The photolysis product of photoinitiator and its preparation route

According to the molecular structure and the location of photosensitive groups, the existing macromolecule photoinitiator can be divided into three categories: linear polymer photoinitiator (LPPI), hyperbranched/crosslinked photoinitiator (HCPPI) and multifunctional photoinitiator (MFPI). LPPI has been widely reported because of its simple preparation method and flexible chemical structure.

There are two main routes of LPPI synthesis:

First, the polymerizable monomer with photoinitiator structure was prepared, and then the LPPI was formed by thermal polymerization.

Second, the linear polymer with active group on the side chain was prepared first, and then the photoinitiator group was grafted onto the side chain.

Conventional reaction methods such as controlled/active polymerization, click chemistry, epoxy ring opening or stepwise addition polymerization can be used for both routes. The photosensitive groups of LPPI can be located at the repeated units of the main or side chain and at both ends of the molecular chain. HCPPI refers to a macromolecule photoinitiator system with branched structure and uncertain number of photoinitiator groups. It is usually prepared based on end-group modification of hyperbranched polymers. There are also a few reports on cross-linked network structure. MFPI refers to those multifunctional photoinitiators with regular structure and determined by photosensitive groups, among which representative are dendritic macromolecules. Due to the low viscosity and high base density of dendritic macromolecules, this class of MFPI has a variety of excellent properties. However, due to the complex synthesis of dendritic macromolecules, there are few groups and reactions that can be used to modify end-group photoinitiators, so there are not many reports on the preparation and application of MFPI.

Common PPI photoinitiator