There are many people who cannot believe this is possible, but all attempts so far to prove that it is not are either subtly begging the question or ultimately rest, one way or another, on intuition (as do materialist positions).

For example, David Chalmers, who originated or developed many favorite anti-materialist positions (the 'hard problem', the explanatory gap, p-zombies) holds many positions that would normally be considered materialistic - for example, that if one were to replace a person's neurons with functionally-equivalent artificial devices, the resulting entity would still be conscious in the same way as the person we started with, and therefore, presumably, capable of feeling pain and pleasure. It would seem tendentious to hold this position and still assert that artificial conscious entities (complete with subjective experiences) are impossible.

Are pain and pleasure prerequisites for consciousness?

The term 'consciousness' is used in many different ways, but I do not think you can simply define away the question of the origin of pain, pleasure and other subjective (or at least personal) experiences.

Probably not but a value system I imagine is. The interesting question is at what point do we have AI ethics for how to treat AI?

Probably not, but we should think if they "emerge" as a consequence of our doings.