As far as I understood it, both are cases of karyokinesis, not followed by cytokinesis.
No. If you google the terms you'll get a lot of sites with definitions. For example:
The process by which a nucleus divides, resulting in the segregation of the genome to opposite poles of a dividing cell.
free nuclear division mitotic division of nuclei without accompanying cytokinesis, i.e. nuclei divide in a common cytoplasm, the cells walls only forming around each later
endomitosis mitosis taking place without dissolution of the nuclear membrane, and not followed by cytoplasmic division, resulting in doubling of the number of chromosomes within the nucleus.
or a bit more revealing:
Duplicated chromosomes produced by endomitosis exist as discrete units in a single polyploid nucleus or may be packaged into separate nuclei, depending on the phase at which mitosis is aborted
So as you see by definition nuclear division is part of a bigger process (cell division), and accoriding to the first source karyokinesis is a synonim for nuclear division (karyo = nucleus kinesis = moving, both come form greek language).
If you check the definition above, you can see that free-nuclear division is a mitosis without cytokinesis, thus chromosome separation still occurs.
In endomitosis the can end up with a polyploid nucleus, in contrast to the other two aforementioned mechanism where no polyploidy occurs.
In the cases of pollen grains free nuclear division occurs. entering into the s phase the chromosome no remains as 46 but the DNA doubles ie 4n condition occurs. During the anaphase the sister chromatids separate and reaches both ends. And when telo phase occurs nuclear membrane is surrounded around 2 genetic material. But cytokinesis is blocked there. But when again this cell enters s phase there again the genetic material replicated ie 2 nucleus having 4n condition is formed.this is free nuclear mitosis. These chromosomes doesn't separate in anaphase due to failure in attachment of spindle fibres. So karyokinesis also get stopped resulting cell to 8n condition or polyploidy. This is endomitosis