Polymer reaction graft polymerization

In the manufacture of highly resident flexible foams and thermoset RIM elastomers, graft or polymer polyols are used. Graft polyols are dispersions of free-radical-polymerized mixtures of acrylonitrile and styrene partially grafted to a polyol. Polymer polyols are available from BASF, Dow, and Union Carbide. In situ polyaddition reaction of isocyanates with amines in a polyol substrate produces PHD (polyhamstoff dispersion) polyols, which are marketed by Bayer (21). In addition, blending of polyether polyols with diethanolamine, followed by reaction with TDI, also affords a urethane/urea dispersion. The polymer or PHD-type polyols increase the load bearing properties and stiffness of flexible foams. Interreactive dispersion polyols are also used in RIM appHcations where elastomers of high modulus, low thermal coefficient of expansion, and improved paintabiUty are needed. 

Photoinduced free radical graft copolymerization onto a polymer surface can be accomplished by several different techniques. The simplest method is to expose the polymer surface (P-RH) to UV light in the presence of a vinyl monomer (M). Alkyl radicals formed, e.g. due to main chain scission or other reactions at the polymer surface can then initiate graft polymerization by addition of monomer (Scheme 1). Homopolymer is also initiated (HRM-). 

Most radiation graft polymerizations are carried out as heterogeneous reactions. The polymer is swollen by monomer but does not dissolve in the monomer. (For semicrystalline polymers, swelling and grafting take place only in the amorphous regions.) The typical reaction system involves equilibration of polymer with monomer followed by irradiation of the... 

Redox initiation is often an efficient method for graft polymerization. Hydroxyl-containing polymers such as cellulose and poly(vinyl alcohol) undergo redox reaction with ceric ion or other oxidizing agents to form polymer radicals capable of initiating polymerization... 

Tsubokawa et al. (12-14) have introduced radical sources of azo or peroxy groups by another methods, and successively conducted the radical polymerization of vinyl compounds, such as styrene or methyl methacrylate, to give polymer-grafted particles see Reaction (3). The grafting by the radical polymerization of methyl methacrylate, initiated from a peroxy group introduced on silica, takes place at relatively high efficiency, compared with those from azo group-introduced particles. 

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