According to Ukrainian Industrial Portal, a company called RAROG (Kharkov, Ukraine) has developed a polymer made disintegrating belt for the PKM machine guns. The standard PKM belts are non-disintegrating (the links are connected to each other) and they are made of metal. Polymer construction of the new belt should allow saving some weight.
Whether switching to the disintegrating belt is a good choice or not … it is hard to tell. It is an arguable matter and both systems have pros and cons. The deputy CEO of the company told that they started to develop the disintegrating belts because of multiple requests from the Ukrainian army soldiers.
There were experimental polymer belts in the Soviet Union. However, probably the lack of experience of working with polymers and/or the lack of proper materials didn’t allow to further develop these projects.
I think the performance of polymer links in extreme temperatures should be the main concern here. If the material performs well both in the arctic cold and desert heat, then it is an improvement indeed. In the video below, they are testing a belt which was frozen to -50°C (-58°F). Looks like they placed the belt into a metal jar full of dry ice to simulate the low temperature.
The manufacturer has finished the development of this belt and will submit it for Ukrainian government trials.