pH响应性P(MMA-co-MAA-co-HEMA)微凝胶的制备及其性能

利用预乳化乳液法制备了不同单体配比的聚(甲基丙烯酸甲酯-co-甲基丙烯酸-co-甲基丙烯酸羟乙酯)(P(MMA-co-MAA-co-HEMA))微凝胶分散液;采用透射电子显微镜、动态光散射仪研究了微凝胶的微观形态、粒径大小及其溶胀率;利用试管倒转法对微凝胶分散液的凝胶化相转变行为进行了研究,借助椎板流变仪考察了所形成胶态凝胶的储能模量与单体配比、微凝胶分散液浓度和温度的关系.结果表明,所制备的微凝胶的数均粒径为90 nm左右,当MMA与MAA的投料质量不变时,随着HEMA含量的增加,分散液凝胶化所需的临界最小浓度增大,临界最大pH值减小,胶态凝胶的储能模量增加.当保持单体MMA与HEMA的投料质量不变时,随着单体MAA投料质量的增多,微凝胶的数均粒径和溶胀率增大,胶态凝胶的储能模量先升高后降低;当MAA占单体总摩尔数的25%时,浓度为15 wt%的微凝胶分散液在扫描频率为100 rad/s时,胶态凝胶的储能模量最高可达2×104Pa.这类微凝胶分散液在组织工程支架材料方面有潜在的应用价值.

PREPARATION AND PERFORMANCE OF pH-RESPONSIVE P(MMA-co-MAA-co-HEMA) MICROGELS

pH-responsive microgels are cross-linked polymer colloids that swell when the pH approaches the pKa of the particles.They have potential application for injectable gels for tissue repair.They can undergo volume phase transition as a function of pH and concentration.However,a major drawback of such materials is the lower mechanical strength.Pre-emulsion technology was used to prepare the pH-responsive poly(methyl methacrylate-co-methacrylic acid-co-2-hydroxyethyl mthacrylate)(P(MMA-co-MAA-co-HEMA) microgels.The morphology,particle size as well as the swelling ratio were investigated by transmission electron microscopy(TEM) and dynamic light scattering(DLS).The TEM data showed the number-average size of the microgel particles was about 90 nm when the mole fraction of MAA was 25%,numbered G(HEMA-25) or G(MAA-25).When keeping the mass of MMA and HEMA the same,the particle size increased with the increasing of the MAA content.The maximum swelling ratio(q) of G(MAA-25) can be up to 1371.The microgels exhibit good pH responsibility and swelling properties.Fluid-to-gel phase diagrams for the G(HEMA-25),G(HEMA-16) and G(HEMA-4.5) dispersions were determined as a function of concentration(cp) and pH using tube-inversion measurements.The results showed that the critical minimum concentration(cp,min) increased and the critical maximum pH(pHc,max) decreased when gelatinization occured.The storage modulus of the gelled dispersions was investigated by using rheometry.The results show that storage modulus of gels increases with the increasing of HEMA contents.Because hydrophilic hydroxyl groups of HEMA may increase the hydrogen bond sites,which not only improve mechanical properties of microgels,but also make the network structure more stable.The storage modulus also depends on the MAA content.The storage modulus increased when the MAA mole fraction increased from 4.5 mol% to 10 mol% and then decreased.The storage modulus decreased with increasing temperature.When the mole fraction of MAA was 25% based on the total monomer and the concentration of G(HEMA-25) was 15 wt%,the storage modulus of colloidal gel reached 20000 Pa at scanning frequency(ω)=100 rad/s.