Narrow molecular weight and particle size distributions of polystyrene 4-arm stars synthesized by RAFT-mediated miniemulsions (original) (raw)
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Polymers
Thermoresponsive poly((N,N-dimethyl acrylamide)-co-(N-isopropyl acrylamide)) (P(DMA-co-NIPAM)) copolymers were synthesized via reversible addition−fragmentation chain transfer (RAFT) polymerization. The monomer reactivity ratios were determined by the Kelen–Tüdős method to be rNIPAM = 0.83 and rDMA = 1.10. The thermoresponsive properties of these copo-lymers with varying molecular weights were characterized by visual turbidimetry and dynamic light scattering (DLS). The copolymers showed a lower critical solution temperature (LCST) in water with a dependence on the molar fraction of DMA in the copolymer. Chaotropic and kosmotropic salt anions of the Hofmeister series, known to affect the LCST of thermoresponsive polymers, were used as additives in the aqueous copolymer solutions and their influence on the LCST was demonstrated. Further on, in order to investigate the thermoresponsive behavior of P(DMA-co-NIPAM) in a confined state, P(DMA-co-NIPAM)-b-PS diblock copolymers were prepare...
Journal of Macromolecular Science Part A
In this work, Macro-Reversible addition fragmentation termination (RAFT) agents based on poly(ethylene glycol) (PEG) possessing different molecular weights and bearing benzoyl xanthate moieties were synthesized by the reaction of PEG potassium xanthate salts with benzoyl chloride, 4-methyl benzoyl chloride and 4-chloro benzoyl chloride. Controlled free radical polymerization of the styrene were carried out in the presence of these macro-RAFT agents using 2,2′-azobisizsobutyronitrile (AIBN) as an initiator to yield PS-b-PEG-b-PS block copolymers. The linear kinetic plot ln [M]o/[M] vs. polymerization time indicated that was first order with reference to monomer concentration. The block copolymerization possessed controlled/living character. The controlled character of the RAFT polymerization of the styrene was confirmed by the formation of narrow polydispersity of the polymers, linear increases in the molecular weight with polymerization time and molecular weight of the products that...
RAFT-Mediated Emulsion Polymerization of Styrene using a Non-Ionic Surfactant
Australian Journal of Chemistry, 2006
We report the successful RAFT-mediated emulsion polymerization of styrene using a non-ionic surfactant (Brij98), the highly reactive 1-phenylethyl phenyldithioacetate (PEPDTA) RAFT agent, and water-soluble initiator ammonium persulfate (APS). The molar ratio of RAFT agent to APS was identical in all experiments. Most of the monomer was contained within the micelles, analogous to microemulsion or miniemulsion systems but without the need of shear, sonication, cosurfactant, or a hydrophobe. The number-average molecular weight increased with conversion and the polydispersity index was below 1.2. This ideal ‘living’ behavior was only found when molecular weights of 9000 and below were targeted. It was postulated that the rapid transportation of RAFT agent from the monomer swollen micelles to the growing particles was fast on the polymerization timescale, and most if not all the RAFT agent is consumed within the first 10% conversion. In addition, it was postulated that the high nucleatio...
Polymer Chemistry, 2021
Herein we report the reversible addition-fragmentation chain transfer (RAFT) solution polymerization of tert-octyl acrylamide (OAA) in 1,4-dioxane using a trithiocarbonate-based RAFT agent. POAA homopolymers were synthesized with good control (M w /M n < 1.22) within 1 h at 70°C when targeting mean degrees of polymerization (DP) of up to 100. Differential scanning calorimetry studies conducted on a series of five POAA homopolymers indicated a weak molecular weight dependence for the glass transition temperature (T g), which varied from 67 to 83°C for POAA DPs ranging from 22 to 99. High blocking efficiencies were observed when chain-extending such homopolymers with OAA, suggesting that most of the RAFT endgroups remain intact. Subsequently, we employed POAA as a steric stabilizer block for the PISA syntheses of spherical nanoparticles in n-heptane via RAFT dispersion polymerization of N,N-dimethylacrylamide (DMAC) at 70°C. Targeting PDMAC DPs between 50 and 250 resulted in reasonably good control (M w /M n ≤ 1.42) and produced well-defined spherical diblock copolymer nanoparticles (z-average diameters ranging from 23 nm to 91 nm, with DLS polydispersities remaining below 0.10) within 5 h. A facile onepot synthesis route to near-monodisperse 36 nm diameter POAA 82-PDMAC 100 nanoparticles was developed in n-heptane that provided similar control over the molecular weight distribution (M w /M n = 1.19). Unfortunately, POAA 85-PDMAC x diblock copolymer nanoparticles tended to deform and undergo film formation prior to transmission electron microscopy (TEM) studies. To overcome this problem, ethylene glycol diacrylate (EGDA) was introduced towards the end of the DMAC polymerization. The resulting core-crosslinked POAA 85-PDMAC 195-PEGDA 20 triblock copolymer nano-objects exhibited a relatively well-defined spherical morphology. Interestingly, the colloidal stability of POAA 85-PDMAC x diblock copolymer dispersions depends on the type of n-alkane. Spherical nanoparticles produced in n-heptane or n-octane remained colloidally stable on cooling to 20°C. However, the colloidally stable POAA-PDMAC nanoparticles prepared at 70°C in higher n-alkanes became flocculated on cooling. This is because the POAA steric stabilizer chains exhibit upper critical solution temperature (UCST)-type behavior in such solvents. Nanoparticle aggregation was characterized by variable temperature turbidimetry and dynamic light scattering experiments. † Electronic supplementary information (ESI) available. See
2005
Synthesis of two surfmers (cationic and anionic) was carried out and the surfmers were used to stabilize particles in miniemulsion polymerization. Surfmers were used to eliminate adverse effects associated with free surfactant in the final product e.g. films and coatings. The Reversible Addition Fragmentation chain Transfer (RAFT) polymerization process was used in miniemulsion polymerization reactions to control the molecular weight distribution. RAFT offers a number of advantages that include its compatibility with a wide range of monomers and solvents. Moreover block copolymer synthesis is possible via chain extension. A comparative study between classical surfactants and surfmers was conducted in regard to reaction rates and molar mass distribution. The rates of reactions of surfmer stabilized RAFT miniemulsion polymerization of Styrene and MMA were similar (in most cases) to classical surfactant stabilized RAFT miniemulsion polymerization reactions. The final particle sizes 2 Corinthians 2 vs 14-16 v Dedication I dedicate this work to my family, friends and my beloved.
Mechanistic and Practical Aspects of RAFT Polymerization
Living and controlled polymerization: …, 2006
Reversible Addition-Fragmentation chain Transfer (RAFT) polymerization is the most recent method developed to control free radical polymerization. The process is living and uses simple organic compounds having a thiocarbonyl thio function to control the polymerization, which otherwise is similar to a conventional free radical polymerization. The review will detail the mechanistic aspects of the process and the use of the method to prepare narrow polydispersity polymers of defined molecular weight and a variety of architectures. A set of guidelines to select the appropriate RAFT agent, the rationale behind such a selection, depending on the monomer to be polymerized, will also be included.
Polymer, 2005
This paper provides an overview and discusses some recent developments in radical polymerization with reversible additionfragmentation chain transfer (RAFT polymerization). Guidelines for the selection of RAFT agents are presented. The utility of the RAFT process is then illustrated with several examples of the synthesis of polymers with reactive end-groups. Thus, RAFT polymerization with appropriately designed trithiocarbonate RAFT agents is successfully applied to the synthesis of narrow polydispersity carboxy-functional poly(methyl methacrylate) and primary amino-functional polystyrene. Methods for removing the thiocarbonylthio end-group by aminolysis, reduction and thermal elimination are discussed. It is shown that the thiocarbonylthio end-group can be cleanly cleaved by radical induced reduction with tri-n-butylstannane, to leave a saturated chain end, or by thermolysis, to leave an unsaturated chain end. q
RAFT microemulsion polymerization with surface-active chain transfer agent
RAFT microemulsion polymerization with surface-active chain transfer agent, 2013
The work described in this dissertation focuses on enhancing the polymer nanoparticle synthesis using RAFT (reversible-addition fragmentation chain transfer) in microemulsion polymerization in order to achieve predetermined molecular weight with narrow molecular weight polydispersity. The hypothesis is that the use of an amphiphilic chain transfer agent (surface-active CTA) will confine the CTA to the surface of the particle and thermodynamically favor partitioning of the CTA between micelles and particles throughout the polymerization. Thus, the CTA diffusion from micelles to polymer particles would be minimized and the breadth of the CTA per particle distribution would remain low. We report the successful improved synthesis of poly(butyl acrylate), poly(ethyl acrylate), and poly(styrene) nanoparticles using the RAFT microemulsion polymerization with surface-active CTA. The polymerization kinetics, polymer characteristics and latex size experimental data are presented. The data analysis indicates that the CTA remains partitioned between the micelles and particles by the end of the polymerization, as expected. We also report the synthesis of well-defined core/shell poly(styrene)/poly(butyl acrylate) nanoparticle, having polydispersity index value of 1.1, using semi-continuous microemulsion polymerization with the surface-active CTA. The surface-active CTA restricts the polymerization growth to the surface of the particle, which facilitates the formation of a shell block co-polymers with each subsequent second monomer addition instead of discrete homopolymers. This synthesis method can be used to create a wide range of core/shell polymer nanoparticles with well-defined morphology, given the right feeding conditions.
Macromolecules, 2010
ABSTRACT Water-soluble poly(N,N-dimethylacrylamide)s (PDMAAm) with a reactive trithiocarbonate group exhibiting different structures were used as macromolecular RAFT (reversible addition−fragmentation chain transfer) agents in the surfactant-free emulsion polymerization of n-butyl acrylate and styrene, under ab initio, batch conditions. Independently of the structure of the RAFT group, the polymerizations were fast and controlled with molar masses that matched well the theoretical values and rather low polydispersity indexes. Monomer conversions close to 100% were reached and the polymerizations behaved as controlled systems, even when solids contents up to 40% were targeted. The system thus led to poly(N,N-dimethylacrylamide)-b-poly(n-butyl acrylate) and poly(N,N-dimethylacrylamide)-b-polystyrene amphiphilic diblock copolymers formed in situ and self-assembled upon chain extension. The stability of the aqueous dispersions, measured by the amount of coagulum formed, improved with increasing length of the stabilizing hydrophilic PDMAAm segments.