This invention is directed generally to processes for the preparation of polysilylenes, and more specifically to processes for the preparation of polysilylene polymers by the simultaneous addition of an alkali metal, and a dihalodisubstituted silane monomer, including dihalodialkyl and dihalodiaryl silane monomers, to a suitable solvent. In one embodiment the present invention is directed to a simple economical process for the preparation of polysilylenes, by the simultaneous addition of a silane monomer and a sodium dispersion to an organic solvent, and thereafter separating the desired product. The aforementioned polysilylene products are useful for incorporation into imaging members comprised of for example, a supporting substrate, a photogenerating layer, and in contact therewith as a charge or hole transport layer the polysilylenes, especially poly(methylphenyl silylene), poly(n-propyl methyl silylene), and other similar silylenes. Additionally, the layer with the polysilylene hole transporting compound can be located as the top layer of the imaging member, or alternatively it may be situated between the supporting substrate and the photogenerating layer. The aforementioned imaging members are particularly useful in electrophotographic, and especially xerographic, imaging processes including those wherein there are selected for development liquid ink compositions.
Imaging members comprised of polysilylenes are illustrated in U.S. Pat. No. 4,618,551, the disclosure of which is totally incorporated herein by reference. More specifically, there is illustrated in this patent a polysilylene hole transporting compound for use in layered imaging members comprised of the formula as recited in claim 1, for example. More specifically, there is described in the aforementioned patent an improved layered photoresponsive imaging member comprised of a supporting substrate, a photogenerating layer, and as a hole transport layer in contact therewith a polysilylene compound of the formula ##STR1## wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, and R.sub.6 are independently selected from the group consisting of alkyl, aryl, substituted alkyl, substituted aryl, and alkoxy; and m, n, and p are numbers that reflect the percentage of the particular monomer unit in the total polymer compound. Preferred polysilylene hole transporting compounds illustrated in this patent include poly(methylphenyl silylenes), which silylenes more preferably have a weight average molecule weight of in excess of 50,000, and preferably are of a weight average molecule weight of about 75,000 to about 1,000,000. The aforementioned polysilylenes can be prepared by known methods, reference the Journal of Organometallic Chemistry, page 198, C27, (1980), R. E. Trujillo. Also, other polysilylenes can be prepared as described in the Journal of Polymer Science, Polymer Chemistry Edition, Vol. 22, pages 225 to 238, (1984), John Wiley and Sons, Inc.. More specifically, the aforementioned polysilylenes can be prepared as disclosed in this article by the condensation of a dichloromethyl phenyl silane with an alkali metal such as sodium. In one preparation sequence, there is reacted a dichloromethyl phenyl silane in an amount of from about 0.1 mole with sodium metal in the presence of 200 milliliters of solvent, and wherein the reaction is accomplished at a temperature of from about 100.degree. C. to about 140.degree. C. There results, as identified by elemental analysis, infrared spectroscopy, UV spectroscopy, and nuclear magnetic resonance, the polysilylene products subsequent to the separation thereof from the reaction mixture. The aforementioned prior art, however, does not disclose the simultaneous addition of an alkali metal and a dihalodialkyl silane monomer.
There is disclosed in U.S. Pat. No. 2,554,976, and British Pat. No. 666,359 the preparation of low molecular weight polymethylsilylenes by the admixing of dimethyldihalogenosilane and sodium, followed by the addition of an inert diluent, such as toluene, and thereafter heating the aforementioned mixture, reference column 1, line 36 to column 2, line 11, for example. Thus, in this process there is no disclosure as to the simultaneous addition of monomer and alkali to a solvent. Accordingly, there results polysilylenes of low molecular weight, for example 2,000 to 3,200, which polysilylenes are not believed to be useful as hole transport molecules in photoconductive imaging members as illustrated in detail hereinafter.
Other patents disclosing similar processes include British 671,773, and 671,774; and U.S. Pat. Nos. 2,606,879 and 4,260,780. Also of background interest are U.S. Pat. Nos. 2,886,582; 4,587,780; 4,588,801 and 4,587,205.
When selecting components for photoreceptors, particularly photogenerating or hole transport substances, it is important that when the member is exposed to light that it retain its stability; and more specifically, that the components thereof are not adversely effected by light causing them to degrade or decompose and thereby rendering them substantially useless for their intended purposes. In addition, during the corona charging step in electrostatic imaging processes, the voltages emitted may cause degradation of the components in the imaging member affecting the undesirable degradation thereof, and permitting emission of products, and in some instances, hazardous products to the environment.
Advantages of the process of the present invention include desirable solvent inertness, and further the polymeric product formed has advantages associated with polymers including excellent mechanical ressitance. Accordingly, there is a need for processes that will permit the preparation of polysilylenes to enable their incorporation into photoconductive imaging members and permitting the resulting members to be useful for extended time periods exceeding, for example, 1,000,000 imaging cycles without degradation. There is also a need for processes wherein the reactions are not exothermic, and wherein there can be obtained high molecular weight polymers, which have low polydispersability and are substantially free of low molecular weight fractions, that is those below a weight average of, for example, 10,000 to 50,000. Additionally, the imaging members within which these polymer products are selected are substantially free of environmental problems.