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S. Ates et al. / Polymer 51 (2010) 825–831
iptycene) units into polymer backbone may enhance lateral inter-
actions by virtue of occupation of triptycene cavities with neigh-
boring polymer chain in order to minimize the free energy arose
from IMFV of triptycene [32]. If a strain applies on polymer, adja-
cent chain begins to thread into the cavity till two opposite trip-
tycene units meet and interlock (Scheme 1).
1740 (s, C]O),1634,1482 cmꢂ1 (s, C]C).1H NMR:
d 7.1 (4H), 6.5–6.4
(2H), 6.1–6.0 (2H), 5.8–5.7 (2H).
2.3.2. Synthesis of triptycene hydroquinone (TH)
TH was prepared by following synthesis route described in the
literature [27] At first step, anthracene (10 gr, 5.6 ꢃ 10ꢂ2 mol)
recrystallized from xylene and dissolved with quinone (7 gr,
6.5 ꢃ10ꢂ2 mol) in 150 mL xylene. Diels–Alder reaction taken placed
in 250 mL round bottom flask at reflux temperature under nitrogen
atm for 3 h. Pale yellow crystals collected and recrystallized from
xylene. At second step 10 gr product of first step dissolved in 70 mL
glacial acetic acid and 4 drops of 40% HBr was added to solution.
Reaction was carried on for an hour at reflux temperature. TH
crystals filtered and collected with high yield (93%). IR (cmꢂ1): 3400
(s, O–H), 3060 (s, C–H), 1635, 1480 (s, C]C), 1034 (b, C–H). 1H NMR:
In this work, we herein report synthesis, characterization and
photocuring behavior of a new cross-linker based on triptycene
molecule. Photopolymerizations were performed with the formu-
lations containing triptycene hydroquinone diacrylate (THDA)
together with monofunctional monomers glycidyl methacrylate
(GMA), 2-hydroxyethyl acrylate (HEA), 2-hydroxyethyl methacry-
late (HEMA), and 2-ethylhexyl methacrylate (EHMA), by using
2,2-dimethoxy-2-phenylacetophenone (DMPA) as the photo-
initiator. Comparative photopolymerization studies were also per-
formed by using structurally similar cross-linker, hydroquinone
diacrylate (HDA) which does not possess triptycene unit. Photo-
polymerization kinetics was analyzed for different compositions of
monofunctional monomers and cross-linked agents by using
photo-differential scanning calorimeter (photo-DSC). Each mono-
functional monomer was reacted with varied percentages of
a difunctional monomer HDA and THDA respectively to observe the
influence of triptycene based cross-linker on rate of polymerization.
d
8.5 (2H), 7.3 (4H), 6.9 (4H), 6.3 (2H), 5.7 (2H).
2.3.3. Synthesis of triptycene hyroquinone diacrylate (THDA)
TH (2 gr, 7 ꢃ 10ꢂ3 mol) and 4 mL triethyl amine dissolved in
50 mLTHF using 100 mL two necked flask. Acryloyl chloride (1.3 mL,
1.6 ꢃ 10ꢂ2 mol) added drop by drop and suddenly transparency of
reaction mixture turns to cloudy white color. Reaction was
continued for 3 h at room temperature under nitrogen atmosphere.
Reaction mixture was taken to a separatory funnel. After work up,
organic phase separated and THDA purified by using column chro-
matography. THDA was obtained as white crystals (mp: 195–197 ꢁC)
with 70% yield. IR (cmꢂ1): 3060 (s, C–H), 1736 (s, C]O), 1635, 1480
2. Experimental
2.1. Materials
(s, C]C), 1034 (b, C–H). 1H NMR:
d 7.3 (4H), 7.0 (4H), 6.8 (2H), 6.7
(2H), 6.6–6.4 (2H), 6.2–6.0 (2H), 5.4 (2H). Anal. Calc. for C26H18O4: C,
78.67; H, 4.57. Found: C, 78.99; H, 4.30.
Glycidyl methacrylate (2,3-epoxypropyl methacrylate) (GMA,
97%, Aldrich), 2-hydroxyethyl acrylate (HEA, 96%, Aldrich),
2-hydroxyethyl methacrylate (HEMA, 97%, Aldrich) and 2-ethyl-
hexyl methacrylate (EHMA, 98%, Aldrich) were used as purchased.
2.2-Dimethoxy-2-phenylacetophenone (DMPA, 99%, Acros) was
also used without any additional treatment. Acryloyl chloride
(96%, Aldrich), hydroquinone (ꢀ98%, Fluka), hydrogen bromide
(HBr, Merck) and quinone (ꢀ98%, Fluka) were utilized without any
purification. Anthracene (ꢀ96%, Fluka) was purified via recrystal-
lization from xylene.
2.4. Preparation of formulations
Basically, formulations were prepared to investigate the effect of
various components in the photopolymerizations. Molar
percentage of cross-linkers in formulations was adjusted with
respect to solubility of THDA in monofunctional monomers. For all
formulations 1.0% molar ratio of DMPA was used. A typical formu-
lation was prepared as follows: 1.0 mol% DMPA (0.020 g, 1.8 wt%),
1.0 mol% THDA (0.030 g, 2.7 wt%) and 98 mol% GMA (1.08 g, 95.5
wt%). The molar percentage of cross-linker was between 1 and 3,
and the amount of monomer was altered accordingly so that the
total molar percentage was 100.
2.2. Characterization
The 1H NMR (250 MHz) solution spectra were recorded on
a Bruker NMR Spectrometer using CDCl3 with TMS as an internal
reference. Fourier transform infrared (FT-IR) spectra were obtained
using a Perkin–Elmer FT-IR Spectrum One spectrometer.
2.5. Photocalorimetry (Photo-DSC)
The photo-differential scanning calorimetry (Photo-DSC)
measurements were carried out by means of a modified Perkin–
Elmer Diamond DSC equipped with a high pressure mercury arc
lamp. A uniform UV light intensity is delivered across the DSC cell to
the sample and reference pans. The intensity of the light was
measured as 18.4 mW cmꢂ2 by a UV radiometer covering broad UV
range. The mass of the samples was 3 mg and the measurements
were carried out in an isothermal mode at 30 ꢁC under a nitrogen
flow of 20 mL minꢂ1. The reaction heat liberated in the polymeri-
zation was directly proportional to the number of acrylate or
methacrylate double bonds reacted in the system. By integrating the
area under the exothermic peak, the conversion of the acrylate or
methacrylate groups (C) or the extent of the reaction was deter-
mined according to Eq. (1):
2.3. Preparation of cross-linkers
2.3.1. Synthesis of hydroquinone diacrylate (HDA)
Although hydroquinone diacrylate (HDA) is commercially
available, it was simply synthesized by acylation of hydroquinone
with acryloyl chloride [33]. (m.p. 87–88 ꢁC) IR (cmꢂ1): 3000 (s, C–H),
C ¼
D
Ht=
D
H0theory
(1)
where
D
Ht is the reaction heat evolved at time t and
D
H0theory is the
Scheme 1. Schematic representation of the steric interactions induced by triptycene
units.
theoretical heat for complete conversion.
D
H0theory ¼ 86 kJ molꢂ1