This document discusses the development of polyurethane-urea coatings using azide-alkyne click chemistry. It provides background on the chemistry of polyurethanes and their properties. It describes the concept of click chemistry and how copper-catalyzed azide-alkyne cycloaddition is a key click reaction. Schemes are proposed for synthesizing hyperbranched polyethers and fluorescent polyurethane coatings using click chemistry approaches. The document acknowledges contributions from researchers involved in the project.

1. Development of polyurethane-urea coatings
using azide-alkyne click chemistry
K.SASIDHAR,
Dr.K.V.S.N.Raju’s
Group,
PFM Division, IICT.
Work Report
3rd October, 2012

2. Brief chemistry of polyurethanes

The underlying chemistry behind polyurethane was first developed
by Professor Dr. Otto Bayer (1902-1982). He invented the
Diisocyanate Polyaddition Process which is the base patent in the
polyurethane industry.

Polyurethanes are formed by the reaction between a
polyisocyanates and hydroxyl(-OH) containing resin
blend
Some properties of Polyurethanes
Have high strength if crosslink density is high
Good solvent resistance
High abrasion resistance
High corrosion resistance
High resistance to O2 and O3
Major use of PU’s in foams(65%)

3. Types of Polyols
•The name polyol refers to chemical compounds containing multiple hydroxyl groups.
•Polymeric polyols may be
(a) Polyether polyol,
(b) Polyester polyol
(c) Acrylic polyol
•Polyol with low molecular weight………….. hard and stiff polymers
(due to high urethane
concentration)
•Polyol with high molecular weight…………. Flexible and soft polymers
•Polyols with long chain……………………....Soft, elastomeric Polymers
•Polyols with short chain………………………Rigid, crosslinked Polymers

4. Linear Vs Dendritic polyols
Linear polyols
Dendritic polyols
(1) Less number of end Functional groups
(1) Large number of end Functional groups
(2) Newtonian relationship between
viscosities and molecular weight
polymers show high viscosities at high
molecular weights.
(2) non-Newtonian relationship between
viscosities and molecular weight
polymers show low viscosities at high
molecular weights.
(3) Degree of branching is zero
(3) Degree of branching is very high
XRD results shows that these are having
spherical or globular structures
(4) Not readily soluble compared to HBP’s
(4) High chemical reactivity and enhanced
solubility
(5) They show less thermal mechanical
stability than dendrimers and HBP’s
(5) These materials show outstanding
mechanical properties such as initial
modulus, tensile strength and
compressive moduli which reflect the
compact highly branched structures

5. Polyester polyols & Polyether polyols
polyester polyols
polyether polyols
(1) Excellent mechanical properties like
abrasion resistance.
(1) High hydrolysis resistance
(2) Heat resistance
(2) Excellent low temperature flexibility
(3) excellent oil resistance
(3) Resistant to microbial degradation
(4) High resistance to oils and chemicals
(4) Excellent clarity
(5) Polyesters exhibit higher cut/tear
resistance and loading capabilities
(5) more durable than polyester based
systems
(6) Not recommended for use in high
humidity and exposure to water.
(6) Better resistance to UV radiation than
polyester systems.

6. Dendrimers Vs Hyperbranched polymers
Dendrimers
Hyperbranched 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
2.Polydisperse [ Mw>Mn] and less than
100%degree of branching
3.Perfectly built onto a core molecule
3.They are an irregular macromolecules
4.Monodisperse [ Mw =Mn] and 100% degree of
branching
5.They are symmetrical and layered
macromolecules
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).
4.These polymers structure consist of three
distinct groups : dendritic groups ;linear
groups and terminal groups.
Examples of hyper branched polymers:
Boltorns (P( bis -MPA) hyper branched polymer),
Hybranet (poly(ester amide)

7. Dendrimers and hyper branched polymers are
synthesized mainly two ways
• Divergent strategy:- Core to Surface
•Convergent strategy :-Surface to core

8. Functionalization of Polyurethanes
 Functionalization of PU leads to highly functional materials
 For many high-tech applications, PU materials and especially PU films and
coatings need to bear functionalities to improve their intrinsic properties such as
wettability, adhesion, biocompatibility, conductivity, cross-linking density and many
others.
 Functionalization possible by physical & chemical methods but it should not affect the
other properties of polymer
In general, the chemical modification of such functional polymers can also suffer of a
certain lack of efficiency since the reactivity of functional groups may be affected by
the structure of the polymer and also by the efficiency of the chemical reactions used.
 In 2001, Sharpless and co-workers introduced innovative approaches, named
“click” chemistry, allowing quantitative reactions. Among the listed reactions, Huisgen
1,3- dipolar Cycloadditions between an azide and an alkyne compound have been
widely explored due to, among others, its efficiency, versatility and inertness toward
other functional groups.

9. Concept of Click Chemistry
“click chemistry” is a chemical philosophy introduced 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

10. DEFINING A “CLICK”CHEMISTRY
“ 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.
10

11. Classes of “Click” Reactions
Azide- Alkyne
cycloaddition
CYCLO ADDITION
REACTIONS
Diels -Alder reaction
NUCLEOPHILIC OPENING OF
HIGHLY STRAINED RINGS
(like epoxides, aziridines cyclic
sulphonates etc)
NON-ALDOL TYPE CARBONYL
CHEMISTRY
(like the formation
of oxime ethers, hydrazones )
ADDITION REACTIONS OF
ALKENES AND ALKYNES
(dihydroxylation of alkenes,
Thiol-ene reaction, Michael addition
etc)

12. Historical Perspective of
Azide/Alkyne Cycloaddition
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

13. Copper Catalyzed Azide/Alkynes
Cycloaddition (CuAAC)

Thermodynamic and kinetically
favorable (50 and 26
kcal/mol, respectively)
R''

+
N3 R'
Regiospecific
Cu(I)


Chemo selective
107 rate enhancement over noncatalyzed reaction
Rostovtsev et al. Angew. Chem. Int Ed. 2002, 41, 2596-2599
N 1
N R'
N
R'' 4

14. CuAAC Catalytic Cycle
CuLx
R'
H
R2
N N N
R'
CuLx
CuLx
Himo, F. et al. J. Am. Chem. Soc, 2005, 127, 210-216.
Ahlquist, M., Fokin, V.V. Organometallics 2007, 26, 4389-4391.

15. Importance of Triazoles

high thermal stability,

anti-microbial nature,

chemical inertness,

easy to prepare,

stable to oxidation and acid hydrolysis.

Triazoles can act as good corrosion
inhibitors.
R''
+
N3 R'
Cu(I)
N 1
N R'
N
R'' 4

16. SCHEME-1
Hyperbranched polyether
using click chemistry and
their polyurethane coatings

17. C-H Str
C-O-C Str
O-H Str
4000
3500
3000
2500
2000
1500
1000
500

18. Hyperbranched polyurethane-urea coatings

19. SCHEME-2
( Future work)
Development of fluorescent
polyurethane coatings
using click chemistry

20. Fluorescent polyurethane coatings
Fluorescent paints 'glow' when exposed to the long-wave “ultraviolet" frequencies
and this effect is known as black-light effect.
There are both visible and invisible fluorescent paints. The visible appear under white
light to be any bright color, turning peculiarly brilliant under black lights. Invisible
fluorescent paints appear transparent or pale under daytime lighting, but will glow only
under UV light- and in a limited range of colors.
these paints have extensive application where artistic lighting effects are
desired, particularly in "black box" entertainments and environments such as
theaters, bars, shrines, etc.
fluorescence-based materials have attracted rapidly growing interest
based on their optical characterization for
Biological sensing
Cell imaging
Disease diagnostics and
real-time detection
Fluorescent paint used
in contemporary art

21. Synthesis of azidated silica nano particles

22. Synthesis of perylene fluorophore containing silica nano
particles
Step-3:- Synthesis of perylene tetra propargylate molecule
Step-4:-synthesis of silica nano particles with perylene through click chemistry

24. Other synthesized HBP’s
Triazole core Hyperbranched
polyester

25. Acknowledgements
Dr. K.V.S.N. Raju
Dr.Ramanuj Narayan
Dr.Ch.Ramakishan Rao
Dr. Aswini Kumar Mishra
Dr. Kishore Kumar Jena
Dr. Siyanbola Tolutope
Mr.Amit Kumar
Mr.Yugandhar Raju
Mr.Shaik Allauddin
Mr.Nagaraj Goud
Mr.A.Ravi
Mr.Sarath
Mr. Ram Keval Yadav
Mr.Rajnish Kumar
Mr.Rupchand prajapath
Mr.Varaprasad
Mr.Rajnish pandey
Ms.Amulya

26. THANK YOU