Microencapsulation Of Organic Silanes And Their Use As Self Healing Materials (Nanyang Technological University)

Microencapsulation Of Organic Silanes And Their Use As Self Healing Materials (Nanyang Technological University)
United States Patent Application 20150079290
Yang; Jinglei ;   et al.   March 19, 2015
Applicant: Nanyang Technological University
Abstract
The disclosure provides a poly(urea-formaldehyde) microcapsule, which comprises encapsulated in the poly(urea-formaldehyde) microcapsule an organofluorine silane of the general formula (I) A.sub.3C(CA.sub.2).sub.xSiR.sup.1.sub.yX.sub.(3-y) (I), wherein in formula (I) A is either fluorine (F) or hydrogen (H), wherein at least 50% of atoms A are fluorine. X is chloro or a group RO, wherein R is a linear or branched alkyl radical of 1 to 4 carbon atoms, R.sup.1 is a linear, branched or cyclic alkyl group of 1 to 8 carbon atoms, n=0 or 2, y=0 or 1 or 2 and m=0 to 20, encapsulated within the microcapsule. The disclosure also provides self-healing coating compositions comprising such polymeric microcapsules and methods of preventing or slowing corrosion using such coating compositions.
FIELD OF THE INVENTION
[0002] The present invention relates generally to microcapsules and a method of microencapsulating an organofluorine silane as core material. The invention also relates to a method for microencapsulation of organofluorine silane in a poly(urea-formaldehyde) microcapsule/shell by means of an in-situ polymerization process in an oil-in-water emulsion system. The invention also provides a process for manufacturing a self-healing anticorrosion coating and a respective coating composition. In accordance with the process of making a self-healing anticorrosion coating, the microcapsules described herein may be dispersed in a resin to yield a self-healing coating. The self-healing effect can be used for corrosion protection application.
BACKGROUND OF THE DISCLOSURE
[0003] Self-healing materials have received considerable attention due to their great potential to diminish degradation and reduce the maintenance cost. Since the first generation self-healing material based on the ring opening metathesis polymerization (ROMP) of encapsulated dicyclopentadiene (DCPD) in the presence of Grubbs' catalyst particles (S. R. White, N. R. Sottos, P. H. Geubelle, J. S. Moore, M. R. Kessler, S. R. Sriram, E. N. Brown and S. Viswanathan, Nature, 2001, 409, 794-797) microencapsulation has been one of the most efficient and widely used approaches in self-healing materials development. Poly(urea-formaldehyde) (PUF) microcapsules containing DCPD as healing agent were prepared through an in situ polymerization in oil-in-water emulsion (E. Brown, M. Kessler, N. Sottos and S. White, J. Microencapsulation, 2003, 20, 719-730; M. R. Kessler, N. R. Sottos and S. R. White, Composites: Part A, 2003, 34, 743-753) and the capsules size was further reduced to nanometre scale with the assistance of a sonication technique (B. J. Blaiszik, N. R. Sottos and S. R. White, Compos. Sci. Technol., 2008, 68, 978-986). Linseed oil (C. Suryanarayana, K. C. Rao and D. Kumar, Prog. Org. Coat., 2008, 63, 72-78), amines (D. A. McIlroy, B. J. Blaiszik, M. M. Caruso, S. R. White, J. S. Moore and N. R. Sottos, Macromolecules, 2010, 43, 1855-1859) and epoxy resins (L. Yuan, G. Liang, J. Xie, L. Li and J. Guo, Polymer, 2006, 47, 5338-5349) were also microencapsulated for self-healing applications. To avoid the contamination of catalyst by the host matrix, a dual capsule system was reported (S. Cho, H. Andersson, S. White, N. Sottos and P. Braun, Adv. Mater., 2006, 18, 997-1000; S. H. Cho, S. R. White and P. V. Braun, Adv. Mater., 2009, 21, 645-649) and this approach has shown good self-healing and corrosion protection features. Most of the capsules applied for self-healing purpose so far were made from PUF, polyurethane (PU) and polyurea. As an alternative, a double-walled polyurethane-poly(urea formaldehyde) (PU-PUF) microcapsule was recently developed through the combination of interfacial polymerization of PU and in situ polymerization of PUF in a single batch reaction (M. M. Caruso, B. J. Blaiszik, H. Jin, S. R. Schelkopf, D. S. Stradley, N. R. Sottos, S. R. White and J. S. Moore, ACS Appl. Mater. Interfaces, 2010, 2, 1195-1199.) Other approaches such as hollow glass fiber embedment, microvascular system, and electrospun hollow fibers have also been extensively investigated for self-healing materials development, and more recently there was reported an oxetane-substituted chitosan precursor incorporated PU showing good scratch closure performance within half an hour under sunlight (B. Ghosh and M. Urban, Science, 2009, 323, 1458-1460).
[0004] Since isocyanates are reactive with moisture and can thus be used as a potential healing agent to develop one-part, catalyst-free self-healing materials that are exposed to moist or aqueous environments, their suitability as self-healing materials has been rather extensively. Early research on encapsulation of isocyanate has been mainly restricted to its blocked form or solid state (I. W. Cheong and J. H. Kim, Chem. Commun., 2004, 2484-2485; H. Yang, S. Mendon and J. Rawlins, eXPRESS Polym. Lett., 2008, 2, 349-356) while Yang et, al. for the first time reported in Macromolecules, 2008, 41, 9650-9655, the microencapsulation of liquid isocyanate monomer. Less reactive isophorone diisocyanate (IPDI) was encapsulated by polyurethane microcapsules based on the polymerization of toluene diisocyanate (TM) prepolymer that was cautiously in-house synthesized.
[0005] Silanes are a further class of potential seal-healing materials. However, to date, the research on organic silane for self-healing materials remains largely unexplored, and only a few publications have appeared. Braun and co-workers reported the polydimethylsiloxane (PDMS)-based silane microcapsules applied for self-healing coatings (S. H. Cho, S. R. White, P. V. Braun, Advanced Materials 2009, 21, 645 and S. Cho, H. Andersson, S. White, N. Sottos, P. Braun, Advanced Materials 2006, 18, 997). A mixture of hydroxyl end-functionalized PDMS (HOPDMS) and polydiethoxysiloxane was directly phase-separated, or encapsulated and then dispersed in epoxy matrix, and the yielding coating exhibited good self-healing ability. However, organo-tin catalyst was necessary for such self-healing system. Another example is the microencapsulation of a self-synthesized silyl ester for self-healing coatings reported by S. J. Garcia, H. R. Fischer, P. A. White, J. Mardel, Y. Gonzalez-Garcia, J. M. C. Mol, A. E. Hughes, Progress in Organic Coatings, 70, 142. Octyldimethylsilyloleate (silyl ester) was synthesized and encapsulated into poly(urea-formaldehyde) (PUP) microcapsules, which were then incorporated into epoxy coating to produce a self-healing coating the self-healing properties of which were demonstrated.
[0006] However, there is still a need to provide further self-healing materials and microcapsules that are suitable for the microencapsulation of such self-healing materials.
SUMMARY OF THE INVENTION
[0007] The present invention addresses these needs by providing new and improved microcapsules, coating compositions comprising such microcapsules and methods for preventing or lowering the grade of corrosion.
[0008] In a first aspect, the disclosure provides a poly(urea-formaldehyde) microcapsule, the poly(urea-formaldehyde) microcapsule comprising encapsulated within the microcapsule an organofluorine silane of the general formula (I) A.sub.3C(CA.sub.2).sub.mSiR.sup.1.sub.yX.sub.(3-y) (I), wherein in formula (I) A is either fluorine (F) or hydrogen (H), wherein at least about 50% of atoms A are fluorine, X is chloro or a group RO, wherein R is a linear or branched alkyl radical of 1 to 4 carbon atoms, R.sup.1 is a linear, branched or cyclic alkyl group of 1 to 8 carbon atoms, y=0 or 1 or 2 and m=0 to 20.
[0009] In a second aspect, the disclosure provides a method of encapsulating an organofluorine silane of the general formula (I) A.sub.3C(CA.sub.2).sub.nSiR.sup.1.sub.yX.sub.(3-y)(I), wherein in formula (I) A is either fluorine (F) or hydrogen (H), wherein at least about 50% of atoms A are fluorine, X is chloro or a group RO, wherein R is a linear or branched alkyl radical of 1 to 4 carbon atoms, R.sup.1 is a linear, branched or cyclic alkyl group of 1 to 8 carbon atoms, y=0 or 1 or 2 and m=0 to 20 in a polymer microcapsule, the method comprising: [0010] forming an oil-in-water emulsion containing a mixture of urea and the organofluorine silane of the general formula (I), [0011] adding formaldehyde to the oil-in-water emulsion, and [0012] polymerizing urea and formaldehyde by in-situ polymerization to form the polymeric microcapsule, thereby encapsulating the organofluorine silane of the general formula (I) in the formed polymeric microcapsule.
[0013] In a third aspect, the disclosure provides a method of preventing or slowing corrosion, the method comprising applying a coating composition on a substrate, wherein the coating composition comprises polymeric microcapsules consisting of a polymerization product of methylene diphenyl diisocyanate (MDI) prepolymer with a polyol, the microcapsule comprising a liquid isocyanate compound encapsulated within the microcapsule.
[0014] In a fourth aspect, the disclosure provides a coating composition comprising poly(urea-formaldehyde) microcapsules, the poly (urea-formaldehyde) microcapsules comprising encapsulated therein an organofluorine silane of the general formula (I) A.sub.3C(CA.sub.2).sub.mSiR.sup.1.sub.yX.sub.(3-y) (I), wherein in formula (I) A is either fluorine (F) or hydrogen (H), wherein at least about 50% of atoms A are fluorine, X is chloro or a group RO, wherein R is a linear or branched alkyl radical of 1 to 4 carbon atoms, R.sup.1 is a linear, branched or cyclic alkyl group of 1 to 8 carbon atoms, y=0 or 1 or 2 and m=0 to 20.
[0015] In yet another aspect, the disclosure provides a method of preventing or slowing corrosion, the method comprising applying a coating composition on a substrate, wherein the coating composition comprises hexamethylene diisocyanate encapsulated within the microcapsule.
[0016] In yet another aspect, the disclosure provides the use of an organofluorine silane of the general formula (I) A.sub.3C(CA.sub.2).sub.mSiR.sup.1.sub.yX.sub.(3-y) (I) as self-healing material, wherein in formula (I) A is either fluorine (F) or hydrogen (H), wherein at least about 50% of atoms A are fluorine, X is chloro or a group RO, wherein R is a linear or branched alkyl radical of 1 to 4 carbon atoms, R.sup.1 is a linear, branched or cyclic alkyl group of 1 to 8 carbon atoms, y=0 or 1 or 2 and m=0 to 20.
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