Photoluminescent polydisilacyclobutanes

Abstract: Photoluminescent polydisilacyclobutanes are made by reacting a dialkenyldihalosilane with an organolithium reagent in the presence of a solvent at 0-25°C. Optional reactants such as aromatic acetylenic hydrocarbons or bicyclic dienes may also be included.

Description: This invention is directed to polycarbosilanes, more particularly to polymers in which silicon atoms are linked through substituted alkylene bridges. Specifically, these substituted polysilalkylenes are polydisilacyclobutanes. While the literature makes reference to processes using components similar to the components used herein, we are not aware of any reference in the literature specific to the use of a halosilane containing two unsaturated radicals. Thus, according to the teachings in the literature, the halosilanes contain only a single unsaturated linkage. See for example, Z. anorg. allg. Chem., Volume 558, pages 55-86, (1988); Chem. Ber., Volume 126, Pages 575-580, (1993); and J. prakt. Chem., Volume 337, Pages 79-92, (1995). By using halosilanes containing two unsaturated linkages, as exemplified in Journal of Organometallic Chemistry, Volume 377, Pages 175-195, (1989), we are surprisingly enabled to produce higher molecular weight materials, i.e., polymers. This invention relates to methods of making photoluminescent polydisilacyclobutanes and to polydisilacyclobutanes having a structural unit corresponding to the formula where a is an integer having a value of 2 to 20 and R1, R2, R3 and R4 represent hydrogen or an alkyl radical containing 2 to 10 carbon atoms. Preferably at least one of R1 or R2 and at least one of R3 or R4 is an alkyl radical containing 2 to 10 carbon atoms. The type of terminal groups of the polydisilacyclobutanes according to the present invention may vary in dependence of the type of the preparation reaction and/or subsequent derivatisation reaction that may be chosen to obtain the desired polydisilacyclobutane. This invention is directed to methods of unexpectedly preparing polymers having low to medium degrees of polymerization based on a disilacyclobutane building block. Our basic reaction involves the use of divinyldichlorosilane and an organolithium reagent like tert-butyllithium, and this basic route may be modified preferably by the addition of 2,5-norbornadiene or diphenylacetylene to obtain the desired products. More unexpectedly, it was found that phenyl-containing polymers exhibit strong photoluminescence in the blue region of the visible spectrum when excited by ultraviolet (UV) light with a wavelength of 337 nanometer (nm). Polymers terminated with chloro and vinyl groups show medium photoluminescence of the same blue color, whereas norbonyl terminated polymers show weaker photoluminescence of the same blue color. One type of polymer representative of our invention is shown generically as: where a is an integer having a value of 2 to 20, R1 to R4 is defined as above and R5 to R8 represent halogen, alkoxy, or an unsaturated radical containing two or more carbon atoms; One species (I) of the genus is shown below: Particles of the above polymer, where a = 10, were irradiated with UV light at a wavelength of 337 nm generated by a pulsed nitrogen laser with 0.1 millijoule (mJ) per pulse. The photoluminescence was deep blue, medium strong, and well visible in ambient room illumination. Another species (II) of the genus is shown below: A compositional analysis of this polymer where a = 10 showed that it consisted of 63.8 percent carbon, 12.7 percent hydrogen, and that the remainder was silicon and some oxygen from the methoxy groups. Gel Permeation Chromatography (GPC) revealed that the molecular weight of the polymer was 1,690 dalton (number average) with a dispersity of 1.34. Analysis by 29 Si Nuclear Magnetic Resonance (NMR) showed that the chemical shifts were 6.4 and 2.9 ppm. The process for making these polymers are illustrated schematically as shown below: While divinyldichlorosilane is shown as the preferred dialkenyldihalosilane component, other unsaturated dihalosilanes can be used. Similarly, while tert-butyllithium is shown as the preferred organolithium reagent, other lithium alkyls or lithium aryls can be used, such as methyllithium, hexyllithium or phenyllithium. An example representing this process is set forth below to further illustrate our invention in greater detail. EXAMPLE I Into a container were combined stoichiometric amounts of divinyldichlorosilane and tert-butyllithium (mole ratio divinyldichlorosilane:tert-butyllithium = 1:2), in pentane as solvent, at 0°C. The reactants were heated to room temperature, i.e., 20-25°C. After removing the solvent, a yellow solid resulted. The yellow solid was identified as species (I) shown above, where a had a value of 10. For purification, a portion of the sample of species (I) was extracted with methanol. Hydrochloric acid was generated and trapped by the addition of a small quantity of diethylamine. As a result, chlorine groups in species (I) were replaced by methoxy groups, yielding species (II) shown above, where a had a value of 10. Another type of polymer representative of our invention is shown generically as: where b is an integer having a value of 2 to 20; R9, R12, R13, and R16 represent aryl radicals; R10, R11, R14 and R15 represent hydrogen or an alkyl radical containing 1 to 10 carbon atoms, preferably one of R10 or R11 and one of R14 or R15 is an alkyl radical containing 1 to 10 carbon atoms and R1 to R4 are defined as above.. One species (III) of this genus is shown below: Particles of the above polymer where b = 3 were irradiated with UV light at a wavelength of 337 nm generated by a pulsed nitrogen laser with 0.1 mJ per pulse. The photoluminescence was blueish white, very strong, and well visible in ambient room illumination. A compositional analysis of this polymer where b = 3 showed that it consisted of 73.6 percent carbon, 11.1 percent hydrogen, and that the remainder was silicon. GPC revealed that the molecular weight of the polymer was 1,130 dalton (number average) with a dispersity of 1.48. Analysis by 29 Si NMR showed that the chemical shifts were 6.4 and 2.9 ppm. The process for making this type of polymer are illustrated schematically as shown below: While diphenylacetylene is shown as the preferred additional component according to this process, other alkyl, aryl, aralkyl, alkaryl, or trialkylsilyl, substituted acetylenic hydrocarbons can be successfully employed. An example representing this process is set forth below to illustrate our invention in more detail. EXAMPLE II Example I was repeated at room temperature instead of 0°C. and diphenylacetylene was added as another component of the reaction mixture. Excess diphenylacetylene was removed by distillation. The resulting yellow oily residue was purified over silica gel in toluene. The yellow oily residue was purified by extraction with methanol, yielding a white powder species (III) shown above, where b had a value of ten. Yet another type of polymer representative of our invention is shown generically as: where d is an integer having a value of 2 to 5; and R17 to R20 represent hydrogen or an alkyl radical containing 2 to 10 carbon atoms, preferably one of R17 or R18 and one of R19 or R20 is an alkyl radical containing 1 to 10 carbon atoms; R1 to R4 are defined as above. One species (IV) of this genus is shown below: Particles of the above polymer where d = 2 to 5 were irradiated with UV light at a wavelength of 337 nm generated by a pulsed nitrogen laser with 0.1 mJ per pulse. The photoluminescence was dark blue, weak and visible in the dark. The Diels-Alder process for making such polymers is illustrated schematically as shown below: While 2,5-norbornadiene is shown as the preferred additional component according to this process, other bicyclic dienes can be successfully employed. An example representing this process is set forth below to illustrate our invention in more detail. EXAMPLE III Example II was repeated accompanied by slow stirring, and 2,5-norbornadiene was added as the additional component of the reaction mixture, instead of diphenylacetylene. Crystallization was used to isolate a crystal species (IV) shown above, where d had a value of three. Isolation of photoluminescent polydisilacyclobutanes were carried out by extraction, crystallization or precipitation by addition of alcohol. Polymers prepared according to our invention are useful as passive or active display materials, and also in electroluminescent devices. In such utility, they are easily incorporated into road signs and lane markers. The polymers also find application in various types of displays as luminescent coatings for improving their visibility.

Claims: A photoluminescent polydisilacyclobutane having a structural unit corresponding to the formula where a is an integer having a value of 2 to 20 and R1, R2, R3 and R4 represent hydrogen or an alkyl radical containing 2 to 10 carbon atoms. The photoluminescent polydisilacyclobutane of claim 1 wherein at least one of R1 or R2 and at least one of R3 or R4 is an alkyl radical containing 2 to 10 carbon atoms. The photoluminescent polydisilacyclobutane of any of the preceding claims having a formula selected from the group consisting of where a is an integer having a value of 2 to 20 and R5 to R8 represent halogen, alkoxy, or an unsaturated radical containing two or more carbon atoms; where b is an integer having a value of 2 to 20; R9, R12, R13, and R16 represent aryl radicals; R10, R11, R14 and R15 represent hydrogen or an alkyl radical containing 1 to 10 carbon atoms; and where d is an integer having a value of 2 to 5; and R17 to R20 represent hydrogen or an alkyl radical containing 2 to 10 carbon atoms; wherein R1 to R4 represent in each formula a substituent as defined in any of the preceding claims. Photoluminescent polydisilacyclobutanes according to any of the preceding claims exhibiting photoluminescence in the blue region of the visible spectrum when excited by ultraviolet light. A method of making photoluminescent polydisilacyclobutanes comprising reacting a dialkenyldihalosilane with an organolithium reagent in the presence of a solvent at a temperature of 0-25°C. The method of claim 5 wherein the dialkenyldihalosilane is reacted with an aromatic acetylenic hydrocarbon in the presence of an organolithium reagent and a solvent at a temperature of 0-25°C. The method of claim 5 wherein the dialkenyldihalosilane is reacted with a bicyclic diene in the presence of an organolithium reagent and a solvent at a temperature of 0-25°C.; stirring the reactants. The method according to any of claims 5-7 further including the step of isolating the photoluminescent polydisilacyclobutane by extraction, crystallization or precipitation by addition of alcohol. Photoluminescent polydisilacyclobutanes obtainable by the method of any of claims 5-8.

Inventors: AUNER NORBERT, PERNISZ UDO C, AUNER, NORBERT, PERNISZ, UDO C.
Applicants: DOW CORNING, DOW CORNING CORPORATION
Application year: 1998
Main classification: C08G77
IPC codes: H01J1, C07F7, C08G77, C09K11