The approach of characterizing the onset of phase separation (PS) and gel time, as well as the effect of tailoring those parameters on the (meth)acrylate-based microstructures, are the subjects of this study. Further to the studies on the copolymerization of marginally incompatible oligomer/monomer photocurable systems, different degrees of turbidity were observed in the photopolymerization of a diluted aliphatic urethane diacrylate oligomer (UDA; Miramer 5216) and bisphenol-A-ethoxylate dimethacrylate monomers (Bis-EMA; SR348C). That light transmission drop has been a result of domain formation through photopolymerization induced phase separation (PIPS) phenomena which is of great interest in tailoring the mechanical properties of polymers used in additive manufacturing technologies. Not only the thermodynamics of the polymerization reactions affects the phase separation, but it is also greatly affected by the reaction kinetics and network formation mechanism. Altering the phase separation development time “PSDT” which is the time at which phase separation begins until the time of getting extensively suppressed by gelation, is the most deterministic parameter to adjust the microstructure of such structure:

{ PSDT}__(s)= { Gel point onset}__(s)- { Phase separation onset}__(s)

A bespoke setup has been designed to achieve PS onset, which is capable of accurately recording the declining point from the complete transparency of resin during polymerization. Also, the crossover of storage and loss modulus at a constant frequency of 1 Hz obtained by IR-photorheometer was taken as gel point. The PSDT values were calculated and given in detail for different irradiation intensities as well as different compositions of the materials in presence of 1% 2,4,6-trimethylbenzoyl diphenylphosphine oxide (TPO) as the photoinitiator. Photopolymerizing an equal proportion of components resulted in a PSDT of +2.83 seconds, which compared to the other ratios showed higher opacity and fracture toughness. Moreover, a gel point onset recorded by photorheometer was found to be nearly identical for all compositions, which can be attributed to the component's similar functionality, followed by quick polymerization and shrinkage. Furthermore, the fracture surface of altered PSDT samples was subjected to qualitative (phase imaging) and quantitative (pinpoint nanomechanical) modes of atomic force microscopy for further study of the effect of PSDT on microstructure, and the resulting structure properties observations were described and analyzed.

Keywords: (Meth)acrylate resins, Photopolymerization, Phase separation Onset, Gel point, Quantitative AFM imaging