A new prepolymer of resol phenol-formaldehyde resin

Full text of DOI:10.1002/mrc.4306

Letter - spectral assignment
Received: 29 April 2015
Revised: 28 June 2015
Accepted: 7 July 2015
Published online in Wiley Online Library: 8 September 2015
(wileyonlinelibrary.com) DOI 10.1002/mrc.4306
A new prepolymer of resol phenol–
formaldehyde resin
a
b
c
b
a
Haipeng Jiang, * Nian Cai, Changjun Wang, Hong Chen, Jing Zou
b
and Xiulian Ju **
2
3
4
) oxygenated methylene protons at δ4.50, which are attributed
Introduction
to the methylol (CH OH) group in the phenol ring, such pro-
2
13
Phenol–formaldehyde resin, a synthetic polymer, has a wide
range of commercial applications in products such as precoated
sand, wood adhesive and fire-retardant materials.
facture involves two stages: (i) prepolymer production by an acid
or base catalyzed condensation reaction between phenol (or
substituted phenols) and formaldehyde; and (ii) curing of these
low molecular weight prepolymers by the use of heat or a
tons have correlation with C NMR resonance of δ59.78 in
the HSQC spectrum;
[
1,2]
13
Their manu-
) methylene protons at δ3.71, which are correlated to C NMR
resonance of δ40.98 in the HSQC spectrum, should be attrib-
uted to para/para methylene bridges according to
[
5,7,8]
literature.
) broad resonances of δ8.34 and δ5.22, are proved be ex-
changeable protons, by using experiment of the addition of
H2O into deuterated solvents.
[3]
cross-linking agent.
Two types of prepolymer, i.e. novolacs and resol, are obtained de-
pending on pH and formaldehyde/phenol molar ratio (F/P).
Novolacs are also referred to as thermoplastic phenolic resins or
linear phenolic resin and can be obtained in an acidic catalysis
and F/P < 1. Whereas resols are also referred to as thermosetting
1
All resonances in the H NMR spectrum are singlets (except resid-
ual solvent signal), indicating the symmetric structure of the com-
pound. Based on the comparison of 1D and 2D NMR data of the
compound I with the published literature,
dimer of tri-methylol phenol (Fig. 1 and Table 1).
[5,7,8]
[1]
it was identified as
phenolic resins and can be obtained in alkaline catalysis and
< F/P < 3; resol prepolymer has mono-, di- and tri-methylol
CH OH) groups in the phenols skeleton.
NMR spectroscopy has proved to be a successful and informative
1
The molecular ion peak of compound II appeared at m/z 455
(
2
À
[
MÀ H] , with a mass difference of 136Da to compound I, the
[
4,5]
molecular weight of one tri-methylol phenol unit. Compound II
tool to analyze resol resins.
However, the isolation, purification
was obtained as a yellow solid; 13.4 mg of the dry solid was fully
dissolved in 0.5-ml DMSO-d . The H NMR spectrum (Fig. s6)
along with C NMR spectrum (Fig. s7), DEPT-135 (Fig. s8), gCOSY
Fig. s9), HSQC (Fig. s10) and HMBC data (Fig. s11) revealed the
presence of:
and spectroscopic studies of the individual prepolymer have been
1
[6]
rarely reported. In the present research, resol resin with F/P= 2.0
was synthesized, and three prepolymers from the resin were iso-
lated, purified and structure identified by 1D and 2D NMR experi-
ments. Among these three prepolymers, a new prepolymer was
discovered. Our results will provide the additional structural infor-
mation of resol resin prepolymer.
6
13
(
1) aromatic protons at δ6.98, δ6.93, δ6.85 and δ6.80, with reso-
13
nance integral of 2:2:1:1, which are correlated to C NMR res-
onance of δ126.71, δ126.49, 125.93 and 129.52 in the HSQC
spectrum;
) oxygenated methylene protons at about δ4.5, which corre-
Results and discussion
2
The synthesized resol resin was subject to HPLC-ESI-MS analysis,
and the prepolymers were monitored by their characteristic UV–
Vis absorption wavelength of 283 nm(Fig. s1). The chromatographic
peak at retention time of 3.07 min, 4.39 min, 7.62 min and 13.65 min
showed molecular weight of 184, 320, 456 and 592 Da in the mass
spectrum, with regular mass difference of 136 Da. The component
at retention time of 4.39min, 7.62 min and 13.65min were isolated
and purified by preparative HPLC, labeled as compound I, II and III,
respectively.
2
spond to the methylene of methylol (CH OH) group in the
phenol ring, correlate to C NMR resonance of δ60 in the
HSQC spectrum; in the gCOSY spectrum, such oxygenated
13
* Correspondence to: Haipeng Jiang, Center of Analysis and Testing, Wuhan
Institute of Technology, Wuhan 430073, People’s Republic of China.
E-mail: jianghp@ wit.edu.cn
* Correspondence to: Xiulian Ju, School of Chemical Engineering and Pharmacy,
Wuhan Institute of Technology, Wuhan 430073, People’s Republic of China.
E-mail: xiulianju2008@aliyun.com
*
The molecular ion peak of compound I appeared at m/z 319
À
[
1
MÀ H] . Compound I was obtained as a light-yellow solid;
a Center of Analysis and Testing, Wuhan Institute of Technology, Wuhan 430073,
People’s Republic of China
6
2.1mg of the dry solid was fully dissolved in 0.5-ml DMSO-d .
The H NMR spectrum (Fig. s2), C NMR spectrum (Fig. s3) along
with HSQC data (Fig. s4) revealed the presence of:
1
13
b School of Chemical Engineering and Pharmacy, Wuhan Institute of Technology,
Wuhan 430073, People’s Republic of China
13
1
) aromatic protons at δ6.96, which are correlated to C NMR
resonance of δ126.46 in the HSQC spectrum;
c Wuhan Lifa Chemical Co., Ltd., Wuhan 430073, People’s Republic of China
Magn. Reson. Chem. 2015, 53, 1080–1082
Copyright © 2015 John Wiley & Sons, Ltd.

A new prepolymer of resol phenol–formaldehyde resin
δ40.33, which is attributed to H-9, has no correlation with any
OH bearing aromatic carbon. Besides, C-9 correlates to C-3′ and
C-5′ of middle phenyl ring, whereas C-10 correlates to only C-3′
of the middle phenyl ring. The key HMBC correlations of
compound II are shown in Fig. 2 and Table 2. The compound
identified as a new prepolymer component had a linear trimer
of tri-methylol phenol structure.
Figure 1. Structures of compound I.
1
13
Table 1. The H and C assignment of phenol-formaldehyde dimer
Compound III with HPLC retention time of 13.65 min was pre-
pared, compound III was obtained as a yellow solid and 10.5mg
of the dry solid was prepared; however, when the compound was
Position (J/Hz)
δ
C
δ
H
1
1
1
2
3
4
7
7
9
,1′
150.20
/
subjected to H NMR experiment, because of the limited solubility
,1′-OH
,2′,6,6′
,3′,5,5′
,4′
8.34 (2H,s)
/
6 6
in DMSO-d ,acetone-d or other deuterated solvent, it was difficult
to obtain spectrum of enough signal intensity to elucidate the
structure of the compound.
128.39
126.46
132.65
59.78
/
6.96(4H,s)
/
,7′,8,8′
,7′,8,8′-OH
4.50 (8H,s)
5.22 (4H,s)
3.71(2H,s)
Experimental
40.98
Nuclear magnetic resonance spectroscopy
Compounds were dissolved in deuterated dimethylsulfoxide
methylene protons have correlation with exchangeable
protons of δ5.21 and δ5.35, so, protons of δ5.21 and δ5.35
(DMSO-d6, purchased from Cambridge Isotope Laboratories) and
put into 5-mm NMR tubes (purchased from NORELL).
are attributed to OH group of methylol (CH OH).
2
The 1D and 2D NMR spectra were recorded on an Agilent 400MR
spectrometer (equipped with 5-mm ASW probe) at 298 K. Chemical
shifts (δ) in parts per million are referenced to TMS at 0.00 ppm for
3
) methylene protons δ3.76 and δ3.66, such protons have corre-
1
3
lation with C NMR resonance of δ35.09 and δ40.61 in the
[
7,8]
HSQC spectrum. According to literature data,
the reso-
1
13
1
H and C NMR. For H NMR acquisition, spectrometer frequency
nances are attributed to para/ortho and para/para methylene
bridges, respectively.
) broad resonances of δ8.35, δ8.33, δ8.29, δ5.35 and δ5.21 are
proved be exchangeable protons, by using experiment of
2
the addition of H O into deuterated solvents (Fig. s12). Pro-
1
(SF) was set at 399.79 MHz, 90° pulse of 13.2 μs for H and spectrum
was recorded with 16 scans, with a relaxation delay of 2 s between
4
13
each scan. For C NMR acquisition, spectrometer frequency (SF)
13
was set at 100.54 MHz, 90° pulse width of 9.0 μs for C, with a re-
13
laxation delay of 2 s between each scan. Decoupling of the
C
tons at δ8.35, δ8.33 and δ8.29 can be attributed to OH group
of phenols.
spins during acquisition was done using the WALTZ-16. All HSQC
and HMBC experiments were carried out using the recommended
gradient-selected pulse sequences from the Agilent pulse se-
The resonance assignment of compound II is shown in Table 2.
From the HMBC spectrum, proton at δ35.09, which is attributed
to H-10, correlates to C-1′ of δ150.65, whereas the proton at
1
quence library, with HSQC optimized for JCH = 145 Hz, and HMBC
n
optimized for JCH = 8 Hz.
1
13
Table 2. The H and C assignment of phenol-formaldehyde trimer
1
13
Position δC
δH (J/Hz)
H→ C HMBC correlations
1
1
1
1
2
2
3
3
3
5
4
4
6
6
7
7
7
7
9
1
,1″
150.22
/
,1″-OH
/
8.35,8.33
1,1″(150.22), 2,2″(128.14)
1′(150.65), 6′(128.46)
′
150.65
/
′-OH
/
8.29
′
128.84
/
,2″
128.14
126.71
126.49
129.52
125.93
132.77,132.59
131.84
128.30
128.46
59.78, 59.85
60.53
/
,5
6.93(4H,s)
6.98(4H,s)
6.80(2H,s)
6.85(2H,s)
/
9(40.33),7,8(59.78,59.85),5,3(126.71)
10(35.09),7″,8″ (59.78,59.85),5″,3″(126.49)
9(40.33),10(35.09),5′(125.93),1′(150.65)
9(40.33),7′(60.53),1′(150.65),3′(129.52)
″,5″
′
′
,4′
″
/
, 6″
/
′
/
,7″,8,8″
4.48(8H,s)
4.48(2H,s)
5.21(4H,s)
5.35(1H,s)
3.66(2H,s)
3.76(1H,s)
1,1″(150.22),6,6″(128.30),5(126.71),5″(126.49)
7,7″,8,8″(59.78,59.85), 6,6″(128.30)
′
,8,7″,8″-OH
′-OH
/
/
40.33
5′(125.93),4(132.77),4′(132.59)
0
35.09
1′(150.65),4″(131.84),2′(128.84),3″(126.49)
Magn. Reson. Chem. 2015, 53, 1080–1082
Copyright © 2015 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/mrc

H. Jiang et al.
total formaldehyde to phenol is 2.0. After the addition of formalde-
hyde was completed, the reaction temperature was maintained
90°C for periods of time; when the desired content of free formal-
dehyde was reached, formic acid was added to stop the reaction.
Then, the solution was dehydrated under vacuum. The dehydration
process was stopped when reaching the desired viscosity.
Figure 2. Structures and key HMBC (arrows) correlations of compound II.
Liquid chromatography-mass spectroscopy
Acknowledgement
HPLC-ESI-MS experiments were performed at Dionex Ultimate 3000
HPLC system connecting vial an ESI-interface with a linear ion trap
mass spectrometer, LTQ-XL-MS (Thermo Finnigan, San Jose, CA,
This study was financially supported by ‘the natural Science Foun-
dation of Hubei Province’ (2014CFB784).
USA). Chromatographic separations were performed at 25 °C on a
TM
250 × 4.6 mm (5 μm) Acclaim
C18 column. The mobile phase
References
contained 0.1% acetic acid solution-methanol (45:55), and the flow
rate was maintained at 1.0ml/min; the monitoring wavelength is at
[1] R. A. Haupt, T. Sellers Jr. Ind. Eng. Chem. Res. 1994, 33, 693–697.
[2] G. Astarloa-Alerbe, J. M. Echeverria, J. L. Egiburu, M. Ormaetxea,
I. Mondragon. Polymer 1998, 39, 3147–3153.
283 nm. The mass spectrometer was operated in the negative
mode, the spray voltage was 4.5kV for the negative mode and
the temperature of the heated capillary was set at 250 °C. Nitrogen
[
[
3] J. Paju, T. Pehk, P. Christjanson. P. Est. Acad. Sci. 2009, 58, 45–52.
4] J. C. Woodbrey, H. P. Higginbottom, H. M. Culbertson. J. Polym. Sci. Pol.
Chem. 1965, 3, 1079–1106.
was used as the nebulizer gas and auxiliary gas. The flow rates of
À1
the sheath gas, and sweep gas were set (in arbitrary units min
at 20 and 2, respectively.
)
[5] R. Rego, P. J. Adriaensens, R. A. Carleer, J. M. Gelan. Polymer 2004, 45,
3–38.
6] M. Carrott. Analyst 1999, 124, 993–997.
[7] T. H. Fisher, P. Chao, C. G. Upton, A. J. Day. Magn. Reson. Chem. 1995, 33,
17–723.
3
[
Preparative HPLC
7
Purification of prepolymer component was performed at Dionex
Ultimate 3000 apparatus with Venusil® PrepG C18 column
[8] T. H. Fisher, P. Chao, C. G. Upton, A. J. Day. Magn. Reson. Chem. 2002, 40,
747–751.
(10 × 100mm), and the flow rate was maintained at 3.0 ml/min.
Supporting information
Synthesis of phenol–formaldehyde (PF) resin
Additional supporting information can be found in the online ver-
sion of this article at the publisher’s web site.
Appropriate ratio of phenol and sodium hydroxide was heated in a
three-necked flask with reflux condenser, a digital thermometer
and a mechanical stirrer. Then formaldehyde aqueous solution
(37%) was fed into the reactor dropwise, and the molar ration of
wileyonlinelibrary.com/journal/mrc
Copyright © 2015 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2015, 53, 1080–1082