Select2 does not work in dx-popup

Hello everyone,
I maintain a MVC 5 project with devextreme UI components (angularjs 1.6)
and I am trying to integrate select2 inside a dx-popup (essentialy is a modal).
The problem is that in the parent page select2 is working perfectly , but in the popup does not.
An extensive research in common problems of select2 troubleshoot page has been made and also in stackoverflow but I cannot find the solution.
The page cshtml constists of html angularjs with typescript and I append in the code a with select2 javascript code.