A Rh(iii)-catalyzed cascade C-H functionalization/cyclization reaction of salicylaldehydes with diazomalonates for the synthesis of 4-hydroxycoumarin derivatives

Article abstract of DOI:10.1039/c8nj04576c

A cascade C-H functionalization/cyclization reaction of salicylaldehydes with α-diazomalonates has been developed for the synthesis of 4-hydroxycoumarin derivatives under the catalysis of rhodium(iii) and in the presence of acetic acid. A plausible mechanism involving aldehydic C(sp²)-H activation by rhodium(iii) and rhodium(iii) catalyzed carbene insertion is also proposed.

Full text of DOI:10.1039/c8nj04576c

IOP Conference Series: Materials Science and Engineering
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Synthesis and properties of amphiphilic hyperbranched polyethers as
pigment dispersant
To cite this article: Q Xu et al 2018 IOP Conf. Ser.: Mater. Sci. Eng. 292 012109
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2nd International Conference on New Material and Chemical Industry (NMCI2017)
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Synthesis and properties of amphiphilic hyperbranched
polyethers as pigment dispersant
Q Xu1, Y J Zhou2, 3, S J Long2, Y G Liu2 and J H Li2
1 Institute of Biology, Guizhou Academy of Sciences, Guiyang 550009, China
2 Institute of Analysis and Testing, Guizhou Academy of Sciences, Guiyang 550002,
China
3 E-mail: zhouyuanjing-8006@163.com
Abstract. Hyperbranched polymers possess prominent properties such as low viscosity, good
solubility, high rheological property, environmental non-toxic,and so on, which have potential
applications in coatings. In this study, the amphiphilic hyperbranched polyethers (AHPs)
consisting of hydrophobic hyperbranched polyethers core and hydrophilic poly (ethylene
glycol) arms with different degree of branching (DB) under various reaction temperatures was
prepared by the cation ring-opening polymerization. Their structures were characterized by IR,
13CNMR and GPC. Their dispersion properties for pigment particles were investigated. The
AHP47 with 0.47 DB was found to have good dispersion properties for Yellow HGR. This
work would provide experimental data and theoretical foundation for the application of
hyperbranched polyethers in environmental protection coating.
1. Introduction
Coating pigment particles are prone to form agaggregates because of their high surface energy, which
affected seriously the quality of the coating. To make use of high-quality dispersant in pigment
dispersing process is the best strategy. Dispersants play a very important role in the production of
coatings. The stability of the dispersion system can avoid many coating problems and coating film
defects. If the formula is reasonable, adding dispersant properly can effectively reduce the cost and
improve the coating performance. Good pigment dispersant can have the following functions: (1)
enhancing the luster and increasing the effect of levelling; (2) preventing floating; (3) improving the
tinting strength; (4) reducing viscosity and increasing pigment loading; (5) reducing the flocculation;
(6) preventing back coarse and increasing the storage stability; (7) increasing the colour saturation; (8)
increasing transparency (organic pigment) or covering power (inorganic pigment); (9) improving the
grinding efficiency and reducing production cost; (10) prevent sedimentation [1, 2].
Hyperbranched polymers with a special topological structure possess many unique and useful
properties, such as high degree of branching (DB), lack of chain entanglement, high solubility, low
melting point and low solution viscosity [3-5]. They have received considerable attention in recent
years, and have potential applications in coatings [6, 7]. In this paper, a series of hyperbranched
polyethers with different DB were synthesized under various reaction temperatures, and the
amphiphilic hyperbranched polyether with a poly(3-ethyl-3-oxetanemethanol) core and multiple linear
poly-(ethylene glycol) arms (AHP) was obtained as the pigment dispersant. Their structures and
dispersion properties for pigment particles were investigated. It would be helpful to promote the
hyperbranched polyethers for applying in environmental protection coating.
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2nd International Conference on New Material and Chemical Industry (NMCI2017)
IOP Publishing
IOP Conf. Series: Materials Science and Engineering 292 (2018) 012109 doi:10.1088/1757-899X/292/1/012109
1234567890‘’“”
2. Experimental
2.1. Reagents and methods
Boron trifluoride etherate BF3O(C2H5)2 was purchased from Fluka. All other chemical reagents used in
this experiment were obtained from commercial sources and were of the highest purity available.
CH2Cl2 was dried by distillation in presence of CaH2 under reduced pressure. Fourier transform
infrared spectroscopy (FTIR) tests were conducted on a Spectrum 100 FTIR spectrometer
(PerkinElmer, US) using KBr discs. 13C NMR spectra were recorded on a Varian MERCURYplus 400
NMR spectrometer operating at 100 MHz. Molecular weight distributions were determined by using
gel permeation chromatography (GPC) on Waters 2690 separations module using a waters 2410
refractive index detector with THF as an eluentand polystyrene as calibration standards. The viscosity
was measured by Brookfield digital viscometer. The sagging test was carried out the sagging coating
machine with 50-270 µm film thickness.
2.2. Synthesis and characterization
The synthetic route of amphiphilic hyperbranched polyether (AHP) was shown in figure 1. According
to the reaction formula, the detailed synthesis process was described as below.
Figure 1. Synthetic routes of amphiphilic hyperbranched polyether (AHP)
2.2.1. Synthesis of 3-ethyl-3-oxetanemethanol (EOX). 3-Ethyl-3-oxetanemethanol (EOX) was
prepared from trimethylolpropane according to the previous report with minor modifications [8].
Briefly, trimethylolpropane (26.8 g), diethyl carbonate (23.6 g) and potassiumhydroxide (10 mg)
dissolved in absolute alcohol (0.5 mL) was refluxed at 105°C for 4h, and the mixture was heated
above 180°C for 2h. The crude product was subjected to reduced pressure distillation, and the pure
product (EOX) was obtained as a fraction boiling at 84–84.5 °C at 2.8 mmHg.FT-IR (cm-1): 3413 (O-
H), 2958, 2875 (C-H), 1050 (C-O), 976 (C-O-C).
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2nd International Conference on New Material and Chemical Industry (NMCI2017)
IOP Publishing
IOP Conf. Series: Materials Science and Engineering 292 (2018) 012109 doi:10.1088/1757-899X/292/1/012109
1234567890‘’“”
2.2.2. Synthesis of hyperbranched polyethers (HPs). HPs were synthesized by cation ring-opening
polymerization according to the previous report with minor modifications [9, 10]. Into a four-necked
round-bottomed flask equipped with a PTFE stirrer, a funnel and a thermometer, nitrogen was flowed
for 30 min to expel the oxygen from the system, then 80 mL of solvent CH2Cl2 and 6.4 mL of catalyst
BF3O(C2H5)2 (0.05 mol) were added via syringe, espectively. The monomer EOX (0.1 mol, 11.6 mL)
was introduced through the funnel within 10 min, and the reaction temperature was kept constant
throughout the polymerization process. The polymerization was quenched with ethanol after 48 h.
Then the mixture was precipitated into distilled water and immersed overnight. Finally, the resulting
solid was obtained by filtration and then dried at 80°C under high vacuum. The same reaction was
repeated at different temperatures. The samples prepared at 0°C, 10°C, 30°C and 50°C were named as
HP35, HP41, HP47 and HP51, respectively, according to the DB value. FT-IR (KBr, cm-1): 3450, 2956,
2927, 2877, 1471, 1383, 1105, 1048, 752. 13C NMR (100 MHz): δ (ppm) 7.9 (–CH3), 22.8(–CH2–),
43.5(–C), 63.0 (–CH2OH), 67.0– 72.0 (–CH2–O–CH2–).
2.2.3. Synthesis of amphiphilic hyperbranched polyethers (AHPs). HP and ethylene oxide were stirred
for 24 h, and the hyperbranched polyether with a poly(3-ethyl-3-oxetanemethanol) core and multiple
linear poly-(ethylene glycol) arms was obtained. FT-IR (KBr, cm-1): 3347, 2958, 2930, 2881, 1480,
1385, 1111, 1050, 758. 13C NMR (100 MHz): δ (ppm) 7.9 (–CH3), 23.5 (–CH2–), 43.7(–C), 62.0 (–
CH2OH), 67.0– 73.0 (–CH2–O–CH2–).
3. Result and discussion
3.1. DB analysis
The DB of a hyperbranched polymer is a measurement on the content of branches in the molecular
structure and is considered to be a main structural feature affecting the properties. DB is expressed
below in equation (1) [11]. L, D and T represent linear unit, dendritic unit and terminal unit,
respectively.
D+T
( 1 )
DB =
D+T+L
H
O
T
OH
OH
OH
OH
O
O
O
O
O
H
O
H
O
O
L
O
H
O
O
D
O
O
OH
O
OH
H
O
H
O
OH
H
O
HP
Figure 2. Structure of HP and 13C NMR spectra of HP for the variation of the three peaks near 43.5
ppm in detail.
From figure 2, it showed in more detail the magnified signal region near 43.5 ppm in 13C NMR
spectra, which was attributed to quaternary carbon atoms of the D, L and T. [12] The DB value can be
calculated by integrating the signals of different quaternary carbon atoms. The DB values for the
samples prepared at 0°C, 10°C, 30°C and 50°C were 0.35, 0.41, 0.47, and 0.51, and the sample was
labelled respectively HP35, HP41, HP47 and HP51, which showed that the DB increased with increasing
3

2nd International Conference on New Material and Chemical Industry (NMCI2017)
IOP Publishing
IOP Conf. Series: Materials Science and Engineering 292 (2018) 012109 doi:10.1088/1757-899X/292/1/012109
1234567890‘’“”
reaction temperature. That is, the structure of the resulting polyether depends on the reaction
temperature: at low temperature, the linear addition is preferred, which leads to mostly linear products;
at higher temperatures, the addition reaction becomes a random process resulting in hyperbranched
polymers, which are consistent with previous reports [9, 10].
3.2. GPC analysis
The molecular weights of amphiphilic hyperbranched polyethers (AHPs) were determined by gel
permeation chromatography (GPC), and the result was listed in table 1. As seen from the table, the
weight average molecular weight (Mw) of the AHP varied from 2300 to 3400, and showed
unregularity.
Table 1. The synthesis condition and characterization data of AHP.
Sample
T (°C)
Yield (%)
DB
Mw
HP35
HP41
HP47
HP51
0
83
85
90
88
0.35
0.41
0.47
0.51
3037
3379
2385
2655
10
30
50
3.3. Dispersion performance analysis
Pigments are usually insoluble in the used medium, and mostly in the form of aggregates. In order to
obtain good coloring power, transparency, chromaticity, and so on, the aggregate of pigment must be
prevented. If the pigment does not have good dispersion, many defects are likely to occur, such as
flocculation, loss of light, color offset, floating, sedimentation, etc. In this paper, the viscosity, color
and sagging performance were discussed. Table 2 showed the dispersion performance of AHPs for
Yellow HGR in xylene and propylene glycol methyl ether acetate. It showed that AHP with different
DB had different dispersion performance for Yellow HGR. The AHP47 with 0.47 DB owned the lowest
viscosity and good color, and the sagging began from 150 µm film thickness, which was superior to
other AHPs.
Table 2. The dispersion performance of AHPs on the Yellow HGR.
Sample Viscosity (5rpm, cps) Viscosity (50rpm, cps)
Color
Sagging (µm)
75
AHP35
1668
1078
too light
AHP41
AHP47
AHP51
1179
896
803
457
769
consistent
good
88
150
100
995
light
As previously reported that the structure of dispersing agent had important influence on the
dispersion of pigment [13-16], the AHP47 with medium DB and lowest Mw among the products of
AHP (figure 2) might interact with pigment particles better, and improve the dispersion performance.
As seen from the table 2, the AHP47 could obviously reduce the viscosity of the color paste obtained,
thus the loading capacity of the pigment could be increased and the production efficiency could be
improved.
4. Conclusion
The amphiphilic hyperbranched polyethers (AHPs) with a poly(3-ethyl-3-oxetanemethanol) core and
multiple linear poly-(ethylene glycol) arms were synthesized by simple and easy chemical reaction
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2nd International Conference on New Material and Chemical Industry (NMCI2017)
IOP Publishing
IOP Conf. Series: Materials Science and Engineering 292 (2018) 012109 doi:10.1088/1757-899X/292/1/012109
1234567890‘’“”
method. The AHPs owned good dispersion performance for coating pigment particles. Among the
products of AHP, AHP47 with 0.47 DB had good potentiality in coating applications. The further study
is underway.
Acknowledgments
This work was financially supported by the Science and Technology Project of Guizhou Province,
China ([2016]1139, JZ [2015]2006, Z [2015]6013) and Youth Fund Project of Guizhou Academy of
Sciences, Guizhou province, China (J [2016]20).
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