Kinetics Of Reversible Addition-fragmentation Chain Transfer Polymerization Research Articles

Kinetics of RAFT polymerization and copolymerization of vinyl monomers by size exclusion chromatography

New method to study kinetics of homo- and copolymerization of vinyl monomers based on size exclusion chromatography (SEC) was developed. The use of this method is associated with some special requirements like identity of an eluent for SEC and the solvent for polymerization, and possessing refractive index increments dn/dc of a monomer and corresponding polymer. Monomer conversion was calculated by comparing intensity of the signals in SEC elution curves attributed to a monomer and corresponding polymer, and taking into account differences in their dn/dc values. The developed method is also applicable to study kinetics of copolymerization including evolution of copolymer composition if one of the monomers is a macromonomer (possess relatively high molecular weight). Suitability of the proposed method was demonstrated by studying kinetics of Reversible Addition Fragmentation Chain Transfer (RAFT) polymerization and copolymerization of 2-hydroxyethyl methacrylate (HEMA) and two poly(ethylene oxide) monomethyl ether methacrylates (PEO5MEMA and PEO9MEMA). It was shown that the new method has some advantages over the other methods used to study kinetics of polymerization (e.g., 1H NMR spectroscopy), since, in the case of SEC with triple detection, it not only enables to calculate monomer conversion and polymerization rate, but simultaneously provides comprehensive information about polymer characteristics (Mn, Mw, Mw/Mn, copolymer composition, etc.) and development of these characteristics during (co)polymerization. It was determined that the synthesized copolymers of HEMA and PEO9MEMA were characterized by low dispersity and gradient distribution of the monomeric units.

Synthesis of Film-Forming Photoactive Latex Particles by Emulsion Polymerization-Induced Self-Assembly to Produce Singlet Oxygen.

The design of photoactive polymer substrates producing singlet oxygen under visible light irradiation has great technological potential. Aqueous dispersion of novel photoactive core-shell particles was synthesized by surfactant-free reversible addition-fragmentation chain transfer (RAFT) emulsion polymerization of n-butyl acrylate. The surface of the nanoparticles is directly decorated thanks to the polymerization-induced self-assembly process using a hydrophilic macromolecular chain transfer agent (macro-CTA) functionalized with the organic photosensitizer. The macro-CTA was synthesized by statistical copolymerization of acrylic acid and 2-Rose Bengal ethyl acrylate (RBEA) at 80 °C mediated with 4-cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoic acid. Monitoring polymerization kinetics of RAFT polymerization highlights that increasing amount of RBEA induces retardation, still more pronounced when using the vinylbenzyl Rose Bengal comonomer. The present work provides insight into the quantum yield of singlet oxygen production in water (ΦΔ = 0.2-0.6) for the three types of synthesized polymers (hydrophilic polymer, latex particles, and polymer film). The photoactive core-shell latex particles enabled the easy preparation of photoactive polymer film by simple casting.

Synthesis of chemically amplified photoresist polymer containing four (Meth)acrylate monomers via RAFT polymerization and its application for KrF lithography

KrF photoresist polymers (PASTMs) were prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization. Four (meth)acrylates with lithographic functionalities including styrene (St), 4-acetoxystyrene (AST), 2-methyl-2-adamantyl methacrylate (MAMA), and tert-butyl acrylate(TBA) were used as monomer components and 2-methyl-2-[(dodecylsulfanylthiocarbonyl) sulfanyl]propanoic acid (MDFC) was used as RAFT agent, varying the RAFT content could modulate molecular weight. Fourier-transform infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance (1H NMR) indicated that the synthesis was successful. Gel permeation chromatography (GPC) showed that the molecular weight decreased with the increased content of MDFC, and all the polymers possessed weight-average molecular weight below ten thousand and polydispersity less than 1.32. Thermogravimetric analysis (TGA) characterized the thermal properties, the results implied that initial thermal decomposition temperature reached 200 °C, which could satisfy the lithography process. Differential scanning calorimetry (DSC) showed that the Tg decreases with molecular weight. The RAFT polymerization kinetics plots demonstrated that the polymerization was first-order, the number-average molecular weights of the polymers with relatively low polydispersity index values increased with total monomer conversions indicating that the concentration of growing radicals was constant throughout the polymerization process. The narrow molecular weight distribution and composition uniformity of the polymers prepared by RAFT polymerization could be beneficial for lithography, after alcoholysis, lithography evaluation under KrF lithography showed that this homogeneous polymer photoresist exhibited better space and line (S/L) pattern with resolution of 0.18 μm according to the SEM image.

RAFT polymerization kinetics and polymer characterization of P3HT rod-coil block copolymers

Here an in-depth analysis of reversible addition–fragmentation chain transfer (RAFT) polymerization kinetics is reported in order to provide better definition of poly(3-hexylthiophene) (P3HT) rod–coil block copolymers thru a more thorough understanding of the RAFT polymerization of the coil block. To this end, a new P3HT macroRAFT agent is synthesized and utilized to prepare rod–coil block copolymers with P3HT and poly(styrene), poly(tert-butylacrylate), and poly(4-vinylpyridine), and the RAFT polymerization kinetics of each system are fully detailed. This is achieved by a comprehensive analysis of characterization data from 1H nuclear magnetic resonance spectroscopy, gel permeation chromatography, and matrix-assisted laser desorption ionization time of flight spectroscopy, which are used as complementary techniques in order to address difficulties in accurately characterizing the synthesized polymer systems. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 3575–3585

Synthesis and characterization of transferrin-targeted chemotherapeutic delivery systems prepared via RAFT copolymerization of high molecular weight PEG macromonomers.

Reversible addition-fragmentation chain transfer (RAFT) polymerization was employed to prepare a nanoparticulate drug delivery system for chemotherapeutics. The nanoparticles contain a PEG "stealth" corona as well as reactive anhydride functionality designed for conjugating targeting proteins. The multifunctional carrier functionality was achieved by controlling the copolymerization of the hydrophobic monomer lauryl methacrylate (LMA), with a reactive anhydride functional methacrylate (TMA), and a large polyethyleneglycol methacrylate monomer (Mn~950 Da) (O950). RAFT polymerization kinetics of O950 were evaluated as a function of target degrees of polymerization (DP), initial chain transfer agent to initiator ratio ([CTA]o/[I]o), and solvent concentration. Excellent control over the polymerization was observed for target DPs of 25 and 50 at [CTA]o/[I]o ratio of 10 as evidenced by narrow and symmetric molecular weight distributions and the ability to prepare block copolymers. The TMA-functional copolymers were conjugated to the tumor targeting protein transferrin (Tf). The targeted copolymer was shown to encapsulate docetaxel at concentrations comparable to the commercial single vial formulation of docetaxel (Taxotere). In vitro cytotoxicity studies conducted in HeLa cells show that the Tf targeting enhances the cancer killing properties relative to the polymer encapsulated docetaxel formulation.

“Grafting through” approach for synthesis of polystyrene/silica aerogel nanocomposites by in situ reversible addition-fragmentation chain transfer polymerization

Aerogel/polystyrene nanocomposites with mixed free and aerogel-attached polystyrene chains were synthesized using reversible addition-fragmentation chain transfer (RAFT) polymerization. 3-methacryloxypropyldimethylchlorosilane containing a double bond, which could be incorporated into polystyrene chains by a “grafting through” approach, was used as an aerogel modifier. Kinetics of RAFT polymerization of styrene in the presence of modified silica aerogel was studied by monitoring conversion and molar mass values. To further study, attached polymers were detached and their molecular characteristics were compared to free chains. According to results, the presence of silica aerogel particles has a sensible influence on polymerization kinetic and more aerogels result in decreased polymerization rate and conversion. The dispersity (Ð) of polymer chains increased by the addition of silica aerogel. In the case of aerogel-attached polystyrene chains, number-averaged molar mass values were slightly lower than that of free chains. Also, thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) techniques were used to observe the effect of loading on thermal properties of synthesized nanocomposites.

Effect of silica nanoparticle loading and surface modification on the kinetics of RAFT polymerization

Abstract S-(thiobenzoyl)thioglycolic acid was used to synthesize poly(methyl methacrylate) via reversible addition-fragmentation chain transfer (RAFT) polymerization. To study the polymerization kinetics, in situ polymerization reactions were performed with different loading of nanoparticles. To investigate the effect of surface modification on the poly­merization kinetics, similar reactions were performed with 3-methacryloxypropyldimethylchlorosilane-modified nanoparticles. Conversion, reaction rate, molecular weight and polydispersity index (PDI) were monitored during poly­merization. According to results, pseudo-first order kinetics is achieved, but the rate constant of chain transfer reaction to the RAFT agent (Ctr) has a very small value. Adding nanoparticles causes no considerable change in the kinetic curves, while there is an optimum value for nanoparticles loading in which the polymerization rate reaches its maximum level. A similar trend is observed for molecular weight; however, increasing silica content results in an increase in PDI values. In comparison with pristine silica nanoparticles, the polymerization rate increases slowly in the case of modified particles. Also, molecular weight and PDI for free and graft chains are studied separately. The molecular weight of free chains increases with increasing nanoparticles loading up to 7 wt% and then decreases, while PDI values increase continually by adding nanoparticles. However, for graft chains, molecular weight and PDI values increase with increasing nanoparticle content.

Poly(dimethylsiloxane-b-styrene) diblock copolymers prepared by reversible addition-fragmentation chain transfer polymerization: Kinetic model

Well-defined polydimethylsiloxane-block-polystyrene (PDMS-b-PS) diblock copolymers were prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization using a functional PDMS-macro RAFT agent. The RAFT polymerization kinetics was simulated by a mathematical model for the RAFT polymerization in a batch reactor based on the method of moments. The model described molecular weight, monomer conversion, and polydispersity index as a function of polymerization time. Good agreements in the polymerization kinetics were achieved for fitting the kinetic profiles with the developed model. In addition, the model was used to predict the effects of initiator concentration, chain transfer agent concentration, and monomer concentration on the RAFT polymerization kinetics. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Kinetic modeling of two-step RAFT process for the production of novel fluorosilicone triblock copolymers

Well-defined poly(dimethylsiloxane)- b-poly(2,2,3,3,4,4,4-heptafluorobutylmethacryl-ate- b-poly(styrene) (PDMS- b-PHFBMA- b-PS) triblock copolymers were prepared by two-step reversible addition–fragmentation chain transfer (RAFT) polymerization. A comprehensive mathematical model for the two-step RAFT polymerization in a batch reactor was presented using the method of moments. The model described molecular weight, monomer conversion and polydispersity index as a function of polymerization time. Good agreements in the polymerization kinetics were achieved for fitting the kinetic profiles with the suggested model. In addition, the model was used to predict the effects of initiator concentration, chain transfer agent concentration and monomer concentration on the two-step RAFT polymerization kinetics. The simulated results showed that for the two-step RAFT polymerizations, the effects initiator concentration, chain transfer agent concentration and monomer concentration are identical and the influence degrees are different yet.

RAFT polymerization kinetics: How long are the cross‐terminating oligomers?

AbstractWe extend a new model for the kinetics of reversible addition‐fragmentation chain transfer (RAFT) polymerization. The essence of this model is that the termination of the radical intermediate formed by the RAFT process occurs only with very short oligomeric radicals. In this work, we consider cross‐termination of oligomers up to two monomers and an initiator fragment. This model accounts for the absence of three‐armed stars in the molecular weight distribution, which are predicted by other cross‐termination models, since the short third arm makes a negligible difference to the polymer's molecular weight. The model is tested against experiments on styrene mediated by cyano‐isopropyl dithiobenzoate, and ESR experiments of the intermediate radical concentration. By comparing our model to experiments, we may determine the significance of cross‐termination in RAFT kinetics. Our model suggests that to agree with the known data on RAFT kinetics, the majority of cross‐terminating chains are dimeric or shorter. If longer chains are considered in cross‐termination reactions, then significant discrepancies with the experiments (distinguishable star polymers in the molecular weight distribution) and quantum calculations will result. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3455–3466, 2009

RAFT Polymerization Kinetics: Combination of Apparently Conflicting Models

We propose a model for the kinetics of reversible addition−fragmentation chain transfer (RAFT) polymerization. The essence of this model is that the termination of the radical intermediate formed by the RAFT process occurs only with the shortest active radicals. This model accounts for the absence of 3-armed stars predicted by other cross-termination models since the short radical makes a negligible difference to the overall molecular weight. The model is tested against experiments on styrene at 60 °C with cyanoisopropyl dithiobezoate (CPDB) as the RAFT agent. The predicted rate coefficients are consistent with slow fragmentation of the RAFT intermediate, and the overall concentration of radicals is consistent with ESR experiments. Overall, it demonstrates that the two conflicting models that have been proposed so far can actually coexist.

RAFT synthesis of poly(N‐isopropylacrylamide) and poly(methacrylic acid) homopolymers and block copolymers: Kinetics and characterization

AbstractReversible addition‐fragmentation chain transfer (RAFT) polymerization was used successfully to synthesize temperature‐responsive poly(N‐isopropylacrylamide) (PNIPAAm), poly(methacrylic acid) (PMAA), and their temperature‐responsive block copolymers. Detailed RAFT polymerization kinetics of the homopolymers was studied. PNIPAAm and PMAA homopolymerization showed living characteristics that include a linear relationship between Mn and conversion, controlled molecular weights, and relatively narrow molecular weight distribution (PDI < 1.3). Furthermore, the homopolymers can be reactivated to produce block copolymers. The RAFT agent, carboxymethyl dithiobenzoate (CMDB), proved to control molecular weight and PDI. As the RAFT agent concentration increases, molecular weight and PDI decreased. However, CMDB showed evidence of having a relatively low chain transfer constant as well as degradation during polymerization. Solution of the block copolymers in phosphate buffered saline displayed temperature reversible characteristics at a lower critical solution temperature (LCST) transition of 31°C. A 5 wt % solution of the block copolymers form thermoreversible gels by a self‐assembly mechanism above the LCST. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1191–1201, 2006