Differential scanning calorimetry and cantilever deflection studies of polymerization kinetics and stress in ultraviolet curing of multifunctional (meth)acrylate coatings

Polymerization kinetics and stress development were measured during the UV curing, of multifunctional acrylate and methacrylate coatings by photodifferential scanning calorimetry and a cantilever deflection method. Higher light intensity leads to higher double-bond conversion but unfortunately also to higher stress. Higher monomer functionality unfortunately leads both to lower conversion and to higher stress; substituting methacrylate for acrylate does likewise. Longer monomer chain length and more plasticizer, though, lead both to higher conversion and to lower stress. In all cases, it is shown that significant stress starts to develop only late in reaction-at the vitrification conversion. The vitrification conversion falls as more rigid networks are formed (with higher functionality, shorter monomer chain length, lower plasticizer concentration, or methacrylate rather than acrylate), but it is not affected by the light intensity. After vitrification-in the Vitrified state-the stress rises monotonically with conversion. The rate of stress growth with conversion in the Vitrified state rises with higher monomer functionality, shorter monomer chain length, or lower plasticizer concentration. It also rises when methacrylate is substituted for acrylate. These trends of stress growth in the vitrified state are consistent with an increase in the elastic modulus as more rigid networks are formed.