Click chemistry appliations in polymer science

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some important applications of click chemistry in polymer and material science

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Click chemistry appliations in polymer science

  1. 1. Click chemistry &its application in material science Presented by: K.SASIDHAR (Dr.K.V.S.N.Raju’s Group) OCP Division,IICT
  2. 2. Concept of Click Chemistry “Click chemistry” is a chemical philosophy introducded by K.Barysharpless in 2001, which describes the chemistry that can generate substances quickly and reliably by joining small units together with high thermodynamic force. Requirements for the click reaction are , The reaction must be 1. Modular 2. Wide in scope 3. High yield of product (nearly 100%) 4. Generate only inoffensive or no byproducts 5. Stereo specific 6. High atom economy The process must be: 7.simple reaction conditions 8.readily available starting materials and reagents 9.simple product isolation by non-chromatographic methods
  3. 3. Defining a “Click” Chemistry Reaction “ A click reaction must be modular, wide in scope, high yielding, create only inoffensive by-products (that can be removed without chromatography), are stereo specific, simple to perform and that require benign or easily removed solvent. ” - Barry Sharpless Kolb, H.C.; Finn, M.G.; Sharpless, B.K. Angew. Chem. Int. Ed. 2001, 40, 2004-2021. 3
  4. 4. Classes of “Click” Reactions R1 Azide- Alkyne cycloaddition R1 N R2 R1 R3 OH O Nu Nu Non-Aldol type Carbonyl Chemistry (likethe formation of oxime ethers, hydrazones and aromatic heterocycles ) ADDITION REACTIONS OF ALKENES AND ALKYNES RS R1 SH R2 R4 R2 R2 (like epoxides, aziridines cyclic sulphonates etc) R3 R4 NUCLEOPHILIC OPENING OF HIGHLY STRAINED RINGS Thiol-ene reaction ,Michael addition etc) N R1 Diels-Alder reaction (di hydroxylation of alkynes, N R2 CYCLO ADDITION REACTIONS N N+ N- R2
  5. 5. Historical Perspective of Azide/Alkyne Cycloadditions 1933- Dipolar nature of azide first recognized by Linus Pauling R N3 R N N N R N N NH2 R N N N 1960- Mechanism of 1,3-dipolar cycloaddition of azides and alkynes pioneered by Rolf Huisgen + N3 R' R'' N 1 N R' N 80oC 5 R'' + N 1 N R' N R'' 4 2001- Copper catalyzed 1,3-Dipolar cycloaddition by Sharpless/Meldal R'' + N3 R' Cu(I) rt N 1 N R' N R'' 4 L. Pauling. Proc. Natl. Acad. Sci. USA 1933, 19, 860-867; Huisgen, R. Angew. Chem. Int. Ed. 1963, 2, 633-696 Sharpless, K.B. et al. Angew. Chem. Int. Ed 2002, 41, 2596-2599; Meldal,M.J. et al. J. Org. Chem. 2002, 67, 3057-3064 5
  6. 6. Copper Catalyzed Azide/Alkynes Cycloaddition (CuAAC) • Thermodynamic and kinetically favorable (50 and 26 kcal/mol, respectively) • Regiospecific R'' + N3 R' Cu(I) • Chemoselective • 107 rate enhancement over noncatalyzed reaction N 1 N R' N R'' 4 • Triazole stable to oxidation and acid hydrolysis Rostovtsev et al. Angew. Chem. Int Ed. 2002, 41, 2596-2599 6
  7. 7. CuAAC Catalytic Cycle N N N R2 [CuLx] H R R' H CuLx R' H+ H+ N N R H N R2 R' 23 kcal/mol CuLx R2 CuLx N N N R2 R2 N N N R1 N N N CuLx RDS 18 kcal/mol Himo, F. et al. J. Am. Chem. Soc, 2005, 127, 210-216. Ahlquist, M., Fokin, V.V. Organometallics 2007, 26, 4389-4391. R' R2 CuLx N N N R' CuLx CuLx 7
  8. 8. Click chemistry Chemistry Applications in polymers Some recent applications of click chemistry in material science are:• Adhesive polymers for Cu metal • Potential Propellent binders • polymer backbone modification • Surface modification of nano particles. • Hydrogels synthesis • In hyperbranched polymers & dendrimers 8
  9. 9. Adhesive polymes for Cu metal from click reaction • David D. Diaz etal have recently synthesised a metal adhesive polymer based on copper catalyzed azide-alkyne cycloaddition. • Di or tri azide and Di or tri alkyne monomers were introduced between copper or zinc plates,which provides necessary Cu(I) ions. 9
  10. 10. • The resulting adhesive polymer was found to possess comparable or superior adhesive strength to standard commercial glues. HO N HO HO N3 HO N HO OH N N N N polymer N N polymer N3 OH N N N OH polymer • The above polymer is showing 268 24 kg load per gram adhesive. where as commercial glue (weld-it) is showing 248 111 kg load per adhesive. Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 45, 5182–5189 (2007)
  11. 11. 1,2,3-triazole-polymers as potential propellant binders 1. Propellant is the chemical mixture burned to produce thrust in rockets and consists of a fuel and an oxidizer ,generally these are held together by polymeric binder 2. Polyurethanes are well known binders for propellants. But there may be a chance of side reactions during and after the polymerization ,that degrade the mechanical properties of the resulting propellant .e.g., loss of elasticity 3. 1,2,3-triazole polymers are recently studied as novel binders for the explosives and high energy propellants Because of high thermal & physical stability 4. Azide and alkynes monomers react readily and form polytriazole with out any side reaction , o these are one of the best alternative for the propellant binders
  12. 12. 5. A typical polyurethane, elastomeric linear matrix for rocket propellants has modulus 0.05-1.9 Mpa 6. Where as the triazole polymers having much improved modulus 0.5-3.9 MPa 7. the mixture of above cross linked polymer with 43wt% aluminum filler greatly improve the modulus of the triazole polymers, which could reach nearly 4MPa. Ling Wang et.al.,Journal of AppliedPolymer Science, Vol. 117, 2612–2621 (2010)
  13. 13. Polyurethane backbone modification by click chemistry •Du Prez et al. synthesized linear polyurethanes (PUs) having alkyne groups •located along the backbone •The polyurethane was formed by reacting with two •different alkyne-functionalized diols with a diisocyanate compound •TGA measurements demonstrated that the incorporated triazoles in the PU materials strongly improves the final char yield
  14. 14. Surface modification of silica Nano particles through ‘click’ chemistry  Any particle with a size from 10 nm to 100nm is generally termed as nano particle. Nano particles have many applications. ex:colloidal gold – useful to stain the glass with an intense red colour ,was done in ancient times. Zinc nano particles are used in the sun block creams and cancer medicine. Silica nano particles in chromatography, bio-seperation, imaging, and multifunctional nano comopostes. surface modification of silica nano particles by click chemistry: functionalisation of nano particles can be achieved by so many ways. But silane coupling agents are widely used to surface modification of silica nano particles. But it has some drawbacks such as,solvent polarity and reaction temperature. in large scale surface capping is not uniform. Click reaction is one of the efficient way to impart desirable funtionalities to nanoparticles without any side reactions. Ex:-pyrene, a fluorophore (which shows excimer emmision) is successfully attached to the silica nano particles.
  15. 15. CURRENT SCIENCE, VOL. 95, NO. 9, 10 NOVEMBER 2008
  16. 16. Hydrogels synthesis from click chemistry • • • • • Hydrogels are Water swollen crosslinked polymers Crosslinks may occur: – by reaction of one or more monomers – hydrogen bonds – Vander Waals interactions Hydro gels traditionally prepared by photo polymerization of water soluble vinyl monomers, such as polyethylene glycol- diacrylates, but has some defects like uncontrollable crosslinking click chemistry concept is utilized In designing controlled hydro gel networks With improved properties. Another advantage of click chemistry is hydrogels can be prepared at room temperature.
  17. 17. Hyper branched Polymers & dendrimers from Click Chemistry Dendrimers hyper branched polymers 1.Dendrimer = Greek words dendron (tree)+ meros (part) 1.Made in a very easy fashion [ Divergent and convergent process 2.Made in a very sophisticated fashion [ Divergent and convergent process] 2.polydisperse [ Mw>Mn] and less degree of branching ( DB >1 ) 3.Perfectly built onto a core molecule 3.They are an irregular macromolecules 4.Monodisperse [ Mw =Mn] and high degree of branching ( DB =1 ) 4.These polymers structure consist of three distinct groups : dendritic groups ;linear groups and terminal groups. 5.They are symmetrical and layered macromolecules Examples of hyper branched polymers: 6.These polymers consist of three distinct areas : polyfunctional central core ( center of symmetry); radial symmetrical layers of repeating units( generations); end standing groups (terminal groups). Boltorns (P( bis -MPA) hyper branched polymer), Hybranet (poly(ester amide)) poly( phenylenes )
  18. 18. Dendrimers and hyper branched polymers are synthesized mainly two ways • Divergent strategy:- Core to Surface •Convergent strategy :-Surface to core
  19. 19. Click chemistry is also an efficient reaction to produce dendrimers and hyperbranched polymers with good yeilds Convergent Approach Divergent approach

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