RAFT Miniemulsion Polymerization Research Articles

Investigation of the water barrier properties of graft copolymer latex films of acrylate and poly(dimethylsiloxane) macromonomers synthesized by RAFT miniemulsion polymerization

It is challenging to improve the water barrier performance for waterborne protective coating. We synthesized a series of acrylic-polydimethylsiloxane (PDMS) graft copolymer latexes p(MMA-co-BA)-g-PDMS) with high PDMS content of up to 50%, which were considered as bottle-brush polymers using reversible addition-fragmentation chain transfer mediated “macromonomer” miniemulsion copolymerization. We investigated the effect of PDMS side chains on the water barrier performance of graft copolymer latex film derived from these particles and their utilization in anti-corrosion coatings. The water contact angle reaches 117° for films cast from aqueous dispersions of graft copolymers with 50% PDMS, which indicates that their surface is significantly enriched with PDMS. The increase in PDMS content has a highly positive effect on the water barrier performance. Differential scanning calorimeter (DSC) on copolymer films after soaking in water indicates that the high PDMS content (50% PDMS) graft copolymer has only freezing bound water in films. Electrochemical impedance spectra tests showed that the graft copolymer exhibited a significant improvement in corrosion resistance over the control polyacrylate sample without PDMS. Furthermore, transmission electron microscopy observations reveal that the PDMS phase changes from a spherical domain texture to a bicontinuous gyroid texture in the bulk of latex films with the increasing PDMS content, which makes them suitable as waterborne anti-corrosion silicone coatings.

Cuprous oxide modified nanoencapsulated phase change materials fabricated by RAFT miniemulsion polymerization for thermal energy storage and photothermal conversion

Phase change materials (PCMs) have great promise in many fields related to energy utilization and thermal management. However, PCMs face great challenges in large-scale applications due to the intrinsic melting leakage, low thermal conductivity and poor photothermal conversion. Herein, nanoencapsulated phase change materials (NanoPCMs) were fabricated by RAFT miniemulsion polymerization using quaternized poly(2-(dimethylamino)ethyl methacrylate)-b-poly(methyl methacrylate) (QPDMAEMA-b-PMMA) as emulsifier. N-octadecane and n-butyl stearate were used as binary cores, and Cu2O nanoparticles were doped into PMMA as hybrid shell. The resulting Cu2O/PMMA-NanoPCMs had an encapsulation efficiency of 86.68%, excellent thermal stability and thermal cycle durability. The thermal conductivity was enhanced by 67.25% compared with the original nanocapsules. Furthermore, the cotton fabrics finished with Cu2O/PMMA-NanoPCMs showed fast thermal response and superior photothermal conversion. Therefore, the synthesized nanocapsules are considered as potential candidates in the field of solar energy utilization and smart thermo-regulated textiles.

Retraction of "Microwave-Assisted Ultrafast RAFT Miniemulsion Polymerization of Biobased Terpenoid Acrylates".

There is a growing preference to move away from traditional petrochemical-based polymers toward biobased alternatives. Here, we report the microwave-assisted RAFT polymerization of several terpenoid acrylates (tetrahydrogeraniol, cyclademol, nopol, and citronellol). These biobased monomers give polymers with a broad range of glass transition temperatures and are excellent candidates to substitute oil-based (meth)acrylates in applications such as coatings and adhesives. First, the process was studied in miniemulsion, finding that all terpenoid acrylates showed a substantial increase in both polymerization rate and reaction control when microwave irradiation was applied. These observations were attributed to nonthermal microwave effects, namely, to changes in the kinetic coefficients under irradiation. The reactions were also carried out in solution, where an amplified nonthermal microwave effect was observed. The results indicate that nonthermal microwave effects allow RAFT polymerization of these terpenoid acrylates to proceed with both improved control and at higher polymerization rates compared to using conventional heating.

Synthesis of Lignin-Based MMA-co-BA Hybrid Resins from Cornstalk Residue via RAFT Miniemulsion Polymerization and Their Characteristics.

The conversion of cornstalk lignin derived from the co-product of bio-refinery into value-added products such as polymeric material has remarkable environmental and economic potential. A novel bio-based methyl methacrylate copolymerized with butyl acrylate (MMA-co-BA) hybrid resin in our research was prepared by the reversible addition–fragmentation chain transfer method using lignin-graft-polyacrylamide (lignin-g-PAM) as a bio-derived macromolecular chain transfer agent. The molecular architecture of lignin-g-PAM and the lignin-based MMA-co-BA hybrid resin was elucidated using 1H nuclear magnetic resonance and attenuated total reflectance–Fourier transform infrared. The thermal behavior and mechanical performance of the resultant lignin-based MMA-co-BA hybrid resins were also investigated through thermogravimetric analysis, differential scanning calorimetry, and a stress–strain test, respectively. The lignin-based acrylate resins system exhibited structure-related thermal and mechanical properties. Compared with pure MMA-co-BA resin, the incorporation of lignin into various lignin-based MMA-co-BA graft copolymers resulted in an improved tensile strength and a higher Young’s modulus. This research could provide not only a new avenue to utilize waste biomass for high-value applications, but also a reference for designing new materials for coatings or adhesives.

Microwave-Assisted Ultrafast RAFT Miniemulsion Polymerization of Biobased Terpenoid Acrylates.

There is a growing preference to move away from traditional petrochemical-based polymers toward biobased alternatives. Here, we report the microwave-assisted RAFT polymerization of several terpenoid acrylates (tetrahydrogeraniol, cyclademol, nopol, and citronellol). These biobased monomers give polymers with a broad range of glass transition temperatures and are excellent candidates to substitute oil-based (meth)acrylates in applications such as coatings and adhesives. First, the process was studied in miniemulsion, finding that all terpenoid acrylates showed a substantial increase in both polymerization rate and reaction control when microwave irradiation was applied. These observations were attributed to nonthermal microwave effects, namely, to changes in the kinetic coefficients under irradiation. The reactions were also carried out in solution, where an amplified nonthermal microwave effect was observed. The results indicate that nonthermal microwave effects allow RAFT polymerization of these terpenoid acrylates to proceed with both improved control and at higher polymerization rates compared to using conventional heating.

Mechanical and Morphological Properties of Waterborne ABA Hard-Soft-Hard Block Copolymers Synthesized by Means of RAFT Miniemulsion Polymerization.

High molecular weight waterborne ABA block copolymers of styrene (St) and 2-ethylhexyl acrylate (2EHA) containing hard and soft domains were synthesized by means of RAFT (mini)emulsion polymerization using a bifunctional symmetric S,S-dibenzyl trithiocarbonate (DBTTC) RAFT agent. Miniemulsion polymerization was initially used for the synthesis of the A-block, which forms hard domains, followed by 2EHA pre-emulsion feeding to build the B-block soft domains. Polymerization kinetics and the evolution of the Molecular Weight Distribution (MWD) were followed during the synthesis of different ABA block copolymers. The thermal properties of the final symmetric block copolymers were studied on dried films by means of DSC. It was found that the block copolymers have two glass transitions, which indicates the presence of a two-phase system. Phase separation was investigated by means of microscopic techniques (AFM and TEM) and SAXS, both of the particles in the latex form, as well as after film formation at room temperature and after different post-treatments. Films were annealed at temperatures well above the glass transition temperature (Tg) of the hard phase to study the bulk morphology of the films after complete particle coalescence. Moreover, for comparison purposes, the films were re-dissolved in THF, and films were again cast directly from the homogeneous THF solutions. As THF is a good solvent for both blocks, such films serve as a reference for the equilibrium morphology. Finally, DMTA studies of the films annealed at different temperatures were performed to correlate the morphology changes with the mechanical properties of the block copolymers.

Exploitation of Compartmentalization in RAFT Miniemulsion Polymerization to Increase the Degree of Livingness

ABSTRACTIt is demonstrated that the degree of livingness (chain‐end fidelity) in RAFT polymerization for a given degree of polymerization can be markedly increased in miniemulsion polymerization relative to the corresponding homogeneous bulk system. Polymerization of styrene was conducted using a poly(methyl methacrylate) benzodithioate as macroRAFT agent in both miniemulsion and bulk. The substantially higher polymerization rate in miniemulsion, which is attributed to the segregation effect (compartmentalization) causing a reduction in the rate of bimolecular termination, makes it possible to reach a given degree of polymerization in a significantly shorter time than in the corresponding bulk system. As a consequence, fewer initiating radicals are required throughout the polymerization, leading to higher livingness in the more rapid miniemulsion system. It is demonstrated how this approach facilitates synthesis of high‐molecular‐weight block copolymers comprising slowly propagating monomers such as styrene and methacrylates. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1938–1946

Synthesis and properties of gradient copolymers of butyl methacrylate and fluorinated acrylate via RAFT miniemulsion copolymerizations

ABSTRACTA series of gradient fluorinated copolymers with a broad variation of the monomer units in the polymer chain were synthesized via semibatch CPDB‐mediated RAFT miniemulsion polymerization technique. In the presence of RAFT agent 2‐cyanoprop‐2‐yl dithiobenzoate (CPDB), the copolymerization of BMA and FMA in miniemulsion exhibited typical features of a controlled molecular weights and narrow polydispersities. The macromolecular structure and thermal behavior of the synthesized fluorinated copolymers were investigated in detail. The DSC analyses show that the gradient copolymers showed a unique thermal behavior with broad range of transition temperature. It was also confirmed that the fluorinated gradient copolymer exhibited obvious surface segregation structure and ultra‐low surface energy between 16.8 and 20.3 mN/m. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 42936.

Effect of living polystyrene costabilizer on styrene miniemulsion polymerization

RAFT miniemulsion polymerizations of styrene with living polystyrene (PSlc) serving as both RAFT reagent and polymer costabilizer were investigated. The miniemulsion upon aging at 25 °C showed satisfactory stability against the Ostwald Ripening process. The rate of polymerization for RAFT miniemulsion polymerization initiated by oil-soluble AIBN is much slower than that for the water-soluble SPS counterpart. In addition to the predominant monomer droplet nucleation, much stronger particle nucleation taking place in the continuous aqueous phase (homogeneous nucleation) for the run with AIBN was observed. It is the different extents of homogeneous nucleation that is responsible for the quite different kinetic behaviors between the RAFT miniemulsion polymerizations initiated by different types of initiator (AIBN versus SPS). Furthermore, increasing initial molar ratio of RAFT reagent to AIBN greatly enhances the characteristics of RAFT polymerization (i.e., better control over polymer chain growth with the progress of polymerization).

Microstructure and mechanical properties of amphiphilic tetrablock copolymer elastomers via RAFT miniemulsion polymerization: influence of poly[styrene-alt-(maleic anhydride)] segments

Tetrablock copolymer elastomers having poly[styrene-alt-(maleic anhydride)] segment (SMA) were synthesized via RAFT miniemulsion polymerization. Different fractions of SMA led to various morphologies and Tgs, affecting the mechaincal properties.

Zero-valent iron (Fe(0)) mediated RAFT miniemulsion polymerization: a facile approach for the fabrication of Fe(0)-encapsulated polymeric nanoparticles

We report a facile approach for the fabrication of Fe(0)-encapsulated nanoparticles via Fe(0)-mediated RAFT miniemulsion polymerization of methyl methacrylate (MMA). The polymerization demonstrated good control/livingness: linear kinetic plots, linear increased molecular weights, narrow molecular weight distributions and high chain end fidelity as characterized by size exclusion chromatography, NMR and matrix-assisted laser desorption ionization time-of-flight mass spectrometry. Crosslinked uniform PMMA nanoparticles (about 130 nm of diameter) with encapsulated Fe(0) were obtained and fully characterized by transmission electron microscopy and dynamic light scattering measurements. This work provides a facile and alternative approach for the fabrication of magnetic polymeric nanoparticles.

Macromol. Theory Simul. 8∕2013

Cover: In RAFT miniemulsion polymerization, the slow fragmentation model reveals essentially the same polymerization rate as the corresponding bulk polymerization, while the intermediate termination model shows a drastic rate increase in a wide droplet size range, and thereby, two controversial models can be discriminated without difficulty. Further details can be found in the article by H. Tobita on page 399.

On the Discrimination of RAFT Models Using Miniemulsion Polymerization

In RAFT miniemulsion polymerization, the slow fragmentation (SF) model reveals essentially the same polymerization rate as the corresponding bulk polymerization, while the intermediate termination (IT) model shows a drastic rate increase in a wide droplet size range, and thereby, two controversial models for the RAFT mechanism can be discriminated without difficulty. The theoretical background why the SF model does not show acceleration in miniemulsion polymerization is discussed. A simple equation to check the inability of rate acceleration for a given set of SF parameters, without resorting to simulation, is also proposed.

Ultrabright Fluorescent Polymeric Nanoparticles Made from a New Family of BODIPY Monomers

Four novel BODIPY derivatives (π-) functionalized by different polymerizable groups, styrene (S), phenyl acrylate (PhA), ethyl methacrylate (EtMA) and ethyl acrylate (EtA) have been synthesized. Following a formerly established one-pot RAFT miniemulsion polymerization process (GrazonMacromol. Rapid Commun. 2011, 32, 699−705), the fluorophores were copolymerized in a controlled way at 2.6 mol % with styrene in water. On the basis of the polymerization-induced self-assembly (PISA) principle, the copolymers assembled during their formation into fluorescent nanoparticles. The distribution of the fluorescent monomers along the polymer backbone was monitored by kinetic studies of the copolymerization reaction. Fluorescent stationary and time-resolved spectroscopy was then performed on both the monomers and the nanoparticles (NPs) and the observed differences are discussed in view of the distribution of the fluorescent monomers in the polymer chain. With two of the novel fluorescent monomers (πS and πPhA), the b...

Effects of Retardation and Variation of Monomer Concentration in RAFT Miniemulsion Polymerization

AbstractThe polymerization kinetics of the RAFT‐mediated radical polymerization inside sub‐µm particles (Dp < 100 nm) is analyzed. The rate retardation by the addition of a RAFT agent in miniemulsion polymerization can be significantly different from that for bulk polymerization. The particle size below which significant rate acceleration occurs can be estimated from a simple equation. It is demonstrated that the reduction of the polymerization rate through the monomer concentration variation effect results from the correlation of concentration variations in monomer and intermediate or, equivalently, monomer and radical.magnified image

Facile Synthesis of Nanocapsules and Hollow Nanoparticles Consisting of Fluorinated Polymer Shells by Interfacial RAFT Miniemulsion Polymerization

AbstractNanocapsules made of a cross‐linked poly(dodecafluoroheptyl acrylate) shell were successfully synthesized by interfacial RAFT miniemulsion polymerization. The well‐defined hollow fluorinated polymer structures were obtained by the subsequent removal of the liquid core materials. The core/shell ratio could be easily tuned up to 1:1 by changing the conditions. In the cases of high core/shell ratio of 1:2 and 1:1, the nanocapsules were severely deformed, which was improved by increasing the cross‐linker amount up to 30 wt.‐%. It was concluded that the utility of the interfacial RAFT miniemulsion polymerization overcame the thermodynamic and kinetic barriers in a conventional miniemulsion polymerization. magnified image

Synthesis of non-collapsed hollow polymeric nanoparticles with shell thickness on the order of polymer gyration radius

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 m 2/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.

RAFT miniemulsion polymerization of methyl methacrylate

Abstract It has been well documented that RAFT miniemulsion polymerization has broader molecular weight distribution, compared with its bulk polymerization counterpart. Interestingly, it was found that the PDI value of RAFT miniemulsion polymerization of methyl methacrylate (MMA) mediated by 2-cyranoprop-2-yl dithiobenzoate (CPDB) was still as low as its corresponding bulk polymerization did. PDI could be as low as 1.13 even with typical sodium dodecyl sulfate (SDS, 1 wt%, surfactant) and n-hexadecane (HD, 2 wt%, costablizer) concentrations. When the polymerization was carried out at 60 °C, a dramatic increase in PDI (>1.4) was observed after 80% monomer conversion since RAFT addition reaction became diffusion-controlled. Increasing the polymerization temperature to 80 °C could reduce the PDI to 1.2 even at 100% monomer conversion. The compartmentalization effect of radicals was surprisingly absence before 30% monomer conversion but became pronounced afterwards in the miniemulsion polymerization. Thus, it still took less time to finish the miniemulsion polymerization with the increase of the surfactant levels.

RAFT Miniemulsion Polymerization Kinetics, 1 – Polymerization Rate

AbstractThe polymerization kinetics of a RAFT‐mediated radical polymerization inside submicron particles (30 < Dp < 300 nm) is considered. When the time fraction of active radical period, ϕA, is larger than ca. 1%, the polymerization rate increases with reducing particle size, as for the cases of conventional emulsion polymerization. The rate retardation by the addition of RAFT agent occurs with or without intermediate termination in zero‐one systems. For the particles with Dp < 100 nm, the statistical variation of monomer concentration among particles may not be neglected. It was found that this monomer‐concentration‐variation (MCV) effect may slow down the polymerization rate. An analytical expression describing the MCV effect is proposed, which is valid for both RAFT and conventional miniemulsion polymerizations.magnified image

Copolymerizations of butyl methacrylate and fluorinated methacrylates via RAFT miniemulsion polymerization

AbstractCopolymerizations of n‐butyl methacrylate (BMA) and fluoro‐methacrylates (including 2,2,3,4,4,4‐hexafluorobutyl methacrylate, HFBMA and 2,2,2‐trifluoroethyl methacrylate, TFEMA) were carried out via reversible addition‐fragmentation chain transfer miniemulsion polymerization, using cumyl dithiobenzoate as a chain transfer agent. The experimental results show that the copolymerizations exhibit “living” fashion, with controlled molecular weights and narrow polydispersities. The reactivity ratios of BMA and fluoromethacrylate in this kind of polymerization system were investigated by size exclusion chromatography and nuclear magnetic resonance, from which the Q‐ and e‐values of HFBMA and TFEMA were calculated. Compared with its corresponding non‐fluoric methacrylate, fluorinated methacrylate exhibits higher resonance stability of the radical adducts. The Q‐value of fluorinated methacrylate is higher (QBMA = 0.82 to QHFBMA = 1.70 and QEMA = 0.76 to QTFEMA = 1.01), and e‐value is much larger (eBMA = 0.28 to eHFBMA = 1.24 to and eEMA = 0.17 to eTFEMA = 1.29) for its rather unique high electron‐withdrawing inductive effect of the fluoroalkyl ester group. The thermal property and the wetting property of copolymers were also discussed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5067–5075, 2007