tailieunhanh - Corrosion Control Through Organic Coatings P2

Acrylics can be somewhat sensitive to alkali environments — such as those which can be created by zinc surfaces [5]. This sensitivity is nowhere near as severe as those of alkyds and is easily avoided by proper choice of copolymers. | 16 Corrosion Control Through Organic Coatings TABLE Main Reactions Occurring in Free Radical Chain Addition Polymerization Radical Polymerization I Initiator M Monomer Initiator breakdown Initiation and propagation Termination by combination Termination by disproportionation I I I I I Mn I M n I M n M mI I M m nI I M n M nI I M n-1 n M-H I M m-i M H Data from Bentley J. Organic film formers in Paint and Surface Coatings Theory and Practice Lambourne R. Ed. Ellis Horwood Limited Chichester 1987. Transfers the free radical to another polymer a solvent or a chain transfer agent such as a low-molecular-weight mercaptan to control molecular weight This process excluding transfer is depicted in Table 4 . Some typical initiators used are listed here and shown in Figure . Azo di isobutyronitrile AZDN Di benzoyl peroxide T-butyl perbenzoate Di -butyl peroxide Typical unsaturated monomers include Methacrylic acid Methyl methacrylate Butyl methacrylate Ethyl acrylate 2-Ethyl hexyl acrylate CH3 cH3 A. CH3-C-N N-C-CH3 B. @-CO-O-O-OC-@ C. tBu-O-O-CO- D. tBu-O-O-tBu FIGURE Typical initiators in radical polymerization A AZDN B Di benzoyl peroxide C T-butyl perbenzoate D Di -butyl peroxide. 2006 by Taylor Francis Group LLC Composition of the Anticorrosion Coating 17 O CH3 II I A. HOC-C CH2 O CH3 B. CH3-O-C-C CH2 O CH3 C. nBu-O-C-C CH2 D. CH3-CH2OOC-CH CH2 E. C4H9-CH-CH2-OOC-CH CH2 C2h5 F. CH3-CH-CH2OOC-C CH2 OH CH3 G. CH2 CH-@ O H. CH2 CH-O -C -CH3 FIGURE Typical unsaturated monomers A Methacrylic acid B Methyl methacrylate C Butyl methacrylate D Ethyl acrylate E 2-Ethyl hexyl acrylate F 2-Hydroxy propyl methacrylate G Styrene H Vinyl acetate. 2-Hydroxy propyl methacrylate Styrene Vinyl acetate see also Figure Saponification Acrylics can be somewhat sensitive to alkali environments such as those which can be created by zinc surfaces 5 . This sensitivity is nowhere near as severe as those of alkyds and is easily avoided by proper choice of copolymers.