Depolymerization of end-of-life poly(dimethylsilazane) with boron trifluoride diethyl etherate to produce difluorodimethylsilane as useful commodity

Article abstract of DOI:10.1080/10426507.2016.1160243

A straightforward protocol for the depolymerization of end-of-life poly(dimethylsilazane) using boron trifluoride diethyl etherate as depolymerization reagent to convert the Si-N to Si-F bonds was set-up. The application of the depolymerization reagent affords difluorodimethylsilane as major products, which can be a suitable synthon for the synthesis of new polymers (e.g., poly(dimethylsiloxanes) and allow an overall recycling of the [Me₂Si]-unit.

Full text of DOI:10.1080/10426507.2016.1160243

Phosphorus, Sulfur, and Silicon and the Related Elements
ISSN: 1042-6507 (Print) 1563-5325 (Online) Journal homepage: http://www.tandfonline.com/loi/gpss20
Depolymerization of End-Of-Life
Poly(Dimethylsilazane) With Boron
Trifluoride Diethyl Etherate to Produce
Difluorodimethylsilane as Useful Commodity
Peter Döhlert, Johannes Pfrommer & Stephan Enthaler
To cite this article: Peter Döhlert, Johannes Pfrommer & Stephan Enthaler (2016):
Depolymerization of End-Of-Life Poly(Dimethylsilazane) With Boron Trifluoride Diethyl Etherate
to Produce Difluorodimethylsilane as Useful Commodity, Phosphorus, Sulfur, and Silicon and
the Related Elements, DOI: 10.1080/10426507.2016.1160243
To link to this article: http://dx.doi.org/10.1080/10426507.2016.1160243
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DEPOLYMERIZATION OF END-OF-LIFE POLY(DIMETHYLSILAZANE) WITH BORON TRIFLUORIDE
DIETHYL ETHERATE TO PRODUCE DIFLUORODIMETHYLSILANE AS USEFUL COMMODITY
Peter Döhlert,[a] Johannes Pfrommer,[a] Stephan Enthaler[a,b]*
[a] Technische Universität Berlin, Institute of Chemistry: Cluster of Excellence “Unifying
Concepts in Catalysis”, Straße des 17. Juni 135/C2, D-10623 Berlin, Germany.
[b] Universität Hamburg - Department Chemie, Institut für Anorganische und Angewandte
Chemie, Martin-Luther-King-Platz 6, D-20146 Hamburg, Germany, E-mail:
stephan.enthaler@chemie.uni-hamburg.de
ABSTRACT
A straightforward protocol for the depolymerization of end-of-life poly(dimethylsilazane) using
boron trifluoride diethyl etherate as depolymerization reagent to convert the Si-N to Si-F bonds
was set-up. The application of the depolymerization reagent affords difluorodimethylsilane as
major products, which can be a suitable synthon for the synthesis of new polymers (e.g.,
poly(dimethylsiloxanes) and allow an overall recycling of the [Me2Si]-unit.
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INTRODUCTION
The efficient treatment of end-of-life polymers will be one of the challenges for future
research.1,2,3 On the one hand the majority of the polymers bases on the steadily decreasing fossil
resources; hence alternative sources for polymer basis chemicals are of great interest. On the
other hand, after the life time of the polymer materials ends the polymer waste is currently
treated via landfill storage, energy recovery (thermal decomposition), downcycling or
mechanical recycling. Based on that, the chemical functions derived from fossil resources are
mainly deposited in problematic sinks (e.g., CO2) and to produce new high quality materials new
equivalents of fossil resources are needed. One option to overcome these problems can be the
creation of an efficient feedstock recycling system means the end-of-life polymer is
depolymerized to low-molecular weight compounds, which can be converted in an associated
polymerization process to form new high quality polymers.4,5,6 In this regard, we have recently
established feedstock recycling concepts for polysiloxanes based on depolymerization-
polymerization-steps.7,8,9 In more detail, we demonstrated that depolymerizations of
poly(dimethylsiloxane)s can be realized in the presence of catalytic amounts of zinc or iron salts.
For instance applying benzoyl fluoride, benzoyl chloride/potassium fluoride or benzoic
anhydride/potassium fluoride as depolymerization reagents, difluorodimethylsilane and 1,3-
difluoro-1,1,3,3-tetramethyldisiloxane were obtained as products, which were polymerized to
new silicones and overall demonstrating a silicone recycling.7,8 In more detail, the Si-O bonds
were converted to Si-F bonds and the oxygen was embedded in the benzoic acid derivative.
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However, due to the low fluorine content (7-15%) in the depolymerization reagents significant
amounts of waste are generated. More recently, boron trifluoride dietherate (fluorine content:
40% (BF3OEt2) or 84% (BF3)10 was successfully applied in the depolymerization of
poly(dimethylsiloxane)s, which can on the one hand act as Lewis acid catalyst for the activation
of Si-O bonds in silicones and on the other hand as depolymerization reagent to convert Si-O to
Si-F bonds (Scheme 1a).11 Interestingly, a boron containing side product Bx(OyRz) is formed,
which can be easily reconverted to BF3 by NaF/H2SO4.12 Based on that concept, we wondered if
this method can be transferred to the depolymerization of end-of-life polysilazanes, an
interesting class of silicon containing polymers with applications in coatings,13 high-temperature
ceramics14,15 and support for functional materials,16 means the conversion of Si-N bonds to Si-F
bonds and in consequence to produce low-molecular weight chemicals such as
difluorodimethylsilane, which can be used for as starting chemical new polymers, e.g.,
poly(dimethylsiloxane)s, poly(dimethylsilazane)s (Scheme 1b).7,8,10,17
RESULTS AND DICUSSION
In accordance to the protocol reported for the depolymerization of polysiloxanes boron
trifluoride diethyl etherate was applied as depolymerization reagent. As a model for the Si-N
bonds in polysilazanes hexamethyldisilazane 1 was chosen. To a solution of
hexamethyldisilazane 1 in chloroform-d1 was added boron trifluoride diethyl etherate 2 in
various ratios at room temperature (Scheme 2). After addition, the mixtures were analysed by
different NMR techniques. For instance the reaction of 1 and 2 in a ratio of 1:1 showed the
formation of new signals in the 1H NMR. Along to the singlet for 1 with a chemical shift of 0.03
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3
ppm a doublet was observed at = 0.20 ppm and a coupling constant of JH-F = 7.42 Hz, which
can be assigned to fluorotrimethylsilane.18 Moreover, a signal appeared with a chemical shift at
0.37 ppm, which could be not assigned (4). The chemicals were found in a ratio of 0.42:1.0:0.26
(1:3:4), which indicates a yield of 60% of 3. In addition, the characteristic signals for
diethylether were observed with a chemical shift of = 1.28 ppm (6H, t, J = 7.07 Hz) and=
3.80 ppm (4H, t, J = 7.07 Hz), but no distinction was possible between BF3 coordinated and
19
uncoordinated diethylether. Also F NMR proves the formation of 3 by a complex signal at -
3
157.8 Hz. The triplet of decet showed a fluorine hydrogen coupling of JF-H = 7.40 Hz and a
1
fluorine silicon coupling of JF-Si = 274.6 Hz. Besides, BF3OEt2 (= -152.8 ppm) and a doublet
of doublets at -141.6 ppm (J = 18.18 Hz) probably for compound 4 were monitored. The
13C{1H} NMR revealed a doublet at -0.01 ppm with a coupling constant of J = 15.22 Hz and in
the 29Si{1H} NMR a signal with a chemical shift of 36.7 ppm was observed, which can assigned
to compound 3.
Interestingly, the yield of 60% of 3 indicates the conversion of both silicon functions of 1 and the
transfer of more than one fluorine atom from 2. Increasing the amount of 2 to 2.0 or 3.0 equiv. an
increased yield of 3 was observed, while the signal for 4 was not observed. Afterwards the
reaction was performed on a larger scale. A flask was charged with 1 (1 equiv.), 2 (1 equiv.) and
1,2-dichloroethane as solvent and a Vigreux column and a distillation head were connected and
the mixture was heated to 80 °C. The collecting flask was cooled to -78 °C and after 2 hours 3
was isolated in 56% yield. The temperature was increased to 120 °C and 140 °C to isolate the
solvent 1,2-dichloroethane and BF3OEt2. After removal of all volatile compounds a grey powder
appeared in the reaction flask, which was dried in vacuum. The grey precipitate was investigated
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by several analytical methods, e.g. powder X-ray diffraction (P-XRD), NMR and IR, but no
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suitable information could be figured out.
Next, the oligomer 1,1,3,3,5,5-
hexamethylcyclotrisilazane 5 was reacted as model for poly(dimethylsilazane)s with boron
trifluoride diethyl etherate 2. In accordance to the described set-up 2 was added carefully to 5
and the low-boiling compounds were collected at low temperature (Scheme 3). Importantly, the
reaction proceeds under solvent-free and protection-gas-free conditions. Noteworthy, an
exothermic reaction was observed during addition of 2 at room temperature. The mixture was
slowly heated to 100 °C. After 3 hours at 100 °C the products were investigated by NMR
techniques. For instance in the 1H NMR a signal with a chemical shift of = 0.31 (t, 3JHF = 6.24
Hz) ppm, which can be assigned to difluorodimethylsilane 6.7,8,10 In addition, the presence of
13
2
19
compound 6 was clarified by C{1H} = -3.45 (t, JCF = 16.67 Hz) ppm, F NMR= -131.4
(sept, 3JHF = 6.18 Hz, 1JSiF = 289.9 Hz) ppm, and 29Si{1H} NMR = -2.4 ppm. On the other hand
diethyl ether was detected (1H NMR = 1.16 (t, 6H, J = 7.01 Hz), 3.44 (q, 4H, J = 7.01 Hz)
ppm). Interestingly increasing the reaction temperature to 120 °C revealed the formation of 6 in
an increased yield of 92%. Noteworthy, the obtained product 6 can be applied as starting
material for polymerization chemistry to produce for instance silicones.7,8,10 In this regard, the
mixture of 6 and diethyl ether were reacted with an aqueous solution of sodium hydroxide to
generate poly(dimethylsiloxane) 7 in 59% yield.20,21
After demonstrating the potential of 2 in the transformation of Si-N bonds, we directed our
attention to the polymer poly(1,1-dimethylsilazane) 8 (Scheme 4).22 In accordance to the reaction
conditions and the reaction set-up described for compound 5 poly(1,1-dimethylsilazane) 8 was
reacted with 2 (3.0 equiv. with respect to the polymer subunit) at 100 °C. After three hours
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difluorodimethylsilane 6 was obtained in 54% yield and was characterized by NMR methods
(vide supra). Moreover, silicon nitride (Si3N4) was reacted with boron trifluoride diethyl etherate
2 to potentially produce SiF4, but no reactivity was observed at 120 °C after 3 hours.
CONCLUSIONS
In summary, we have set up a straightforward depolymerization protocol of the treatment of end
of-life polysilazanes. The depolymerization of poly(1,1-dimethylsilazane) was carried out with
boron trifluoride diethyl etherate as a depolymerization reagent to obtain difluorodimethylsilane
as well-defined product in good yields. Interestingly, difluorodimethylsilane can be applied as
starting material for polymerization chemistry to produce new polysilazanes or polysiloxanes.
Moreover, a BxNyRz compound is formed as a side product, which can be potentially recycled by
reformation to BF3.
EXPERIMENTAL
General
1
All chemicals were used as received without further manipulations. H, 11B, 19F, 13C{1H}, and
29Si{1H} NMR spectra were recorded on a Bruker Avance II 200 MHz (1H: 200.13 MHz; 11B: 64.21
MHz, 13C: 50.32 MHz; 19F: 188.31 MHz, 29Si: 39.71 MHz) in CDCl3 at 25 °C using the proton
signals of the deuterated solvents as reference or external standards. PXRD data was obtained
on a Panalytical X’Pert Pro with Cu K radiation ( = 1.54060 nm). GC-MS measurements were
carried out on a Shimadzu GC-2010 gas chromatograph (30 m Rxi-5ms column, 40-300 °C)
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linked with a Shimadzu GCMS-QP 2010 Plus mass spectrometer. The Supplemental Materials
contains some sample spectroscopic characterization of the products (Figures S 1 – S 7)
Procedure for the conversion of hexamethyldisilazane 1
A NMR tube was charged with chloroform-d1 (0.5 mL), 1 (0.19 mmol) and boron trifluoride
diethyl etherate 2 (1.0-3.0 equiv., 0.095-0.57 mmol). After 10 min at room temperature the
samples were investigated by NMR methods. Fluorotrimethylsilane 3: 1H NMR: δ = 0.20 (d, 3JHF
= 7.4 Hz) ppm. 13C{1H} NMR: δ = -0.01 (d, 2JCF = 15.2 Hz) ppm. 19F NMR: δ = -157.8 (dec, 3JHF = 7.4
Hz, ddec, 1JSiF = 274.6 Hz) ppm. 29Si{1H} NMR: δ = 36.7 ppm.
Procedure for the isolation of fluorotrimethylsilane 3
A flask was charged with compound 5 (6.2 mmol) and boron trifluoride diethyl etherate 2 (3.0
equiv., 18.6 mmol). A Vigreux column and a distillation head were connected. The mixture was
stirred and heated to 100 °C (oil bath). The formed fluorotrimethylsilane (bp = 16 °C23) was
continuously distilled off and collected. After 3 h the yield was determined and the quality was
1
3
analysed by NMR. Fluorotrimethylsilane 3: H NMR: δ = 0.20 (d, JHF = 7.4 Hz) ppm. 13C{1H}
NMR: δ = -0.01 (d, 2JCF = 15.2 Hz) ppm. 19F NMR: δ = -157.8 (dec, 3JHF = 7.4 Hz, ddec, 1JSiF = 274.6
Hz) ppm. 29Si{1H} NMR: δ = 36.7 ppm.
Procedure for the depolymerization of 1,1,3,3,5,5-hexamethylcyclotrisilazane 5
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A flask was charged with compound 5 (4.6 mmol) and boron trifluoride diethyl etherate 2 (3.0
equiv., 13.8 mmol, based on the subunit). A Vigreux column and a distillation head were
connected. The mixture was stirred and heated to 100 °C (oil bath). The formed
difluorodimethylsilane (bp = 16 °C24) was continuously distilled off and collected. After 3 h the
yield was determined and the quality was analysed by NMR. Difluorodimethylsilane 5: 1H NMR:
δ = 0.31 (t, 3JHF = 6.2 Hz) ppm. 13C{1H} NMR: δ = -3.45 (t, 2JCF = 16.7 Hz) ppm. 19F NMR: δ = -131.4
(sept, 3JHF = 6.2 Hz, 1JSiF = 289.9 Hz) ppm. 29Si{1H} NMR: δ = -2.4 ppm. Diethyl ether: 1H NMR: δ =
3
3
3.69 (q, JHH = 7.0 Hz, CH2), 1.26 (t, JHH = 7.0 Hz, CH3) ppm. 13C{1H} NMR: δ = 67.0 (CH2), 14.7
(CH3) ppm.
Procedure for the depolymerization of 1,1,3,3,5,5-hexamethylcyclotrisilazane 5 and
polymerization of difluorodimethylsilane 6
A flask was charged with compound 5 (22.8 mmol) and boron trifluoride diethyl etherate 2 (3.0
equiv., 68.3 mol, based on the subunit). A Vigreux column and a distillation head were
connected. The mixture was stirred and heated to 120 °C (oil bath). The formed
difluorodimethylsilane was continuously distilled off and collected. After 3 h the yield was
determined and the quality was analysed by NMR. The solid residue in the reaction flask was
dried in vacuum and subjected to PXRD measurements. Difluorodimethylsilane 5: 1H NMR: δ
= 0.31 (t, 3JHF = 6.2 Hz) ppm. 19F NMR: δ = -131.4 (sept, 3JHF = 6.2 Hz, 1JSiF = 289.9 Hz) ppm.
1
3
3
Diethyl ether: H NMR: δ = 3.69 (q, JHH = 7.0 Hz, CH2), 1.26 (t, JHH = 7.0 Hz, CH3) ppm.
13C{1H} NMR: δ = 67.0 (CH2), 14.7 (CH3) ppm. Afterwards the mixture of 5 and diethyl ether
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were slowly added to an aqueous solution (50 mL) of KOH (136.8 mmol, 2 equiv. based on the
polymer subunit) at -78 °C. The mixture was warmed to room temperature over a period of one
hour. Afterwards the mixture was refluxed for 1 h. The mixture was cooled to room
temperature and the aqueous solution was extracted with dichloromethane (3x 10 mL). The
organic layers were collected and dried over Na2SO4. After filtration, the solvent was removed
in vacuum to yield a colourless oil (2.39 g, 59% yield based on the polymer subunit). [Me2SiO]n
7: 1H NMR: = 0.170, 0.131, 0.113, 0.093, 0.055 ppm. 13C{1H} NMR: = 0.99, 0.95, 0.83, 0,76,
0.68, 0.25, -1.0, -1.4 ppm. 29Si{1H} NMR: = -8.3 ppm. Octamethylcyclotetrasiloxane 7a
MS (ESI) m/z = 5.342 min [Me2SiO]4: 296 (<1, M+), 281 (100), 265 (14), 249 (13), 207 (13), 193
(18), 133 (11), 73 (23).
Procedure for the depolymerization of poly(1,1-dimethylsilazane) 8
A flask was charged with polymer 8 (6.9 mmol based on the polymer subunit) and boron
trifluoride diethyl etherate 2 (3.0 equiv., 20.6 mmol based on the polymer subunit). A Vigreux
column and a distillation head were connected. The mixture was stirred and heated to 100 °C
(oil bath). The formed difluorodimethylsilane was continuously distilled off and collected. After
3 h the yield was determined and the quality was analysed by NMR. Difluorodimethylsilane 6:
1H NMR: δ = 0.31 (t, 3JHF = 6.2 Hz) ppm. 13C{1H} NMR: δ = -3.45 (t, 2JCF = 16.7 Hz) ppm. 19F NMR:
3
1
δ = -131.4 (sept, JHF = 6.2 Hz, JSiF = 289.9 Hz) ppm. 29Si{1H} NMR: δ = -2.4 ppm. Diethyl ether:
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3
1H NMR: δ = 3.69 (q, JHH = 7.0 Hz, CH2), 1.26 (t, 3JHH = 7.0 Hz, CH3) ppm. 13C{1H} NMR: δ = 67.0
(CH2), 14.7 (CH3) ppm.
Acknowledgements
Financial support from the Cluster of Excellence “Unifying Concepts in Catalysis” (funded by
the Deutsche Forschungsgemeinschaft and administered by the Technische Universität Berlin) is
gratefully acknowledged.
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REFERENCES
[1] Newborough, M.; Highgate, D.; Vaughan, P. Appl. Therm. Eng. 2002, 22, 1875–1883.
[2] Kaminsky, W.; Hartmann, F. Angew. Chem. Int. Ed. 2000, 39, 331−333; Angew. Chem.
2000, 112, 339−341.
[3] Brandrup, J.; Bittner, M.; Michaeli, W. Recycling and Recovery of Plastics;
Hanser Gardner: nchen, Germany, 1996.
[4] Barnes, D. K. A.; Galgani, F.; Thompson, R. C.; Barlaz, M. Philos. Trans. R. Soc.
London Ser. B 2009, 364, 1985–1998.
[5] Hopewell, J.; Dvorak, R.; Kosior, E. Phil. Trans. R. Soc. B 2009, 364, 2115-2126.
[6] Ignatyev, I. A.; Thielemans, W.; Vander Beke, B. ChemSusChem 2014, 7, 1579-1593.
[7] (a) Enthaler, S. Angew. Chem. Int. Ed. 2014, 53, 2716-2721; (b) Döhlert, P.; Weidauer,
M.; Peifer, R.; Kohl, S.; Enthaler, S. J. Chem. Educ. 2015, 92, 703–707.
[8] Enthaler, S.; Kretschmer, R. ChemSusChem 2014, 7, 2030−2036.
[9] Enthaler, S. J. Appl. Polym. Sci. 2014, DOI: 10.1002/APP.41287.
[10]
[11]
The diethyl ether can be easily reused for the synthesis of new BF3OEt2.
(a) Döhlert, P.; Pfrommer, J.; Enthaler, S. ACS Sustainable Chem. Eng. 2015, 3,
163−169; (b) Döhlert, P.; Weidauer, M.; Enthaler, S. J. Appl. Poly. Sci. 2015, DOI:
10.1002/APP.42814; (c) Döhlert, P.; Enthaler, S. Catal. Lett. 2015, DOI:
10.1007/s10562-015-1665-6; (d) Döhlert, P.; Weidauer, M.; Enthaler, S. J. Energy Chem.
2015, DOI: 10.1016/j.jechem.2015.11.012.
12
ACCEPTED MANUSCRIPT

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[12]
Wiberg, N., Ed.; De Gruyter: Berlin, Germany, 1995; pp 1028−1029.
[13] Günthner, M.; Kraus, T.; Dierdorf, A.; Decker, D.; Krenkel, W.; Motz, G. J. Eur.
Ceram. Soc. 2009, 29, 2061-2068.
[14] Bernard, S.; Weinmann, M.; Cornu, D.; Miele, P.; Aldinger, F. J. Eur. Ceram.
Soc. 2005, 25, 251-256.
[15] Pitcher, M. W.; Arslan, Y.; Edinç, P.; Kartal, M.; Masjedi, M.; Metin, Ö.; Şen, F.;
Holleman, A. F.; Wiberg, E. Lehrbuch der Anorganischen Chemie, 101st ed.;
Türkarslan, Ö.; Yiğitsoy, B. Phosphorus Sulfur Silicon Relat. Elem. 2007, 182, 2861-
2880.
[16]
Zaheer, M.; Keenan, C. D.; Hermannsdörfer, J.; Roessler, E.; Motz, G.; Senker, J.;
Kempe, R. Chem. Mater. 2012, 24, 3952-3963.
[17]
See for instance for Si-N bond cleavage: (a) Shipov, A. G.; Kramarova, E. P.;
Murasheva, T. P.; Artamkina, O. B.; Negrebetskii, V. V.; Baukov, Y. I.; Pogozhikh, S.
A.; Ovchinnikov, Y. E.; Voronkov, M. G.; Bassindale, A. R.; Taylor, P. G. Russ. Chem.
Bull. 2006, 55, 579-582; (b) Thrasher, J. S.; Clark, M.; Morken, P. A. J. Fluorine Chem.
1988, 39, 235-243; (c) Lerner, H.-W.; Wiberg, N.; Bats, J. W.; J. Organomet. Chem.
2005, 690, 3898-3907; (d) Taylor, S. L.; Martin, J. C. J. Org. Chem. 1987, 52, 4147-
4156; (e) Bowser, J. R.; Williams, P. J.; Kurz, K. J. Org. Chem. 1983, 48, 4111-4113; (f)
Roeschenthaler, G. V.; Storzer, W.; Schmutzler, R. Z. Naturforschung, Teil B: Anorg.
Chem. Org. Chemie 1980, 35B, 1125-1129; (g) Gibson, J. A.; Marat, R. K.; Janzen, A. F.
Can. J. Chem. 1975, 53, 3044-3052; (h) Elter, G.; Glemser, O.; Herzog, W. J.
Organomet. Chem. 1972, 36, 257-265.
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[18]
A. J. Fluorine Chem. 2009, 130, 667-670.
[19] The P-XRD data was analysed with the X’Pert HighScore Software package,
revealing evidences for a boron and nitrogen containing compound.
Levin, V. V.; Dilman, A. D.; Belyakov, P. A.; Struchkova, M. I.; Tartakovsky, V.
[20]
Bassindale, A. R.; Pannell, K. H. J. Chem. Soc. Perkin Trans. 1990, 2, 1801-1804.
(a) Mohoric, I.; Sebenik, U. Polym. Int. 2013, 62, 1022-1028; (b) Yashiro, T.;
Kricheldorf, H. R.; Schwarz, G. Macromol. Chem. Phys. 2010, 211, 1311-1321.
[21]
[22]
3189.
Krüger, C. R.; Rochow, E. G. J. Polym. Sci., Part A: Polym. Chem. 1964, 2, 3179-
[23]
[24]
Voronkov, M. G.; Roman, V. K.; Maletina, E. A. Synthesis 1982, 277-280.
Newkirk, A. E. J. Am. Chem. Soc. 1946, 68, 2736-2737.
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Scheme 1. Potential recycling concept for polysiloxanes (a) and polysilazanes (b).
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Scheme 2. Reaction of hexamethyldisilazane 1 with boron trifluoride diethyl etherate 2.
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Scheme 3. Reaction of 1,1,3,3,5,5-hexamethylcyclotrisilazane 5 with boron trifluoride diethyl
etherate 2 and subsequent polymerization.
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Scheme 4. Reaction of poly(1,1-dimethylsilazane) 8 with boron trifluoride diethyl etherate 2 and
subsequent polymerization.
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