Preparation of highly impermeable hyperbranched polymer thin-film coatings using dendrimers first as building blocks and then as in situ thermosetting agents
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This report describes the synthesis, characterization, and passivation properties of durable, polyfunctional, and highly cross-linked hyperbranched dendrimer/polyanhydride composite thin films. Such films are prepared from either amine- or hydroxyl-terminated poly(amidoamine) (PAMAM) dendrimers or amine-terminated poly(iminopropane-1,3-diyl) dendrimers (64-Cascade), and the copolymer poly(maleic anhydride)-c-poly(methyl vinyl ether), Gantrez. The dendrimers serve two roles in these composite films. First, they serve as building blocks, which permeate into and covalently cross-link a chemisorbed Gantrez copolymer. Then, in a separate thermal processing step, the dendrimers form highly impermeable monolithic films. In the case of amine- terminated dendrimers, the amic acid groups that attach the dendrimers to the original Gantrez network polymer form imides. Additionally, internal - amino groups within both the amine- and hydroxyl-terminated PAMAM dendrimers undergo retro-Michael reactions. Subsequently, a combination of interdendrimer Michael reactions and interdendrimer imidization reactions leads to additional cross-links in the heated film. Before heating, the permeability of dendrimer/Gantrez composite films is pH-dependent. After heating, they become highly blocking over the pH range studied (3-11). These films have been prepared on Au, Si, and Al. When a hydrophobic octadecyl layer is attached as a final step on these composites on Al, Al is passivated against corrosion in alkaline solution or from pitting in neutral chloride- containing solution by these new materials.
