, ethane, propane, methane, butene, isobutylene, propylene and ethylene; halogenated hydrocarbon gases such as methyl chloride, and inert gases such as nitrogen and carbon dioxide. Preferable quantities are from 3% to 15% by weight of the total quantity of monomer. Particularly desirable nitrites are those having polymerization inhibiting properties and which are water-soluble, e.g. sodium nitrite and potassium nitrite either singly or as a mixture in the range of from 0.0001% to 0.15% by weight of the total quantity of monomer. Any catalyst commonly used in suspension polymerization may be used in quantities of 1% or less by weight of the total monomer. Benzoyl peroxide and lauroyl peroxide are mentioned in the examples. The expandable beads may be directly expanded in a mould or they may be pre-expanded in boiling water and fully expanded in a mould. |
