Styrene ionomers comonomer

Fig. 1 Glass transition and density vs. ionic comonomer content for styrene ionomers.

Fig. 2 Mol % ions in multiplets or clusters vs total mol % of ionic comonomer in the styrene ionomers (from dielectric data).

Typically, carboxylate ionomers are prepared by direct copolymerization of acrylic or methacrylic acid with ethylene, styrene or similar comonomers by free radical copolymerization (65). More recently, a number of copolymerizations involving sulfonated monomers have been described. For example, Weiss et al. (66-69) prepared ionomers by a free-radical, emulsion copolymerization of sodium sulfonated styrene with butadiene or styrene. Similarly, Allen et al. (70) copolymerized n-butyl acrylate with salts of sulfonated styrene. The ionomers prepared by this route, however, were reported to be "blocky" with regard to the incorporation of the sulfonated styrene monomer. Salamone et al. (71-76) prepared ionomers based on the copolymerization of a neutral monomer, such as styrene, methyl methacrylate, or n-butyl acrylate, with a cationic-anionic monomer pair, 3-methacrylamidopropyl-trimethylammonium 2-acrylamlde-2-methylpropane sulfonate. 

Ionomers of practical interest have been prepared by two synthetic routes (a) copolymerization of a low level of functionalized monomer with an olefinically unsaturated monomer or (b) direct functionalization of a preformed polymer. Typically, carboxyl containing ionomers are obtained by direct copolymerization of acrylic or methacrylic acid with ethylene, styrene and similar comonomers by free radical copoly-merization. Rees (22) has described the preparation of a number of such copolymers. The resulting copolymer is generally available as the free acid which can be neutralized to the degree desired with metal hydroxides, acetates and similar salts. Recently, Weiss et al.(23-26) have described the preparation of sulfonated ionomers by copolymerization of sodium styrene sulfonate with butadiene or styrene. 

Polyolefin, PO [of ethylene, propylene, butylene, 4-methylpentene, and their copolymers with 1-aUcenes, vinyls, (meth)acrylates - preferably PP], was grafted at a ratio 1 9-4 1 with 1-20 wt% of (meth)acrylic acid and >30 wt% of styrene and/or aUcyl- and/or halo-substituted styrene, methacrylic ester, and 0-60 % of other comonomers [e.g., vinyl aromatic, ester], at least some of the acid units of methacrylic acid and/or acrylic acid bearing a charge and being associated with non-polymeric counterions [e.g., 90 % methyl methacrylate, 5 % butyl acrylate, and 5 % methacrylic acid with either or Mg ". The ionomer could be blended with PO either during or after manufacturing. 

Polyolefins constitute the largest volume class of polymeric materials. Polyethylene, polypropylene, and ethylene-propylene rubber are major products in this family, with many subset variations with each material. Polyethylene variants include high density polyethylene (HDPE), low density polyethylene (LDPE), ultrahigh molecular weight polyethylene (UHMWPE), linear low density polyethylene (LLDPE), very low density polyethylene (VLDPE) and various ethylene copolymers (including comonomers of vinyl acetate, ethyl and methyl acrylate, acryhc acid and methacryhc acid and their metal salts (ionomers)). Polypropylene has fewer variations, of which low amounts of ethylene are included while maintaining crystaUinity. More recently, ethylene-styrene copolymers have been introduced. 

---