Co-reporter:Kun Yan
Reaction Chemistry & Engineering (2016-Present) 2017 vol. 2(Issue 2) pp:159-167
Publication Date(Web):2017/04/04
DOI:10.1039/C6RE00168H
The seeded RAFT emulsion polymerization of styrene at low initiator concentrations was modelled using population balance equations and Monte Carlo simulations. Without any adjusting parameter, the models accurately predicted the polymerization kinetics, particle size, particle size distribution (PSD), and the characteristic changing trend of molecular weight distribution (MWD) at various initiator concentrations. An initiator concentration-dependent particle activation/deactivation process (PADeP), which played a decisive role in PSD and MWD at very low initiator concentrations, was highlighted to account for the unexpected simultaneous increase in the dispersities of PSD (PDIPS) and MWD (PDIMW) with the decrease of the initiator concentration. It was concluded that at low initiator concentrations, both PDIPS and PDIMW should be mappings of the dispersity of the number of PADeP experienced by particles during the whole polymerization course. The random nature of PADeP caused the dramatic increases in both PDIPS and PDIMW with the decrease of the initiator concentration. However, in the cases of higher initiator concentrations where the average number of PADeP was above 15, the effect of PADeP became much weaker. In such cases, PDIMW should be mainly controlled by the RAFT reaction.
Co-reporter:Jie Mao;Tiefeng Li
Journal of Materials Chemistry C 2017 vol. 5(Issue 27) pp:6834-6841
Publication Date(Web):2017/07/13
DOI:10.1039/C7TC01221G
Dielectric elastomers (DEs) can be deformed in response to an electric field. Combining many muscle-like attributes like mechanical compliance, a very fast response, large actuation strain, a high energy density, noiseless actuation, and light weight, DEs are considered to be leading materials for “artificial muscles”. Herein, we report a new strategy to significantly improve the electromechanical performance of an elastomer by decreasing the chain entanglement density. A series of symmetric polystyrene–polyalkylacrylate–polystyrene triblock copolymers were synthesized using reversible additional fragmental transfer polymerization, where the chain entanglement density was varied by changing the bulkiness of the side groups of polyalkylacrylate. It is found that the voltage-induced maximum strain and energy density both quickly increase because the modulus is quickly decreased while the electric breakdown is little affected with an increase of the bulkiness of the alkyl side groups. The maximum actuation strain of polystyrene–poly(2-ethylhexyl acrylate)–polystyrene (SEHAS, 25% at 28 kV mm−1, without prestretch) and energy density (4.4 kJ m−3) are significantly higher than those of the state-of-the-art single component thermal plastic DEs. The actuation performance of SEHAS is comparable to that of the mammalian skeletal muscle. The other attractive attributes of SEHAS include thermal plasticity, relatively high tensile strength and a very low glass temperature (−68 °C) of the elastic phase.
Co-reporter:Peile Xie;Xuxu Yang;Tiefeng Li
Journal of Materials Chemistry C 2017 vol. 5(Issue 38) pp:9865-9872
Publication Date(Web):2017/10/05
DOI:10.1039/C7TC02778H
Herein, highly stretchable, transparent, and colorless, electrodes free of liquid and non-volatile components were fabricated for the first time. Crosslinkable diblock copolymers of poly[(ethylene glycol)9 methyl ether acrylate-b-n-butyl acrylate] with preset molecular weights and compositions were synthesized via reversible addition–fragmentation chain transfer polymerization in solution. The electrodes were made of diblock copolymer/LiClO4 composites. It was found that the dielectric elastomer actuators (DEAs) made of an acrylic dielectric elastomer (VHBTM4910) and the electrodes of the crosslinked poly[(ethylene glycol)9 methyl ether acrylate140-b-n-butyl acrylate80]/LiClO4 could exhibit actuation area strains over 100% when driven by voltage. The DEAs showed over 90% light transmittance in the entire range of the visible wavelengths. The block architecture and composition were crucial for the electrode performance although only the block of poly[(ethylene glycol)9 methyl ether acrylate] contributed to ionic conductivity. The presence of poly(butyl acrylate) blocks avoided dewetting during electrode fabrication such that a transparent electrode was achieved.
Co-reporter:Yue Zhu;Xiang Gao
Journal of Applied Polymer Science 2016 Volume 133( Issue 1) pp:
Publication Date(Web):
DOI:10.1002/app.42833
ABSTRACT
Poly(methyl methacrylate) (PMMA) block copolymer is interesting because it is compatible with many polymers. A series of poly(methyl methacrylate)-b-poly(n-butyl acrylate) (PMMA-b-PnBA) diblock copolymers with various compositions was synthesized via reversible addition–fragmentation chain-transfer (RAFT) emulsion polymerization with the amphiphilic oligo(methacrylic acid41-b-methyl methacrylate8) RAFT agent as both the polymerization mediator and surfactant. The molecular weights of the block copolymers agreed well with the theoretical prediction, although the polydispersity indices were relatively broad. The resulting core [poly(n-butyl acrylate)]–shell (PMMA) particles of PMMA-b-PnBA were found to be very effective impact modifiers for polycarbonate (PC). The diblock copolymer was well dispersed in 100–300-nm particles in the PC matrix, and the dispersed particle size was highly dependent on the block copolymer compositions. PMMA250-b-PnBA550 (the subscripted number signifies the designed degree of polymerization), which was dispersed into 100-nm particles, presented the best capability for improving the impacting properties. Compared with the neat PC, the notched impact strength of PC toughened by 5 wt % PMMA250-b-PnBA550 was increased by four times to 62.81 kJ/m2 with the same yield strength, a slightly decreased modulus, an increased elongation at break, and an increased tensile strength. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 132, 42833.
Co-reporter:Fei Zhou Wang
Macromolecular Reaction Engineering 2016 Volume 10( Issue 1) pp:63-70
Publication Date(Web):
DOI:10.1002/mren.201500033
Polystyrene/poly(butyl acrylate)/montmorillonite (PS/PBA/MMT) ternary hybrid films were fabricated by colloid blending of oligo(acrylic acid)-functionalized core–shell particles of PS-b-PBA diblock copolymers and Na+-MMT aqueous dispersions. The particles were synthesized by RAFT emulsion polymerization using oligo(acrylic acid-block-styrene) RAFT as a reactive surfactant. Coherent hybrid films could be formed when the particles possessed a relatively thick soft PnBA shell (core–shell ratio = 1:1 or 3:7) without adding any coalescing agent even when 15 wt% MMT was added. TEM observations revealed that around 20 nm thick clay stacks were well dispersed throughout the hybrid films. Increasing the levels of PS or MMT could much increase the modulus and tensile strength of the hybrid films. However, simply increasing PS composition would be limited by the crack formation and brittleness of the resultant films. The ternary hybrid design would allow one to gain good balance between mechanical properties and coherent film formation. The enhancing efficiency of MMT for the modulus and tensile strength was much higher when placing the clay stacks in PS domains than in PBA domains, which was particularly obvious when MMT levels were higher than 10 wt%.
Co-reporter:Qing Xiang, Yingwu Luo
Polymer 2016 Volume 106() pp:285-293
Publication Date(Web):5 December 2016
DOI:10.1016/j.polymer.2016.09.071
•A simple and facile method to fabricate films with structural blue color is proposed.•Well-defined core/shell particles are synthesized via RAFT emulsion polymerization.•Color quality is affected by size, shape and separation degree of the dispersed phase.•The films show relatively high tensile properties.•The method is scalable-up to fabricate large-scale films.A new scalable-up approach to the nanostructured films with high quality non-iridescent blue color was demonstrated by cast of soft shell/hard core latex spheres synthesized via RAFT emulsion polymerization. A series of PnBA soft shell/PSt hard core latex nanospheres with different core/shell structures were synthesized via RAFT emulsion polymerization. In contrast to conventional colloidal photonic crystals, the nanostructured films possessed relatively high tensile mechanical properties resulting from the dense structures and non-iridescent structural blue color because of random phase structures. It was found that the color quality of the nanostructured films was highly dependent on the size, shape and separation degree of the dispersed phase. Unexpectedly, the irregular-shape dispersed phase around 120 nm in size and sharp phase interface were found to significantly improve the quality of blue color. When films are too thick (>0.25 mm), the color saturation would be affected, which could be partly eliminated by adding carbon black.
Co-reporter:Kun Yan;Xiang Gao
Macromolecular Rapid Communications 2015 Volume 36( Issue 13) pp:1277-1282
Publication Date(Web):
DOI:10.1002/marc.201500052
Co-reporter:Yue Zhu;Shangyu Bi;Xiang Gao
Macromolecular Reaction Engineering 2015 Volume 9( Issue 5) pp:503-511
Publication Date(Web):
DOI:10.1002/mren.201400058
The comparison between methyl methacrylate (MMA) and styrene (St) RAFT emulsion polymerization using oligo(methacrylic acid41-b-methyl methacrylate8) RAFT agent (oligo(MAA41-b-MMA8) RAFT) as surfactant is investigated in order to gain a better understanding on RAFT emulsion polymerization of MMA. It is found that the colloidal stability during MMA emulsion polymerization is much more sensitive to the initiator concentrations and temperature than that of St polymerization. The coagulum-free latex of highly living PMMA can be achieved only at 80 °C and low initiator concentrations. The final PDI is higher in RAFT emulsion polymerization of MMA than that of St. It is revealed that about 40% acid groups of oligo(MAA41-b-MMA8) RAFT should be buried within the final particles of PMMA, indicating that particle coagulation should occur in the very beginning of the polymerization. The poorer performance of the MMA polymerization could be well explained by the homogeneous nucleation mode of particles combined with relatively slow transporting rate of oligo(MAA41-b-MMA8) RAFT molecules from the partly frozen micelles to the newly-born particles.
Co-reporter:Yunlong Guo;Xiang Gao
Journal of Polymer Science Part B: Polymer Physics 2015 Volume 53( Issue 12) pp:860-868
Publication Date(Web):
DOI:10.1002/polb.23709
ABSTRACT
The mechanical properties of linear and V-shaped compositional gradient copolymer of styrene and n-butyl acrylate with composition of around 55 wt % styrene were investigated by comparing with their block copolymer counterparts. Compared with their block copolymer counterparts, the gradient copolymers showed lower elastic modulus, much larger elongation at break, and similar ultimate tensile strength at room temperature. This performance could be ascribed to that the local moduli continuously change from the hardest nanodomains to the softest nanodomains in the gradient copolymer, which alleviates the stress concentration during tensile test. Compared with the V-shaped gradient (VG) copolymer, the linear gradient copolymer showed much higher elastic modulus but lower elongation at break. The mechanical properties of the gradient copolymers were more sensitive to the change in temperature from 9 °C to 75 °C. With recovery temperature increased from 10 °C to 60 °C, the strain recovery of VG copolymer would change steadily from 40% to 99%. However, the elastic recovery of linear and triblock copolymer was poor even at 60 °C. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 860–868
Co-reporter:Yunlong Guo;Xiang Gao
Journal of Polymer Science Part A: Polymer Chemistry 2015 Volume 53( Issue 12) pp:1464-1473
Publication Date(Web):
DOI:10.1002/pola.27578
ABSTRACT
Reversible addition-fragmentation chain transfer (RAFT) emulsion polymerization is becoming an important technique to synthesize the latex of block copolymers. A previous study showed that in the synthesis of polystyrene-b-poly(butyl acrylate)-b-polystyrene triblock copolymer via RAFT emulsion polymerization using amphiphilic oligo(acrylic acid-styrene) macroRAFT as surfactant and mediator, the molecular weight distribution could be much broadened to PDI higher than 2. In this study, an in-depth investigation was performed to decrease PDI. It was found that long-chain branches could be formed in the synthesis of triblock block copolymer, leading to the appearance of a higher molecular weight shoulder in the GPC curve of the final product. The lower neutralization degree of acrylic acid (AA) units on the macroRAFT and shorter AA chains would help to suppress the formation the long-chain branches, leading to PDI around 1.5. It is evidenced that the successful suppression is due to the promotion of radical entry as a result of decreased interfacial transport impedance. It is also evidenced that the presence of styrene during the polymerization of butyl acrylate could promote the formation of long chain branches. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 1464–1473
Co-reporter:Kun Yan;Xiang Gao
Journal of Polymer Science Part A: Polymer Chemistry 2015 Volume 53( Issue 16) pp:1848-1853
Publication Date(Web):
DOI:10.1002/pola.27654
Co-reporter:Feizhou Wang, Yingwu Luo, Bo-Geng Li, and Shiping Zhu
Macromolecules 2015 Volume 48(Issue 5) pp:1313-1319
Publication Date(Web):February 20, 2015
DOI:10.1021/ma502564m
A coagulatable and redispersible poly(styrene-block-n-butyl acrylate) (PS-b-PnBA) copolymer latex system was developed. A series of PS-b-PnBA diblock copolymers with the PnBA content up to 70 wt % were prepared via a reversible addition–fragmentation chain transfer (RAFT) emulsion polymerization. An amphipathic poly(acrylic acid-b-styrene) trithiocarbonate was synthesized and employed as macro-RAFT agent and surfactant. The resulted latex particles contained a soft poly(n-butyl acrylate) core and a hard polystyrene shell. The hard plastic shell could prevent the elastomer core from deformation and fusion at room temperature. It was found that the latex particles with the nBA content ⩽60 wt % could be easily coagulated by HCl and redispersed by NaOH with some ultrasound treatment. The coagulation and redispersion processes were repeatable. When the nBA content reached 70 wt %, the plastic shell became too thin, resulting in collapsed sticky particles. The critical shell thickness for redispersible latexes was about 8 nm.
Co-reporter:Jie Huang, Shumiao Zhao, Xiang Gao, Yingwu Luo, and Bogeng Li
Industrial & Engineering Chemistry Research 2014 Volume 53(Issue 18) pp:7688
Publication Date(Web):April 11, 2014
DOI:10.1021/ie501146t
Ab initio RAFT emulsion copolymerization of styrene (St) and acrylonitrile (AN) was investigated by using poly(acrylic acid)20-b-polystyrene5 trithiocarbonate as surfactant and RAFT agent. The well-controlled polymerization in terms of linear growth of molecular weight, low PDI, and little coagulum could be achieved only when the mass ratio m(St)/m(AN) was greater than 1:1 and suitable polymerization temperature depending on the monomer ratios. A significant amount of coagulum was formed when more AN was used. The gel effect, which led to the diffusion-controlled RAFT addition reactions in the late stage of the polymerization, played a significant influence on the PDI, the degree of which was highly dependent on the targeted molecular weight and monomer compositions. For the copolymerization of styrene and acrylonitrile with the azeotropic composition (75 wt % styrene), the gel effect could be relieved by increasing the reaction temperature from 70 to 90 °C after the nucleation period, resulting in PDI as low as 1.20. However, in the cases of the higher AN composition, the gel effect was still pronounced. Unexpectedly, the particle number was insensitive to the RAFT agent concentrations.
Co-reporter:Jie Huang;Shuai Zhao;Xiang Gao;Bogeng Li
Macromolecular Reaction Engineering 2014 Volume 8( Issue 10) pp:696-705
Publication Date(Web):
DOI:10.1002/mren.201400010
Abstract
Reversible addition fragmentation chain transfer (RAFT) ab initio emulsion polymerization of styrene using poly(acrylic acid)-b-polystyrene trithiocarbonate (AAx-b-Sty macroRAFT) as both mediator and surfactant was investigated with systematically changed y from 0 to 7 and x from 15 to 30. A well-controlled polymerization in terms of little coagulum, well predicted molecular weight and low polydispersity (PDI) (≈1.2) could only be achieved by using the macroRAFTs of hydrophile-lipophile balance (HLB) values between 13 and 20. The final latex particle size could be tuned from 80 to 172 nm in diameter simply by changing x and y values while the molecular weight was targeted the same (30 K).
Co-reporter:Shaohong Xu, Jie Huang, Song Xu, Yingwu Luo
Polymer 2013 Volume 54(Issue 7) pp:1779-1785
Publication Date(Web):22 March 2013
DOI:10.1016/j.polymer.2013.02.007
RAFT ab initio emulsion copolymerization of γ-methyl-α-methylene-γ-butyrolactone (MeMBL) and styrene with various monomer ratios was investigated with PAA20-PS5 trithiocarbonate being mediator and surfactant at 70 °C. The polymerization was fully controlled as evidenced by stable latexes, well predicted molecular weights and low PDIs about 1.2 when [MeMBL]:[St] ≤ 1:2. However, in the case of [MeMBL]:[St] = 1:1, the molecular weight became out of control due to gel effect of RAFT reactions. The relatively water-soluble MeMBL was found to dramatically influence the polymerization kinetics and copolymer properties, as evidenced by (1) No inhibition period was observed; (2) The copolymer compositions in the early stage of polymerization were much higher than those predicted by the Mayo-Lewis equation in the case of [MeMBL]:[St] = 1:2, leading to the formation of linear gradient copolymer. (3) Tgs of the copolymers from emulsion copolymerization were higher than those from bulk copolymerization. It was concluded that we could synthesize the gradient copolymer with preset molecular weight and low PDI in RAFT emulsion polymerization, Tg of which should be much higher than 100 °C.Graphical abstract
Co-reporter:Renzhong Wei, Yingwu Luo, Wang Zeng, Feizhou Wang, and Shaohong Xu
Industrial & Engineering Chemistry Research 2012 Volume 51(Issue 47) pp:15530-15535
Publication Date(Web):November 12, 2012
DOI:10.1021/ie302067n
It was demonstrated that gel-free styrene–butadiene–styrene triblock copolymer (SBS) latex with a molecular weight about 90 kg/mol and styrene composition about 34% could be synthesized by reversible addition–fragmentation chain transfer miniemulsion polymerization. The resulted SBS might be an excellent thermoplastic elastomer as indicated by its mechanical properties with ultimate tensile strength of 16 MPa and about 800% elongation at break.
Co-reporter:Yingwu Luo, Changhuai Ye
Polymer 2012 Volume 53(Issue 25) pp:5699-5705
Publication Date(Web):30 November 2012
DOI:10.1016/j.polymer.2012.10.012
A new strategy using the performed nanocapsules with well-defined highly crosslinked polymer shell as building blocks was proposed to fabricate the organic polymeric nanofoam. This new strategy allowed us to fabricate the high performance organic polymeric nanofoam, for the first time, under normal drying conditions. The thermal conductivities of the nanofoams in the forms of powder and monolith were far lower than that of the stagnant air and half those of the standard commercial polymer foams. The nanofoam monoliths showed the crush strength up to 8.55 ± 2.10 MPa and compressive strain at break up to 45% ± 6%.
Co-reporter:Zhijuan Sun and Yingwu Luo
Soft Matter 2011 vol. 7(Issue 3) pp:871-875
Publication Date(Web):18 Nov 2010
DOI:10.1039/C0SM00983K
The non-collapsed hollow polymeric nanoparticles with shell thicknesses in the order of 10 nm are prepared by interfacially confined reversible addition fragmentation transfer (RAFT) miniemulsion polymerization. The void fraction and average diameter of the hollow polymeric nanoparticles could be largely tuned up to 0.58 and from 68 nm to 180 nm, respectively. The non-collapsed hollow polymeric nanoparticles could be a building block for nanoporous materials, which hold promise in many fields such as anti-reflection coatings, ultra-thermal insulation materials, catalysis and sensors.
Co-reporter:Hao Chen
Macromolecular Chemistry and Physics 2011 Volume 212( Issue 7) pp:737-743
Publication Date(Web):
DOI:10.1002/macp.201000664
Co-reporter:Gongwei Pu, Yingwu Luo, Anni Wang, and Bogeng Li
Macromolecules 2011 Volume 44(Issue 8) pp:2934-2943
Publication Date(Web):March 16, 2011
DOI:10.1021/ma1026719
We investigated the influence of the chain asymmetry of the styrene (S)−methyl methacrylate (MMA) copolymer (surfactant) on the morphology of the polystyrene (PS)/poly(methyl methacrylate) (PMMA) blends. It was, for the first time, demonstrated that the chain asymmetry of the block copolymer surfactant would have significant influence on the structure of the polymer blend in the melt mixing process. In the PS/PMMA = 30/70 blends, the addition of asymmetric AB diblock copolymers tuned the morphology from the droplet-in-matrix structure to the cocontinuous structure. At 20 wt % asymmetric AB block copolymer (PMMA110-block-PS430) dosage, the onset of the cocontinuous interval of the PS/PMMA blends was lowered to PS/PMMA = 20/80 and the cocontinuous interval was broadened to PS/PMMA = 20/80−30/70, compared with the onset at PS/PMMA = 45/55 and the interval at PS/PMMA = 45/55−50/50 of the PS/PMMA blends without the copolymers. The reason was that the packing of the asymmetric block copolymer on the interface provided the bending energy being against the interfacial energy when the longer block of the copolymer was in the minor phase side, suppressing the breakup of the minor phase fibers during melt mixing. With the addition of 20 wt % AC block copolymer (P(S-ran-MMA)220-block-PS320), which was more asymmetric than the AB block copolymer (PMMA110-block-PS430) of the same molecular weight and monomer composition, the PS/PMMA blends showed an even wider cocontinuous interval at PS/PMMA = 10/90−30/70.
Co-reporter:Renzhong Wei;Pinghong Xu
Journal of Polymer Science Part A: Polymer Chemistry 2011 Volume 49( Issue 13) pp:2980-2989
Publication Date(Web):
DOI:10.1002/pola.24736
Abstract
Ab initio reversible addition fragmentation chain transfer (RAFT) emulsion polymerization of butadiene was investigated by using the amphiphilic poly(acrylic acidn-b-styrene5) trithiocarbonate as both surfactant and mediator. The neutralization on acrylic acid (AA) units played significant influence on the gelation. When half of the AA units were neutralized, the gelation occurred in the early stage of the polymerization so that the highest accessible molecular weight of polybutadiene was as low as 5 kg mol−1. In the non-neutralized conditions, the gelation was much retarded so that the highest accessible molecular weight was increased up to 23 kg mol−1. In the non-neutralized conditions, potassium persulfate could not initiate the polymerization. When azobisisobutyronitrile was used as initiator, the polymerization mediated by poly(acrylic acid27-b-styrene5) trithiocarbonate could proceed much faster than the solution polymerization did. The latex was stable. Before the gel point, molecular weight agreed well with the theoretical prediction while PDI was relatively high due to the branching reaction. The poly(butadiene-b-styrene) core/shell particles could obtained by extending polybutadiene. When the n value in poly (acrylic acidn-b-styrene5) trithiocarbonate was lower than 20, the coalescence would occur, leading to the formation of some coagulum. On the other hand, when n value was as high as 60, the molecular weight was out of control. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011
Co-reporter:Ying Zhao, Ying-Wu Luo, Bo-Geng Li, and Shiping Zhu
Langmuir 2011 Volume 27(Issue 18) pp:11306-11315
Publication Date(Web):August 6, 2011
DOI:10.1021/la2011875
A series of gradient copolymers of methacrylic acid (MAA)/methyl methacrylate (MMA) with four end-to-end composition profiles (uniform, linear gradient, triblock with linear gradient midblock, and diblock) but all having an average chain composition of F̅MMA ≈ 0.5 and an average chain length of 200 were synthesized via model-based, computer-programmed, semibatch atom-transfer radical copolymerization (ATRcoP). These samples allowed us to investigate systematically the effects of the gradient composition profile on the pH responsivity and micelle formation of the copolymers in an aqueous solution. Measurements included light transmittance, TEM, AFM, DLS, 1H NMR, and pH titration. It was found that linear gradient, triblock, and diblock copolymers formed spherical micelles at high pH. The micelles of the linear gradient copolymer contained MMA units in their hydrophilic shells, and those of the triblock and diblock copolymers had all of their MMA units residing in their cores. The composition profile showed a strong effect on the degree of acid dissociation at a given pH. The conformational transition of the copolymer chains was determined by both the pH value and composition profile. Copolymers having sharper gradients required a lower pH to trigger the conformational transition and a narrower pH range to complete the transition.
Co-reporter:Ye Changhuai, Luo Yingwu, Liu Xuesong
Polymer 2011 Volume 52(Issue 3) pp:683-693
Publication Date(Web):3 February 2011
DOI:10.1016/j.polymer.2010.12.030
The hollow polymeric nanoparticles of poly(styrene-co-divinylbenzene) of ultra-thin shell were synthesized by the interfacial RAFT miniemulsion polymerization with various particle sizes, void fractions and crosslinking degrees. With the void fraction increased, the hollow nanoparticles were more likely to collapse once dried. This collapse could be suppressed by simply increasing the level of crosslinker. The fraction of the collapsed hollow particles decreased nearly linearly with the increasing level of crosslinker. The non-collapsed hollow nanoparticles with a void fraction about 60% and shell thickness of 11.5 nm were fabricated with the crosslinker (divinylbenzene) of 0.67 mass fraction based on monomers. The resulted polymeric shell of the hollow nanoparticles was mesoporous, which had high surface area 514 m2/g, extremely large pore volume 2.74 ml/g and a most probable pore diameter of 9 nm. The structures of the hollow nanoparticles were mechanically stable not only in the solvent but also under harsh conditions like high temperature (200 °C) and strong shear. Additionally, the hollow nanoparticles were able to be fully re-dispersed in the solvent. The average hollow particle diameter was tuned from 70 nm to 199 nm by decreasing the level of the amphiphilic RAFT agent. The shell thickness was tuned from 10.6 nm to 19.3 nm by changing the core/shell ratios.
Co-reporter:Renzhong Wei, Yingwu Luo, Zhengshang Li
Polymer 2010 Volume 51(Issue 17) pp:3879-3886
Publication Date(Web):4 August 2010
DOI:10.1016/j.polymer.2010.06.023
The structured nanoparticles of styrene (St) and butadiene (Bd) block copolymers were prepared by RAFT seeded emulsion polymerization of butadiene. It was confirmed that the block copolymers of PSt-b-P(St-co-Bd) was formed with controlled molecular weight and rather low PDI at low composition of the P(St-co-Bd) segment. With more incorporation of butadiene, the branching reaction of polybutadiene became obvious, leading to higher PDI and positive deviation of Mn from the theoretical predication. At the gel point, the composition of the P(St-co-Bd) segment was estimated to be 0.72. After this, the gel fraction increased quickly. The morphology of structured nanoparticles could be largely tuned simply by the copolymer composition. With the composition of the P(St-co-Bd) segment increased from 0.37 to 0.92, the morphology within the structured particles changed from the polybutadiene domains-in-polystyrene matrix, perforated concentric-spherical layer, concentric-spherical multi-layers, bi-continuous, to broken layers of polystyrene in polybutadiene matrix. It was found that the morphology of the block copolymer within nanoparticles was dependent on d/L values, which was in excellent agreement with the theoretical prediction.
Co-reporter:Gongwei Pu;Qianchuan Lou ;Bogeng Li
Macromolecular Rapid Communications 2009 Volume 30( Issue 2) pp:133-137
Publication Date(Web):
DOI:10.1002/marc.200800579
Co-reporter:Lei Yang, Yingwu Luo, Xinzhi Liu, Bogeng Li
Polymer 2009 50(18) pp: 4334-4342
Publication Date(Web):
DOI:10.1016/j.polymer.2009.07.002
Co-reporter:Ying Zhao;Ying-Wu Luo;Changhuai Ye;Bo-Geng Li;Shiping Zhu
Journal of Polymer Science Part A: Polymer Chemistry 2009 Volume 47( Issue 1) pp:69-79
Publication Date(Web):
DOI:10.1002/pola.23121
Abstract
Methyl methacrylate (MMA)/tert-butyl methacrylate (tBMA) gradient copolymers having linear and hyperbolic composition profiles were synthesized. These special copolymer products were achieved via a model-based computer-controlled semibatch atom transfer radical copolymerization (ATRcoP) process. A simple ATRcoP model was developed based on the terminal model. The equilibrium constants in the ATRP of MMA and tBMA were estimated by the data correlation. The model was verified by batch experiments and was found to give good correlation for the polymerization rate, molecular weight, and copolymer composition data. The model coupled with a reactor model was then applied to the semibatch ATRcoP and was used to calculate comonomer feeding rates for the targeted gradient composition profiles. It was found that the experimental monomer conversion, molecular weight, and cumulative copolymer composition were in good agreement with their targeted theoretical values. The gradient copolymers had low polydispersities close to 1.1. This work demonstrated the feasibility of the model-based semibatch ATRcoP in fine-tuning gradient copolymer composition profiles. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 69–79, 2009
Co-reporter:Rui Wang, Yingwu Luo, Bo-Geng Li and Shiping Zhu
Macromolecules 2009 Volume 42(Issue 1) pp:85-94
Publication Date(Web):December 3, 2008
DOI:10.1021/ma802006c
The reversible addition−fragmentation chain transfer radical polymerization (RAFT) with branching/cross-linking is theoretically investigated on the basis of the method of moments. The system considered consists of the copolymerization of vinyl monomer in the presence of a small amount of divinyl comonomer. It is found that the gel point is significantly postponed by increasing the RAFT agent concentration. Flory’s criterion, ρrw,0 = 1, is found to be satisfied at the gel point in the RAFT cross-linking process regardless of the unequal reactivities of vinyl/divinyl monomers in the absence of cyclization. The gel conversion can be analytically expressed and is determined by the polymerization recipe and the relative reactivities of various double bonds. The gel point is postponed by the presence of intramolecular cyclization, and its effect becomes significant in a dilute polymerization system. Branching distribution is found to be very broad with a large fraction of linear primary and slightly branched chains. By the introduction of the dependence of the reactivity of the pendant double bond on the local heterogeneity, the branching distribution becomes narrower and can be fine-tuned.
Co-reporter:Jing Gao, Yingwu Luo, Rui Wang, Xiaojuan Zhang, Bo-Geng Li, Shiping Zhu
Polymer 2009 50(3) pp: 802-809
Publication Date(Web):
DOI:10.1016/j.polymer.2008.12.014
Co-reporter:Lei Yang;Bogeng Li
Journal of Polymer Science Part A: Polymer Chemistry 2006 Volume 44(Issue 7) pp:2293-2306
Publication Date(Web):21 FEB 2006
DOI:10.1002/pola.21340
The surfactant coverage of minidroplets was tuned by postaddition of more surfactants after preparation of the miniemulsion of styrene. The influence of surfactant coverage on reversible addition-fragmentation chain transfer (RAFT) miniemulsion polymerization of styrene was investigated. When the surfactant (sodium dodecyl sulfate; SDS) coverage was as low as 40%, two kinds of particles, denoted as polymer and oligomer particles, were formed in the early stage of the polymerization. Polymer chains within two kinds of particles grew in a parallel way during the rest period of the polymerization. The oligomer particles contributed less than 10% to the final monomer conversion but consumed over one in third the original RAFT agent molecules. Oligomer particles were larger in size but much lower in molecular weight. Both the particle size and molecular weight distributions were bimodal. With increase of SDS coverage, the formation of oligomer particles was suppressed. As a result, the nucleation efficiency of the minidroplets was greatly enhanced and the molecular weight and particle size distributions were dramatically narrowed. The formation of the oligomer particles was ascribed to the superswelling occurring in the beginning stage of the polymerization. The experimental observations are in excellent accord to the superswelling theory. Postaddition of surfactant presents a novel method to narrow particle size and molecular weight distributions in RAFT miniemulsion polymerization. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2293–2306, 2006
Co-reporter:Jie Mao, Tiefeng Li and Yingwu Luo
Journal of Materials Chemistry A 2017 - vol. 5(Issue 27) pp:NaN6841-6841
Publication Date(Web):2017/06/12
DOI:10.1039/C7TC01221G
Dielectric elastomers (DEs) can be deformed in response to an electric field. Combining many muscle-like attributes like mechanical compliance, a very fast response, large actuation strain, a high energy density, noiseless actuation, and light weight, DEs are considered to be leading materials for “artificial muscles”. Herein, we report a new strategy to significantly improve the electromechanical performance of an elastomer by decreasing the chain entanglement density. A series of symmetric polystyrene–polyalkylacrylate–polystyrene triblock copolymers were synthesized using reversible additional fragmental transfer polymerization, where the chain entanglement density was varied by changing the bulkiness of the side groups of polyalkylacrylate. It is found that the voltage-induced maximum strain and energy density both quickly increase because the modulus is quickly decreased while the electric breakdown is little affected with an increase of the bulkiness of the alkyl side groups. The maximum actuation strain of polystyrene–poly(2-ethylhexyl acrylate)–polystyrene (SEHAS, 25% at 28 kV mm−1, without prestretch) and energy density (4.4 kJ m−3) are significantly higher than those of the state-of-the-art single component thermal plastic DEs. The actuation performance of SEHAS is comparable to that of the mammalian skeletal muscle. The other attractive attributes of SEHAS include thermal plasticity, relatively high tensile strength and a very low glass temperature (−68 °C) of the elastic phase.
![2-Propenoic acid, 2-[[[(1,6-dihydro-4-methyl-6-oxo-2-pyrimidinyl)amino]carbonyl]amino]ethyl ester](/data/chemimg/3781900/931110-05-3.png)
![2-Propenoic acid, 2-[[[(1,6-dihydro-4-methyl-6-oxo-2-pyrimidinyl)amino]carbonyl]amino]ethyl ester](/data/chemimg/3781900/931110-05-3_b.png)
