Hi Stuart
This is what you taught us in one other thread
"many of them" just sounds horrible in that construction; "many of whom" is proper usage.
Here's a general rule (although there are some exceptions): if "many of xxx" is followed by a simple verb, use "whom"... if "many of xxx" is followed by a preposition, use "them".
Some examples:
... many of whom eat fish every day.
... many of whom used to be lawyers.
... many of them under the poverty line.
... many of them in red shirts.
Can we extend this rule to conclude that
many/some/each of them - is to be followed by a preposition
and
many/some/each of whom/which - is to followed by a VERB
IF you approve of the same , then the following sentences are incorrect
Our class has comparatively older students,each of them is highly graded.
INCORRECT - run on sentence
Our class has comparatively older students, each is highly graded.
INCORRECT - run on sentence
Our class has comparatively older students, each student is highly graded
INCORRECT - run on sentence