Self-healing coatings based on thiol-ene chemistry
Date
2009-03
Authors
Van den Dungen, Eric T. A.
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : University of Stellenbosch
Abstract
The work presented in this dissertation describes the development of self-healing
coatings based on thiol-ene chemistry. The approach was to synthesize capsules with
thiol and ene compounds separately encapsulated. These capsules were embedded in
various coating formulations and upon the formation of a crack with a razor blade, these
capsules ruptured. This caused the healing agent to flow into the crack via capillary
action and the thiol-ene healing mechanism was initiated. This resulted in recovery of the
damaged coating and provided continued protection to the substrate.
Pentaerythritol tetrakis(3-mercaptopropionate) (TetraThiol), 1,6-hexanediol diacrylate
(DiAcrylate) and 1,6-hexanediol di-(endo, exo-norborn-2-ene-5-carboxylate)
(DiNorbornene) are the thiol and ene compounds used in this study. Kinetic experiments
indicated that both TetraThiol-DiAcrylate and TetraThiol-DiNorbornene monomer pairs
undergo rapid polymerization and form a network within minutes upon exposure to UV
radiation and with the addition of a photoinitiator. The TetraThiol-DiNorbornene
monomer pair also showed a high rate of polymerization without the addition of a
photoinitiator and/or exposure to UV radiation. Styrene-maleic anhydride (SMA)
copolymers and chain-extended block copolymers with styrene (P[(Sty-alt-MAh)-b-Sty])
were synthesized via Reversible Addition-Fragmentation chain Transfer (RAFT)-
mediated polymerization. These copolymers were used as surfactant in
miniemulsification for the synthesis of core-shell particles with TetraThiol as the core
material. It appeared that P[(Sty-alt-MAh)-b-Sty] block copolymers, sterically stabilized
via the addition of formaldehyde, provide optimal stability to the core-shell particles.
DiNorbornene is encapsulated via miniemulsion homopolymerization of styrene and
well-defined, stable nanocapsules were obtained. TetraThiol and DiAcrylate
microcapsules were synthesized via in-situ polymerization of urea and formaldehyde.
Microcapsules with a particle size of one to ten micrometers and with a very smooth
surface were obtained. These microcapsules and nanocapsules were embedded in
poly(methyl acrylate) (PMA), styrene-acrylate and pure acrylic films and the self-healing
ability of these coatings, after introduction of a crack with a razor blade, was assessed.
Description
Thesis (PhD (Chemistry and Polymer Science)--University of Stellenbosch, 2009.
Keywords
Self-healing, Thiol-ene chemistry, Urea-formaldehyde microcapsules, Dissertations -- Polymer science, Theses -- Polymer science, Thiols, Coatings, Coating processes, Polymerization