Reversible Addition-fragmentation Chain Transfer Emulsion Polymerization Research Articles

In situ polarity functionalization and properties of styrenic triblock copolymers synthesized via RAFT emulsion polymerization

ABSTRACTThe in situ polarity functionalization of the styrenic triblock copolymers was accomplished via the block introduction of polar monomer, n‐butyl acrylate, with the help of reversible addition‐fragmentation chain transfer (RAFT) emulsion polymerization. The polarity functionalization, microphase separation, static and dynamic mechanical properties, water resistance, transparency, and thermal stability of the synthesized polarity‐functionalized triblock copolymers, polystyrene‐block‐poly(n‐butyl acrylate)‐block‐polystyrene (SAS), were extensively studied. The poly(n‐butyl acrylate) (PBA) middle block higher than 10 wt % has the favorable toughening effect on polystyrene (PSt) two‐end block due to the microphase separation in SAS. The glass transition of the continuous plastic phase (mainly composed of PSt block) has a much greater influence on the storage modulus than that of the dispersed rubber phase (mainly composed of PBA block). The polarity‐functionalized SAS has good water resistance, high transparency, and robust thermal stability. The polarity‐functionalized SAS will have such a potential application broadening as polar adhesive. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44603.

A Comparative Study of Chemical Routes for Coating Gold Nanoparticles via Controlled RAFT Emulsion Polymerization

The synthesis of core‐shell Au nanoparticles protected by an amphiphilic block copolymer is investigated by distinct reversible addition fragmentation chain transfer (RAFT) emulsion polymerization routes. The controlled polymerization of polymer shells onto Au nanoparticles is attempted by using the macroRAFT (MR) agent based on 2‐(dodecylthiocarbonothioylthio)‐2‐methylpropionic acid synthesized via RAFT polymerization of poly(ethylene glycol) methyl ether acrylate and exploring several approaches, which include (i) post‐modification; (ii) in situ synthesis and (iii) “grafting from” strategies. In the conditions investigated here all these strategies lead to Au polymer nanocomposites but morphological well‐defined core‐shell nanoparticles are only obtained by applying the “grafting from” strategy. In particular, conditions that promote chain extension from the MR agent adsorbed onto the Au nanoparticles are found necessary to obtain nanostructures with such morphological characteristics and that still show the localized surface plasmon resonance typical of colloidal Au nanoparticles.

Kinetics of RAFT emulsion polymerization of styrene mediated by oligo(acrylic acid‐b‐styrene) trithiocarbonate

The kinetics of ab initio reversible addition‐fragmentation chain transfer (RAFT) emulsion polymerization of styrene using oligo(acrylic acid‐b‐styrene) trithiocarbonate as both polymerization mediator and surfactant were systematically investigated. The initiator concentration was set much lower than that in the conventional emulsion polymerization to significantly suppress the irreversible termination reaction. It was found that decreased rapidly but the nucleation efficiency of micelles increased with the decrease of the initiator concentrations due to the significant radical exit. The particle number ( ) did not follow the classic Smith–Eward equation but was proportional to [I]−0.4[S]0.7. It was suggested that RAFT emulsion polymerization could be fast enough for commercial use even at extremely low initiator concentrations and low macro‐RAFT agent concentrations due to the higher particle nucleation efficiency at lower initiator concentration. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2126–2134, 2016

Synthesis and characterization of poly(styrene-block-n-butyl acrylate) pentablock copolymer via RAFT emulsion polymerization mediated by amphiphilic macroRAFT agent combined with pre-emulsion technology

Well-defined poly(styrene-block-n-butyl acrylate) pentablock copolymers were synthesized via RAFT (reversible addition-fragmentation chain transfer) emulsion polymerization with the combination of using a carefully designed amphiphilic macroRAFT at the nucleation stage and the pre-emulsion technology at the growth stage. The multiblock copolymers were produced within seven hours with narrow latex particle size distribution, high solid content and good latex stability. The thermal stability, thermal processability, microphase separation and mechanical properties of multiblock copolymers as well as corresponding random and blending (co)polymers were also investigated by thermogravimetric analysis (TG) instrument, Haake torque rheometer, differential scanning calorimetry (DSC) and scanning electron microscope (SEM), tensile and impact tests, respectively. The TG results revealed the multiblock copolymer has a good thermal stability with the initial decomposition temperature higher than 350 °C. Rheological results demonstrated that the multiblock copolymers have higher torque values than corresponding random and blending (co)polymers. DSC and SEM analysis denoted that there exists phase separation of multiblock and blending (co)polymers. For multiblock copolymer, the impact strength increased by 27.39 % to 7. 44 kJ m−2 with the composition of 60 wt% of styrene units and 40 wt% of n-butyl acrylate units. The tensile strength of multiblock copolymer increased with the increase of styrene composition.

Poly(glycerol monomethacrylate)–Poly(benzyl methacrylate) Diblock Copolymer Nanoparticles via RAFT Emulsion Polymerization: Synthesis, Characterization, and Interfacial Activity

A poly(glycerol monomethacrylate) (PGMA) macromolecular chain transfer agent has been utilized to polymerize benzyl methacrylate (BzMA) via reversible addition–fragmentation chain transfer (RAFT)-mediated aqueous emulsion polymerization. This formulation leads to the efficient formation of spherical diblock copolymer nanoparticles at up to 50% solids. The degree of polymerization (DP) of the core-forming PBzMA block has been systematically varied to control the mean particle diameter from 20 to 193 nm. Conversions of more than 99% were achieved for PGMA51–PBzMA250 within 6 h at 70 °C using macro-CTA/initiator molar ratios ranging from 3.0 to 10.0. DMF GPC analyses confirmed that relatively low polydispersities (Mw/Mn < 1.30) and high blocking efficiencies could be achieved. These spherical nanoparticles are stable to both freeze–thaw cycles and the presence of added salt (up to 0.25 M MgSO4). Three sets of PGMA51–PBzMAx spherical nanoparticles have been used to prepare stable Pickering emulsions at variou...

Poly(methyl methacrylate)-b-poly(butyl acrylate) Block Copolymers Synthesized via RAFT Emulsion Polymerization

A new trithiocarbonate with carboxyl group was synthesized and used as chain transfer agent (CTA) in reversible addition-fragmentation chain transfer (RAFT) polymerization of methyl methacrylate (MMA) and butyl acrylate (BA). A series of well-controlled PMMA-b-PBA diblock copolymers with different monomer compositions were prepared by RAFT polymerization in emulsion within several hours. The thermal properties of block copolymers were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Experimental results showed that the monomer compositions of block copolymers had important influence on their thermal properties. The morphologies of polymer particles with different monomer compositions obtained during polymerization were observed by TEM.

Effect of the pH on the RAFT Polymerization of Acrylic Acid in Water. Application to the Synthesis of Poly(acrylic acid)-Stabilized Polystyrene Particles by RAFT Emulsion Polymerization

The reversible addition–fragmentation chain transfer (RAFT) polymerization of acrylic acid (AA) in water was studied in detail at different pHs using 4-cyano-4-thiothiopropylsulfanyl pentanoic acid (CTPPA) as a control agent and 4,4′-azobis(4-cyanopentanoic acid) (ACPA) as an initiator. Well-defined hydrophilic macromolecular RAFT agents (PAA-CTPPA) were obtained and further used directly in water for the polymerization of styrene. The corresponding polymerization-induced self-assembly (PISA) process was evaluated at different pHs and it was shown that working in acidic conditions (pH = 2.5) led to well-defined amphiphilic block copolymer particles (Đ < 1.4) of small size (below 50 nm). When the pH increased, the control over the growth of the polystyrene (PS) block was gradually lost. Chain extension experiments of PAA-CTPPA with N-acryloylmorpholine (NAM), a hydrosoluble and non-pH sensitive monomer, performed at different pHs showed that the very first addition–fragmentation steps that occurred in water were impeded when PAA was ionized leading to partial consumption of PAA-CTPPA and thus to PS molar masses higher than expected. Varying the PAA-CTPPA concentration at pH = 2.5 led in all cases to stable particles composed of well-defined block copolymers with PS segments of different molar masses.

Synthesis of single‐core and multiple‐core core‐shell nanoparticles by RAFT emulsion polymerization: Lead sulfide‐copolymer nanocomposites

AbstractWe report here a simple and direct route for the preparation of lead sulfide (PbS) quantum dots (QDs) embedded into polymeric nanospheres by emulsion polymerization. In this process, QDs are first dispersed in an aqueous solution containing a statistical oligomer constituted of five butyl acrylate and ten acrylic acid units prepared by reversible addition fragmentation chain transfer (RAFT) polymerization using a trithiocarbonate as RAFT agent. Then, the dispersion of PbS QDs is engaged into an emulsion polymerization process to form core‐shell nanoparticles. Transmission electron microscopy reveals the presence of single‐core core‐shell particles at low concentration of PbS QD, whereas multiple‐core core‐shell particles containing either well separated or aggregated PbS QDs are formed at high concentration of PbS QDs. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Synthesis of Polystyrene-b-poly(n-butyl acrylate)-b-Polystyrene Triblock Copolymers as Binder for Pigment Dyeing

Well-controlled polystyrene-b-poly (n-butyl acrylate)-b-polystyrene (PSt-b-PnBA-b-PSt) triblock copolymers were prepared by RAFT (reversible addition-fragmentation chain transfer) emulsion polymerization process. The mechanical properties of the triblock copolymers were investigated in comparison to the P(nBA-co-St) statistical copolymers. When the PSt content is 20%, the ultimate tensile strength of triblock copolymer is nearly six times the strength of statistical copolymer, while their modulus are all around 3.0×103 Pa. The triblock copolymer films feel smooth and non-tacky as the PSt content is higher than 20%. It indicates that PSt-b-PnBA-b-PSt triblock copolymers can be used as binders in pigment dyeing, providing the dyed fabrics with soft non-tacky handle and good fastness properties.

Ab initio RAFT emulsion polymerization of butadiene using the amphiphilic poly(acrylic acid-b -styrene) trithiocarbonate as both surfactant and mediator

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

Toward Well-Controlled ab Initio RAFT Emulsion Polymerization of Styrene Mediated by 2-(((Dodecylsulfanyl)carbonothioyl)sulfanyl)propanoic Acid

Reversible addition−fragmentation chain transfer (RAFT) ab initio emulsion polymerization of styrene mediated by 2-(((dodecylsulfanyl) carbonothioyl) sulfanyl) propanoic acid was investigated with sodium dodecyl sulfate (SDS), poly(acrylic acid)29-b-polystyrene5 trithiocarbonate macro-RAFT agent (PAA29-PSt5-RAFT), and poly(acrylic acid)29-b-polystyrene5 diblock co-oligomer (PAA29-PSt5) as the surfactant, respectively. Polystyrene latex having controlled molecular weight, relatively low PD and narrow particle size distribution was obtained by postneutralizing PAA29-PSt5-RAFT and PAA29-PSt5. This result was in agreement with the superswelling hypothesis that superswollen oligomer-containing particles caused the colloidal instability in the early stage of RAFT emulsion polymerization with SDS as surfactant. The successes of PAA29-PSt5-RAFT and PAA29-PSt5 were due to the high interfacial tensions of the styrene/water/surfactant systems that suppressed the superswelling and thus improved the colloidal instabil...