Deoxybenzoin-containing polysulfones and polysulfoxides: Synthesis and thermal properties

Article abstract of DOI:10.1016/j.polymer.2015.12.031

Novel poly(arylene ether) sulfones, sulfoxides, and sulfides containing deoxybenzoin subunits were synthesized by step growth polymerization involving bishydroxydeoxybenzoin (BHDB) and the corresponding sulfur-containing monomers. The isolated polymers de

Full text of DOI:10.1016/j.polymer.2015.12.031

Polymer 84 (2016) 59e64
Contents lists available at ScienceDirect
Polymer
journal homepage: www.elsevier.com/locate/polymer
Deoxybenzoin-containing polysulfones and polysulfoxides: Synthesis
and thermal properties
a
b
b
b
Aabid A. Mir , Sebastian Wagner , Roland H. Kr a€ mer , Peter Deglmann ,
Todd Emrick
a
a, *
Polymer Science and Engineering Department, University of Massachusetts, 120 Governors Drive, Amherst, 01003 MA, USA
BASF SE, 67056 Ludwigshafen, Carl-Bosch-Strasse 38, Germany
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Novel poly(arylene ether) sulfones, sulfoxides, and sulfides containing deoxybenzoin subunits were
synthesized by step growth polymerization involving bishydroxydeoxybenzoin (BHDB) and the corre-
sponding sulfur-containing monomers. The isolated polymers demonstrated good solubility in organic
solvents, making them easily processible into transparent, flexible, and creasable films upon solution
casting. All of the polymers prepared exhibited exceptionally low flammability characteristics, with total
heat release (THR) values as low as 6 J/g-K, and char yield values as high as 54%. Inclusion of deoxy-
benzoin monomers into polysulfones with 4,4’-biphenyl led to heat release capacity (HRC) values less
than half that of commercial polysulfones in use today, placing deoxybenzoin-based polysulfones and
polysulfoxides into the ultra-low flammability category.
Received 14 November 2015
Accepted 16 December 2015
Available online 19 December 2015
Keywords:
Deoxybenzoin
Polysulfone
Heat release capacity
©
2015 Elsevier Ltd. All rights reserved.
1
. Introduction
both materials performance and flammability requirements
simultaneously, without the need for additives of any sort. At the
same time, new non-halogenated polymeric additives that reduce
the flammability of commodity polymers without sacrificing per-
formance are also desirable. Each approach represents a significant
challenge that, if met successfully, will contribute towards
improved polymer materials safety.
Polymer flammability represents a pressing and persistent so-
cietal problem of growing importance with increasing global
polymer production, consumption, and waste accumulation [1].
The abundance of synthetic polymers in construction, and trans-
portation vehicles places safety concerns, such as flammability, at a
high priority. Efforts to overcome the inherent flammability of high
volume polymer materials, as well as specialty products, can
improve the safety of polymers and reduce the frequency of fire-
related catastrophic events [2].
Many large volume synthetic polymers are highly flammable,
such as polyethylene, polystyrene, and poly(methyl methacrylate).
Polymers with well-recognized intrinsically low flammability, such
as Teflon and Kevlar, cannot nearly cover the range of materials
applications for which polymer flammability is problematic. Thus,
flame retardant additives, such as halogenated compounds and
inorganic fillers, are employed in many finished polymer products.
However, some additives carry drawbacks, ranging from toxicity to
weakening of mechanical properties and diminished materials
performance. New polymers are thus needed that, ideally, satisfy
Recent efforts to reduce the flammability of polymer materials
range from new polymer syntheses, to additives and blends, to
novel approaches in coating methodology. For example, Grunlan
described environmentally friendly anti-flammable nanocoatings
for textiles using coating techniques on foam that lead to pore
blockage, while fibers coated with a clay-filled flame-retardant film
retained their desired flexibility [3]. Morgan reported the synthesis
and flammability evaluation of new boron- and phosphonate-
containing aromatic flame retardant polymers produced by
metal-catalyzed coupling, and found that adding boronic or phos-
phonic acids significantly lowered the heat release of the materials
as a result of a condensed phase charring mechanism.[ [4e6]] These
polymers were blended with thermoplastic polyurethanes and
evaluated by microscale combustion calorimetry (MCC) to afford
low heat release polyurethane, with the boronic acids giving opti-
mum performance. Wilkie showed that additives such as ammo-
nium sulfamate, sodium diphenylamine-4-sulfonate, and 3-(1-
pyridino)-1-propane sulfonate exhibited flame retardant effects
*
Corresponding author.
E-mail address: tsemrick@mail.pse.umass.edu (T. Emrick).
http://dx.doi.org/10.1016/j.polymer.2015.12.031
032-3861/© 2015 Elsevier Ltd. All rights reserved.
0

60
A.A. Mir et al. / Polymer 84 (2016) 59e64
on both polystyrene and poly(methyl methacrylate).[ [7]] In
another approach, reduction of polyurethane foam flammability
was achieved by carbon nanofiber (CNF) network formation, in
which the network reduces dripping of melted material, and lowers
heat release values. [8] Gilman described polymer nanocomposites
based on nanoclay particles and the formation of a continuous
protective solid carbonaceous layer following burning,[ [9,10]]
while Shen employed borates as flame retardants and smoke sup-
pressants in both halogen-containing and halogen-free polymers.[
recrystallization from acetic acid. Desoxyanisoin, pyridine hydro-
chloride, bis(4-fluorophenyl)sulfone (99%), potassium carbonate,
0
4,4 -thiodiphenol (99%), thionyl chloride and aluminium chloride
0
were purchased from SigmaeAldrich. 4,4 -Biphenol (pu-
rity > 99.0%) was purchased from TCI and used as received. Sulfo-
lane and fluorobenzene were distilled under vacuum prior to use.
Bis(4-fluorophenyl)sulfoxide was synthesized as reported [42] and
purified twice by recrystallization from hexane.
[11e13]] Fire-resistant intumescent coatings protect a range of
2.2. Characterization
materials including wood, textiles and polymer composites, such as
acrylic paints with inorganic flame retardant coating compositions.
Monomer syntheses were monitored by thin layer chromatog-
raphy (TLC) and high performance liquid chromatography (HPLC)
[14] In other approaches, nanoparticles and layer-by-layer (LbL)
1
coatings were applied to the outer layers of thermosets for fire
protection, [15e19] with the LbL approach on fabrics, foams, and
thin films imparting dramatic improvements in anti-drip behaviour
and char formation, while inhibiting flame spread. [20] The
distinction of the approach we describe in this manuscript is seen
in char-forming ability of deoxybenzoin-based structures, despite
its hydrocarbon composition.
eluting with methanol and utilizing UV-detection at 254 nm. H
13
and C NMR spectra were recorded on a Bruker DPX300 spec-
trometer. Thermogravimetric analysis (TGA) was performed on a
ꢀ
Q500 machine (TA Instruments) at a heating rate of 20 C/min
under N2(g) atmosphere (flow rate of 200 mL/min), and TGA values
are reported as the temperature at which 5% weight loss was
observed (T ). Polymer glass transition temperature (T ) was
d g
The selection of deoxybenzoin moieties for the preparation of
low flammability polymers stems from their propensity to undergo
substantive char formation upon burning, thus limiting the escape
of flammable gas as a source of fuel. [21e23] The deoxybenzoin
structure is set up for dehydration at high temperature – under
flash vacuum pyrolysis conditions diphenylacetylenes were noted
to form from deoxybenzoin precursors. [24e26] Such a functional
group transformation in the solid/melt state of a fire would produce
polymeric phenylene ethynylenes that should quickly aromatize,
cross-link, and char. With respect to characterizing polymer flam-
mability, doing so on an experimental (milligram) scale is
extremely useful for probing the potential suitability of novel
polymers prior to scale-up efforts. For example, microscale com-
bustion calorimetry (MCC), an oxygen consumption technique,
identifies the heat release capacity (HRC) and total heat release
determined by differential scanning calorimetry (DSC) on a Q200
machine (TA Instruments) with a heating rate of 10 C/min under
ꢀ
N2(g) atmosphere. Specific heat release rate (HRR, W/g), heat release
capacity (HRC, J/(g-K)), and total heat release (THR, kJ/g) were
measured on a microscale combustion calorimeter (MCC). MCC was
ꢀ
conducted over a temperature range of 80e750 C at a heating rate
ꢀ
3
of 1 C/s in an 80 cm /min stream of nitrogen. The anaerobic
thermal degradation products in the nitrogen gas stream mix with
a 20 cm /min stream of oxygen prior to entering the combustion
3
ꢀ
furnace (900 C). Heat release is quantified by standard oxygen
consumption, [39,40] and HRR is obtained from dQ/dt at each time
interval and from the sample mass employed (5 mg). HRC is ob-
tained by dividing the maximum HRR by the heating rate. Polymer
molecular weight was measured by gel permeation chromatog-
ꢀ
raphy (GPC) in DMF with 0.01 M LiCl at 50 C and calibrated against
(
THR) of polymers, both key parameters for predicting polymer
poly(methyl methacrylate) (PMMA) standards. GPC was operated
at an eluent flow rate of 1 mL/min with a Sonntek K-501 pump, one
50 ꢁ 7.5 mm PL gel mixed guard column, one 300 ꢁ 7.5 mm PL gel
flammability in large scale tests, such as the widely implemented
UL-94 test. [27e29] The bisphenol of deoxybenzoin, termed bish-
ydroxydeoxybenzoin (BHDB), has now been integrated into several
polymer compositions, including polyesters, polyurethanes and
epoxy networks, [21,30e32] each giving materials with distinctly
low HRC and THR values, while a BHDB-containing polyester was
characterized as having a 5 VA rating in the UL94 test, indicative of
a very low flammability possessed by a material under these test
conditions.
High performance polymers such as polyetherketone (PEK) and
polyethersulfone are known for their thermal stability and flame
resistant properties. [33,34] Nonetheless, with increasingly
rigorous flammability standards, [35e37] we wanted to examine
whether the properties of such polymers could be improved further
by integrating deoxybenzoin moieties into these structures. This
would require compatible polymerization chemistry of the deox-
ybenzoin monomers with the selected sulfur-containing mono-
mers, such as nucleophilic displacement chemistry performed on
the corresponding aromatic difluorides. Examples of polymers that
proved amenable to inclusion of deoxybenzoin in the structure are
described in this manuscript, as shown in Fig. 1 for deoxybenzoin-
containing sulfones 1, sulfoxides 2, and sulfone/sulfide copolymers
5
mm mixed C column, one 300 ꢁ 7.5 mm PL gel 5
mm mixed D
column, and using a Knauer refractive index detector (K-2301) and
an Alltech model 3000 solvent recycler.
2.3. Synthesis of 4,4’-bishydroxydeoxybenzoin 4 (BHDB)
BHDB was prepared according to a published procedure.[38] In
short, desoxyanisoin (100 g, 390 mmol) and pyridine hydrochloride
(180 g, 1.56 mol) were added to a round bottom flask equipped with
a condenser and magnetic stir bar. The mixture was refluxed at
ꢀ
200 C for 5 h, cooled to room temperature, poured into cold water,
filtered, and crystallized from acetic acid to afford BHDB as an off-
ꢀ
1
white crystalline solid (76 g, 85%), mp 210e212 C. H NMR (DMSO-
, 300 MHz): 10.35 (s, 1H, OH- AreCO), 9.28 (s, 1H, OH-Ar-CH ),
d
6
d
2
7.91 (d, 2H), 8.7 (AreH), 7.04 (d, 2H), 8.5 (AreH), 6.84 (d, 2H), 8.7
(AreH), 6.68 (d, 2H), 8.5 (AreH), 4.11 ppm (s, 2H, AreCOeCH2-Ar).
13
C NMR (DMSO-d
6
): d 196.5, 162.3, 156.2, 131.3, 130.7, 128.1, 125.9,
115.5, 115.4, 43.7 ppm.
2.4. Synthesis of polysulfone 1
3
2
2
.
To a 100 mL three-necked, roundbottom flask equipped with a
Dean Stark trap, condenser, magnetic stirrer, and nitrogen inlet was
added BHDB (2.280 g, 10 mmol), bis(4-fluorophenyl)sulfone (2.60 g,
. Experimental
.1. Materials
2 3
10.2 mmol), anhydrous K CO (1.40 g, 10.2 mmol), sulfolane (9.5 g),
and toluene (10 mL). The mixture was heated to remove water from
toluene by azeotropic distillation. The resulting mixture was stirred
BHDB was prepared from desoxyanisoin [38] and purified by

A.A. Mir et al. / Polymer 84 (2016) 59e64
61
O
O
O
O
O
S
O
S
O
n
O
O
1
n
2
O
O
O
S
O
O
S
O
S
O
O
0.5
O
0.5
3
Fig. 1. Chemical structures of deoxybenzoin-containing polymeric sulfones 1, sulfoxides 2, and sulfone/sulfide copolymers 3.
ꢀ
ꢀ
at 160e180 C for 2e3 h. When the mixture became too viscous to
was added, and stirring was continued at 180 C for 30 min. The
mixture was then cooled to room temperature and diluted with
dichloromethane. This solution was poured into methanol (200 mL)
containing acetic acid (2 mL), which resulted in precipitation of the
polymer. The precipitated polymer was collected by filtration and
redissolved in dichloromethane. The dichloromethane solution was
filtered through a thin layer of Celite to remove inorganic salts, and
the polymer was purified further by precipitation into methanol.
Polymer 9 was collected by filtration and dried under vacuum at
allow stirring, an additional 2e3 g of sulfolane was added, and
stirring was continued at 180 C for 30 min. The mixture was cooled
to room temperature and diluted with dichloromethane. This so-
lution was poured into methanol (300 mL) containing acetic acid
2 mL), which resulted in precipitation. The precipitated polymer
was collected by filtration and redissolved in dichloromethane, and
the solution was filtered through a thin layer of Celite to remove
inorganic salts. This solution was added to methanol for precipi-
tation. Polymer 1 was collected by filtration and dried under vac-
uum at 80 C for 24 h to afford a white fibrous material (4.20 g, 95%
yield). H NMR (CDCl
.00e7.40 (m, 8H, AreH), 7.28e7.30 (d, 2H, AreH), 7.84e7.97 (m,
H, AreH), 8.05 (d, 2H). C NMR (CDCl
19.34, 120.54, 130.09, 131.09, 132.629, 135.45, 136.72, 153.87,
55.06, 159.44, 160.28, 161.85, 195.98 ppm. FT-IR (cm ): 3078,
677, 1579, 1486, 1408, 1291, 1234, 1102, 1009, 993, 871, 832, 685.
18400, M 57000, PDI 3.1.
ꢀ
(
ꢀ
1
80 C for 24 h to afford white fibrous polymer (2.0 g, 95% yield). H
NMR (CDCl , 300 MHz): 4.30 (s, 2H, AreCOeCH -Ar), 7.12e7.29
(m, 19H), 7.60 (s, 4H), 7.92e8.01 (m, 10H). C NMR (CDCl
(CH2eCO),117e120,129e137, 153e154,159e161,196. FT-IR (cm ):
3068, 1678, 1582, 1484, 292, 1233, 1163, 1103, 1007, 830, 686. M
34000, M 64000, PDI 1.9.
ꢀ
3
d
2
1
13
3
, 300 MHz):
d
4.29 (s, 2H, AreCOeCH2-Ar),
3
):
d
44.52
ꢂ1
7
4
13
3
): 44.41, 115.56, 117.84,
n
1
1
w
ꢂ1
1
2.7. Representative synthesis of copolymer 10
M
n
w
To a 25 mL three-neck round bottom flask equipped with a Dean
2.5. Synthesis of polysulfoxide 2
Stark trap, condenser, magnetic stirrer, and N2(g) inlet was added
BHDB (0.570 g, 2.5 mmol), 4,4’-thiodiphenol (0.545 g, 2.50 mmol),
To a 25 mL three-necked, roundbottom flask equipped with a
2 3
bis(4-fluorophenyl)sulfone (1.271 g, 5.00 mmol), anhydrous K CO
Dean Stark trap, condenser, magnetic stirrer, and N2(g) inlet was
added BHDB (1.14 g, 5.00 mmol), bis(4-fluorophenyl)sulfoxide
(0.76 g, 5.5 mmol), sulfolane (4.5 g), and toluene (5 mL). The
mixture was heated to remove water from toluene by azeotropic
distillation, then heated at 160e180 C for 2e3 h. When the
ꢀ
(
1.19 g, 5.00 mmol), anhydrous K
2
CO
3
(0.71 g, 5.2 mmol), sulfolane
(
4.5 g), and toluene (5 mL). The mixture was heated to remove
mixture became too viscous to stir, an additional 2 g of sulfolane
was added, and stirring was continued at 180 C for 30 min. The
ꢀ
water (from toluene) by azeotropic distillation. The resulting
mixture was heated at 170e180 C for 15 h. When the mixture
became viscous it was cooled to room temperature and diluted
with dichloromethane. This solution was poured into methanol
ꢀ
mixture was then cooled to room temperature and diluted with
dichloromethane. This solution was poured into methanol (200 mL)
containing acetic acid (2 mL), which resulted in precipitation. The
precipitated polymer was collected by filtration and redissolved in
dichloromethane, and this solution was filtered through a thin layer
of Celite to remove inorganic salts. The polymer was purified
further by precipitation into methanol, then collected by filtration
(
200 mL) containing acetic acid (2 mL), which resulted in precipi-
tation. The precipitated polymer was collected by filtration and
redissolved in dichloromethane, and the solution was filtered
through a thin layer of Celite to remove inorganic salts. The poly-
mer was purified further by precipitation into methanol. Polymer 2
was collected by filtration and dried under vacuum at 80 C for 24 h
to afford white fibrous polymer. (1.72 g, 80.6% yield). H NMR
ꢀ
and dried under vacuum at 80 C for 24 h to afford a white fibrous
ꢀ
1
material (2.01 g, 92% yield). H NMR (CDCl
3
, 400 MHz): 4.33 (s, 2H,
1
AreCOeCH2-Ar), 7.01e7.13 (m, 16H, AreH), 7.28e7.31 (d, 2H,
(
CDCl
3
, 300 MHz): 4.27 (s, 2H, AreCOeCH2-Ar), 6.90e7.26 (m, 10H,
J ¼ 12), 7.36e7.38 (d, 4H, J ¼ 8), 7.85e7.95 (m, 8H, AreH), 8.06e8.08
13
13
AreH), 7.56e7.69 (m, 4H), 8.03e8.06 (d, 2H, AreH). C NMR
(
1
(d, 2H, J ¼ 8). C NMR (CDCl
3
): 45.50, 119.30, 120.66, 121.97, 131.33,
CDCl
3
): 44.50, 116.85, 118.22, 120.14, 127.09, 131.03, 138.71, 140.56,
132.84, 134.45, 136.58, 155.38, 161.24, 163.50, 197.30 ppm. FT-IR
ꢂ1
ꢂ1
54.61, 158.21, 160.53, 195.99 ppm. FT-IR (cm ): 3060, 1675, 1597,
(cm ): 3078, 1678, 1578, 1481, 1233, 1175, 1103, 1009, 829, 691.
1
504, 1483, 1087, 1041, 871, 829. M
.6. Representative synthesis of copolymer 9
To a 25 mL three-necked, roundbottom flask equipped with a
n
13400, M
w
43500, PDI 3.2.
n w
M 48,100; M 128,000; PDI 2.6.
2
3. Results and discussion
0
4,4 -Bishydroxydeoxybenzoin (BHDB), prepared readily by
Dean Stark trap, condenser, magnetic stirrer, and nitrogen inlet was
added BHDB (0.570 g, 2.50 mmol), 4,4 -biphenol (0.465 g,
demethylation of desoxyanisoin in neat pyridine hydrochlo-
ride,[38] was utilized in step growth polymerization with sulfur-
containing aromatic monomers. Scheme 1 shows the polymeriza-
tion of BHDB with the selected sulfur-containing aromatic
difluorides, accomplished by nucleophilic aromatic substitution in
aprotic solvents using potassium carbonate as base and sulfolane as
a stable, high boiling solvent.
0
2
.50 mmol), bis(4-fluorophenyl)sulfone (1.270 g, 5.00 mmol),
anhydrous K CO (0.72 g, 5.2 mmol), sulfolane (4.2 g), and toluene
5 mL). The mixture was heated to remove water from toluene by
2
3
(
ꢀ
azeotropic distillation and stirred at 160e180 C for 3e4 h. When
the mixture became too viscous to stir, an additional 2 g of sulfolane

62
A.A. Mir et al. / Polymer 84 (2016) 59e64
16000
O
n
HO
n
F
X
F
14000
12000
OH
4
5
X = SO2
10000
6
X = SO
Mn 8000
K CO
2
O
3
6000
O
sulfolane
70 °C
O
X
4000
2000
0
n
1
1
X = SO2
2
X = SO
0
5
10
15
Time (hrs)
Scheme 1. Polycondensation of BHDB with difluoroaromatic sulfone and sulfoxide
monomers 5 and 6.
Fig. 2. Plot of number-average molecular weight as a function of time (hrs) for poly-
sulfoxide 2.
Polysulfone 1 was synthesized by polycondensation of BHDB
and bis(4-fluorophenyl)sulfone in sulfolane to afford polymer
creasing without inducing damage. The relative ratio of the two
0
products with relatively high molecular weight (M
n
approaching
bisphenols (4,4 -thiodiphenol and BHDB) incorporated into poly-
1
5
0 kDa) relative to PMMA standards. These solution polymeriza-
sulfone 10 was calculated by integration of the solution H NMR
ꢀ
tions were conducted at 170e180 C for 2e3 h using magnetic
stirring under a N2(g) atmosphere. While other polar aprotic sol-
vents, such as dimethylsulfoxide (DMSO) or N-methylpyrrolidone
spectra. For example, the singlet at
methylene protons of the deoxybenzoin was integrated against the
resonance at 7.36 ppm for the four aromatic protons adjacent to
d 4.33 ppm representing the two
d
0
13
(
NMP) could be used, sulfolane was preferred for the high reaction
the sulfur of 4,4 -thiodiphenol. C NMR spectroscopy showed
signals at 197.3 and 45.5 ppm, representing the deoxybenzoin
carbonyl and methylene groups, respectively. Infrared spectroscopy
confirmed the expected carbonyl content in the copolymer, with
temperatures it allows, and toluene (10 mL) was added to the re-
action mixture to afford an anhydrous system by its azeotropic
distillation with water. The polymerization mixture was heated to
ꢂ1
ꢀ
ꢀ
1
40e150 C while stirring for 2 h, then to 180 C under constant
characteristic stretching at 1678 cm , and additional bands at
ꢂ1
ꢂ1
purging with N2(g). The mixture was cooled to room temperature,
diluted with dichloromethane, and precipitated into methanol/
acetic acid. The precipitated polymer was collected by filtration,
redissolved in dichloromethane, and filtered through Celite to
remove inorganic salts. The polymer was purified further by pre-
1163 cm
and 1103 cm
reflecting the sulfone functionality.
Molecular weights and polydispersity indices (PDI, Mw/Mn) of
these polymers were measured by GPC in DMF against PMMA
standards (Table 1). In the samples used for GPC in Fig. 4 (plotting
retention time vs. refractive index intensity), polymer 10 had an
estimated Mn of 48,100 g/mole, and polymer 9 34,000 g/mole, with
respective PDI values of 2.6 and 1.9 that are typical outcomes of step
growth polymerization.
cipitation into methanol, then isolated by filtration as a white
1
fibrous material. H NMR spectroscopy of polysulfone 1 in CDCl
3
showed a signal for the methylene protons of BHDB at 4.30 ppm,
13
while C NMR revealed the carbonyl carbon resonance of the
deoxybenzoin moiety at 196 ppm, a signal at 44.5 ppm for the
methylene carbon, and aromatic resonances from 115 to 162 ppm.
Aromatic polysulfoxides 2 were synthesized similarly, using bis(4-
fluorophenyl)sulfoxide as the sulfoxide monomer, which was syn-
thesized by FriedeleCrafts acylation of fluorobenzene with thionyl
chloride.[42].
Thermal characterization and heat release measurements. All of
the synthesized polymers exhibited a glass transition temperature
(Tg) indicative of an amorphous or glassy morphology. The pres-
ence of deoxybenzoin reduced the Tg relative to a commercially
ꢀ
available poly(aryl ether) (220 C) [43]: for example copolymers 9
ꢀ
and 10 had Tg values of 200 and 172 C respectively, whereas
ꢀ
polymers 1 and 2 showed Tg values of 173 and 150 C (Table 1).
The polymerization of BHDB with bis(4-fluorophenyl)sulfone
was conducted over 2 h to afford polysulfone 1 of molecular weight
Mn 18,400 and Mw 57,000 (Mn ¼ number-average molecular
weight; Mw ¼ weight-average molecular weight). Under similar
conditions, BHDB polymerization with sulfoxide 6 affording poly-
sulfoxide 2 proceeded more slowly, requiring 15 h to afford poly-
mer samples of Mn 13,400 and Mw 43,500. The faster
polymerization in the sulfone case is attributed to its greater
electron withdrawing capacity and CeF bond activation. [41,42] The
temporal evolution of molecular weight was monitored by gel
permeation chromatography (GPC) against PMMA calibration
standards, performed on aliquots taken at several time intervals
during the course of the polymerization (shown in Fig. 2 for poly-
sulfoxide 2).
These deoxybenzoin-containing polymers exhibit significant ther-
ꢀ
mal stability, with decomposition temperatures in the 375e470 C
range at 5% weight loss. The presence of deoxybenzoin in the
polymer backbone impacts decomposition onset, T
d
, as shown in
ꢀ
Fig. 5. Char yields at 800 C, revealed by TGA measurements, for
deoxybenzoin-containing polysulfone 1 and polysulfoxide 2 were
42% and 54%, respectively, whereas char yields of the polysulfone
copolymer 9 and polysulfone-sulfide copolymer 10 were 46% and
43% respectively.
Thermal characterization of these sulfur-containing deoxy-
benzoin polymers revealed exceptionally low heat release capacity
ꢂ1 ꢂ1
(HRC) values of <70 J g
K , and a total heat release (THR) of
<7 kJ/g. This data, obtained by pyrolysis combustion flow calo-
rimerty (PCFC), an oxygen consumption technique, places these
novel deoxybenzoin containing polymers in the ultra-low flam-
mability category, despite the absence of halogen in the structure.
Similarly constructive data was obtained in PCFC analysis:
polymer 2, having a char yield of 54%, exhibited HRC of 66 J/g-K and
THR of 6.5 kJ/g, a significant reduction relative to the commercially
available homopolymer (polymer 9 (m ¼ 0) has a reported HRC of
228 J/g-K and THR of 13.5 K J/g (Table 2). [44] Pyrolysis combustion
flow calorimetry (PCFC) revealed that the HRC and THR values of
the new polymers prepared decreased significantly with increasing
incorporation of deoxybenzoin moieties (defining HRC as the
Copolymerization of BHDB with bis(4-fluorophenyl)sulfone and
4
,4’-biphenol or 4,4’-thiodiphenol (Scheme 2) was performed in
sulfolane in the presence of potassium carbonate to afford the
desired polymers 9 and 10. The polymer products were soluble in
common organic solvents, and casting from ~2 to 5 mg/mL
dichloromethane solution produced transparent flexible films, such
as seen for polysulfone 10 in Fig. 3.
These films exhibited excellent properties, judged qualitatively,
with apparent transparency and amenability to manual folding and

A.A. Mir et al. / Polymer 84 (2016) 59e64
63
O
O
K CO
2 3
m HO
n
HO
Ar
OH
m+n
F
S
F
OH
sulfolane
4
O
5
7
8
: Ar =
: Ar =
S
O
O
S
O
S
O
O
O
m
Ar
O
O
O
n
9
: Ar =
1
0 : Ar =
S
Scheme 2. Copolymerization of BHDB with aromatic monomers 5,7 and 8.
1
3
2
1
00
00
00
0
2
9
1
0
9
12
15
18
Retention Time (minutes)
Fig. 4. Overlaid GPC traces of polymers 1, 2, 9, and 10 (y-axis is the refractive index (RI)
response).
1
00
1
Fig. 3. Solution cast film of deoxybenzoin-containing polysulfone 10.
2
9
8
0
10
Table 1
Data obtained for deoxybenzoin-containing polymers and copolymers with 4,4’-
biphenol and 4,4’-thiodiphenol.
a
b
c
M c
(g/mole)
PDIc
Polymer
m
n
X
T
(
g
ꢀ
T
d
ꢀ
M
n
w
60
C)
( C)
(g/mole)
1
2
9
0
0
0.5
0.5
1
1
0.5
0.5
SO
SO
SO
SO
2
173
150
200
172
452
375
439
468
18400
13400
34000
48100
57000
43500
64000
3.1
3.2
1.9
2.6
4
0
2
2
1
0
128000
a
ꢀ
Obtained by DSC in N
Measured by TGA in N
2
at a heating rate of 10 C/min.
0
200
400
600
o
800
b
ꢀ
2
at a heating rate of 20 C/min; T
d
¼ 5% weight loss
Temperature ( C)
2
temperature in N .
c
ꢀ
Determined by GPC in DMF at 1.0 mL/min at 50 C calibrated with PMMA
Fig. 5. TGA analysis (weight loss versus temperature) of polymers 1, 2, 9, and 10 under
standards.
N2(g) atmosphere.
maximum heat released divided by the heating rate). Describing
these systems in terms of HRC eliminates reliance on heating rate
that is typical of standard flammability measurements, rendering
HRC a characteristic material property.[27e28]. THR is the total
heat of complete combustion of the pyrolysis products per initial
mass of the sample. Low HRC and THR values are thus useful in-
dicators of flame retardancy, and predict non-flammable behavior
in larger scale tests.[29] Microscale combustion calorimetry (MCC)
characterization of the aromatic deoxybenzoin polysulfones 1 and
while polysulfone copolymer 9 containing deoxybenzoin as a
comonomer with equal molar amounts of 4,4’-biphenyl exhibited
ꢂ1 ꢂ1
HRC of 86 Jg
K
and THR of kJ/g. (Fig. 6) Thus, introduction of
deoxybenzoin into a polyphenylsulfone backbone leads to a sub-
stantial HRC reduction (Table 2) relative to a commercial poly-
phenylsulfone, [44] and opens opportunities for the use of these
polymers in materials applications that benefit from low flamma-
bility plastics.
In summary, we described the integration of deoxybenzoin-
based monomers into sulfur-containing polymers, affording novel
poly(aryl ether deoxybenzoin) sulfone, sulfoxide and sulfide
ꢂ1
ꢂ1
polysulfoxides 2 revealed HRC values of 120 Jg
K
and
ꢂ1 ꢂ1
6
6 Jg
K , and THR values of 10 kJ/g and 6.5 kJ/g, respectively,

64
A.A. Mir et al. / Polymer 84 (2016) 59e64
Table 2
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Heat release capacity (HRC), total heat release (THR), and charring properties of
deoxybenzoin-containing polymers and commercial polyether sulfone.
3926e3931.
Entry Polymer
m
n
X
HRC
THR
[KJ g
Char
[%]
[6] A.B. Morgan, S.P. Putthanarat, Polym. Degrad. Stab. 96 (2011) 23e32.
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ꢂ1 ꢂ1
ꢂ1
a
[
J g
K
]
]
[
8] (a) M. Zammarano, R. Kramer, R. Harris, J. Thomas, J.R. Shields, S.S. Rahatekar,
1
2
3
4
5
BHDB-sulfone (1)
0
0
1
1
SO
SO
2
120
66
86
138.5
228
10
6.5
8
10.7
13.5
42
54
46
43
c
S. Lacerda, J.W. Gilman, Polym. Adv. Technol. 19 (2008) 588e595;
BHDB-sulfoxide (2)
BHDB/biphenyl (9)
BHDB/sufide (10)
Poly (aryl ether) (9)b
(b) J.W. Gilman, C.L. Jackson, A.B. Morgan, H. Richard, Chem. Mater 12 (2000)
0.5 0.5 SO
0.5 0.5 SO
0
2
2
2
1866e1873.
[9] J.W. Gilman, T. Kashiwagi, Nanocomposites:
retardant approach,
A revolutionary new flame
b
b
1
SO
SAMPE J. 33 (1997) 40e46.
a
b
c
ꢀ
ꢀ
ꢂ1
Obtained from TGA at 800 C in nitrogen (heating rate 20 C min ).
Data obtained from reference [44].
Not determined.
[
[
10] J.W. Gilman, C.L. Jackson, A.B. Morgan, H. Richard, Chem. Mater 12 (2000)
866e1873.
1
11] K.K. Shen, Boran-based flame retardants and fire retardancy, ch, in:
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[
[
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2
9
8
6
4
2
0
0
0
0
0
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0
[
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(
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[
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[
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National Technical Information, Service, DOT/FAA/AR-00/42, Springfield, VA,
(
2
00
400
600
800
o
Temperature ( C)
Fig. 6. Heat release rate (HRR) verses temperature for polymers 1, 2, 9 and 10.
2001.
[
[
[
26] T. Emrick, R.E. Lyon, Polym. Adv. Technol. 19 (2008) 609e619.
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polymers having low heat release properties and amenability to
solution processing. Integration of deoxybenzoin units as co-
monomers considerably reduces the heat release capacity values of
commercial aromatic polysulfones and other engineering thermo-
plastics, and further studies detailing the use of these new poly-
mers in blends, and their resultant mechanical properties, will be
reported subsequently.
[29] A.B. Morgan, M. Bundy, Fire Mater 31 (2007) 257e283.
[
[
[
30] M.W. Szyndler, J.C. Timmons, Y.H. Zhan, A.J. Lesser, T. Emrick, Polymer 55
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Part A Polym. Chem. 45 (2007) 4573e4580.
(
[
[
33] J.S. Jurs, J.M. Tour, Polymer 44 (2003) 3709e3714.
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Acknowledgment
[35] Protecting America’s Families from Toxic Chemicals Act of 2014, S. 2656
113th).
(
[
36] Certain Polybrominated Diphenylethers; Significant New Use Rule, 71 Fed.
The authors acknowledge with thanks financial support of this
research from BASF, Inc through the BASF-NORA alliance, as well as
the Federal Aviation Administration (FAA award #14-G-012) and
the facilities of the UMass Amherst Materials Research Science and
Engineering Center on Polymers at UMass Amherst (NSF DMR-
Reg. 34,015 (Jun.13, 2006).
[37] A.B. Morgan, C.A. Wilkie, Non-halogenated flame retardant handbook, ch,
Scrivener Publ. Wiley 1 (2014) 1e16.
[
[
[40] ASTM Standard Test Method for Determining Flammability Characteristics of
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41] R.N. Johnson, A.G. Farnham, R.A. Clendinning, W.F. Hale, C.N. Merriam,
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