i establish the same application now where i can find the best ic to convert from rs232 to rs 485
You can't, there is no such IC. B&B electronics has some converters that work pretty well.

However, why do you want to convert? if you attach a 485 transciever to your UART, you have RS485, if you attach a 232 transciever to your UART, you have RS232.

Erik