【作者】 顾相伶；

【导师】 孔祥正； 谭业邦；

【作者基本信息】 山东大学 ， 高分子化学与物理， 2010， 博士

【摘要】 单分散聚合物微球及其组装形成的组合粒子在许多领域具有重要的应用价值。传统的制备单分散聚合物微球的方法都需要在聚合过程中加入表面活性剂或稳定剂,导致聚合体系的组分更复杂,产物纯度降低。上世纪90年代发展起来的沉淀聚合技术因聚合过程中无需加入表面活性剂和稳定剂使单分散微球的研究获得突破性进展。然而,迄今为止沉淀聚合制备单分散微球的相关研究仍普遍存在溶剂毒性高、微球产率低等问题。针对这一问题,本工作以低毒性溶剂乙醇及其与水的混合物作反应介质,探讨了获得高产率单分散微球的新途径,并在此基础上使用一种简单的微球自组装方法—液滴模板法制备了高尔夫球型的组合粒子。以三羟甲基丙烷三丙烯酸酯(TMPTA)作交联剂,苯乙烯(St)作共聚单体,偶氮二异丁腈(AIBN)作引发剂,分别在乙醇和乙醇-水混合溶剂中沉淀聚合反应4h制备了单分散交联微球。实验发现,当TMPTA用量保持在10 wt%～60 wt%之间时,反应能够制得单分散微球。通过提高交联剂用量、引发剂用量和改变反应介质中水的用量探讨了提高单体转化率的方法。结果表明,提高引发剂用量和增加溶剂中水的用量都能有效提高单体转化率并制得粒径分布较窄的微球。保持其它条件不变,在乙醇中使用2 wt% AIBN仅能得到79%的单体转化率,提高AIBN用量至6 wt%或在介质中增加水的用量至28 vol%,单体转化率可以达到95%以上。使用三至五官能度的交联剂,包括季戊四醇三丙烯酸酯(PETA)、季戊四醇四丙烯酸酯(PETRA)和双季戊四醇五丙烯酸酯(DPHA)与St在乙醇及其与水的混合物中反应8h制备了单分散聚合物微球。研究发现,制得单分散微球所需PETA、PETRA和DPHA的用量范围分别为5 wt%～35 wt%、5 wt%～35 wt%和5 wt%～15 wt%。增加交联剂的官能度能够有效提高单体转化率并制得粒径分布较窄的微球。使用35 wt%PETA或PETRA,6 wt%的AIBN,以含水量25 vol%的乙醇作介质,在制得单分散微球的同时分别能够获得93%和99%的单体转化率。保持其它条件不变,使用15 wt%DPHA,以含水量20 vol%的乙醇作介质,沉淀聚合亦可以得到77%的单体转化率。以N-异丙基丙烯酰胺(NIPAM)作单体,N,N’-亚甲基双丙烯酰胺(MBAAM)作交联剂,过硫酸铵(APS)作引发剂,水作反应介质,通过沉淀聚合制备了温敏性的水凝胶微球。结果表明,保持MBAAM用量在5 wt%～10 wt%之间,聚合制得了单分散的水凝胶微球。在此范围内增加交联剂用量,反应的单体转化率显著提高,微球粒径逐渐增大,溶胀率逐渐减小,微球的温敏性逐渐减弱。对微球-水复合体系的透光率测试结果表明,水凝胶微球的低临界溶解温度在30℃～36℃之间,随交联剂用量增加微球体积转变的温度范围逐渐增大。固定单体浓度为2 wt%,MBAAM用量10 wt%,保持APS用量在0.5 wt-／～2 wt%之间,沉淀聚合制得了单分散的水凝胶微球。在此范围内提高APS用量,单体转化率略有增大,微球粒径逐渐减小。对微球热失重分析结果表明,所制备微球的内部和外层由不同交联度的聚合物组成。控制微球的交联度、溶液的pH及温度可实现P(NIPAM-MBAAM)微球对蛋白的吸附与脱附。以乙醇与水的混合物作为连续相,加入甲苯构建液滴模板,通过沉淀聚合得到的P(TMPTA-St)初级粒子的自组装制备了高尔夫球型组合粒子。改变振荡器的振荡频率、甲苯用量、醇／水比例、交联剂用量以及反应时间,组装形成的组合粒子形貌发生显著变化。当甲苯用量为18 mL,乙醇／水体积比为7／3,TMPTA用量为20 wt%,反应时间4 h,振荡频率为120／min时,组装得到了形态规则的高尔夫球型组合粒子。对粒子自组装的机理研究表明,初级粒子在乙醇-水的混合溶剂中形成,粒子与甲苯的相容性作为驱动力使其向甲苯中定向迁移并有序组装。扫描电镜观察的结果表明,高尔夫球型组合粒子具有明显的核壳结构。高尔夫球型组合粒子表面具有纳米级孔结构和次级结构。将高尔夫球型组合粒子涂覆于压敏胶膜表面,其疏水性显著增强。更多还原

【Abstract】 Monodisperse polymer microspheres and supraparticles fabricated from microsphere assembly had significant application values in many fields. The traditional methods to prepare monodisperse microspheres all needed surfactants or stabilizers, which made the components of the polymerization system more complicated and led to microspheres with lower purity. Precipitation polymerization developed in the 1990’s made a breakthrough in the preparation of monodisperse microspheres because it didn’t need surfactants or stabilizers. However, the development of precipitation polymerization was limited with the commonly existing problems, such as high toxicity of solvents and low yield of microspheres. Facing this challenge, we used low-toxic solvents, ethanol, water and their mixture to explore the new way to obtain monodisperse microspheres with high yield. Based on this work, a facile route to achieve self-assembly of primary particles on an organic droplet was employed to prepare golf-ball-like supraparticles.First, monodisperse microspheres were prepared through precipitation polymerization of trihydroxymethyl propane triacrylate (TMPTA)-styrene (St) in ethanol and ethanol-water mixture with azobisisobutyronitrile (AIBN) as initiator when TMPTA amounts was kept at 10%～60% relative to the total mass of monomers. Impact of TMPTA amounts, initiator concentrations and water content in the solvent mixture were studied. Monodisperse microspheres were obtained within 4 hours along with higher monomer conversion. Results demonstrated clearly that increase in initiator amount and use of water as a cosolvent were indeed very effective to promote the polymerization to high conversions and to get uniform microspheres. With no water under otherwise the same experimental conditions, only about 79% of monomer conversion was detected; while monomer conversion was remarkably increased to 95% when 28 vol% of water was added into ethanol. To reach to this high conversion with no water in the medium,6 wt% of AIBN was needed.Secondly, with pentaerythritol triacrylate (PETA)、pentaerythritol tetraacrylate (PETRA) or dipentaerythritol pentaacrylate (DPHA) as crosslinkers, St as co-monomer and AIBN as initiator, the precipitation polymerizations were carried out in ethanol and ethanol-water mixture. It was found that uniform microspheres were obtained when the amounts of PETA, PETRA and DPHA were kept at 5 wt%～35 wt%,5 wt%～35 wt% and 5 wt%～15 wt%, respectively. Results indicated that increasing functionality of crossslinkers was an effective method to promote the polymerization to high conversions. Using 35 wt% of PETA or PETRA and 6 wt% of AIBN, uniform microspheres and high conversions of 93% and 99% respectively were obtained by precipitation polymerization in the mixed solvents with 25 vol% of water. Under otherwise the same experimental conditions but 15 wt% of DPHA, precipitation polymerization in the mixed solvents containing 20 vol% of water led to a conversion of 77%.Thirdly, N-isopropylacrylamide (NIPAM) and an aqueous crosslinker, methylenebisacrylamide (MBAAM) were employed to prepare thermal-sensitive hydrogel microspheres via precipitation polymerization in water with ammonium persulfate (APS) as initator. Poly(NIPAM-MBAAM) microspheres with narrow size distribution were synthesized in a defined range of MBAAM levels, namely between 5% and 10% relative to the total mass of monomers. With increase in MBAAM, the polymerization conversion was significantly promoted and the swelling ratio of mcirospheres gradually decreased, which indicated that thermal-sensitivity of hydrogel microspheres was gradually weakened. Photometer was carried out to measure the thermal-sensitivity of these microspheres. It was found the hydrogel microspheres had lower critical temperatures (LCST) at 30～36℃, but the LCST occurred in a wider temperature range with increase in crosslinker. Amounts of APS imposed an import influence on morphology of poly(NIPAM-MBAAM). Uniform hydrogel microspheres were obtained when 0.5 wt%～2 wt% of APS was used with other conditions kept unvaried. In this range, adding more APS into the polymerization system led to increase of monomer conversion and decrease of microsphere size. Thermogravimetric analysis (TGA) results indicated that the structure of the microspheres was composed of two parts of polymers:one is of high-crosslinking in the core and the other is of low-or non-crosslinking on the surface layer. The experiment results demonstrated that the adsorption and desorption of protein on the microsperes could be controlled by adjusting the crosslinking of polymer, pH and temperature of the complex system of microsphere and water.Finally, an easy way to achieve self-assembly of primary particles on an organic droplet was presented. With the mixed solvents of ethanol and water as continuous phase, toluene was added into them to fabricate the droplet template. Self assembly was then optimized with regard to shaking frequency, polymerization time, toluene volume in the ternary solvent system as well as the amount of TMPTA in the monomers. Golf-ball-like supraparticles were achieved by assembly of poly(TMPTA-St) primary particle obtained from the precipitation polymerization when the experimental condition was fixed at:TMPTA amount of 20 wt%, reaction media composed of 18 mL of toluene, 56 mL of ethanol and 24 mL of water, shaking frenquency at 120/min and reaction time of 4 h. The investigation of formation mechanism of golf-ball-like supraparticles indicated that the primary particles were formed in the mixture of ethanol and water. The compatibility of the primary particles and toluene acted as a driving force making the primary particles directionally migrate into toluene droplet. The golf-ball-like supraparticles were demonstrated with a core-shell structure through the observation with scanning electronic microscope. After coating the supraparticles on the surface of the film of pressure sensitive adhesive, its hydrophobicity was significantly enhanced.更多还原