A biomimetic approach to water-borne surface coatings

Broadbridge, Simon Glenn (1998) A biomimetic approach to water-borne surface coatings. University of Southampton, Doctoral Thesis.

Abstract

The volatile organic compounds (VOCs) used in many surface coatings may have a deleterious effect upon the environment. Considerable effort is being invested in the development of alternative formulations which, along with orthodox paint technologies, are reviewed. Water-borne systems represent a route towards eradicating VOCs.

The process by which insect cuticle is stabilised, sclerotization, provides the stimulus for an alternative, biomimetic approach to water-borne surface coatings. The catechol (ortho-dihydroxybenzene) functionality, e.g. dopamine, plays a crucial role in sclerotization through its action as a crosslinker of biological macromolecules. The incorporation of this mechanism in a synthetic system is explored.

In an approach to the development of synthetic polymeric systems containing the unstable catechol functionality, 1,3-benzo-dioxol-protected precursors were synthesised. Deprotection of the dihydroxy functionality via boron tribromide to yield the catechol was found to be incompatible with other functionality within the target materials. An alternative protection strategy was investigated, employing phase transfer catalysis to incorporate a benzyl ether protecting group across the dihydroxy group. The product of the reaction between 4-methylcatechol and benzal chloride was found to be 4-[(4,5-dihydroxy-2-methylphenyl)(phenyl)methyl-5-methyl-1,2-benzenediol, while reaction between dopamine and benzal bromide gave 1-phenyl-1,2,3,4-tetrahydro-6,7-isoquinolinediol. Mechanistic and structural analysis indicated that the reactions were following the Pictet-Spengler mechanism.

Studies of metal -7,7',8,8'-tetracyano-p-quinodeimethane (TCNQ) salts revealed that (15-crown-5)₂Tl(TCNQ)₂ crystallised from acetonitrile undergoes a structural rearrangement on heating to 380 K which generates a crystal structure very similar to that of (15-crown-5)₂KTCNQ. The phase change, detected by variable temperature electron spin resonance spectroscopy, may be driven by the increased stability of the architecture or by the formation of an extended TCNQ system.

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