Okay, let's get the confession out of the way.
I don't actually know if it is impossible to live as a materialist.
What I do know is that I have been talking with people about their lives and about what they believe for a long time - since 1972 - and I have yet to find anyone who lives as a materialist.
It is actually very hard to find anyone who claims to be a materialist, but you can do it if you keep looking. However, on the few occasions I have found someone who claimed to be a materialist, they never lived like one. And, after a few minutes' conversation, they did not pretend to live like one.
So, to be precise, I don't know if it is impossible to live as a materialist. All I know is, I have never found anyone who even claimed to do so. And I would be fascinated to hear from anyone who thinks that they do.
For the sake of this article, I am going to define a materialist as someone who believes that the material world is the sum total of reality.
This is a reasonable definition. It agrees with, for example, Chambers: "materialism, the doctrine that denies the independent existence of spirit, and maintains that there is but one substance - matter."
So a materialist is, by definition, an atheist: if there is no such thing as spirit, then there can be no God or gods. But an atheist does not have to be a materialist: you can believe there is no God or gods, but also believe that there is some spiritual dimension to life which does not involve any deity.
The key point here is that I am not using the word 'materialist' as a description of someone who is too interested in material goods ("excessive devotion to bodily wants or financial success" - Chambers, again). After all, it is far too easy to live as a materialist in that sense.
Defining the term 'materialist' is fairly straightforward. The next bit is much harder: what does it mean to live as a materialist?