Programmed photodegradation of polymeric/oligomeric materials derived from renewable bioresources

Article abstract of DOI:10.1002/anie.201408492

Renewable polymeric materials derived from biomass with built-in phototriggers were synthesized and evaluated for degradation under irradiation of UV light. Complete decomposition of the polymeric materials was observed with recovery of the monomer that was used to resynthesize the polymers.

Full text of DOI:10.1002/anie.201408492

Angewandte
Chemie
DOI: 10.1002/anie.201408492
Green Chemistry
Programmed Photodegradation of Polymeric/Oligomeric Materials
Derived from Renewable Bioresources**
Saravanakumar Rajendran, Ramya Raghunathan, Ivan Hevus, Retheesh Krishnan,
Angel Ugrinov, Mukund P. Sibi,* Dean C. Webster,* and Jayaraman Sivaguru*
Abstract: Renewable polymeric materials derived from bio-
mass with built-in phototriggers were synthesized and eval-
uated for degradation under irradiation of UV light. Complete
decomposition of the polymeric materials was observed with
recovery of the monomer that was used to resynthesize the
polymers.
polymers are mainly derived from fossil fuels.[1f] Great
demand with diminishing fossil fuels necessitates finding
alternate sustainable sources for building polymeric materi-
als.[2a] To address the above issues of degradability and
sustainability, we have invested our efforts toward polymer
building blocks from renewable resources with built-in
photocleavable unit(s) to obtain photodegradable polymers
that can be pre-programed for degradation with light. To
showcase our strategy, we have employed an FDCA-derived
polymer that features a nitrobenzyl chromophore to trigger
photo-degradation upon shining light (Figure 1). Our proof of
principle strategy has shown that one can successfully append
triggering units to monomers derived from biomass and
recover them after degradation so that the monomers can be
reused to minimize impact on the environment making the
process both green and sustainable.
I
n the past two decades considerable efforts have been made
to convert biomass especially carbohydrates into value-added
chemicals and as suitable alternates for constantly depleting
fossil fuels. Biomass is inexpensive, abundant, and more
importantly renewable.[1] There are a plethora of reports on
conversion of carbohydrates, glucose or fructose into
a number of industrially important intermediates[2] such as
dimethyl furan,[2c,i] g-valerolactone, ethyl levulinate, capro-
lactam, caprolactone, 1,6-hexanediol, adipic acid, 2,5-bishy-
droxymethyl furan, and 2,5-furandicarboxylic acid (FDCA).
The common key chemical for accessing the chemicals
mentioned above is 5-hydroxymethylfurfural (HMF).[1–3]
FDCA an oxidation product of HMF was identified as an
important building block for polymer synthesis.[4] Due to their
industrial importance, both HMFand FDCA are listed among
the top 14 bio-based chemicals by the U.S. Department of
Energy.[1a] FDCA could possibly replace terephthalic acid in
polyethylene terephthalate (PET), a polyester prepared in
tons every year and the FDCA-glycol polymer has properties
similar to PET.[4a] Though synthetic polymers play vital roles
in daily life, their non/poor-degradability increases concerns
regarding their impact on the environment (as they are mostly
disposed in landfills). In addition, building blocks for
Figure 1. Concept of programmed photodegradation of bio-based
oligomers/polymers derived from FDCA.
[*] Dr. S. Rajendran, R. Raghunathan, Dr. R. Krishnan, Dr. A. Ugrinov,
Prof. Dr. M. P. Sibi, Prof. Dr. J. Sivaguru
Department of Chemistry and Biochemistry
North Dakota State University, Fargo, ND 58108-6050 (USA)
E-mail: mukund.sibi@ndsu.edu
To evaluate the feasibility of our strategy, we first
employed model compounds to establish the reaction con-
ditions and to investigate degradation efficiency and recover-
ability (Scheme 1). We started with established literature
procedures[3g] to convert fructose 1 to furan-based derivatives
that is HMF 2 and FDCA 3 as they are synthetically
accessible (Scheme 1).[3g] These bio-based furan derivatives
were employed both as building blocks for model compounds
and as monomers and were functionalized with 2-nitro-1,3-
benzenedimethanol 6, which served as a phototrigger. We
chose to employ the 2-nitrobenzyl group to establish the proof
of principle for our investigation as it has been widely used as
a phototrigger[5] to evaluate photoresponsive micelles,[6]
hydrogels,[7] and copolymers.[8] In addition, the photo-trigger-
sivaguru.jayaraman@ndsu.edu
Dr. I. Hevus, Prof. Dr. D. C. Webster
Department of Coatings and Polymeric Materials
North Dakota State University, Fargo, ND 58108-6050 (USA)
E-mail: dean.webster@ndsu.edu
[**] This work is based on the support from the National Science
Foundation (grant numbers EPS-0814442 and IIA-1355466) for the
Center for Sustainable Materials Science (CSMS), North Dakota
State University, Fargo, ND 58108-6050 (USA).
Supporting information for this article including syntheses and
characterization of monomers derived from biomass, model
compounds, oligomers/copolymers, irradiation conditions for
photodegradation, and analysis of the photoproducts is available on
the WWW under http://dx.doi.org/10.1002/anie.201408492.
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with the model compounds clearly substantiated that the
strategy of employing a nitrobenzyl trigger for the pro-
grammed degradation of oligomers/polymers derived from 5
(Scheme 1) was indeed viable as we could not only use
monomers derived from biomass but also recover them with
high fidelity.
With the knowledge gained through the photocleavage of
model compounds, we proceeded to synthesize polymer/
oligomers from FDCA 3 that featured the nitrobenzyl
functionality to evaluate the efficiency of photocleavage as
well as the recovery of monomer 3. In a one-pot reaction, 3
was converted to the corresponding acid chloride with thionyl
chloride and reacted with nitrobenzyl phototrigger 6 to obtain
a pale brown solid (Scheme 3). The insoluble product was
Scheme 1. Synthesis of model compounds from renewable materials
for programmed degradation. Bz=benzyl, TIPS=triisopropylsilyl, and
DMF=N,N-dimethylformamide.
ing mechanism of 2-nitrobenzyl functionality is well estab-
lished in the literature.[9]
Scheme 3. Synthesis of polymer/oligomer 11 derived from biomass.
Irradiation of model compounds was carried out in
a Rayonet reactor equipped with sixteen 14-Watt lamps (ca.
350 nm). A known concentration of symmetrically substituted
esters 7a or 7b in a THF/H2O mixture (7a: 1 mm or 0.1 mm
and 7b = 1 mm or 0.1 mm; THF = tetrahydrofurane) was
irradiated at approximately 350 nm (Scheme 2). Progress of
washed with methanol to remove any unreacted monomer.
The product was then triturated followed by the addition of
acetone and CH2Cl2 to remove low-molecular-weight oligo-
mers. The leftover insoluble solid was then washed with
methanol and dried under reduced pressure and was
characterized by FTIR spectroscopy, GPC, powder X-ray
diffraction (PXRD), NMR spectroscopy, thermogravimet-
ric analysis (TGA), and differential scanning calorimetry
(DSC).[10] As the residue was partially soluble in THF at
room temperature, the material was suspended in THF and
sonicated for 5 h. The solution was filtered and the
supernatant was analyzed by GPC (Figure 2B). Inspection
of Figure 2B shows that the material is a mixture of
polymer (Mw = 81000; Mn = 54000 and PDI = 1.5) and
oligomer (Mw = 450; Mn = 340 and PDI = 1.3). The syn-
thetic procedure for accessing the polymer/oligomer 11 was
repeated for reproducibility and characterized by PXRD.
Inspection of the FTIR spectrum of the pale brown solid
(Figure 2A) revealed a strong vibration band at 1739 cmÀ1
indicating an ester functionality. In addition, the presence of
the nitro group was unequivocally established by its charac-
teristic asymmetric and symmetric stretching at 1529 and
1367 cmÀ1, respectively. All these clearly pointed out that the
insoluble solid material 11 was a polymer/oligomer between 3
and 6.
Scheme 2. Photodegradation of model compounds derived from biomass.
A) symmetrical ester 7. B) unsymmetrically ester 9.
the reaction was monitored every 30 minutes by both UV/Vis
1
1
and H NMR spectroscopy. Analysis of H NMR spectra[10]
revealed that the photocleavage of 7a and 7b was very
efficient with excellent mass balance of 89 and 80, respec-
tively. The ortho-nitrobenzyl proton resonance at 5.45 ppm
was used as an NMR handle to monitor the reaction progress.
As expected, we observed the formation of the nitrosoalde-
hyde 8 that was substantiated by the appearance of the
aldehyde proton resonance at 9.17 ppm. The nitrosoalde-
hyde 8 underwent further decomposition to give furan
carboxylic acid 5 (based on the methylene proton resonance
at ca. 4.82 ppm). As the model compound 7 was a symmetri-
cally substituted substrate, we also evaluated the unsym-
metrically substituted ester 9 and found that it underwent
decomposition with equal effectiveness. This proof of study
To further characterize the material obtained from the
condensation of 3 and 6, we made a completely soluble
solution of 11 by heating a suspension in [D6]DMSO at 60–
808C as it was insoluble in common organic solvents (CHCl3,
EtOAc, MeOH) at room temperature. The solution was
1
analyzed by H NMR spectroscopy[10] that showed aromatic
resonances corresponding to the furan and phenyl function-
alities.[10] In addition, two singlet resonances at 5.48 ppm and
5.29 ppm indicated two distinct benzylic functionalities with
2
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24.34% using cristobalite (SiO2) as the
reference standard. Upon heating the
sample to 2008C and cooling 11, there
was a complete loss of crystallinity
with a broad peak in the PXRD
indicating that the sample was likely
amorphous (Figure 2F).
While 11 was not soluble in
common organic solvents, we were
interested in evaluating its photode-
gradability and in gauging the amount
of the monomer that could be recov-
ered for recycling. Photodegradation
of 11 was evaluated as a suspension in
a 4:1 THF/H2O mixture (Scheme 4).
Irradiation of the slurry at about
350 nm resulted in a slightly turbid
solution after 1 h and the solution
became completely transparent after
3 h of light exposure. The irradiated
samples were analyzed by NMR spec-
troscopy that showed complete
decomposition of 11 to give the mo-
nomer, FDCA 3 (Scheme 4). The for-
mation of the parent monomer was
further confirmed by comparing the
NMR spectra of the sample after
irradiation with an authentic sample
of 3 synthesized by an independent
route (Figure 3). Irradiation of 11 was
Figure 2. Characterization of 11 by A) FTIR spectroscopy. B) GPC of 11 synthesized from
a monomer derived from biomass. C) GPC data from recycled monomer, D) TGA, E) DSC, and
F) powder XRD. In the GPC data Mw =Weight average molar mass, Mn =number average molar
mass, and PDI=polydispersity index.
a ratio of about 11:1.[10] The mixture of polymers/oligomers is
consistent with the NMR studies that showed two singlet
resonances for the benzylic protons once again reflecting the
distinct oligomer/polymer compounds present in our system
(consistent with GPC data). TGA analysis of polymer/
oligomer 11 showed that it was thermally stable with no
considerable weight loss up to 2348C (Figure 2D). When the
temperature was increased to 3028C, a 50% weight loss was
observed which is likely because of decomposition of the
Scheme 4. Programmed degradation of 11 as a suspension in a 4:1
THF/water mixture.
polymer/oligomer. Decomposition of the remaining residue
was complete at 6488C. DSC analysis (Figure 2E) of polymer/
oligomer 11 showed a glass-transition temper-
ature (Tg) at 1598C followed by melting at
1848C during the first heating cycle suggesting
that polymer/oligomeric 11 was a mixture of
amorphous and crystalline states.[10] The cooling
cycle showed a slight recrystallization but was
not sharp as expected because of the lack of
crystallinity in the oligomer. The second heat-
ing cycle showed a more discernible Tg at 1138C
suggesting a mostly amorphous oligomer. To
substantiate this observation we analyzed the
synthesized oligomer/polymer 11 by powder
XRD diffraction (PXRD). Closer inspection
of the PXRD data (Figure 2F) indicated that 11
Figure 3. 1H NMR spectra (500 MHz, [D6]DMSO) of polymer 11 A) before irradiation
as synthesized had sharp peaks (2q value) and
the percentage crystallinity was estimated to be and B) after irradiation. C) The authentic FDCA 3.
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also evaluated in solid state
under UV light irradiation
that showed slow degrada-
tion, when compared to
slurry irradiation where com-
plete
degradation
was
observed.[10] Based on recov-
ery after irradiation as
a slurry (THF/H2O = 4:1), 40-
(Æ 5)% of monomer 3 was
isolated. We were also suc-
cessful in recycling the recov-
ered monomer 3 back to the
polymer (Figure 2C) that
highlighted the viability and
practicality of our strategy.[10]
To evaluate if our strategy
can be extended to copoly-
mers incorporating glycols
other than the phototrigger 6,
we synthesized copolymer 12.
In
a
single-pot reaction Figure 4. Characterization of copolymer 12 by a) TGA, b) DSC, and c) GPC.
(Scheme 5), FDCA 3 was
(retention time 9.789 minutes). TGA analysis of the
copolymer 12 showed that it was thermally stable up to
2308C. A weight loss of 13% was observed in the
temperature range of 230–3458C, and a 56% weight loss
was observed in the temperature range of 345–4148C that
likely indicated a decomposition of the co-oligomer/
polymer. The decomposition was complete at 6608C.[10]
The DSC thermogram of 12 showed two glass-transition
temperatures at 123 and 1408C during the first heating
cycle that were likely due to the mixture of copolymers
present in the material that is a FDCA-glycol-nitrobenzyl
copolymer and a FDCA-glycol polymer. There was an
endotherm at 1688C that did not correspond to a melting
point as no visible crystallization exotherm was observed
during the cooling cycle. During the second heating cycle,
a shift in the glass-transition temperature (758C) was
observed that indicated an amorphous material. The DSC
data for 12 was strikingly similar to the one observed for 11
(Figure 2E). Having characterized the copolymer 12, we
proceeded to evaluate its photodegradability. A suspension
of the copolymer mixture in 4:1 THF/H2O was irradiated at
about 350 nm. The turbid solution turned transparent after
irradiation and the solution was concentrated under reduced
pressure. Analysis of the residue by 1H NMR spectroscopy[10]
indicated that the copolymer 12 with the nitrobenzyl unit
photodegraded efficiently. Thus our strategy of employing
phototriggers to degrade oligomers/polymers derived from
biomass was successful with good recoverability of the
monomer.
Scheme 5. Synthesis and photocleavage of copolymer 12.
converted to the corresponding acid chloride with thionyl
chloride and subsequently reacted with a mixture of ethylene
glycol (0.9 equiv) and 6 (0.1 equiv). After the reaction was
complete, methanol was added to the reaction that resulted in
the copolymer 12, which was characterized as before.[10]
Due to the presence of the ethylene glycol unit, copoly-
mer 12 showed a higher solubility than 11 and was partially
soluble in common organic solvents (acetone, CHCl3, DMSO)
at room temperature but was completely soluble in DMSO at
1
758C. H NMR spectroscopic analysis[10] of copolymer 12 in
[D6]DMSO showed proton resonances for the furan function-
ality around 7.39 ppm and the resonances of the nitrophenyl
unit appeared around 7.76 and 5.45 ppm.[10] The proton
resonances of the ethylene glycol units appeared at 4.91,
4.59, 4.28 and 3.65 ppm.[10] FTIR spectra of 12 showed the
ester carbonyl vibration at 1739 cmÀ1 as well as the character-
istic asymmetric and symmetric stretching vibrations of the
nitro group at 1581 and 1308 cmÀ1, respectively.[10] The
copolymer 12 (Scheme 5) was sonicated in THF and the
residue was filtered followed by GPC analysis of the super-
natant. Inspection of Figure 4 shows that the residue is
a mixture of polymer (Mw: 69000; Mn: 47000 and PDI: 1.5),
oligomer (Mw: 1685; Mn: 1275 and PDI: 1.3) and unreacted 6
Our efforts towards addressing degradability of oligo-
mers/polymers derived from biomass-based monomers have
the potential to foster development to address the need to use
renewable resources to build materials that are environ-
mentally benign.[11] While our initial study detailed in this
report is only on model systems, the test of our hypothesis
4
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Romꢂn-Leshkov, C. J. Barrett, Z. Y. Liu, J. A. Dumesic, Nature
2007, 447, 982 – 985.
demonstrated that programmed degradation of oligomers/
polymers derived from biomass is indeed feasible. In addition,
our strategy allowed for recovery of the monomer(s) derived
from biomass and reuse them to build polymers/oligomers.
Our strategy has the potential to build novel materials from
biomass that are degradable with light after usage mitigating
the stress of unwanted chemicals in our environment. Studies
to address these aspects are currently underway in our
laboratories.
[3] a) D. M. Alonso, S. G. Wettstein, J. A. Dumesic, Chem. Soc. Rev.
2012, 41, 8075 – 8098; b) G.-Q. Chen, M. K. Patel, Chem. Rev.
2012, 112, 2082 – 2099; c) M. E. Zakrzewska, E. Bogel-Łukasik,
R. Bogel-Łukasik, Chem. Rev. 2011, 111, 397 – 417; d) A. Corma,
S. Iborra, A. Velty, Chem. Rev. 2007, 107, 2411 – 2502; e) G. W.
Huber, S. Iborra, A. Corma, Chem. Rev. 2006, 106, 4044 – 4098;
f) J. Lewkowski, ARKIVOC 2001, 17; g) J. B. Binder, R. T.
Raines, J. Am. Chem. Soc. 2009, 131, 1979 – 1985.
[4] a) A. Gandini, A. J. D. Silvestre, C. P. Neto, A. F. Sousa, M.
Gomes, J. Polym. Sci. Part A 2009, 47, 295 – 298; b) M. Gomes,
A. Gandini, A. J. D. Silvestre, B. Reis, J. Polym. Sci. Part A 2011,
49, 3759 – 3768; c) A. F. Sousa, M. Matos, C. S. R. Freire, A. J. D.
Silvestre, J. F. J. Coelho, Polymer 2013, 54, 513 – 519; d) M. Jiang,
Q. Liu, Q. Zhang, C. Ye, G. Zhou, J. Polym. Sci. Part A 2012, 50,
1026 – 1036; e) J. Ma, Y. Pang, M. Wang, J. Xu, H. Ma, X. Nie, J.
Mater. Chem. 2012, 22, 3457 – 3461.
Received: August 24, 2014
Published online: && &&, &&&&
Keywords: bio-renewable materials · green chemistry ·
.
photodegradation · phototriggers · sustainable materials
ˇ
[5] a) P. Klꢂn, T. Solomek, C. G. Bochet, A. Blanc, R. Givens, M.
Rubina, V. Popik, A. Kostikov, J. Wirz, Chem. Rev. 2013, 113,
119 – 191; b) C. G. Bochet, J. Chem. Soc. Perkin Trans. 1 2002,
125 – 142; c) H. Zhao, E. S. Sterner, E. B. Coughlin, P. Theato,
Macromolecules 2012, 45, 1723 – 1736; d) J. Jiang, X. Tong, D.
Morris, Y. Zhao, Macromolecules 2006, 39, 4633 – 4640.
[6] a) D. Han, X. Tong, Y. Zhao, Macromolecules 2011, 44, 437 –
439; b) D. Han, X. Tong, Y. Zhao, Langmuir 2012, 28, 2327 –
2331.
[7] a) D. R. Griffin, A. M. Kasko, J. Am. Chem. Soc. 2012, 134,
13103 – 13107; b) P. K. Jain, D. Karunakaran, S. H. Friedman,
Angew. Chem. Int. Ed. 2013, 52, 1404 – 1409; Angew. Chem.
2013, 125, 1444 – 1449.
[1] a) R.-J. van Putten, J. C. van der Waal, E. de Jong, C. B.
Rasrendra, H. J. Heeres, J. G. de Vries, Chem. Rev. 2013, 113,
1499 – 1597; b) M. Besson, P. Gallezot, C. Pinel, Chem. Rev. 2014,
114, 1827 – 1870; c) R. Auvergne, S. Caillol, G. David, B.
Boutevin, J.-P. Pascault, Chem. Rev. 2014, 114, 1082 – 1115;
d) A. A. Rosatella, S. P. Simeonov, R. F. M. Frade, C. A. M.
Afonso, Green Chem. 2011, 13, 754 – 793; e) C. Moreau, M.
Belgacem, A. Gandini, Top. Catal. 2004, 27, 11 – 30; f) K. Yao, C.
Tang, Macromolecules 2013, 46, 1689 – 1712.
[2] a) A. D. Sutton, F. D. Waldie, R. Wu, M. Schlaf, L. A. ꢀPeteꢁ
Silks, J. C. Gordon, Nat. Chem. 2013, 5, 428 – 432; b) O.
Casanova, S. Iborra, A. Corma, ChemSusChem 2009, 2, 1138 –
1144; c) T. Thananatthanachon, T. B. Rauchfuss, Angew. Chem.
Int. Ed. 2010, 49, 6616 – 6618; Angew. Chem. 2010, 122, 6766 –
6768; d) G. A. Halliday, R. J. Young, V. V. Grushin, Org. Lett.
2003, 5, 2003 – 2005; e) H. Zhao, J. E. Holladay, H. Brown, Z. C.
Zhang, Science 2007, 316, 1597 – 1600; f) T. Buntara, S. Noel,
P. H. Phua, I. Meliꢂn-Cabrera, J. G. de Vries, H. J. Heeres,
Angew. Chem. Int. Ed. 2011, 50, 7083 – 7087; Angew. Chem. 2011,
123, 7221 – 7225; g) F. Koopman, N. Wierckx, J. H. de Winde,
H. J. Ruijssenaars, Bioresour. Technol. 2010, 101, 6291 – 6296;
h) X. Tong, Y. Ma, Y. Li, Appl. Catal. A 2010, 385, 1 – 13; i) Y.
[8] J. A. Johnson, M. G. Finn, J. T. Koberstein, N. J. Turro, Macro-
molecules 2007, 40, 3589 – 3598.
[9] a) M. Gaplovsky, Y. V. Ilꢁichev, Y. Kamdzhilov, S. V. Kombarova,
M. Mac, M. A. Schworer, J. Wirz, Photochem. Photobiol. Sci.
2005, 4, 33 – 42; b) Y. V. Ilꢁichev, M. A. Schwçrer, J. Wirz, J. Am.
Chem. Soc. 2004, 126, 4581 – 4595; c) A. P. Pelliccioli, J. Wirz,
Photochem. Photobiol. Sci. 2002, 1, 441 – 458.
[10] Refer to supporting materials.
[11] H. Webb, J. Arnott, R. Crawford, E. Ivanova, Polymers 2013, 5,
1 – 18.
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Communications
Green Chemistry
Biodegradable and recyclable: Renewable
polymeric materials derived from bio-
mass with built-in phototriggers were
synthesized and evaluated for degrada-
tion under irradiation by UV light (see
picture). Complete decomposition of the
polymeric materials was observed with
recovery of the monomer that was used
to resynthesize the polymers.
S. Rajendran, R. Raghunathan, I. Hevus,
R. Krishnan, A. Ugrinov, M. P. Sibi,*
D. C. Webster,*
J. Sivaguru*
&&&& — &&&&
Programmed Photodegradation of
Polymeric/Oligomeric Materials Derived
from Renewable Bioresources
6
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