Ring-opening metathesis polymerization (ROMP) of norbornenyl-functionalized fatty alcohols

Article abstract of DOI:10.1016/j.polymer.2009.11.011

Novel biorenewable-based thermosets have been successfully synthesized by the ring-opening metathesis polymerization (ROMP) of norbornenyl-functionalized fatty alcohols derived from soybean oil (NMSA), Dilulin (NMDA), ML189 (NMMA) and castor oil (NMCA). The effects of the monomer structure on the polymerization process, and the thermal and mechanical properties of the resulting thermosets have been extensively investigated. The number of ROMP-reactive rings appended to the fatty acid chain and the viscosity play an important role in controlling the initiation and propagation processes of the polymerization and the final properties of the thermosets obtained. The thermosets have been characterized by Soxhlet extraction, DMA, TGA, and tensile tests. It has been found that polyNMDA and polyNMMA have best thermo-mechanical properties. Compared with polyNMSA, the polyNMDA and polyNMMA thermosets exhibit lower soluble fractions, and higher thermal stabilities and mechanical properties, because of more effective crosslinking; whereas, polyNMCA exhibits a higher soluble fraction, and lower thermal stability, resulting from incomplete polymerization of the more viscous NMCA monomer.

Full text of DOI:10.1016/j.polymer.2009.11.011

Polymer 51 (2010) 53–61
Contents lists available at ScienceDirect
Polymer
journal homepage: www.elsevier.com/locate/polymer
Ring-opening metathesis polymerization (ROMP) of norbornenyl-functionalized
fatty alcohols
*
Ying Xia, Yongshang Lu, Richard C. Larock
Department of Chemistry, Iowa State University, Ames, IA 50011, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
Novel biorenewable-based thermosets have been successfully synthesized by the ring-opening
metathesis polymerization (ROMP) of norbornenyl-functionalized fatty alcohols derived from soybean oil
(NMSA), Dilulin (NMDA), ML189 (NMMA) and castor oil (NMCA). The effects of the monomer structure
on the polymerization process, and the thermal and mechanical properties of the resulting thermosets
have been extensively investigated. The number of ROMP-reactive rings appended to the fatty acid chain
and the viscosity play an important role in controlling the initiation and propagation processes of the
polymerization and the final properties of the thermosets obtained. The thermosets have been charac-
terized by Soxhlet extraction, DMA, TGA, and tensile tests. It has been found that polyNMDA and
polyNMMA have best thermo-mechanical properties. Compared with polyNMSA, the polyNMDA and
polyNMMA thermosets exhibit lower soluble fractions, and higher thermal stabilities and mechanical
properties, because of more effective crosslinking; whereas, polyNMCA exhibits a higher soluble fraction,
and lower thermal stability, resulting from incomplete polymerization of the more viscous NMCA
monomer.
Received 10 September 2009
Received in revised form
5 November 2009
Accepted 7 November 2009
Available online 15 November 2009
Keywords:
ROMP
Thermoset
Biorenewable
Published by Elsevier Ltd.
1. Introduction
alkene comonomers. These new polymers exhibit thermophysical
and mechanical properties that are comparable to those of
Bio-based materials have attracted much attention because of
their sustainability and environmental concerns [1]. Recently,
renewable materials synthesized from plant products have shown
great promise as a replacement for petroleum-based materials [2].
Thermosetting resins [3], biodegradable polymers [4], bio-
composites [5] and polyurethane dispersions [6,7] from acylated
epoxidized soybean oil, soy protein and vegetable oil-based pol-
yols have been successfully synthesized by free radical, ring-
opening and addition polymerizations. In our previous work, we
have taken advantage of the carbon-carbon double bonds in
soybean [8], linseed [9], tung [10], corn [11] and fish [12] oils to
develop a variety of new polymeric materials by cationic or
thermal copolymerization of these natural oils with styrene (ST)
and divinylbenzene (DVB). The resulting thermosetting polymers
can be varied from elastomers to tough and rigid plastics by
simply changing the stoichiometry, and the nature of the oil and
commercially available elastomers and conventional plastics and
may serve as replacements for petroleum-based polymers in
many applications.
Olefin metathesis has also been employed in the synthesis of
vegetable oil-based polymers, primarily through acyclic diene
(triene) metathesis polymerization (ADMET/ATMET) [13,14] and
ring-opening metathesis polymerization (ROMP) [15,16]. Recently,
Meier et al. investigated the ADMET and ATMET bulk polymeriza-
tions of vegetable oil-based undecyl undecenoate and glyceryl
triundec-10-enoate, respectively, using Grubbs’ and Hoveyda–
Grubbs’ ruthenium catalysts, leading to high-molecular-weight
triblock and branched polyesters [13,14]. Moreover, the molecular
weight of the resulting polyesters can be controlled by adjusting
the ratio of the monomer and the chain stopper in a one-step, one-
pot procedure.
In our previous work, we reported the synthesis of vegetable
oil-based polymers by ROMP, which is a powerful tool to convert
cyclic olefins to various polymeric materials (see Scheme 1 for an
example) [17]. In our work, two kinds of vegetable oil-based
ROMP thermosetting polymers have been obtained successfully
* Corresponding author. Tel.: þ1 5152944660; fax: þ1 5152940105.
E-mail address: larock@iastate.edu (R.C. Larock).
0032-3861/$ – see front matter Published by Elsevier Ltd.
doi:10.1016/j.polymer.2009.11.011

54
Y. Xia et al. / Polymer 51 (2010) 53–61
2. Experimental section
2.1. Materials
Scheme 1. A general example of ROMP.
Soybean oil was purchased at the local supermarket. Dilulin was
supplied by Cargill (Chicago, IL). ML189 was obtained from
Northern Sun,
a division of Archer Daniels Midland (ADM)
Company (Red Wing, MN). Castor oil, 5-norbornene-2,3-dicarboxy-
late anhydride (endo) and the 2nd generation Grubbs catalyst were
purchased from Sigma-Aldrich (Milwaukee, WI). Lithium
aluminum hydride (LAH) was purchased from Acros (Geel,
Belgium). Benzene, ethyl acetate, methylene chloride and hydro-
chloric acid were obtained from Fisher (Fair Lawn, NJ). Tetrahy-
drofuran (THF) was distilled over sodium/benzophenone under N2.
Unless otherwise stated, all reagents were used as received without
further purification.
by the copolymerization of Dilulin, a commercially available
norbornene-modified linseed oil [18], with dicyclopentadiene
(DCPD) [15] and a norbornene-functionalized castor oil (BCO)
with cyclooctene [16] using Grubbs 2nd generation catalyst. Their
good thermal and mechanical properties indicate great promise
for these environmentally-friendly, vegetable oil-based materials
as a new class of plastics. However, phase separations were
observed in both the Dilulin/DCPD and BCO/cyclooctene ther-
mosets, because of the large difference in reactivity between the
vegetable oil-based monomers and the petroleum-based como-
nomers. The relatively low reactivity of the vegetable oil-based
monomers can be attributed to their high viscosity and the free
fatty acid chains, which may hinder coordination between the
catalyst and the norbornene moiety present in the Dilulin and
BCO. Similar results have also been observed in the vegetable oil-
based thermosets from Dilulin and norbornene-based cross-
linkers [19].
To address the phase separation, which occurred in the vege-
table oil-based ROMP systems, while maintaining the good ther-
mophysical and mechanical properties of the resulting polymers, in
this work, four novel norbornenyl-functionalized fatty alcohols
with different side chain structures have been successfully
synthesized from soybean oil, Dilulin, ML189 and castor oil by first
reducing the vegetable oil triglycerides to fatty alcohols, which
were then reacted with 5-norbornene-2,3-dicarboxylate anhydride
(see Scheme 2 for an example). These norbornenyl-functionalized
biorenewable monomers can easily undergo ring-opening
metathesis homopolymerization under Grubbs 2nd generation
catalyst, leading to vegetable oil-based thermosets with good
thermophysical and mechanical properties with no apparent phase
separation.
2.2. Synthesis of norbornenyl-functionalized fatty alcohols
The synthesis of the norbornenyl-modified soybean alcohol
(NMSA) is shown in Scheme 2. LAH (15.7 g, 0.41 mol) was dissolved
in 100 mL of THF and stirred in a 500 mL two-neck round bottom
flask. Soybean oil (120 g, 0.14 mol) was dissolved in THF (150 mL)
and then added dropwise to the LAH solution. The reaction was
carried out at 0 ꢀC overnight. The reaction mixture was poured into
ice water, followed by the addition of 1 M HCl, until the solution
was clear. Then, 300 mL of ethyl acetate was added, resulting in two
layers. The organic layer was washed with water to remove the
glycerol, and then dried over MgSO4 and filtered. Finally, the clear
soybean alcohol was obtained after removal of the organic solvent
under vacuum.
The soybean alcohol (50 g, 0.19 mol) was added to a 250 mL
round bottom flask, and then 34.2 g (0.21 mol) of 5-norbornene-2,3-
dicarboxylate anhydride (endo) was added, followed by 21.04 g
(0.21 mol) of triethylamine. The mixture was stirred at 65 ꢀC for 24 h
and then diluted by the addition of 100 mL of ethyl acetate. The
mixture was poured into a 1M aqueous HCl (400 mL) solution and
stirred overnight to convert excess 5-norbornene-2,3-dicarboxylate
anhydride to water soluble 5-norbornene-2,3-dicarboxylic acid.
Scheme 2. Synthesis of norbornenyl-modified soybean alcohol (NMSA).

Y. Xia et al. / Polymer 51 (2010) 53–61
55
2.4. Polymerization
Ten grams of monomer was weighed into a PTFE-coated 20 mL
vial. Freeze-dried Grubbs 2nd generation catalyst (50 mg, 0.5 wt%)
was mixed with the monomer using a spatula until all of the
catalyst was dissolved and a homogeneous solution was obtained.
The mixture was heated at 65 ꢀC for 1 h and 150 ꢀC for 3 h. The
resulting thermosets were slightly transparent and retain the oil’s
original color.
2.5. Soxhlet extractions
A 2–3 g sample of the bulk polymer was extracted with 100 mL
of refluxing methylene chloride for 24 h using a Soxhlet extractor.
Following extraction, the resulting solution was concentrated
under reduced pressure and dried in a vacuum oven at 60 ꢀC
overnight.
Scheme 3. Representative chemical structures of soybean oil, Dilulin, ML189 and
castor oil.
2.6. Characterization
1H NMR spectroscopic analysis of the monomers and the soluble
substances extracted from the thermosets by methylene chloride
were recorded in CDCl3 using a Varian spectrometer (Palo Alto, CA)
at 300 MHz.
The viscosities of the monomers were measured with a cone (1ꢀ,
40 mm diameter) and detachable sample plate on an AR2000ex (TA
Instruments, New Castle, DE) at 25 ꢀC, while the shear rate was
increased from 0 to 500 sꢁ1. The gelation time was also determined
on the AR2000ex by applying an oscillating strain to the sample and
measuring the response stress. All experiments were performed at
65 ꢀC, using stress control mode at 1 Hz, with 25 mm diameter
disposable parallel plates and a 0.5 mm gap.
Then the mixture was extracted by ethyl acetate, washed by 1 M HCl
and brine, and dried over MgSO4. After evaporating the solvent
under vacuum, a near quantitative yield of endo-norbornenyl-
modified soybean alcohol (NMSA) was obtained (see later for peak
assignments and integration in 1H NMR).
The other vegetable oil-based monomers, norbornenyl-modi-
fied Dilulin alcohol (NMDA), norbornenyl-modified ML189 alcohol
(NMMA) and norbornenyl-modified castor oil (NMCA) were
synthesized and purified using the same method as that mentioned
above.
2.3. Freeze-drying of the Grubbs catalyst
Differential scanning calorimetry (DSC) cure analyses of the
monomers were recorded on a TA Instruments Q20. Monomers
were mixed with the Grubbs 2nd generation catalyst, and then the
mixtures were transferred to an aluminum DSC pan and loaded into
the DSC chamber immediately. The samples were scanned from
ꢁ50 ꢀC to 240 ꢀC at a heating rate of 10 ꢀC/min.
To improve the solubility of the Grubbs catalyst in the mono-
mers, freeze-drying of the catalyst was carried out according to
a literature procedure [20]. The 2nd generation Grubbs catalyst
(250 mg) was dissolved in 5 mL of benzene and the solution was
frozen in a liquid nitrogen bath. The frozen sample was then placed
in a vacuum oven at room temperature for 5 h to sublime the
benzene. This process provided catalyst with larger surface areas.
The dynamic mechanical analyses (DMA) was recorded on a TA
Instruments Q800 dynamic mechanical analyzer using a three-
point bending mode at 1 Hz. Rectangular samples 1.5 mm thick and
Fig. 1. 1H NMR spectra of NMSA.

56
Y. Xia et al. / Polymer 51 (2010) 53–61
Fig. 2. 1H NMR spectra of NMSA, NMDA, NMMA and NMCA.
10 mm wide were used for the analysis. Samples were cooled and
held isothermally for 3 min at ꢁ80 ꢀC before the temperature was
increased at 3 ꢀC/min to 200 ꢀC.
volume of the sample, was obtained from the area under the
corresponding tensile stress-strain curves.
Thermogravimetric analysis (TGA) of the specimens was carried
out on a TA Instruments (New Castle, DE) Q50. Samples were
scanned from 50 ꢀC to 650 ꢀC in air with a heating rate of 20 ꢀC/min.
The mechanical properties of the thermosets were determined
using an Instron universal testing machine (model 4502) with
3. Results and discussion
3.1. Monomer characterization
Structures representative of the commercially available vege-
table oils employed in this study are shown in Scheme 3. Soybean
oil is a triglyceride structure consisting of mainly unsaturated oleic,
linoleic and linolenic fatty acids [21]. Dilulin and ML189 are linseed
oil-based commercial industrial oils with complex components,
a
crosshead speed of 50 mm/min. Rectangle specimens of
70 ꢂ 10 ꢂ 3 mm3 (length ꢂ width ꢂ thickness) were used. An
average value of five replicates of each sample was taken. The
toughness of the polymer, which is the fracture energy per unit
80
NMSA
NMDA
NMMA
70
NMCA
60
10
0
0
50 100 150 200 250 300 350 400 450 500
-1
Shear Rate (s
)
Fig. 3. Viscosities of the monomers.
Fig. 4. Curing kinetic curves for the monomers.

Y. Xia et al. / Polymer 51 (2010) 53–61
57
which have been characterized before [22]. Dilulin with approxi-
Gelation Time
mately one norbornene ring per triglyceride is prepared by the
Diels–Alder reaction between linseed oil and cyclopentadiene
under high temperature and pressure [18], while ML189 is also
a dicyclopentadiene-modified linseed oil [23], which appears to
contain approximately one cyclopentene ring per triglyceride. The
ROMP of Dilulin or ML189 results in soft, but weak, polymers,
which indicates that the rings appended onto the fatty acid chains
can be ring-opened to form polymers. Castor oil, consisting of
approximately ninety percent ricinoleic acid, has about 2.7
hydroxyl groups per triglyceride [16]. The variety of fatty acid
chains present in these oils makes it possible to vary the nature of
the monomer and examine the properties of the resulting
thermosets.
10000
1000
100
10
storage shear modulus G
loss shear modulus G
1
Fig. 1 shows the detailed 1H NMR spectra of NMSA with inte-
grations. The signals at 6.1–6.4 ppm (b) correspond to the norbor-
nene protons, and the vinylic hydrogens of the fatty acid chains (c)
are typically found at 5.2–5.5 ppm. The peaks centered at about
4.0 ppm (d) are attributed to the methylene protons close to the
ester group of the monomer. Fig. 2 illustrates the 1H NMR spectra
for the four monomers and the new peaks not present in NMSA are
assigned. Compared to NMSA, peaks at 5.9–6.1 (p) and 5.6 ppm (s)
are observed in NMDA and NMMA, which are attributed to the
norbornene and cyclopentene rings attached to the fatty acid
chains in NMDA and NMMA, respectively. For the monomer NMCA,
the tertiary hydrogen on the fatty acid chain is observed around
4.8 ppm (t) and a new methylene peak is seen at 2.2 ppm (u). These
norbornenyl-modified fatty alcohols are suitable for ring-opening
metathesis polymerization, due to the strained norbornene ring
present in the monomer. For NMDA and NMMA, approximately one
third of the fatty acid side chains are appended with a norbornene
ring or a cyclopentene ring (calculated from the integration of the
1H NMR spectra), which leads to crosslinking in the resulting
thermosets. Compared with the other three monomers, 90% of
NMCA has two norbornene rings, which should result in an even
higher crosslink density.
0.1
0
200
400
600
800
Time (s)
Fig. 5. Evolution of shear moduli during the reaction of the monomer/catalyst blend.
Shown here is the NMDA/catalyst mixture curing at 65 ꢀC.
NMSA. This can be explained by the fact that the cyclopentene rings
present in the side chains of NMMA are less strained than the
norbornene rings present in the side chains of NMDA. In addition,
NMCA with nearly two norbornene rings exhibited lowest cure
heat, probably due to incomplete polymerization of the NMCA
monomers within the DSC scan time. More specifically, NMCA
monomers having a much higher viscosity were constrained by
strong hydrogen bonding between monomers, which significantly
restricts the mobility of the monomer.
The gelation time for the four monomers was determined
rheologically using a reported procedure [25]. Generally, the
viscosity of the system increases dramatically when gelation
occurs. A parallel plate oscillatory rheometer was used to measure
the time dependence of the storage shear modulus, G0, and the loss
shear modulus, G00, for the monomer/catalyst mixture. As shown in
Fig. 5, both G0 and G00 increase gradually with time, the build-up rate
of G0 was much higher than that of G00 due to the formation of elastic
polymers from chemical crosslinking. The differential in rates leads
to a crossover of G0 and G00, which is defined as the gel time, indi-
cating the transition of the system from liquid phase dominated to
a solid phase dominated viscoelastic behavior, also suggesting
three-dimensional (3-D) network formation [26]. Table 1 summa-
rizes the gelation time of the monomer/catalyst mixtures at 65 ꢀC.
As seen from the table, the monomer gelation times follow the
order: NMDA < NMMA < NMCA z NMSA, indicating that the
gelation time is not only determined by the monomer structure, but
also the viscosities of the monomers. Thus, the low viscosity NMDA
with a more reactive norbornene ring present in the side chain
3.2. ROMP of the monomers
In the ROMP initiation process using the 2nd generation Grubbs
catalyst, the phosphine ligand first dissociates, then the olefin in
the monomer coordinates to the reactive ruthenium center to
initiate the polymerization process [24]. However, if the bulk
monomer is too viscous, it may be more difficult to coordinate with
the metal center, resulting in a slow initiation process and propa-
gation of the polymerization [16]. Fig. 3 illustrates the viscosities of
the four monomers. NMCA has a much higher viscosity than the
other three monomers due to the stronger hydrogen bonding
through the extra carboxylic acid groups. The relatively high
viscosity of NMCA presumably prevents the movement of the
monomer and this affects the initiation process and propagation of
the polymerization process. Similar results have been reported
previously [16].
Fig. 4 illustrates the peak temperatures (Tp) and cure heat for the
curing kinetic curves of all four monomers. The Tps increase as the
viscosities of the monomers increase, which is in good agreement
with the fact that the olefin in the monomer can coordinate to the
ruthenium center more easily and thus initiate polymerization with
the less viscous monomers. The exothermic peaks are due to the
heat release from the strained rings present in the monomer and
the cure heat was calculated based on the data obtained from DSC
and molecular weight of the monomer. NMDA exhibits the largest
cure heat of 47.0 kJ/mol which results from the additional norbor-
nene ring in the monomer. However, NMMA containing an extra
cyclopentene ring shows only a slightly higher cure heat than
Table 1
Gel time, extraction data and DMA data for the polymers.
Polymer
Gel
Soluble(wt%) E0 at 25 ꢀC (Pa) Tg (ꢀC)b ye (mol/m3)c
Time/sa
polyNMSA
polyNMDA
polyNMMA
1495
220
889
13
5
5
1.6 ꢂ 108
5.9 ꢂ 108
5.5 ꢂ 108
7.3 ꢂ 108
50.0
66.5
70.3
68.2
159
307
267
331
polyNMCA 1456
18
a
Gel time was determined at 65 ꢀC.
b
Glass transition temperatures represent the maxima of the tan
by DMA analysis.
d
curves obtained
c
Crosslink densities have been calculated at temperatures 50 ꢀC above the Tg.

58
Y. Xia et al. / Polymer 51 (2010) 53–61
Fig. 6. Sample pictures for the polymers (from left to right: polyNMSA, polyNMDA, polyNMMA, and polyNMCA).
exhibits the shortest gelation time, while the highly viscous NMCA
with an extra norbornenyl ring present in the side chain shows
a much longer gelation time than the other three monomers.
As shown in Fig. 6, all polymer samples are fairly transparent
and exhibit essentially the same color as the original oils. Both
polyNMDA and polyNMMA exhibit smooth surfaces due to the fact
that the extra reactive rings present in the side chain of the oil and
the appropriate viscosities of the monomers afford the best incor-
poration of the polymer chains. However, polyNMSA and poly-
NMCA exhibit coarse surfaces and lower transparencies, which is
probably due to their relatively low crosslink densities and
incomplete polymerization of the monomers as discussed later.
To investigate how the polymer structure is affected by the
chemical structure of the monomer, all polymer samples have been
subjected to Soxhlet extraction to extract the soluble materials
present in the final polymers. As shown in Table 1, about 13 wt% of
polyNMSA was soluble; while both polyNMDA and polyNMMA
afforded only 5 wt% of soluble materials, indicating that the extra
norbornene or cyclopentene rings play an important role in
increasing the crosslink densities of the resulting thermosets.
However, about 18 wt% of polyNMCA was extracted, presumably
due to incomplete polymerization of the NMCA. Fig. 7 illustrates
the 1H NMR spectra of the soluble materials extracted from the four
polymers. Compared to Fig. 2, the peaks between 0.5 and 2 ppm
indicated that the soluble fractions mainly consist of the oil frac-
tions. The intensity of the characteristic peaks assigned to the
norbornene ring is dramatically decreased in the soluble fractions
obtained from polyNMSA, polyNMDA and polyNMMA indicating
that almost all of the norbornene rings were ring-opened. However,
a significant portion of the norbornene rings remain unreactive in
the resulting polyNMCA soluble fraction apparently because the
propagation process is hindered by the high viscosity of the
monomers.
3.3. Thermal and mechanical properties
Fig. 8 shows the storage modulus (E0) and loss factor (tan
d)
curves as a function of temperature for the four polymers. All
polymers exist in the glassy state at a very low temperature, and the
modulus deceases slightly with increasing temperature. Then,
a sharp decrease in the E0 value is observed in the temperature
range from 0 to 100 ꢀC. This corresponds to the primary relaxation
process (
a) of the resulting thermosets, where a maximum is
observed in the loss factor curve, which is taken as the Tg. The
Fig. 7. 1H NMR spectra for the extracted materials from (a) polyNMSA, (b) polyNMDA, (c) polyNMMA, and (d) polyNMCA.

Y. Xia et al. / Polymer 51 (2010) 53–61
59
104
103
102
101
100
10-1
polymer networks, resulting in higher crosslinked vegetable oil-
based thermosets with a resulting enhancement in the rubbery
modulus. As molecular motions became more restricted due to the
crosslinking, the amount of energy that can be dissipated
throughout the polymer specimen decreases dramatically. There-
fore, a shift of the loss factor peak to higher temperature is observed
polyNMSA
polyNMDA
polyNMMA
polyNMCA
for polyNMDA, polyNMMA and polyNMCA as shown in the tan
curves when compared with polyNMSA. The tan intensities also
diminish. Meanwhile, a significant broadening of the -relaxation is
observed. For the sample polyNMCA, a shoulder peak around 30 ꢀC
is observed in the -relaxation process, which might be attributed
d - T
d
a
a
to the relaxation of NMCA oligomer-rich phases, because of
incomplete polymerization of the viscous NMCA monomers.
Fig. 9 shows the TGA analysis of the resulting thermosets and
the corresponding data are summarized in Table 2. As seen in Fig. 9,
the polymers are stable up to 150 ꢀC in air and undergo three major
thermal degradation processes. The weight loss of the first degra-
dation process from 180 ꢀC to 250 ꢀC approximately equals the
soluble fraction as shown in Table 1 and can be attributed to
evaporation of any unreacted monomers and oil fragments. In this
stage, more than 20% of the overall weight was lost for polyNMCA,
because of incomplete polymerization of the NMCA monomers.
Less than 10% of the overall weight was lost for polyNMDA and
polyNMMA, apparently due to higher crosslinking by the extra
-75 -50 -25
0
25
50
75 100 125 150
Temperature (oC)
0.8
0.6
0.4
0.2
0.0
polyNMSA
polyNMDA
polyNMMA
polyNMCA
100
polyNMSA
polyNMDA
polyNMMA
polyNMCA
80
60
40
20
0
-75 -50 -25
0
25
50
75 100 125 150
Temperature ( oC )
Fig. 8. Tan
d and storage modulus curves for all polymers.
100
200
300
400
500
600
o
Temperature ( C)
polymer polyNMSA shows a relatively low storage modulus, and its
loss factor shows a very sharp relaxation process centered at about
50 ꢀC. When compared with polyNMSA, the E0 values of polyNMDA,
polyNMMA and polyNMCA were significantly increased over the
entire temperature range, due to incorporation of the extra reactive
rings present in the side chains. For instance, the E0 values for
polyNMDA, polyNMMA and polyNMCA at room temperature (Table
1) are approximately 3.7, 3.4 and 4.6 times higher, respectively,
than that of polyNMSA. The rubbery plateau modulus can be
explained by qualitative consideration of the crosslinking density
polyNMSA
polyNMDA
polyNMMA
polyNMCA
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
degradation of the
polymer backbone
further degradation
of crosslinked materials
(ne) of the thermosets, according to rubber elasticity theory, using
evaporation of the more
volatile fractions
the following equation [27,28]:
E0 ¼ 3veRT
where E0 is the storage modulus at Tg þ 50 ꢀC in the rubbery
plateau, R is the gas constant, and T is the absolute temperature. As
seen in Table 1, the thermosets from the monomers with reactive
rings in the side chains exhibit much higher crosslink densities
100
200
300
400
500
600
then polyNMSA and are typically in the range of 2.6 ꢂ 102
–
o
Temperature ( C)
3.3 ꢂ102 mol/m3. This indicates that the extra reactive rings in the
side chains of the monomers are effectively incorporated into the
Fig. 9. TGA curves and their derivative curves for all polymers.

60
Y. Xia et al. / Polymer 51 (2010) 53–61
Table 2
TGA data and mechanical properties for the polymers.
Polymer
TGA data (ꢀC)
E (MPa)
Mechanical Propertiesd
Toughness (MPa)
a
b
c
T10
T50
Tmax
sb (MPa)
3b (%)
polyNMSA
polyNMDA
polyNMMA
polyNMCA
215
243
240
196
435
450
449
390
447
451
450
429
–
–
–
–
311.4 ꢃ 16.7
154.8 ꢃ 1.1
–
15.4 ꢃ 0.5
9.9 ꢃ 0.3
–
34.5 ꢃ 4.7
41.0 ꢃ 4.2
–
4.1 ꢃ 0.6
2.9 ꢃ 0.3
–
a
10% Weight loss temperature.
50% Weight loss temperature.
Temperature of maximum thermal degradation.
E ¼ Young’s modulus, sb ¼ tensile strength, and 3b ¼ elongation at break.
b
c
d
olefinic rings present in the side chains. The second loss at around
400–500 ꢀC is believed to be caused by decomposition of the
polymer backbone. The final loss at around 500–600 ꢀC is indicative
of further decomposition of the crosslinked fragments and oxida-
tion of the carbon residue. Table 2 summarizes the interesting
parameters from the TGA curves for these thermosets taken from
the onset of degradation, which is usually taken as the temperature
at which 10% degradation occurs (T10), the midpoint temperature of
the degradation (T50), and the maximum degradation temperature
(Tmax). As expected, the samples polyNMDA and polyNMMA exhibit
polyNMMA. This is expected, since the extra rigid cyclopentane
rings obtained after ring-opening of the norbornene ring present in
the NMDA side chains should increase the rigidity and toughness of
polyNMDA, whereas the linear polymer chains obtained after the
ring-opening of the cyclopentene rings in NMMA would not be
expected to increase the modulus and toughness all that much.
4. Conclusions
Four different vegetable oil-based monomers, NMSA, NMDA,
NMMA and NMCA, have been synthesized from soybean oil, Dilulin,
ML189 and castor oil, respectively, followed by esterification with
a bicyclic anhydride, and then homopolymerized using the Grubbs
2nd generation ruthenium catalyst to obtain biorenewable ther-
mosets. The differences in the structures of the side chains and the
viscosities of the monomers result in different properties in the
final thermosets. Compared with polyNMSA, the polyNMDA and
polyNMMA thermosets exhibit lower soluble fractions, and higher
thermal stabilities and mechanical properties, because of the
successful incorporation of the side chain into the polymer matrix
to form effective crosslinking. However, polyNMCA affords a higher
soluble fraction, and lower thermal stability, resulting from
incomplete polymerization of the highly viscous NMCA monomer.
Note that polyNMDA and polyNMMA exhibit tensile stress-strain
behaviors of ductile plastics with Young’s moduli ranging from 155
to 310 MPa, ultimate tensile strengths ranging from 10 to 15 MPa,
and percent elongation at break values ranging from 35 to 41%,
affording materials comparable to petroleum-based plastics, like
HDPE and poly(norbornene). This work provides a new way of
utilizing renewable resources to prepare environmentally-friendly
bioplastics with high performance.
the best thermal stability with similar values of T10, T50 and Tmax
.
However, lower T10, T50 and Tmax values are observed for polyNMCA
due to the incomplete polymerization of the NMCA monomer,
because of its high viscosity.
Table 2 also summarizes the mechanical properties for the two
most promising thermosets, polyNMDA and polyNMMA. These two
samples exhibit Young’s moduli ranging from 155 to 310 MPa,
tensile strengths ranging from 10 to 15 MPa, elongation at break
values in the range of 35–41% and toughness values ranging from 2.9
to 4.1 MPa. It is worth noting that the Young’s moduli and tensile
strengths of polyNMDA and polyNMMA are comparable to petro-
leum-based commercial plastics, such as high density polyethylene
(HDPE) and poly(norbornene) [29]. The stress-strain curves of the
polyNMDA and polyNMMA are shown in Fig. 10. Both polyNMDA
and polyNMMA exhibit behaviors typical of ductile plastics.
Differing from polyNMMA, polyNMDA shows yielding behavior,
followed by strain softening. No strain hardening behavior is
observed before the specimen breaks. PolyNMDA exhibits higher
values of Young’s modulus, tensile strength and toughness than
20
polyNMDA
polyNMMA
Acknowledgment
We are grateful for financial support from the Center for Crops
Utilization Research (CCUR) at Iowa State University and thankful to
Professor Michael Kessler from the Department of Materials
Science and Engineering at Iowa State University for the use of his
thermal analysis equipments. In addition, we thank Dr. Xia Sheng
from the Department of Materials Science and Engineering at Iowa
State University for his help with the rheometer tests.
15
10
5
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