How to build a dynamic script to update column with datatype xml to nvarchar(max) in few tables in Sql?

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SQL-Server-2008R2

How to build a dynamic script to update column with datatype xml to nvarchar(max) in few tables in Sql?

My script right now is as follows:

select @ColumnList= @ColumnList+','+
     column_name 
    from information_schema.columns  where
     table_name = @TableName  and DATA_TYPE not in ('timestamp')