Preparation And Characteization Of Polysiloxane-Polyacrylics-Polyurethane Tri-component Hybrid Latexes

In this work, both polysiloxane and PAC were used for WPU modification. Difunctional hydroxyalkyl-containing polysiloxanes of different dimethylsiloxane segment length were firstly synthesized and reacted with diisocyanate to get polysiloxane modified polyurethane. At the same time, two new coupling agents with dihydroxyl and vinyl groups were synthesized and used to get polysiloxane-acrylics-polyurethane tri-component hybrid latexes.Dihydroxyl containing glyceryl methacrylate (GM) and allyl glyceroether (AG), used as coupling agent between PU and PAC, were synthesized through hydrolysis of glycidyl methacrylate (GMA) and allyl glyidylether (AGE) respectively, and their structure were confirmed through NMR, FTIR and gas chromatography. GMA conversion increased with hydrolysis time, and its hydrolysis rate was promoted with increase in reaction temperature.In order to study the reactivities of GM and AG towards isocyanate (NCO) and AC monomers, each was used to react with isocyanate terminated PU prepolymers to input vinyl group with objective to conduct graft-polymerization with acrylics in a subsequent step, and to get acrylic modified polyurethane latexes. Hydroxyethyl acrylate (HEA) was also used in the same way as GM and AG, and the results were compared. A simple method to determine the PU grafting to PAC was established. When AG was used as coupling agent, PU grafting was not detected; whereas chemical bonds were built up when HEA and GM were used as coupling agents. AG was therefore excluded as effective coupling agent. The results showed that, under the same reaction temperature for PU with coupling agents (HEA and GM), higher NCO conversion combined with a lower PU grafted to PAC were observed with GM. As regard to the influence of temperature in the reaction of PU with the coupling agents, results indicated that both NCO conversion and PU grafting to PAC in the final latex polymers were increased when increasing the reaction temperature, regardless of using GM or HEA. The molecular weight of the PU prepolymers remained nearly constant upon reaction of PU with HEA, and a slight increase in the particle size in the final hybrid latex was detected. However, when using GM, the impact of this reaction temperature on the PU prepolymers was different from the case when HEA was used. For both coupling agents, PU grafting to PAC was enhanced with more coupling agent when OH/NCO molar ratio was inferior to 1, and this enhancement was nearly disappeared when OH/NCO molar ratio was superior to 1.There are two important characters for polysiloxanes used in PU modification. The first is the molecular weight of polysiloxanes is controllable, and the second is polysiloxanes are termined by two hydroxylalkyl groups. Bis(methyoxyl hydroxyl) polysiloxanes (PMTS) with different dimethylsiloxane segment length were prepared. The preparation includes three steps:the first is the synthesis of 1,3-bis(glycidoxypropyl)tetramethyldisiloxane via hydrosilylation of AGE with tetramethyldisiloxane, followed by a subsequent methoxylation of the resultant compound from the hydrosilylation to yield 1,3-bis(3-(1-methoxy-2-hydroxypropoxy)propyl)tetramethyldisiloxane (MTS), with which an equilibrium reaction of octamethylcyclotetrasiloxane (D4), was carried out to achieve the target product PMTS. The ratio of D4/MTS was varied in order to prepare PMTS with different segment length. At each step, the outcome compounds were characterized through FTIR and NMR. In addition, the molecular weights of the PMTS with varying dimethylsiloxane length were estimated by hydroxyl group analysis,1H-NMR and GPC, which showed a good agreement between the theoretical molecular weights and those from these tests except that determined by GPC.As to the preparation of polysiloxane-polyacrylics-polyurethane tri-component hybrid latexes, isophorone diisocyanate was first reacted with PMTS to input NCO groups in polysiloxane chains, followed by reaction of these NCO-containing polysiloxanes with polypropylene and dimethylol propanic acid to get polysiloxanes modified polyurethane (PSU) prepolymers. HEA (or GM) was then used as coupling agent to react with the PSU prepolymers to introduce vinyl groups with objective to conduct graft-polymerization with acrylics in a subsequent step in order to get final polysiloxane-polyacrylic modified polyurethane (denoted PSU-H-AC, when using HEA as coupling agent, and PSU-G-AC, when GM was used) tri-component grafting hybrid latexes. Non-grafting PSU-AC tri-component hybrid latexes were also prepared under the same experimental conditions without coupling agent. The properties of the three types of latexes and of their films were compared. Regardless of using coupling agent, the stability of the tri-component hybrid latexes was enhanced by the presence of PAC. When compared with the tri-component non-grafting PSU-AC latexes, the grafted tri-component PSU-H-AC and PSU-G-AC latexes prepared with HEA and GM demonstrated smaller particle size, narrower size distribution, along with lower surface tension. Phase separation was not observed in grafting hybrid tri-component materials except in cases where PMTS of high molecular weight were used. Using of the coupling agents was effective to improve the mechanical properties and water resistance of the hybrid materials. No significant impacts of PMTS level and of its molecular weight were noted with regard to the particle size, the surface tension and the viscosity of the latexes. However, upper limits were observed both for PMTS level and for its molecular weight when it comes to the properties of the PSU-G-AC latex films. Mechanical properties of the latex films started to deteriorate either when the molecular weight of PMTS was higher than 2000 or more than 10 wt% of PMTS was used in PSU-G-AC latex. Below these limits, use of PMTS in the tri-component PSU-G-AC latexes contributed to enhancements of mechanical property and of water resistance. To achieve good water resistance of the ternary PSU-H-AC latex films when HEA was used as coupling agent, PMTS molecular weight should also be limited to 2000, and its content should be kept not less than 5 wt% in PSU prepolymers.