Use of renewable resource vanillin for the preparation of benzoxazine resin and reactive monomeric surfactant containing oxazine ring

Article abstract of DOI:10.1016/j.polymer.2014.01.041

A renewable natural resource, vanillin, is used to synthesize polybenzoxazine with the expected desirable benzoxazine properties as well as a high char yield of 55.3%. The synthesized monomer provides an unused aldehyde group from vanillin. The aldehyde can be further reacted with other materials to enhance properties. As a model, the unused aldehyde is reacted with amine terminated poly(ethylene oxide) to form a surfactant which retains 1,3-benzoxazine's reactivity. The chemical structure of the synthesized monomers, surfactant and polymers are characterized by Fourier transform infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance spectroscopy (¹H NMR). Thermal properties are also characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Miniemulsions with stability up to 2 weeks are created with the newly synthesized surfactant and polystyrene. Dynamic light scattering (DLS) indicates 627 nm as the average diameter of the emulsion droplets.

Full text of DOI:10.1016/j.polymer.2014.01.041

Polymer 55 (2014) 1443e1451
Contents lists available at ScienceDirect
Polymer
journal homepage: www.elsevier.com/locate/polymer
Use of renewable resource vanillin for the preparation of benzoxazine
resin and reactive monomeric surfactant containing oxazine ring
*
Amy Van, Kevin Chiou, Hatsuo Ishida
Department of Macromolecular Science and Engineering, Case Western Reserve University, Cleveland, OH 44106, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
A renewable natural resource, vanillin, is used to synthesize polybenzoxazine with the expected desir-
able benzoxazine properties as well as a high char yield of 55.3%. The synthesized monomer provides an
unused aldehyde group from vanillin. The aldehyde can be further reacted with other materials to
enhance properties. As a model, the unused aldehyde is reacted with amine terminated poly(ethylene
oxide) to form a surfactant which retains 1,3-benzoxazine’s reactivity. The chemical structure of the
synthesized monomers, surfactant and polymers are characterized by Fourier transform infrared spec-
troscopy (FT-IR) and proton nuclear magnetic resonance spectroscopy (1H NMR). Thermal properties are
also characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA).
Miniemulsions with stability up to 2 weeks are created with the newly synthesized surfactant and
polystyrene. Dynamic light scattering (DLS) indicates 627 nm as the average diameter of the emulsion
droplets.
Received 12 November 2013
Received in revised form
22 January 2014
Accepted 26 January 2014
Available online 1 February 2014
Keywords:
Polybenzoxazine
Renewable resource
Vanilin
Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction
opening reactions. While benzoxazine resins are often used as
polymerized bulk material, the properties in monomer form lead to
Polybenzoxazine is a class of polymers that exhibits various
desirable properties such as near-zero volume changes, low water
absorption, high char yield, high glass transition temperature, high
tensile strength, and excellent chemical and thermal stability [1].
As a high performance thermoset, polybenzoxazine was utilized as
matrix material for composites containing cellulose [2e4], glass
fibers [5], carbon fibers [6e15], silicate nanofillers [16e32], and
carbon nanofillers [33e42].
Polybenzoxazine monomers, 1,3-benzoxazine, can be synthe-
sized in a 1-pot method from phenolic derivative, primary amine,
and formaldehyde [43]. The functional groups on reactants are not
utilized, therefore they allow customization of monomer and
polymer for specialized properties. If functional groups do not
interfere with polybenzoxazine polymerization, then different
polybenzoxazine’s properties remain similar [1]. Monomeric 1,3-
benzoxazine undergoes ring-opening polymerization in the tem-
perature range of 150e220 ꢀC. This temperature range can be
altered by additives or functional groups on the phenol and amine
moieties used. Various functional groups, such as hydroxyl [44],
carboxyl [45], and thiol [44], can be used to catalyze the ring-
various uses for constructing secondary structures [46].
Due to the environmental policies becoming ever more strin-
gent and financial incentives from industries increasing, various
fields in material science have shifted toward incorporating natural
renewable resources into their products. With its flexible monomer
synthesis mechanism, polybenzoxazine is a good candidate for
incorporating naturally produced products and reducing reliance
on petroleum derivatives as starting material [47]. Polybenzoxazine
has been synthesized from waste byproducts of other industries,
such as cardanol from the cashew nut industry, levulinic acid from
cellulose degradation [48e51] and glycerin from biodiesel pro-
duction [52]. Use of natural renewable resources for benzoxazine
synthesis has recently been reviewed [48].
Aside from government and industry incentives, natural
renewable resources often contain reactive functional groups that
remain after synthesis to provide additional function to the
resulting material [53,54]. Thus, each benzoxazine monomer syn-
thesized using natural material can be complex in its interaction to
other material in applications such as blend [55,56], composite [2e
5], and molecular structure [46]. One natural renewable source that
is underutilized is lignin, which is a major waste byproduct from
the paper manufacturing. Lignin is a natural biopolymer that can be
found in wood, aquatic plants, grasses, and other plant substances
[57,58]. Lignin can be found in many forms in nature as it is often an
* Corresponding author.
E-mail address: hxi3@cwru.edu (H. Ishida).
0032-3861/$ e see front matter Ó 2014 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.polymer.2014.01.041

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A. Van et al. / Polymer 55 (2014) 1443e1451
amorphous polymer consisting of phenylpropane monomers [58].
Reports on the use of lignin for polybenzoxazines as a blend
component have been reported [59,60].
chloroform (99.5%), toluene (99.5), and anhydrous sodium sulfate
(99.4%) were used as received from Fischer Scientific. Jeffamine
M1000 (90%) and Epon 828 epoxy were courtesy from Huntsman
and Momentive, respectively, and used as received.
Vanillin contain one open ortho position adjacent to the hy-
droxyl group, which makes vanillin a candidate for 1,3-benzoxazine
synthesis. Vanillin can be synthesized from lignin and other
renewable sources [61e64]. Currently, vanillin is used predomi-
nantly in the food and beverage industry, as well as in perfumes and
pharmaceuticals. Vanillin can be found naturally produced by va-
nilla plants, but the majority of vanillin used in industry is created
through chemical synthesis [62]. In addition to synthesis from
lignin, vanillin can also be biosynthesized from many other com-
pounds such as eugenol, ferulic acid, and aromatic amino acids
using fungi, bacteria, or other genetically engineered microorgan-
isms [62]. Vanillin is of great interest as a natural renewable reac-
tant for benzoxazine chemistry, because vanillin contains an
aldehyde group. The aldehyde is not consumed during synthesis.
This aldehyde can be further used to react with other chemical
groups or provide function to the benzoxazine monomer.
1,3-Benzoxazine groups are hydrophobic and do not dissolve into
aqueous solutions, which makes benzoxazine groups useful as hy-
drophobic groups on a surfactant [65,66]. Previous benzoxazine sur-
factants were synthesized by incorporating a long hydrophilic
polyetheramine tail as the amine during monomer synthesis. In the
case of a benzoxazine monomer synthesized from natural renewable
resources, such as vanillin, the monomers have functional groups to
react to hydrophilic segments to form an amphiphilic molecule
capable of supporting an emulsion. With benzoxazine groups acting
as hydrophobic groups, stable emulsions can be produced.
An emulsion is a mixture of multiple immiscible fluids. In its
simplest state, a two-phase system consisting of a dispersed phase
and a continuous phase is stabilized by a surfactant. A surfactant
ideally exists at the interphase of the two phases to reduce the
interfacial tension and stabilize the regions. A miniemulsion of
polystyrene in water was designed to take advantage of benzox-
azine’s affinity to polystyrene and polyetheramine’s affinity to
water to demonstrate a benzoxazine surfactant based on natural
renewable resource’s ability to perform its functions as a surfactant.
Miniemulsion requires shearing with high shear process such as
ultrasound to disperse the immiscible phases into quasi-stable
droplets. Emulsion technique can be used for emulsion polymeri-
zation, drug delivery, food emulsion, and more [67].
2.2. Methods
2.2.1. Synthesis of 8-methoxy-3-phenyl-3,4-dihydro-2H-benzo[e]
[1,3]oxazine-6-carbaldehyde
8-Methoxy-3-phenyl-3,4-dihydro-2H-benzo[e][1,3]oxazine-6-
carbaldehyde (hereinafter abbreviated as V-a) was synthesized
from vanillin, aniline, and paraformaldehyde according to Scheme
1. Vanillin (5.70 g, 0.037 mol), aniline (3.49 g, 0.037 mol), and
paraformaldehyde (1.13 g, 0.038 mol) were dissolved in toluene
and heated under reflux for 72 h in a round-bottom flask. Schiff
base product between aniline and vanillin was considered as im-
purities and minimized by using a low dielectric constant solvent,
toluene. Product was purified by washing with approximately
500 mL of 1 N sodium hydroxide solution. After the wash, the
toluene solution was dried with anhydrous sodium sulfate and
filtered. Solvent was allowed to evaporate to leave yellow needle-
like V-a crystals for collection. Yield was 83% as determined by
weight.
A sample of synthesized V-a was polymerized by heating at
220 ꢀC for 2 h. This temperature was selected based on the DSC
results, which indicated an exotherm at 246 ꢀC.
FT-IR: 1692 cmꢁ1 (C]O), 1600 cmꢁ1 (C]C), 1495 cmꢁ1 (Ar),
1144 cmꢁ1 (Ar-O), 1234 cmꢁ1 (OeCH2), 1076 cmꢁ1 (OeCH3),
912 cmꢁ1 (CeC, out of plane ring bending with an attached oxazine
ring).
NMR: 3.93 ppm (3H, OeCH3), 4.72 ppm (2H, AreCH2-N),
5.54 ppm (2H, OeCH2eN), 6.80e7.50 ppm (7H, AreH), 9.81 ppm
(1H, HC]O).
2.2.2. Synthesis of (E)-61,64-dimethyl-N-((8-phenoxy-3-phenyl-
3,4-dihydro-2H-benzo[e][1,3]oxazin-6-yl)methylene)-
2,5,8,11,14,17,20,23,26,29,32,35,38,41,44,47,50,53,56,59,62,65-
docosaoxaoctahexacontan-67-amine
(E)-61,64-dimethyl-N-((8-phenoxy-3-phenyl-3,4-dihydro-2H-
benzo[e][1,3]oxazin-6-yl)methylene)-
2,5,8,11,14,17,20,23,26,29,32,35,38,41,44,47,50,53,56,59,62,65-
docosaoxaoctahexacontan-67-amine (hereinafter abbreviated as
V-a-Jeff) synthesized from V-a and Jeffamine M1000 is shown in
Scheme 3. V-a (0.211 g, 0.787 mmol) and Jeffamine (0.847 g,
0.847 mmol) were mixed and heated at 100 ꢀC for 24 h in a round-
bottom flask. A yellow liquid was obtained and used without
further purification. Yield was 75%, as later determined by FT-IR and
NMR.
2. Experimental
2.1. Materials
Vanillin (99%), aniline (99.5), and paraformaldehyde (95%) were
used as received from Sigma Aldrich. Sodium hydroxide (97%),
Scheme 1. Synthesis of vanillin-aniline benzoxazine monomer from vanillin, aniline, and paraformaldehyde.

A. Van et al. / Polymer 55 (2014) 1443e1451
1445
Scheme 2. Polymerization of vanillin-aniline monomer.
FT-IR: 1601 cmꢁ1 (C]C), 1495 cmꢁ1 (AreH), 1144 cm1 (AreO),
1234 cmꢁ1 (OeC), 1076 cmꢁ1 (OeCH3), 934 cmꢁ1 (CeC, out of plane
ring bending with an attached oxazine ring).
NMR: 1.12 ppm (9H, CH3), 3.40e3.70 ppm (85H, OeCH3),
3.93 ppm (1H, OeCH3), 4.65 ppm (2H, AreCH2eN), 5.47 ppm (2H,
OeCH2eN), 6.80e7.50 ppm (7H, AreH), 8.17 ppm (1H, HC]N), 9.80
(1H, HC]O).
deuterated chloroform (CDCl3 e d) with 0.001%wt tetramethylsi-
lane (TMS) as an internal standard. A relaxation time of 10 s was
used for the integrated intensity measurement with 64 transients.
Fourier transform infrared spectroscopy (FT-IR) was performed
using a Bomem Michaelson MB 110 spectrophotometer with a
deuterated triglycine sulfate detector. Thirty two scans were co-
added to obtain a spectrum at a resolution of 4 cmꢁ1 after purg-
ing the spectrometer with dry air. Solid samples were ground and
pressed into a potassium bromide (KBr) pellet for analysis. Liquid
samples were smeared between two KBr plates for analysis.
Differential scanning calorimetry (DSC) was conducted on a TA
Instrument DSC Model 2920. The DSC thermograms were obtained
at a temperature ramp rate of 10 ꢀC/min under nitrogen purge with
the flow rate of 60 mL/min. A few milligram samples were crimped
in hermetic aluminum pans with lids.
Thermal stability of polymerized V-a was studied by thermog-
ravimetric analysis (TGA) using a TA Instruments Model High Res
TGA 2950. TGA was performed with a heating rate of 5 ꢀC/min
under nitrogen purge rate of 60 mL/min from room temperature to
900 ꢀC. The char yield is defined as the percent residual weight at
800 ꢀC under nitrogen atmosphere. Approximately 5 mg of samples
were used for each analysis. Differential TGA thermogram was also
obtained to better visualize the transitions occurring.
2.2.3. Miniemulsion polymerization of styrene stabilized by
benzoxazine based surfactant
Miniemulsion of styrene and benzoxazine surfactant V-a-Jeff
was obtained by emulsifying two separate phases. An organic phase
composed of cyclohexane (100 mg), benzophenone (50 mg) and
styrene (1.5 g) were dissolved in a 10 ml beaker. Separately, an
aqueous phase composed of water (10.0 g) and V-a-Jeff surfactant
(0.375 g) were dissolved in another 10 ml beaker. The organic and
aqueous phases were then mixed by an Ultra Turrax homogenizer
at 20,000 rpm for 10 min as pre-emulsification process. The
mixture was then subjected to ultrasound at 280 W with 2 s
agitation and 2 s rest intervals with a combined total of 1 min of
agitation. The styrene emulsion was stirred at 60 ꢀC for 24 h to
obtain polystyrene particles.
Emulsification of styrene and benzoxazine surfactant were
performed using an IKA T-10 Basic Ultra Turrax and Branson
Ultrasonifier S-450. Branson Ultrasonifier was equipped with a
tapped disruptor horn.
2.2.4. Equipment
Molecular structures were studied by proton nuclear magnetic
resonance spectroscopy (1H NMR) using Varian Oxford AS300 with
a proton frequency of 300 MHz. NMR spectra were acquired in
Scheme 3. Synthesis of benzoxazine-based surfactant from vanillin-aniline and Jeffamine M1000.

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A. Van et al. / Polymer 55 (2014) 1443e1451
Micro Raman scattering studies were carried out at room tem-
perature using a Horiba Jobin-Yvon LabRam HR800 spectrometer
which is equipped with a charge coupled detector and two grating
systems (600 and 1800 lines/mm). A HeeNe laser (
with an optical power of 17 mW and a spot size of 1
l
¼ 632.8 nm),
m
m2 was
focused on the sample with an Olympus microscope. Raman shifts
were calibrated with a Si (100) wafer using the 520 cmꢁ1 line.
Dynamic light scattering (DLS) was taken using a VI-200SM
Goniometer with a HeeNe laser (
l
¼ 632.8 nm) at room temper-
ature. Distilled water was used as the solvent, and angle of the
detector was 90ꢀ with the size of the pinhole 2 mm. Duration of the
experiment was 5 min.
3. Results and discussion
Molecular structure of V-a was confirmed by FT-IR, Raman, and
NMR analyses. Phenol-aniline type benzoxazine (P-a) was used as
reference to compare and assign benzoxazine bands and shifts. IR
spectrum of V-a is shown in Fig.1 with key bands indicated. Band at
1692 cmꢁ1 indicates aldehyde at the para position of the aromatic
ring remains unaffected during the synthesis of benzoxazine
monomer. Two sets of aromatic bands are present within the V-a
spectrum. The first set of bands at 1600 cmꢁ1 and 1490 cmꢁ1 are
respectively associated with aromatic C]C bonds and mono-
substituted aromatic ring off of the amine. The second set of bands
at 1585 cmꢁ1 and 1463 cmꢁ1 are respectively associated with ar-
omatic C]C bonds and substituted aromatic ring in the benzox-
azine ring. P-a also have both sets of aromatic IR bands with the
same signals for monosubstituted benzene and slightly shifted
Fig. 2. Raman spectra of V-a (lower) and P-a (upper).
electronic contributions from the functional groups. V-a has addi-
tional methyl ether and aldehyde, while P-a does not have any
other functional groups. Thus, P-a is missing the bands at
1692 cmꢁ1 and 1078 cmꢁ1. The different functional groups methyl
ether and para-position aldehyde on V-a, can both be seen on the IR
spectrum (Fig. 1).
To complement and verify the FT-IR spectra, Raman spectra
were also recorded. All complementing peaks have been high-
lighted as seen in Fig. 2 below. While Raman Spectroscopy and IR
spectroscopy are both vibrational spectroscopic techniques to
examine the chemical structure of a material, certain features are
more prominently displayed in one technique over the other. Using
Raman spectroscopy, peaks showing 1,3-benzoxazine of V-a were
also detected at corresponding wavelengths. At 1690 cmꢁ1, the
aldehyde group on V-a is predominantly featured. Using the
Raman, the monosubstituted benzene ring was identified at
1600 cmꢁ1 for both P-a and V-a. The Raman bands of substituted
benzene of benzoxazine are found at wavenumbers corresponding
to IR counterparts. The methyl ether exclusive to V-a is present at
1076 cmꢁ1 as compliment to IR counterpart, but it is absent in the
spectrum for P-a.
bands for the benzoxazine benzene at 1585 cmꢁ1 and 1456 cmꢁ1
,
which is expected due to the similarities.
The band at 1076 cmꢁ1 is the CeO stretch of the methyl ether,
which also remains unaffected by the closing of 1,3-benzoxazine
ring during synthesis. The band at 1234 cmꢁ1 is associated with
AreOeCH2 stretching of the benzoxazine ring. The band at
1138 cmꢁ1 is associated with OeAr stretching of the oxazine ring.
The out-of-plane (CeC) bending of benzene ring to which oxazine
is attached gives rise to a band at 921 cmꢁ1. The presence of a tri-
functional benzene ring and heterocyclic benzoxazine ring fea-
tures indicate successful synthesis of benzoxazine monomer. As
expected, the spectra of V-a and P-a show significant overlap in key
benzoxazine bands such as the aromatic bands and oxazine ring
bonds. However, slight differences on the out-of-plane CH bending
activity can be seen as V-a band is at 912 cmꢁ1 and P-a’s band is at
943 cmꢁ1. The difference can be associated with the different
The 1H NMR spectra of V-a and P-a are illustrated in Fig. 3. The
resonance at 9.81 ppm corresponds to the aldehyde resonance at
the para position on the aromatic ring, which reassures the result
from IR and Raman for the preservation of aldehyde group during
Fig. 1. FT-IR spectra of V-a (lower) and P-a (upper).
Fig. 3. NMR spectra of V-a (lower) and P-a (upper).

A. Van et al. / Polymer 55 (2014) 1443e1451
1447
Scheme 4. Alternative pathway for V-a polymerization onto monosubstituted benzene ring.
benzoxazine monomer synthesis. As expected, P-a spectrum lacks
any shift in the 9.00e11.0 ppm region. The resonances ranging from
7.50 to 6.80 ppm are indications of the protons on the aromatic
portion of the 1-3-benzoxazine ring and the phenyl functional
group on both V-a and P-a. The resonances at 5.54 ppm and
4.72 ppm from V-a are from the oxazine ring for (OeCH2eN) and
(AreCH2eN), respectively. These oxazine methylene singlets
display pairwise appearance of equal integrated intensity in the
chemical shift range of 3.50e5.50 ppm [1]. Furthermore, the oxa-
zine peaks show a separation of 0.70e0.90 ppm [1]. The equal in-
tensities of these observed resonances further support the
successful benzoxazine synthesis without loss of the functional
group of interest. Corresponding resonances on P-a can be found
slightly shifted at 5.39 ppm and 4.66 ppm. Slight difference in
chemical shift is common for benzoxazine chemistry and can be
accredited to the lack of functional groups on P-a as compared to V-
a.
Thermal activities of V-a monomer were studied using DSC,
which is represented in the thermograms in Fig. 5. Sharpness of the
melting endotherm minimum indicates the high purity of the
sample. P-a shows typical melting endotherm peak at 61 ꢀC and
polymerization exotherm peak at 263 ꢀC of a non-functional ben-
zoxazine monomers [1]. On the other hand, the melting endotherm
peak of V-a was observed at 83 ꢀC, whereas the polymerization
exotherm maximum was observed at 231 ꢀC. Polymerization exo-
therm for V-a is 143 j/g. V-a does not have obvious catalytic func-
tional groups, such as hydroxyl, carboxyl and sulfonic groups.
Despite this fact, noticeable reduction of the polymerization exo-
therm temperature and polymerization exotherm might be due to
hydrogen bonding environment and presence of aldehyde group.
Hydrogen bond forming environment has been reported to
compete with the phenol group that was created by the oxazine
ring opening from forming intramolecular 6-membered ring to
terminate the propagation of the polymer chain, thus reducing the
polymerization temperature [70,71]. Secondly, the aldehyde group
has been reported to participate in polymerization reaction with
the ortho position to the phenolic group further increasing the rate
of polymerization [68,69]. As a result, the V-a monomer showed
lower polymerization exotherm temperature than the non-
functional analog, P-a.
Using 1H NMR, the different functional groups were identified.
Methyl ether can be found at 3.93 ppm on V-a spectrum only. Lastly,
the resonances at 2.37 ppm from the V-a spectra is from the toluene
solvent used during synthesis, while the resonance at 1.58 ppm
from the P-a spectra is from trace water in deuterated chloroform.
The resonances at 5.54 ppm and 4.72 pm from the V-a spectrum are
indicative of the reaction between vanillin and aniline of the
desired products. Chemical shifts at 9.81 ppm and 3.93 ppm
demonstrate the presence of functional groups and differences
between V-a and P-a.
As shown in Fig. 6, polymerized V-a, abbreviated as poly(V-a),
has a higher char yield, highest onset temperature, and slower
rate of degradation than the corresponding polymer from P-a,
abbreviated as poly(P-a). Char yield of poly(V-a) is 55.3%, while that
of poly(P-a) is 36.0%. The slope of poly(P-a) degradation is also
Polymerization of V-a follows complex benzoxazine ring open-
ing mechanism. The ring opening results in the disappearance of
oxazine ring bands at 1234 cmꢁ1 and 914 cmꢁ1. IR bands from the
chemical groups that did not undergo changes, such as the AreO
band at 1144 cmꢁ1 and 1076 cmꢁ1, were not altered. Aromatic
addition of benzoxazine groups onto substituted benzene ring can
be observed in the appearance of 1427 cmꢁ1 band as shown in
Scheme 2. However, monofunctional benzene rings are available to
undergo aromatic addition, which can be observed as the disap-
pearance of 1600 cmꢁ1 and the shift of 1490 cmꢁ1 band to
1495 cmꢁ1. The addition onto monofunctional benzene ring follows
the structures outlined in Scheme 4. The two pathways for poly-
merization compete, but the kinetics of competition is a subject for
further study. In both pathways, hydroxyl group resulting from
polymerization can be seen as the broad band between 3178 and
3668 cmꢁ1. The band at 2934 cmꢁ1 can be attributed to the CeH
asymmetric stretch of the methyl group. Aldehyde band remains
after polymerization. However it has shifted to 1662 cmꢁ1 due to
chemical changes. Significant change in aldehyde band’s magni-
tude can be observed, which is likely due to the participation of
aldehyde groups in benzoxazine polymerization [68,69].
Fig. 4. FT-IR spectra of polymerized V-a.

1448
A. Van et al. / Polymer 55 (2014) 1443e1451
polymerization step is shown in Fig. 4 by the shift and reduction of
strong 1692 cmꢁ1 band to a weak 1682 cmꢁ1 band [68,69]. Thus, no
weight loss event was registered for the decarboxylation reaction.
This can also be observed in Fig. 4, with the disappearance of
aldehyde peak at 1690 cmꢁ1 after polymerization.
As an application of this reactive functional benzoxazine
monomer, preparation of benzoxazine-functional surfactant was
considered. The synthesis of V-a-Jeff surfactant was confirmed via
FT-IR and NMR analyses. The FT-IR spectrum of V-a-Jeff is shown in
Fig. 7 with key bands highlighted. The band at 1690 cmꢁ1 corre-
sponds to unreacted aldehyde groups of V-a. The key indication of
the formation of V-a-Jeff from V-a is the weaker absorbance of the
aldehyde band at 1690 cmꢁ1. The ratio of the intensity of the
aldehyde peak to the aromatic stretch just below 1500 cmꢁ1 in the
spectrum of V-a-Jeff is 1:4, while the ratio of the same peaks in V-a
was 1:1. This indicates that 75% of the aldehyde groups have been
reacted with the polyetheramine, which indicates a 75% yield of V-
a-Jeff. The bands at 1600 cmꢁ1 and 1490 cmꢁ1 are respectively C]C
double bonds and mono-substituted benzene rings. The band at
1076 cmꢁ1 is the methyl ether band. The usual benzoxazine related
bands at 1254 cmꢁ1 and 933 cmꢁ1 are observed. The presences of
1,3-benzoxazine bands suggest that benzoxazine retains its struc-
ture and reactivity even after the Schiff base formation. The broad
and intense band at 1100 cmꢁ1 can be attributed to the long pol-
yether tail that has been attached to the benzoxazine to provide
hydrophilic attribute.
Fig. 5. DSC thermograms of V-a (lower) and P-a (upper).
much sharper than that of poly(V-a), which indicates that poly(V-a)
has a much slower rate of degradation. These high char yield and
broader degradation temperature with slower rate are favorable
characteristics for good anti-flammable materials. The onset tem-
perature can be seen in Fig. 6, which illustrates the derivative of the
residual percent weight. The onset temperature for poly(P-a) is
249 ꢀC while the onset temperature for poly(V-a) is 347 ꢀC. Despite
similarity in structures, these two materials show significant dif-
ference in degradation pattern. The poly(P-a) shows a dTGA peak
around 210 ꢀC which is not present in the poly(V-a) thermogram.
Polybenzoxazines typically shows three temperature ranges for
degradation where the lowest temperature regime is assigned to
the amine evaporation from the branched or terminal portion of
the molecules [72]. This indicates that poly(P-a) has a significant
concentration of the chain ends. Considering that the majority of
monofunctional benzoxazine does not show crosslinked structure,
but result in small oligomers with molecular weight range of 500e
2000 Da, and further P-a is one of the exceptions that shows
crosslinked structure amongst mono-functional benzoxazines, it is
not surprising to see large concentration of chain ends that might
have resulted from the branches grown from the various reactive
sites on the benzene rings. Although decarboxylation reaction is
expected of this temperature range for V-a [69], the polymerization
conditions adopted to prepare poly(V-a) eliminated the aldehyde
groups prior to the TGA analysis. Usage of aldehyde group in
The 1H NMR spectrum of V-a-Jeff can be found in Fig. 8. The
chemical shifts ranging from 7.50 ppm to 6.80 ppm are all in-
dications of the aromatic protons on the aromatic portion of the
benzoxazine and the phenyl functional group. The chemical shifts
at 5.47 ppm and 4.65 ppm are from the oxazine ring, (OeCHeN)
and (AreCH2eN), respectively. Benzoxazine peaks represent closed
ring structure, which confirms the suggestion by IR that benzox-
azine ring remains post reaction. Methyl ether can be found at
3.93 ppm, while the chemical shifts at 3.61 ppm and 3.37 ppm
correspond to the CH2 groups on the polyether chain. The chemical
shift at 1.12 ppm is from methyl groups on the propyl component of
the polyether chain. The shift at 9.80 ppm corresponds to any
unreacted aldehyde groups of V-a. The chemical shift at 8.17 ppm
corresponds to the Schiff base proton (HC]N) [73]. The percent
yield can be calculated by using the ratio of the unreacted para
position aldehyde versus the Schiff base proton. Upon integration of
the 9.80 ppm and the 8.17 ppm resonances, the ratio is 1.00: 3.08,
indicating a 75.5% yield which is in close agreement with the result
from the FTIR analysis.
Fig. 6. TGA thermograms of poly(V-a) and poly(P-a). Derivative of TGA thermogram of
percentage sample weight of polymerized V-a and polymerized P-a. All graphs shown
as labeled.
Fig. 7. FT-IR spectrum of V-a-Jeff.

A. Van et al. / Polymer 55 (2014) 1443e1451
1449
Fig. 10. FT-IR spectra of miniemulsion of V-a-Jeff and polystyrene after heating.
Fig. 8. The NMR spectrum of V-a-Jeff.
4. Conclusion
While V-a-Jeff has emulsion stabilizing capability of a surfac-
tant, it retains its benzoxazine group, as shown in the DSC ther-
mogram in Fig. 9. Melting of crystalline regions is observed at
65.8 ꢀC while polymerization occurs at 256 ꢀC. Polymerization
temperature has been increased due to the dilution effect caused by
the long polyetheramine tail. Degradation of poly(ether amine)
chains occur at 333 ꢀC [74].
Novel benzoxazine monomer was synthesized from vanillin, a
natural renewable resource. The monomer was competitive with
other high performance thermoset as a primary material, especially
the high char yield. The aldehyde on the unreacted monomer
provides further functions to V-a as a reactive intermediate. The
additional function studied was V-a’s ability to be the hydrophobic
region of a surfactant. Quasi-stable miniemulsions were produced
using such a surfactant suspending polystyrene.
To confirm formation of the miniemulsion of V-a-Jeff containing
polystyrene, an FT-IR spectrum was recorded and shown in Fig. 10.
The CH2 bands at 2845 cmꢁ1 and 1107 cmꢁ1 can be accredited to
the sp3 hybridized (CeH) bonds and the ether groups on the
polyamine tail. Bands at 1600 cmꢁ1, 758 cmꢁ1, and 698 cmꢁ1 are
from polystyrene. Polystyrene aromatic (C]C) stretching is located
at 1600 cmꢁ1. Bands associated with aromatic (CeH) out-of-plane
vibrations from the monosubstituted benzene ring of polystyrene
Note added during the review process
During the review process, one of the reviewers alerted that a
similar paper using vanilla appeared online. It is now published as:
“Renewable benzoxazine monomer from vanillin: Synthesis,
are located at 758 and 698 cmꢁ1
.
Emulsification using V-a-Jeff was successful in producing poly-
styrene particles of 627 nm in average diameter with a poly-
dispersity of 1.24, determined by DLS. The miniemulsion was stable
for up to 2 weeks without significant deposition. A picture of the
miniemulsion after 2 weeks period at room temperature showed
little aging of the miniemulsion (Fig. 11). The stability is akin to
other miniemulsion with particle diameters in the meso-scale [53].
The possibility to incorporate benzoxazine groups into surfactants
as hydrophobic groups was first studied by Tadden et al. [65,66].
However, this is the first example incorporating natural renewable
resource based benzoxazines into stable surfactant activity.
Fig. 9. DSC thermogram of V-a-Jeff.
Fig. 11. Miniemulsion after 2 weeks at room temperature show little to no deposition.

1450
A. Van et al. / Polymer 55 (2014) 1443e1451
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One of the authors (A.V.) gratefully acknowledges the partial
financial support of SURES Program at Case Western Reserve Uni-
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