MDS for 300-mer polymer using OPLSAA/CHARMM

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I need to run MDS for 300-mer PEG using OPLSAA and CHARMM/Gromacs. The problem is how to get itp file for this size of molecule?

I have used this web ( From PDB to GROMACS via OPLS — Group of Characterization of Materials. GCM — UPC. Universitat Politècnica de Catalunya for OPLS-AA)to get itp file for 250-mer and less, and this web ( , to get str file, but these webs have a limited number of atoms. Also, I have used the pdb2gmx but that did not work for my pdb file.
It came with the error which I have posted below:

Problem with chain definition, or missing terminal residues.
This chain does not appear to contain a recognized chain molecule.
If this is incorrect, you can edit residuetypes.dat to modify the behavior.
8 out of 8 lines of specbond.dat converted successfully

Program: gmx pdb2gmx, version 2018.2
Source file: src/gromacs/gmxpreprocess/resall.cpp (line 639)

Fatal error:
Residue ‘*’ not found in residue topology database

Any idea?