[Show abstract][Hide abstract] ABSTRACT: Precipitation polymerization of toluene diisocyanate and 4,4'-oxydianiline was carried out in acetone. At 1.0 wt% monomer concentration and 30 ºC for the polymerization temperature, polymers of different morphologies were obtained depending on the ways of agitation. Under mechanical stirring, rope-form polymer was obtained at low stirring rate and aggregate of granular polymer was observed with stirring rate at 600 r/min or higher; whereas polymer nanofibers were observed with quiescent polymerization and reciprocating shaking. Under quiescent polymerization with monomer concentration at 1.0 wt%, influence of polymerization temperature on the morphology of the polymer was studied. It was found that spherical particles were formed at 0 ºC, whereas fibrous polyurea was observed at 30 ºC or higher. Study on the influence of the monomer concentration at 30 ºC revealed that nanofibers were obtained at 2.0 wt% of monomer concentration or lower; and spherical particles were formed with higher monomer concentration. The basic properties of the polymers were characterized. This paper provides a novel and facile pathway to the fabrication of a novel type nanofiber of polyurea based on toluene diisocyanate and 4,4'-oxydianiline.
[Show abstract][Hide abstract] ABSTRACT: Porous polyurea (PPU) is prepared through a simple protocol by reacting toluene diisocyanate (TDI) with water in binary solvent of water-acetone, and the process is optimized. Porosimetric test demonstrates that PPU possesses typical properties of porous materials. The structure of the material is characterized by Fourier transform infrared (FTIR), NMR (1H & 13C) and X-ray diffraction (XRD). FTIR analysis shows that TDI is full reacted. Microstructure analysis of PPU by NMR reveals that PPU is consisting of short polyurea chains with degree of polymerization about 15. The presence of crystallinity in PPU is confirmed by XRD, which shows three diffraction peaks, for which the corresponding chain conformations, based on interplanar spaces owing to different hydrogen-bonding, are depicted. TGA analysis demonstrates that PPU is of high thermal stability, and no degradation is seen before 270 °C. DSC test reveals that no obvious glass transition is observed owing to intensive hydrogen-bonding.
[Show abstract][Hide abstract] ABSTRACT: Four polymer latexes, including Base latex synthesized using styrene and butyl acrylate as the main monomers, Latex Si prepared with 4.0 wt% of vinyl triethoxysilane, Latex F with 4.0 wt% of dodecafluoroheptyl methacrylate and Latex D4 with 8.5 wt% of octamethyl cyclotetrasiloxane (D4), were prepared through a semi-continuous emulsion polymerization. Characterization of the latex films revealed that water absorption of the films of Latex D4 and the Base latex were lower than those of Latexes F and Si; whereas their contact angle with water were also smaller than those of the other two latex films. The latexes were applied as coating onto steel and Al metals of different forms to evaluate their performance in corrosion and anti-icing tests. Coated on steel plates for water resistance test, it was found that Latex D4 and Base latex showed poorer performance; whereas the films made from Latex F and Latex Si showed better performance. In anti-icing tests, with the coating applied either on Al circular helix coils followed by refrigeration after water spray, or on Al stranded power line followed by anti-icing test in an IWT (ice wind tunnel), Latex D4 showed the best anti-icing performance, Base latex with the lowest performance, and the other two, Latex F and Latex Si, located in between. The test in IWT was also conducted with the latexes coated on stainless steel rods used in Al stranded power line with reinforced steel core. The anti-icing effectiveness was quite similar to those observed on Al coils or stranded power transmission lines: Latex D4 showed the highest performance and Base latex the lowest, although the differences of the magnitude in their performance were obviously different in different tests.
Journal of Polymer Research 06/2014; 21(6). DOI:10.1007/s10965-014-0473-9 · 1.92 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Crosslinked polyurea (PU) microspheres were prepared by precipitation polymerization of isophorone diisocyanate (IPDI) and diethylenetriamine (DETA) in the binary solvent of water-acetone. The influence of polymerization temperature, solvent composition, shaking rate and DETA amount on the microspheres was studied. Highly uniform microspheres were obtained when the polymerization was conducted at 30 °C to 50 °C. A slight decrease in the size of microspheres along with a slightly broadened size distribution was detected with increase in polymerization temperature. With increased water amount in the solvent, the polymerization rate was promoted, the size of the microspheres regularly reduced and the yield regularly enhanced slightly. Microspheres with the best uniformity were observed with water content from 30 wt% to 40 wt%. The results demonstrate that, although PU crosslinking was changed with H2O-acetone ratio in the solvent and polymerization temperature, DETA-IPDI ratio was the most effective means for control of PU crosslinking. The crosslinking was also confirmed by tests on microsphere swellability and light transmittance of the spheres' dispersion in acetic acid. TGA analysis demonstrates that the crosslinked PU was thermally stable. An attempt, based on infrared analysis, to describe the PU structure and its variation with monomer ratio was established. The results were in good agreement with those obtained by theoretical estimation. This work provides a reliable pathway to the preparation of uniform PU microspheres with easily controllable crosslinking.
[Show abstract][Hide abstract] ABSTRACT: A novel type of hollow polymer particles, polyurea (PU) microspheres with uniform morphology, is prepared via precipitation polymerization of isophorone diisocyanate (IPDI) in acetone–H2O as the solvent in three steps. In the first step, IPDI reacts with H2O to form the core particles consisting of linear PU, followed, in the second step, by addition of triethylene tetramine (TETA) and supplementary IPDI; the microspheres of core–shell structure are therefore obtained with a shell consisting of crosslinked PU thanks to the copolymerization of TETA with IPDI. Hollow microspheres are finally obtained by dissolving the core template of linear PU. The influence of the amounts of TETA, IPDI and their molar ratio on the formation and the morphology of the core–shell and the hollow microspheres are studied. The morphologies of the core–shell and of the hollow microspheres are characterized by scanning electron microscopy. The polymers are examined using Fourier-transform infrared spectra, differential scanning calorimetry and thermogravimetric analysis.
[Show abstract][Hide abstract] ABSTRACT: This paper presents a novel and facile route to preparation of highly uniform polymeric microspheres through a quiescent polymerization with the reactor standing still without any stirring. Using one single monomer, isophorone diisocyanate (IPDI), highly uniform polyurea microspheres are achieved with high yield via precipitation polymerization of IPDI with water in water–acetone mixed solvent. Full conversion of IPDI to polymer is readily achieved thanks to the step polymerization mechanism involved. The monomer concentration can go up to 11 wt.% with the polymerization accomplished within 2 h, with a much higher yield of microspheres in a much shorter time than those reported with vinyl monomers. The size of the microspheres is adjustable by changing IPDI concentration, acetone/H2O ratio in the solvent or polymerization temperature. Without need of any stirring or shaking during the polymerization, the protocol renders the fabrication of uniform microspheres more practical and economical, particularly for large scaled production.
Chemical Engineering Journal 12/2012; 213:214–217. DOI:10.1016/j.cej.2012.09.111 · 4.32 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Isophorone diisocyanate was first reacted with bis (3-(1-methoxy-2- hydroxypropoxy) propyl) terminated polysiloxanes (PMTS) to attach cyanate groups to polysiloxane chain terminals, followed by reaction of these cyanate-containing polysiloxanes with poly (propylene glycol) to get polysiloxanes modified polyurethane prepolymers (PSU). Hydroxyethyl acrylate (HEA) was then used as coupling agent to react with the PSU to introduce vinyl groups in order to conduct graft-polymerization with acrylics in the subsequent step to finally get polysiloxane-polyacrylic modified polyurethane (PSU-H-AC) ternary grafting hybrid latexes. Non-grafting polysiloxane-polyacrylic- polyurethane (PSU-AC) ternary hybrid latexes were also prepared under the same experimental conditions without HEA used. Results revealed that, regardless of use of HEA, the particle size of the ternary latexes was decreased when PMTS was used. This decrease was more pronounced with a narrower size distribution in PAC grafted ternary latexes than that observed in the latexes without HEA, i. e. PSU-AC series. Higher surface tension in the PAC grafted ternary latexes was also detected as compared with the corresponding ternary latexes without grafting between PU and PAC. Examination of the latex film morphology on the intersection by SEM showed that homogeneous latex films without any phase separation were obtained from the ternary latexes when HEA was used, while aggregates and defaults were observed in the ternary films without HEA. Both measurements of water absorption of the films and of contact angle of water on surface of the films indicated that water resistance was significantly enhanced by PAC grafting on PU through incorporation of HEA during the preparation of the ternary latexes. Employment of PMTS of different molecular weight in the latex preparation and property characterization demonstrated that, to achieve an optimum for the performance of the ternary latex films, molecular weight of PMTS should be limited to 2000 and its content should be not less than 5 wt% in PMTS-PU prepolymers.
[Show abstract][Hide abstract] ABSTRACT: Polyurethane-acrylics (PU-AC) hybrid latexes were prepared using isophorone diisocyanate and polypropylene oxides as main monomers for the PU component, butyl acrylate and methyl methacrylate as AC monomers, and hydroxyethyl acrylate (HEA) as coupling agent to build up chemical bonds between PU prepolymers and AC polymers (PAC). A simple method to determine the PU grafted to PAC chains at one end and at both ends was established, which showed that PU grafted to PAC at both terminals was obviously increasing with HEA, and soon became predominant over that grafted by one end when the HEA/NCO molar ratio reached 0.67. With HEA/NCO < 1, PU grafting, particle size of the hybrid latex and film tensile strength increased with the HEA amount; while with HEA/NCO > 1, these properties remained relatively stable.
[Show abstract][Hide abstract] ABSTRACT: Cationic latexes based on styrene and butyl acrylate using cetyl trimethyl ammonium bromide (CTAB) as surfactant were carried out using both batch and semicontinuous emulsion polymerization. Monomer conversion, particle size and its distribution, ζ potential, latex surface tension were determined as function of CTAB levels. Evolutions of these properties were followed, and the results from batch compared to those from semicontinuous process. It was revealed that polymerization rate in batch process was enhanced with CTAB, and the polymerization rate was controlled by addition rate of the preemulsion in semicontinuous process. Molecular adsorption area of CTAB on latex particle surface was calculated, which showed clearly that ζ potential and surface tension in the latex were directly related with surfactant adsorption on the particle surface. The molecular surface adsorption area of CTAB on latex particle could be used to explain the evolution of latex properties such as ζ potential and latex surface tension.
[Show abstract][Hide abstract] ABSTRACT: Polyurethane–acrylic (PU–AC) hybrid latexes were prepared. Main monomers for PU preparation were isophorone diisocyanate, DMPA (dimethylol propanic acid) and polypropylene oxides (PPO) of different molecular weights. Acrylic monomers included butyl acrylate, methyl methacrylate and a crosslinker, trihydroxymethyl propane triacrylates (TMPTA). Several important ingredients in PU–AC latex preparation, such as surfactants, initiator, DMPA and PU/AC ratio, etc., were varied, and their effects on latex properties studied. Compared with surfactant free latexes, a sharp increase in particle size was observed in latexes done with 0.1% of surfactant regardless of the nature of the surfactants used (anionic, nonionic and anionic with long chain of amphiphilic alkylphenyl polyethoxylate). Further increase in surfactant content, however, led to latexes with smaller particle size and narrower particle size distribution when compared between latexes prepared using a same surfactant. When amount of the oil soluble initiator, azobisisobutyronitrile, was increased, AC monomers conversion was increased. It is interesting to observe that PPO with long propylene oxides brought about larger particle size combined with broader size distribution and less charge on particle surface; whereas lower DMPA levels led to latexes also of larger size combined with broader size distribution but more charges on particle surface. AC monomer crosslinker, TMPTA, contributed to reduce particle size, narrower size distribution and lower particle surface charges. By increasing AC amount in PU–AC latex, latex particle size significantly increased accompanied by a remarkable increase in particle surface charges. Mechanisms of particle formation and of DMPA stabilization were discussed in order to understand the experimental results.