Structural and Residual Stress Analysis of UV Curable Hyperbranched Acrylates

Polymerization shrinkage is a well known problem common to all crosslinked polymers 1], often
leading to residual stresses in case conversion gradients develop during cure, and in case the polymer is in contact with a rigid material (such as the substrate of a thin film, the reinforcement in a composite, or the encapsulation of an electronic component). In organic coatings for example, these stresses may cause defects such as cracking, bending and delamination 2, 3]. Several methods exist to reduce internal stress in polymers, such as optimized post-cure cooling and annealing cycles to promote viscoelastic relaxation processes, or low profile additives 4]. The approaches present drawbacks, including a loss of stiffness in the latter case. An interesting alternative is based on the development of reactive blends with hyperbranched polymers, known to exhibit low polymerization shrinkage 5, 6], and, potentially, low levels of residual stresses without sacrificing the mechanical properties of the cured material. Nevertheless, the interplay between stiffness build-up, shrinkage and residual stress has not been explored systematically for this class of polymers.