A monomer of formula (1a) or (1b) is provided wherein A is a polymerizable group, R1-R6 are monovalent hydrocarbon groups, X1 is a divalent hydrocarbon, group, Z1 is an aliphatic group, Z2 forms an alicyclic group, k=0 or 1, m=1 or 2, n=1 to 4. A useful polymer is obtained by polymerizing the monomer. A resist composition comprising the polymer has improved development properties and is processed to form a negative pattern having high contrast, high resolution and etch resistance which is insoluble in alkaline developer.