This work investigates the volume changes effected during multicomponent resin polymerization/crosslinking (cure shrinkage) in an effort to reduce or eliminate this phenomenon (zero-shrinkage polymerization). The systems under study contained: a polyfunctional monomer; a second, difunctional low-boiling monomer; and a thermoplastic polymer additive. These components are miscible forming a single (transparent) phase, which remains stable and shows the expected cure shrinkage in slow polymerization. Upon rapid cure (within 2-10 minutes) these systems undergo phase separation and show significantly reduced cure shrinkage, attaining zero shrinkage within certain composition ranges. Experimental evidence based on Scanning Electron Microscopy, polymerization under pressure, photopolymerization, and solvent extraction indicates that the reduction in cure shrinkage is due to the nucleation and growth of vapor bubbles of the low-boiling monomer within separate microdomains formed during rapid polymerization and precipitated by the high temperatures attained at peak exotherm, as well as negative hydrostatic pressures arising from cure shrinkage of the crosslinked polymer phase.