High Refractive Index Thermally Stable Phenoxyphenyl and
Phenylthiophenyl Silicones for Light-Emitting Diode (LED) Applications
Supplemental Information
David W. Mosley, Garo Khanarian, David M. Conner, David L. Thorsen, Tianlan Zhang,
Marty Wills
Materials. Anhydrous diethyl ether, magnesium (50 mesh), 4-bromodiphenylether,
and tetrabutylammonium hydroxide from Sigma Aldrich were used as received. All
silicon-containing chemicals and platinum catalysts were acquired from Gelest, Inc.
Reaction solvents were purchased from Fisher/Acros, including ‘Acros-Seal’ THF.
Phenyltrimethoxysilane from Gelest was purified by short-path distillation prior to
use.
1H NMR:
POP monomer:
PSP monomer:
Vinyl A:
Hydride A:
Calculation of refractive index of silicones
A graph of the calculated versus measured refractive indices for compounds in this
paper is shown in Figure 1.
0.7
nexp -1
0.6
0.5
Equation
y = a + b*x
Weight
No Weighting
Residual Sum of
Squares
0.00116
Pearson's r
0.98473
0.96463
Adj. R-Square
0.4
Standard Error
Value
0.4
B
Intercept
B
Slope
0.5
ncalc -1
-0.02907
0.04349
1.06717
0.07703
0.6
Figure 1. Graph of nexp -1 vs. ncalc-1 showing the expected linear relationship. The linear regression
analysis is shown as well.
Choice of TBAH as Synthesis Catalyst
When using a base-catalyzed condensation reaction with phenyl-containing
monomers, it is expected that cyclic phenylcyclosiloxanes may form, based on both the
catalyst type and the monomers involved. In particular diphenyl D monomers are known
to readily form insoluble hexaphenyltricyclosiloxane and octaphenyltetracyclosiloxane
when polymerized under basic conditions, due to the thermodynamic stability of the
cyclosiloxanes 1. Therefore, catalyst screening was done to minimize this known reaction
using a model condensation reaction*. For a set monomer mixture containing 59%
diphenyldimethoxysilane,
33%
phenylmethyldimethoxysilane,
and
8%
divinyltetramethyldisiloxane, numerous catalysts were screened. It was assumed that a
low MW peak in the GPC represented cyclic diphenylsiloxanes. Based on this screening,
tetrabutylammonium hydroxide gave the best combination of polymerization rate, ease
of handling, and a presumed low cyclics formation. The assumption that the low MW
peak represents cyclic siloxanes is justified based on the MALDI-MS information
presented for Vinyl A and Vinyl C, as well as MALDI analysis of diphenylsiloxane
polymerizations without POP or PSP. Our empirical observations of white solid
formation or haze also correspond with the assumption that for the monomer mixture
above, the low molecular weight fraction is predominantly cyclic diphenylsiloxanes and
*
Barium hydroxide is a known basic catalyst that results in low cyclic siloxane formation, as disclosed in
US5109094.
hence forms insoluble species. However, it should be pointed out that high molecular
weight cyclic siloxanes are very difficult to rule out as well2.
Compound
Zinc acetate
Zinc carbonate
Zinc oxide/hydroxide
Barium hydroxide
Barium sulfate
Barium acetate
Barium carbonate
Barium carbonate and
ammonium hydroxide
Calcium carbonate
Calcium hydroxide
Calcium phosphate
Calcium acetate
Magnesium hydroxide
Lanthanum oxide
Tetramethylammoniumhydroxide
Copper acetate
Tetraethylammonium hydroxide
Tetrabutylammonium hydroxide
(TBAH)
Tetrabutylammonium hydroxide
(TBAH)
DMAP
BisDMAP
Trioctylamine
Guanidine
Ethanolamine
Tris(2-aminoethyl)amine
Cesium hydroxide
Potassium hydroxide
1:1 Tetramethylguanidine/sulfuric
acid
1:1
Tetramethylguanidine/trifluorome
thanesulfonic acid
n-Hexyl amine
t-Butyl amine
Catalyst
Mol%
%Cyclics
by GPC
2.2
3.6
2.1
2.4
2.8
1.7
NR
NR
NR
8.4%
NR
NR
NR
NR - cyclics by
TLC
NR
100.0%
100.0%
NR
minimal reaction
minimal reaction
Slight rxn
100.0%
33.0%
4.3
5.8
2.4
3
7.5
1.9
1.2
2.4
1.7
1.1
5
3.9
1.6
1.3
4.2
10.6
4.1
3.3
7.7
21.0%
1hr@110=32%
2hr@110=27%
41.0%
NR
NR
37.0%
38.0%
100.0%
69.4%
63.6%
2.2
25.2%
2.9
4.7
7.4
30.5%
35.0%
25.0%
Table 1. Catalyst screening study for selection of a siloxane condensation catalyst that gives as few
cyclic siloxanes as possible.
SEC-MALDI Analysis:
SEC system:
Column:
Eluent:
Flow rate:
Detection:
Agilent 1100
2 X PLgel 5µ Mixed-D (300 x 8 mm ID) with 5µ guard
Tetrahydrofuran
1.0 mL/min
RI @ 40oC
Injected volume of sample solution: 100 µL.
MALDI-TOF mass spectra were acquired on a Bruker Daltonics Ultraflex instrument
equipped with a nitrogen laser (=337 nm). In the experiment, 20 mg of DHB was
dissolved in 1 mL of THF as MALDI matrix solution and NaI was added into matrix
solution to facilitate ionization. Each of 0.5 mL SEC fractions was concentrated to ~50
µL. The fraction solution was premixed with matrix solution at a ratio of 1:10. 0.3 μL of
the sample/matrix mixture was then placed on the sample target plate and was air dried
for MALDI-MS analysis.
3000
907.2
Intens. [a.u.]
To examine molecular composition, SEC fractions were collected and analyzed by MALDI
mass spectrometry. The MALDI mass spectrum of the Vinyl A fraction at 13-13.5 mL is
shown in Figure 2 for the lower MW region of the distribution. The spectrum mainly
represents short chain, cyclic polysiloxanes. There is also a small amount of hydroxy
terminated polysiloxane in the spectrum. The MALDI mass spectrum of the 10.5-11.0 mL
fraction is shown in Figure 3 for the higher MW region of Vinyl A. Based on their
masses, there are the two kinds of polymeric species in the mass spectrum of Figure 3:
polysiloxanes capped by phenylmethylvinylsilyl at both ends as major components, and
polysiloxanes capped by one phenylmethylvinylsilyl and one methoxy.
A
A
999.3
2500
2000
1500
B
A
1381.4
1289.4
A
1019.3
976.2
927.3
1091.3
883.2
C
C
A
1197.3
819.2
791.1
A
805.1
500
A
1105.3
B
727.1
713.1
1000
0
700
800
900
1000
1100
1200
1300
1400
m/z
Figure 2. MALDI mass spectrum analysis of Vinyl A SEC Fraction of 13.0-13.5 min. The letters indicate (A)
short chain, cyclic polysiloxanes; (B) hydroxyl terminated polysiloxanes; (C) polysiloxanes capped by
phenylmethylvinylsilyl at both ends.
C
C
2195.0
2088.0
C
1250
C
2286.1
1995.9
2181.0
D
C
2485.2
2392.2
2247.0
D
C
C
2577.3
2170.0
2062.0
D
2155.0
500
C
D
D
1969.9
C
1903.9
750
C
1797.9
1000
2378.2
Intens. [a.u.]
1500
C
250
0
1800
2000
2200
2400
2600
2800
3000
m/z
Figure 3. MALDI mass spectrum analysis of Vinyl A SEC Fraction of 10.5-11.0 mL. The letters indicate (C)
polysiloxanes capped by phenylmethylvinylsilyl at both ends and (D) polysiloxanes capped by
phenylmethylvinylsilyl at one end and methoxy at the other.
Solvent Extraction of Crosslinked POP Formulations
Formulations of Vinyl A with Hydride A in a 1:2 ratio of functional groups were
crosslinked with Ossko catalyst at a level of 1 ppm platinum metal. Oligomers of Vinyl A
but with different endgroups (as in Figure 3 of the paper) were treated in the same
way. The crosslinked materials were soaked in toluene overnight after being broken up
with a spatula. The toluene fraction was isolated and rotovaped to give a wt%
extractable content. The results are summarized in Table 2. Additionally, the extracted
material was examined on an Oligopore SEC column versus typical Vinyl A oligomers
before extraction (Figure 4). The extracted material overlaps precisely with the incoming
low molecular weight portion of Vinyl A.
Endgroup
Wt% Extractables
Wt% Extractables
Wt% Extractables
6 hr cure@130 C
6 hr cure@130 C and
16 hr@160 C
6 hr cure@130 C and 16 hr@160 C
and 24 hr@ 200 C
VinPhMeSi-
25%
28%
25%
Vin2MeSi-
41%
39%
35%
VinMe2Si-
28%
25%
21%
Table 2. Solvent extraction of cured formulations with toluene.
Figure 4. GPC of extractable study on an Oligopore™ column which resolves oligomers of Vinyl A. Shown
are two batches of Vinyl A, along with extracted fractions for the three different cure times of
formulated Vinyl A plus Hydride A.
FTIR Cure Study
FTIR data was gathered on a Mattson RS-1 FTIR. Formulations were prepared using
Hydride A, 1 ppm of platinum catalyst (Ossko), and 2 equivalents of hydride versus one
equivalent of vinyl. A few drops were placed between salt plates. The salt plates were
cured in an oven for 30, 60, 120, 240, and 1200 minutes. The cure temperature was 130
oC for the first 4 hrs, and then the temperature was 160 oC for the final 16 hrs. The
reduction in the Si-H stretch at 2128 cm-1 was followed as the formulations cured
between salt plates. For all formulations, the reduction in Si-H was normalized versus
the C-C aryl stretch at 1600 cm-1, which is expected to remain constant during the cure
process.
UV-Vis Characterization
Ocean Optics Heat Aging data. Spectra were acquired using an Ocean Optics USB 4000
spectrophotometer with a tungsten light source and an Ocean Optics integrating sphere
accessory. Data were adjacent averaged over 7 points. Spectral artifacts at 611.66614.27 nm; 435.8-437.71 nm; and 405.18-406.15 nm were removed from several of the
curves.
Refractive Index Measurements
Refractive indices on films were measured with a Metricon 2010 instrument
(Pennington , NJ) . Refractive indices of liquid oligomers were measured with a Reichert
Abbe Mark II refractometer.
LED Testing Method
The system is shown below. A heated water flask was used to maintain the relative
humidity at ~50% during temperature cycling. Temperature inside the box was cycled
from -10 oC to 85 oC every 12 hrs with relative humidity inside the box kept at 50%. The
LEDs were powered at 1 amp forward bias for the duration of the test. A track carried an
optical detector (Ocean Optics) that moved along and measured the light output in
lumens from each LED and recorded it periodically. About 50% of the repackaged
devices failed to produce good quality light output for further testing due to various
problems such as air bubble formation or wire bond breakage, problems which are not
unexpected when reusing a previously made device.