Conjugated Polymer Nanoparticles as Coinitiator- Free, Water-Soluble, Visible-Light Photoinitiators of Vinyl Polymerization

SPADA R; C. PREVITALI; C. A. CHESTA; GALLASTEGUI, A.; MARTINEZ, S.; PALACIOS R; CAGNETTA, G.; PONZIO R.A; GÓMEZ, M. L.

Viña del Mar

Congreso; XIV Elafot; 2019

Free-radical photopolymerization reactions are extensively used in many industrial processes. These processes involve a polymerizable mixture composed by one or more vinylic monomers and a photoinitiator system (PIS) able to generate radical species using light as energy source. PIS are generally classified into two main categories: Type I PIS produce free radicals through the homolytic cleavage of C-C or C-X bonds usually under UV irradiation. Type II PIS comprise at least two components: a photosensitizer that absorbs UV or visible light and a co-initiator that serves as electron or hydrogen donor.We report herein the use of conjugated polymer nanoparticles (CP NPs) of poly(9,9-dioctylfluorene-altbenzothiadiazole) (F8BT) and poly(9,9-di-n-octylfluorenyl-2,7-diyl) (PFO) as efficient photoinitiator systems (PIS) for vinyl polymerization in water. CP NPs are biocompatible, excitable with blue commercial LEDs (∼450 nm) and, unlike visible light Type II PIS, do not need co-initiators to trigger monomer chain reaction. CP NPs photoinitiate polymerization of a variety of acrylic monomers with initiation rates comparable to those observed for well-known Type II PIS. Given the extraordinarily large molar absorption coefficients of CP NPs (ε = 108 M-1 cm-1) very low particle concentration is required for effective polymerization (∼5-20 ppm of polymer or what is equivalent ∼10-40 nM in NPs), making these PIS suitable to synthesize polymeric materials for biomedical and other applications. CP NPs photoinduced polymerization was studied using different techniques such as FT-NIR, Dynamic Light Scattering (DLS) and fluorescence microscopy Single Particle Tracking (SPT). CP NPs PIS were also used to synthesize hydrogels and nano-hydrogels with relatively narrow and controlled size distribution in the absence of surfactants. The use of different types and proportion of monomers and crosslinkers with these novel PIS allows the preparation of polymer NPs useful for a number of technological applications such as: drug delivery, selective sensing/removal of molecular targets (molecularly-imprinted nanopolymers), fluorescent probes for imaging of molecular targets in biological systems, etc. Although the photoinitiation mechanism could not be fully established, experimental evidence suggests that polymerization is initiated at the CP NPs surface by photogenerated free polarons in close analogy to the mechanism proposed for PIS based on inorganic semiconductor NPs.Figure 1. Schematic representation of the photoinitiation mechanisms of vinyl polymerization by CP NP (Left). F8BT NPs size distribution measured by SPT during polymerization of an HEMA/BAAM mixture photoinitiated using F8BT NPs 12 ppm (Right)