Novel fluoropolymers formed by an unprecedented SRN1 condensation polymerization mechanism

Article abstract of DOI:10.1016/j.jfluchem.2008.02.010

A condensation copolymerization reaction between bis-phenol A and p-bis-(chlorodifluoro-methyl)benzene has been carried out to form a novel fluoropolymer that has excellent thermal and solubility properties. It is proposed that this polymerization reaction occurs via an unprecedented S_RN1 mechanism. This demonstration of the use of S_RN1 chemistry for condensation polymerizations of fluorinated monomers creates the opportunity for preparation of new fluoropolymers which are otherwise inaccessible.

Full text of DOI:10.1016/j.jfluchem.2008.02.010

Journal of Fluorine Chemistry 129 (2008) 991–993
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Journal of Fluorine Chemistry
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Short communication
Novel fluoropolymers formed by an unprecedented SRN1 condensation
polymerization mechanism
a
a
a
William R. Dolbier Jr.a, , Valerie Rodriguez-Garcia , Kai Wu , Alexander Angerhofer ,
*
Lotfi Hedhli b, Maher Elsheikh b
a Department of Chemistry, University of Florida, Gainesville, FL 32611-7200, United States
b Arkema, Inc., 900 First Avenue, King of Prussia, PA 19406-0936, United States
A R T I C L E I N F O
A B S T R A C T
Article history:
A condensation copolymerization reaction between bis-phenol A and p-bis-(chlorodifluoro-methyl)-
benzene has been carried out to form a novel fluoropolymer that has excellent thermal and solubility
properties. It is proposed that this polymerization reaction occurs via an unprecedented SRN1 mechanism.
This demonstration of the use of SRN1 chemistry for condensation polymerizations of fluorinated
monomers creates the opportunity for preparation of new fluoropolymers which are otherwise
inaccessible.
Received 25 January 2008
Received in revised form 28 February 2008
Accepted 28 February 2008
Available online 18 March 2008
Keywords:
ß 2008 Elsevier B.V. All rights reserved.
S
RN1 mechanism
Fluoropolymers
Condensation polymerization
1. Introduction
processes [6], we decided to determine whether a bis-phenolate or
bis-thiolate monomer might be able to take part in a condensation
p-Bis-(chlorodifluoromethyl)benzene (1) is the precursor of
1,1,2,2,9,9,10,10-octafluoro[2.2]paracyclophane (AF4) [1], which
itself is the CVD precursor of a highly thermally stable thin film
Parylene polymer [2,3], which forms via p-xylylene monomer (2)
(Scheme 1).
Unfortunately, when monomer 2 is generated in solution by
variousmeans itforms an insoluble, amorphous polymer that has no
commercial value. Because of the generally strong bonds of most
atoms to CF2 groups, we considered it of interest to attempt the
preparation of copolymers of monomer 2 using its dichloride
precursor 1 as a substrate in a condensation polymerization process.
However, our own experience and knowledge of the literature told
us that compounds bearing a CF2X group are not good substrates for
SN2 nucleophilic substitution reactions. Indeed, we have found that
dichloride 1 will not react with excellent nucleophiles, such as
cyanide ion (HMPA/130 8C) or azide ion (HMPA/60 8C).
polymerization process with monomer 1.
2. Results and discussion
Indeed, after some optimization of conditions, bis-phenol A was
found to act as an effective comonomer in the copolymerization of
dichloride 1. A yellow solid was obtained in 81% yield, the structure
of which was assumed to be 5 (Scheme 3). The solid state fluorine
NMR spectrum of the product (Fig. 1) exhibited a single major
signal in the region of the spectrum which would be consistent
with the Ar–CF2–O– group present in 5, the simplicity of the
spectrum also indicating it to be a polymer of relatively uniform
structure. The relative lack of signal in the CF2H end group region
(ꢀ130 ppm) was consistent with the 36,300 molecular weight
(Mw) determined for the polymer by gpc, with Mn being 21,400.
Mw/Mn thus has a value of 1.7 for polymer 5. As would be expected
for a condensation polymerization process, the Mw increased to
50,000 when the concentration of dichloride monomer was
increased from 15 to 20%.
On the other hand, additional experience we had with
dichloride 1 indicated that it would react quite will with a good
SRN1 nucleophile such as phenyl thiolate anion, and even
phenolate anion to give bis-adducts in very good yield (Scheme
2) [4,5]. On the basis of this experience, and in spite of the
acknowledged complex free radical chain/SET mechanism of SRN1
The TM value for the polymer was 240 8C, and TGA experiments
determined that it had good thermal stability in the liquid phase
(10 wt.% loss at 335 8C) (Fig. 2). DSC experiments showed a
transition peak at about 234 8C during the first heat. Upon cooling
and second heat, a sharp transition was observed at 240 8C,
seemingly followed by decomposition, such results being con-
sistent with the TGA results.
* Corresponding author. Tel.: +1 352 392 0591; fax: +1 352 846 1962.
E-mail address: wrd@chem.ufl.edu (W.R. Dolbier Jr.).
0022-1139/$ – see front matter ß 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2008.02.010

992
W.R. Dolbier Jr. et al. / Journal of Fluorine Chemistry 129 (2008) 991–993
Scheme 1.
polymer 5 with the analogous fluorine free polymer, 6, for which a
‘‘maximum of polymer degradation temperature’’, PDT of 350 8C
was reported [7]. The PDT value of polymer 5 is 530(ꢁ20) 8C.
Scheme 2.
To our knowledge, an SRN1 mechanism has never previously
been invoked for a polymer forming process [8–11]. That the
mechanism of the above polymerization process is almost
certainly SRN1, was first indicated by the earlier mentioned result
that dichloride monomer 1 was unreactive with CNꢂ and N3
ꢂ
under conditions where phenoxide and thiophenoxide reacted
smoothly. SRN1 processes are known to be enhanced by light and
inhibited by the presence of O2. Indeed, the model reaction of
dichloride monomer with phenoxide ion in HMPA at 120 8C
normally reaches 70% conversion after about 12 h, whereas when
the reaction was irradiated by a sunlamp, 70% was attained in less
than 3 h. With bubbling O2, 70% was attained only after about 30 h.
Lastly, when the ‘‘normal’’ thermal model reaction of phenoxide
with dichloride monomer 1 was stopped after 2 h and the reaction
mixture examined by EPR, a spectrum was observed that was
consistent with that which would be expected for the radical anion
of dichloride 1, a quintet derived from coupling to four equivalent
hydrogens (Fig. 3). The observed spectrum was very similar in
structure to that reported for the radical anion of p-xylene [12,13].
Polymers of similar nature and quality were obtained using a
number of other bis-phenolate and bis-thiolate comonomers,
including 4,40-dihydroxybenzophenone, 4,40-dihydroxybiphenyl,
and 1,3-propane dithiol, the properties of which will be reported in
due course.
Scheme 3.
Polymer 5 also has good solubility characteristics, with 10 mL of
DMSO dissolving 6 g at 180 8C.
That the presence of the fluorine substituents is enhancing the
thermal stability of the polymer is indicated by a comparison of
Fig. 1. 19F NMR spectrum (solid state) of polymer 5.

W.R. Dolbier Jr. et al. / Journal of Fluorine Chemistry 129 (2008) 991–993
3. Experimental
993
3.1. Preparation of polymer 5
Bis-phenol A (0.46 g, 2.0 mmol), p-bis-(chlorodifluoromethyl)-
benzene (0.50 g, 2.0 mmol) [14], NaH (95%, 0.29 g, 12.1 mmol) and
hexamethylphosporamide (anhydrous, 8 mL) were added to a
25 mL round bottomed flask. The reaction mixture was stirred at
120 8C under N2 overnight. After the reaction mixture was cooled
to room temperature, it was added to water (100 mL) dropwise
with stirring. One molar HCl was added to the solution until pH 1–
2. The precipitate was then collected and washed by water (50 mL),
acetone (10 mL) and ethanol (10 mL). It was then dried by a flow of
N2 to give a yellow solid (0.671 g, 87%).
Acknowledgement
Fig. 2. TGA of polymer 5.
Funding of this research, in part, by Arkema, Inc. is acknowl-
edged with thanks.
References
[1] W.R. Dolbier Jr., J.-X. Duan, A.J. Roche, Org. Lett. 2 (2000) 1867–1869.
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detrimental mechanistic pathway that can compete with desired SNAr processes
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In conclusion, novel fluoropolymers with potentially interest-
ing properties can be prepared from 1,4-bis-(chlorodifluoro-
methyl)benzene via an unprecedented
polymerization process.
SRN1 condensation