Chloromethyl methyl ether polystyrene reaction

The chloromethylated polystyrene resin used for Merrifteld solid-phase peptide synthesis is prepared by treatment of polystyrene with chloromethyl methyl ether and a Lewis acid catalyst. Propose a mechanism for the reaction. 

Quaternary ammonium ion exchange resins were produced initially by chloromethylating crosslinked polystyrene beads with chloromethyl methyl ether, followed by quaternization with tertiary amines. We have circumvented exposure to the highly carcinogenic bis(chloromethyl) ether, a common contaminant of commercial chloromethyl methyl ether, by employing l,4-bis(chloromethoxy)butane or 1-chloromethoxy-4-chlorobutane and have produced chloromethylated poly(oxy-2,6-dimethyl-1,4-phenylene) and polysulfone. Alternatively, chloromethyl methyl ether can be generated from acetyl chloride and methylal, and the reaction mixture utilized directly in chloromethylation of activated aromatic repeat units. 

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