Synthesis and properties of biobased epoxy resins. part 1. Glycidylation of flavonoids by epichlorohydrin

Article abstract of DOI:10.1002/pola.24659

Biobased epoxy resins were synthesized from a catechin molecule, one of the repetitive units in natural flavonoid biopolymers also named condensed tannins. The reactivity of catechin toward epichlorohydrin to form glycidyl ether derivatives was studied using two model compounds, resorcinol and 4-methylcatechol, which represent the A and B rings of catechin, respectively. These model molecules clearly showed differences in reactivity upon glycidylation, explaining the results found with catechin monomer. The reaction products were characterized by both FTIR and NMR spectroscopy and chemical assay. The glycidyl ether of catechin (GEC) was successfully cured in various epoxy resin formulations. The GECs thermal properties showed that these new synthesized epoxy resins displayed interesting properties compared to the commercial diglycidyl ether of bisphenol A (DGEBA). For instance, when incorporated up to 50% into the DGEBA resin, GEC did not modify the glass-transition temperature. Epoxy resins formulated with GEC had slightly lower storage moduli but induced a decrease of the swelling percentage, suggesting that GEC-enhanced crosslinking in the epoxy resin networks.

Full text of DOI:10.1002/pola.24659

Synthesis and Properties of Biobased Epoxy Resins. Part 1. Glycidylation
of Flavonoids by Epichlorohydrin
1
HELENE NOUAILHAS, CHAHINEZ AOUF,2,3,4 CHRISTINE LE GUERNEVE,2,3,4 SYLVAIN CAILLOL,5 BERNARD BOUTEVIN,5
´
`
2,3,4
´
`
HELENE FULCRAND
1Innobat, Cap Alpha, Avenue de l’Europe, 34830 Clapiers, France
2INRA, UMR1083 Sciences Pour l’Oenologie, F-34060 Montpellier, France
3Montpellier SupAgro, UMR1083 Sciences Pour l’Oenologie, F-34060 Montpellier, France
4Universite´ Montpellier I, UMR1083 Sciences Pour l’Oenologie, F-34060 Montpellier, France
5Institut Charles Gerhardt, UMR CNRS 5253, Equipe Inge´nierie et Architectures Macromole´culaires, ENSCM, 8 rue de l’Ecole
Normale, 34296 Montpellier Cedex 05, France
Received 2 November 2010; accepted 28 February 2011
DOI: 10.1002/pola.24659
Published online 28 March 2011 in Wiley Online Library (wileyonlinelibrary.com).
ABSTRACT: Biobased epoxy resins were synthesized from a cate-
chin molecule, one of the repetitive units in natural flavonoid
biopolymers also named condensed tannins. The reactivity of
catechin toward epichlorohydrin to form glycidyl ether deriva-
tives was studied using two model compounds, resorcinol and
4-methylcatechol, which represent the A and B rings of catechin,
respectively. These model molecules clearly showed differences
in reactivity upon glycidylation, explaining the results found
with catechin monomer. The reaction products were character-
ized by both FTIR and NMR spectroscopy and chemical assay.
The glycidyl ether of catechin (GEC) was successfully cured in
various epoxy resin formulations. The GECs thermal properties
showed that these new synthesized epoxy resins displayed
interesting properties compared to the commercial diglycidyl
ether of bisphenol A (DGEBA). For instance, when incorporated
up to 50% into the DGEBA resin, GEC did not modify the glass-
transition temperature. Epoxy resins formulated with GEC had
slightly lower storage moduli but induced a decrease of the
swelling percentage, suggesting that GEC-enhanced crosslink-
C
V
ing in the epoxy resin networks. 2011 Wiley Periodicals, Inc.
J Polym Sci Part A: Polym Chem 49: 2261–2270, 2011
KEYWORDS: polyphenols; recycling; renewable resources;
resins; thermoplastics
INTRODUCTION In the field of green chemistry development,
scientists, and especially chemists, are facing new stakes and
have to deal with new constraints to answer to increasing
needs in terms of food, energy, clean water, health, cosmet-
ics, and transport of a growing world population in a sus-
tainable development context. Current chemical emphasis is
based on oil derivatives, but fossil resources are limited, and
their prices are volatile. Therefore, global aims were set for
an increase of use of renewable resources by chemicals com-
panies. As a consequence of new regulations based on Euro-
pean directives focused on reduction wastes and pollutants
volume,1–4 substitutions have to be found for a large number
of carcinogen, mutagen, and reprotoxic (CMR) classified sub-
stances.5 Some of these substances are constituents of
widely used plastics. Among them, bisphenol A (BPA), which
is classified as CMR R3, is one of the main components of
epoxy resins.
tective coatings, and many other products. BPA-based resins
are also encountered in human health applications such as
filling materials or sealants in dentistry. However, these poly-
mers are sensitive to hydrolysis and leaching of BPA leading
to widespread human exposure as revealed by numerous
studies.6–10 Moreover, high BPA levels in various human flu-
ids and tissues have been detected, which can be responsible
for health damages.11–14
Recent awareness on BPA toxicity combined with the limita-
tion and high cost of fossil resources implies necessary
changes in the field of epoxy resins. Major issues are to find
both alternative to the typical synthesis route for epoxy res-
ins and substitutes for BPA. In this sense, Cheng described
the synthesis of a novel epoxy resin based on a polyaromatic
phenolic compound synthesized from resorcinol and acetone
with higher thermal resistance than standard epoxy resin
based on diglycidyl ether of bisphenol A (DGEBA).15
Commercialized for more than 50 years, BPA is the most
common phenol derivative used in epoxy resin formulations
to produce adhesives, laminates, structural composites, pro-
New requirements for increased recycling have prompted
other studies on the use of renewable resources such as
Correspondence to: H. Fulcrand (E-mail: helene.fulcrand@supagro.inra.fr)
C
V
Journal of Polymer Science Part A: Polymer Chemistry, Vol. 49, 2261–2270 (2011) 2011 Wiley Periodicals, Inc.
SYNTHESIS AND PROPERTIES OF BIOBASED EPOXY RESINS, NOUAILHAS ET AL.
2261

JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
wood derivatives as substitutes for BPA allowing reduced
waste production. Thus, epoxy resins were synthesized from
methanol soluble lignin extracted out of unused bamboo.16
Other teams have developed wood-based epoxy resins syn-
thesized by a two-step process from wood powder: liquefied
wood was obtained by reacting wood powder with resor-
cinol and then the glycidyl etherification of liquefied wood
was conducted with epichlorohydrin.17,18 The purpose of the
latter work was a wood valuation and not a study of the
reactivity of hydroxyl groups present in wood compounds to-
ward epichlorohydrin. Indeed, the wood powder was used
without any further purification and hydroxyl groups present
in liquefied wood can come from various wood components
such as cellulose, lignin, and polyphenols. Wood tannins
were also extensively studied by Pizzi and coworkers in
formo-phenolic resins. Tannins were reacted with formalde-
hyde and with formaldehyde substitutes, such as glyoxal, in
wood adhesives formulations.19–22
SCHEME 1 Structure of catechin, resorcinol, and 4-
Polyphenols, and more specifically condensed tannins,
extracted from wastes produced by the wood and wine
industries can be an alternative to BPA to produce epoxy
resins. The work reported here aims at studying the reactiv-
ity of tannins based on a catechin model before identifying
tannins as potential substitutes for BPA in the synthesis of
biobased epoxy resins. The synthesis of epoxy resins actually
requires a first step of functionalization of phenolic hydroxyl
groups that cannot be directly investigated on tannins them-
selves for three main reasons. The first one is that con-
densed tannins are polymers, the structures and chain
lengths of which greatly depend on the plant (even species,
organ, and tissue) that produces them, meaning that there is
a great structural diversity of tannins in the plant kingdom.
Second, due to their polymeric nature, these macromolecules
are difficult to analyze and characterize precisely. Therefore,
it would be much more challenging to characterize their
functionalized products. The third reason is that tannins are
not commercial chemicals although tannin extracts can be
produced in large quantities but their chemical composition
cannot be completely established. They can be prepared in
the laboratory with high purity and with a relatively low-
production scale (typically several hundred milligrams),
which limits their use for chemical synthesis. For all these
reasons, the goal of this work was to use a representative
model for studying tannin reactivity, namely catechin.
Indeed, the common feature of tannin structures is the build-
ing block of the polymeric chains, which is based on a flavan
(2-phenyl chroman)-type structure, consisting of two aro-
matic rings bearing several hydroxyl groups referred to as A
and B rings which are connected through a central pyran
ring, the latter being referred to as C-ring. The most widely
spread subunits of tannins in the plant kingdom are (ꢀ)-epi-
catechin and (þ)-catechin, two flavan-3-ol epimers. The two
phenolic rings within the catechin structure differ by their
hydroxylation pattern: the two hydroxyl groups of A-ring are
in the meta position, while they are in the ortho position on
the B-ring. To evaluate the effect of the hydroxylation pattern
of aromatic rings toward glycidylation, the reactivity of
methylcatechol.
hydroxyl groups was investigated using three different phe-
nolic molecules. Resorcinol and 4-methylcatechol were cho-
sen to mimic the A- and B-rings of catechin, respectively, and
the glycidylation was finally applied to catechin itself
(Scheme 1). Furthermore, the functionalized catechin was
cured, and some properties of the resulting epoxy resin were
compared to the standard DGEBA epoxy resin.
EXPERIMENTAL
Materials
High performance liquid chromatography (HPLC)-grade etha-
nol and acetone were purchased from Merck. Catechin [(þ)-
Catechin hydrate ꢁ 98%], epichlorohydrin, sodium hydrox-
ide, resorcinol (SigmaUltra
ꢁ
98%), 4-methylcatechol
(ꢁ98%, HPLC) diglycidyl ether of resorcinol (DGER), potas-
sium hydrogen phthalate, 4-methyl-2-pentanone (ACS Rea-
gent ꢁ 98.5%) and tetrahydrofuran (THF, puriss.p.a., ACS
Reagent> 99.5%) were purchased from Sigma-Aldrich.
DGEBA (Epikote 828-Resolution Performance Products) and
Epamine PC19 (PO.INT. ER S.r.l.) were supplied by Nanoledge
Chemicals. Epamine PC 19 is composed by benzyl alcohol
(<50%), 1,3-bis(aminomethyl)benzene (<25%), 3-amino-
methyl-3,5,5-trimethylcyclohexylamine (<25%) and BPA-epi-
chlorohydrin polymer (<20%).
Glycidylation of resorcinol, 4-methylcatechol, and catechin
hydroxyl groups were conducted following the method of St
Clair.23 The described process leads to the preparation of
epoxyalkylaryl ether by the reaction of compounds contain-
ing hydroxyl groups directly attached to an aromatic nucleus
with a haloepoxyalkane in the presence of a strong alkali.
Glycidylation of Resorcinol
Resorcinol (2 g, i.e., 0.02 mol, i.e., 0.04 mol AOH) was dis-
solved in epichlorohydrin (14.8 g, i.e., 0.16 mol) and heated
under a reflux condenser in a 100-mL three-neck round-bot-
ꢂ
tomed flask at 98 C while stirring. An ethanolic solution of
2262
WILEYONLINELIBRARY.COM/JOURNAL/JPOLA

ARTICLE
sodium hydroxide (1.6 g, i.e., 0.04 mol, 15-mL ethanol) was
added dropwise using a dropping funnel while stirring and
heating at 98 C. After 3 h, the reaction mixture was diluted
(C3), 118.8 (C6), 123.5 (C5), 131.9 (C4), 142.5 (C2), 144.2
(C1).
ꢂ
Glycidylation of Catechin
to 200 mL with acetone. Salts released as by-products in the
reaction medium were filtered out over a 1-lm glass-fiber
filter. The acetone and nonreacted excess of epichlorohydrin
were evaporated using a rotary evaporator at 80 ꢂC under
reduced pressure. The reaction product was then redissolved
in acetone (40 mL), filtered over a 1-lm glass-fiber filter,
Catechin (2 g, i.e., 0.0069 mol, and 0.0345 mol -OH) was dis-
solved in epichlorohydrin (12.7 g, i.e., 0.137 mol) and heated
under reflux condenser in a 100-mL three-neck round-bot-
ꢂ
tomed flask at 98 C while stirring. An ethanolic solution of
sodium hydroxide (1.37 g, i.e., 0.034 mol, 12-mL ethanol)
was added dropwiꢂse using a dropping funnel while stirring
and heating of 98 C. The synthesis proceeded as previously
described for resorcinol. The product (1.6 g) was finally
obtained after silica gel chromatography (yield ¼ 48%).
ꢂ
and the filtrate was evaporated under vacuum at 80 C. This
last step was repeated twice. The reaction product was fur-
ther purified by silica gel chromatography and 3.89 g of the
desired product, namely, the DGER was obtained (molar
yield ¼ 87%).
NMR Chemical Shifts of Catechin Rings
1H NMR (500 MHz, DMSO-d6), d (ppm): 2.89–3.10 (2H, H4),
3.90–4.07 (1H, H3), 4.64–4.99 (1H, H2), 6.03 (1H, H6), 6.28
NMR Chemical Shifts of Resorcinol Derivatives with
Methyloxirane Functions
0
0
0
(1H, H8), 6.73–7.21 (3H, H2 , H5 , H6 ).
1H NMR (500 MHz, DMSO-d6), d (ppm): 2.73 and 2.87 (2H,
13C NMR (125.7 MHz, DMSO-d6), d (ppm): 28.9–29.7 (C4),
67.3 (C3), 81.9–83.5 (C2), 94.3 (C6), 95.7 (C8), 103.7 (C10),
0
0
Hc and Hc ), 3.72 (1H, Hb), 3.84 and 4.34 (2H, Ha and Ha ),
6.58 (3H, H2, H4, and H6), 7.21 (1H, H5).
0
0
0
0
114.8–121.9 (C2 , C5 and C6 ), 133.8–134.2 (C1 ), 143.9–
13C NMR (125.7 MHz, DMSO-d6), d (ppm): 45.5 (CHc and
0
0
151.0 (C3 , C4 ), 156.6 (C9), 158.8 (C5), 159.5 (C7).
0
0
CHc ), 51.4 (CHb), 70.8 (CHa and CHa ), 103.1 (C2), 109.0 (C4
and C6), 131.8 (C5), 161.2 (C1 and C3).
NMR Chemical Shifts of Methyloxirane
Function on Catechin
1H NMR (500 MHz, DMSO-d6), d (ppm): 2.71–2.93 (2H, Hca
Glycidylation of 4-Methylcatechol
4-Methylcatechol (2.48 g, i.e., 0.02 mol, i.e., 0.04 mol AOH)
was dissolved in epichlorohydrin (14.8 g, i.e., 0.16 mol) and
heated under a reflux condenser in a 100 mL three-neck
round-bottomed flask at 98 ꢂC while stirring. An ethanolic
solution of sodium hydroxide (1.6 g, i.e., 0.04 mol, 15 mL
ethanol) was added dropwise using a dropping funnel while
stirring and heating at 98 ꢂC. The synthesis proceeded as
previously described for resorcinol. 3.86 g of product was
obtained after the glycidylation of methylcatechol. The reac-
tion mixture was further purified by silica gel chromatogra-
phy and the separation was followed by thin layer chro-
matography (TLC). Two fractions were collected. The first
fraction containing the expected reaction product corre-
sponds to 2.90 g (yield ¼ 61%).
0
and Hc a), 3.32–3.41 (1H, Hba), 3.75–3.93 and 4.28–4.42 (2H,
0
Haa, and Ha a).
13C NMR (125.7 MHz, DMSO-d6), d (ppm): 45.3 (CHca and
CHc a), 51.4 (CHba), 70.7–71.6 (CHaa and CHa a).
0
0
NMR Chemical Shifts of Dioxane Function on Catechin
1H NMR (500 MHz, DMSO-d6), d (ppm): 3.68–3.86 (2H, Hcb,
0
0
and Hc b), 3.93–4.07 and 4.28–4.42 (2H, Hab, and Ha b), 4.15–
4.24 (1H, Hbb).
13C NMR (125.7 MHz, DMSO-d6), d (ppm): 61.2 (CHcb and
CHc b), 66.8 (CHab and CHa b), 75.2 (CHbb).
0
0
Substitution of resorcinol, 4-methylcatechol, and catechin
phenolic hydroxyl groups by methyloxirane functions is
described in a recent patent.24
NMR Chemical Shifts of Methylcatechol with
Methyloxirane Function
FTIR Spectroscopy
1H NMR (500 MHz, DMSO-d6), d (ppm): 2.28 (3H, CH3a),
Infrared spectral acquisition was performed with an Avatar
360 spectrophotometer equipped with Omnic software
(Nicolet, Madison). The samples were placed in contact with
the ATR single reflection cell consisting of germanium crys-
tal. A micrometric screw applying constant pressure ensured
good contact between the sample and the crystal. The back-
ground spectrum was acquired in air. Each spectrum is the
average of 22 scans from 600 to 4000 cmꢀ1 at an ambient
0
2.75 and 2.88 (2H, Hca, and Hc a), 3.38 (1H, Hba), 3.80–3.90
0
and 4.26–4.37 (2H, Haa, and Ha a), 6.77 (1H, H5), 6.88 (1H,
H3), 6.93 (1H, H6).
13C NMR (125.7 MHz, DMSO-d6), d (ppm): 22.1 (CH3a), 45.4
0
0
(CHca and CHc a), 51.4 (CHba), 71.6 (CHaa and CHa a), 114.7
(C3), 116.6 (C6), 123.1 (C5), 132.2 (C4), 147.4 (C2), 149.5 (C1).
ꢂ
temperature in the range of 20 C.
NMR Chemical Shifts of Methylcatechol with Dioxane
Function
NMR Spectroscopy
1H NMR (500 MHz, DMSO-d6), d (ppm): 2.23 (3H, CH3b),
NMR spectra were acquired on a Varian Unity Inova 500
MHz spectrometer (Varian Palo Alto, CA) at 298 K using a 3-
mm indirect detection probe equipped with a z-gradient coil.
Samples (ꢃ5 mg) were dissolved in deuterated dimethyl
sulfoxide (DMSO-d6) in the presence of sodium 3-trimethyl-
silylpropionate-d4 (TMSP) as an internal reference. All
0
3.63 and 3.67 (2H, Hcb, and Hc b), 4.15 (1H, Hbb), 4.04–3.90
0
and 4.29–4.36 (2H, Hab, and Ha b), 6.63 (1H, H5), 6.72 (1H,
H3), 6.78 (1H, H6).
13C NMR (125.7 MHz, DMSO-d6), d (ppm): 21.8 (CH3b), 61.4
0
0
(CHcb and CHc b), 66.7 (CHab and CHa b), 75.2 (CHbb), 117.0
SYNTHESIS AND PROPERTIES OF BIOBASED EPOXY RESINS, NOUAILHAS ET AL.
2263

JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
spectra were referenced on the 1H and 13C signals of TMSP
at 0 ppm. One-dimensional (1D) 1H, two-dimensional (2D)
homonuclear 1H (COSY, ROESY), and 2D heteronuclear
1H-13C (HSQC, HMBC) spectra were performed.
Proton 2D diffusion-ordered experiments (2D DOSY) were
performed using the Varian pulse sequence DgcsteSL. Diffu-
sion delay time and gradient pulse width were 200 and 4
ms, respectively. The gradient strength (g) was incremented
in 16 steps with equal g2 spacing from 0.3 to 32 G cmꢀ1
that allowed the NMR signals of interest to be attenuated at
ꢃ5% of the original intensity. The 1D spectra were proc-
essed by multiplication with Gaussian curves followed by
Fourier transformation. Additionally, the spectra were then
phase and baseline corrected. The DOSY processing program
implemented in the VNMR software was used to calculate
the diffusion coefficient and to create 2D spectra with NMR
chemical shifts along 1D and the calculated diffusion coeffi-
cient along the other.
FIGURE 1 IR transmission spectra of resorcinol and glycidyl
ether of resorcinol.
was a maximum. Two specimens of each composition were
tested.
Determination of the Epoxy Index
Swelling Measurements
The epoxy index (epoxide equivalent/kg of resin) was deter-
mined by chemical assay using a previously described
method.25 When epoxy products are present in the reaction
media, addition of HBr leads to the opening of epoxy func-
tions. When all the epoxy functions are opened by HBr, fur-
ther addition of HBr results in the blue-green end of crystal
violet indicator.
Swelling measurements of the networks were carried out
using THF as the diffusing agent. The swelling percentage
was calculated from the differences in weight between dried
and swollen networks. Bars samples (3 mm3) of the cured
epoxy resins were cut, weighed, and immersed in THF for 24
h. The samples were then swollen with solvent quickly blot-
ted between sheets of paper and finally weighted. The swel-
ling percentage was calculated as follows:
Formulation of the Cured Epoxy Resins
The cured samples of 25DGEBA/75GEC and 50DGEBA/
50GEC were the abbreviations of the reaction systems con-
taining DGEBA/glycidyl ether of catechin (GEC) with 25:75
and 50:50 weight ratio, respectively. All the reaction systems
were prepared in a 1:1 molar ratio of epoxy group to active
H of amine in the curing agent to obtain the optimal cross-
linking architecture of cured epoxy materials. Epoxy samples
Swelling ð%Þ ¼ ðWs ꢀ WdÞ=Wd ꢄ 100
where Ws and Wd are the weights of the swollen bar and the
dried bar, respectively.
The swollen bars were put in an oven at 60 ꢂC for 24 h to
dry them. Then, the bars were weighed (Wdo):
ꢂ
were cured at 60 C for 24 h.
Soluble part ð%Þ ¼ 100 ꢀ ½ðWdo=WdÞ ꢄ 100ꢅ
Thermal Analysis
Thermogravimetric analyses (TGA) of various cured resins
composed of glycidyl ether products were performed on a
Perkin Elmer TGA6 instrument. The initial weight of each
sample tested was approximately 5 mg. Each sample wꢀas1
heated from 20 to 900 ꢂC at a heating rate of 10 ꢂC min
under nitrogen atmosphere. Degradation temperatures at 5%
(Td5) and 30% (Td30), weight loss, and the char yield at 800
ꢂC (Char800) were then recorded for various cured resins.
RESULTS
Resorcinol, 4-methylcatechol, and catechin were reacted with
epichlorohydrin in alkaline medium to synthesize the corre-
sponding glycidyl ether derivatives afterward referred to as
GER, GEMC, and GEC, respectively. For each phenolic com-
pound, the reaction products were characterized by both
FTIR and NMR spectroscopy.
Dynamic Mechanical Analysis
FTIR Analysis
The temperature dependencies of the viscoelastic properties
(storage modulus: G0 and mechanical loss tangent: tand) of
the cured resins were evaluated by dynamical analyses
(DMA) in the bending mode using a frequency of 5 Hz. The
instrument used was a DMTA Metravib VA815-RDS. DMA
specimens were in the form of rectangular bars of nominal
size 2 ꢄ 10 ꢄ 30 mm3. The samples were tested over a tem-
perature range from ambient temperature to 120 ꢂC with a
The product obtained from the glycidylation of resorcinol
was analyzed by FTIR spectroscopy and compared to resor-
cinol (Fig. 1). Functionalization of the hydroxyl groups in res-
orcinol was revealed by the disappearance of the broad band
in the region of 3500–3000 cmꢀ1 associated with the
stretching vibration of the inter- and intra-molecular hydro-
gen bonded phenolic AOH. It was also revealed by the
appearance of a band at 1100 cmꢀ1 attributed to the vibra-
tion of an aliphatic ether. Moreover, new bands emerged at
2880, 2930, 3010, and 3080 cmꢀ1, which were assigned to
heating rate of 3 C minꢀ1. The glass-transition temperature
ꢂ
(Tg) was assigned as the temperature where the loss factor
2264
WILEYONLINELIBRARY.COM/JOURNAL/JPOLA

ARTICLE
The average number of methyloxirane functions per resor-
1
cinol ring, calculated from the ratio of H signal integrations
of the Ha aliphatic protons of methyloxirane to the H5 aro-
matic protons of resorcinol rings are indicated in Figure 3,
and was about 1.8. The same value was found for commer-
1
cial DGER from its H 1D spectrum.
The Epoxy index of synthesized GER determined by chemical
assay is 7.7, which represents 1.5 methyloxirane functions
per molecule. For comparison, the epoxy index of commercial
DGER is 8.0, which lead to 1.6 methyloxirane functions per
molecule.
This set of analytical data clearly showed the formation of
DGER as the main reaction product.
FIGURE 2 IR transmission spectra of catechin and glycidyl
ether of catechin.
1
The H 2D DOSY spectrum obtained after the glycidylation of
4-methylcatechol (Figure not shown) showed the presence of
two major products that differ by a slight modification in
both the diffusion coefficient values and 1H chemical shifts.
the vibration of methylene groups of the methyloxirane func-
tions. Additionally, the band appearing at 910 cmꢀ1 (shown
as the dotted line in Fig. 1) was attributed to the vibration
of epoxy groups. FTIR analyses, thus, showed the presence
of methyloxirane groups after reaction.
This indicated
compounds.
a
structural similarity of these two
The 1H-13C HMBC spectrum was used to characterize these
two main products. We, thus, found that these compounds
consisted of 4-methylcatechol derivatives, alkylated on the
hydroxyl groups at the C1 and/or C2 positions. Moreover,
the NMR spectra allowed two kinds of substitution patterns
to be distinguished: the expected methyloxirane group and a
benzodioxane-type moiety, namely the 6-methyl-2-hydroxy-
methyl-1,4-benzodioxane (Fig. 4) involving the two phenolic
hydroxyl groups of methylcatechol. This benzodioxane-type
substituent is composed of as many protons and carbons as
the methyloxirane group but some of its chemical shifts and
proton coupling constants are different, especially the Hbb
For the glycidylation product of methylcatechol, the specific
bands related to methyloxirane groups were also present on
the IR spectrum confirming that some substitution occurred
in the course of the reaction (Figure not shown). Unlike res-
orcinol product, the presence of hydroxyl groups in the reac-
tion products of methylcatechol was suggested by the shift
to slightly higher values of the broad band in the region of
3500–3000 cmꢀ1 corresponding to the inter- and intra-mo-
lecular hydrogen bonded phenolic AOH stretching vibration
in methylcatechol.
The IR spectrum of GEC is well resolved and can be com-
pared to the IR spectrum of its starting material, namely cat-
echin (Fig. 2). The broad band in the region of 3500–3000
cmꢀ1 shifted to slightly higher values as was already noted
for methylcatechol product, indicating the presence of
hydroxyl groups in glycidyl ether derivatives of catechin as
well. New bands emerged at 1100 cmꢀ1, attributed to the
0
and HcbHc b, which emerged to as higher chemical shifts. The
NMR chemical shifts for this kind of structure reported in
the literature or calculated using ChemDraw software are
consistent with the values found.26,27 Moreover, the C-alkyla-
tion of 4-methylcatechol has not been detected from neither
1H spectrum nor HMBC spectrum.
vibration of aliphatic ether, between 2900 and 3000 cmꢀ1
,
which corresponds to the vibration of methyl groups of the
methyloxirane functions and at 910 cmꢀ1, which corre-
sponds to the vibration of epoxy groups indicating the for-
mation of methyloxirane functions. Again, FTIR analyses con-
firmed the presence of methyloxirane functions on catechin.
NMR Analysis and Chemical Assay
1
The H 2D DOSY spectrum of glycidyl ether product of resor-
cinol (GER) (Figure not shown) showed that the most
intense signals in the spectrum appeared with the same dif-
fusion coefficient value, indicating the presence of one major
reaction product. The typical 1H resonances and the 1H-13
C
long range correlations allowed the major product to be
identified as the glycidyl ether of resorcinol. The heteronu-
clear multiple bond coherence (HMBC) spectrum also
showed that O-alkylation occurred at both the C1 and C3
ring positions, whereas no C-alkylation could be detected.
Signals arising from minor species (likely by products) were
also observed on the DOSY spectrum.
FIGURE 3 1H NMR spectrum of glycidyl ether of resorcinol.
SYNTHESIS AND PROPERTIES OF BIOBASED EPOXY RESINS, NOUAILHAS ET AL.
2265

JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
ylcatechol are two 4-methylcatechol derivatives, obtained in
the following proportions: 60% of benzodioxane-type 4-
methylcatechol derivative and 40% of the diglycidyl ether of
4-methylcatechol. This product distribution should lead to
0.8 epoxy function per 4-methylcatechol molecule. A value of
ꢃ0.9 methyloxirane function per 4-methylcatechol molecule
was found by chemical assay in accordance with the NMR
characterization.
DOSY spectrum of glycidylation products of catechin (GEC)
(Fig. 5) displayed most of the diffusion coefficient values of
catechin derivatives in a narrow width distribution indicating
that the reaction products have comparable molecular
weights. Moreover, we found that these diffusion coefficient
values were in the same order of magnitude with that of
pure catechin in the same solvent (result not shown), mean-
ing that the main reaction products were monomeric cate-
chin unit derivatives. The HMBC spectrum showed that alkyl-
ation occurred on all hydroxyl positions of the phenolic
rings, that is, at C5 and C7 of A ring and at C30 and C40 of B
ring. However, neither O-alkylation on the hydroxyl position
at C3 of the heterocyclic C ring nor C-alkylation at the car-
bons adjacent to hydroxyl groups of the phenolic A and B
rings (see Scheme 1 for catechin labeling) were detected.
Besides, the chemical shifts of benzodioxane-type substituent
different from those of methyloxirane group that was first
detected in the methylcatechol product spectrum, were also
FIGURE 4 1H NMR spectrum of glycidyl ether of 4-methylcate-
chol. The structures of the two major products are shown
above. The protons of the different substituents and their re-
spective chemical shifts have been labeled as follows: the
Greek character referred to as the proton location within the
substituent whereas the second character referred to as the
type of substituent (a for methyloxirane-type and b for benzo-
dioxane-type).
NMR chemical shifts of the methyl protons assigned to 4-
methylcatechol derivatives with methyloxirane functions (a-
type) were slightly higher than the chemical shifts of methyl
protons assigned to 4-methylcatechol derivatives with benzo-
dioxane-type substitution (b-type) (Fig. 4). Thus, the percent-
age of 4-methylcatechol derivatives with benzodioxane-type
function, calculated from the CH3a and CH3b proton signal
1
present in the H 1D NMR spectrum of GEC.
The average number of substituents per catechin molecule,
1
determined from the H 1D NMR spectrum using signal inte-
gration of all Ha (Haa and Hab) and aromatic protons of B
0
0
0
ring (H2 , H5 , and H6 ), (Fig. 5) was approximately 3.4. How-
ever, based on the ratio of 1H signal integrations of methyl-
0
integrations, was 60%. Moreover, using Hca (or Hc a) and
0
oxirane Hc protons (Hca and Hc a) to B ring aromatic protons,
CH3a proton signal integrations, it was found that the num-
ber of methyloxirane groups (a-type) per 4-methylcatechol
ring was 2. Consequently, the glycidylation products of meth-
an average number of methyloxirane groups per catechin
molecule was found approximately at 2.9. These calculations
FIGURE
5
1H 2D DOSY NMR
spectrum of glycidyl ether of cat-
echin. The structures of the two
major products are shown
above. The protons of the differ-
ent substituents and their respec-
tive chemical shifts have been
labeled as those of methylcate-
chol products.
2266
WILEYONLINELIBRARY.COM/JOURNAL/JPOLA

ARTICLE
Thermal Stability and Dynamic Mechanical Properties
of Various Cured Epoxy Resins
Figure 6 displays the plots of TGA obtained from DGEBA and
DGEBA/GEC cured epoxy resins. The characteristic values
calculated from these curves are given in Table 1. The statis-
tic heat-resistant index temperature (Ts) is characteristic of
the thermal stability of the cured resins. This value is deter-
mined from the temperatures at 5% weight loss (Td5) and
30% weight loss (Td30) of the sample obtained by thermog-
ravimetric analysis (TGA). The statistic heat resistant index
temperature (Ts) is calculated by eq 1.28–30
FIGURE 6 Thermogravimetric analysis traces of DGEBA,
Ts ¼ 0:49½Tds þ 0:6 ꢄ ðTd30 ꢀ Td5Þꢅ
(1)
75DGEBA/25GEC, and 50DGEBA/50GEC cured epoxy resins.
The values of statistic heat-resistant index (Ts) of the resins
containing synthesized GEC were lower compared to com-
mercial DGEBA. The addition of GEC into DGEBA slightly
lowered the thermal stability of the cured resins.
led to a 52:48 molar ratio of benzodioxane-(a-type) to meth-
yloxirane-(b-type) catechin derivatives. The benzodioxane-
type catechin derivative contains two methyloxirane func-
tions located on the A-ring per catechin molecule, whereas
the methyloxirane-type catechin derivative contains four
methyloxirane functions per catechin molecule. Given the rel-
ative proportions found for a- and b-type catechin deriva-
tives, this means that the glycidylation of catechin leads, in
average, to 73% of methyloxirane functions and 27% of ben-
zodioxane-type functions per catechin molecule. Using pro-
ton signal integration of Hcb as indicated in Figure 5, it was
actually found approximately ꢃ20% of benzodioxane-type
substituent against all catechin substituents.
ꢂ
Residual materials of resins at 800 C are presented in Table
1. Char800 values were higher for the resins containing GEC
compared to commercial DGEBA and the presence of GEC in
DGEBA resins induced a significant increase of the Char800
values. These results indicated that the GEC had a positive
effect in that they diminished the resin decomposition.
To evaluate the effect of the GEC content on glass-transition
temperature and crosslinking density of cured epoxy resins,
the storage modulus (G0) and loss factor (tan d) were calcu-
lated by using DMA. Figure 7 shows the temperature de-
pendence of the storage modulus G0 of cured DGEBA/GEC
specimens. The storage modulus G0 of the cured DGEBA/GEC
specimens slightly decreased when increasing GEC content.
The glass-transition temperature (Tg) was assigned as the
temperature where the loss factor was at a maximum. The
crosslinking density (q) of cured specimens was calculated
from the equilibrium storage modulus (G0) in the rubber
region over the a-relaxation temperature according to rubber
elasticity theory given by eq 2.31
Epoxy Resins Formulation
GEC was tested in an epoxy resin formulation and compared
to a pure commercial DGEBA. Resins were formulated at am-
bient temperature and cured at 60 ꢂC for 24 h. The curing
agent was Epamine PC 19, a commercial amine hardener for
epoxy systems based on a cycloaliphatic amine, providing
low viscosity and fast curing even at low temperatures. Com-
position of Epamine PC 19 is given in the Experimental
section.
q ¼ G0=ð/RTÞ
(2)
As GEC was a solid compound at ambient temperature, it
was mixed with DGEBA to lower the viscosity of the epoxy
resin and to formulate at ambient temperature. In this case,
DGEBA was actually used as reactive diluent. Thermal stabil-
ity, swelling properties, and dynamic mechanical properties
of the resins were tested and compared to the commercial
DGEBA. The DGEBA/GEC mixtures used were done at two
different weight ratios 75/25 and 50/50.
Tg is the a-relaxation glass temperature, G0 the storage mod-
ꢂ
ulus at Tg þ 30 C, / the front factor (approximated to 1 in
the Flory theory),32 R the gas constant, and T the absolute
ꢂ
temperature at Tg þ 30 C.
The obtained Tg, storage moduli (G0), and crosslinking den-
sities (q) of the specimens are summarized in Table 2. Tg is
TABLE 1 Parameters Related to Thermal Stability, Swelling Percentage, and Soluble Part of Various Cured Epoxy Resins
Td5 (ꢂC)a
Td30 (ꢂC)b
Ts
Char800 (%)d
Swelling (%)
Soluble Part (%)
c
Samples
DGEBA
209
221
202
355
337
323
145
142
135
10
14
18
17
4
1
1
1
75DGEBA/25GEC
50DGEBA/50GEC
1
a
c
Temperature of 5% weight loss as given by TGA.
Temperature of 30% weight loss as given by TGA.
Statistic heat resistant index temperature calculated by eq 1.
Char yield at 800 ꢂC.
b
d
SYNTHESIS AND PROPERTIES OF BIOBASED EPOXY RESINS, NOUAILHAS ET AL.
2267

JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
Moreover, the replacement of DGEBA by 25 or 50% of GEC
did not modify the soluble part of the resin, which stayed
equal to 1%. These results indicate that all components of
the GEC product do participate to the network.
DISCUSSION
Two models compounds were picked for this study. Resor-
cinol was chosen as a model of the catechin A ring, because
it bears two free hydroxyl groups in the same meta positions
as catechin, and 4-methylcatechol was chosen as a model of
the catechin B ring, because it bears two OH groups in the
same ortho positions as catechin (see Scheme 1). Even
though epicatechin, a stereoisomer of catechin, is the most
common monomeric unit of tannins in the plant kingdom,
catechin was preferred as a model molecule due to price
consideration. This choice is justified by the fact that the
reactivity of these two stereoisomers toward glycidylation
should be similar, because they have the same hydroxyl phe-
nolic patterns.
FIGURE 7 Storage modulus (G0) of the DGEBA and DGEBA/
GEC-cured epoxy resins as a function of temperature.
a parameter, which can be used to show the differences in
crosslinking density or degree of cure. The Tg of the cured
DGEBA epoxy resins polyblended with 25 and 50% of GEC
were the same as the Tg of the cured pure commercial
DGEBA. The addition of GEC in DGEBA epoxy resins does not
modify the Tg, indicating that the presence of GEC does not
significantly modify the internal structure of the polymer
network. However, crosslinking densities calculated by eq 2
were lowered by increasing the amount of GEC in the epoxy
resins.
The structural characterization of the products obtained by
the glycidylation of the model molecules clearly showed a
difference in reactivity of the two phenolic OH groups
according to their positions on the aromatic ring.
Thus, both FTIR and NMR analyses indicated a complete gly-
cidylation of the phenolic OH in meta positions of the resor-
cinol ring after reaction with epichlorohydrin. A low propor-
tion (ꢃ10%) of by products could be estimated from the
DOSY NMR experiment. Some of these by-products with dif-
fusion coefficient close to that of GER may result from poly-
addition of epichlorohydrin [Fig. 8(a)], formation of b-chloro-
hydrin [Fig. 8(b)], or a-glycol [Fig. 8(c)]. Other by-products
detected as traces in the DOSY spectrum and having lower
diffusion coefficient value (i.e., higher molecular weight) may
correspond to reaction by-products resulting from homopoly-
merization of the resin [Fig. 8(d)]. All of these by-products
have also been observed in the case of BPA glycidylation.33,34
Swelling Properties
The swelling test leads to two characteristic properties: the
swelling provides information about the crosslinking density
of resins and the soluble part gives quantitative information
about molecules, which are not implicated in the cured resin
network.
The higher the crosslinking density, the shorter the distance
between crosslinking nodes and, thus, the lesser solvent
(THF) the material absorbs. Results obtained for the various
cured epoxy resins are displayed in Table 1.
The swelling proportions and soluble parts were both in
agreement with the structural characterization of the cate-
chin glycidyl ether products. Samples containing GEC exhib-
ited lower swelling percentages than DGEBA, and the swel-
ling percentage decreases with increased GEC contents. This
finding indicates an increase of the crosslinking density.
The slight difference in the average number of methyloxirane
functions per resorcinol ring given by the chemical assay
TABLE 2 Dynamic Mechanical Analysis of the DGEBA/GEC-
Cured Epoxy Resins
Storage Modulus
(GPa)
Tg
Glassy
Rubbery
Samples
DGEBA
(ꢂC) Regiona Regionb q 10ꢀ3 mol cmꢀ3
)
209 2.81
0.019
0.016
0.014
6.06
5.12
4.48
75DGEBA/25GEC 221 2.46
50DGEBA/50GEC 202 2.40
FIGURE 8 Possible by-products resulting from polyaddition of
epichlorohydrin (a), formation of b-chlorohydrin (b), formation
of a-glycol (c), or homopolymerization of the resin (d) obtained
during glycidylation of resorcinol.
a
Storage modulus at 30 ꢂC.
Storage modulus at Tg þ 30 ꢂC.
b
2268
WILEYONLINELIBRARY.COM/JOURNAL/JPOLA

ARTICLE
(1.5) and calculated from NMR data (1.8) may be explained
by the presence of residual salts that were not removed in
the work up of the reaction: these residual salts are taken
into account in weighting the sample for chemical assay of
methyloxirane functions whereas, in NMR, only the proto-
nated species are used for the ratio calculation.
functions. The preferred formation of the benzodioxane de-
rivative may be explained by the higher kinetics of the intra-
molecular cyclization compared to the intermolecular pro-
cess yielding the dimethyloxirane derivative.
The benzodioxane function, representing roughly 20% of
GEC substituents, was not really intended because it does
not participate to the polymer network when GEC was for-
mulated with Epamine PC19. However, no decrease in the
glass-transition temperature was observed when incorporat-
ing GEC into the DGEBA resin up to 50%. Indeed, the cate-
chin derivatives substituted by a benzodioxane-type function
on the B ring have also two methyloxirane functions on the
A ring and thus participate to the network.
The preferential formation of DGER as the main reaction
product showed that the meta-substitution pattern of resor-
cinol hydroxyl groups is particularly suitable for the double
O-alkylation.
Conversely, the ortho positions of the two phenolic OH groups
on the benzene ring of 4-methylcatechol leads to two competi-
tive substitution pathways once the first glycidylation
occurred: either the second phenolate anion reacts with a sec-
ond molecule of epichlorohydrin to finally give the expected
diglycidylether of 4-methylcatechol; or the oxirane ring intro-
duced in the first substitution step undergoes an intramolecu-
lar nucleophilic attack from the second phenolate anion to
yield the benzodioxane-type derivative. The two products aris-
ing from these competitive reactions could not be isolated sep-
arately by silica gel chromatography, as they were coeluted.
Nevertheless, their relative proportions (60:40, benzodioxane-
type/methyloxirane-type) in the crude material recovered af-
ter the chromatography purification could be achieved by
NMR analyses, in agreement with the chemical assay.
Epoxy resins formulated with GEC have a higher crosslinking
density (result found by the swelling tests) in accordance
with the number of methyloxirane functions per aromatic
molecule, which was found to be close to 3 for catechin,
whereas it was ꢃ2 for DGEBA. In addition, the presence of
two methyloxirane functions on the same aromatic ring (A
ring) in GEC restricts the distance between nodes in the
polymer network and thus increases the crosslinking density.
On the contrary, crosslinking densities calculated from eq 2
based on rubber elasticity theory using DMA analysis
showed lower crosslinking densities for epoxy resins formu-
lated with GEC. As discussed above, these results are quite
surprising as both the internal structure of catechin and the
higher functionality of GEC compared to DGEBA was sup-
posed to lead to an increase in the rigidity and the crosslink-
ing density of the network and a restriction of the motions
within the molecular chains. The theoretical value of 1 taken
for the front factor can be an explanation of these results,
because the front factor is strongly dependent on the func-
tionality of the network junctions. The conformation of the
network in DGEBA epoxy resin surely differs from the con-
formation of the network when GEC was added, and, conse-
quently, the value of the front factor should be different.37
Thus, it was found that the ortho-substitution pattern of the
hydroxyl groups on the benzene ring of 4-methylcatechol is
prone to a benzodioxane-type substitution in addition to the
double O-alkylation.
With respect to resorcinol and 4-methylcatechol, flavan-3-ols
such as catechin exhibit competitive deprotonation on both
B and A rings leading to a mixture of different monopheno-
lates. The first dissociation constants of all four phenolic OH
groups are close, and the different hydroxyl groups can be
0
ordered according to their acidity in the sequence: pK3 -OH
¼
9.02, pK4 -OH ¼ 9.12, pK5-OH ¼ 9.43, pK7-OH ¼ 9.58.35,36 As
NaOH was in large excess for catechin glycidylation, hydroxyl
groups on the A and B rings are successively under pheno-
late form, which should result in a large majority of catechin
with four methyloxirane functions.
0
CONCLUSIONS
The first part of this study led to conclude that differences
in the reactivity of phenolic OH groups do exist according to
their meta and ortho positions on the benzene ring of resor-
cinol and 4-methylcatechol, respectively, chosen to represent
the A and B rings of the flavonoid repetitive unit in tannins.
Indeed, under the same reaction conditions, substitution of
the two hydroxyl groups in the meta position by methyloxir-
ane functions is observed in resorcinol whereas only one
hydroxyl group on average is substituted in 4-methylcate-
chol, where the hydroxyl groups are both in ortho positions.
The reactivity of the two phenolic moieties within the cate-
chin molecule remains the same during the reaction of cate-
chin with epichlorohydrin because catechin derivatives with
three methyloxirane functions on average were mostly
obtained.
The preferential formation of the catechin derivatives with
three methyloxirane functions on average was, thus, consist-
ent with the glycidylation products obtained with the pheno-
lic ring models: two methyloxirane functions on the A ring
and about one methyloxirane function on average on the B
ring. In particular, the benzodioxane-type structure observed
on glycidylation of 4-methylcatechol was also detected in cat-
echin products. Thus, the benzodioxane-type catechin deriva-
tive actually contains two methyloxirane functions on the A
ring and the benzodioxane-type substituent on the B ring,
whereas the methyloxirane-type catechin derivative contains
four methyloxirane functions on A and B rings. Here again,
the molar proportion of the catechin derivative bearing the
benzodioxane-type moiety is slightly higher than the propor-
tion of the catechin derivative bearing solely methyloxirane
The synthesized GEC was tested in epoxy resins formulation
and exhibited good thermal properties in comparison with
an epoxy resin based on pure commercial DGEBA.
SYNTHESIS AND PROPERTIES OF BIOBASED EPOXY RESINS, NOUAILHAS ET AL.
2269

JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
12 Vom Saal, F. S.; Hugues, C. Environ Health Perspect 2005,
This work shows the feasibility of epoxy resin formulation
based on flavonoid building blocks. The next step will be to
carry out an alternative two-step chemical synthesis (allyla-
tion followed by epoxidation) of glycidylether derivatives to
overcome eventually the incomplete functionalization of the
phenolic hydroxyls groups of catechin observed with epichlor-
ohydrin. Afterward, the synthesis of epoxy resin with the cor-
responding polymerized forms, that is, condensed tannins as
starting materials, will be performed. Nevertheless, it already
opens up new prospects on the valorization of industrial by-
products rich in tannins such as grape pomaces, wood, or
algae. These renewable phenolic resources seem to be promis-
ing for the replacement of BPA in epoxy resin formulation. In
comparison to lignin, tannins are water-soluble extractible
materials, usually less polymerized macromolecules and with
a higher content of free phenolic hydroxyl groups, offering a
great potential of functionalization and network formation.
113, 926–933.
13 Wolff, M. S.; Teitelbaum, S. L.; Windham, G.; Pinney, S. M.;
Britton, J. A.; Chelimo, C.; Godbold, J.; Biro, F.; Kushi, L. H.;
Pfeiffer, C. M.; Calafat, A. M. Environ Health Perspect 2007,
115, 116–121.
14 Dorey, C. K. Chemical Legacy: Contamination of the Child;
Greenpeace: London, 2003.
15 Cheng, J.; Chen, J.; Yang, W. T. Chin Chem Lett 2007, 18,
469–472.
16 Asada, C.; Nakamura, Y.; Kobayashi, F. Biochem Eng J
2005, 23, 131–137.
17 Kishi, H.; Fujita, A. Environ Eng Manag J 2008, 7, 517–523.
18 Kishi, H.; Fujita, A.; Miyazaki, H.; Matsuda, S.; Murakami, A.
J Appl Polym Sci 2006, 102, 2285–2292.
19 Garnier, S.; Huang, Z.; Pizzi, A.; Huang, Z. Holz Roh Werkst
The authors are grateful to the Carnot CED2 Institute in Mont-
pellier and to the Innobat Company for their financial support.
The authors thank the Nanoledge Chemicals Company for sup-
plying DGEBA and Epamine PC19, and for their assistance in
formulation. The authors also thank Jean-marc Souquet (SPO,
INRA, France), Jean-Claude Boulet (SPO, INRA, France), and
Le´na Saint-Macary (Innobat, France) for their help on analyses,
as well as Andrew Burns for its assistance in english correction.
2001, 59, 46–46.
20 Garnier, S.; Pizzi, A. J Appl Polym Sci 2001, 81, 3220–3230.
21 Pizzi, A.; Stephanou, A. J Appl Polym Sci 1993, 50, 2105–2113.
22 Pizzi, A.; Tondi, G.; Pasch, H.; Celzard, A. J Appl Polym Sci
2008, 110, 1451–1456.
23 St. Clair, W. E. U.S. Patent 2,892,849, 1959.
24 Nouailhas, H.; Burguiere, C.; Caillol, S.; Boutevin, B.; Ful-
crand, H.; Rapior, S. FR Patent 2,946,049, 2010.
REFERENCES AND NOTES
25 Lee, H.; Neville, K. In Handbook of Epoxy Resins; McGraw-
1 European Parliament Council. Directive 2002/95/EC Restric-
tion of the use of certain Hazardous Substances in Electrical
and Electronic Equipment 2002.
Hill Publishing Company, NY, 1967, pp 4.1–4.70.
26 Morreel, K.; Ralph, J.; Lu, F. C.; Goeminne, G.; Busson, R.;
Herdewijn, P.; Goeman, J. L.; Van der Eycken, J.; Boerjan, W.;
Messens, E. Plant Physiol 2004, 136, 4023–4036.
2 European Parliament Council. Directive 2002/96/EC Waste
Electrical and Electronic Equipment 2002.
27 Maes, D.; Syngel, V. K.; Debenedetti, S.; De Kimpe, N. Tetra-
3 European Parliament Council. Directive 2000/53/EC End-of-
hedron 2006, 62, 4426–4429.
Life Vehicles 2000.
28 Lehrle, R. S.; Williams, R. J. Macromolecules 1994, 27,
4 European Parliament Council. Directive 2000/60/EC Water
3782–3789.
Framework Directive 2000.
29 Jiang, B. B.; Hao, J. J.; Wang, W. Y.; Jiang, L. X.; Cai, X. X.
5 Council. Directive 1967/548/EC Dangerous Substances Direc-
Eur Polym J 2001, 37, 463–470.
tive 1967.
30 Chiu, Y. C.; Chou, I. C.; Tseng, W. C.; Ma, C. C. M. Polym
6 Cao, X. L.; Corriveau, J.; Popovic, S. J Agric Food Chem
Degrad Stab 2008, 93, 668–676.
2009, 57, 1307–1311.
31 Iijima, T.; Yoshioka, N.; Tomoi, M. Eur Polym J 1992, 28,
7 Joskow, R.; Barr, D. B.; Barr, J. R.; Calafat, A. M.; Needham,
573–581.
L. L.; Rubin, C. J Am Dental Assoc 2006, 137, 353–362.
32 Flory, J. P. Polymer 1979, 20, 1317–1320.
8 Lopez-Espinosa, M. J.; Granada, A.; Araque, P.; Molina-
Molina, J. M.; Puertollano, M. C.; Rivas, A.; Fernandez, M.; Cer-
rillo, I.; Olea-Serrano, M. F.; Lopez, C.; Olea, N. Food Addit
Contam Part A 2007, 24, 95–102.
33 Gulino, D.; Galy, J.; Pascault, J. P.; Pham, Q. T. Makromol
Chem 1984, 185, 297–316.
34 Gulino, D.; Galy, J.; Pascault, J. P.; Tighzert, L.; Pham, Q. T.
Makromol Chem 1983, 184, 411–429.
9 Maragou, N. C.; Makri, A.; Lampi, E. N.; Thomaidis, N. S.;
35 Cren-Olive, C.; Wieruszeski, J. M.; Maes, E.; Rolando, C. Tet-
Koupparis, M. A. Food Addit Contam Part A 2008, 25, 373–383.
rahedron Lett 2002, 43, 4545–4549.
10 Matsumoto, H.; Adachi, S.; Suzuki, Y. Arch Environ Contam
36 Cren-Olive, C.; Lebrun, S.; Hapiot, P.; Pinson, J.; Rolando, C.
Toxicol 2005, 48, 459–466.
Tetrahedron Lett 2000, 41, 5847–5851.
11 Kuruto-Niwa, R.; Tateoka, Y.; Usuki, Y.; Nozawa, R. Chemo-
37 Charlesworth, J. M. Polym Eng Sci 1988, 28, 230–236.
sphere 2007, 66, 1160–1164.
2270
WILEYONLINELIBRARY.COM/JOURNAL/JPOLA