Co-reporter:Jianbo Tan, Xin Rao, Xionghao Wu, Hancheng Deng, Jianwen Yang, and Zhaohua Zeng
Macromolecules November 13, 2012 Volume 45(Issue 21) pp:8790-8795
Publication Date(Web):November 13, 2012
DOI:10.1021/ma301799r
A straightforward dispersion polymerization procedure for the synthesis of monodisperse functional polymeric microspheres is proposed in this article. This method overcomes the problems deriving from the highly sensitive nucleation stage by introducing both photoinitiation and a RAFT chain transfer agent to the reaction. The process of the formation and growth of particles in the procedure was investigated and found to be quite different from that in a traditional dispersion polymerization. Various kinds of PMMA-based functional microspheres with high size uniformity were synthesized in a single step by this strategy. The microspheres remained uniform in size, even at concentrations of cross-linker or functional comonomer up to 10 wt %.
Co-reporter:Mingguang Yu, Jianbo Tan, Jianwen Yang and Zhaohua Zeng
Polymer Chemistry 2016 vol. 7(Issue 22) pp:3756-3765
Publication Date(Web):02 May 2016
DOI:10.1039/C6PY00605A
In a common RAFT dispersion polymerization induced self-assembly (PISA) formulation, R-type macro-RAFT agents with a solvophilic chain attached at the leaving group side are normally used to mediate the polymerization, meanwhile Z-type macro-RAFT agents with a solvophilic chain attached at the Z-group side are seldom employed. In this paper, we have tried to use a Z-type macro-RAFT agent (mPEG113-BTPA) to mediate RAFT dispersion polymerization of styrene, and found that the process exhibited a poorer PISA tendency and weaker molecular weight control. In comparison, we have conducted the same process mediated with an R-type macro-RAFT agent (mPEG113-DDMAT), and found that the formulation exhibited a typical PISA process, and nanoparticles were produced in situ. Further experiments suggest that the location of RAFT groups plays a key role for the PISA process in RAFT dispersion polymerization. The RAFT groups will be embedded in the produced particles when an R-type macro-RAFT agent is employed, but locate on the particle surface in the case of the Z-type macro-RAFT agent. We have tried to employ the RAFT groups on the surface of the mPEG113-BTPA stabilized particles to modify the particle surface, and successfully removed the solvophilic block via breaking the RAFT group, and generated the poly(dimethylacrylamide) block by surface-initiated RAFT polymerization. Based on the above mechanism perspective, we have designed a preliminary experiment, and found that well-defined monodisperse nanospheres could be prepared by heterogeneous RAFT dispersion polymerization mediated with a Z-type macro-RAFT agent-based block copolymer which was synthesized via pre-polymerization of styrene in 1,4-dioxane mediated with mPEG113-BTPA.
Co-reporter:Jianbo Tan, Mingguang Yu, Xin Rao, Jianwen Yang and Zhaohua Zeng
Polymer Chemistry 2015 vol. 6(Issue 37) pp:6698-6708
Publication Date(Web):04 Aug 2015
DOI:10.1039/C5PY00889A
Highly monodisperse PMMA microspheres covered with a thermo-responsive shell were synthesized in a single step by means of photoinitiated RAFT dispersion polymerization at room temperature. Thermo-responsive macro-RAFT agents (P(mPEGA-co-MEA)-TTCs) with different lower critical solution temperatures (LCST) were used as stabilizers in the process. Particle yields of over 95% were achieved within 45 min of UV irradiation, showing a fast process. The microspheres obtained were well-dispersed in water at a temperature below the LCST, and precipitated from the aqueous dispersion at a temperature above the LCST, exhibiting reversible thermo-responsive properties. The particle size can be precisely controlled by adding a monomer to the reaction in batches, and the microspheres maintained their high uniformities during the reaction. The thermo-responsive PMMA microspheres can be effectively conjugated to proteins via the carboxyl groups on the macro-RAFT chains. A thermo-responsive PMMA/ZIF-8 core–shell structure was also synthesized by using P(mPEGA-co-MEA)-b-PAA stabilized PMMA microspheres as the template, and exhibited good adsorption properties for methylene blue.
Co-reporter:Jianbo Tan, Xin Rao, Jianwen Yang and Zhaohua Zeng
RSC Advances 2015 vol. 5(Issue 24) pp:18922-18931
Publication Date(Web):09 Feb 2015
DOI:10.1039/C4RA15224G
Cross-linked PMMA microspheres have been synthesized by photoinitiated RAFT dispersion polymerization with dipropylene glycol diacrylate (DPGDA) or trimethylolpropane triacrylate (TMPTA) as the cross-linker. Monodisperse microspheres were obtained in the presence of 0.5 wt% S,S′-bis(α,α′-dimethyl-α′′-acetic acid) trithiocarbonate (BDMAT, a RAFT agent) with DPGDA concentration up to 5 wt% or TMPTA concentration up to 2 wt%. The particle formation process was investigated, and the results reveal that the cross-linking reaction was retarded to a certain extent by the RAFT process, which is crucial for the formation of uniform particles under high cross-linker concentrations. The phase diagrams for the methodology have been built up, and show that the procedure could only give polydisperse microspheres at a low DPGDA concentration or coagulum at a high DPGDA concentration in the absence of a RAFT agent, and monodisperse microspheres were obtained at DPGDA concentration up to 5 wt% when the RAFT agent concentration reached an appropriately high level, e.g. 0.5 wt% BDMAT or 0.75 wt% DDMAT. By adjusting the reaction conditions, we have prepared monodisperse cross-linked PMMA microspheres with 10 wt% DPGDA added at the beginning of the reaction. Furthermore, we have functionalized the cross-linked microspheres by adding a functional comonomer to the system at the beginning of polymerization, or by surface-initiated RAFT polymerization via the RAFT groups attached on the particle surface.
Co-reporter:Jianbo Tan, Guangyao Zhao, Zhaohua Zeng, and Mitchell A. Winnik
Macromolecules 2015 Volume 48(Issue 11) pp:3629-3640
Publication Date(Web):May 22, 2015
DOI:10.1021/acs.macromol.5b00688
Functional poly(methyl methacrylate) (PMMA) microbeads with a very narrow size distribution were synthesized by photoinitiated RAFT dispersion polymerization in aqueous ethanol using an acrylic acid–oligo(ethylene glycol) copolymer as a macro-RAFT agent. These particles are a prototype for multiparameter bead-based assays employing mass cytometry, a technique in which metal-encoded beads are injected into the plasma torch of an inductively coupled plasma mass spectrometer (ICP-MS), and the metal ions generated are detected by time-of-flight mass spectrometry. To label the beads, the polymerization reaction was carried out in the presence of various types of small (ca. 5 nm) lanthanide fluoride (LnF3) nanoparticles (e.g., LaF3, CeF3, and TbF3) with polymerizable methacrylate groups on their surface. The type of metal ion and the metal content of the PMMA microbeads could be varied by changing the composition of the reaction medium. An important feature of these microbeads is that acrylic acid groups in the corona are available for covalent attachment of biomolecules. As a proof of concept, FITC–streptavidin (FITC-SAv) was covalently coupled to the surface of a Ln-encoded microbead sample. The number of FITC-SAv binding sites on the beads was determined through three parallel assays involving biotin derivatives. Interaction of the beads with a biotin–tetramethylrhodamine derivative was monitored by fluorescence, whereas interaction of the beads with a biotin-DOTA-Lu derivative was monitored both by ICP-MS and by mass cytometry. Each measurement detected an average of ca. 5 × 104 biotins per microsphere. Control experiments with beads covalently labeled with FITC–bovine serum albumin (FITC-BSA) showed only very low levels of nonspecific binding.
Co-reporter:Jianbo Tan, Xin Rao, Dan Jiang, Jianwen Yang, Zhaohua Zeng
Polymer 2014 Volume 55(Issue 10) pp:2380-2388
Publication Date(Web):13 May 2014
DOI:10.1016/j.polymer.2014.04.006
One-stage photoinitiated RAFT dispersion polymerization (PRDP) has been studied. It was found that the structure of the RAFT agent has a strong influence on the particle morphology. Carboxyl-functionalized trithiocarbonates, including S,S′-bis(α,α′-dimethyl-α″-acetic acid) trithiocarbonate (BDMAT), S-1-dodecyl-S′-(α,α′-dimethyl-α″-acetic acid) trithiocarbonate (DDMAT), S-1-ethyl-S′-(α,α′-dimethyl-α″-acetic acid) trithiocarbonate (EDMAT), were found to be suitable RAFT agents for preparing highly monodisperse microspheres. GPC traces suggested that the polymerization does not follow the typical controlled/living process due to the low RAFT agent concentration in comparison with photoinitiator concentration. Particle size and uniformity changed very little with a wide range of concentrations of the stabilizer and photoinitiator. Highly monodisperse microspheres were obtained even at low stabilizer concentration (5 wt% PVP). Increasing the monomer concentration led to an increase in particle diameter with an exponent of 0.63, which is similar in scale to conventional dispersion polymerization. The microspheres were monodisperse at monomer concentrations ranging from 5 to 15 wt%.
Co-reporter:Jianbo Tan, Xin Rao, Jianwen Yang, and Zhaohua Zeng
Macromolecules 2013 Volume 46(Issue 21) pp:8441-8448
Publication Date(Web):October 21, 2013
DOI:10.1021/ma401909a
Highly monodisperse PMMA microspheres have been synthesized by photoinitiated RAFT dispersion polymerization in the presence of a Macro-RAFT agent and a small molecular RAFT agent. A particle yield of over 90% was achieved within 3 h under UV irradiation at room temperature. The Macro-RAFT agent acts as a stabilizer and stabilizes the particles via formation of block copolymers in situ, and XPS analysis shows that about 29.9% of the particle surface was covered by the stabilizer. Various surface functional microspheres were prepared by using four kinds of Macro-RAFT agents, including poly(methoxy poly(ethylene glycol) acrylate)-based trithiocarbonate (P(mPEGA)-TTC), poly(methoxy poly(ethylene glycol) acrylate-co-acrylic acid)-based trithiocarbonate (P(mPEGA-co-AA)-TTC), poly(acrylic acid)-based trithiocarbonate (PAA-TTC), and poly(methoxy poly(ethylene glycol) acrylate-co-4-vinylpyridine)-based trithiocarbonate (P(mPEGA-co-4VP)-TTC). Ag/PMMA nanocomposite spheres were prepared using the P(mPEGA-co-AA)-TTC stabilized microspheres. The PAA-TTC stabilized microspheres showed pH sensitivity. The colloidal stability of the particles prepared by this photoinitiated RAFT dispersion polymerization was also investigated.
Co-reporter:Jianbo Tan, Xin Rao, Xionghao Wu, Hancheng Deng, Jianwen Yang, and Zhaohua Zeng
Macromolecules 2012 Volume 45(Issue 21) pp:8790-8795
Publication Date(Web):2017-2-22
DOI:10.1021/ma301799r
A straightforward dispersion polymerization procedure for the synthesis of monodisperse functional polymeric microspheres is proposed in this article. This method overcomes the problems deriving from the highly sensitive nucleation stage by introducing both photoinitiation and a RAFT chain transfer agent to the reaction. The process of the formation and growth of particles in the procedure was investigated and found to be quite different from that in a traditional dispersion polymerization. Various kinds of PMMA-based functional microspheres with high size uniformity were synthesized in a single step by this strategy. The microspheres remained uniform in size, even at concentrations of cross-linker or functional comonomer up to 10 wt %.
Co-reporter:Bo Wu;Jianbo Tan;Jianwen Yang
Journal of Polymer Science Part A: Polymer Chemistry 2011 Volume 49( Issue 21) pp:4660-4667
Publication Date(Web):
DOI:10.1002/pola.24910
Abstract
Photoinitiated precipitation polymerization of acrylic acid (AA) and methoxy polyethylene glycol acrylate (MPEGA) was carried out in liquid carbon dioxide using ethanol as cosolvent and trimethylol propane triacrylate (TMPTA) as crosslinker. Monodisperse crosslinked microspheres were obtained with size polydispersity index as low as 1.027. The particle yield rose sharply after irradiation and reached to 52% at 5 min, then gently increased to 65% at 60 min, suggesting that most of microspheres were produced in the first 5 min of irradiation. The particle number increased incessantly till very late stage of reaction, which could be attributed to the direct generation of stable nuclei from the fast crosslinking polymerization instead of oligomer aggregation. The effect of ethanol content, feeding ratio of monomers and crosslinker concentration on the morphologies, size, and dispersity of microspheres has been investigated. X-ray photoelectron spectroscopy showed that the microspheres obtained by this procedure were covered with abundant carbon double bonds. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011
Co-reporter:Jianbo Tan, Bo Wu, Jianwen Yang, Yedan Zhu, Zhaohua Zeng
Polymer 2010 Volume 51(Issue 15) pp:3394-3401
Publication Date(Web):8 July 2010
DOI:10.1016/j.polymer.2010.05.052
Polyurethane based macrophotoinitiator (PU-PI) had been designed and synthesized, and applied to photoinitiated dispersion polymerization of methyl methacrylate as both photoinitiator and stabilizer, with ethanol/water mixture as reaction medium. Monomer conversion over 90% was achieved within 25 min of UV irradiation at room temperature, and monodisperse PMMA microspheres were obtained. The structure of the microspheres had been analyzed by XPS, showing that about 50% of surface of the microspheres were covered with the stabilizer. PU-PI effectively stabilized the polymeric particles in photoinitiated dispersion polymerization due to the unique stabilization process. The size and size distribution of the microspheres became insensitive to the reaction condition such as stabilizer/initiator concentration, initial monomer concentration and reaction medium. The size of the microspheres obtained changed in the range from 0.88 μm to 1.06 μm at different reaction condition, with polydispersity index as low as 1.011. The research may provide a quick and facile approach to prepare monodisperse microspheres with tailored functional surface.
Co-reporter:Liang Huang, Yuming Li, Jianwen Yang, Zhaohua Zeng, Yonglie Chen
Polymer 2009 50(18) pp: 4325-4333
Publication Date(Web):
DOI:10.1016/j.polymer.2009.07.004
Co-reporter:Jia Chen;Jianwen Yang ;Yonglie Chen
Journal of Polymer Science Part A: Polymer Chemistry 2008 Volume 46( Issue 4) pp:1329-1338
Publication Date(Web):
DOI:10.1002/pola.22473
Abstract
Photoinitiated dispersion polymerization of methyl methacrylate was carried out in a mixture of ethanol and water as dispersion medium in the presence of poly(N-vinylpyrrolidone) (PVP) as the steric stabilizer and Darocur 1173 as photoinitiator. 93.7% of conversion was achieved within 30 min of UV irradiation at room temperature, and microspheres with 0.94 μm number–average diameter and 1.04 polydispersity index (PDI) were obtained. X-ray photoelectron spectroscope (XPS) analysis revealed that only parts of surface of the microspheres were covered by PVP. The particle size decreased from 2.34 to 0.98 μm as the concentration of PVP stabilizer increased from 2 to 15%. Extra stabilizer (higher than 15%) has no effect on the particle size and distribution. Increasing medium polarity or decreasing monomer and photoinitiator concentration resulted in a decrease in the particle size. Solvency of reaction medium toward stabilizer, which affects the adsorption of stabilizer on the particle surface, was shown to be crucial for controlling particle size and uniformity because of the high reaction rate in photoinitiated dispersion polymerization. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1329–1338, 2008
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