Research Publications

4. Contents lists available at ScienceDirect
European Polymer Journal
journal homepage: www.elsevier.com/locate/europolj
A multifunctionalization of octafluorocyclopentene under mild conditions
Ranganathan Krishnan
⁎
, Anbanandam Parthiban
⁎
Institute of Chemical and Engineering Sciences, Agency for Science and Technology and Research (A*STAR), 1 Pesek Road, Jurong Island, Singapore 627833, Singapore
A R T I C L E I N F O
Keywords:
Octafluorocyclopentene
Nucleophilic substitution reaction
Fluorinated polymers
MALDI-TOF MS
Chain end-groups
A B S T R A C T
Octafluorocyclopentene (OFCP) undergoes multiple substitutions with nucleophiles derived from phenols in a
stepwise manner. The vinylic fluorine atoms at 1 and 5-positions undergoes displacement exclusively in the first
step followed by the displacement of two fluorine atoms, one each at 2 and 4-positions and no further sub-
stitution occurs beyond the tetrasubstitution. Two types of semi-fluorinated linear polymers bearing various
pendant groups were synthesized. In the first type, the polymer chain was formed by substitution at 1 and 5-
positions with bisphenols and pendant groups at 2 and 4-positions. In the second type, the pendant groups were
introduced at 1 and 5-positions first followed by the nucleophilic substitutions at 2 and 4-positions with bi-
sphenols. Azo group (eN]Ne) was one of the functional moieties introduced among the various pendant
groups. Both small organic compounds as well as polymers were thoroughly characterized by various analytical
techniques including 19
F NMR spectroscopy, electrospray ionization time-of-flight mass analysis (ESI-TOF MS),
matrix assisted laser desorption/ionization time-of-flight mass spectroscopy (MALDI-TOF MS), UV–Vis spec-
trophotometric analysis, etc. The stepwise, multiple substitution occurring in OFCP is highly useful for making
semi-fluorinated functional organic compounds and polymers.
1. Introduction
High performance materials derived from fluorine rich organic
compounds (FOC), perfluorinated compounds (PFC) and fluorinated
polymers are applied in many fields such as surfactants [1–3], herbicide
and insecticide formulations [4–6], greases and lubricants [7–9], paint
and coatings [10–12], adhesives [13–15], dielectric materials [16,17],
hydrophobic surfaces and films [18,19], etc. The fluorinated polymers
are also used in polyelectrolytes [20–22] and gas separation mem-
branes [23,24] due to excellent film formation, high thermal stability
and microporous nature of the polymers. Arylene ethers and poly(ar-
ylene ethers) are synthesized by nucleophilic aromatic substitution re-
action between (bis)phenols and halide (X = F, Cl) compounds in the
presence of base. The linear copolymers are obtained by reacting two
bifunctional monomers of the type AA and BB [25–27]. The polymer
architecture such as ladder polymers [28,29] and cyclic ladder poly-
mers [30,31] with microporous structures can be obtained by varying
the reactivity of monomers involved in polycondensation. Highly
fluorinated non-aromatic i.e. alicyclic compounds such as octa-
fluorocyclopentene (OFCP) is very useful to synthesize fluorinated
small organic compounds and poly(arylene ether)s [32–34]. OFCP
contains eight fluorine atoms with 2:4:2 ratios at three positions {(1,5),
(2,4), and (3)} and the reactivity depends on the position of fluorine
atom. The two fluorine atoms (2F) at vinylic positions (1,5) are highly
reactive, while the reactivity of other two fluorine atoms (2F) at allylic
(2,4) positions are moderate whereas the remaining fluorine atoms at
(2,4) and (3) positions (2F,2F) are unreactive [35,36]. This difference
in reactivity enables the synthesis of various symmetrical and un-
symmetrical semi-fluorinated organic compounds in a one-pot, one step
or two step process under mild conditions (room temperature or
above). Due to highly reactive nature of fluorine atoms, the initial bi-
substitution reaction occurs selectively at the vinylic (1,5) position with
two equivalents of nucleophiles. The addition of two more equivalents
of nucleophiles replaces two more (2F) fluorine atoms at allylic (2,4)
positions yielding a tetrasubstituted arylene ethers. Using this metho-
dology, we synthesized a variety of bi- and tetrasubstituted arylene
ether compounds in a one or two step process.
The reaction between OFCP and bisphenols at 1:1 equivalent yields
(1,5) linear polymers. The linear polymers were post-modified with the
addition of two more equivalents of mono-functional phenols (2F re-
placement at (2,4) positions). Earlier we synthesized ladder copolymers
by using bisphenols in place of mono-functional phenols [36] under
mild reaction conditions. Here we report various bi- and tetra-
substituted organic compounds with variety of monohydroxy phenol
compounds. The pre and post modified (2,4) and (1,5) linear polymers
containing various pendant groups under mild conditions.
https://doi.org/10.1016/j.eurpolymj.2018.01.024
Received 31 October 2017; Received in revised form 4 January 2018; Accepted 24 January 2018
⁎
Corresponding author.
E-mail addresses: Ranganathan_Krishnan@ices.a-star.edu.sg (R. Krishnan), A_Parthiban@ices.a-star.edu.sg (A. Parthiban).

6. COVER PICTURE
Jieyan Lim, Barindra Sana,
Ranganathan Krishnan, Jayasree Seayad,
Farid J. Ghadessy, Satyasankar Jana,*
Balamurugan Ramalingam*
&& – &&
Laccase-Catalyzed Synthesis of Low-
Molecular-Weight Lignin-Like
Oligomers and Their Application as
UV-Blocking Materials
The Cover Feature illustrates a laccase-
catalyzed oligomerization of guaiacol
and its analogues, utilizing oxygen as
an oxidant, with a representative mode
of chain growth by dehydrogenative CÀ
C coupling. The promising UV blocking
characteristics of the oligomers is repre-
sented as an umbrella blocking the UV
rays from the sun. The UV spectra show
the differences in the absorption behav-
ior of monomeric vanillyl alcohol and its
oligomer. The natural or bio-derived
oligomers could be sustainable alterna-
tives to conventional synthetic UV sta-
bilizers and attractive to coating, food
packaging, and sunscreen industries.
These oligomeric UV blockers are less
vulnerable to leaching from formulated
polymers or plastics owing to their
larger size. More information can be
found in the Full Paper by Balamurugan
Ramalingam, Satyasankar Jana et al.

9. Polymer
Chemistry
COMMUNICATION
Cite this: Polym. Chem., 2015, 6,
4560
Received 13th March 2015,
Accepted 1st May 2015
DOI: 10.1039/c5py00359h
www.rsc.org/polymers
Soluble, microporous ladder polymers formed by
stepwise nucleophilic substitution of
octafluorocyclopentene†
Krishnan Ranganathan* and Parthiban Anbanandam*
Octafluorocyclopentene (OFCP) has been demonstrated as a non-
aromatic tetrafunctional monomer suitable for making soluble
ladder polymers of intrinsic microporosity. Ladder polymers with a
varying surface area were prepared by reacting one mole of OFCP
with 2 moles of bisphenols of the same or different types. BET ana-
lysis of ladder polymers indicated that the surface area formed is
comparable to that of microporous polymers derived from poly-
imides. MALDI-TOF MS indicated the presence of one OFCP and
two bisphenol moieties in every repeating unit thereby confirming
the presence of ladders in the polymer backbone.
Adsorption and separation of gases and liquids are important
industrial processes where porous materials derived from acti-
vated carbon and zeolites play a significant role. Polymers of
intrinsic microporosity (PIM) have been proposed as suitable
substitutes for the above mentioned nanoporous materials.1,2
Inherent characteristics of polymers such as the ease of tuning
of properties like surface area, pore volume, etc. along with the
ease of processing make them attractive alternatives. Other
than gas separation applications, some of these PIM polymers
bearing pendant –SO3H groups have also been explored as
proton exchange membranes for fuel cell applications.3
Although many classes of porous organic polymers have been
reported, processing of these polymers to form membranes
remains a challenge4
because of the intractable nature of these
polymers.
The synthesis of organosoluble and thus solution process-
able ladder polymers of intrinsic microporosity is an important
development in this area.1,2
One of the methods for preparing
solution processable PIMs is by reacting activated tetrafunc-
tional phenols5
and tetrafunctional fluoroaromatic com-
pounds by nucleophilic aromatic substitution reaction. In
order to fine tune the surface area and porosity characteristics
of these solution processable porous polymers, the scope of
substrates available for making such ladder polymers needs to
be broadened. In this regard, we hereby report the synthesis of
soluble ladder polymers from a non-aromatic tetrafunctional
monomer, octafluorocyclopentene (OFCP), with various
bisphenols at room temperature or above room temperature
(RT – 80 °C). These polymers are characterized using BET ana-
lyses to confirm their porous nature.
Octafluorocyclopentene (OFCP) contains eight fluorine
atoms in 2 : 4 : 2 ratio at three different positions. OFCP has
been reported to undergo nucleophilic substitution at the
vinylic position [1,5] previously by Smith Jr. et al.6
In a sub-
sequent publication, these authors have ruled out the allylic
substitution of OFCP.7
It has also been reported in the litera-
ture that the ratio of vinylic to allylic substitution depends on
factors like ring size, nature of the nucleophile, reaction con-
ditions employed, etc. More importantly, it has been reported
that the formation of the vinyl substituted product as the
major product is always favoured unless the allylic position
has a better leaving group.8
In contrast to the above observations, we have noticed that
OFCP undergoes nucleophilic substitution of vinyl fluorine
atoms in a facile manner under ambient conditions with two
equivalents of (substituted) phenol. Allylic substitution occurs
upon introducing two more equivalents of phenol of the same
or different type at room temperature or above (Scheme 1).
Scheme 1 Stepwise di- and tetra-substitution of OFCP with (substi-
tuted) phenols at RT.
†Electronic supplementary information (ESI) available: Experimental details of
model reaction, linear and ladder polymer synthesis, characterization data of
compounds, gel permeation chromatograms of linear and ladder polymers, and
the nitrogen adsorption/desorption isotherm of ladder polymers. See DOI:
10.1039/c5py00359h
Institute of Chemical and Engineering Sciences, Agency for Science, Technology and
Research (A*STAR), 1 Pesek Road, Jurong Island, Singapore 627833.
E-mail: Ranganathan_krishnan@ices.a-star.edu.sg, a_parthiban@ices.a-star.edu.sg
4560 | Polym. Chem., 2015, 6, 4560–4564 This journal is © The Royal Society of Chemistry 2015

12. Green Processing of Nanofibers for
Regenerative Medicine
Ranganathan Krishnan, Subramanian Sundarrajan,*
Seeram Ramakrishna*
1. Introduction
Regenerative medicine is a method of creating living and
functional tissues and organs in the laboratory and
implanting them into the human body to repair or replace
tissues or organ functions lost due to age, disease, damage,
or congenital defects. This method empowers scientists to
grow tissues and organs in the laboratory and safely
implant them when the body cannot heal itself. Impor-
tantly, regenerative medicine has the potential to solve the
problem of the shortage of organs available for donation
compared to the number of patients that require life-saving
organ transplantation. This approach also solves the
problem of organ transplant rejection, since the organ’s
cells match that of the patient.[1–3]
In this paper, we mainly discuss the electrospinning of
natural and synthetic polymers and their blends using
water or aqueous solution as a media. Some of the polymer
structures used for electrospinning of nanofibers are
Review
Dr. R. Krishnan,[+]
Dr. S. Sundarrajan,[+]
Prof. S. Ramakrishna
Center for Nanofibers and Nanotechnology Lab, Department of
Mechanical Engineering, National University of Singapore,
9 Engineering Drive 1, Singapore 117581, Singapore
E-mail: sundarnus1@gmail.com, seeram@nus.edu.sg
Prof. S. Ramakrishna
National University of Singapore, Nanoscience and
Nanotechnology Initiative (NUSNNI), 2 Engineering Drive 3,
Singapore 117576, Singapore
E-mail: seeram@nus.edu.sg
Dr. R. Krishnan
Current Address: Institute of Chemical and Engineering Sciences
(AÃ
STAR), 1 Pesek Road, Jurong Island, Singapore 627833,
Singapore
Dr. S. Sundarrajan
Current Address: Technology Development Centre, Institute of
Technical Education, ITE College East, 10 Simei Avenue, Singapore
486047, Singapore
[þ]
These authors contributed equally to the manuscript.
Electrospinning of polymer scaffolds is mostly carried out using organic solvents, but the
drawbacks are: solvent costs, environmental hazards, and presence of traces of solvent
impurities. The use of water-soluble polymers (WSPs), water or aqueous solutions as an
electrospinning medium (green processing) is a very attractive method to avoid such issues.
However, a few WSP such as polyelectrolytes are not spinnable as such, but have been
electrospun by addition of WSPs, additives, and salts. This paper covers solution properties,
polyelectrolyte nanofibrous scaffolds
(polysaccharides, biopolymers, etc.),
fabrication through green processing,
and their regenerative medical appli-
cations such as wound dressing, drug
delivery, and tissue engineering. This is
the first review to cover the above
issues, the drawbacks of current
methods, and future challenges.
1034
Macromol. Mater. Eng. 2013, 298, 1034–1058
ß 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com DOI: 10.1002/mame.201200323