Macromolecules 1987,20, 2654-2659
2654
Identification of Organic Compounds, 4th ed.; Wiley: New York, 1981. (6) Charton, M. J. Org. Chem. 1963, 28, 3121. (7) Gordon, A. J.; Ford, R. A. The Chemist's Companion: A
Handbook of Practical Data, Techniques, and References; Wiley: New York, 1972; pp 59-60. ( 8 ) Mayo, F. R.; Lewis, F. M. J. Am. Chem. SOC.1944,66, 1594. (9) Kelen, T.; Tudos, F. J. Macromol. Sci. Chem. 1975, A9, 1.
Poly(dimethylsi1oxane-co-diphenylsiloxanes):Synthesis, Characterization, and Sequence Analysis G . N. Babu,*+ S.S.Christopher,+and R. A. Newmarkt Industrial Tape Division and 3M Corporate Research Laboratory, 3M Company, St. Paul, Minnesota 55144. Received February 10, 1987 ABSTRACT Poly(dimethylsi1oxane-co-diphenylsiloxane)copolymers have been prepared by ring-opening and step-growth condensation polymerizations. Composition of the copolymers has been determined by 'H and 29SiNMR spectroscopy. Sequence distribution up to the pentad level is observable in the 29SiNMR spectrum. Copolymers have been characterized by GPC and DSC measurements. The glass transition temperatures increase with an increase in the proportion of diphenylsiloxane content.
Introduction Silicone elastomers have long been known for their exceptional ability to exhibit and retain superior mechanical properties over a broad temperature range.' The main interest in these materials stems from the fact that they possess unique properties such as good low-temperature flexibility, excellent electrical properties, chemical inertness, water repellency, and biocompatibility not common in hydrocarbon polymer^.^^^ Various structural modifications have been investigated in order to modify some of the properties. For example reinforcement by silica fillers help in modifying the weak cross-linked network of conventional silicone r ~ b b e r .Segmented ~ copolymers comprising hard and soft segments are an alternative approach to obtain polymers with specific end uses.67 Synthesis of low and high molecular weight poly(dimethylsi1oxane-codiphenylsiloxanes)have also been reported.g'10 It has been shown that introduction of diphenylsiloxane segment usually disrupts the low-temperature crystallization of polydimethylsiloxane and also increases the thermal and radiation stabi1ity.l There has been no systematic study of the structure-property relationship of these novel copolymers. The objective of this investigation is to synthesize and characterize high molecular weight poly(dimethylsiloxane-co-diphenylsiloxanes) and determine their sequence by '?3i NMR spectroscopy. An attempt has also been made to correlate sequence distribution with the physical properties of the copolymers. Experimental Section Spectra. Proton and 29Si NMR spectra were obtained on Varian XL-100 and XL-400 NMR spectrometers, respectively, at 100 MHz ('H) and 79.46 MHz (%Si). Chemical shifts are given relative to tetramethylsilane internal reference. Integrals on the proton spectra were obtained directly on concentrated solutions in chloroform-d. Ten milligrams (0.01 M) Cr(aca& relaxation reagent was added to each 3 cm3 solution of the samples before the %Si spectra was obtained in order to eliminate the nuclear Overhauser enhancement and reduce the relaxation times ( T l ) . Measurement of TIand nOe on a representative sample indicated all silicons in the polymer multiplets had comparable T1 values of 5.0 s and that the nOe was 0.9. Quantitative %Si spectra were obtained by using 35' pulses and a 1.9-s recycle time to maximize the signallnoise. This partial saturation of the peaks will not effect Industrial Tape D. t 3M Corporate Research Laboratory.
integrals used to calculate the sequence distribution since all the polymeric absorptions had similar relaxation times. Also, the ratios of SiPh20:SiMe20observed in the 'H spectra match those observed in the 29Sispectra. Materials. Octamethylcyclotetrasiloxane(methyl tetramer, D4),octaphenylcyclotetrasiloxane (phenyl tetramer, D4Ph),and diphenylsilanediol (DSD) were obtained from Petrarch Systems or Silar Laboratories. Bis(dimethy1amino)dimethylsilane and 1,7-bis(dimethylamino)hexamethyltrisiloxane(Silar Lab.) were freshly distilled before use. Synthesis. Bis(pyrrolidiny1)dimethylsilane. A dry 1-L three-necked, round-bottom flask was fitted with a reflux condenser, dropping funnel, mechanical stirrer, and an argon inlet. The apparatus was degassed by alternately evacuating and filling with argon. With argon flow through the system, freshly distilled dimethyldichlorosilane (90 g, 0.7 mol) and dry heptane (150mL) were placed in the reaction vessel (eq 1). Dry pyrrolidine (199 Me
Me
u
g, 2.8 mol) was added dropwise over a period of 3 h with stirring and cooling in an ice bath. After completion of the addition, the reaction mixture was stirred overnight at ambient temperature. The amine hydrochloride precipitate was removed by filtration with positive argon pressure. The solvent was removed under vacuum. The residue was distilled at 85-87 "C (0.1 mm) in 95% yield IR (neat) C-H, 3000,2960,2875 cm-' (s, s, s); Si-Me, 1265 cm-' (s), Si-N, 995 cm-' (m). Bis[ phenyl( 1-pyrrolidinylcarbonyl)amino]dimethyl(Referred to as Diureidosilane). A 1-L,three-neck round-bottom h k was equipped with mechanical stirrer, an argon inlet, a reflux condenser, and a dropping funnel. The apparatus was alternately evacuated and filled with argon six to eight times. Freshly distilled dipyrrolidinyldimethylsilane(100 g, 0.5 mol) and 350 mL of dry ether were added, and the mixture was stirred in a 0-5 "C ice bath for approximately 10 min (eq 2). Dry phenyl isocyanate (119 g, 110 mol) was added to the chilled solution over a I-h period. A white solid slowly separated during addition. Stirring was continued for an additional 3 h to ensure the completion of the reaction. The compound was then filtered under positive argon pressure and washed with dry pentane. The product was isolated in 90% yield: mp 125 "C lit." mp 124-125 "C. Purity of the product was confirmed by elemental analysis. IR (KBr): C-H, 3000, 2960, 2875 cm-' (s, s, s),Si-Me, 1260 cm-' (s), N-H, 3475 cm-I (s). 0 1987 American Chemical Society
Macromolecules, Vol. 20, No. 11, 1987 Me
Me
Polymer Synthesis. Ring-Opening Polymerization of Methyl Tetramer and Phenyl Tetramer (Polymers 1-5). Predetermined amounts of methyl tetramer and phenyl tetramer were charged to the reaction kettle (eq 3) fitted with a mechanical stirrer, thermometer, argon inlet, and dry ice condenser. The
contents were heated to 165 "C in an oil bath. Polymerization was initiated by the addition of potassium hydroxide (10-25 ppm). The reaction mixture was heterogeneous during the first 3-4 h and became homogeneous as the reaction proceeded. The reaction was run from 15 to 24 h depending on the content of phenyl tetramer in the feed. At the end of the reaction, the catalyst was deactivated with acetic acid. The low molecular weight and the cyclic products were stripped off under vacuum. The copolymer was purified by repeated precipitation in methanol from toluene solution. The purified polymer was dried under vacuum at 80 "C to constant weight. The yields in all cases were greater than 80%. Preparation of Poly(dimethylsi1oxane-co-diphenylsiloxane) from Diphenylsilanediol and Bis(dimethy1amin0)dimethylsilane (Polymer 6).13 Diphenylsilanediol (15 g, 0.0694 mol) was placed in a weighed three-necked 250-mL round-bottom flask and dried overnight in a vacuum oven at 50 O C . The flask was reweighed, fitted with a thermometer, a mechanical stirrer, and a two-outlet adaptor supporting a reflux condenser and a septum-sealed opening. The system was then alternately evacuated and filled with argon several times. To the flask was added 50 mL of dry toluene while positive argon pressure was maintained. The reaction mixture was heated to a gentle reflux. Under argon atmosphere, 10.13 g (0.0694 mol) of bis(dimethy1amino)dimethylsilanewas withdrawn into a dried, preweighed syringe. The silane was injected through the septum into the reaction flask. Approximately 2.5 g of silane was added to the flask. This addition was repeated four times over 24-h period. The remaining silane (0.1-0.2 g) in the syringe was diluted with 2 mL of dry toluene and was added twice in a 6-h period. The reaction was further refluxed for 4 more hours. The viscous polymer solution was precipitated in 500 mL of methanol. The polymer was further purified and dried at 80 "C under vacuum to constant weight. Low tack opaque polymer was obtained in 65% yield. IR (neat): C-H, 3000,2960,2875cm-' (s, s, s), Si-Me, 1260 cm-' (m), Si-0-Si, 1060-1110 cm-' (s), Ph-Si
