why do new firms require patent rights etc when there products are well distinguished from each other in monopolistic competition.  Why isn't it easy for them to enter the market?

Monopolistically competitive market is characterised by differentiated products which are close substitutes of each other. This implies that if a new potential competitor is willing to enter in the market, then it must distinguish its product from the already existing products in the market. Otherwise, the already existing firms will file a patent or copyright suit for the new entrant. Hence, new firms require patents to enter in the market.