Can I say 'I can't imagine him behaving as that'?

[Ginny]

Dear teacher,
can you say somethings about the usegas of verb 'imagine'?
can i say or write ' i can't imagine him behaving as that'?
are the following structures correct?
'S+imagine+that=clause'
'imagine sb/sth'
how many are there structures with verb 'imagine'? can you give me some examples and explanation?
sincere :idea:

[Mister Micawber]

I can't imagine him behaving like that.
I can't imagine his behaving like that.
I imagine (that) I shall never see you again.
I always imagined myself as a self-starter.
I imagine unbelievable paradoxes in my dreams
_________________
Native English teacher at Mister Micawber's

[Ginny]

dear Mister Micawber,
thank you for your clear answer.
But why can't i use 'as' in this sentence? and is phrase 'him behaving' accept? my teacher used to say i was wrong when i write'i can't imagine him doing...'. she said i had to use 'his doing'. is that right?and why?