1.  Field of the Invention
The present invention relates to novel compounds comprising piperidyl functional groups bonded to a siloxane backbone, and to the use of such novel compounds for the light stabilization of polymer substrates. 
2.  Description of the Prior Art
It is known to this art that organic polymers and more particularly polyolefins and polyalkadienes are degraded when they are subjected to extraneous agents, especially the combined action of air and ultraviolet radiation in sunlight. 
Such degradation is typically restricted by introducing small amounts of stabilizers into the polymer. 
At present, some of the most effective of these anti-UV stabilizers are the sterically hindered amines, in particular 2,2,6,6-tetramethylpiperidines. 
In practice, however, one of the major problems in the use of these anti-UV stabilizers is to provide a good compromise between their effectiveness, which implies mobility within the polymer and the persistence of their activity, which implies the use of molecules of high molecular weight, which do not exude. 
It is for this reason that it has been proposed to use polyalkylpiperidines of high molecular weight, in order to limit the losses thereof, especially if the polymers are intended for use at high temperature.  Thus, U.S. Pat.  No.  4,698,381 describes a great number of high molecular weight or polymeric tetramethylpiperidines; it also describes N,N',N"-tris-(2,2,6,6-tetramethylpiperidyl-triazinyl)-undecanetriamines having molecular weights above about 1,500. 
Published European Patent Application No.  0,162,524 proposes another solution, i.e., the use of compounds which contain, per molecule thereof, sterically hindered amine groups and hydrolyzable silyl groups. 
Nonetheless, these latter compounds can result in the formation of complex resinous structures by reaction in the polymer or over the course of time. 
Such compounds appear to have an effective stabilizing action according to the examples in EP-A 0,162,524, but they also present certain disadvantages. 
Thus, crosslinking results in the formation of an alcohol from the hydrolyzable groups, which thus modifies the complex polymeric formulations in which all of the constituents serve a particular function. 
Moreover, the presence of the hydrolyzable groups in these compounds makes it difficult to preserve them. 
Finally, the formation of a complex resin structure limits the mobility of the stabilizing structure in the polymer.