Change individual material element offset in animation

I have a character model with 3 material element:

• Element 0: the eyes

• Element 1: the mouth

• Element 2: the body

Each element uses a different material, but 3 of them use a same texture image. Since the texture does include the close/open state of the eyes and the mouth, i can change the character facial expression by changing the Y offset of the materials of the eyes and the mouth.

The problem is, I can change a single material in Inspector window and the other materials offset X and Y remain intact. But if I turn on record mode to create keyframe for animation, changing offset value of one material will cause the other 2 changing with the same value

can anyone tell me how can I just change the offset value for only 1 material during keyframe record ?