Water-Developable Poly(2-oxazoline)-Based Negative Photoresists

Copoly(2‐oxazoline)‐based photoresists are prepared from pEtOx80Bu=Ox20 and pPhOx80Dc=Ox20, respectively, a tetrathiol, and a photosensitive initiator. It is possible to prepare copoly(2‐oxazoline)s bearing unsaturated side chains in a microwave reactor on a decagram scale in reaction times of 100 min or shorter. UV irradiation of dried polymer films through a quartz mask induces the thiol‐ene reaction in the illuminated areas. Subsequent development of the polymer films in halogen‐free solvents reproduces the negative pattern of the mask with a resolution of 2 μm. The pEtOx80Bu=Ox20‐derived photoresists can also be developed in water. Copoly(2‐oxazoline)s bearing unsaturated side chains can be used for the formulation of negative photoresists, crosslinking of which is achieved by the functional principle of UV‐induced thiol‐ene reactions. These photoresists adhere to various substrates commonly used in printed circuit board industries. After illumination through a quartz mask and subsequent development in halogen‐free solvents, these photoresists exhibit resolution in the 2 μm range.