C O M M U N I C A T I O N S
Table 1. Properties of Guest-Host Polymers Containing o-HP,
PQDM-2OH, and LP in PES
b
d
e
guest in PES
(wt %)
NDa
λmax
nm
Tg
r33
3
cm-
nc
°
C
pm/V
o-HP(5)
4 × 1019
7 × 1019
10 × 1019
13 × 1019
7 × 1019
4 × 1019
724
717
707
1.6286
1.6291
1.6304
1.6317
1.6187
1.6302
202
192
175
154
116
212
25
44
65
22
23
18
o-HP (10)
o-HP (15)
o-HP (20)
PQDM-2OH (5)
LP (5)
699/486
704
712
a Number density of PQDM. b Absorption of guest-host polymer films.
c Refractive index at 1.55 µm. d Measured by DSC in nitrogen with a heating
rate of 10 °C/min. e At 1550 nm.
(Td ) 276 °C for 5% weight loss in nitrogen) were characterized
by differential scanning calorimetry (DSC) and thermogravimetry,
respectively. An exothermic peak starting around 195 °C was
observed from the first DSC heating scan, because of the cross-
linking reaction of BCBO groups, and was absent in the second
scan. After being treated above 200 °C, o-HP became insoluble
and its blends in poly(ether sulfone) (PES) were partially soluble
or swelled in organic solvents (e.g., DMF), indicating the formation
of cross-linked, interpenetrating networks.
Figure 1. Temporal stability of the poled and cross-linked o-HP/PES (15
wt %) blend at 85 °C in nitrogen. Normalized r33 as a function of time.
observed enhancement in EO coefficients with the o-HP/PES system
indicates a higher poling efficiency, presumably due to higher chain
mobility and less chromophore interaction.
In conclusion, we demonstrated a new approach toward highly
efficient NLO materials by using a cross-linkable, hyperbranched
NLO oligomer as a macromolecular guest and a commercially
available polymer as a host. This approach offers advantages over
other known routes involving the use of side-chain NLO polymers
and molecular chromophore-doped polymer systems, such as larger
EO coefficients, excellent temporal stability, and versatility and
flexibility in material preparation and formulation.
Acknowledgment. We thank Nortel Networks and the Natural
Sciences and Engineering Research Council of Canada for financial
support.
Supporting Information Available: Syntheses and characteriza-
tions of PQDM-2OH, o-HP, and LP. This material is available free of
For electric poling and EO studies, o-HP was doped into a high
Tg (220 °C) PES (Ultrason E3010). Other polymers such as poly-
(bisphenol A carbonate) (PC), poly(vinyl pyrrolidinone) (PVP), and
polyetherimide (PEI) also appeared as a good matrix for o-HP. The
Tg and refractive indices (nTE) of o-HP/PES blends were in a range
of 154-202 °C and 1.628-1.632 (at 1550 nm), as determined by
DSC and prism coupling method, respectively (Table 1). No phase
separation in films was noticed by examination under optical
microscope (50×) until the o-HP loading reached up to 20 wt %,
which is equivalent to the number density of PQDM of 13 × 1019
cm-3. At this point, a sharp blue-shifted absorption band appeared
at 486 nm in the UV-vis spectrum of the o-HP/PES film.
The o-HP/PES films with thickness of 2-3 µm were prepared
by casting a solution in DMF (3 wt %/v) onto ITO glass substrates.
The films were vacuum-dried at 100 °C overnight to remove
residual solvent before sputtering a thin layer of gold (∼150 nm)
onto the films as the top electrode for parallel electrode poling.
The poling was done at temperatures near the Tg (i.e., 170-190
°C) for 30-40 min, followed by further heating at 200-210 °C
for 5 min. The poling voltages applied across the films were 0.7-
0.9 MV/cm. EO coefficients (r33) of the poled o-HP/PES films were
measured using the Teng-Man setup.9 A continuous increase of
r33 values can be seen with the increase of o-HP content in PES
(Table 1). The highest r33 value of 65 pm/V was obtained for the
sample containing 15 wt % of o-HP (ND ) 10 × 1019 cm-3), which
is significantly larger than that (45 pm/V) of side-chain NLO
polyimides containing a similar amount of PQDM.7 Further increase
of the o-HP content (e.g., 20 wt %) led to a sharp decrease in EO
coefficients, due to severe aggregation of chromophores. The
temporal stability of EO response was founded to be excellent, as
the r33 value of the poled o-HP/PES sample (15 wt %) maintained
more than 90% of its original value after holding at 85 °C in
nitrogen over 1200 h (Figure 1).
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For comparison, a linear analogue (LP) derived from PQDM-
2OH and isophthaloyl chloride (see Supporting Information) and
PQDM-2OH were blended in PES, respectively. Phase separation
was observed when the number density of PQDM in both blends
was higher than 7 × 1019 cm-3. The obtained EO coefficients were
much lower, being 18 pm/V for LP/PES and 23 pm/V for PQDM-
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