The present invention provides photoresist monomers, photoresist polymers derived from the same, processes for producing such photoresist polymers, photoresist compositions comprising such polymers, and processes for producing a photoresist pattern using such photoresist compositions. In particular, photoresist monomers of the present invention comprise a moiety of Formula 4: where R1, R2, R3 and R4 are those defined herein. Photoresist polymers of the present invention have a relatively high etching resistance, and therefore are useful in a thin resist process and a bilayer photoresist process. Moreover, photoresist polymers of the present invention have a high contrast ratio between an exposed region and a non-exposed region.