Organik ve sulu ortamlarda serbest radikal polimerizasyonu için tek bileşenli tip II fotobaşlatıcı olarak poli(vinil alkol)-tiyoksanton

In recent years, photoinitiated polymerization has received revitalized interest as it congregates a wide range of economic and ecological anticipations. The most important elements of photoinitiated polymerization are the photoinitiators, which absorps the light to yield the species responsible for the initiation of polymerization. Thus, development of new photoinitiating systems became an important subject for the synthetic researchers in the past few years. Both free radical and cationic photoinitiators are intensively examined and their initiating mechanisms are examined in detail. Free radical photoinitiators can be divided into Type I (α or less common β cleavage) and Type II (H-abstraction). Some of the most influential Type I initiators are benzoin ether derivaties, benzil katals, hydroxylalkylphenones, a-aminoketones and acylphosphine oxides. Besides that typical Type II photoinitiators include aromatic carbonyl ssuch as benzophenone and derivatives thioxanthone (TX), benzil, quinones, and organic dyes, however alcohols, ethers, amines, and thiols are used as hydrogen donors. Type II photoinitiators are the most widely used in many technologically important UV curing applications because of their excellent light absorption characteristics. The radicals formed on the thioxanthone moiety do not actually participate in the initiation process on account of the steric hindrance and delocalization of the single electron on the π-system. Although they exhibit excellent initiation efficiency, the hydrogen donor compounds at high concentrations, have several intrinsic disadvantages such as offensive odor, toxicity, and migration in UV-curing technology. Several strategies have been developed to overcome these problems. The usual approach is to chemically incorporate the hydrogen-donating sites into TX chromophores. In this current work, TX moiety was incoperated to the side chains of commercially available poly(vinyl alcohol) (PVA) by a simple acetalization reaction. Initially, the designed thioxanthone structure with aldehyde functionality (TX-A) was facilely synthesized. Afterwards, the obtained TX-A was linked to the PVA counterpart by a simple addition reaction to yield the desired PVA-TX macroinitiator. PVA-TX polymeric photoinitiator exhibits typical TX absorption characteristics and soluble in water and some polar organic solvents such as DMF and DMSO. Moreover, PVA-TX displays one-component nature and initiates the polymerization in both organic and aqueous media without the necessity of additional hydrogen donor donor due to the presence of remaining hydrogen donating hydroxyl groups in the structure.