Is there such a thing as a union for plastic pipes where it is impossible , or nearly impossible to join two otherwise immovable sections?

Simple question, simple answer.

Yes.

One is just like other unions but has an "O" ring to seal the two halfs.

Then other has two flanges that bolt to gether with a gasket between them.

Wish I had used them on a couple of jobs. Now I have to re-pipe.

Thanks, WOW. The Home Depot people didn't seem to know that. I know where to come for good information in the future.

Another alternative which is carried at Home Depot is a rubber sleeve that comes with two hose clamps.

They come in various sizes and lengths.