1998 IUPAC and characterization Ramanathan, P. G. Shukla And - PDF document

1998 IUPAC and characterization Ramanathan, P. G. Shukla And is dried under vacuum room temperature for 4 h to get free flowing polyurethane microspheres. Yield: 90 IR (KBr): 3400 cm-' (-NH); 1750 cm-' (-COO); 1710 cm-' (-NHCOO-) -aromatic); 4.1-4.3(br; 1.1-1.5 (br; polyurethane microparticles suspension polymerization: a four neck 250 round bottom flask fitted with a stirrer, condenser, nitrogen inlet and a thermowell, block copolymer and 50 g paraffin oil were added and stirred rpm. The mixture was heated to 65°C and TDI was added. The reaction was continued for 5 polyurethane microspheres formed was washed with hexane to remove paraffin oil and dried under vacuum at room temperature for 4 h to free flowing polyurethane microspheres. Yield: 65 3400 cm-' (-NH); 1750 cm-' (-COO); 1710 cm-' (-NHCOO-). the macrodiols were determined according to ASTM procedure D1957. [Annual book ASTM standards vol. 06.03, sec 6 (1991)l. Molecular weight of the macrodiol was determined KNAUER vapour pfessure osmometer at 35°C. IR spectra were recorded on a Perkin Elmer 16 PC FT-IR spectrometer. 'H spectra were recorded on a 200 Particle size and size distributions were measured using a Malvern Photon Correlation Photometer, model 4700 using a vertically polarized He-Ne laser as light source. The macrodiols were prepared the reaction TMP with a carboxyl terminated poly (lauryl methacrylate) (ref.7). The properties shown in Table TABLE 1 The observed functionality indicates near quantitative presence the 1,3-glycol moiety in the steric stabilizer. Dispersion polymerization of EHG and TDI was carried out in paraffin oil in the presence macrodiol stabilizers (Table 2). With macrodiol no dispersion could obtained as the whole mass coagulated. However, stable dispersion could obtained at the specified concentration of the stabilizer. The particle size histogram Fig. 1 which indicate that nearly monodisperse particles nanometer size are obtained when was used as a the concentration increased from to 15 no significant change either in particle size or particle distribution. When the concentration is decreased from to 5 size polyurethane particles are formed with broad particle size distribution. Polyurethane microspheres Macrodiol Concentrationa, Particle TABLE 2: Properties polyurethane particles obtained using macrodiol stabilizers. 15 Coagulated Partially agglomerated isocyanate forming reactants. the concentration the stabilizer particle size decreases. particle size distribution was broad higher stabilizer concentration. experiment without macrodiol stabilizer did not produce polyurethane in a particulate form. The the polyurethane particle shows an ester (1775 cm-') and an urethane (1710 This observation indicates that macrodiol stabilizer participates in urethane forming reaction. The pendant hydrophobic PLMA moiety stabilizes the polyurethane particle formed steric stabilization is in accordance with proposed theories particle forming mechanism (ref 8). The decrease particle size polyurethane dispersion an increase concentration can understood based the premise that in dispersion polymerization nucleation takes place at early stages where particle number reaches final value (ref.9). higher stabilizer concentration prevents coagulation the initially formed nuclei particle size. phenomenon was observed in the radical dispersion polymerization using macrodiol stabilizer (ref.4 and 1.16 95 1.24 95 Diameter (nm) molecular weight and concentration macrodiol stabilizer particle size and size polyurethane particles. microspheres using block copolvmer steric stabilizer. Suspension polymerization of EG and TDI was carried out using block copolymer, namely, poly (butadiene-b-ethylene oxide) steric stabilizer. The block copolymer was prepared sequential anionic polymerization technique. The properties polyurethane particles prepared from such process are shown in Table Poly (butadiene-b-ethylene oxide) was chosen as steric stabilizer because it contains an hydrophilic anchor block (PEO segment) and freely soluble stabilizing moiety (poly butadiene segment) in the dispersion medium. Hence should stabilize the polyurethane particles effectively according to steric stabilization (ref.8). anchor to stabilizing moiety ratio increases, the particle size decreases. However when 7.14, there an increase particle size. This could be due to the poor solubility in paraffin oil, because higher PEO segment length. poly (butadiene-b-ethylene oxide) copolymer. The effect stabilizer concentration particle size and size distribution was carried out using block (Fig 2). increase in stabilizer concentration has significant effect Nevertheless, as the stabilizer concentration increases, change from bimodal to unimodal size distribution was observed. Here, the PU particle formed stabilized mainly the adsorption the amphiphilic block copolymer on the particle surface. at higher stabilizer concentration, the amount stabilizer adsorbed on the particle surface more and hence stabilizes the particle effectively. stabilizer concentration on particle size and particle size distribution microspheres prepared using poly (butadiene-b-ethylene oxide) steric stabilizer. (a) Stabilizer Concentration Particle Size =21.8 (b) Stabilizer Concentration Particle Size (c) Stabilizer Concentration Particle Size novel polycondensable macrodiol with long hydrophobic acrylate ester moiety and an amphiphilic block copolymer were successfully used the particle forming polymerization diisocyanate and diol. The performance of the macrodiol and block copolymer as stabilizers depends both weight and concentration. The particle size decreases as the concentration the stabilizer increases and nearly monodisperse polyurethane microspheres are formed in nanometer size range in the case macrodiol stabilizer. This new macrodiol steric stabilizer participates in urethane forming enchained in polymer. Further studies are in progress fully elucidate the mechanism Polyurethane microspheres stabilization and compare the efficiency steric stabilization polymerizable stabilizer with conventional steric stabilizer which functions solely adsorption mechanism. The authors would like to thank Prof. E N de chemie, Mulhouse, France the block copolymer samples. LSR would like Scientific Industrial Research Delhi, India, for Senior Research fellowship. R. Arshady, 101 (1980) E.D. Sudol and J Polym. 1393 (1993) Kobayashi, H.Uyama, J.H.Choi and Y.Matsumoto, 4. E. Bourgeat-Lami and Amrstorng Cork. Co., Ramanathan and K.E.J. Barrett, Dispersion polymerization in organic Wiley, London 9. S. Kawaguchi, M.A.Winnik, and K.Ito 28, 1159, (1995) 10. S. Kobayashi, H.Uyama, Polym. Sci., Polym. Chem.