import pyodbc
import pandas as pd
# Some other example server values are
# server = 'localhost\sqlexpress' # for a named instance
# server = 'myserver,port' # to specify an alternate port
driver = 'ODBC Driver 17 for SQL Server'
server = 'localhost' 
database = 'Test' 
username = 'sa' 
password = 'REDACTED'  
cnxn = pyodbc.connect('DRIVER='+driver+';SERVER='+server+';DATABASE='+database+';UID='+username+';PWD='+ password)
cursor = cnxn.cursor()
query = """SELECT SomeBigChar
	, SubString(Convert(VARCHAR(MAX), SomeBigChar), 1, 65536) AS Char65536 -- this works
	, SubString(Convert(VARCHAR(MAX), SomeBigChar), 1, 65537) AS Char65537 -- this doesn't
	FROM [LargeChar]"""
df = pd.read_sql(query, cnxn)
print(df.SomeBigChar)
print(df.Char65536)
print(df.Char65537)