EXPLORATION OF PHOTOINITIATORS IN
IONIC LIQUIDS
Joanna Rush, (Steven W. Anderson), Department of Chemistry,
University of Wisconsin – Whitewater, Whitewater, WI 53190
Salt (1.67 x 10-5 M) photodecomposition
in acetonitrile with 185/254 nm lamps
Background
0.6
Photoinduced cationic polymerization has been employed
in a wide variety of industrial applications, including adhesives
and non-stick release coatings. The key to the development of
this technology is the availability of highly photosensitive and
efficient cationic photoinitiators, which can be designed to be
responsive to various UV wavelengths.
102 k, sec-1
Absorbance
0.5
Synthesis of 2-dimethyl(2-phenyl-1,3indandionesulfonium) triflate
0.3
0.2
0
0
S( CH3 ) 2
Br
O
O
What’s the Point?
2
3
0.5
1.28 + 0.38
DPIB
5.26 + 0.05
1.
24 hours AgOTf,
(CH3)2S, CH3CN,
25ºC
2.
1.0 hour NaOTf,
(CH3)2 S,
acetone, reflux
3.
1.5 hours NaOTf,
(CH3)2S, 3pentanone, reflux
4.
1.0 hour BMIM,
NaOTf, (CH3)2S
4
Reaction Conditions
DPIB pairs a
hard base
Linear (DAIST) (BF4-) with a
soft acid
Linear (DPIST)
(sulfonium
ion)
Poly. (DPIB)
reducing
stability.
1
1.5
2
2.5
3
DPIST (0.1 M) photodecomposition
with 185/254 nm lamps
104k, sec-1
4
in DMSO-d6
3.5
in CD3CN
• The development of short wavelength photoinitiators
•Synthesize photoinitiators in more environmentallysafe (green) solvents such as ionic liquids.
3
Synthesis of
2-dimethyl(2-phenyl-1,3indandionesulfonium) tetraphenylborate
in 99% Bmim/1%
DMSO-d6
in 99% Hmim/1%
DMSO-d6
2.5
ln(Co/(Co-C))
that may be employed in the preparation of electronic
microcircuits.
Linear (in DMSO-d6)
•Evaluate synthesis, utilization, and efficiency of
photoinitiators in green solvents.
AgOTf , ionic liquid,
Br
3.44 + 0.29
151 + 16
129 + 11
Linear (in 99%
Bmim/1% DMSO-d6)
1.5
Linear (in 99%
Bmim/1% DMSO-d6)
Linear (in 99%
Hmim/1% DMSO-d6)
O
Ph
2.71 + 0.20
Linear (in CD3CN)
2
1
O
1.64 + 0.01
Time, minutes
OTf
100
90
80
70
60
50
40
30
20
10
0
1
DPIST
Linear (DPIP)
0.1
Ph
Ph
1.43 + 0.22
DAIST
O
O
% yield
0.4
DPIP
increasing solvent polarity* & reaction rate
Ph
0.5
DMSO-d6 < CD3CN < Hmim < Bmim
S( CH3 ) 2
( CH3 ) 2 S
O
O
* using Reichardt's ET values.
0
BPh4
0
20
40
60
80
100
120
140
Time, seconds
80
70
% Yield
60
50
1.
24 hours, [Bmim][BF4]
2.
26 hours, [Hmim][BF4]
40
30
BF4
N
20
N
[ Bmim] [ BF4 ]
10
0
1
2
Reaction conditions
BF4
N
N
Conclusions
Photoinitiators
O
O
• DPIST has been synthesized in good yield by silver ion assisted
alkylation and moderate yield by metathesis in less toxic
conventional solvents.
h
Ar •
S( CH3 ) 2
Y
or
O
S( CH3 ) 2
OSO2 CF3
+
HY +
[ Hmim] [ BF4 ]
R•
2-dimethyl-(2-phenyl-1,3-indandione)
sulfonium triflate (DPIST); Y = OSO2CF3
(  = 238 nm,
 = 24,560 )
2-dimethyl-(2-phenyl-1,3-indandione)
sulfonium tetrafluoroborate (DPIB);
Y = BF4 ( = 237 nm,
 = 27,844 )
2-dimethyl-(2-phenyl-1,3-indandione)
sulfonium tetraphenylborate (DPIP);
Y = Ph4
2-dimethyl-(3-phenyl-1-indanone)
sulfonium triflate (DAIST)
•Compounds which absorb light in the UV-visible spectral range and
produce reactive intermediates (e.g., free radicals and reactive cations).
• Reactive intermediates may be used to initiate polymerization reactions.
• May be used to prepare photoresists designed for placement on the surface
of microcircuits.
• Possible applications for cationically photopolymerizable coatings:
container and beverage coatings, UV curable inks, adhesives, antiabrasion
coatings for leather and vinyl, and paper release coatings.
•Isolation procedure in ionic liquids still needs to be perfected.
Acknowledgements:
UWW Undergraduate Research Grant,
Brandice Luckett (assistance with NMR collection).
Kevin O’Rourke (selected NMR data in DMSO).
•Hard-soft acid-base theory can explain the greater reactivity of DPIB.
•Kinetics of the decomposition of DPIST in Bmim and Hmim gives
evidence that an ionic liquid stabilizes the transition state more
and reaction is independent of solvent viscosity.