Free-radical polymerization blowing agent

NFPA Health 3, Reactivity 2 Uses Catalyst/initiator for vinyl polymehzations and for curing unsaturated polyester resins free radical generator blowing agent for plastics esp. for PVC prod, of floats, buoys polymerization catalyst for paper/paperboard in contact with aq.ffatty foods catalyst in food-contact crosslinked polyesters in food-pkg. adhesives... 

The Polymer. Amorphous Polystyrene. All of the expandable polystyrene referred to above is the amorphous type that is obtained by free radical initiation. This polymer is completely noncrystalline, and in the absence of impurities such as monomer and blowing agent it exhibits a glass-transition temperature of about 100°C. Both the rate of expansion and the extent of expansion are enhanced by reducing molecular weight, but the foam becomes less resistant to collapse on further steaming (63). Other polymeric modifications are discussed below. 

The overwhelming majority of foams are TPs, but TSs are also foamed with CBAs, although some of them do create problems. Popular TS foams are made from polyurethane, polyester, phenolic, epoxy, and rubber. Thermal decomposition of the blowing agent with certain plastics such as TS polyesters cannot be applied in this system because the heat of polymerization is not high enough to induce decomposition. But chemical reactions simultaneously produce gas and free radicals they typically involve oxidation and reduction of a hydrazine derivative and peroxide. The reactions are catalyzed by metals, which can be used repeatedly. 

Spherical beads that can be expanded into foam under the influence of heat or steam are produced directly by suspension polymerization in the presence of blowing agent. The term suspension polymerization describes a process in which water-insoluble monomers are dispersed as liquid droplets with suspension stabilizer and vigorous stirring to produce polymer particles as a dispersed solid phase. Initiators used in suspension polymerization are oil-soluble. The polymerization takes place within the monomer droplets. The kinetic mechanism of the suspension process is considered to be a free radical, water-cooled microbulk polymerization [1]. 

Azobisisobutyronitrile is used as a catalyst in vinyl polymerization and as a blowing agent for making foam rubber [114]. Azobisisobutyronitrile also is used as a free radical initiator (FRI) in graft copolymerization. 

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