The first thing you really need to look at is, "What is intentionalism?" And, "What is physicalism?"
If I'm correct in my understanding of intentionalism, the idea is that raw experiences (qualia) are inseparable from the concepts that we subconsciously associate with those perceptions.
So imagine qualia (raw experiences without conceptual meaning). A state of mind that lacks all thought and logical categorization. Everything is simply in a state of being
Now imagine our subconscious drive for identifying experiences. Every time we think of a cat, we aren't actually experiencing the cat, we are recalling the conceptual network of ideas we associate with that experience. And optical illusions are a perfect example of how the part of our brain responsible can become tricked and confused.
If you can recognize that these two things can be separate and can exist separately you are not an intentionalist. If you believe that these two parts of perception cannot be separated and the presence of one always obligates the other, you are an intentionalist.
That said, let's move onto the second point.
Physicalism (materialism) is the concept that our experiences originate from definite external elements of reality which can be tested, analyzed and catagorized. For example, a dream is thought to have physical value in terms of the interaction of brain tissue. In a very crude way of saying it, to accept physicalism would be like accepting the proposal every experience can fit into a single coherent conceptual design. And everything can be understood relative to an umbrellaing paradigm (such as physics or chemistry, or any other paradigm based on catagorization).
Categorization is utterly dependant on the existence of conceptual objects that can neatly be compared and contrasted.
If raw experiences and the conceptual forms are absolutely inseparable (if intentionalism is true), then that means that every experience can be categorized in terms of their conceptual properties.
Let me explain and reword that a little bit. If the light and colours you are sensing and experiencing right now have a definite relationship to different patterns of light and colour in the future (different frame of reference), then all patterns of light must have meaning, and must be able to be categorized because they are equivalent to certain thought forms. If all experiences relate to thought forms, than all experiences can be categorized and analyzed through contrast and comparison - meaning everything must pertain to physicalism.
Because there is no way to prove the proposition of intentionalism one way or another through means of conceptual analysis, I do not perceive it to be true. I believe that you can have elements of reality that are formless experiences, free of any subconscious or physical meaning. However, I do respect all angles on this subject, and my personal views are a reflection of how much I feel our linguistic capabilities fail us in approximating reality. That's just my two cents, anyway.
Hope that helped.