1404293 Treatment of polymers; porous polymers MATEK CORP 12 June 1973 [12 June 1972] 27883/73 Headings C3C and C3P Polymers are converted to a desired morphological state by adding a form stable modifying material which fills the intramolecular free volume of the polymer without causing material dislocation of the normal molecular configuration and effects an apparent increase in the glass transition temperature to at least 20‹ C., converting the polymer while in the glassy state to the desired form and restoring the normal glass transition temperature by removing the form stable material. Preferred additives are sugars which may be added to solid polymer or a latex and are removed by leaching or orthoboric acid which may be mixed with a melt and co-crystallized with the polymer. The polymers are converted to powders or foams. Foams having small pores in the outer surface and relatively larger pores internally are made by foaming a liquid suspension of an elastomeric polymer containing the modifying material, casting to the desired form, rapidly heating in a manner which sets the surface first without further expansion then continuing with gradual heating to expand the interior and rigidify only after this further expansion. The product is brittle until the modifying material has been removed. Products made in this manner are particularly useful as ink pads in stencil-printing machines. Examples relate to (a) foaming a mixture of acrylonitrile rubber copolymer latex, vinyl chloride copolymers, curing agents and sugar by beating, heating to rigidify and leaching out the sugar, (b) mixing neoprene rubber latex with compounding ingredients and sugar, beating, drying, powdering and leaching out the sugar, (c) moulding the powder from (b), (d) treating plasticized vinyl latex as (b) but without the compounding ingredients.
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