Preparation And Property Characterization Of Modified Acrylic Polymer Latexes

Styrene-acrylic latexes (SB) were prepared by semi-batch emulsion polymerization usingstyrene, butyl acrylate as the main monomers. Based on this polymerization, functionalmonomers, including vinyl triethoxy silane (VTES), dodecafluoroheptyl methacrylate (G04)and N-hydroxyethyl methacrylate (NHMA), were incorporated in the SB copolymer in orderto prepare functional monomer modified SB latexes, denoted as V-SB, G-SB and N-SB,respectively hereafter.Firstly, the effects of the functional monomers on the performance of the styrene-acryliclatexes were studied. When VTES was used, the particle sizes of the resulted latexes and theirsize distribution (PDI) were increased, probably due to particle coalescence through silanolgroups from VTES hydrolysis.Secondly, water absorption of SB, V-SB, G-SB and N-SB latex films was tested. It iscommonly accepted that silicone and fluoro-containing polymers were of excellent waterresistance. The latex films did not exhibit this way, due to probably their too low amounts used.Forther,, when SB base latex was modified by VTES and G04, the particle size was enlargedcompared to that modified by NHMA and the base latex. Latex films cast from latexes withsmaller particles manifest often better water resistance. In contrast, latex films made fromNHMA-modified latex showed a lower water absorption than the film of the SB base latex,since–OH and-CONH-can form hydrogen bonding in the latex films, leading to a morecompact structure in the latex films.Thirdly, the addition time of NHMA to the reactor during the polymerization process wasstudied. When NHMA was all added at beginning, most of NHMA were embedded inside ofthe latex particles, so that it was not useful to form a compact structure through hydrogenbonding. However, if NHMA was added at end of the polymerization where styrene andacrylates were exhausted, it would form its homopolymer, and this would contribute toincrease water absorption in the resulting latex films. Therefore, only when NHMA additionwas done when about1/3of the main monomers were polymerized, its copolymerization withthe main monomers was better controlled, and the latex film manifested the lowest waterabsorption among all the latex films tested. The anticorrosive property of the latex coated on metal surface was also tested, whichshowed that all the modified latexes were of good anti-corrosion.Knowing the low amount of VTES used in modified V-SB latex, the performance wasimproved at a limited extend. Octamethyl tetracyclosiloxane (D4) andmethacryloxypropyltrimethoxysilane (KH570) were then used to modify the SB base latex.And the theoretical solid of the latexes was increased from30%to40%. At the same time, thetime of DBSA addition, the amounts of APS, D4, KH570and HEA were also studied. Theoptimized experimental conditions to prepare the modified latexes of good stability and lowwater absorption for the latex films were obtained as following: amount of APS, D4, KH570and HEA at0.18wt%,8.0wt%,1.8wt%and6.6wt%of total monomers.