The synthesis of molecular and polymeri̇c initiator via heterocyclic aromatic molecules

As part of our continuous interest in developing new photoinitiator systems to prevail over the existing problems of the photopolymerization, the synthesis of various photoinitiators was achieved. The name of initiators are 5H-thieno[3,2-b]thioxanthen-5-one (TX-Bt), 13H-benzo[4,5]thieno[3,2-b]tiyokzanten-13-one (1TX-DBT), thieno[3,2-b: 4,5-b']bis(thioxanthene)-14,17-dione (2TX-DBT), indeno[1,2-b]thioxanthene-7,13-dione (TX-FN) and 9-hydroxythiochromeno[2,3-b]carbazol-13(7H)-one (TX-Cz-OH) respectively. The structures of TX-Bt, 1TX-DBT, 2TX-DBT, TX-FN, TX-CzOH were determined by 1H NMR, FT-IR nd GC- or LC-Mass spectroscopic methods. The photoinitiation mechanism of thichromeno[2,3-b] carbazol-13(7H)-on (TX-Cz) was clarified by using of various analytical methods icluding Laser Flash Photolysis. According to results, intermolecular hydrogen abtsraction mechanism of TX-Cz lead to the formation of initiating radical. Photophysical and photochemical properties about the excited states of TX-BT, 1TX-DBT, 2TX-DBT, TX-FN, TX-Cz ve TX-CzOH were clarified by fluorescence and phosphorescence emission spectroscopy. It is clear that all of the photoinitiators possess excellent optical absorption properties in the visible region ensuring efficient light absortion for several targeted applications. Fluorescence quantum yield of most photoinitiators are reasonably high. Similar above mentioned methods were followed to determine the initiation efficiencies and initiation mechanisms of the photoinitiators, the polymerization experiments of methyl methacrylate with initiators in DMF in the prescence and absence of oxygen atmosphere were performed. Additionally, a tertiary alkyl amine namely N- methyldiethanolamine (MDEA) was also added to the same formulation to see the inhibition effect of oxygen beside the synergistic effect of the amine. The different kind of light sources were used as irradiation source. From the polymerization results, all initiators initiated polymerization of MMA in DMF with reasonable conversion percentage values. Also, it should state that TX-Bt, 1TX-DBT, 2TX-DBT, TX-Cz initiated the photopolymerization of MMA in the absence of a co-initiator and by using of spectroscopic techniques, it was detected that initiators bonded chemically to polymethyl metacrylate (PMMA). In order to clarify the photoinitiation mechanism of TX-Bt, 1TX-DBT, 2TX-DBT, TX-FN and TX-Cz, laser flash photolysis experiments were also performed. In this way, the triplet lifetimes of the photoinitiators were calculated. According to initiation mechanism of TX-FN can be classed as Type II initiator. Due to importance of investigating the kinetics of the photopolymerization reactions, the photo-DSC technique was used. The polymerization rates and conversion percentage values of photopolymerization reactions of multifunctional acrylates with TX-Bt, TX-FN and TX-Cz were calculated by Photo-DSC. In photoinitiated polymerization reactions, the photoinitiating efficiencies of TX-Bt, TX-FN and TX-Cz were compared to commercialy available and widely used thioxanthone (TX) and/ or camphorquinone (CQ) in conjunction with hydrogen donor. Nowadays, to stabilize the polymeric materials under visible light is an important issue. So, in the last part of our study, the photostabilizing effect of TX-CzOH was investigated. It was used as a radical scavenger and photodegradation of PMMA in the presence of TX-CzOH was followed by Gel Permission Chromatography (GPC). TX-CzOH was chemically linked to poly (styrene-co-chloromethyl styrene) (P(S-co-MS)) so that a new macroinitiator 2-(Poly(styrene-co-chloromethylstyrene)oxyl)-9-H-carbazole (P(S-co-MS)-O-Cz) was synthesized. After characterization of P(S-co-MS)-CzOH by 1H NMR and FT-IR spectroscopy, it was used for the photodegradation study of PMMA and the results were compared with the results of TX-CzOH. To display the radical scavengering effect of hydroxy (-OH) subsitituent on the ring.