沉淀聚合制备单分散聚脲微球及其表征
Preparation of Uniform Polyurea Microspheres through Precipitation Polymerization and Their Characterization

作者: 李 彬 , 曹红岩 , 孔祥正 , 姜绪宝 :济南大学化学化工学院,山东 济南;

关键词: 沉淀聚合单分散微球产率聚脲胺基Precipitation Polymerization Uniform Microspheres Sphere Yield Polyurea Amine Groups

摘要:
以异佛尔酮二异氰酸酯(IPDI)为单体,在水与丙酮或水与乙腈的混合溶剂中通过沉淀聚合制备了单分散聚脲(PU)微球。探讨了单体用量和混合溶剂种类及其配比对微球产率及粒径等的影响,并对静置与振荡两种聚合条件下的聚合过程进行了比较,通过红外和热失重对微球进行了表征。结果表明,微球产率及粒径随单体用量逐渐增加。当水/丙酮质量比及IPDI用量相同时,静置和振荡两种聚合方式下所得微球的产率基本相同,但在保证所制备微球高度单分散的前提下,静置聚合条件下能够允许的单体加入量比振荡时高,而且所得微球的单分散性更好。在静置聚合条件下以水和丙酮为溶剂制备单分散微球时,单体用量最高为11.0%,微球产率为88.5%;而在水和乙腈混合溶剂中制备单分散微球时,IPDI用量最高可达21.0%,微球产率为93.1%,比在水丙酮中聚合时的微球产率明显提高。红外和热失重检测显示,所得微球富含胺基,且微球聚合物具有较高的热稳定性。

Abstract: Uniform polyurea (PU) microspheres were prepared through precipitation polymerization using isophorone diisocyanate (IPDI) as the only monomer in mixed solvent of water-acetone (H2O-AT) or water-acetonitrile (H2O-AN) under shaking or with a quiescent process. The effects of IPDI loading, H2O/AT and H2O/AN mass ratio on the formation of PU microspheres were studied, and the properties of the microspheres obtained were tested. The results showed that the yield and size of the microspheres increased with the amount of IPDI added. The yield of the microspheres obtained was basically the same under shaking or quiescent process, while higher IPDI loading with better uniformity of the microspheres was achieved under the quiescent process. To get uniform PU microspheres in H2O-AT mixture under the quiescent condition, the maximal IPDI loading was 11.0 wt% with the yield of the microspheres of 88.5%. With acetone replaced by acetonitrile, the maximal IPDI loading reached 21.0% combined with a yield of 93.1%, a significant increase in the productivity of the microspheres in comparison with the yield obtained by polymerization in H2O-AT mixture. Infrared and thermo gravimetric data showed that the PU microspheres were rich in amine groups, and of higher thermal stability.

1. 引言

聚合物单分散微球在药物控释 [1] 、色谱分析 [2] 、酶固定 [3] 和光子晶体 [4] 等领域具有广泛应用。其传统制备方法有乳液聚合 [5] 、分散聚合 [6] 和玻璃膜乳化及后聚合 [7] 等技术。所有这些方法必须使用表面活性剂或稳定剂,这些组分难以去除,制约了聚合物单分散微球的应用,尤其是在生物和医药等领域。

沉淀聚合制备单分散聚合物微球时不需表面活性剂或稳定剂,所得微球因表面洁净而备受关注 [8] [9] [10] 。但通过自由基沉淀聚合制备单分散微球时的单体用量一般不超过2.0%,单体转化率和微球产率也较低(<70%) [10] [11] [12] [13] 。Stöver等 [10] [11] 以乙腈为溶剂,将二乙烯基苯(DVB)与不同烯类单体进行沉淀聚合制备了聚合物单分散微球,并提出了微球的增长机理 [11] ,其中单体用量都在2.0%左右,70℃下反应24 h时单体的转化率不超过70%。Choe等 [12] 将甲基丙烯酸甲酯与DVB进行共聚制备了聚合物单分散微球,单体用量也未超过2.0%;Irgum等 [13] 采用光引发DVB等单体进行沉淀聚合,发现只有当单体用量低于4.0%时才可获得单分散微球,而聚合112 h微球产率只有23%。

在几乎所有的聚合过程中对反应介质的搅拌或振荡是必不可少的。搅拌或振荡是使聚合体系保持均质及反应热及时扩散从而使聚合反应顺利进行的基本条件之一,尤其是在制备聚合物粒子分散体系的过程中(如乳液聚合和悬浮聚合等),搅拌还能够防止聚合物粒子的粘结、聚并和凝胶化。对聚合体系进行搅拌或振荡一般需要使用专门的搅拌机或振荡器使聚合体系达到均质、散热和分散的目的 [14] [15] 。这些相应的专用设备当然也使得生产成本显著增加。

本工作仅使用异佛尔酮二异氰酸酯一种单体,以水和丙酮或水和乙腈的混合溶剂为反应介质,在振荡或者完全静置 [16] [17] 的条件下通过沉淀聚合高产率制备聚脲单分散微球。比较了两种条件下所得微球的差异,探讨了溶剂配比和单体用量对微球产率和粒径的影响,并通过红外和热重分析对微球的化学结构和性能进行了初步表征。

2. 实验部分

2.1. 实验原料

异佛尔酮二异氰酸酯(IPDI),工业品,德国Degussa公司;丙酮和乙腈,分析纯,天津富宇精细化工有限公司;二次蒸馏水,实验室自制。

2.2. 聚脲(PU)微球的制备

在120 mL反应瓶中加入90.0 g一定质量比的水/丙酮或水/乙腈混合溶剂及10.0 g IPDI单体,混合均匀后将反应瓶置于70℃的恒温振荡水浴中,在120 osc/min振频下聚合2 h。静置条件下聚合时将装载有混合溶剂和IPDI单体的反应瓶混合均匀后,直接静置于70℃的恒温水浴中,原本清澈透明的(单体和溶剂)聚合体系在数分钟内会变浑浊,而后继续反应2 h。最后将聚合体系在12,000 r/min转速下离心,分离出聚合物微球并用丙酮洗涤2次,然后在80℃烘箱中干燥12 h制得PU微球粉体。

2.3. PU微球的表征

使用Hitachi公司S-2500型扫描电子显微镜(SEM)观察微球的形貌。从所得SEM照片中量取不少于200个粒子的粒径,计算微球的重均(Dw)和数均(Dn)粒径及其分布(Dw/Dn)。使用Perkin-Elmer公司的Spectrum GX傅里叶变换红外光谱仪以KBr压片法对微球进行红外分析。采用Perkin-Elmer公司Diamond TG/DTA热重分析仪,在升温速率10℃/min及N2保护条件下对微球进行热失重分析。

3. 结果与讨论

3.1. 聚合反应的机理

本工作以IPDI为单体,利用其与水的反应制备聚脲,化学反应机理由图1给出。IPDI中的部分异氰酸酯基(NCO)先与水反应生成对应的单取代及双取代的胺,同时放出CO2。随后,体系中尚未与水反应的NCO再与生成的胺通过逐步聚合制得聚脲 [16] [17] 。由于实验过程中水的用量相对NCO基团过量,聚合完成后NCO完全转化,聚脲分子被胺基封端。

3.2. 以水和丙酮为反应介质在振荡条件下制备PU单分散微球

首先,以水和丙酮为反应介质,在反应温度为70℃和振荡频率为120 osc/min的条件下使用不同水/丙酮质量比和不同IPDI用量进行实验,测定了所得微球的产率、粒径及其多分散系数,结果见表1

Figure 1. Chemical reactions involved in formation of PU through reaction of IPDI with H2O

图1. IPDI与水反应制备PU的反应式

Table 1. Influence of H2O/acetone mass ratio and IPDI loading on the formation of PU microspheres in polymerization under shaking

表1. 在振荡条件下制备PU微球时水/丙酮的质量比及IPDI用量的影响

*体系中存在凝胶。

由表可见,当水/丙酮质量比为50/50和20/80时所得PU微球的粒径分布系数(Dw/Dn)较高,微球的单分散性较差。图2(a)和图2(f)给了上述两个配比下所得微球的SEM照片,由此可见所得PU微球的大小不一。水/丙酮质量比为50/50及IPDI用量为3.0%时,IPDI用量超过了其溶解度,单体在溶剂中不能完全溶解而是以液滴的形式存在。这些液滴的形状及大小不稳定,且可与水进行界面聚合,从而形成聚合物凝胶。水/丙酮质量比为20/80时的丙酮用量较高,使得聚脲从反应介质中析出形成初级微球的时间变长,即导致微球的成核期延长,从而造成微球大小不一,Dw/Dn变大。当水/丙酮质量比为40/60时,微球产率及粒径随着单体用量逐渐增加,但制备单分散微球的单体用量最高为4.6% (图2(b)),单体用量提升至5.0%时所制聚合物微球大小不一(图2(c)),这也是由于此时单体的用量超过了其溶解度,单体在溶剂中未能完全溶解所致。提高混合溶剂中丙酮用量至70%,即当水/丙酮质量比为30/70时,能够制备单分散微球的单体用量显著提高,达到了8.8% (图2(d)),微球产率达到了86.39%。我们认为,这是由于混合溶剂中丙酮用量的增加提高了IPDI的溶解度。

3.3. 以水和丙酮为反应介质在静置条件下制备PU微球

以水和丙酮为反应介质,固定反应温度为70℃,在静置不搅拌条件下进行聚合制备PU微球,探讨了水/丙酮质量比及IPDI用量对聚合过程和微球单分散性的影响,结果见表2。在静置条件下,当水/丙酮质量比为40/60和30/70时能够制得单分散的PU微球(见图3),这与振荡条件下制备单分散微球的水/丙酮比完全相同(见表1)。不同的是,在静置条件下制备单分散微球时的单体用量显著提高。当水/丙酮比为40/60时,制备单分散微球的单体用量最高为5.4% (图3(b)),水/丙酮比为30/70时单体用量达到了11.0% (图3(d)),明显高于振荡时4.6%和8.8%的单体用量(表1)。我们认为,这是由于静置条件下外力对体系的扰动较小所致。Stöver [11] 等曾指出,沉淀聚合体系中粒子的稳定主要依赖于微球表面聚合物被溶剂溶胀而形成的松散溶胀层或毛发层。这种稳定作用较弱,与乳液聚合或悬浮聚合中非离子型乳化剂或稳定剂的作用类似。对于本体系而言,当单体用量较高时,体系中的粒子较多,粒子间距离较近,较易发生聚并而使体系凝胶。当存在外界的扰动时这种效果将会加剧。相对于无扰动的静置聚合,振荡条件下制备单分散微球时单体的最大用量因此降低。也正是由于静置对体系的扰动较小,体系中粒子的稳定性相对较高,在静置条件下所得微球的单分散性(Dw/Dn表2)因此也明显高于振荡条件下的微球(表1)。另外,比较表1表2中微球的产率可知,当水/丙酮比和单体用量相同时,如水/丙酮比为40/60及IPDI用量为4.0%时,静置与振荡条件下所得微球的产率基本相同(77%),说明两种方式对微球产率的影响不明显。

Figure 2. SEM photos of PU microspheres prepared in mixed solvent of different H2O/acetone mass ratio and IPDI loading under shaking (H2O/acetone ratio & IPDI loading: (a) 50/50 & 3.0%; (b) 40/60 & 4.6%; (c) 40/60 & 5.0%; (d) 30/70 & 8.8%; (e) 30/70 & 9.0%; (f) 20/80 & 9.0%).

图2. 在振荡条件下水/丙酮质量比及单体用量不同时所得PU微球的SEM照片(水/丙酮比&IPDI用量:(a) 50/50 & 3.0%; (b) 40/60 & 4.6%; (c) 40/60 & 5.0%; (d) 30/70 & 8.8%; (e) 30/70 & 9.0%; (f) 20/80 & 9.0%).

Figure 3. SEM photos of PU microspheres prepared in mixed solvent of different H2O/acetone mass ratio and IPDI loading under quiescent polymerization (H2O/acetone ratio & IPDI loading: (a) 50/50 & 3.0%; (b) 40/60 & 5.4%; (c) 40/60 & 5.6%; (d) 30/70 & 11.0%; (e) 30/70 & 12.0%; (f) 20/80 & 11.0%)

图3. 在静置条件下不同水/丙酮质量比及单体用量时所得PU微球的SEM照片(水/丙酮比&IPDI用量:(a) 50/50 & 3.0%; (b) 40/60 & 5.4%; (c) 40/60 & 5.6%; (d) 30/70 & 11.0%; (e) 30/70 & 12.0%; (f) 20/80 & 11.0%)

Table 2. Influence of H2O/acetone mass ratio and IPDI loading on the formation of PU microspheres under quiescent polymerization

表2. 在静置聚合条件下制备PU微球时水/丙酮质量比及IPDI用量的影响

*体系中存在凝胶。

3.4. 以水和乙腈为溶剂在静置条件下制备PU微球

在本部分实验中,固定反应温度为70℃,用乙腈代替丙酮,在水和乙腈混合溶剂中进行聚合,探讨了水/乙腈质量比和IPDI用量对微球产率和粒径等的影响(表3)。由表可见,当水/乙腈质量比为25/75及15/85时所得PU微球粒径分布较宽,图4(a)和图4(d)给出的SEM照片显示所得微球大小明显不一。当水/乙腈比为20/80及单体用量低于22.0%时,可制得单分散的PU微球(图4(b))。单体用量为21%时对应单分散微球的产率达到了93.13%。由此可见,使用乙腈与水组成的混合溶剂为反应介质制备单分散微球时单体加入量及微球产率得到显著的提高。

如前所述,传统的自由基沉淀聚合制备聚合物单分散微球时的效率较低。若按照单体用量为2.0%及单体转化率为70%计算,通过一吨反应釜一次最多只能获得约14 Kg聚合物单分散微球。相比而言,本工作制备聚合物单分散微球的效率显著提高。以水和丙酮为反应介质在静置条件下制备单分散微球时,单体用量最高可达11.0%,微球产率为88.46%,一吨反应釜一次可获得约97 Kg聚合物单分散微球,微球收率约为传统方法的7倍。当使用水和乙腈为反应介质时,按照单体用量为21.0%及微球产率为93.13%计算,一吨反应釜一批次最多可获得约195 Kg单分散微球,微球收率是使用水和丙酮为反应介质时的2倍,约为传统自由基沉淀聚合体系的14倍之多。同时,本工作制备单分散微球时无需任何搅拌及振荡设备,生产成本及能耗较低,有利于实现单分散微球规模化生产。

Figure 4. SEM photos of PU microspheres prepared in mixed solvent of different H2O/acetonitrile mass ratio and IPDI loading under quiescent polymerization (H2O/acetonitrile ratio & IPDI loading: (a) 25/75 & 10.0%; (b) 20/80 & 21.0%; (c) 20/80 & 22.0%; (d) 15/85 & 21.0%)

图4. 静置条件下不同水/乙腈质量比及单体用量时所得PU微球的SEM照片(水/丙酮比&IPDI用量:(a) 25/75 & 10.0%; (b) 20/80 & 21.0%; (c) 20/80 & 22.0%; (d) 15/85 & 21.0%)

Table 3. Influence of H2O/acetonitrile mass ratio and IPDI loading on the formation of PU microspheres under quiescent polymerization

表3. 静置聚合条件下制备PU微球时水/乙腈质量比及IPDI用量的影响

*体系中存在凝胶。

3.5. PU微球表征

通过红外对在静置和振荡条件下以及不同溶剂中制备的PU微球进行了表征,结果显示所有聚合物红外吸收光谱完全相同,表明所制备聚合物微球具有完全相同的化学结构。图5给出了70℃下在水和乙腈混合溶剂(20/80质量比)中所制微球的红外吸收光谱。为便于比较,图中也给出了IPDI单体的红外谱图。

图中2247 cm−1处的强吸收峰是由于IPDI中NCO的伸缩振动引起的。相比之下,PU的谱图在2247 cm−1处没有吸收峰,说明IPDI聚合后NCO被水完全消耗。脲基中C=O的伸缩振动峰出现在在1637 cm−1处。在PU微球的谱图中,在3371和1558 cm−1的强吸收峰分别是由于胺基的伸缩振动和弯曲振动引起的,这表明微球富含胺基,便于微球的进一步功能化及应用拓展。

对上述PU微球进行了热失重分析(图6)。结果表明,当温度低于300℃时微球几乎没有失重;温度升高至365℃时,微球失重约5%;当温度达到370℃时,PU迅速分解,至400℃时微球失重约80%。这表明PU微球聚合物具有较高的热稳定性。

Figure 5. Infrared spectra of IPDI and PU microspheres

图5. IPDI及PU微球的红外谱图

Figure 6. TGA curve of the PU microspheres

图6. PU微球的热失重曲线

4. 结论

以IPDI为单体,分别在水和丙酮及水和乙腈的混合溶剂中进行沉淀聚合制备了单分散的聚脲微球。结果表明,在振荡与静置条件进行聚合,在同样单体用量条件下所得微球产率基本相同,而静置条件下所得微球单分散性更好。将振荡聚合与静置聚合两种方法进行比较,在确保微球高度单分散的前提下,静置聚合方法下能够使用的单体量更高。同样在静置条件下进行聚合,比较混合溶剂的影响发现,以质量比介于40/60~30/70之间的水/丙酮为溶剂,可制得单分散微球的单体最高用量为11.0%,微球产率为88.5%;以质量比为20/80的水/乙腈为溶剂时,可制得单分散微球的单体最高用量为21.0%,微球产率可达93.1%。本工作制备聚合物单分散微球的收率较以往的自由基沉淀聚合体系显著提高,是传统方法的14倍,有利于实现微球的规模化生产。所得微球富含胺基,便于进行功能化及应用,同时所得微球具有较高热稳定性,在365℃下的失重仅为5%。

致谢

感谢国家自然科学基金(21274054, 21304038和51473066)、山东省重点研发计划(2017GGX202009)和济南大学科研基金(XKY1604)的资助。

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[3] Tang, T., Fan, H., Ai, S., Han, R. and Qiu, Y. (2011) Hemoglobin (Hb) Immobilized on Amino-Modified Magnetic Nanoparticles for the Catalytic Removal of Bisphenol A. Chemosphere, 83, 255-264. https://doi.org/10.1016/j.chemosphere.2010.12.075

[4] Li, F., Josephson, D.P. and Stein, A. (2011) Colloidal Assembly: The Road from Particles to Colloidal Molecules and Crystals. Angewandte Chemie International Edition, 50, 360-388. https://doi.org/10.1002/anie.201001451

[5] Binauld, S., Delafresnaye, L., Charleux, B., Agosto, F.D. and Lansalot, M. (2014) Emulsion Polymerization of Vinyl Acetate in the Presence of Different Hydrophilic Polymers Obtained by RAFT/MADIX. Macromolecules, 47, 3461-3472. https://doi.org/10.1021/ma402549x

[6] Warren, N.J. and Armes, S.P. (2014) Polymerization-Induced Self-Assembly of Block Copolymer Nano-objects via RAFT Aqueous Dispersion Polymerization. Journal of the American Chemical Society, 136, 10174-10185. https://doi.org/10.1021/ja502843f

[7] Ma, G., Sone, H. and Omi, S. (2004) Preparation of Uniform-Sized Polystyrene-Polyacrylamide Composite Microspheres from a W/O/W Emulsion by Membrane Emulsification Technique and Subsequent Suspension Polymerization. Macromolecules, 37, 2954-2964. https://doi.org/10.1021/ma035316g

[8] Li, G.L., Möhwalda, H. and Shchukin, D.G. (2013) Precipitation Polymerization for Fabrication of Complex Core–Shell Hybrid Particles and Hollow Structures. Chemical Society Reviews, 42, 3628-3646. https://doi.org/10.1039/c3cs35517a

[9] Kong, X.Z., Gu, X.L, Zhu, X.L. and Zhang, L.N. (2009) Precipitation Polymerization in Ethanol and Ethanol/Water to Prepare Uniform Microspheres of Poly(TMPTA-styrene). Macromolecular Rapid Communications, 30, 909-914. https://doi.org/10.1002/marc.200800772

[10] Downey, J.S., Frank, R.S., Li, W.H. and Stöver, H.D.H. (1999) Growth Mechanism of Poly(divinylbenzene) Microspheres in Precipitation Polymerization. Macromolecules, 32, 2838-2844. https://doi.org/10.1021/ma9812027

[11] Downey, J.S., McIsaac, G., Frank, R.S. and Stöver, H.D.H. (2001) Poly(divinylbenzene) Microspheres as an Intermediate Morphology between Microgel, Macrogel, and Coagulum in Cross-Linking Precipitation Polymerization. Macromolecules, 34, 4534-4541. https://doi.org/10.1021/ma000386y

[12] Shim, S.E., Yang, S. and Choe, S. (2004) Mechanism of the Formation of Stable Microspheres by Precipitation Copolymerization of Styrene and Divinylbenzene. Journal of Polymer Science: Part A: Polymer Chemistry, 42, 3967-3974. https://doi.org/10.1002/pola.20188

[13] Limé, F. and Irgum, K. (2009) Preparation of Divinylbenzene and Divinylbenzene-co-Glycidyl Methacrylate Particles by Photoinitiated Precipitation Polymerization in Different Solvent Mixtures. Macromolecules, 42, 4436-4442. https://doi.org/10.1021/ma900150b

[14] Dolata-Grosz, A., Hufenbach, W., Sleziona, J., Gude M. and Czulak, A. (2009) Design, Manufacture and Technological Verification of SiC/C Composite Stirrer. Archives of Materials Science and Engineering, 39, 29-37.

[15] Clegg, J., Marvin, A.C., Dawson, J.F. and Porter, S.J. (2001) Optimization of Stirrer Designs in a Reverberation Chamber. IEEE Transactions on Electromagnetic Compatibility, 47, 824-832. https://doi.org/10.1109/TEMC.2005.860561

[16] Jiang, X.B., Zhu, X.L. and Kong, X.Z. (2011) A Novel Protocol for Preparation of Uniform Polymer Microspheres with High Yields through Step Polymerization of Isophorone Diisocyanate and Water. Journal of Polymer Science Part A: Polymer Chemistry, 49, 4492-4497. https://doi.org/10.1002/pola.24890

[17] Jiang, X.B., Zhu, X.L. and Kong, X.Z. (2012) A Facile Route to Preparation of Uniform Polymer Microspheres by Quiescent Polymerization with Reactor Standing Still without any Stirring. Chemical Engineering Joural, 213, 214-217. https://doi.org/10.1016/j.cej.2012.09.111

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左侧“国际文献总库”进入,输入文章标题,即可查询

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NOTES

*通讯作者。

文章引用: 李 彬 , 曹红岩 , 孔祥正 , 姜绪宝 (2018) 沉淀聚合制备单分散聚脲微球及其表征。 材料化学前沿, 6, 11-19. doi: 10.12677/AMC.2018.62002

参考文献

[1] Anderson, J.M. and Shive, M.S. (2012) Biodegradation and Biocompatibility of PLA and PLGA Microspheres. Advanced Drug Delivery Reviews, 64, 72-78.
https://doi.org/10.1016/j.addr.2012.09.004

[2] Wang, J., Cormack, P.A.G., Sherrington, D.C. and Khoshdel, E. (2003) Monodisperse, Molecularly Imprinted Polymer Microspheres Prepared by Precipitation Polymerization for Affinity Separation Applications. Angewandte Chemie International Edition, 42, 5336-5338.
https://doi.org/10.1002/anie.200352298

[3] Tang, T., Fan, H., Ai, S., Han, R. and Qiu, Y. (2011) Hemoglobin (Hb) Immobilized on Amino-Modified Magnetic Nanoparticles for the Catalytic Removal of Bisphenol A. Chemosphere, 83, 255-264.
https://doi.org/10.1016/j.chemosphere.2010.12.075

[4] Li, F., Josephson, D.P. and Stein, A. (2011) Colloidal Assembly: The Road from Particles to Colloidal Molecules and Crystals. Angewandte Chemie International Edition, 50, 360-388.
https://doi.org/10.1002/anie.201001451

[5] Binauld, S., Delafresnaye, L., Charleux, B., Agosto, F.D. and Lansalot, M. (2014) Emulsion Polymerization of Vinyl Acetate in the Presence of Different Hydrophilic Polymers Obtained by RAFT/MADIX. Macromolecules, 47, 3461-3472.
https://doi.org/10.1021/ma402549x

[6] Warren, N.J. and Armes, S.P. (2014) Polymerization-Induced Self-Assembly of Block Copolymer Nano-objects via RAFT Aqueous Dispersion Polymerization. Journal of the American Chemical Society, 136, 10174-10185.
https://doi.org/10.1021/ja502843f

[7] Ma, G., Sone, H. and Omi, S. (2004) Preparation of Uniform-Sized Polystyrene-Polyacrylamide Composite Microspheres from a W/O/W Emulsion by Membrane Emulsification Technique and Subsequent Suspension Polymerization. Macromolecules, 37, 2954-2964.
https://doi.org/10.1021/ma035316g

[8] Li, G.L., Möhwalda, H. and Shchukin, D.G. (2013) Precipitation Polymerization for Fabrication of Complex Core–Shell Hybrid Particles and Hollow Structures. Chemical Society Reviews, 42, 3628-3646.
https://doi.org/10.1039/c3cs35517a

[9] Kong, X.Z., Gu, X.L, Zhu, X.L. and Zhang, L.N. (2009) Precipitation Polymerization in Ethanol and Ethanol/Water to Prepare Uniform Microspheres of Poly(TMPTA-styrene). Macromolecular Rapid Communications, 30, 909-914.
https://doi.org/10.1002/marc.200800772

[10] Downey, J.S., Frank, R.S., Li, W.H. and Stöver, H.D.H. (1999) Growth Mechanism of Poly(divinylbenzene) Microspheres in Precipitation Polymerization. Macromolecules, 32, 2838-2844.
https://doi.org/10.1021/ma9812027

[11] Downey, J.S., McIsaac, G., Frank, R.S. and Stöver, H.D.H. (2001) Poly(divinylbenzene) Microspheres as an Intermediate Morphology between Microgel, Macrogel, and Coagulum in Cross-Linking Precipitation Polymerization. Macromolecules, 34, 4534-4541.
https://doi.org/10.1021/ma000386y

[12] Shim, S.E., Yang, S. and Choe, S. (2004) Mechanism of the Formation of Stable Microspheres by Precipitation Copolymerization of Styrene and Divinylbenzene. Journal of Polymer Science: Part A: Polymer Chemistry, 42, 3967-3974.
https://doi.org/10.1002/pola.20188

[13] Limé, F. and Irgum, K. (2009) Preparation of Divinylbenzene and Divinylbenzene-co-Glycidyl Methacrylate Particles by Photoinitiated Precipitation Polymerization in Different Solvent Mixtures. Macromolecules, 42, 4436-4442.
https://doi.org/10.1021/ma900150b

[14] Dolata-Grosz, A., Hufenbach, W., Sleziona, J., Gude M. and Czulak, A. (2009) Design, Manufacture and Technological Verification of SiC/C Composite Stirrer. Archives of Materials Science and Engineering, 39, 29-37.

[15] Clegg, J., Marvin, A.C., Dawson, J.F. and Porter, S.J. (2001) Optimization of Stirrer Designs in a Reverberation Chamber. IEEE Transactions on Electromagnetic Compatibility, 47, 824-832.
https://doi.org/10.1109/TEMC.2005.860561

[16] Jiang, X.B., Zhu, X.L. and Kong, X.Z. (2011) A Novel Protocol for Preparation of Uniform Polymer Microspheres with High Yields through Step Polymerization of Isophorone Diisocyanate and Water. Journal of Polymer Science Part A: Polymer Chemistry, 49, 4492-4497.
https://doi.org/10.1002/pola.24890

[17] Jiang, X.B., Zhu, X.L. and Kong, X.Z. (2012) A Facile Route to Preparation of Uniform Polymer Microspheres by Quiescent Polymerization with Reactor Standing Still without any Stirring. Chemical Engineering Joural, 213, 214-217.
https://doi.org/10.1016/j.cej.2012.09.111

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