Poly(aryl ether)s (PAEs) are useful industrial polymers that can be synthesized via nucleophilic aromatic substitution (SNAr). One such PAE is poly(oxy-1,4-phenyleneethynylene-1,4-phenylene) (POPEP) which was polymerized from 4,4-Fluorophenylethynyl phenol (FPEP) via SNAr. The research aimed to characterize POPEP through NMR and TGA analysis and investigate reactions across the alkyne group, such as hydration. POPEP was successfully synthesized with a 55% yield but was insoluble in common NMR solvents. NMR and TGA analysis provided limited characterization. Attemp

1. Poly(aryl ether)s (PAEs) are extremely useful industrial polymers that
contain diphenyl ether links (Ph-O-Ph). Polyether ether ketone (PEEK)
is a notable example of a PAE sub-family, poly(aryl ether ketone)s
(PAEKs), and is used as a highly durable, industrial thermoplastic with
good impact strength and low moisture absorption.1,2
Often PAEs are synthesized via nucleophilic aromatic substitution
(SNAr). During SNAr a strong nucleophile replaces a halogen leaving
group on an aromatic ring with the assistance of an electron
withdrawing group (EWG) substituent (Scheme 1). The EWG allows
for the production of a resonance stabilized intermediate, and
therefore allows the reaction to occur.3
In 1994, Hay and associates4,5 reported that alkyne groups use as EWGs
in SNAr reactions and patented the SNAr polymerization of several
monomers, one of which being 4,4-Fluorophenylethynyl phenol (FPEP)
(Scheme 2). However, no data was provided on the polymer that
resulted from the AB polymerization of FPEP, Poly(oxy-1,4-
phenyleneethynylene-1,4-phenylene)(POPEP).
This research proposes to reexamine a relatively unexplored and
uncharacterized polymer. Specifically, attempt to characterize POPEP
through multiple methods, as well as investigate possible reactions
across the alkyne group.
SNAR POLYMERIZATION AND ATTEMPTED HYDRATION OF POLY(OXY-1,4-PHENYLENEETHYNYLENE-1,4-PHENYLENE)
KEAGAN R. ANDERSON AND THOMAS W. NALLI
WINONA STATE UNIVERSITY, DEPARTMENT OF CHEMISTRY. WINONA MN, 55987
References
(1) Montz, B.; Nalli. T. W. “Preparation of a simple acetylenic poly(aryl ether)”
249th National Meeting of the American Chemical Society, Denver, CO, March
2015. Abstract CHED 1195.
(2) Labadie, J. W.; Hedrick, J.L.; Ueda, M. Journal of the American Chemical
Society 1996, 624, 210- 225
(3) Klein, D. Organic Chemistry; John Wiley & Sons: Hoboken, 2012.
(4) Hay, A.S.; Paventi, M. U.S. Patent 5,374,701, Dec. 20, 1994.
(5) Hay, A.S.; Paventi, M,; Strukelj, M. Macromolecules 1993, 26, 1777-1778.
(6) Vasudevan, A.; Verzal, M. K. Synlett 2004, 631-634.
Ongoing Work
The hydration was most likely unsuccessful due to the
aromatic rings acting as EWGs in the polymer. Upon
reviewing the original literature6, we found that success of
the reaction decreased significantly when EWGs were
attached to the triple bond. In accordance to this finding, the
next adjustment in the microwave hydration reaction will be
to add 2 mol % AuBr3 as a catalyst. Finding an alternative
method of hydration is also a possibility. Another potential
reaction route involves the bromination of the triple bond.
Acknowledgements
I would like to thank Winona State University for an Undergraduate
Research and Creative Projects grant that funded this research and for
providing my education. I would like to acknowledge Composite Materials
Engineering Department for the use of their TGA instrument. Finally, I
would like to thank Dr. Thomas Nalli and Brian Montz for helping guide this
project, as well as Michael Strauss, Sumar Quint, Eden Wilcox, and Zac
Littlefield for sharing their space and their emotional support.
Figure 1: 4,4’-Fluorophenylethynyl phenol (FPEP) 1H NMR (CDCl3 ,
32 scans)
Figure 2: Dissolved portion on Poly(oxy-1,4-phenyleneethynylene-1,4-
phenylene) (POPEP) 1H NMR (THF-d8, 16,000 scans)
Figure 4: Assumed Poly(oxy-1,4-deoxybenzoin) (PODOB) 1H NMR (CDCl3 ,
32 scans)
Figure 3: Poly(oxy-1,4-phenyleneethynylene-1,4-phenylene) (POPEP)
Thermogravimetric Analysis
d c
e b
CHCl3
a
a
b
a/eb/d
c
CHCl3
Results
Conclusion
The AB polymerization of POPEP was successful with a yield of 55%. 1H NMR of the product showed two peaks
at 7.0 and 7.5 that correspond to the polymer, although the peaks were barely above the noise threshold, they
are still indicators of the polymer as the insoluble nature would not lead to a clean reading on an NMR. TGA
found the onset of degradation at 378 ˚C and degradation temperature at 458 ˚C. Examination of the melting
temperature of the polymer exceeded the maximum measureable temperature, but as the heat was increased
the color darken and the polymer became sticker in nature. Finally, attempts to hydrate the triple bond were
carried out using a microwave accelerated technique, and were unsuccessful.
Background
Scheme 1. An Example of SNAr with a ketone EWG and Fluorine leaving group
Scheme 2. The AB Polymerization of FPEP to form POPEP
Discussion
The FPEP monomer was polymerized according to standard SNAr procedure,
and the resulting polymer (POPEP) (0.574 g, 55%) was purified by
thoroughly washing with water, chloroform, and acetone. POPEP was found
to be insoluble in chloroform, water, acetone, and other common NMR
solvents. It was slightly soluble in THF-d8 and a 16,000 scan 1H NMR
(Figure 2) was required to detect the resonances of the aromatic protons
(7.0, 7.5 ppm). These peaks were assigned based on the chemical shifts, to
the hydrogens ortho- to the alkyne and the hydrogens ortho- to the ether
links, respectively. Furthermore, the spectrum matched spectra of POPEP
obtained previously in our lab.1 Due to the high noise level, integration did
not produce any useful values for the calculation of a molecular weight.
Thermogravimetric Analysis (Figure 3), showed the onset of degradation as
not sharply defined possibly due to adsorbed water, entrapped solvents,
and variable degree of polymerization. Due to these conditions, the shoulder
of the curve was used to determine onset of degradation for the polymer
(388 ˚C) with the fastest point of degradation at 458 ˚C.
Additionally, the melting behavior of POPEP was observed on a Fisher-Johns
Melting Point Apparatus. No change was observed up to 200 ˚C (the
maximum temperature for the instrument). At higher temperatures it
darkened in color and became stickier in nature. No other physical changes
were observed and the exact temperature for the discoloration remains
unknown.
POPEP was combined with tosic acid, TBAB, and water (3 mL), and was
heated under microwave irradiation an attempt to hydrate the triple bonds
(Table 1). The study showed for trial 1, extraction of the aqueous layer with
ether followed by solvent removal gave a small yield of substance with the
NMR shown in Figure 4. The spectra appeared to match expectations for the
desired product, poly(oxy-1,4-deoxybenzoin) (PODOB), with peaks at 4.16
ppm assigned to the CH2 and the peaks centered at 6.85 and 7.43 ppm as the
hydrogens on the aromatic rings. However, integrations lead to the
conclusion that only 4% of the triple bonds would have been. Based on the
improbability of such a slight structural modification leading to such a large
change in solubility and inability to repeat these results in subsequent trials,
trial 1 must be discounted and this method of hydration concluded to be
ineffective. A possible explanation for the first trial’s results is contamination
of the flask used to evaporate solvent from a POPEP trimer that was being
synthesized as part of a separate project.
Experimental Methods
Polymerization of FPEP4: FPEP(1.160 g, 5.467 mmol), K2CO3 (0.710
g, 7.71 mmol), anhydrous toluene (30 mL) and NMP (10 mL) were
added to a dry round bottom flask under positive pressure of nitrogen.
The FPEP monomer (98.0%) was purchased from TCI America. The 1H
NMR (Figure 1) established that the monomer did not need further
purification. The flask was then attached to a Dean-Stark reflux
apparatus and heated (~202 ˚C). During this process the toluene and
any excess water was removed via the Dean-Stark Trap. The solution
quickly became a dark green liquid, then transitioned to brown. After 4
hours, the NMP had been distilled into the Dean-Stark trap and a brown
solid, POPEP, was caked onto the flask. The polymer was ground with a
mortar and pestle in presence of water, chloroform, acetone and then
water again in order to remove trapped NMP and inorganic salts. The
polymer was vacuum filtered between before adding the next solvent
and then returned to the mortar. After the four washes, the polymer
was placed in a vacuum oven (48, 90˚C). The yield was 0.574 g (54.7%)
1H NMR (THF-d8; 7.0, 7.5 ppm) (Figure 2) and TGA (378 ˚C, 458 ˚C)
(Figure 3) taken on a TA instruments TGA 2050 thermogravimetric
analyzer.
Attempted Hydration of POPEP6: POPEP (0.197 g, 1.02 mmol), p-
toluenesulfonic acid (TsOH) (0.015 g, 0.008 mmol), tetra-n-
butylammonium bromide (TBAB) (0.322 g, 1.03 mmol), and water (~3
mL) were added to a GlassChemTM pressure tube. A magnetic
microstirbar was then added to the tube and the tube was then sealed
with a torque tool. The solution was then heated in a Microwave
Accelerated Reaction System (MARS) for 30-45 minutes at 165 ˚C. The
solution was left to sit at room temperature for two weeks, then
decanted into an Erlenmeyer flask and extracted twice with diethyl
ether (2 mL each time). The organic layers were removed an combined
in a separate flask, then washed with brine. Then the organic layer was
extracted once more, and dried over sodium sulfate. Finally, the organic
layer was decanted into a 10 mL round bottom flask and was subject to
rotary evaporation to remove the solvent. A small amount of red solid
was left behind, and was characterized with 1H NMR in CDCl3 (Figure
4). Several other attempts at the hydration were made and can be seen
in Table 1.
Melting Point: A small portion of POPEP was tested on a Fisher-Johns
Melting Point Apparatus to try determine any physical changes that
occur during heating. The apparatus was set to 30 percent heating
power, and ran until the thermometer reached its maximum measuring
value at 200 ˚C. After that point, the thermometer was removed, and
qualitative observations were made.