While many microcontrollers today offer slave USB, like Arduino, usually only 32-bit microcontrollers (e.g. ARM) offer usb host ports.
Why is a host necessary? RS-232 is a two way protocol. The PC can be host and an USB to Serial adapter can be the device just fine.
I need to send data from arduino 1 board to a PC via rs232 interface.
You mean an original Arduino board with RS232 interface? I would suggest something like a FTDI cable or the Arduino USB to Serial board connected directly to pins 0 and 1 of the Arduino board. This will allow for USB communication with the PC on an Arduino that doesn't have a USB to Serial chip already.