Preparation Of PDVB And PTMPTA Microspheres Through Precipitation Of Polymerization In Supercritical Carbon Dioxide

In this paper, monodisperse micro-size polydiviylbenzene (PDVB) microspheres, poly diviylbenzene-co-maleic anhydride (P(DVB-MAH)) microspheres and polytrihydroxy methylpropane triacrylate (PTMPTA) microspheres with clean surfaces were synthesized by precipitation polymerization in supercritical carbon dioxide system. Influences of monomer concentration, reaction time, reaction pressure, reaction temperature, species of cosolvent, the dosage of cosolvent, initiator concentration and monomer ratio on morphology and size of polymers were investigated; the morphology of the polymers were observed via scanning electron microscopy (SEM). The growth of polymer microsphere and the mechanism of polymer microsphere formation were also discussed; at the same time, the structure of polymers was characterized by IR and thermal property of polymers was determined by TDA. The total amount of detected vinyl groups in PDVB microspheres was determined by bromine titration.Results demonstrated that PDVB, P(DVB-MAH) and PTMPTA were white powder solid and the conversions in all polymerization systems were above 97 %. It was found difficult to prepare PDVB, P(DVB-MAH) or PTMPTA microspheres in pure supercritical carbon dioxide, but monodisperse microspheres of these polymers were obtained in supercritical carbon dioxide with an amount of cosolvent (for example: n-pentane, acetic acid and acetone). Therefore, selecting the proper cosolvents and reaction pressure, reaction concentration to adjust solubility parameters of reaction medium were important in preparing monodisperse polymer microspheres.The results showed that monodisperse PDVB microspheres were obtained with monomer concentration of 0.38 mol/L, reaction pressure of 16.0 MPa and reaction time of 24 h, solubility parameters of reaction medium of 10.58~11.01 MPa1/2 in supercritical carbon dioxide using appropriate acetone dosage. It was also demonstrated that monomer concentration, reaction time, reaction pressure and cosolvent had no effect on the appearance, conversions and thermal property, but had a pronounced effect on morphology of the polymers. At the same time, P(DVB-MAH) microspheres were also prepared with MAH loading of 5 mol % ~10 mol %; the structures of copolymers were characterized by IR and the content of MAH in the copolymers was relatively high. PTMPTA were producted with monomer concentration of 0.067 mol/L, reaction pressure of 16.0 MPa and reaction time of 8 h in supercritical carbon dioxide using appropriate ethanol dosage system.In this experiment, the residual double bonds of the polymer microspheres were also determined by bromine addition and were characterized by IR. The presence of the residual double bonds in polymer microspheres was comfirmed via comparing the IR spectra of the polymers prior to and after bromine addition and elimination in the microspheres. The content of residual double bonds in polymer microspheres was determined by bromine titration. The results showed that the total amount of the residual double bonds in the microspheres was about 3.0×10-3 mol/g and the amount of the residual double bonds at the microspheres surfaces was about 1.8×10-3 mol/g. The PDVB microspheres, which have relatively high concent of residual double bonds, can be further functionalized.