?Conjugated polymers nanoparticles as new visible light polymerization initiators

G. CAGNETTA; A. GALLASTEGUI; R. SPADA; R. A. PONZIO; C. M. PREVITALI; R. E. PALACIOS; C. A. CHESTA; M. L. GOMEZ

Mar del Plata

Simposio; SLAP 2018 ? XVI Simposio latinoamericano de Polímeros ? XIV Congreso Iberoamericano de Polímeros; 2018

INTEMA

INTRODUCTIONWe report a study on the use of conjugated polymer nanoparticles (NPC) as photoinitiators of vinyl polymerization. To this end, aqueous suspensions of NPC of poly (9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) and poly (9,9-dioctylfluorene) (PFO) were synthesized and characterized. These NPCs are highly biocompatible, show significant absorption even a very low concentration (< 5 ppm) and can be excited in a wide spectral range (300-600 nm).1 Upon excitation, the NPCs undergo efficient intra and inter Singlet-Singlet energy transfer processes useful for amplifying the generation of free radical of typical photoinitiators systems (Eosin Y/ triethanolamine, methylene blue/ triethanolamine, etc.). All these properties make these NPC ideal for use as photosensitizers of vinyl polymerization.EXPERIMENTAL METHODSThe NPCs were synthesized using the technique of controlled precipitation2 and characterized by AFM and DLS. The photochemical behaviour of the photoinitiatior systems were studied by steady state and time resolved absorption and emission spectroscopies. Photopolymerization essays in water using different monomers (acrylamide, bisacrylamide, methacrylic acid, HEMA, etc.) were carried out in a photoreactor equipped with LEDs at 470 (F8BT NPCs) and 430 nm (PFO NPCs). NPC concentration was kept at 5 ppm in all cases. After irradiation the polymers obtained were precipitated adding methanol or THF and their yields were quantified by gravimetry. Polymerization rates were measured using FTIR spectroscopy, following the disappearance of the C=C stretching bands of monomers at 6200 cm-1.RESULTS AND DISCUSSION NPCs of 30 nm and 50 nm mean diameter were obtained for F8BT and PFO, respectively. Both NPCs are capable of initiate the photopolymerization process without co-initiators. Acrylic monomers efficiently quench the emission of F8BT and PFO NPCs trough photo-induced electron transfer. Hence, F8BT NPCs behave as efficient macrophotoinitiators. A comparative study of the polymerization rate of acrylamide in water using different photoinitiator systems is shown in Figure 1. As shown, the rate observed for F8BT NPC is slightly larger than that obtained for the reference system riboflavin/ triethanolamine at equal irradiation dose. As expected, a control experiment irradiating acrylamide in water does not lead to appreciable polymerization. PFO NPCs are also able to photoinitiate the vinyl polymerization by direct reaction with the monomer. The differences observed in the mechanisms of generation of free radicals in both systems is rationalized according to the intrinsic properties of the polymers.CONCLUSIONWe show that F8BT and PFO NPCs behave as macroinitiators of radical polymerization in aqueous media when used at extremely low concentrations. The initial photopolymerization rate is slightly faster than that observed for a known photoinitiator systems. Thus these NPCs show several advantages as polymerization photoinitiators: do not need a co-initiator, are water soluble and highly biocompatibile.