Subscriber access provided by UNIVERSITY OF ADELAIDE LIBRARIES
Article
Synthesis of Fully Bio-based Polyesters from Plant Oil Liejiang Jin, Keyu Geng, Muhammad Arshad, Reza Ahmadi, and Aman Ullah ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.7b01668 • Publication Date (Web): 14 Sep 2017 Downloaded from http://pubs.acs.org on September 15, 2017
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
ACS Sustainable Chemistry & Engineering is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 28
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Sustainable Chemistry & Engineering
1
Synthesis of Fully Bio-based Polyesters from Plant Oil
2
Liejiang Jin†, Keyu Geng†‡, Muhammad Arshad†, Reza Ahmadi†, Aman Ullah†*
3
†Department of Agricultural, Food and Nutritional Science, 4-10 Agric/For Centre, University of
4
Alberta, Edmonton, Alberta, Canada T6G 2P5
5
‡Department of Polymer Science and Engineering, Zhejiang University, Zhe Da Road 38,
6
Hangzhou 310027, China
7
*Corresponding author: Dr. Ullah, Email:
[email protected] 8
Tel: +1 (780) 492-4845,
Fax: +1(780) 492-4265
9 10 11 12 13 14 15 16 17 18 19 20 21 22 1
ACS Paragon Plus Environment
ACS Sustainable Chemistry & Engineering
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
1
Abstract
2
Self-metathesis of fatty acid methyl esters (FAMEs) from natural oils and commercial oleic acid
3
was carried out using microwave reactor in solvent free conditions. Self-metathesis products
4
were further identified and quantified by gas chromatography-mass spectroscopy (GC-MS) and
5
gas chromatography-flame ionization detector (GC-FID). Conversion of ~50% was achieved
6
within short span (~2 min) in the presence of 0.05 mol% Hoveyda-Grubbs 2nd generation catalyst
7
(HG2) giving an equilibrium mixture of alkenes, α,ω-diester and FAMEs. Highly pure
8
dimethyl-9-octadecene-1,18-dioate (diester) was separated and the desired quantity of it was
9
reduced to 9-octadecene-1,18-diol (diol). Condensation polymerization of diester and diol as
10
monomers was performed using conventional heating, microwave irradiation and microwaves
11
coupled with conventional heating. Characterization and analysis of synthesized biopolyesters
12
were carried out using different techniques including nuclear magnetic resonance (NMR),
13
Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), gel
14
permeation chromatography (GPC), thermal gravimetric analysis (TGA), dynamic mechanical
15
analysis (DMA) and tensile tests. Polyesters with highest molecular weight of 337KDa, ~50 oC
16
melting point, degradation temperature of about 400 oC, and the maximum strength of ~5.5MPa
17
were obtained. These materials have great future potential to be used in different applications as
18
a substitute of non-renewable polyesters.
19
Keywords: plant oil, self-metathesis, microwave irradiation, aliphatic polyester, renewable
20
resources
21
Introduction
22
Fossil feedstocks, which are abundant and cheap, have been supplying the vast majority of raw
23
materials for polymer production over the last few decades. However, fossil oil as non-renewable
24
resource is gradually depleting and its exploitation and combustion have negative impacts on
25
environment and ecosystem1. As an alternative to avoid these disadvantages, renewable 2
ACS Paragon Plus Environment
Page 2 of 28
Page 3 of 28
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Sustainable Chemistry & Engineering
1
resources which meet the requirements of environment protection and sustainable development
2
are now being considered as building blocks for the preparation of polymeric materials and are
3
attracting a growing interest from academia and industry.
4
The largely available and easily accessible renewable resources are taken into consideration,
5
such as plant oils. In Canada, millions of tons of plant oils are being produced every year, as
6
renewable feedstocks which can be used for production of fine chemicals and polymers. Plant
7
oils, including canola oil have abundant unsaturated hydrocarbon chains. They are generally
8
converted to fatty acids (FAs) or fatty acid methyl esters (FAMEs) for the simplicity of
9
modification. Many reactions have been developed to modify FAs and FAMEs into α,
10
ω-functionalized compounds as valuable monomers of polyesters, polycarbonates and
11
polyamides. For instance, alkoxycarbonylation2-3 is effective to convert unsaturated FAMEs to
12
compounds with esters on both ends. Other reactions, such as ozonolysis4-5 and thiol-ene click
13
reaction6-7 have also been used to provide additional carboxyl acid, ester or amine groups to fatty
14
acids.
15
Moreover, olefin self-metathesis 8, a type of reaction which allows the exchange of substituents
16
on olefinic double bonds, is also a powerful tool for the preparation of bifunctional monomers.
17
The olefin metathesis due to its operational simplicity, mild reaction conditions, and environment
18
friendliness is considered an attractive technique for synthetic transformations. The
19
self-metathesis of unsaturated FAMEs was initially investigated by Boelhouwer’s group. Using
20
WCl6 and Me4Sn as catalytic system in chlorobenzene solution, methyl oleate and methyl
21
elaidate were transformed to desired alkene and diesters with ~50% conversion in 24 hours9.
22
Solvent free self-metathesis was successfully carried out in a later stage and then commonly used.
23
For instance, Mecking et al. obtained C20 diester with 33% yield from self-metathesis of
24
10-undecenoic acid at 48 oC within 4 hours10. Recently, Meier et al. reported higher conversion
25
98% of FAMEs from linseed and chia seed oil at 100 °C for 24h in the presence of 0.15 mol% 3
ACS Paragon Plus Environment
ACS Sustainable Chemistry & Engineering
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
1
Grubbs 1st generation catalyst and 0.30 mol% 1,4-benzoquinone (BQ) as olefin isomerisation
2
suppressant. However, for relatively larger scale batch of methyl linolenate ~ 30 grams, longer
3
reaction time of 36 hours and higher catalyst loading of 0.45 mol % (three different batches of
4
0.15 mol%) were required11. With the advantages of low catalyst loading, solvent free and
5
moderate conditions, olefin self-metathesis has extraordinary performance to build α,
6
ω-functionalized acids or esters from plant oils but catalyst deactivation due to longer reaction
7
times still remains a challenge.
8
Microwaves, having wavelengths between infrared and radio waves, have been widely used as
9
an unconventional technique for the acceleration of various organic reactions from late 20th
10
century12-13. A few studies on olefin metathesis under microwave irradiation have been reported,
11
particularly microwave-assisted ring-closing self-metathesis14-15 of several α,ω-dienes and
12
cross-metathesis16-17 of α-olefins. Reaction time was cut down to a few minutes or even seconds
13
from number of hours usually required by conventional heating method without affecting the
14
yield (>70%). However, microwave-enhanced olefin metathesis of natural resources has rarely
15
been investigated. To the best of our knowledge, there are no reports on the microwave-assisted
16
self-metathesis of plant oils such as canola and soybean oil. In addition to olefin metathesis,
17
research work regarding polycondensation of fossil fuel based monomers using microwave
18
technology has also attracted attention all over the world18-19. Takeuchi et al. obtained
19
poly(butylene succinate) (PBS) with weight average molecular weight (Mw) of 23,500 g/mol
20
using microwave technology in a short time period (~20 min)20.
21
Recently, our group has reported cross-metathesis (ethenolysis and alkenolysis) of canola oil
22
methyl esters using microwaves under solvent free conditions21. In this study, for the first time
23
we are reporting microwave-assisted self-metathesis of FAMEs from plant oils for the
24
production of diester. The desired quantity of this diester was reduced to diol, and both of these
25
monomers (diester and diol) were used for the synthesis of biopolyesters. Though a few 4
ACS Paragon Plus Environment
Page 4 of 28
Page 5 of 28
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Sustainable Chemistry & Engineering
1
examples of conventional polycondensation of plant oil derived diesters and diols have been
2
successfully carried out2-3, 10. To the best of our knowledge, microwave-induced polymerization
3
of these monomers has never been reported. The current study also includes the comparison of
4
conventional and microwave-enhanced polycondensation of plant oil derived diester and diol
5
under optimized conditions.
6
Result and Discussion
7
Olefin Metathesis of FAMEs
8
Plant oil methyl esters (POMEs) are generally mixtures of several FAMEs with different chain
9
lengths and unsaturation. Some of common FAME types are depicted in figure 1, containing
10
saturated, monounsaturated and polyunsaturated hydrocarbon chains.
11 12
Figure 1. Fatty acid methyl esters from different plant sources.
13
The self-metathesis of polyunsaturated POMEs produce several cyclo-olefins and short-chain
14
olefins which are volatile, including cyclohexa-1,4-diene and hex-3-ene11. Therefore, to
15
minimize product complexity by self-metathesis, the natural oil sources predominantly having
16
oleic acid (c18:1) were selected for this study using self-metathesis under microwave conditions.
17
For this purpose, firstly the fatty acids from oils were converted to monomeric methyl esters for
18
the simplicity of quantification and elimination of acidic group to quench its ability potentially
19
involved for the deactivation of catalyst. The compositions of POMEs were identified by GC-MS
20
and quantified by GC-FID, as shown in table 1. Polyunsaturated FAMEs (c18:2/c18:3) from all 5
ACS Paragon Plus Environment
ACS Sustainable Chemistry & Engineering
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 6 of 28
1
three sources are less than 17%, while the monounsaturated FAMEs (c16:1/c18:1) are
2
predominant compounds (> 75%).
3
Table 1. Composition of different POMEs FAMEs*
c14:0
c16:0
c18:0
c16:1c
c18:1c
c18:2c
c18:3c
A
-
6.7%
-
-
77.0%
13.3%
3.0%
B
-
7.4%
5.6%
-
82.5%
4.4%
-
C
3.4%
5.8%
-
5.8%
79.2%
5.8%
-
4 5
(*A: canola oil methyl ester, B: high oleic soybean oil methyl ester,
6
Hoveyda Grubbs 2nd generation catalyst (HG2) was particularly employed in this study for its
7
high tolerance to polar and protic environments. The self-metathesis of pure methyl oleate using
8
conventional heating has suggested that increase in reaction temperature leads to a drop of
9
observed conversion.22 . Therefore, medium temperature of 50oC was selected in this work.
C: methyl oleate technical grade) determined by GC-FID.
O O O O O O
self-metathesis
H3C(H2C)7 (a)
(CH2)4CH3
H3C(H2C)7
H3C(H2C)7 (b)
(c)
(CH2)7CH3
O (d)
O (e)
O O (f)
O
O O
O
10
(g)
11
Scheme 1. Self-metathesis of canola oil methyl esters.
O
6
ACS Paragon Plus Environment
O
Page 7 of 28
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Sustainable Chemistry & Engineering
1
A good conversion rate for self-metathesis of canola oil methyl esters was observed with in very
2
short reaction time (2 min), while the product structures were deduced/characterized by their
3
elution time, peak areas and MS spectra (figure 2). The unsaturated methyl esters in canola oil
4
and their products after self-metathesis are depicted in scheme 1. The products have been
5
classified into three types: olefins with internal double bonds (a, b, c); unsaturated FAMEs (d, e,
6
f); and unsaturated diester (g). Both cis- and trans- isomers were identified for compounds e, f
7
and g from GC-MS. Commonly the cis- compound has larger dipole moment and higher polarity,
8
so trans- isomers are suggested to be eluted ahead of cis-isomers based on the separation
9
principles of GC. This point of view was confirmed by comparing the elution time of c18:1t
10
(trans) in the spectrum of metathesis products and c18:1c (cis) in FAMEs (figure 2).
11
Generally, during self-metathesis using conventional heating, the diesters with shorter or longer
12
chain lengths may be generated due to olefin isomerization23, leading to difficulty in separation
13
of diester products. In this study, only peaks of C18 diester were identified. The absence of C17
14
or C19 diesters peaks in GC-MS spectrum strongly suggests that olefin isomerization did not
15
take place during microwave reaction.
7
ACS Paragon Plus Environment
ACS Sustainable Chemistry & Engineering
3x105 (1) COME (2) SM-Products
f(c18:1t)
Abundance
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 8 of 28
2x105
c
e(trans) c16:0
1x10
5
a e(cis)
g(trans)
b d
f(c18:1c)
c16:0
g(cis)
c18:1c18:2 c18:3
(2) (1)
0 20
30
40
50
60
70
80
90
Retention time (min)
1 2 3
Figure 2. GC-MS spectrum of canola oil methyl esters (COME) and self-metathesis (SM) products.
4
However, the existence of c18:1t (f) indicated that the reactants were not fully converted due to
5
equilibrium state of alkene self-metathesis. Conversion rate of ~50% was widely observed from
6
publications. For instance, Thomas A. FoGlia observed exactly 50% conversion rate from
7
olefin-metathesis of methyl oleate using Re2O3·Al2O3·Me4Sn catalyst24. Roland Winde reported
8
conversion rate of 49.6% for methyl oleate self-metathesis using a phoban-indenylidene
9
ruthenium catalyst25.
10
Herein, to investigate the chemical equilibrium state directly, the real conversion (Conv(R)) was
11
defined as the ratio of olefins and diesters amount to total amount of products26. To simplify the
12
conversion rate calculation, three assumptions were established: (1) The mass response factors
13
(MRF) of double-bond isomers were considered the same; (2) MRF of analogical compounds
14
(for olefins, FAMEs and diesters, respectively) were assumed the same; (3) the amount of
15
generated olefins equals to that of diesters. By considering all these factors, MRFs of
16
representative FAME (methyl oleate) and diester (dimethyl-9-octadecene-1,18-dioate isomers) 8
ACS Paragon Plus Environment
Page 9 of 28
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Sustainable Chemistry & Engineering
1
were obtained after calibration, as presented in Figure S6 & S7. Conv(R) was determined using
2
the following formula (1), where "c" represent concentration for each components. ConvR% =
3
=
× 100
--------- (1)
4
In case of canola oil methyl ester, 50.6% Conv(R) was observed (table 2). The reliability of
5
calculation was reconfirmed via yield calculation from an amplified reaction. 14.5g of
6
dimethyl-9-octadecene-1,18-dioate (Conv(R) ≈ 43%) was separated after the self-metathesis
7
reaction of 63g FAMEs. Considering percentage of saturated FAMEs and loss of products during
8
purification, the actual Conv(R) was supposed to be more close to the result calculated based on
9
GC-FID.
10
Though the calculated conversions were in line with the reported results, it was still unknown
11
whether the reaction was in equilibrium state under microwave irradiation or not. To figure out
12
the equilibrium point of microwave-assisted self-metathesis, aliquots were taken out for GC-FID
13
analysis at different time intervals (2, 6, 10, 20, 30 and 60 minutes). The conversion of FAMEs
14
into olefins and diesters was found to be around 50% after the chemical equilibrium was
15
achieved. Moreover, figure S8 also represent that olefin metathesis was completed within 2
16
minutes by microwave heating as compared to conventional heating which requires number of
17
hours. In this way, a rapid and efficient method has been established using microwaves.
18
Further, FAME mixtures from two other sources were investigated for microwave-induced
19
self-metathesis. Technical grade methyl oleate and high oleic soybean oil methyl esters were
20
successfully converted into diester. For methyl oleate, around 50% Conv(R) was achieved (table
21
2, entry 3), which is similar to the previously reported data on self-metathesis of methyl oleate.
22
However, only 39.2% conversion was observed in case of high oleic soybean oil methyl esters
23
self-metathesis (table 2, entry 2). Residual glycerol in FAMEs might be a conceivable reason for
24
lower conversion, as catalyst get deactivated after forming a Grubbs hydride complex with 9
ACS Paragon Plus Environment
ACS Sustainable Chemistry & Engineering
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 10 of 28
1
alcohol27. As, we have observed that crude FAMEs with residual glycerol have not displayed any
2
conversion even after 20 min under microwave radiation.
3
Table 2. The conversion of FAMEs by self-metathesis Entry
FAMEsa
Reaction Time(mins)b
Conv(R)%
1
A
2
50.6
2
B
2
39.2
3
C
2
51.3
4 5
a
6
Effect of Catalyst Loading on Conversions
7
The effect of catalyst concentration on conversion rate of FAMEs (methyl oleate) for their self
8
metathesis was also investigated using different catalyst loadings of HG2 (0.05 to 0.005 mol%).
9
HG2 loading was gradually reduced from 0.05 mol% to 0.005 mol% (table 3). Once the HG2
10
loading was decreased to 0.01 mol%, the required reaction time was prolonged from 2 to 6
11
minutes to achieve similar conversion (~50.8%) as given in table 3 and entry 3. Further lowering
12
of HG2 concentration to 0.005 mol% led to a sharp drop of conversion rate to 8.5% (table 3,
13
entry 4). Even with extended reaction time, the conversion was not improved. We hypothesized
14
that very low concentration of HG2 has completely been degraded/deactivated before the
15
completion of reaction. Therefore, catalyst loading of 0.01 mol% was considered as a preferred
16
concentration for self-metathesis.
17
18
A: canola oil methyl ester, B: high oleic soybean oil methyl ester, C: methyl oleate technical grade.
b
Conditions: 50 oC under microwave radiations at 0.05 mol% HG2 loading.
Table 3. The conv(R) of FAMEs (methyl oleate) after self-metathesis.
a
Entry
HG2 Loading (%)
Reaction Time(min)a
Conv(R)%
1
0.05
2
51.3
2
0.01
2
40.9
3
0.01
6
50.8
4
0.005
2
8.5
Conditions: 50oC under microwave radiations.
10
ACS Paragon Plus Environment
Page 11 of 28
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Sustainable Chemistry & Engineering
1
Preparation and Characterization of Polyesters
2
Polyesters were prepared by polycondensation of diester (Dimethyl-9-octadecene-1,18-dioate)
3
and diol (9-octadecene-1,18-diol) in the presence of SnCl2 or Ti(OBu)4 as catalyst at suitable
4
temperature as shown in scheme 2. Whereas, diol was obtained by reducing diester with lithium
5
aluminum hydride (LiAlH4, see supp. info.). The preparation of polyester was carried out using
6
three different approaches; (a) by conventional heating, (b) by microwave and (c) by coupling
7
microwave and conventional heating.
8 9
Scheme 2: Polycondensation of diester (Dimethyl-9-octadecene-1,18-dioate) and diol
10
(9-octadecene-1,18-diol) in the presence of catalyst (SnCl2 or Ti(OBu)4)
11
Polycondensation by Conventional Heating
12
Firstly, the polycondensation of diester and diol was carried out at 200°C by conventional
13
heating using two different catalysts (SnCl2 and Ti(OBu)4) for different time intervals to explore
14
optimum conditions for polyester preparation as shown in table 4 and S1. Polyesters obtained in
15
the presence of both catalysts for different time intervals are of almost similar molecular weight
16
having their melting temperatures (Tm) in the range of 50-51 oC.
17
11
ACS Paragon Plus Environment
ACS Sustainable Chemistry & Engineering
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
1
Page 12 of 28
Table 4. Polycondensation of diester and diol by conventional heating Entry
Catalyst
Time (h)
Tm (oC)
∆Hm (J/g)
1
2% SnCl2
8
51.6
85.4
2
2% SnCl2
16
50.0
78.8
2
Melting temperatures and melting enthalpy (∆Hm) of polyesters obtained by conventional
3
heating were determined by DSC as shown in table 4 and S1. A very slight difference in the Tm
4
and ∆Hm values of polyesters was observed, which means there is no significant effect of catalyst
5
nature and reaction time interval. However, the melting point of polyesters prepared with
6
unsaturated long-chain monomers is lower than the saturated aliphatic polyesters. Mecking and
7
his colleagues have prepared saturated long-chain C19 3 and C20
8
both of these have 103 oC melting temperature, while the ∆Hm of those saturated polyesters were
9
144 J/g and 178 J/g respectively which are much higher than our synthesized polyesters. The
10
reported high ∆Hm values indicate that these saturated polyesters possess higher degree of
11
crystallization. While in our case, ∆Hm is only 78-88 J/g (table 4 and table S1), which could be
12
attributed to unsaturation of polyesters restricting the free motion of hydrocarbon chains.
13
Therefore, the arrangement of unsaturated long-chain in microstructure is less organized than
14
saturated polyester, which leads to lower degree of crystallization and melting point.
15
Microwave Assisted Polycondensation
16
Microwave-induced polycondensation of diester/diol was carried out in a CEM discover
17
microwave reactor, using open vessel mode under high vacuum (~0.1 bar). Initially, trials using
18
2% Ti(OBu)4 were attempted and only after few seconds of microwave irradiation, blue plasma
19
occurred. The starting materials were charred and glassware was cracked immediately (figure
20
S9a). Initially, it was assumed that under high pressure the microwave energy was mostly
21
absorbed by the polymer debris attached on the vessel wall causing a rapid temperature rise of
22
glassware18. Therefore, the vacuity was reduced (0.7 bar) to decrease polymerization rate and 12
ACS Paragon Plus Environment
10
polyesters and reported that
Page 13 of 28
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Sustainable Chemistry & Engineering
1
avoid energy accumulation. Unfortunately, experiment using Ti(OBu)4 as catalyst failed again
2
with the occurrence of plasma. This was probably due to titanium causing sparking leading to
3
occurrence of plasma. Then SnCl2 was tried as catalyst under ~0.7 bar vacuum and it worked
4
well for polymer preparation without occurrence of any plasma.
5 6
Table 5. Polycondensation of diester/diol using 2% SnCl2 under microwave irradiations at 200°C. Entry
Atmosphere
Time (min)
Tm(oC)
∆Hm(J/g)
1
N2
15
50.9
111.4
2
N2
60
50.6
97.2
60
51.0
108.6
3 *
*
0.7 bar vacuum
7 8
pressure to 0.7 bar.
9
So further microwave assisted reactions were studied using SnCl2 under nitrogen atmosphere and
10
in the absence of inert nitrogen at 0.7 bar vacuum (table 5). The formation of polymer was
11
accomplished within 15 minutes in both cases (figure S9b) compared to polymerization by
12
conventional heating which took longer reaction times. While melting point of polyesters from
13
microwave induced method was also observed in the range of 50-51oC (figure 3, table 5).
14
Slightly lower molecular weight polyester was obtained by microwave heating in comparison to
15
those obtained by conventional heating (figure S10)
16
The molecular masses, strength and stiffness of polyesters prepared by conventional heating and
17
by microwave irradiation were found to be different. It was observed that the polyesters by
18
microwave-assisted method have lower strength and stiffness as compare to those obtained by
19
conventional heating, which could be attributed to entrapped residual methanol, difference in the
20
ratio of monomers used and lower molar mass of polyesters. It was difficult to prepare the film
21
of this polyester for mechanical study, therefore, a coupled method was established, where both
22
microwave and conventional heating were used for polycondensation.
The reaction was performed under nitrogen atmosphere for 15 minutes on a microwave before reducing the
13
ACS Paragon Plus Environment
ACS Sustainable Chemistry & Engineering
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 14 of 28
1
Polycondensation by Coupling Microwave and Conventional Heating
2
In coupled method, initially polycondensation reaction was performed for 15 minute on a
3
microwave reactor at under nitrogen atmosphere. After that, the reaction was continued at
4
reduced pressure (0.7 bar) for particular time intervals (table 6). These microwave assisted
5
polyesters were further heated to 200°C on a hot plate using high vacuum (~0.1 bar). The heat
6
source was removed after 2.5 hours to obtain much stronger and hard polyester with molecular
7
weight approximately equal to the polyester from conventional heating (figure S10). By using
8
this coupled method, the polyester was obtained with molecular weight close to that prepared by
9
conventional heating, where total reaction time was cut down to half compared to
10
polycondensation reaction by conventional heating. Table 6. Polycondensation of diester/diol with 2% SnCl2 (0.7 bar) under microwave conditions
11
*
Entry
T(oC)
1
200
2
*
Tm(oC)
∆Hm(J/g)
15
51.2
100.0
200
30
51.4
96.5
3
200
60
50.1
94.2
4
200
90
51.1
94.6
5
220
15
50.8
103.9
6
220
30
50.9
97.0
7
220
60
50.4
106.5
Time (min)
12 13
pressure to 0.7 bar.
14
Almost all of polyesters prepared by different heating methods displayed glass transitions
15
temperatures at 0 °C or below 0 °C. The polyester synthesized with heating method had Tg of
16
0°C while the polyesters synthesized by microwaves and coupled method using microwaves and
17
conventional heating displayed Tg of ~ -26°C and -1°C respectively. The polyesters also showed
18
similar melting temperatures (Tm) ranging from 50-51°C as have been determined by DSC given
19
in figure 3. The enthalpy (∆Hm) of all synthesized polyesters was also determined from DSC.
20
Higher value of melting enthalpy (∆Hm) for microwave based polyesters was observed as
Each reaction was performed under nitrogen atmosphere for 15 minutes on a microwave before reducing the
14
ACS Paragon Plus Environment
Page 15 of 28
1
compared to those obtained by heating method. As we discussed above, ∆Hm is a valuable index
2
of degree of crystallization. Commonly, for polymers with same compositions and structures, the
3
increase of molecular length will result in more difficulty of crystallization. Though quantitative
4
relation between Mw and ∆Hm cannot be determined, it is generally considered that ∆Hm will
5
decrease with the rise of molecular weight.
0.5
second heating
Exo up
0.0 Heat flow (J/g)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Sustainable Chemistry & Engineering
-0.5 -1.0 -1.5 Ht MW+Ht MW
-2.0 -2.5 -20
0
20
40
60
80 100 120 140 160
Temperature (oC)
6 7 8
Figure 3. DSC curves of polyesters from heating (Ht), microwave irradiation (MW) and coupled methods (MW+Ht). Curves have been offset for clarity.
9
Using ∆Hm as a reference of molecular weight, microwave conditions were optimized by
10
adjusting reaction temperature and time (table 6). At 200°C, ∆Hm decreased continuously with
11
increase of reaction time and remained constant afterwards. However, when the temperature was
12
increased to 220°C, a rise in ∆Hm was observed from 30 to 60 minutes, which might have
13
resulted from polymer degradation (table 6). Thermal degradation of polymer under microwave
14
conditions have been reported by few groups20, 28-29. Hence, high temperature and long reaction
15
times
16
polymerization.
under
microwave
irradiations
are
not
recommended
15
ACS Paragon Plus Environment
for
microwave-assisted
ACS Sustainable Chemistry & Engineering
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 16 of 28
1
The prepared polyesters and monomers were characterized and evaluated with different
2
analytical techniques such as ATR-FTIR, 1H-NMR, GPC, TGA, DSC, DMA and tensile testing.
3
In addition, for polycondensation, the purity level and the ratio of each component are critical
4
factors which directly influence the molecular weight of eventual polymer. Prior to
5
polymerization, the purity and structure of dimethyl-9-octadecene-1,18-dioate (diester) and
6
corresponding diol (9-octadecene-1,18-diol) was confirmed by GC-MS, HRMS and nuclear
7
magnetic resonance spectroscopy (NMR), using both 1H and
8
S1-S4). NMR and FTIR of different polyesters presented similar profiles therefore the NMR and
9
FTIR spectra of polyester (entry 2, table 4) were plotted representatively. The 1H-NMR spectrum
10
of polyester is given in figure 4. All significant peaks associated with different protons have been
11
clearly labeled in the structure of polyester given in figure 4. In addition to these significant
12
peaks, two small peaks at chemical shifts of 3.66 ppm (singlet) and 3.62 ppm (triplet) shown in
13
the expanded region of figure 4 corresponds to terminal hydroxyl and methoxy protons of the
14
polyester. The presence of all these significant peaks and the absence of the hydroxyl and diester
15
methoxy protons of monomers indicated the successful preparation of polyesters.
16
results also support the formation of polyester as shown in figure S5 (supp. info.).
16
ACS Paragon Plus Environment
13
C-NMR analysis (see figure
13
C-NMR
Page 17 of 28
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Sustainable Chemistry & Engineering
1 2
Figure 4. 1H NMR spectrum (400MHz, C2D2Cl4) of polyester.
3
Moreover, ATR-FTIR analysis of diol, diester and polyesters were also performed to further
4
confirm their structure as shown in figure 5. The characteristic absorption bands at 1735 cm-1
5
(-C=O) and 1170 cm-1 (-C-O-C-) of diester have been completely disappeared in the spectrum of
6
diol, which was obtained by reducing diester. In addition to that, the presence of new band at
7
3350 cm-1 affiliated to hydroxyl group indicates the complete conversion of diester into diol. The
8
absence of characteristic hydroxyl band and the presence of absorption bands associated to
9
carbonyl and ether functional groups with higher intensity in the polyester spectrum confirms the
10
successful polycondensation of diester and diol.
17
ACS Paragon Plus Environment
ACS Sustainable Chemistry & Engineering
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 18 of 28
(1)
(2) -OH
(3) C=O (1) diester (2) diol (3) polyester
C-O-C
3500 3000 2500 2000 1500 1000
500
-1
1
wavenumbers (cm )
2 3
Figure 5. ATR-FTIR spectra of (1) dimethyl-9-nonadecene-1,18-dioate, (2) 9-octadecene-1,18-diol, (3) poly(1,18-9-nonadecendiyl-1,18-9-nonadecenedioate).
4
Polyesters displayed very high molecular weight (Mw), when analysed with the help of gel
5
permeation chromatography (GPC) as shown in figure S10 (supp. info.). The polyester prepared
6
by conventional heating displayed slightly higher molecular weight (Mw = 337 KDa, Mw/Mn =
7
7.3) as compared to the polyester obtained by microwave heating (Mw = 275 KDa, Mw/Mn = 8.8)
8
and by coupling microwave and conventional heating (Mw = 315 KDa, Mw/Mn = 9.5). Due to
9
uncontrolled polymerization process, a high polydispersity index (Mw/Mn ) values were observed
10
in all polyesters obtained by different methods.
11
Furthermore, the thermal degradation behavior of diester, diol and selected polyester (entry 2,
12
table 4) was investigated by thermogravimetric analysis (TGA). Polyesters obtained from
13
heating, microwave or coupled method displayed similar TGA curves, therefore, only the curves
14
of polyester from heating method was plotted. Diester and diol displayed initial weight loss at
15
very low temperature (~160°C) as they exist as an individual molecule having less thermal
16
stability and intermolecular forces. It is obvious from figure 6 that compare to diester, diol has 18
ACS Paragon Plus Environment
Page 19 of 28
1
less thermal stability as its volatilization/decomposition took place in the temperature range of
2
160-265°C, while the volatilization/decomposition of diester was observed in temperature range
3
of 160-285°C. This difference in their stability/ weight change behavior can be attributed to their
4
divergent intermolecular interaction as they carry dissimilar functional groups. While the
5
polyester obtained after condensation of diol and diester demonstrated higher thermal stability
6
showing initial weight loss starting at 375°C. The polyester remains under continuous
7
degradation up to 485°C with final weight loss of 100%. The higher thermal stability of polyester
8
and its degradation at higher temperature corresponds to high molecular weight and strength of
9
polyester. 100 diester diol polyester
80
Weight (%)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Sustainable Chemistry & Engineering
60 40 20 0 100
200
300
400
500
600
o
10
Temperature ( C)
11 12
Figure 6. Thermogravimetric analysis (weight % versus temperature) curves of diester, diol and polyester.
13
Mechanical properties of polyesters were studied by preparing films of the powdered materials
14
(hot pressed) using a Carver Press. The polyester obtained by microwave heating was not strong
15
enough to form a film. Therefore, the mechanical and tensile testing results of polyesters 19
ACS Paragon Plus Environment
ACS Sustainable Chemistry & Engineering
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 20 of 28
1
obtained by conventional heating and coupled heating method are reported in supporting
2
information (figure S11, S12 & S13). The polyester obtained by coupled heating method (MW +
3
Ht) demonstrated 2.3 MPa break stress, which is almost half of the maximum break stress (5.5
4
MPa) achieved with polyesters prepared by conventional heating (figure S13). However, the
5
elongation at break of polyester from coupled heating method is up to 11%, which is almost
6
double compared to the polyester obtained by conventional heating method. The higher break
7
stress and less elongation at break (strain) value for polyester obtained by heating method could
8
be attributed to its higher molecular weight making it more strong and rigid as compared to the
9
polyesters from coupled heating method.
10
Dynamic mechanical studies of polyesters were conducted in two different temperature ranges
11
due to dissimilar behavior of polyesters as shown in figure S12. Because of higher rigidity of
12
polyester from heating method, it broke quickly below -50°C, so temperature range for its
13
measurement was set from -50 to 60°C. A slight difference was observed in the storage modulus
14
of both types of polyesters. With the rise of temperature, storage modulus of both polyesters
15
decreases gradually and then above 50°C their storage modulus went down rapidly to zero.
16
Overall polyester from heating method displayed bit higher storage modulus as compare to the
17
one obtained by coupled method.
18
A high decomposition temperature and medium strength was observed for the polyester we
19
synthesized. Nevertheless, the melting point of our synthesized polyester was lower compared to
20
fossil fuel derived synthetic polyesters such as polyethylene terephthalate which has a melting
21
temperature of ~250 oC. The low melting point of this synthesized biopolyester may limit its
22
high temperature applications in its current state. Nevertheless, applications at low temperature,
23
such as packaging could be expected from the biopolyester. For high temperature applications,
24
further crosslinking of -C=C- double bonds is likely to enhance the strength and thermal 20
ACS Paragon Plus Environment
Page 21 of 28
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Sustainable Chemistry & Engineering
1
properties of polyester enormously, which could benefits potential applications in wider
2
temperature range.
3
Conclusion
4
Fully renewable plant oil based polyesters were successfully prepared using conventional and
5
microwave heating from monomers obtained by self-metathesis of FAMEs. Self-metathesis of
6
FAMEs from different sources was completed within 2 min, providing ~50% conversion using
7
microwave technique. The products of self-metathesis were identified and quantified by GC-MS
8
and GC-FID analysis. Similar conversion was achieved within 6 minutes, when HG2 catalyst
9
loading was decreased from 0.05 mol% to 0.01 mol%. Diester was separated from
10
self-metathesis products of FAMEs. Diol with high purity and yield was obtained via reduction
11
of diester. Polycondensation of diester and diol was carried out using conventional heating,
12
microwave irradiation and by coupling microwave and conventional heating. In all cases, the
13
polyesters were prepared successfully, but with slightly different molecular weights. The
14
polyesters were characterized by various analytical techniques including NMR, FTIR, GPC,
15
DSC, TGA, DMA and tensile testing. The polyesters obtained by coupled method (microwave
16
and conventional heating, Mw = 315 KDa) and by conventional heating (Mw = 337 KDa) were of
17
enough strength for film preparation to be used for mechanical study as compared to the
18
polyester obtained entirely by microwave irradiation (Mw = 275 KDa). Higher elongation at
19
break (11%) and lower storage modulus was observed for polyesters using coupled method,
20
while lower elongation at break (6.5%) and higher storage modulus was achieved for polyester
21
by conventional method. By using microwave irradiation, polyesters were obtained in 15
22
minutes, while the coupled microwave and conventional heating method afforded polyester with
23
good strength in 4 hours, which could only be achieved within 8 hours by conventional heating.
21
ACS Paragon Plus Environment
ACS Sustainable Chemistry & Engineering
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 22 of 28
1
Experiment Section
2
Materials
3
High oleic soybean and canola oil samples were kindly provided by Bung Canada. Oleic acid
4
(technical grade) was supplied by Anachemie. Hoveyda-Grubbs catalyst 2nd generation, lithium
5
aluminum hydride, tin(II) chloride, titanium butoxide, silica gel (technical grade, 63-200µm),
6
1,1,2,2-tetrachloroethane-d2, chloroform-d were purchased from Sigma Aldrich. Thin layer
7
chromatography plates (TLC silica gel 60 F254) were from Merck Group.
8
Organic solvents, including tetrahydrofuran (THF) was dried by stirring over CaH2 for three days
9
and then filtered in nitrogen atmosphere., dichloromethane (DCM), methanol, acetone, ethyl
10
acetate and inorganic materials, such as potassium hydroxide, sodium sulfate, sodium hydroxide,
11
sodium sulphate were purchased from Sigma Aldrich. Hexane solvent was purchased from
12
Caledon chemicals. Unless specified, these chemicals were used as received.
13
General Consideration
14
Attenuated Total Reflectance- Fourier Transform Infrared (ATR-FTIR). Spectroscopic analyses
15
were performed on a Nicolet 8700 spectrometer (Madison, WI, USA). For FTIR analysis, the
16
solid or liquid samples were placed directly onto the surface of the ATR crystal and analyzed.
17
Nuclear Magnetic Resonance (NMR). 1H NMR and 13C NMR analyses were carried out at room
18
temperature on Varian INOVA instrument at 400 MHz and 100 MHz frequencies respectively.
19
Gas Chromatography – Flame Ionization Detector (GC-FID). Perkin Elmer GC Clarus 500
20
instrument equipped with fused silica capillary column SP2560 (100 m × 0.25 mm × 0.2 µm film
21
thickness), detector 5975B inert XL MSD and
22
and quantify fatty acid methyl esters (FAMEs) and products from olefin metathesis. Temperature
23
of 280 oC was set for detector and 240 oC for injector. Hydrogen and air gases were used as flow
24
phases at a rate of 450 mL/min and 45 mL/min respectively. A 2 µL sample was injected and
25
20:1 ratio of split mode was selected. Oven temperature was held at 45 oC for 4 min and then
flame ionization detector (FID) was used to identify
22
ACS Paragon Plus Environment
Page 23 of 28
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Sustainable Chemistry & Engineering
1
increased to 175 oC at a rate of 13 oC/min. After holding for 27 min, it was eventually increased
2
to 215 oC at heating rate of 4 oC/min and maintained for 35min.
3
Gas Chromatography-Mass Spectrometry (GC-MS). GC-MS analysis were conducted on Agilent
4
6890N (USA) equipment. The used column and other conditions were set the same as GC-FID.
5
The molecular structures were identified by mass spectroscopy with scanning range of 50-600
6
amu at a rate of 2.66/second. While the microwave assisted reactions were carried out in an open
7
vessel mode microwave reactor (CEM Discover Labmate) equipped with infrared temperature
8
sensor (Maximum pressure = 250 psi, maximum power = 200 W).
9
Differential Scanning Calorimetry (DSC) Measurement. DSC measurements were performed on a
10
TA Instrument (2920 Modulated DSC, USA) in nitrogen atmosphere. Samples (4.0-7.0 mg) were
11
sealed in a pan and were placed into a DSC cell. The thermograms were recorded by heating the
12
samples up to 150oC at a rate of 3 oC/min after equilibrating at -30 oC. DSC data from 2nd heating
13
cycle of samples was reported to eliminate the thermal history of the materials.
14
Thermogravimetric Analysis(TGA). TGA was performed on a Q50 TGA instrument in the
15
presence of nitrogen flow at a rate of 60 ml/min. Samples with 5.0-20.0 mg was taken in a pan
16
and placed in a furnace for analysis. The weight loss/thermal behavior of the samples was
17
recorded by heating the samples up to 600oC at heating rate of 10oC/min.
18
Gel Permeation Chromatography (GPC). The average molecular weights (Mw) of prepared
19
polyesters were determined by Gel permeation chromatography. Styragel HR 4E column (4.6
20
mm × 300 mm) and 2000 ELSD detector were equipped with GPC instrument. The samples with
21
concentration of 0.5 mg mL−1 in THF were used, where THF was used as an eluent with flow
22
rate of 0.5 mL min−1. A series of polystyrene standards was used to calibrate the instrument.
23
Film Preparation. For polyesters film preparation, the polyesters (~1.5g) were crushed in a
24
mortar and then taken on steel plates for compression molding. Carver press was used to press 23
ACS Paragon Plus Environment
ACS Sustainable Chemistry & Engineering
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 24 of 28
1
the samples, where a temperature of 80oC and a pressure of 100 psi were applied for ~8 min. The
2
prepared polyester films were cut into a desired size before their mechanical study.
3
Tensile Testing. The mechanical properties of polyester films were studied by a universal testing
4
machine (autograph AGSX Shimadzu) at room temperature. Both ends of the film were fixed to
5
50N load cell. The film was stretched at a rate of 0.90mm/s until ruptured.
6
Dynamic Mechanical Analysis (DMA). The viscoelastic properties of polyester films were
7
measured using a TA Instrument (DMA Q800). At an oscillatory frequency of 1 Hz with applied
8
deformation of 0.2% during heating, the measurement was carried out in a tensile mode where
9
temperature was programmed from -90 oC to 60 oC at a rate of 2 oC/min.
10
Microwave Assisted Self-metathesis of Different Methyl Esters. Fatty acid methyl esters
11
(FAMEs) derived from oils (2 g) were placed into a 10 mL microwave tube equipped with a
12
stirring bar. HG2 (0.05 mol%) catalyst was weighed and added into the reaction vessel in an
13
inert atmosphere using glove box. A line of nitrogen flow was provided into reaction vial and the
14
reaction was performed on a microwave reactor at a set temperature for required time period.
15
Product mixtures were passed through small column of silica gel to remove the catalyst. A
16
sample with concentration of 0.5 mg/ml in dichloromethane was prepared and run for GC-MS
17
and GC-FID analysis to characterize and quantify the products. The required product component
18
dimethyl-9-octadecene-1,18-dioate (diester) was separated/purified with silica gel column
19
chromatography using 2% ethyl acetate in hexane as an eluent.
20
Polycondensation by Conventional Heating. Equal amounts of diester (0.5 mmol) and diol (0.5
21
mmol) were taken into a 10 mL glass tube and then 2.0 mol% catalyst either SnCl2 or Ti(OBu)4
22
was added. Initially, at reduced pressure (~0.7 bar) the reaction was run at 100 oC and then its
23
temperature was raised gradually from 100oC to 200oC at a heating rate of 10 oC/20 min. The
24
ACS Paragon Plus Environment
Page 25 of 28
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Sustainable Chemistry & Engineering
1
reaction was stopped after 16 hours and the polyesters obtained in yellow colored solid was
2
washed with THF and dried prior to any analysis.
3
Microwave Assisted Polycondensation. Equimolar ratio of diester and diol was taken in a 10
4
ml microwave glass vial and after adding the desired amount of catalyst, the reaction vial was
5
placed in cavity of microwave reactor. The microwave assisted reaction was performed at 200 oC
6
under nitrogen atmosphere for 15 minutes and then at reduced pressure (0.7 bar) for certain time
7
period (table 5). The prepared polyester was washed with THF and dried before proceeding for
8
different analysis.
9
Polycondensation by Coupling Microwave with Conventional Heating. In coupled method,
10
firstly polycondensation of diester and diol was carried out using similar method as mentioned
11
above in microwave assisted synthesis. These microwave assisted polyesters were further heated
12
to 200°C on a hot plate using vacuum (~0.1 bar). The heat source was removed after 2.5 hours.
13
The obtained polyesters were thoroughly washed with THF and dried before proceeding for
14
various analyses.
15
Supporting Information. Contains methodology for preparation of methyl oleate, diol, canola
16
and soybean oil methyl esters, HRMS and 1H NMR of diester and diol, 13C NMR of diester, diol
17
and polyester, GC-MS and GC-FID data of self-metathesis reactions, table for polyesters
18
prepared by cconventional heating using Ti(OBu)4 as catalyst, polyesters film images and their
19
GPC, DMA and mechanical testing results.
20
Acknowledgements. Authors gratefully acknowledge the financial support for current work by
21
The Alberta Innovates Bio Solutions (AI Bio). The plant oils were kindly provided by Bunge
22
Canada, Dupont Pioneer and Soy 2020.
25
ACS Paragon Plus Environment
ACS Sustainable Chemistry & Engineering
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35
Page 26 of 28
References: 1. Bilgen, S., Structure and environmental impact of global energy consumption. Renew. Sustainable Energy Rev. 2014, 38, 890-902. doi: 10.1016/j.rser.2014.07.004 2. Roesle, P.; Stempfle, F.; Hess, S. K.; Zimmerer, J.; Río Bártulos, C.; Lepetit, B.; Eckert, A.; Kroth, P. G.; Mecking, S., Synthetic polyester from algae oil. Angew. Chem. Int. Ed. 2014, 53 (26), 6800-6804.doi: 10.1002/anie.201403991. 3. Quinzler, D.; Mecking, S., Linear semicrystalline polyesters from fatty acids by complete feedstock molecule utilization. Angew. Chem. Int. Ed. 2010, 49 (25), 4306-4308. doi: 10.1002/ange.201001510. 4. Meier, M. A.; Metzger, J. O.; Schubert, U. S., Plant oil renewable resources as green alternatives in polymer science. Chem. Soc. Rev. 2007, 36 (11), 1788-1802. doi: 10.1039/b703294c. 5. Santacesaria, E.; Sorrentino, A.; Rainone, F.; Di Serio, M.; Speranza, F., Oxidative cleavage of the double bond of monoenic fatty chains in two steps: a new promising route to azelaic acid and other industrial products. Ind. Eng. Chem. Res. 2000, 39 (8), 2766-2771. doi: 10.1021/ie990920u. 6. Türünç, O.; Meier, M. A., The thiol‐ene (click) reaction for the synthesis of plant oil derived polymers. Eur. J. Lipid Sci. Technol. 2013, 115 (1), 41-54. doi: 10.1002/ejlt.201200148. 7. Türünç, O.; Meier, M. A., Fatty Acid Derived Monomers and Related Polymers Via Thiol‐ ene (Click) Additions. Macromol. Rapid Commun. 2010, 31 (20), 1822-1826. doi: 10.1002/marc.201000291. 8. Rybak, A.; Fokou, P. A.; Meier, M. A., Metathesis as a versatile tool in oleochemistry. Eur. J. Lipid Sci. Technol. 2008, 110 (9), 797-804. doi: 10.1002/ejlt.200800027. 9. Van Dam, P.; Mittelmeijer, M.; Boelhouwer, C., Metathesis of unsaturated fatty acid esters by a homogeneous tungsten hexachloride–tetramethyltin catalyst. J. Chem. Soc., Chem. Commun. 1972, (22), 1221-1222. doi: 10.1039/C39720001221. 10. Trzaskowski, J.; Quinzler, D.; Bährle, C.; Mecking, S., Aliphatic Long‐Chain C20 Polyesters from Olefin Metathesis. Macromol. Rapid Commun. 2011, 32 (17), 1352-1356. doi: 10.1002/marc.201100319. 11. Mutlu, H.; Hofsäß, R.; Montenegro, R. E.; Meier, M. A., Self-metathesis of fatty acid methyl esters: full conversion by choosing the appropriate plant oil. RSC Adv. 2013, 3 (15), 4927-4934. doi: 10.1039/c3ra40330k. 12. Gedye, R.; Smith, F.; Westaway, K.; Ali, H.; Baldisera, L.; Laberge, L.; Rousell, J., The use of microwave ovens for rapid organic synthesis. Tetrahedron Lett. 1986, 27 (3), 279-282. doi: 10.1016/S0040-4039(00)83996-9.
26
ACS Paragon Plus Environment
Page 27 of 28
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36
ACS Sustainable Chemistry & Engineering
13. Lidström, P.; Tierney, J.; Wathey, B.; Westman, J., Microwave assisted organic synthesis—a review. Tetrahedron 2001, 57 (45), 9225-9283. doi: 10.1016/S0040-4020(01)00906-1. 14. Thanh, G. V.; Loupy, A., Microwave-assisted ruthenium-catalyzed olefin metathesis under solvent-free conditions. Tetrahedron Lett. 2003, 44 (51), 9091-9094. doi: 10.1002/chin.200413050. 15. Appukkuttan, P.; Dehaen, W.; Van der Eycken, E., Microwave-Enhanced Synthesis of N-Shifted Buflavine Analogues via a Suzuki− Ring-Closing Metathesis Protocol. Org. Lett. 2005, 7 (13), 2723-2726. doi: 10.1021/ol050806+. 16. Morris, T.; Sandham, D.; Caddick, S., A microwave enhanced cross-metathesis approach to peptidomimetics. Org. Biomol. Chem. 2007, 5 (7), 1025-1027. doi: 10.1039/b700804j. 17. Bargiggia, F. C.; Murray, W. V., Cross-metathesis assisted by microwave irradiation. J. Org. Chem. 2005, 70 (23), 9636-9639. doi: 10.1021/jo0514624. 18. Nagahata, R.; Sano, D.; Suzuki, H.; Takeuchi, K., Microwave‐Assisted Single‐Step Synthesis of Poly (lactic acid) by Direct Polycondensation of Lactic Acid. Macromol. Rapid Commun. 2007, 28 (4), 437-442. doi: 10.1002/marc.200600715. 19. Cao, H. L.; Wang, P.; Yuan, W. B., Microwave‐Assisted Synthesis of Poly (L‐lactic acid) via Direct Melt Polycondensation Using Solid Super‐Acids. Macromol. Chem. Phys. 2009, 210 (23), 2058-2062. doi: 10.1002/macp.200900231. 20. Velmathi, S.; Nagahata, R.; Sugiyama, J. I.; Takeuchi, K., A Rapid Eco‐Friendly Synthesis of Poly (butylene succinate) by a Direct Polyesterification under Microwave Irradiation. Macromol. Rapid Commun. 2005, 26 (14), 1163-1167. doi: 10.1002/marc.200500176. 21. Ullah, A.; Arshad, M., Remarkably Efficient Microvawe‐Assisted Cross‐Metathesis of Lipids in Solvent Free Conditions. ChemSusChem. 2017, 10 (10), 2167-2174. doi: 10.1002/cssc.201601824. 22. Doll, K. M., Increased functionality of methyl oleate using alkene metathesis. Int. J. Sustain. Eng. 2014, 7 (4), 322-329. doi: 10.1080/19397038.2013.852269. 23. Lehman, S. E.; Schwendeman, J. E.; O'Donnell, P. M.; Wagener, K. B., Olefin isomerization promoted by olefin metathesis catalysts. Inorg. Chim. Acta 2003, 345, 190-198. doi: 10.1016/S0020-1693(02)01307-5. 24. Kohashi, H.; Foglia, T. A., Metathesis of methyl oleate with a homogeneous and a heterogeneous catalyst. J. Am. Oil Chem. Soc. 1985, 62 (3), 549-554. doi: 10.1007/BF02542330. 25. Forman, G. S.; Bellabarba, R. M.; Tooze, R. P.; Slawin, A. M.; Karch, R.; Winde, R., Metathesis of renewable unsaturated fatty acid esters catalysed by a phoban-indenylidene ruthenium catalyst. J. Organomet. Chem. 2006, 691 (24), 5513-5516. doi: 10.1016/j.jorganchem.2006.06.021.
27
ACS Paragon Plus Environment
ACS Sustainable Chemistry & Engineering
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
1 2 3 4 5 6 7 8 9 10 11 12
26. Ngo, H. L.; Jones, K.; Foglia, T. A., Metathesis of unsaturated fatty acids: Synthesis of long-chain unsaturated-α,ω-dicarboxylic acids. J. Am. Oil Chem. Soc. 2006, 83 (7), 629-634. doi:10.1007/s11746-006-1249-0. 27. Beach, N. J.; Lummiss, J. A.; Bates, J. M.; Fogg, D. E., Reactions of Grubbs Catalysts with Excess Methoxide: Formation of Novel Methoxyhydride Complexes. Organometallics 2012, 31 (6), 2349-2356. doi: 10.1021/om201288p. 28. Kéki, S.; Bodnár, I.; Borda, J.; Deák, G.; Zsuga, M., Melt polycondensation of D, L-lactic acid: MALDI-TOF MS investigation of the ring-chain equilibrium. J. Phys. Chem. B 2001, 105 (14), 2833-2836. doi: 10.1021/jp003581n. 29. Brunel, R.; Marestin, C.; Martin, V.; Mercier, R.; Schiets, F., Assisted microwave synthesis of high molecular weight Poly (ArylEtherKetone)s. High Perform. Polym. 2008, 20 (2), 185-207. doi: 10.1177/0954008307079617.
13 14 15 16
Page 28 of 28
For Table of Contents Use Only
17
Synopsis:
18
The current study describes rapid synthesis of unsaturated α, ω-bifunctional aliphatic monomers
19
(diester & diol) from plant oils using microwave-assisted self-metathesis and fully biobased
20
polyesters thereof using polycondensation process.
21
28
ACS Paragon Plus Environment