Preparation Of Nano-Latexes By A UV-Induced Routine Eulsion Polymerization

Recently,routine emulsion polymerization leads to the polymer latexes with diameter in the order of micrometers.Microemulsion polymerization is a facile method to produce polymer latexes with the size of 10-50 nm.However, the high amount of surfactant concentration has restricted its application. Therefore,it is of great significance to obtain polymer nanoparticles through emulsion polymerization instead of microemulsion.Firstly in this paper,transparent polystyrene(PS)latexes were prepared by photo-polymerization of a routine styrene(St)emulsion with a surfactant concentration of 0.4 wt%and a monomer concentration of 10 wt%,by using UV light as well as a hydrophilic photo-initiator Irgacure 2959.The entire polymerization could be performed within 1-2 hours and display a conversion higher than 90%.The particle sizes could be tuned in the range 20-40 nm. The formation mechanism for these of nano-sized latex particles was attributed to an in-situ formation of PS chains with terminal hydroxyl groups. The presence of the hydroxyl-functionalized polymer chains seemed to promote a colloidal stability of the small latex particles and prevent coagulation even at low surfactant concentrations.Afterwards,the transparent nano-sized PS latexes were produced through a routine emulsion initiated by a hydrophobic photo-initiator Irgacure 1173, the surfactant concentration and particle sizes similar to the Irgacure 2959 system.The effects of initiator concentration,emulsifier concentration and light intensity on the polymerization were studied,and a nanoparticles formation mechanism was proposed:faster polymerization rate can produce more loci,which will decrease the particle size without needing the co-stabilized effect of hydroxyl.Next,PS nanogels were obtained through UV-initiated emulsion polymerization,with a photo-initiator Irgacure 2959 and a cross-linker divinylbenzene(DVB).The size of the nanogel particles was about 20 nm. And it was estimated that the cross-linker concentration and light intensity had little effects on size of the nanogel particles.