Facile synthesis of digestible , rigid-and-flexible, bio-based building block for high-performance degradable thermosetting plastics

Article abstract of DOI:10.1039/c9gc04020j

Plastics are indispensable in modern society, but are non-sustainable resources, releasing hazardous chemicals during their service life, and post-disposal issues make traditional plastics a risk. Herein, we report a digestible , rigid-and-flexible, bio-sourced building block for high-performance degradable plastics. This building block was synthesized from the bioresources vanillin (lignin derivative) and glycerol through solvent-free acetalization with a high conversion rate and high selectivity. It could be extremely rapidly degraded into non-toxic vanillin and glycerol under mild acidic conditions even at a similar pH and temperature to gastric juice in the human stomach ( digested ), resulting in the outstanding chemical degradability of its corresponding epoxy thermosets, which is beneficial for their recycling. By virtue of the benzene ring, heterocycle, and methoxyl group-related hydrogen bond, the degradable thermosetting plastic showed much higher mechanical properties (stronger and tougher) and comparable thermal properties relative to a commercial high-performance counterpart based on bisphenol A (BPA). This favorable performance combination has never been reported for plastics. Thus, this bio-derived building block exhibits great potential as a sustainable and upgraded alternative to petroleum-sourced aromatic chemicals such as BPA for high-performance plastics.

Full text of DOI:10.1039/c9gc04020j

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Page 1 of 32
Green Chemistry
Facile synthesis of “digestible”, rigid-and-flexible, and bio-based building
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DOI: 10.1039/C9GC04020J
block for high-performance degradable thermosetting plastics
Binbo Wang1,2, Songqi Ma1*, Qiong Li1, 4, Hua Zhang1, Junjie Liu3, Rong Wang1, Zhiquan Chen3, Xiwei
Xu1, Sheng Wang1, 4, Na Lu1, 4, Yanlin Liu1, Shifeng Yan2, Jin Zhu1
1
Key Laboratory of Bio-based Polymeric Materials Technology and Application of Zhejiang Province,
Division of Polymers and Composites, Ningbo Institute of Materials Technology and Engineering, Chinese
Academy of Sciences, Ningbo 315201, P. R. China;
2 School of Materials Science and Engineering, Shanghai University, Shanghai 200072, P. R. China;
3 School of Physics and Technology, Wuhan University, Wuhan 430000, P. R. China;
4 University of Chinese Academy of Sciences, Beijing 100049, P. R. China.
*Corresponding authors: (Songqi Ma) E-mail: masongqi@nimte.ac.cn, Tel: 86-574-87619806
ABSTRACT: Plastics are indispensable in modern society, but non-sustainable sources, releasing hazards
during service life, and post-disposal issues put the traditional plastics at risk. Here, we report a “digestible”,
rigid-and-flexible and bio-sourced building block for high-performance degradable plastics. The building
block was synthesized from bioresources vanillin (lignin derivative) and glycerol through solvent-free
acetalization with high conversion rate and high selectivity. It could be extremely rapidly degraded into non-
toxic vanillin and glycerol under mild acidic conditions even at similar pH and temperature of gastric juice in
human stomach (“digested”), resulting in the outstanding chemical degradability of its corresponding epoxy
thermosets, which is beneficial to the recycle. In virtue of the benzene ring, heterocycle, and methoxyl group-
related hydrogen bond, the degradable thermosetting plastic showed much higher mechanical properties
(stronger and tougher) and comparable thermal properties relative to a commercial high-performance
counterpart based on bisphenol A (BPA). Such a favorable performance combination has never been reported
for plastics. This bio-derived building block exhibits great potential to be as a sustainable and upgraded
alternative to petroleum-sourced aromatic chemicals such as BPA for high-performance plastics.

Green Chemistry
Page 2 of 32
Introduction
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DOI: 10.1039/C9GC04020J
Plastics have been widely utilized in food packages, water cups, baby bottles, garbage bags, electronic
packaging materials, automotive plastic parts and other plastic parts, which made them indispensable in our
daily life. However, the issues of traditional plastics during their life cycles are gradually exposed over time.
Firstly, the overwhelming majority of traditional plastics are from non-renewable fossil resources, and
environmental issues of greenhouse gas emissions from utilizing fossil resources appear, as a result, the search
for new sources is increasingly concerned. Secondly, there are potential threats to the use of some traditional
plastics. For instance, aromatic chemicals such as bisphenol A (BPA), styrene, and terephthalates are key
building blocks to endow plastics with high mechanical and thermal properties; however, many of them are
harmful for human health and cause pollution of the environment1. The stable structure of the vast majority of
the traditional plastics makes them arduous to spontaneously degrade in the natural environment or chemically
degraded into useful monomers or oligomers, which will occupy a large amount of land resources, give rise to
environmental pollution and waste resources2-6.
The use of bio-renewable raw materials7-14 and the incorporation of degradable groups into plastics15-21 are
considered to be effective ways to address these issues. Until now, several bio-sourced degradable
thermoplastics such as polylactic acid (PLA), poly (butylene succinate) (PBS), polyhydroxyalkanoates (PHA),
poly-β-hydroxybutyrate (PHB) have been developed and commercialized. Recent years also witnessed the
academic development of bio-based degradable thermosetting plastics based on cleavable linkages such as
ester bond14, 22-25, Schiff base26-28, acetal linkage25, 29, dilactones30, Diels−Alder adduct31. Nevertheless, high-
performance thermosetting plastics (mechanically strong and high Tg above 150 °C) often combine brittleness
issue due to their highly covalently cross-linked networks. Therefore, designing bio-based, degradable, non-
toxic plastics that are not only high-performance but also tough is still a challenge.
Vanillin is a mono-aromatic bio-based compound industrially produced from lignin which is the second

Page 3 of 32
Green Chemistry
most abundant biomass and the only scalable one comprising of aromatic monomers32, 33, and it has already
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DOI: 10.1039/C9GC04020J
shown great potential to produce high-performance thermosetting plastics33-37. For example, Caillol and
coworkers developed series of vanillin-derived monomers including epoxy monomers for thermosetting
plastics23, 35, 38, 39; and in our previous work40, we introduced phosphorus into the framework of the vanillin-
derived epoxy thermosets; and Zhao and Abu-Omar41 used it to produce multi-functional epoxy monomers
and thermosets. Bio-based (or bio-sourced or bio-derived) doesn’t mean bio-degradable. Although the above-
mentioned vanillin-derived thermosetting plastics are bio-based (derived from bionewable resources), they are
not bio-degradable and also can’t be chemically recycled. Cyclic acetal/ketal structure could endow polymers
with excellent properties and degradability42-45. To produce degradable thermosetting plastics from vanillin, in
our previous works25, 29, we exploited the acid-catalyzed degradability of the vanillin-derived spiro diacetal
and developed several thermosetting plastics25 inspired by the vanillin-based spiro diacetal epoxy monomer
reported by Ochi et al.46 and Koike 47, and further develop fully bio-based epoxy monomer containing another
bicyclic diacetal structure from vanillin and bio-derived erythritol29.
Thus, in this work, a “digestible”, rigid-and-flexible and bio-sourced building block containing a monocyclic
acetal structure was designed to produce high-performance and tough degradable plastic which has never been
reported before for degradable thermosetting plastic with such superior comprehensive property. Glycerin, a
bio-sourced, abundant, commercially available trifunctional alcohol, was used together with vanillin to
synthesize a monocyclic acetal-containing building block through solvent-free acetalization with high
conversion rate and high selectivity under catalyzation of phosphoric acid. The chemical structure as well as
physical and chemical properties were investigated and compared with BPA. The building block was further
utilized to produce epoxy thermoset. The degradability, stability as well as the mechanical and thermal
properties were systematically investigated.

Green Chemistry
Page 4 of 32
Experimental
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DOI: 10.1039/C9GC04020J
Materials
Vanillin, phosphoric acid (H3PO4), p-toluenesulfonic acid monohydrate (p-TSA·H2O), tetrabutyl ammonium
bromide, diaminodiphenylmethane (DDM) and potassium hydroxide were purchased from Aladdin Reagent,
China. Glycerin, tetrahydrofuran (THF), acetone, dimethyl sulfoxide (DMSO), methanol, ethanol, N,N-
dimethylformamide (DMF), petroleum ether (boiling range: 60-90 °C), dichloromethane, hydrochloric acid
(HCl), sulfuric acid (H2SO4), acetic acid were bought from Sinopharm Chemical Reagent Co., Ltd., China.
Epichlorohydrin (purity ≥99.9%) was supplied by SINOPEC Qilu Petrochemical Company, China. Bisphenol
A epoxy monomer (DGEBA, trade name D.E.R.331, epoxide equivalent 182-192 g per eq.) was supplied by
DOW Chemical Company, USA. All the chemicals were used as received unless otherwise indicated.
Synthesis of HMDO
15.2 g (0.1 mol) of vanillin and 10.1 g (0.11mol) of glycerol were added to a one-neck flask and heated to 110
°C. After the vanillin was completely dissolved in glycerin, 0.15 g of phosphoric acid was added, and a vacuum
was applied using a water pump, and the reaction was stirred for 3 h. A white solid was obtained by the end of
the reaction. The obtained product was ground in a mortar and washed once with 200 mL of water, twice with
100 mL of acetone, and once again with 200 mL of water. After drying in an oven at 60 °C for 3 h, 16.3 g of
a white solid powder HMDO with a yield of 72.1% was obtained. The synthetic route of HMDO is illustrated
in Scheme 1.
Melting point measured by DSC: 194.3 °C (Fig. S1). Molecular weight measured by TOF-MS: 226 g mol-1.
1H NMR (400 MHz, DMSO‑d6) δ = 8.99 (s, 1H), 7.02 (s, 1H), 6.84 (d, J = 8.4 Hz, 1H), 6.74 (d, J = 8.1 Hz,
1H), 5.41 (s, 1H), 4.98 (d, J = 5.3 Hz, 1H), 4.04 – 3.89 (m, 4H), 3.77 (s, 3H), 3.48 (d, J = 5.0 Hz, 1H).
13C NMR (101 MHz, DMSO‑d6) δ = 147.58, 147.16, 130.66, 119.46, 115.14, 110.72, 101.01, 71.83, 62.89,
56.02, 40.60, 40.39, 40.18, 39.97, 39.76, 39.55, 39.35.

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Green Chemistry
FTIR: 689, 749, 799, 832, 852, 866, 936, 950, 976, 993, 1027, 1072, 1086, 1027, 1071, 1086, 1131, 1150,
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DOI: 10.1039/C9GC04020J
1166, 1192, 1213, 1241, 1271, 1378, 1407, 1439, 1454, 1469, 1523, 1606, 2858, 2906, 2943, 2983, 3255,
3437, 3515 cm−1 .
Scheme 1 Synthetic route of HMDO.
Molecular calculation
Density functional theory (DFT) calculations were performed using the Gaussian 09 program package.
Geometries were optimized using the restricted or unrestricted CAM-B3LYP 39 hybrid exchange-correlation
functional with the 6-311G-(d,p) basis set48. CAM-B3LYP is known to reliably describe radicals and extended
conjugated systems49. Frequency calculations performed at the same level of theory on fully optimized
geometries showed no imaginary frequencies, confirming optimized geometries as local minima on their
potential surfaces50. Energies reported are the sum of electronic and thermal enthalpies at 298.15 K and are
converted to kcal mol−1 from hartrees (1Eh = 627.509608 kcal mol−1). Visualization of optimized geometries
and electrostatic potential (ESP) maps were performed using GaussView 5.0.9.
All structures were optimized using the M0651-53/6-31G (d, p) method. At the level of M06/6-311 + + G (d,
p), using the optimized structure, the SMD54 model was selected, the solvent effect was simulated in DMSO,
and the electronic energy was calculated. At 298.15 K, 1 atm, the M06/6-31G (d, p) method was used to
analyze the frequency of the optimized structure, and the Gibbs free energy correction value was calculated.

Green Chemistry
Page 6 of 32
The Gibbs free energy was obtained by the addition of electron energy and Gibbs free energy correction, and
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DOI: 10.1039/C9GC04020J
Conf_1 was selected as the energy zero point.
In vitro stem cell culture
The P5 passage SD rat bone marrow mesenchymal stem cells (BMSCs) supplied by the Medical School of
Ningbo University were seeded in 48-well plates with a density of 1.2 x 105 cells per mL in low glucose
DMEM basal medium with 10% fetal bovine serum and 1% penicillin/streptomycin and cultured in a
55
humidified incubator at 37 °C with 5% CO2 .
1 mg and 10 mg of HMDO were accurately weighed and dissolved in 4 mL DMSO/PBS (phosphate buffered
saline) (1/3; v/v) mixed solution, respectively. The same processing was implemented to BPA. Then we
obtained two working concentrations of 1 mmol L-1 and 10 mmol L-1 HMDO (or BPA) solution. 10 μL different
concentrations of HMDO and BPA were added to get 4 test group, and 10 μL of the pure DMSO/PBS (1/3,
v/v) mixed solution was added to the 48-well plates in the presence and absence of BMSCs, respectively, to
obtain two control groups.
The cell growth and proliferation in 48-well plates were assessed by using CCK-8 assay according to the
protocol. The cell morphology was visualized using optical microscope (Nexcope NIB400, China) before
loading the HMDO and BPA and after loading and culturing for 24 hours, respectively.
Hydrolysis of HMDO
Degradation under acidic conditions: the degradability and the chemical changes during the degradation
process for HMDO were investigated by capturing real-time 1H NMR spectra of HMDO immersed in a NMR
tube with 0.1 M, 0.01 M and 0.001 M HCl solution (DMSO-d6 /H2O = 9/1, v/v) at 23 °C.
As shown in Scheme 2, the conversion between HMDO and HDMP and the hydrolysis of acetal exist
simultaneously in the hydrolysis of HMDO. We assume degradation reaction is 1st order with respect to acetal.

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Green Chemistry
The hydrolysis rate of acetal could be written as:
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DOI: 10.1039/C9GC04020J
―
푑[퐴푐푒푡푎푙] = k[퐴푐푒푡푎푙]
(1)
(2)
푑푡
[퐴푐푒푡푎푙]푡 = [퐴푐푒푡푎푙]0 × e ―푘푡
[퐴푐푒푡푎푙]푡
[퐴푐푒푡푎푙]0
[퐻푀퐷푂]0 ― [푉푎푛푖푙푙푖푛]푡
[퐻푀퐷푂]0
=
= e ―푘푡
(3)
(4)
ln( 1 ― [푉푎푛푖푙푙푖푛] ) = ―푘푡
t
[퐻푀퐷푂]0
1
The hydrolysis reaction was tracked by real-time H NMR technology, and the kinetic constants (k) in
different concentrations of acid were calculated.
O
O
HO
OH
O
HMDO
O
H+
HO
OH
O
H
H+
H2O
+
+
OH
HO
Vanillin
Glycerin
HO
O
O
HO
O
HDMP
Acetal
Scheme 2 Hydrolysis mechanism of HMDO.
Synthesis of DGHMDO
10 g of HMDO powder and 0.2 g of tetrabutylammonium bromide were added to 100 g potassium hydroxide
aqueous solution (50 wt%), and reacted at 50 °C for 1 h. Thereafter, the reaction system was put in an ice bath
(≤10 °C) for 30 min, and 100 mL of epichlorohydrin was added dropwise over 30 min, then the system reacted
at room temperature for 48 h. After the reaction, 50 mL of dichloromethane (it was used to dilute the mixture
to achieve the quick layering during the wash process; if no dichloromethane was added, the product could
also be obtained) was added to the system, and the mixture was washed three times with 300 mL of water.
After drying with anhydrous magnesium sulfate, the solvent was evaporated to impart a pale-yellow solid

Green Chemistry
Page 8 of 32
powder. To get product with high purity and accurately disclose relationships between structure and property,
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DOI: 10.1039/C9GC04020J
the yellow powder was further washed with 50 mL of absolute ethanol, 50 mL of water and dried to get 7.6 g
of white solid powder DGHMDO (yield = 51.7%). The synthetic route of DGHMDO is shown in Scheme 3.
Melting point measured by DSC is 111.5 °C (Fig. S1). The molecular weight measured by TOF-MS spectrum
is 338 g mol-1.
1H NMR (400 MHz, CDCl3) δ = 7.08 (d, J = 2.0 Hz, 1H), 7.01 (dd, J = 8.2, 2.0 Hz, 1H), 6.88 (d, J = 8.3 Hz,
1H), 5.49 (s, 1H), 4.39 – 4.28 (m, 2H), 4.20 (dd, J = 11.3, 3.5 Hz, 1H), 4.09 – 3.98 (m, 3H), 3.94 (dd, J =
12.0, 2.8 Hz, 1H), 3.88 (s, 3H), 3.51 (dd, J = 12.0, 5.9 Hz, 1H), 3.43 (t, J = 1.8 Hz, 1H), 3.39 – 3.33 (m, 1H),
3.24 – 3.20 (m, 1H), 2.87 (t, J = 4.5 Hz, 1H), 2.80 (t, J = 4.6 Hz, 1H), 2.71 (dd, J = 5.0, 2.6 Hz, 1H), 2.65
(dd, J = 5.0, 2.6 Hz, 1H).
13C NMR (101 MHz, CDCl3) δ = 149.45, 148.35, 132.02, 118.77, 113.63, 109.77, 101.12, 77.42, 77.11,
76.79, 71.00, 70.26, 69.44, 68.64, 55.94, 51.14, 50.10, 44.95, 44.20.
FTIR: 696, 758, 770, 801, 826, 861, 876, 916, 950, 996, 1013, 1029, 1091, 1102, 1141, 1170, 1232, 1265,
1329, 1387, 1417, 1459, 1517, 1596, 2869, 2973 cm−1.
Scheme 3 Synthetic route of epoxy monomer DGHMDO from HMDO.
Preparation of thermosetting plastics
10 g of DGHMDO (or DGEBA) and 2.84 g of 4,4'-diaminodiphenylmethane (DDM) (or 2.53 g of DDM) with
the molar ratio of epoxy group to N-H of 1:1 were placed in a beaker, melted in a vacuum oven at 130 °C,
stirred for 5 min, and poured into a mold. After being pre-cured at 100 °C for 2 h, the sample was removed

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Green Chemistry
from the mold and post-cured in a vacuum oven at 130 °C for 2 h, 155 °C for 2 h, 180 °C for 2 h. The final
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thermosetting plastic DGHMDO-DDM (or DGEBA-DDM) was obtained after natural cooling.
Preparation of thermosetting plastic coatings
10 g of DGHMDO (or DGEBA) and 2.84 g of DDM (or 2.53 g of DDM) with the molar ratio of epoxy group
to N-H of 1:1 were dissolved in 30 g N,N-dimethylformamide (DMF), reacted at 100 °C for 30 min and coated
on a cleaned tinplate. After volatilizing the solvent in the fume hood for 12 h, the coating was pre-cured in a
100 °C oven for 2 h and post-cured in a vacuum oven at 130 °C for 2 h, 155 °C for 2 h, 180 °C for 2 h. The
DGHMDO-DDM (or DGEBA-DDM) coating was obtained after natural cooling.
Degradation of the thermosetting plastic DGHMDO-DDM
The chemical changes during the degradation process for DGHMDO-DDM were investigated by capturing
real-time 1H NMR spectra of DGHMDO-DDM immersing in an NMR tube with 0.1 M HCl DMSO‑d6/water
(9/1, v/v) solution at 50 °C. Chemical degradation was determined by immersing DGHMDO-DDM with
dimensions of 6 mm (length) × 6 mm (width) × 1 mm (thickness) in the corresponding solutions at 50 °C or
25 °C. The samples were weighed after placing in a vacuum oven at 80 °C for 2 h, and recorded as initial
weights. Degradation times refer to the times when the samples were completely dissolved in the solution. The
samples that could not be completely dissolved were transferred to a vacuum oven and dried at 80 °C for 8 h,
and weighed to calculate the degree of degradation. The liquid wettability of DGHMDO-DDM was evaluated
by static contact angle determined with a contact angle measuring system (OCA25, Dataphysics Instrument)
using the sessile-drop method at room temperature. Data were read at 1 min after deposition of 10 μL distilled
water or solvent. The degradation rate test was carried out by degrading 11 identically sized DGHMDO-DDM
under the same conditions for 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 and 5.5 h. After degrading, it was dried in an
80 °C oven for 8 h, and then weighed to obtain a corresponding relationship between mass and time.

Green Chemistry
Page 10 of 32
Hygrothermal aging resistance of the thermosetting plastics
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The thermosetting plastics DGHMDO-DDM and DGEBA-DDM were examined by using a Xenon test
chamber at a humidity level of 70% and a temperature of 60 °C. Samples were taken every three days until 15
days, and dried in an 80 °C vacuum oven for 8 h to measure the Tgs by DSC.
Characterization
1H NMR and 13C NMR spectra were recorded using an AVANCE III Bruker NMR spectrometer (Bruker,
Switzerland) with DMSO-d6 and CDCl3 as the solvents, respectively. FTIR spectra were recorded using a
NICOLET 6700 FTIR (NICOLET, America) through the KBr pellet method. TOF-MS spectra were measured
using a Triple TOF 4600 time of flight mass spectrometer (AB Sciex, America) in a positive mode using
DMSO as the solvent. The tensile properties of the cured samples were evaluated using an Instron 5567
electrical universal testing machine (Instron, America). The cured samples with dimensions of 80 mm (length)
× 6 mm (width) × 1 mm (thickness) were measured with a gauge length of 20 mm at a cross-head speed of 20
mm min-1. The data were taken from an average of at least 7 specimens for accuracy. The temperature-
dependent FTIR measurements were carried out on a NICOLET 6700 (Thermo, America) using the KBr pellet
method from 25 to 125 °C. TGA was performed on a Mettler-Toledo TGA/DSC1 thermogravimetric analyzer
(METTLER TOLEDO, Switzerland) with air as the purge gas at a scanning rate of 20 °C min-1 from 50 to 800
°C. DSC curves were recorded using a Mettler-Toledo MET DSC (METTLER TOLEDO, Switzerland) under
a nitrogen atmosphere. They were heated from 25 to 200 °C at a heating rate of 20 °C min-1 and held there for
10 min to eliminate any thermal history. Then, they were cooled to 25 °C at a cooling rate of 50 °C min-1,
followed by heating again to 200 °C at a heating rate of 20 °C min-1. The glass transition temperature (Tg) was
obtained from the peak temperature of the differential curve of the second heating curve of the cured samples.
Dynamic mechanical analysis (DMA) was carried out on a TA Instruments Q800 DMA in tension mode to
measure the dynamic mechanical properties of the thermosetting plastics. The thermosetting plastics with

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Green Chemistry
dimensions of 25 mm (length) × 6 mm (width) × 1 mm (thickness) were prepared and tested from -130 to 250
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°C at a heating rate of 5 °C min-1 and a frequency of 1 Hz. The coefficient of thermal expansion was obtained
by using DIL402C from 25 to 250 °C at a heating rate of 3 °C min-1. Coating properties: Pencil hardness and
reverse impact resistance were measured according to ASTM D 3363 and ASTM D 2794, respectively. The
adhesion of the coatings was evaluated using the ASTM D 3359 crosshatch adhesion method. The positron
annihilation lifetime spectra of the samples were measured at room temperature using a fast-fast coincidence
lifetime spectrometer. A 22Na positron source with radiation activity of 10 Ci was sandwiched between two
identical sample pieces. Each spectrum contains more than 106 counts. The lifetime spectra were analyzed into
three positron lifetime components using the PATFIT program56.
Results and discussion
Synthesis of bio-sourced building block HMDO
The synthesis process of HMDO is green, efficient and productive, as illustrated in Scheme 1. Its chemical
structure was confirmed via 1H NMR, 13C NMR, FTIR and TOF-MS spectra (Fig. 1). As shown in 1H NMR
spectrum of HMDO (Fig. 1a), the peak at 5.41 ppm indicates the existence of the acetal structure, the peak at
8.99 ppm is attributed to Ar-OH and the peak of alcohol-OH is at 4.98 ppm, the peaks at 7.02, 6.84 and 6.74
ppm belong to the protons on benzene ring. The peak numbers and their chemical shift in the 13C NMR
spectrum (Fig. 1b) both match the carbons of HMDO. In the FTIR spectrum of HMDO (Fig. 1c), there is a
characteristic peak at 1132 and 1071 cm−1 belonging to acetal structure. TOF-MS spectra (Fig. 1d) also
correspond to the molecular weight of HMDO. These all indicate the successful synthesis of HMDO.

Green Chemistry
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Fig. 1 Structure characterization of HMDO: a) 1H NMR spectrum. b) 13C NMR spectrum. c) FTIR spectrum.
d) TOF-MS spectrum.
The acetalization of glycerol and aldehyde is believed to result in the formation of two isomers (a five-
membered cyclic compound and a six-membered cyclic compound) (Fig. 2a), and there is a conversion
between two isomers under the catalysis of acid (Fig. 2b)57-59. To clearly capture the chemical change during
the reaction, real-time 1H NMR technology was utilized to track the acetalization (Fig. 2c). As shown in Fig.
1d and Table 1, high selectivity of the six-membered cyclic acetal HMDO (~90.9%) was achieved without
unique catalysts, which was attributed to the reactive crystallization of HMDO (Fig. 2e). At the beginning of
the reaction, the ratio of HMDO remained unchanged, while the conversion rate of vanillin gradually increased
(Fig. 2d). After the reaction reached to a certain level, the proportion of HMDO gradually increased, and the
reactants changed from clear to turbid and became solid finally (Fig. 2e). This phenomenon was due to the
fact that the solubility of HMDO in glycerol was much lower than that of its isomer (five-membered cyclic
compound HDMP). As the reaction proceeded, HMDO reached saturation point and crystallized, and HDMP

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Green Chemistry
gradually converted to HMDO since the solution system needed to maintain the balance betweenVitehweArtticwleoOnline
DOI: 10.1039/C9GC04020J
products, leading to the high selectivity of HMDO. The reactive crystallization can directly obtain a
crystallized and pure product, which is commonly used in industrial synthesis59, 60, thus, there is a great
potential to directly obtain HMDO crystals continuously.
Table 1 Effect of conditions on reaction conversion rate and selectivity
Molar ratio
Amount of
Time Conversion Selectivity
Adjusted condition (vanillin/ catalyst
glycerin)
Temperature(°C)
catalyst (wt%)
(h)
rate (%)a
(%)b
1:1
H3PO4
H3PO4
H3PO4
H3PO4
p-TSA
-
1
1
110
110
110
110
110
110
110
110
110
110
90
2.5
4
6
2
-
89.43
94.85
97.44
94.85
-
90.9
90.58
87.64
90.58
-
The ratio of
1:1.1
1:1.5
1:1.1
1:1.1
1:1.1
1:1.1
1:1.1
1:1.1
1:1.1
1:1.1
1:1.1
1:1.1
1:1.1
1:1.1
glycerin /vanillin
1
1
The type of
catalyst
1
1
5
4
4
3
3
3
4
4
5
-
77.36
87.54
94.85
93.83
81.75
78.74
86.25
94.85
92.35
-
35.24
82.84
90.58
88.89
88.43
89.37
87.64
90.58
85.4
H3PO4
H3PO4
H3PO4
H3PO4
H3PO4
H3PO4
H3PO4
H3PO4
H3PO4
0.5
1
The amount of
catalyst
2
5
1
1
100
110
120
130
Temperature
1
1
1
-
a The conversion rate of vanillin. b The selectivity of HMDO.
High vanillin conversion rate and high HMDO selectivity were achieved by preliminary exploration of the
reaction conditions (Table 1). The acetalization of aldehyde and alcohol is a reversible reaction, as a result,
the conversion rate is often low. In this work, in order to achieve the high conversion rate of ~97.4% (Table
1), the generated water was removed under reduced pressure during the reaction (Fig. 2a) to promote the
acetalization. All reaction systems stopped after the reaction mixture became solid, and the vanillin conversion rate

Green Chemistry
Page 14 of 32
and selectivity of HMDO were measured. As the molar ratio increased, the vanillin conversion rate increased
View Article Online
DOI: 10.1039/C9GC04020J
and the selectivity of HMDO decreased. With increasing temperature, the vanillin conversion rate and HMDO
selectivity both increased and then decreased. When the temperature was higher than 70 °C, the reaction system
using p-TSA as the catalyst became black which might be due to the carbonization of reactants, as a result, it
was difficult to obtain the HDMO. Without catalyst, the reaction could be carried out above 130 °C, which
achieved conversion rate of 77.36 % but low HMDO selectivity of 35.24%. Therefore, medium strong acid
phosphoric acid was chosen as the catalyst. The use of phosphoric acid catalysis can make the reaction stably
process below 120 °C. The effect of catalyst content is similar to the temperature, and an excess catalyst content
might also cause side reactions.
Fig. 2 Synthesis of bio-sourced building block HMDO. a) Synthetic route of HMDO. b) Mechanism of mutual
1
conversion between HMDO and HDMP. c) Real-time H NMR spectra of the reaction systems for HMDO
after reacting for different times. d) Vanillin conversion rate and HMDO selectivity vary with time. e)
Synthetic phenomenon of reactive crystallization.

Page 15 of 32
Green Chemistry
Physical and chemical properties of HMDO
View Article Online
DOI: 10.1039/C9GC04020J
Calculations were used to reveal the structural features including reactivity, ring planarity, and bond lengths
of HMDO, in order to provide a theoretical basis for studying the properties of HMDO. HMDO has similar
chemical structure to the heavily used building block BPA for high-performance plastics (Fig. 3a), thus BPA
was used as the control. Geometry optimization of HMDO and BPA was performed at the same level of theory
and exhibited in top-down and side-on perspective (Fig. 3b-3c), which manifests that the benzene ring is planar,
and six-membered heterocycle is non-planar. As can be seen in the electrostatic potential (ESP) maps (Fig.
3d), the two oxygen atoms in the two hydroxyl groups of HMDO had different ESPs, oxygen atom in aromatic
hydroxyl group exhibited lower ESP (-0.043) than that in alcoholic hydroxyl group (-0.035). The lower ESP
of oxygen atom indicates higher electronic density, corresponding to the higher reactivity during nucleophilic
reactions, which means that aromatic hydroxyl group and alcoholic hydroxyl group in HMDO should possess
different reactivity toward other reactants, and should exhibit higher and comparable relativities during
nucleophilic reactions relative to the hydroxyl groups in BPA with ESP of -0.037, respectively.
Fig. 3 Physical and chemical properties of HMDO. a) Chemical structures, Geometry-optimized structures
(CAMB3LYP/6-311G(d,p)): b) side-on and c) top-down view highlight planarity, and d) Electrostatic
potential (ESP) maps of HMDO and BPA.

Green Chemistry
Page 16 of 32
Fig. 4 exhibits the typical conformational transition process of the six-membered heterocycle ofVHiewMArDticlOe O.nline
DOI: 10.1039/C9GC04020J
The chair conformation Conf_1 underwent the transition state TS_1 to generate the left partial ship
conformation Conf_3. In the structure TS_1, the oxygen atoms outside the paper surface vibrated up and down,
causing the structure to switch between the chair conformation and the left partial ship conformation. After
that, the two oxygen atoms in the left-handed ship conformation were turned over to the paper surface, and
converted into a right-handed ship conformation through the ship transition state. We believe that the
combination of high rigidity (benzene ring and heterocycle) and high flexibility (conformational transition
ability of heterocycle) can ensure a high strength of the material while achieving toughness.
Fig. 4 Some different conformations of HMDO calculated from density functional theory.
Heavily used aromatic building blocks such as BPA, styrene, etc. can provide excellent performance for
plastics, but they were gradually banned due to their high toxicity. If HMDO possesses low toxicity or non-
toxicity, it will address some toxicity issue for plastics. In order to investigate its toxicity, in vitro cytotoxicity
of the HMDO was evaluated and compared with BPA (Fig. 5). Obviously, the HMDO-containing culture
systems showed much higher cell viability than BPA after 24 h. For the 1 mmol L-1 HMDO culture solution,
cell viability reached 87 %, while it was 58 % for 1 mmol L-1 BPA culture solution. Increasing the
concentration to 10 mmol L-1, BPA system exhibited very low cell viability of 35 %, while HMDO system still
kept high cell viability of 70 %. This demonstrates that HMDO showed much lower toxicity than BPA even if
HMDO can bio-accumulate in human body like BPA for a long time. Oral absorption of BPA through ingestion

Page 17 of 32
Green Chemistry
of food and beverages contaminated by BPA from packaging materials is the main route of human exVpieowsAurtricele61O,nline
DOI: 10.1039/C9GC04020J
62. Through this route, it seems impossible for HMDO to accumulate in human body due to its outstanding
degradability. Owing to the presence of acetal linkage, HMDO could be rapidly hydrolyzed in acidic aqueous
solutions. Fig. 6a manifests that 0.04 M monomer was completely degraded in a 0.001 M HCl solution at
37 °C (at similar pH of gastric juice in human stomach) within 3 min, and the products were non-toxic and
harmless vanillin and glycerin. This indicates that HMDO should be readily degradable in human stomach and
can be considered to be digestible. As seen from Scheme 2, the degradation mechanism of HMDO followed
1
the conversion of HMDO to HDMP and hydrolysis of acetals, which was also determined by real-time H
NMR spectra of HMDO degradation in HCl DMSO-d6/H2O solution (Fig. S4-S6). The hydrolysis is 1st order
with respect to HMDO, and increasing acid concentration, hydrolysis rate could be increased largely (Fig. 6b,
Fig. S2-S3).
Fig. 5 In vitro cytotoxicity of HMDO and BPA.

Green Chemistry
Page 18 of 32
View Article Online
DOI: 10.1039/C9GC04020J
Fig. 6 a) Real-time 1H NMR spectra of HMDO degradation in 0.001M HCl D2O solution at 37 °C (at similar
pH of gastric juice in human stomach). b) Hydrolysis of HMDO in 0.001M HCl DMSO-d6/H2O (9/1, v/v)
solution at 23 °C, a the ratio is the percentage of HMDO in the undegraded acetals.
Mechanical and thermal properties of the thermosetting plastics
On account of the high chemically cross-linked networks, thermosetting plastics (or thermosets) often exhibit
high performance but are more difficult to be degraded or recycled than thermoplastics. Thus, thermosetting
plastic was prepared from HMDO to evaluate the potential of HMDO to prepare high-performance degradable
plastics. Epoxy resin is one of the most paramount thermosetting plastics, and therefore a novel epoxy
monomer DGHMDO was synthesized from HMDO (Scheme 3, Fig. 7). As shown in Fig. 7a, there is no peak
at 8.99 and 4.98 ppm for Ar-OH and alcohol-OH, respectively, while six characteristic peaks for epoxy group
appear at 3.36, 3.22, 2.87, 2.80, 2.71, 2.65 ppm, the peaks at 3.51, 3.94, 4.02, 4.20 ppm are attributed to -CH2-
next to epoxy group. Similar to those in Fig. 1a, the peak at 5.49 ppm belongs to acetal structure. The peak

Page 19 of 32
Green Chemistry
numbers and chemical shift in the 13C NMR spectrum (Fig. 7b) match well with the carbons of DGHMDO.
View Article Online
DOI: 10.1039/C9GC04020J
The FTIR spectrum (Fig. 7c) of DGHMDO also proves the generation of epoxy resin, as the disappearance of
the hydroxyl group in the range of 3517-3254 cm-1 and the appearance of characteristic peak in 915 cm-1. TOF-
MS spectrum (Fig. 7d) also correspond to the molecular weight of HMDO. DGHMDO was cross-linked by
4,4-diaminodiphenyl methane (DDM) to obtain thermosetting plastic DGHMDO-DDM (Fig. 8a). BPA-based
epoxy account for 90% market share of the commercial epoxies, so a high-performance BPA epoxy monomer
(DGEBA, trade name: D.E.R.331) was also cross-linked with DDM to get DGEBA-DDM as the control. It is
worth mentioning that DGHMDO-DDM system has lower curing activation energy than DGEBA-DDM
system, which was determined by Kissinger’s method and Ozawa’s method (Fig. S7-S9, Table 2).
1
Fig. 7 Structural characterization of DGHMDO: a) H NMR spectrum. b) 13C NMR spectrum. c) FTIR
spectrum. d) TOF-MS spectrum.

Green Chemistry
Page 20 of 32
View Article Online
DOI: 10.1039/C9GC04020J
Table 2 The curing kinetic parameters of the thermosetting plastic systems
Tp (ºC) at different heating rate
sample
Ea (kJ mol-1)
Kissinger Ozawa
5 ºC min-1 10 ºC min-1 15 ºC min-1 20 ºC min-1
DGHMDO+DDM
DGEBA+DDM1
121.5
135.9
143.5
142.8
149.7
155.9
164.6
166.2
49.4
57.1
53.6
60.9
Fig. 8 Mechanical properties of the thermosetting plastics. a) Chemical structures of DGHMDO and
DGHMDO-DDM. b) Representative stress-strain curves of the thermosetting plastics. c) Reverse impact test
of the thermosetting plastic coatings. d) Non-isothermal FTIR spectra of DGHMDO-DDM. e) DMA curves
of the thermosetting plastics. f) Positron lifetime spectra of the thermosetting plastics.
Fig. 8b presents the representative stress-strain curves of the thermosetting plastics. Obviously, DGHMDO-
DDM exhibited much higher mechanical properties with Young's modulus of 2165 MPa, tensile strength of
104.9 MPa, elongation at break of 9.9 % and fracture energy of 700.8 J m-2 than DGEBA-DDM with Young's
modulus of 1893 MPa, tensile strength of 76.4 MPa, elongation at break of 7.4 % and fracture energy of 349.2
J m-2 (Table 3). The higher elongation at break and fracture energy of DGHMDO-DDM than those of DGEBA-
DDM reflects the higher toughness of DGHMDO-DDM, which was also confirmed by the higher reverse
impact strength of DGHMDO-DDM coating than that of DGEBA-DDM coating (Fig. 8c, Table S2). This was

Page 21 of 32
Green Chemistry
mainly due to the conformational transition of heterocycle and the hydrogen bonding of methoxyl VgierwoAurtpicleinOnline
DOI: 10.1039/C9GC04020J
HMDO. As mentioned above, the six-membered heterocycle of HMDO has multiple conformations, and
molecular dynamics simulations indicate that these conformations can transform during external forces or
applied energy. The conformational transformation of the six-membered non-planar ring may absorb external
energy and improve the molecular motion of the polymeric material, resulting in the improved toughness of
polymers22, 63-66. What's more, the methoxyl group on the benzene ring is also believed to increase the toughness
of the material. A large amount of hydroxyl groups existed in the amino-cured epoxy resin, which would form
hydrogen bonds with the methoxyl groups to form eight-membered rings (Fig. 8a)46, 67. It was characterized
by non-isothermal FTIR spectra that the break of the hydrogen bond via increasing temperature led to the FTIR
peak of the hydroxyl group to shift to higher wavenumber positions (Fig. 8d). Therefore, motion of the
hydroxyl-ether structure of DGHMDO-DDM at low temperatures was suppressed, indicating the weaker β
relaxation peak of DGHMDO-DDM relative to DGEBA-DDM (Fig. 8e). At the same time, there was an
obvious β' relaxation peak in 80 °C (Fig. 8e), which was the result of the movement of the p-phenylene group
after the hydrogen bond was broken. The presence of β' relaxation is believed to increase the toughness of the
material46, 67. In general, modulus of a thermosetting plastic has a close tie with its cross-link density and the
rigidity of its segment structure. The higher the cross-link density and the rigidity of segment structure, the
higher the modulus22, 23. The cross-link density of the thermosetting plastics was theoretically estimated from
the average molecular weight between cross-link points (Mc). The higher Mc is, the lower the cross-link density
is. As shown in Table 3, DGHMDO-DDM exhibited lower Mc (874 g mol-1) than DGEBA-DDM (944 g mol-
1), which means that it owned higher cross-link density. The cross-link density of the thermosetting plastics
can also be experimentally reflected from their free volume (fv). Higher fv often corresponds to lower cross-
link density. Thus, the higher cross-link density of DGHMDO-DDM could also be confirmed by its lower fv
(2.69%) relative to DGEBA-DDM (fv = 4.08%) (Fig. 8f, Table S3). Owing to the conformational transition

Green Chemistry
Page 22 of 32
ability of heterocycle in HMDO, the HMDO should be more flexible than BPA, but the methoxyl group on
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DOI: 10.1039/C9GC04020J
benzene ring of HMDO could form hydrogen bond with adjacent hydroxyl group (Fig. 8a), which could hinder
the movement of benzene ring, leading to the increased rigidity of the HMDO. As a result, DGHMDO-DDM
owned higher Young’s modulus than DGEBA-DDM. The increase of cross-link density will enhance the
tensile strength of a polymer, while high cross-link density will also produce high internal stress for the
polymer and decrease its tensile strength. The toughening factors of polymer will effectively reduce its internal
stress68. Thus, the higher tensile strength of DGHMDO-DDM should be related to its higher toughness as well
as its higher cross-link density.
Table 3 Mechanical Properties of the thermosetting plastics
Tensile
strength
(MPa)
Young’s
modulus
(MPa)
Elongation
at break
(%)
Fracture
energy
(J m-2)
Sample
DGHMDO-DDM
DGEBA-DDM
104.9±5
76.4±6
2165±132
1893±140
9.9±0.4
7.4±0.5
700.8
349.2
Fig. 9 Thermal properties of the thermosetting plastics. a) Non-isothermal DSC curves of the thermosetting
plastics. b) Non-isothermal TGA curves of the thermosetting plastics under air atmosphere. c) Linear thermal
expansion curves of the thermosetting plastics (α1 and α2 are the thermal expansion coefficients in glassy state

Page 23 of 32
Green Chemistry
(T < Tg) and rubbery state (T > Tg), respectively).
View Article Online
DOI: 10.1039/C9GC04020J
Beside the excellent mechanical properties, DGHMDO-DDM also exhibited outstanding thermal properties
including Tg, thermal stability, and thermal expansion. The higher cross-link density (Table S3) and lower fv
(Fig. 8f) of DGHMDO-DDM than those of DGEBA-DDM should result in higher Tg; but the conformational
transition ability of heterocycle of HMDO, and methoxyl group-associated hydrogen bonding would be broken
during the heating process, corresponding to the flexible feature of segment structure of DGHMDO-DDM,
which should lead to lower Tg. These two competing factors resulted in a comparable Tg (164 °C) of
DGHMDO-DDM with DGEBA-DDM (169 °C) (Fig. 9a, Table 4). The initial degradation temperature (Td5%
)
of DGHMDO-DDM under air atmosphere was slightly lower than that of DGEBA-DDM, while it was still as
high as 330 °C (Fig. 9b) which is thermally stable enough for most applications of plastics. Interestingly, the
char residue of DGHMDO-DDM at 600 °C reached 36.2 % much higher than that of DGEBA-DDM (2.1 %),
which makes it potential to be flame retardant material. Moreover, DGHMDO-DDM possessed similar thermal
expansion coefficients in glassy state (T < Tg) and rubbery state (T > Tg) to DGEBA-DDM (Fig. 9c).
Table 4 Thermal properties of the thermosetting plastics
Mc
(g mol-1)
Tg
Td5%
Td30%
R600
Ts
Sample
(°C)
(°C)
(°C)
(%)
(ºC)
DGHMDO-DDM
DGEBA-DDM
874
944
164
169
330
356
387
390
36.2
2.1
179
184
Chemical degradability and stability of the HMDO-based thermosetting plastic
Owing to the excellent degradability of HMDO, HMDO-based thermosetting plastic DGHMDO-DDM
exhibited favorable controlled degradability. As shown in Fig. 10a, DGHMDO-DDM sample with a dimension
of 8 mm × 8 mm × 1 mm was completely destructed after immersing in a 0.1 M HCl acetone/water (9/1, v/v)
solution at 50 °C for 5.5 h. The degradation mechanism can be considered as surface corrosion, since the
degradation mainly occurred in the region near the surface (Video S1)69. For the surface corrosion mechanism,

Green Chemistry
Page 24 of 32
the degradation rate was mainly controlled by the swelling rate and the acetal hydrolysis rate. The degradation
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DOI: 10.1039/C9GC04020J
mechanism was also investigated by real-time 1H NMR spectra of DGHMDO-DDM degradation system (Fig.
10b). With degradation proceeded, the peak strength for protons on aromatic formyl group, benzene ring and
hydroxyl group increased, and no peak for cyclic acetal structure was captured. This indicates that the dissolved
chemicals in acidic solution are completely degraded ones. After degradation, the dissolved chemicals were
collected and their molecular weights were mainly from 600 to 1200 g mol-1 characterized by TOF-MS
spectrum (Fig. 10c). In conclusion, the degradation mechanism of DGHMDO-DDM from the chemical aspect
can be followed the hydrolysis of cyclic acetal structure and the production of oligomers with formyl group
and hydroxyl group (Fig. 11). Theoretically, this multifunctional oligomer can be easily recycled by utilizing
the reaction of a hydroxyl group with an isocyanate and the condensation reaction of an aldehyde group and
an amino group. For example, by adding a certain amount of polyfunctional isocyanate or amine curing agent,
new materials should be obtained, which needs further exploration. Degradation kinetics of DGHMDO-DDM
studied in 0.1M HCl acetone/water (9/1, v/v) solution could match well with the degradation model equation
1 ― (1 ― 훼 )1/3 = 푘푡,
(
α is the mass fraction of the sample remaining at time t.) 70, 71, the degradation rate
constant k was calculated to be 0.12 mm-1 h-1 (Fig. 10d).

Page 25 of 32
Green Chemistry
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DOI: 10.1039/C9GC04020J
Fig. 10 Chemical degradability of the HMDO-based thermosetting plastic. a) Degradation of DGHMDO-
DDM in 10 mL 0.1M HCl acetone/water (9/1, v/v) solution at 50 °C for different times. b) Real-time 1H NMR
spectra of DGHMDO-DDM degradation system in 0.1M HCl acetone-d6/water (9/1, v/v) solution. c) TOF-MS
spectrum of the degraded DGHMDO-DDM. d) Degradation kinetics of DGHMDO-DDM in 0.1M HCl
acetone/water (9/1, v/v) solution. e) Degradation ratio of DGHMDO-DDM after degradation in different 0.1M
HCl acetone/water solutions for 12 h and the contact angles of their corresponding acetone/water solutions.

Green Chemistry
Page 26 of 32
View Article Online
DOI: 10.1039/C9GC04020J
Fig. 11 Degradation mechanism of DGHMDO-DDM.
The degradation rate of DGHMDO-DDM in different acidic conditions varied a lot (Table S4). The type
and concentration of acid and organic solvents as well as temperature all impacted the rate of degradation. The
choice of a strong acid or a higher concentration of acid would accelerate the degradation rate. For weak acid
acetic acid, DGHMDO-DDM could not be degraded. After immersing in 0.1 M acetic acid acetone/water (9/1,
v/v) solution at 50 °C for 12 h, no weight loss was observed. Besides, the acid-catalyzed degradation of
DGHMDO-DDM also showed obvious temperature dependence. The increase of temperature increased the
rate of acetal hydrolysis and the rate of swelling, accelerating the degradation rate. As an example, DGHMDO-
DDM could completely dissolved in 0.1 M HCl acetone/water (9/1, v/v) solution after degradation at 50 °C
for 5.5 h, while only 5.46% of DGHMDO-DDM was degraded at 25 °C for 12 h. In addition, the degradation
rate depended on the choice of solvent. The degradation of DGHMDO-DDM was extremely efficient in 0.1
M HCl solutions with acetone or THF as the main solvent (completely destructed within 6 h at 50 °C), while
only 3.13% of the sample could be degraded in 0.1 M HCl aqueous solution (without organic solvent) at 50 °C
for 12 h. In general, for a liquid which can degrade a solid, the liquid should stay on the surface of the solid
and diffuse to its inside. Thus, the wettability and the swellability of solvents for acidic solutions toward solid
DGHMDO-DDM was investigated. Contact angle (θ) is an important wettability indicator of solid by certain

Page 27 of 32
Green Chemistry
liquid, the smaller θ corresponds to the better wettability59. Fig. 10e presents the relationship of tVhieew AθrtsicleoOfnline
DOI: 10.1039/C9GC04020J
solvents on DGHMDO-DDM and the degradation ratio of DGHMDO-DDM after degradation in 0.1 M HCl
solutions with different solvents for 12 h. Water and acetone exhibited θs of 81.8 ° and 8.9 ° (Table 5, Fig.
S10), respectively, which manifests that the acetone possesses much better wettability than water toward
DGHMDO-DDM; the degradation ratio increased with the increase of acetone content in acidic solutions.
Meanwhile, the swelling degree of DGHMDO-DDM in different solvents increased with the increase of
acetone content and the corresponding degradation rate (Table 5, Fig. 10e). These indicates that the
degradation rate of DGHMDO-DDM was positively correlated with the wettability and swellability of the
solution.
Table 5 Contact angle and swelling degree of DGHMDO-DDM in different solvents
Acetone/water, v/v
Solvent
Water THF
DMSO DMF Ethanol
10/0 9/1
8/2
7/3
6/4
5/5
Contact
angle (°)
a Swelling
81.8
0.97
11.8
2.70
40.6
0.40
22.2
0.10
30.0
0.47
8.9 38.3 41.3 47.0 50.6 56.6
2.90 2.87 2.16 1.58 1.25 1.02
degree (%)
a The sample was immersed in solvent at 50 °C for 12 h.
As a degradable plastic, its chemical stability is overwhelmingly crucial for its utilization. As mentioned
above, DGHMDO-DDM was relatively stable at room temperature even in acidic condition, and could not be
degraded in heavily used acid in our daily life (acetic acid), or in acidic condition without organic solvents.
Besides, the chemical stability of DGHMDO-DDM was also investigated by immersing samples in 50 °C
water and basic aqueous solution. After 48 h, no appearance change and no weight loss were observed for
DGHMDO-DDM sample (Fig. S11, Table S5), which is indicative of its excellent stability in neutral and basic
conditions. This was attributed to the poor wettability and swellability of water toward DGHMDO-DDM as

Green Chemistry
Page 28 of 32
mentioned above. High humidity and high temperature environments may accelerate materials' aging, and
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DOI: 10.1039/C9GC04020J
hygrothermal aging resistance is currently a significant part of evaluating the stability of plastics, especially
hydrolysable plastics. Thus, the hydrothermal aging test was also carried on. The Tg of DGHMDO-DDM only
reduced by 6 °C at a humidity of 70 % and a temperature of 60 °C for 15 days, analogous to DGEBA-DDM
(Fig. 12), which indicates its excellent hygrothermal aging resistance. The slightly decline of Tg for both
DGHMDO-DDM and DGEBA-DDM was ascribed to the plasticization from the absorbed water.
Fig. 12 Non-isothermal DSC curves of DGHMDO-DDM and DGEBA-DDM after hygrothermal aging at 70%
humidity and 60 °C for 15 days.
Conclusions
In this paper, we successfully synthesized a “digestible”, rigid-and-flexible, and bio-sourced building block
HMDO for high-performance degradable plastics. High conversion rate and high selectivity were achieved
through evaporating water and reactive crystallization, respectively, which indicates great industrial prospects.
HMDO exhibited much lower cytotoxicity than BPA and even non-toxicity for human body because it could
be almost 100% hydrolyzed (“digested”) into original non-toxic raw materials vanillin and glycerol within 3
min at similar pH and temperature of gastric juice in human stomach. The corresponding thermosetting plastic

Page 29 of 32
Green Chemistry
could be depolymerized into soluble oligomers with formyl group and hydroxyl group in mild acidic sVoielwutAiroticnlesO.nline
DOI: 10.1039/C9GC04020J
The superior chemical stability was further confirmed to ensure the practicality of degradable plastics in service
life. The calculation of the chemical structure of HMDO confirmed its conformational transition ability, and
non-isothermal FTIR measurement and DMA technology testified the existence of methoxyl-related hydrogen
bond in the plastic, which lead to the high toughness of the plastic. Besides, the plastic exhibited much higher
mechanical properties and comparable thermal properties relative to a heavily used high-performance
counterpart from BPA. In general, this work provides a building block that has great potential to produce high-
performance and sustainable plastics.
Acknowledgements
This work was financially supported by National Natural Science Foundation of China (No. 51773216), Youth
Innovation Promotion Association, CAS (No. 2018335), and Natural Science Foundation of Zhejiang Province
(No. LQ20E030005).
Author contributions
S.M. conceived the ideas, W.B. and S.M. designed the experiments. W.B. performed all experiments and X.X.,
S.W. and N.L. contributed to some characterizations. L.Q. contributed to the calculations of chemical
structures. H.Z. and R.W. contributed to the measurement of in vitro stem cell viability. J.L. and Z.C.
contributed to the measurement of positron lifetime spectra. W.B. and S.M. organized and wrote the
manuscript. S.M. supervised the whole project and revised manuscript. J.Z., S.Y. and Y L. provided valuable
insights for the study.