Synthesis and Properties of Silicones and Silicone-Modified Materials

Chapter 26

Downloaded by CORNELL UNIV on May 12, 2017 | http://pubs.acs.org Publication Date: March 10, 2003 | doi: 10.1021/bk-2003-0838.ch026

Poly(dimethylsiloxane)-graft-oligo(hexafluoropropeneoxide) Via Ring-Opening Polymerization M a r k A . Buese, Jose F . Gonzalez, Curtis G. Harbaugh, Garrett M. Stearman, and Michael S. Williams Clariant L S M (Florida) Inc., P.O. Box 1466, Gainesville, F L 32602

Cyclotetrasiloxanes with an oligo(hexafluoropropeneoxide) substituent were prepared and ring-opening polymerized. The synthesis of the cyclosiloxanes with three different linkages between the siloxane and fluoroether is described. The cationic and anionic polymerizations were examined. The equilibrium cyclosiloxanes were extracted from the polymer and characterized. The copolymerization with a polycyclosiloxane resulted in the formation of cross-linked networks.

Variousfluorosiliconehomopolymers and copolymers are quite useful as lubricating oils for severe environmental conditions, crude-oil antifoams, magnetic media lubricants, pressure-sensitive adhesive release-liners, selective oxygen permeable membranes, very low temperature elastomers, low refractive index elastomers, and oil and soil resistant rubbers, sealants, and coatings. Polytrifluoropropylmethylsiloxane, PTFPMS, is the most widely available fluorosilicone and is used in applications where resistance to hydrocarbons and other organic compounds is required. Although it has a lower affinity for

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© 2003 American Chemical Society

Clarson et al.; Synthesis and Properties of Silicones and Silicone-Modified Materials ACS Symposium Series; American Chemical Society: Washington, DC, 2003.

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hydrocarbons, PTFPMS displays a higher liquid surface tension than PDMS (7). Surface properties are determined primarily by the composition and orientation of the atoms at the surface layer. Although the C F group intrinsically donates the lowest surface energy of any fragment, it cannot dominate the surface of PTFPMS and cannot overwhelm the contributionfromthe ethylene link between the C F and siloxane backbone (2). To achieve a fluorosilicone with lower surface tensions than PDMS, the polymer must have a high density of aliphatic fluorine-containing groups. The group must not affect the backbone flexibility of the polysiloxane in a detrimental manner and the linking group between the fluorocarbon and silicone must be sufficiently removed from the surface such that its contribution is negligible (3). This requires a larger fluoroorgano substituent on the siloxane unit. The polymerization of cyclic oligomers is the primary route to the majority of silicone polymers and copolymers. The polymerization of octamethylcyclotetrasiloxane, D , to polydimethylsiloxane, PMDS, and other unstrained cyclosiloxanes, those larger than the trimer, with relatively small substituents at silicone has been extensively documented (4). The process results in a mixture of linear and cyclic structures. The proportions of these structures are relatively easily predicted from statistical considerations where the linear homologues displaying a Flory-Schultz distribution (J) and the cyclic homologues display a modified Jacobson-Stockmayer distribution (6). The experimentally observed equilibrium cyclic oligomer concentrations for the cyclic tetramer through hexamer are higher than those predicted by JacobsonStockmeyer theory, and the cyclic octamer through approximately the 21-mer are lower than predicted (7,8,9). The larger the substituents on the silicon, the more pronounced is the deviation from the theoretical equilibrium cyclization constants for any given siloxane homopolymer (10). 3


3

4

The equilibrium constants for the cyclic tetramer, pentamer, and hexamer of PTFPMS are high, with the tetramer and pentamer nearly an order of magnitude greater than that of their counterpart in equilibrium with PDMS. The summation of the product of the equilibrium constants for the tetramer through pentadecamer and their molecular weight indicate that linear polymer cannot exceed 26% by weight in an attempt to prepare high polymer (70). The critical volume concentration for PTFPSO is approximately 10%, which virtually excludes typical condensation polymerizations such as the hydrolysis of dichlorosilanes, as the leaving group is a sufficient diluent to preclude linear polymer formation (4). For these reasons PTFPS is prepared by kinetically controlled ring-opening polymerization of the strained cyclic trimer. Even under these conditions, if the catalyst is not destroyed immediately upon the attainment of high polymer, depropogation to a mixture dominated by cyclic oligomers results (77). The ring-opening polymerization of unstrained



308 cycloperfluoroorganosiloxane with large perfluoroalkyl substituents is even less successful than the polymerization of the PTFPS cyclic tetramer, as implied during the condensation of lH,lH,2H,2H-perfluorooctylmethyldichlorosilane with water (12). The use of cyclic trimers has been extended to the preparation of dimethylsiloxane copolymers where the ring contains a single silicon with one or two large perfluoroorgano substituents (13,14). In both cases high polymers were prepared by cationic and anionic polymerization. The patent literature describes a trimer containing one to three fluoroalkoxyalkyl groups (75) and a single hexafluoropropylene oxide oligomer attached to the ring (16,17). They were claimed to be polymerizable. The preparations of the cyclic trimers were not trivial, requiring the use of solvents and tetramethyldisiloxane-l,3-diol. Polytrifluoropropylmethyl-siloxane-co-dimethylsiloxane has been prepared from cyclic tetramers where the weight of linear polymer prepared in solution increased from 0 to 31 to 45% as the proportion of trifluoropropyhnethylsiloxy units decreased from 100 to 50 to 25% by mole (18). The preparation of copolymers of larger perfluoroalkylsiloxane and dimethylsiloxane via copolymerization of octamethylcyclotetrasiloxane and unstrained perfluoroalkylmethylsiloxane cyclic oligomers has resulted in commercialized fluids (72). The weight fraction of perfluoroalkyl groups can be increased without significantly increasing the magnitude of the equilibrium constants for the cyclosiloxanes from that of thosefromdimethylsiloxane by copolymerization. This report describes the preparation andring-openingpolymerization of an oligo(oxyperfluoropropylene)heptamethylcyclotetrasiloxane, using acidic and basic initiators, to poly(dimethylsiioxane)-gra^-oligo(oxyperfluoropropylene) and to networks. The properties of polyfluoroalkylpolyethers are complimentary to properties of silicones desirable for many applications such as high shear and thermal stability, nonflammability, and high compressability. They have the potential to significantly enhance some properties of silicones, such as low surface energy and low refractive index. Perhaps most importantly, they have the potential to significantly improve some of the shortcomings of silicones, such as their solubility in common organic solvents. The cyclotetrasiloxanes had a single large oligomer of hexafluoropropeneoxide attached via a propylamide or a propylester linkage. This route was chosen as all the starting materials for the cyclic tetramer are commercially available and the intermediates could be prepared in high yield without the use of solvents. The polymerization of the tetramer resulted primarily in a linear polymer and cyclosiloxanes. The cyclosiloxanes could be extracted with hydrocarbons. The extracted cyclosiloxanes could be polymerized in like manner to the starting tetramer, resulting in essentially the same polymers. In this manner the effective yield of these copolymer can be quite high.


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Experimental All chemicals were purchasedfromLancaster Synthesis with the exception of methylallylamine, which was purchased from Aldrich. Heptamethylcyclotetrasiloxane, 1, was prepared as previously described (19). l,3,5,7-Tetra-(2heptamethylsUoxane-ylethyl)-l,3,5,7-tetramethylcyclotetrasiloxane, 9, was pre pared and isolated as previously described (20). Gas Chromatography was carried out using a Hewlett-Packard 5890 Series II Chromatograph with a thermal conductivity detector and a SPB-1 30 m x0.53 mm capillary column with a 0.5 mm thick film. IR spectra were recorded using a Nicolet 5PC FTIR Spectrometer. NMR spectra were recorded using a JEOL JNM GX400 FT NMR Spectrometer. Synthesis of [3-(perfluoro-2,5,8-trimethyl-3,6,9-trioxadodecan-oyl)-oxypropyi]heptamethylcyciotetrasiloxane As illustrated in Figure 1, a 1L round bottom flask was charged with 500 g of 1 and was heated to 80°C and 200 pL of Pt 1,3-di-vinyltetramethyldisiloxane complex in xylene (3% Pt) was added. The mixture was stirred and 125 g of allyl alcohol was added dropwise. The reaction was exothermic. Addition was carried out at 90-120°C over a period of 2 hours. A GC trace indicated the presence of (3-hydroxy)heptame1hylcyclotetrasiloxane 2, at 84%. Distillation at 70°C and 0.2rnrnHggave 450g (75% yield) with 98% purity by GC analysis. ?

V *Si'

/ *Si

Ο \

Ο +

1

F C F F F F F 3 F F 3

O

FC FF FF F 3

Figure 1. Preparation of[3-(perfluoro-2,5,8-trimethyl-3,6,9-trioxadodecanoyl)-oxy-propyl]heptamethylcyclotetrasiloxane where x=3


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As illustrated in Figure 1, a 50 mL round bottomflaskwas charged with 7.7 g of 2 and 2.3 g of triethylamine. The mixture was stirred and 15.0 g of 97% perfluoro-2,5,8-trimethyl-3,6,9-trioxadodecanoyl fluoride, 3 where χ = 3, was added dropwise. A GC trace indicated that all of 3 and most of 2 were consumed with predominately the formation of [3-(perfluoro-2,5,8-trimethyl3,6,9-trioxadodecan-oyl)-oxypropyl]heptamethylcyclotetrasiloxane, 4 where χ = 3. The product was washed once with dilute HC1, and twice with water. The crude product was distilled at 110°C and 0.3 mrnHg resulting in 14.7 g of 4 where χ = 3 (66%) which was 97% pure by GC analysis. 1 H NMR 400 MHz, CDCI3 δ 0.1(s 21 H), 0.6 (t 2 H), 1.8 (p 2 H), 4.4 (m 2 H); 19 F NMR 376 MHz, CDC13: δ -81 (CF3). -82 (CF3), -83 (CF3), -85 (CF3), -130 (CF2), -132 (CF2), -144 (CF); IR (neat liquid on NaCl): cm" : 2970 (m), 1780 (s), 1245 (vs), 1200 (s), 1145 (s), 1070 (vs), 995 (s), 970 (s), 810 (vs) 750 (m). In like manner 4 where χ = 4, 5, 6,7, and χ averages 8 were synthesized.


1

r

Synthesis of A -(3-heptamethylcyclotetrasiloxan-yl)-propylperfluoro-2,5,8,trimethyl-3,6,9,-trioxadodecanamide As illustrated in Figure 2, a 100 mL round bottom flask equipped with a magnetic stirring bar and an addition funnel was charged with 9.0 g of allyl amine. The liquid was stirred and 40 g of 97% 3 where R = Η, χ = 3 was added dropwise. The addition of dilute HC1 resulted in two phases. The amide layer was washed with dilute HC1 and twice with water. Distillation at 101°C and 3 mrnHg yielded 21.6 g (52%) of >99% iV-allyl-perfluoro-2,5,8,-trimethyl-3,6,9,trioxadodecanamide, 5 where R = Η, χ = 3.

F

u rF C 3

F F

5 if R=H

F

F F

F

7 if R=CH

3

F F FF F

n

F F

3

Figure 2 Preparation ofN-(3-heptamethylcyclotetrasiloxan-yl)propylperfluoro-2,5,8,-trimethyl-3,6,9,-trioxadodecanamide where R=Handx=3 or N-methyl-N-(3-heptamethylcyclotetrasiloxan^ trimethyl-3,6,9,-trioxadodecanamide where R=Me andx=3


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As illustrated in Figure 2, a 3-necked 25 mL round bottom flask was equipped with a magnetic stirring bar, a condenser, and a temperature probe. The flask was charged with 10.0 g of >99% 5 and 4.0 g of 1. The mixture was heated to 100°C and 10 pL of a Pt 1,3-di-vinyltetramethyldisiloxane complex in xylene (3% Pt) was added. A very exothermic reaction occurred. A gas chromatographic analysis indicated a high conversion to a single product. Distillation at 116-20°C and 0.04 mrnHg resulted in 5.7 g (43% yield) of >99% Af-(3-heptame&ylcyclotetasiloxan^ trioxadodecanamide 6 where R = Η, χ = 3. *H NMR 400 MHz, CDC1 : δ 0.1 (m 21 H), 0.6 (t 2 H), 1.7 (ρ 2 H), 3.4 (m 2 H), 6.7 (s 1 H); IR (neat liquid on NaCl): cm : 3460 (m), 2970 (m), 1705 (s), 1550 (m), 1310 (m), 1245 (vs), 1200 (s), 1150 (s), 1070 (vs), 995 (s), 970 (s), 810 (vs), 750 (m). In like manner runs using 6 where χ = 4, 5, and 6 were synthesized. 3


1

Synthesis of 7V-methyl-iV-(3«heptamethylcyclotetrasiloxan-yl)-propylperfluoro-2,5,8,-trimethyl-3,6,9,-trioxadodecanamide As illustrated in Figure 3, in an equivalent manner to the preparation of 5, 5.0 g of N-methylallylamine and 17.5 g of 97% 3 reacted and were distilled at 98°C and 2.4 mrnHg to give 14.3 g (77% yield) of >99% iST-methyl-iV-allylperfluoro-2,5,8,-trimethyl-3,6,9,-trioxa-dodecanamide, 7 where R = Me, χ = 3. As illustrated in Figure 3, in an equivalent manner to the preparation of 6, 7.0 g of of >99% 7 and 2.8 g of 1 reacted in the presence Pt 1,3-di-vinyltetramethyldisiloxane complex and were distilled at 100-5°C and 0.04 mrnHg to yield a 5.2 g (53% yield) of >99% iV-methyl-iV-(3-heptamethylcyclotetrasiloxanyl)-propyl-perfluoro-2,5,8,-trimethyl-3,6,9,-trioxa 8 where R = Me, χ = 3. The product was analyzed by spectroscopy with the following results: H NMR 400 MHz, CDC1 : δ 0.1 (m 21 H), 0.5 (m 2 H), 1.7 (m 2 H), 3.1 (m 3 H), 3.5 (m 2 H) ); IR (neat liquid on NaCl): cm : 2970 (m), 1685 (s), 1410 (w), 1300 (m), 1245 (vs), 1200 (s), 1140 (m), 1080 (vs), 995 (s), 970 (s), 810 (vs), 750 (m). In like manner syntheses using 8 where χ = 4, 5, 6, 7, and with mixtures where χ averages 7.3 were carried out. l

3

1

Cationic Polymerization As illustrated in Figure 4, a 1.5 dram vial containing 1.0 g of 4 where χ = 3, was injected 2.0 pL of trifluoromethanesulfonic acid and the mixture was shaken to form a polymer. The vial was warmed for 10 minutes. A viscous oil resulted upon cooling to room temperature. The oil was warmed and allowed to stand for 4 hours with little or no apparent change. To the vial was added 0.01 g of MgO and the oil was warmed to facilitate dispersion of the salt. Upon


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cooling, 1 mL of pentane was added to the vial and the mixture shaken. Two liquid phases and a solid phase were apparent. The liquid layers were filtered using a 3 mL syringe equipped with a 0.45 micron filter. A series of peaks was observed by GC analysis of thefreshlyformed suspension. After separation, the upper layer was removed and placed in a vial. The polymer was extracted with additional pentane. Evaporation of the pentane from the extract resulted in a liquid residue of 0,2 g. TTie GC trace of this residue displayed the same signals for siloxanes observed for the polymer suspension. The copolymer layer was heated with a stream of N to remove the pentane. The resulting 0.6 g of a gum displayed no flow. A small portion was shaken with pentane and the suspension immediately analyzed by GC. Only a peak for pentane was observed. Similar results were observed for all of the polymers. In like manner, polymers were preparedfrom1.0 g of 6 where χ = 3 and 1.0 g of 8 where χ = 3 by the injection of 2.0 pL of trifluoromethanesulfonic acid. A viscous linear-cyclic mixture, similar to that of 4, resulted in the case of 8 and the mixture from 6 was much more viscous than the fluid from 4. The polymerizations of 8 where χ = 4 and 8 where χ = 7.3 were examined.


2

Anionic Polymerization As illustrated in Figure 3, a 1.5 dram vial containing 2.0 g of 6 where χ = 3.4 was injected with 19.0 pL of 1M tetrabutylammonium fluoride in tetrahydrofuran and the mixture shaken to form a polymer. The vial was warmed gently over 10 minutes and upon cooling increased in viscosity. The heating was repeated until, upon cooling, it resulted in a heavy oil that displayed almost no flow when the vial was inverted at room temperature. No apparent increase in viscosity was observed upon subsequent heating. After 24 hours the vial was heated strongly with the formation of bubbles, presumably from the decomposition of the tetrabutylammonium salt. A linear-cyclic mixture similar to that observed in the cationic polymerization was observed by GC analysis. In like manner, polymers were preparedfrom8 where χ = 4 and 8 where χ = 7.3 by the addition of tetrabutylammonium fluoride solution. Viscous linearcyclic mixtures resulted but the were of notably lower viscosity than thatfrom6 and lower in viscosity than thosefromcationic polymerization. The miscibility of these polymers in acetone, cyclohexane, and toluene is shown in Table I.

Table I Miscibilities of solvents with polymersfrom8 where χ = 4 and χ = 7.3 % Increase in Volume of Polymer after 24 hr Cyclohexane Toluene Acetone χ= 6.1 9.4 12.7 4 5.4 5.3 8.5 7.3


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4ifX=0, 6ifX=NH,or 8ifX=N(CH ) 3

HOS0 CF or 2

3

+

„ (H C ) N F" 9

0


\

/

J

4

4

F F

F C F F F F F

o^si-

3

+

ί ^ ο ^ ο Κ F F

F

-si^o O

F F F F CF

(

3

Figure 3 Polymerization of oligo(oxyperfluoropropylene)heptamethylcyclotetrasiloxanes

Polymerization to Networks As illustrated in Figure 4, cationic copolymerizations of 9 and 8 where x=4 and χ = 7.3 were carried out in proportions calculated to give similar low cycle ranks networks as given in Table 2 (21). Placing the rubbers in MgO terminated the siloxane redistribution. For comparison, rubbers were prepared by the copolymerization of D and 9, D , 8 where χ = 7.3 and 9, and 8 where χ = 7.3, 8 where χ = 4 and 9. In all cases, soft rubbers were formed. Swelling of the rubbers was examined in cyclohexane and toluene as given in Table 2. 4

4

Table Π Preparation and swelling studies of networksfrom8 % Mass Increase MW Cycle Massing MW CeHi2 Rank" X= 8 9 RU Jto J* 710 310 11,000 10.0007 0.1515 74.15 30.9 0 8.7 8.5 9,500 10.0026 0.1548 290.47 28.8 4 7.6 6.0 7,100 0.1977 429.66 28.8 10.0062 7.3 8.1 6.1 10,000 30.7 6.6" 10.0239 0.1803 346.43 8.9 16,000 26.2 0.0156 290.91 4.0 1.1490 a t 1 Λft "Calculated, 100(Final ,/W Wt-Initial Wt)/Initial Wt, ' ϋ , M i x o f x = 4 andx = 7.3, Mix of χ = 7.3 and D C

e

b

J

4

e

4


314


8 +

_

V

W

\

/

\

/

\

/

\

-

S

l

^ ° CH,

CH,

F F

F F

A c *

F,C F F F F F

FC FF FF F 3

Fîgwre 4 Copolymerization with 1,3,5,7-Tetra-(2-heptamethylsiloxaneylethyl)-l,3,5,7-tetramethylcyclotetrasiloxane to Networks

Results and Discussion The synthesis of 4 occurred in high conversion with nearly complete consumption of 3. Likewise, the preparations of 6 and 8 were carried out in high conversion. Although 6 could be prepared by either of the synthetic routes (Figures 1 and 2), 4 was prepared in only modest yield via the route given in Figure 2 and attempts to produce 8 via the route given in Figure 1 were unsuccessful. In all cases, the Si was linked to the carbonyl through a threecarbon bridge with no evidence of a two-carbon bridge. All the cyclosiloxanes were dense (d >1.4), low viscosity liquids with low refractive indices (RI

Synthesis and Properties of Silicones and Silicone-Modified Materials

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