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polymer. The rigid crosslinked structure was essential to the
high BET surface area in polymer, which was very important for
catalytic activity.
The element analysis gave the results: C 84.12%, H 6.53%, P
4.31% (found); C 84.09%, H 6.58%, P 4.34% (calculated). The
element analysis agreed well with the structure given in Scheme
1, which indicated that the quaternization and condensation
occurred smoothly during the synthetic process. Based on P
content, the IL loading amount was 1.40 mmol gꢀ1. In addition,
the C and H content indicated that almost all the aromatic rings
were connected via the methylene groups, which formed the
highly crosslinked structures in polymer. The IL moiety was
embedded in polymeric framework and acted as the composi-
tion of the polymeric skeleton, which beneted to IL loading
amount and BET surface area. Also, the ICP analysis of the
polymer showed little Sn content (below the minimum detect-
ability), which indicated that SnCl4 was totally removed from
the polymer during the synthetic process.
Fig. 1 The SEM images of the polymers with different molar ratio ((a, b
and c) n(triphenylphosphine)/n(p-xylylene dichloride) ¼ 0.25, 0.5, 1.0).
boundaries. The BET surface area analysis of the polymer gave
the result of 377.7 m2 gꢀ1, which decreased greatly. This further
conrmed that the amount of p-xylylene dichloride greatly
inuenced the surface are. Although the IL loading amount
increased to 1.98 mmol gꢀ1, the low BET surface area added the
mass transfer hindrance. Further increasing the triphenyl-
phosphine amount to molar ratio of 1.0, bulky blocks formed
instead of small particles (Fig. 1c). The low p-xylylene dichloride
amount resulted in low crosslinking degree. The phase sepa-
ration occurred slowly to form the large particles. The polymer
had very low BET surface area of 5.5 m2 gꢀ1. The IL loading
amount was as high as 2.49 mmol gꢀ1, but most active sites
were embedded inside. Therefore, the molar ratio should be
carefully controlled. Both the IL amount and BET surface area
were important for high catalytic activity. Therefore, the poly-
mer with triphenylphosphine and p-xylylene dichloride molar
ratio of 0.25 was chosen.
FT-IR spectrum of the polymer was shown in Fig. 2. The
peaks at 2932–3002 cmꢀ1 were assigned to the stretching
vibration of the aromatic C–Hs in the polymer. The strong
absorption at 1579 cmꢀ1 was attributed to P–C bonds, which
indicated the phosphonium IL moiety in polymer. The FT-IR
also showed the strong absorption at 1423 cmꢀ1, which was
derived from C]C bonds in aromatic rings. The C–H stretching
vibration at 1156 cmꢀ1 conrmed the methylene groups in
p-xylylene dichloride. The peaks at 860, 689, 649 and 619 cmꢀ1
showed the multi-substituted structures of the aromatic rings in
the polymer, which derived from the crosslinked structure in
3.2 The catalytic activities for aza-Michael addition
The aza-Michael additions of amines and electron decient
alkenes using polymer were investigated (Table 1). The polymer
was very efficient for the reactions with average yields over 95%
in several minutes. The dimethylamine with low steric
hindrance showed very high reactivity with almost complete
conversion in 4 minutes (entry 1). The yield decreased a little for
the higher steric hindrance of diethylamine (entry 2). As to dii-
sopropylamine, the reaction is much slower, but a 95.8%
conversion yield was still obtained aer 20 min (entry 3). Besides
secondary amines, the primary amines were also efficiently
transformed. Ethylamine had the yield of 98.7% only aer 6 min
(entry 4). The single substituted product was obtained in high
selectivity. The product owned much higher steric hindrance
than ethylamine, which hindered the multi-substitution. In
addition, the mild reaction condition such as low temperature
and low alkene amount beneted the high selectivity of single
substitution. The double substituted product formed with more
methyl acrylate amount and higher reaction temperature. Both
amino groups of ethylenediamine reacted with methyl acrylate
with the yield of 97.3% in 10 min (entry 5). This further
conrmed the high activity of the polymer. The amine with
hydroxyl group also gave high yield aer 15 min, which indicated
that the functionalities such as hydroxyl group would not affect
the reaction (entry 6). As to the cyclic amines, the yields were
quite high due to the low steric hindrances (entries 7 and 8).
Besides amines, the electron decient alkenes also affected the
yields. Ethyl acrylate owned relatively lower reactivity than the
methyl acrylate for longer carbon chains (entries 9–13). As to
dimethyl maleate, morpholine showed high yield of 98.7% in 8
min (entry 16). For the xation of the morpholine ring, the
amino group was easily attacked by dimethyl maleate, which
resulted in high yield. Ethylenediamine showed the high yield of
95.3% in 16 min (entry 14). Both amino groups were substituted
by dimethyl maleate, which further conrmed the high activity
of polymer. For the reactions between diisopropylamine and
dimethyl maleate, the yield decreased to 92.8% aer 25 min
Fig. 2 The FT-IR spectrum of the polymers.
99450 | RSC Adv., 2015, 5, 99448–99453
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