Synthesis and flame retardant potential of polyols based on bisphenol-S

Article abstract of DOI:10.1002/pola.28077

Polyether polyols based on bisphenol-S were prepared by alkoxylation and compared with analogs based on bisphenol-A, as well as standard aromatic polyester, and polyether polyols for viscosity and temperature stability. Thermo-oxidative stability was determined by thermo-gravimetric analysis, pyrolysis gas chromatography/mass spectroscopy, and evolved gas analysis mass spectroscopy. Incorporation of the sulfone moiety was found to dramatically improve the thermo-oxidative stability of the neat polyol. Significant char formation was observed with gas phase evolution of flame retardant SO₂ and aromatic sulfone only apparent at about 600 °C.

Full text of DOI:10.1002/pola.28077

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Synthesis and Flame Retardant Potential of Polyols Based on Bisphenol-S
Mark F. Sonnenschein,1 Justin M. Virgili,1* David A. Babb,2 Bruce M. Bell,1 Brian C. Nickless1
1Corporate Research and Development, Midland, Michigan, 48674
2Polyurethanes Research and Development, Freeport, Texas, 77541
Correspondence to: M. F. Sonnenschein (E-mail: mfsonnenschein@dow.com)
Received 11 January 2016; accepted 3 February 2016; published online 8 March 2016
DOI: 10.1002/pola.28077
ABSTRACT: Polyether polyols based on bisphenol-S were pre-
pared by alkoxylation and compared with analogs based on
bisphenol-A, as well as standard aromatic polyester, and poly-
ether polyols for viscosity and temperature stability. Thermo-
oxidative stability was determined by thermo-gravimetric anal-
ysis, pyrolysis gas chromatography/mass spectroscopy, and
evolved gas analysis mass spectroscopy. Incorporation of the
sulfone moiety was found to dramatically improve the thermo-
oxidative stability of the neat polyol. Significant char formation
was observed with gas phase evolution of flame retardant SO2
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and aromatic sulfone only apparent at about 600 8C.
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2016, 54, 2102–2108
KEYWORDS: double-metal cyanide catalyst; flame retardance;
polyethersulfone
izable building blocks. A detailed procedure for producing
alkoxylated bisphenol-S is presented. Bisphenol-S is alkoxy-
lated with propylene oxide to various useful molecular
weights. Thermo-oxidative performance of these new build-
ing blocks are assessed versus comparable materials pro-
duced from the non-sulfone functional bisphenol-A, and
conventional polyether and aromatic polyester polyols, the
latter of which could be used for FR resistant PU rigid insu-
lation foams.
INTRODUCTION Environmental, health, and safety regulations
are creating increasing demand for halogen-free flame
retardants (FRs).1,2 In addition, there is increasing scrutiny
of other FRs based on phosphorous. Acceptable FR are
expected to mitigate flame initiation and inhibit post ignition
behavior such as heat release rate, smoke obscuration, and
evolved gas toxicity. Many FR additives are utilized for poly-
urethane, polycarbonate, and polyester containing products.3
These plastics are produced by addition or condensation pol-
ymerizations, and hydroxyl functional polymer building
blocks are commonly employed.4 There is growing explora-
tion of reactive FR agents that can be incorporated in the
polymer network.5,6 These can be useful compared with
small molecule FR additives which may become fugitive in
the environment, or expose unsuspecting consumers by
touch or ingestion. Polymerizable FR feedstocks that contain
hydroxyl functional materials become part of the main poly-
carbonate, polyurethane, or polyester polymer network, and
are held captive in the plastic until such time as its FR func-
tion is required.
EXPERIMENTAL
Materials
Bisphenol-S (98%), bisphenol-A (97%), propylene carbonate
(99.7%), and all other reagents were purchased from Sigma-
Aldrich and used as received. Aromatic polyester polyol IP
9001, propylene oxide, and polypropylene oxide (725 Da)
were obtained from Dow Chemical. DMC catalyst (Arcol 3TM
)
was obtained from Bayer Material Science (Covestro). DMC
catalyst (double metal cyanide) is a compound of zinc hexa-
cyanocobaltate and tert-butyl alcohol useful for epoxide poly-
merizations.12 IP 9001 is an aromatic polyester polyol; the
reaction product of terephthalic acid with diethylene glycol
and 200 g/mol polyethylene glycol with functionality 2.0 and
polymerized to result in OH number of 205–220, and a vis-
cosity at 25 8C of 2000 cps.
Polysulfones are well known to possess outstanding thermo-
oxidative stability,7,8 resistance to burning, and low smoke
emission.9–11 Their use as selective FR agents however, is
apparently missing from the literature. This article will
explore the first alkoxylation of bisphenol-S, a commercially
available feedstock for making hydroxyl functional polymer-
*Present address: Justin M. Virgili, Tactus Technology Fremont, California, 94555.
Additional Supporting Information may be found in the online version of this article.
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SCHEME 1 Synthesis of HPPS by reaction of bisphenol S with propylene carbonate.
Synthesis of Polyols
carbonate between 150 8C and 170 8C and catalytic KOH
(0.59 g, 0.01 mol) was added to the flask.
Synthesis of HPPS [1,10-((Sulfonylbis(4,1-phenylene))
bis(oxy))bispropan-2-Ol)] and HPPA [1,10-((Propane-2,
2-Bis(4,1-phenylene))bis(oxy))bis(propan-2-Ol)]
The crude product was dissolved in warm methylene chlo-
ride, washed with brine three times, and dried over MgSO4.
HPPS was isolated by rotary evaporation followed by vac-
uum drying overnight. Yield of a transparent yellow viscous
liquid was 90.3% of theoretical. Composition was verified by
1H-NMR (981% apparent purity) in d6-acetone. While 1H-
NMR was found to be sensitive to the disappearance of two
distinct aromatic resonances (d 5 7.7 ppm and 6.85 ppm)
The method utilized for the synthesis of HPPS is an adapta-
tion of that published by Liaw et al.13 and is here expanded
to the synthesis of HPPA. As illustrated in Scheme 1,
bisphenol-S (125 g, 0.5 mol) and anhydrous propylene car-
bonate (112.6 g, 1.1 mol) were introduced to a 500 mL
three-neck flask with stirring, and heated to 215 8C under
N2 and reflux. The bisphenol-S dissolved in the propylene
TABLE 1 Identification of HPPS Components by ESI/LC/MS Analysis
Peak
A
Assignments
Peak
B
Assignments
C
D
E
Molar percentages are rounded on nearest significant figure.
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TABLE 2 Relative Molar Percentages of Primary–Primary, Pri-
mary–Secondary, and Secondary–Secondary Hydroxyl Species
in HPPS
bisphenol-A dissolves in propylene carbonate, catalytic KOH
(0.13 g, 0.0023 mol) was added to the reaction at room
temperature.
Upon cooling, the crude product was dissolved in warm
methylene chloride, washed with brine 33, and dried with
MgSO4. HPPA was isolated by removal of methylene chloride
by rotary evaporation, followed by vacuum drying overnight.
Yield of a clear, yellow near-glass liquid was 77% of theoreti-
cal, and the composition was verified by 1H-NMR (961%
apparent) in d6-acetone. As in the case of HPPS, 1H-NMR
was found to be sensitive to the disappearance of two dis-
tinct aromatic resonances (d 5 7.05 and 6.75 ppm) present
in neat bisphenol-A, and the appearance of two distinct aro-
matic resonances (d5 7.15 and 6.85 ppm) in the HPPA prod-
uct, but unable to distinguish between products with greater
than one propylene oxide unit added per phenol group of
bisphenol-A.
Compositional
Isomers of Peak B in Table 1
Abundance
45.8
44.1
10.1
LC/ESI/MS analysis was utilized to establish the product
composition and the relative abundance of each species esti-
mated from UV peak absorption area from the LC analysis.
In Table 3 all major reaction products are observed to pos-
sess two hydroxyl groups with an average product (hereafter
called HPPA) molecular weight of 347 g/mol. The distribu-
tion of isomers with primary versus secondary hydroxyl
groups present in the species corresponding to peaks B, C,
and D in Table 3 was further analyzed by GC/MS analogously
to the analysis on HPPS and the results shown in Table 4.
This product is used as a polyol itself and as an initiator to
make higher equivalent weight polyols as subsequently
described.
present in neat bisphenol-S, and the appearance of two dis-
tinct aromatic resonances (d 5 7.85 ppm and 7.05 ppm) in
the HPPS product, the technique was unable to distinguish
between products with greater than one propylene oxide
unit added per phenol group of the bisphenol-S.
LC/ESI/MS (liquid chromatography/electro-spray ionization/
mass spectrometry) analysis14 was utilized to establish the
product composition and the relative abundance of each spe-
cies estimated from the UV peak absorption obtained follow-
ing liquid chromatographic separation. All reaction products
(Table 1, hereafter termed HPPS) possess two hydroxyl
groups with average molecular weight 378 g/mol and 8.5 wt
% sulfur. This product is used as a polyol itself and as an ini-
tiator to make higher equivalent weight polyols as subse-
quently described.
It is worth noting from comparing Tables 2 and 4, that the
choice of bisphenol-S or bisphenol-A appeared to have exer-
cised substantial influence on the distribution of primary
and secondary hydroxyl produced from the reactions with
propylene carbonate. The cause of this director effect is
ambiguous, but may be due to the difference in inductive
electronic effects between the sulfone and the isopropylidene
bridges altering the nucleophilicity of the phenol.
The distribution of isomers with primary versus secondary
hydroxyl groups in the major product corresponding to peak
B in Table 1 was analyzed via GC/MS and GC FID after HPPS
was derivatized with bis(trimethylsilyl)trifluoroacetamide.
The relative molar percentages of primary–primary, pri-
mary–secondary, and secondary–secondary hydroxyls are
given in Table 2.
Synthesis of BIS-S and BIS-a Containing Polyols by
Propoxylation with DMC Catalyst
Alkoxylation of HPPS
Direct alkoxylation of bisphenol-S is not practical using DMC
catalysis since the diphenol monomer is a high melting solid
(m.p. 5 245 8C–247 8C) that is incompatible with the alkoxy-
lation process.15 Instead, the viscous product (polyol)
obtained by reacting bisphenol S with propylene carbonate
(Table 1) was used as an initiator for DMC catalyzed
HPPA was synthesized following a similar procedure to that
used to synthesize HPPS. Bisphenol-A (25.0 g, 0.11 mol) and
anhydrous propylene carbonate (24.7 g, 0.24 mol) were
added to a 250 mL three-neck flask with stirring and heated
to 200 8C under N2 and reflux for 3–4 h (Scheme 2). As the
SCHEME 2 Synthesis of HPPA.
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TABLE 3 Constituents of HPPA Determined by ESI/LC/MS
Peak
A
Assignments
Peak
B
Assignments
C
D
E
F
Molar percentages are rounded on nearest significant figure.
alkoxylation. HPPS initiator (45.8 g, 0.125 mol) was added to
a 500 cc ZipperclaveTM reactor along with aqueous phos-
phoric acid (0.15 M, 1.21 ll) followed by DMC catalyst
(0.0125 g)16 and aluminum isoproxide (0.095 g). The mix-
ture was heated to 145 8C with a N2 purge for 2 h to dry
the mixture. The N2 purge was stopped, the reactor sealed
and then heated to 150 8C. Propylene oxide (PO) (99.29 g,
116.8 ml) was added at a rate of 1 mL/min up to an internal
reactor pressure of 20 psig, and then added at a rate of
0.75 mL/min to maintain 20 6 1 psig reactor pressure. Fol-
lowing residual PO digestion, the reactor was cooled and the
product (140.5 g, 96.9% yield) was isolated. GPC analysis of
the alkoxylated product indicated a polyether product with
Mn of 1265 g/mol and a polydispersity (Mw/Mn) of 1.03.
TABLE 4 Relative Molar Percentages of Primary–Primary, Pri-
mary–Secondary, and Secondary–Secondary Hydroxyl Species
in HPPA
Isomers Distribution in HPPA
Peaks B, C,D in Table 1
Compositional
Abundance
74.6 (UV)
78.1 (GC/MS)
23.6 (UV)
21.0 (GC/MS)
In a second alkoxylation reaction, a polyol with Mn 5 700 g/
mol was targeted. The HPPS initiator was combined with
phosphoric acid followed by DMC catalyst and aluminum iso-
propoxide as above. Following drying, the reactor was
sealed, heated to 150 8C, and PO (54.2 g, 66.1 mL) was
added to the reactor to maintain a reactor pressure ꢀ14
psig. The residual PO was digested, the reactor cooled, and
1.7(UV)
0.1 (GC/MS)
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TABLE 5 Viscosity of Bisphenol-S and Bisphenol-A Based Poly-
ols at Three Temperatures and Comparison to Aromatic Poly-
ester Polyol (IP-9001)
analysis. GPC analysis indicated a polyol with Mn 5 1271 g/
mol and polydispersity of 1.03.
In a second preparation, the HPPA initiator was alkoxylated
based on a design to produce a polyol with Mn 5 800 g/mol.
HPPA initiator (43.1 g), phosphoric acid (0.15 M, 1.1 lL),
DMC catalyst (0.005 g) and Al isopropoxide (0.019 g) was
reacted with 56.9 g PO (69.4 mL) using a similar procedure
as outlined above. A total of 96.4 g of polyol was obtained
(96% yield) with a Mn 5 794 g/mol and a polydispersity of
1.05.
Polyol (g/mol)
35 8C (cps)
60 8C (cps)
80 8C (cps)
HPPS 378
1.2 3 107
3.5 3 103
1.3 3 103
3.7 3 104
7.2 3 102
4.9 3 102
1 3 103
8 3 105
7 3 102
3 3 102
1 3 103
1 3 102
1 3 102
1.3 3 102
7 3 103
3 3 102
1 3 102
1.5 3 102
<102
HPPS 847
HPPS 1,265
HPPA 347
HPPA 794
HPPA 1,271
PTA polyol 492
<102
<102
Viscosity of the Polyols
Viscosity is a practical, but critical property of polyols since
for many applications process equipment limitations dictate
acceptable flow properties. The inability to adequately adjust
polyol viscosity to meet prosaic issues such as flowability
and mixing requirements can result in an innovation that is
little more than a laboratory curiosity. For instance, polyur-
ethane process equipment for rigid insulation foams usually
set a room temperature viscosity limit of between 5000 and
20,000 cps at room temperature.12,17
the product (97.8 g, 87.8% yield) collected for analysis. GPC
analysis of the reaction product indicated a polyol with
Mn 5 847 g/mol and polydispersity of 1.05.
Alkoxylation of HPPA Monomer
The viscous product (polyol) obtained by reacting bisphenol
A with propylene carbonate (Table 3) was used as an initia-
tor for DMC catalyzed alkoxylation. Alkoxylation of HPPA ini-
tiator (Table 3) to produce a 1200 g/mol polyol was carried
out in a similar manner to alkoxylation of HPPS initiator
described previously. HPPA initiator (43.1 g) was added to
the alkoxylation reactor along with phosphoric acid (0.15 M,
1.1 lL) followed by DMC catalyst (0.0125 g) and Al isoprop-
oxide (0.094 g). The reactor was heated and dried as before.
After drying, the N2 purge was stopped, the reactor heated
to 150 8C and then sealed. PO was added at a rate sufficient
to maintain reactor pressure less than 15 psig throughout
the addition, until a total of 106.9 g (130.4 mL) was added.
The residual PO was digested to a constant reactor pressure,
the reactor cooled, and the product (153.5 g) collected for
Temperature dependant viscosities were measured using a
Rheometrics ARES II rheometer with a cone-and-cup geome-
try (x 5 1 rad/sec, 2 8C/min ramp rate). The bisphenol-S
polyols possessed the highest viscosity among all the compa-
ratives at any particular molecular weight and at any partic-
ular temperature. HPPS initiator (polyol from reacting
bisphenol
S with propylene carbonate) with molecular
weight 378 g/mol was a glass at room temperature so all
viscosity measurements were begun at 35 8C. Table 5 pro-
vides the viscosity of the bis-S polyols and the comparatives
at several temperatures. Two trends are observed, (1) the
increased hydrogen bond potential of bisphenol-S versus
FIGURE 1 Total ion response versus retention time from pyrolysis of sulfone polyols of varying molecular weight heated ballisti-
cally to 600 8C. Inset shows detail of SO2 response with lowest response for polyol having highest percentage sulfur content.
[Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
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TABLE 6 Td,5% Determined Using Thermogravimetric Analysis
for Conventional Aromatic Polyester Polyol, Polyether Polyols,
and Polyols Produced by Functionalization of Bisphenol-A and
Bisphenol-S
samples were selectively sampled by temperature range
(100 8C–400 8C and 375 8C–400 8C) and also ballistically
heated to 600 8C for 6 sec. Species thermally desorbed were
transported to a GC and focused with a cryotrap at 2195 8C.
GC parameters were injection port 320 8C, with a GC oven
program set to ramp from 40 8C to 100 8C at 8 8C/min fol-
lowed by 100 8C–320 8C at 20 8C/min followed by isother-
mal condition at 320 8C for 8 min. The column was 30 M 3
0.25 mm, 1.0 mm 5% phenyl methylsilicone, with a He col-
umn flow rate of 0.6 mL/min at 5.0 psi. Mass spectral
parameters were an electron energy of 270 V, electron cur-
rent 271 lA, ion source temperature 250 8C acquisition rate
20 spectra/sec, acquisition delay of 60 sec, and a mass range
from 14 to 600.
Sample
% Aromatic
% Sulfur
Td, 5% (8C)
IP 9001 (492 g/mol)
PPG (425 g/mol)
PPG (725 g/mol)
HPPA (347 g/mol)
HPPS (378 g/mol)
HPPS (847 g/mol)
HPPS (1,265 g/mol)
12
0
0
132
153
260
184
305
344
331
0
0
0
43.9
41.3
18
12
0
8.5
4
2.7
All percentages are based on weight.
For pyrolyzed HPPS and alkoxylated HPPS polyols, sulfur-
containing degradation species were only observed for sam-
ples heated to 600 8C and in each example SO2 was the only
detectable S containing degradation species (Fig. 1). Samples
heated to 400 8C showed evidence only of polyether degra-
dation products, primarily propanal and dioxane derivatives
(data not shown). Samples heated to 600 8C evolved SO2, but
the amount was inversely correlated to polyol sulfur content
suggesting that char layer formation impedes thermoxidative
formation of volatile degradation products.21,22 In addition
to SO2, phenol is also observed upon heating to 600 8C. The
dependence of degradation products on thermoxidative
path reflects the complexity of thermo-oxidative pathways
involved.
bisphenol-A moieties leads to higher viscosity at comparative
molecular weights, (2) the addition of racemic propylene
oxide to bisphenol-S and bisphenol-A moieties disrupts the
strong intermolecular interactions leading to reduced polyol
viscosity as molecular weight increases. The beneficial vis-
cosity reduction effect of propoxylation is leveled at high
equivalent weight as all polyols converge to 100 cps at the
highest molecular weight. Thus, with increasing molecular
weight conventional polymer rheology effects dominate over
inter- and intramolecular hydrogen bonding interactions.18
Thermo-Oxidative Stability of Sulfone Polyols
Pyrolysis gas chromatography/mass spectroscopy19,20 was
performed using an Agilent 7890 GC coupled to a Frontier
Labs PY-2020iD pyrolyzer. Analyses were performed on
about 100 lg samples, solvent (methylene chloride) depos-
ited into a sample cup under varying heating conditions. The
For thermogravimetric analysis (TGA), 5–10 mg samples
were weighed into platinum sample pans, dried overnight
under vacuum, and analyzed under N2 purge with a 10 8C/
min temperature ramp rate using a TA Q5000 instrument.
Table 6 documents the dramatic increase in the temperature
FIGURE 2 Total ion response versus temperature from evolved gas analysis (EGA/MS) of HPPS, HPPA, aromatic polyester, and
polyether polyols. Samples were heated at 20 C/min from 50 8C to 650 8C. [Color figure can be viewed in the online issue, which
is available at wileyonlinelibrary.com.]
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REFERENCES AND NOTES
at which HPPS 5% weight loss is observed (Td,5%), compared
with the bisphenol-A analogue and polyether and polyester
comparatives (TGA curves are supplied in Supporting Infor-
mation). Along with the substantial retarding effect of sul-
fone on thermal degradation, the 5% degradation
temperature also shows that higher molecular weight poly-
propylene oxide polyols possess greater thermal stability
than lower molecular weight homologs, which complicates
quantitative estimation of the effect of sulfone moiety by this
measurement technique.
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