Tkinter Entry widget is returning an empty list when used in a toplevel window

Question

I am attempting to open a new window when the New Window button is pressed in the main "root" window. This currently works and does indeed open a second window. In the second window I want to ask the user for an input and then this input will be turned into a list of strings.

An example input would be "Amy, Bob, Carl". The expected output would be ['Amy', 'Bob', 'Carl'] but currently the program just returns [''].

My current code is:

from tkinter import *

root = Tk()
root.title("Welcome screen")
root.geometry("300x300")

def open_new_window():

    top = Toplevel()
    top.title("second window")

    entities = Entry(top)
    entries = entities.get().split(", ")
    entities.pack()
    entities.focus_set()
    print(entries)

    sub_button = Button(top, text="Submit", command= ?)
    sub_button.pack(pady=20)
    close_btn = Button(top, text="Close", command=top.destroy)
    close_btn.pack()

open_button = Button(root, text="New Window", command=open_new_window)
open_button.pack(pady=20)
exit_button = Button(root, text="Close", command=root.destroy)
exit_button.pack(pady=20)
root.mainloop()

I am new to Tkinter and I am unsure why this is happening. I'm sure it's a simple silly mistake but I can't find where I am going wrong. I also am unsure as to whether I need a Submit button as I don't know what command should be passed to it.

Any advice is appreciated. Please let me know if any additional information is required.