GB1093804A - Method for preparing expandable thermoplastic polymer particles containing a volatileluid foaming agent symmetrically encapsulated therein - Google Patents

Abstract

Expandable thermoplastic particles which are spherical and have a volatile liquid foaming agent symmetrically encapsulated within them are made by dispersing a monomer containing the foaming agent in a non-solvent dispersing medium to form a plurality of droplets and polymerizing the monomer in the presence of a redox catalyst system having a catalyst component, a reducing agent component and an activator. One of the components of the catalyst is dispersed and substantially soluble in the monomer and essentially insoluble in the dispersing medium and the other component is dispersed and substantially soluble in the non-solvent medium and generally insoluble in the monomer. The catalyst component may be one or more peroxides which are soluble in aqueous media, for example, persulphates of ammonium, sodium and potassium, perborates and percarbonates of the latter two and hydrogen peroxide. Organic peroxides soluble in the monomer may also be used either alone or in addition to an inorganic peroxide, for example, benzoyl, cumene, tetralin, acetyl and caproyl peroxides, t-butyl hydroperoxide, t-butyl perbenzoate and diperphthalate and methyl ethyl ketone peroxide. The catalyst component is used in an amount from 0.01-3% by weight of the monomer mixture. Reducing agents which may be used are hydrazine, sodium hydrosulphite, sodium metabisulphite, potassium sulphite, sodium formaldehyde sulfoxylate and calcium bisulphite. The activator may be ferrous ions, a tertiary amine soluble in the reaction medium such as dimethyl ethanol amine or triethanolamino or an oil soluble activator such as metal naphthenates, acetyl acetonates, oleates and octoates. The amount of reducing agent used is 0.5-6% based on the weight of the monomers. Monomers used in the examples are styrene, methyl methacrylate, o-chlorostyrene, ethyl methacrylate and p-t-butyl styrene and mixtures of two of these. Small amounts of divinyl benzene, divinyl toluene and ethylene glycol dimethacrylate may be added as cross-linking agents. Blowing agents specified in the examples are neopentane and neohexane. The beads obtained are expanded by heating to form mono cells.