Preparation Of Amino-Functionalized Polystyrene Nanoparticles By Photoinitiated Emulsion Polymerization

Nowadays, functionalized polymeric nanoparticles have attracted great attention since they have widely potential applications. Among them, amino-functionalized nanoparticles become a hot issue because they can be easily further functionalized by using those amino groups as the handle. However, most researches focused on the amino functionalization of metal or semiconductor nanoparticles, and few studies concentrate on the polymeric nanoparticles. In this study, amino-functionalized polystyrene nanoparticles were prepared by photo-induced emulsion polymerization with photo-inisurfs (Method 1) or amino-functionalized comonomer (Method 2), respectively.Method 1:Amino-functionalized polystyrene nanoparticles were prepared by surfactant free emulsion polymerization. The polymerization was carried out by using amino functionalized photo-inisurfs, which combines the properties of photo-initiator and surfactant. The effects of the lenghth of the alkyl group of photo-inisurfs molecules, monomer concentrations, co-initiator, crosslinking agent, acetic acid and cleavage photo initiator polymerization system were studied. Ninhydrin reaction was used to qualitatively identify the existence of the amino groups on the polystyrene nanoparticles. The results showed that the diameters of amino-functionalized polystyrene particles ranged from 60 nm to 500 nm. The lenghth of the alkyl group of photo-inisurfs molecule could influence the emulsification effect of photo-inisurfs. With the increase of monomer concentration, polymer particle size increases. The Co-initiator could enhance the initiating efficiency, whearas the particle size was larger and the side products present. Although the addition of acetic acid could increase the photo-inisurfs amount, but it led to larger particle sizes, and made the emulsion system instabe, or even emulsion breaking. The addition of water-soluble photo-initiator 4-(2-hydroxyethoxy)phenyl-(2-hydroxy-2-propyl)ketone (Irgacure 2959) can lead to smaller particle sizes.Method 2:Step1, dichloromethane and 1,3-propane diamine were used to synthesize the amino-functionalized monomer N-(3-aminopropyl)-p-vinylbenzylimine (CVPD). Step2, P (St-co-CVPD) nano-latex were prepared by UV-initiated emulsion polymerization. The used photo-initiator was Irgacure 2959, and the concentration was in the range of 0.01-0.02 mol·L-1. The used surfactant was cetyltrimethylammonium bromides (CTAB), and the concentration was only 0.1-0.8 wt% of the total system which was greatly lower than that of micoemulsion polymerization system. The particle morphology was observed by TEM, and the diameter and PDI of the P(St-co-CVPD) nanoparticles were characterized by DLS. The particle sizes were between 30 nm to 600 nm. The present of amino groups of P(St-co-CVPD) nanoparticles were characterized by FT-IR and NMR. The amino group contents were 1.2×10-5-1.6×10-4 mol·g-1, which was characterized by ninhydrin reaction. The influences of St/CVPD ratios, initiator concentrations, surfactant amount and UV light intensity on the polymerization system were systematically investigated.