No, there are no standard gauge tracks between Moscow and the Polish border.

Until recently, all direct cars got their bogies exchanged at the border point (from what I read, the passengers have to get off, but that is also combined with the border control).

Since last december, there is a connection between Moscow and Berlin which is operating with gauge-change Talgo equipment. At the system border, the train moves at about pace through the gauge-changing station, and then can continue. This system has been around for decades already, at the border between Spain and France, and the famous "Catalan Talgo" TEE, or the "Pau Casals" EuroNight train were using it. There are also several gauge changing places within Spain, connecting the high-speed lines with the classic network.

Besides the Talgo system, there are two other gauge-changing systems coming to my mind.

The Swiss Prose system is in deployment for the next generation of "Golden Pass" trainsets, which will then be able to run through between Montreux and Interlaken, changing between meter gauge and standard gauge in Zweisimmen.

The Japanese system, developed by the JRRA (JR research organization) and the industry is used in prototypes which eventually should allow through-running from the high-speed network to places on the conventional network.