Synthesis And Properties Of Self Cross-linkable Core-shell Latex At Ambient Temperature

Three kinds of self cross-linkable core-shell latex which containing epoxy groups, ketone carbonyl groups and acetoacetate groups, respectively, were synthesized by seeded semi-continuous emulsion polymerization. The structure of latexes and the synthetic process of emulsion polymerization were optimized. High performance waterborne wood coatings were prepared by the above self cross-linkable core-shell latexes.The core-shell latexes were synthesized by seeded semi-continuous emulsion polymerization of methyl methacrylate (MMA), butyl acrylate (BA), 2-ethylhexyl acrylate (EHA) and methacrylic acid (MAA). The distribution of emulsifier in every polymerization stage was calculated by mathematic model. The amount emulsifier needed in the second and third polymerization stage, respectively, is decided by both the amount of emulsifier added in the seeded polymerization stage and the particle size of seeds. The size distribution and morphology of the latex particles have been investigated by dynamic light scattering (DLS) and transmission electron microscope (TEM). The latex particles have core-shell structure showing narrow-dispersed and there is no secondly nucleation in the polymerization.Emulsion copolymerization of MMA, EHA, BA and MAA by semi-continuous emulsion polymerization with reactive ionic and non-ionic emulsifier has been investigated. The emulsion polymerization can be proceeded fluently at the amount of emulsifier is 3.0~3.5% with the ratio of ionic and non-ionic emulsifier is more than 1:1 and the polymerization at about 72℃.The core-shell latexes containing epoxy groups in the core layer or on the shell layer were synthesized by copolymerization of glycidyl methacrylate (GMA), methyl methacrylate (MMA) and n-butyl acrylate (BA) uses seeded semicontinuous emulsion polymerization. The core-shell latexes containing carboxyl groups on the shell layer were synthesized by seeded semicontinuous emulsion of AA with BA and MMA.Two types of reactive blend latexes were obtained by blending epoxy group functional latex and carboxyl group functional latex. The core-shell morphology of latex particles was clearly observed by TEM. The size and distribution of the latex particles were measured by DLS analysis. The latex particles exhibited narrowdispersed with polydispersity of 0.062 and number-average diameter of 76 nm. The diffusion and cross-linking of polymer chains for blend latex particles were investigated by measurement of gel content, swell ratio and FTIR. The influences of different core-shell structure of blend latexes on mechanical properties of the films were observed. The results indicated that it is facilitate to the polymer chains diffusion and cross-linking reactions when the epoxy groups bear on core lay and carboxyl groups on the shell lay of latex particles, as a result, the physical and chemical performance of latex films are improved.Three kinds of functional latex with non core-shell structure, core-shell structure and semi-interpenetrating polymer networks (semi-LIPN) structure which containing ketone carbonyl groups were synthesized by copolymerization of diacetone acrylamide (DAAM), MMA, EHA, BA and MAA using seeded semi-continuous emulsion polymerization. The reaction of ketone groups and hydrazide groups was studied by FTIR. The results show that the formation of imino bonds between ketone and hydrazide groups occurs rapidly after the evaporation of water and ammonia in the course of film formation at ambient temperature. The balance properties of latex films are improved greatly by incorporating 5% DAAM in the non core-shell structure latexes. The average number of the polymer molecular weight included between two crosslinkings is 2400~3100 g/mol, the pencil hardness , water absorption, gel content of latex films is 2~3H, 6.5%, 95% .respectively. The core-shell structure latexes which core layer and shell layer polymer with different Tg were synthesized. The ability of film formation of latex and cross-linking density, water absorption, Tg and mechanical properties of films have been investigated. The results show that the latex films had a superior balance property when the shell layer polymer Tg higher than that of core layer polymer. The films pencil hardness is 3H when the Tg of core layer andshell layer polymers are 0°C and 30°C, respectively, and 5% DAAM is incorporated into the shell layer polymer. Functional semi-interpenetrating polymer networks (semi-LIPN) containing ketone carboxyl groups were synthesized by multi-stage emulsion polymerization of MMA, EHA, BA, MAA, 1,6-hexanediol diacrylate (HDDA) and DAAM. The latex particles were characterized by FTIR, transmission electron microscope (TEM), dynamic light scattering (DLS) and differential scanning calorimetry (DSC). A unique feature of the semi-LIPN is able to crosslink and form thermosetting full-IPN polymers through the reaction of ketone carboxyl and hydrazide in the course of film formation at ambient temperatures. A series of latex particles with various level cross-linking density in the first network and second network and varied composition of LIPN were obtained. The effect of the LIPN composition and the level of crosslinking density in the first and second networks domain on films' density, swell ratio, mechanical properties and contact angle with water have been investigated. The LIPN films have a single Tg indicating that there is a good compatibility between the first network and the second network polymer. The LIPN films have the bi-continuous network structure when the core/shell ratio is 40/60-60/40. Maximum synergy effects obtained at around 50/50 in terms of mechanical property, density and contact angle with water indicating that the maximum degree of interpenetration is obtained at this composition.Three kinds of latex with non core-shell structure, core-shell structure and semi-LIPN structure which containing acetoacetate groups were synthesized by seeded semi-continuous emulsion polymerization of MMA, EHA, BA, MAA, and acetoacetoxy ethyl methacrylate (AAEM). The reaction of acetoacetate groups and diamine was studied by FTIR. The results show that the reaction of acetoacetate groups and diamine is more rapidly than that of ketone groups and hydrazide in the course of film formation at ambient temperature. The influence of films' Tg and the content of AAEM on the properties of films have been investigated. The results show that the crosslinking density and pencil hardness of films increase with increasing of both latex Tg and the content of AAEM. The Tg of films increases 11°C~13OC, gel content is more than 95% and pencil hardness is 2~3H when 5% AAEM isincorporated into the latexes. The core-shell structure latexes which core layer and shell layer polymer with different Tg were synthesized and their properties have been investigated. The results show that the latex films had a superior balance property when the shell layer polymer Tg higher than that of core layer polymer. The effect of the LIPN composition and the level of crosslinking density in the first and second networks domain on mechanical properties of films have been studied. The LIPN films have the bi-continuous network structure when the core/shell ratio is 50/50~70/30. Maximum synergy effects obtained at around 50/50 in terms of mechanical property.The formulations of waterborne wood coatings have been investigated. The performances of DAAM systems waterborne wood coatings are reached the Chinese national standard.