Of course not, PIC and handling pilot are not the same thing. No reason why A can't give B control while in IMC.
But (to play devil's advocate)...if A gives the controls to B then A is no longer the "sole manipulator of the controls" and in a single pilot aeroplane can no longer log PIC. If they can no longer log PIC then logic dictates that they are no longer PIC. As B is the sole manipulator of the controls, then B actually becomes Pilot In Command of a single pilot aeroplane. Explain that one.....
