Atom Transfer Radical Polymerization Polymerization Research Articles

Prediction and Experimental Characterization of the Molecular Architecture of FRP and ATRP Synthesized Polyacrylate Networks

AbstractSummary: This work reports experimental and modeling studies concerning the conventional (FRP) and atom transfer radical polymerization (ATRP) of acrylate/diacrylate monomers. In the framework of a recently developed general approach, kinetic models including crosslinking reactions and branching by chain transfer to polymer are discussed for FRP and ATRP polymerization systems. Besides molecular weight distribution (MWD), fairly good predictions of the z‐average radius of gyration could be obtained for these non‐linear polymers. A set of experiments was performed at 1 L scale in a batch reactor using n‐butyl acrylate (BA) or methyl acrylate (MA) as monovinyl monomers and 1,6‐Hexanediol diacrylate (HDDA) or bisphenol A ethoxylate diacrylate (BEDA) as crosslinkers. In FRP experiments, AIBN was used as initiator and ATRP polymerizations were initiated by ethyl 2‐bromopropionate (EBrP) and mediated by CuBr using PMDETA (N,N,N′,N″,N″‐pentamethyldiethylenetriamine) as ligant. Polymerizations were carried out in solution at 60 °C with different dilutions using toluene and DMF as solvents. Products formed at different polymerization times were analyzed by SEC/RI/MALLS yielding average MW, MWD, z‐average radius of gyration and monomer conversion. Important differences in the molecular architecture of the synthesized FRP and ATRP highly branched polyacrylates have been identified. Comparisons of experimental results with predictions have put into evidence the important effect of intramolecular cyclizations at all dilutions, even with ATRP polymerizations.

Synthesis of Polymer Thin Film Gradient with Nanometer Thickness through Water Diffusion Controlled Surface Polymerization

We report here a unique, simple method for synthesizing polymer film gradients with nanometer thickness through diffusion controlled surface polymerization. Polar solvents, especially water, have previously been shown to increase the rate of atom transfer radical polymerization (ATRP) of numerous monomers. That result made it apparent that the rate of ATRP polymerization could be regulated by the concentration of water in the polymerization solution. On the basis of this observation, we successfully developed a simple method for preparing polymer thin film gradients on substrates by water concentration gradient formed along the surface of substrates. An initiator attached substrate was placed in a two-layer system of water and a polymerization solution in which the diffusion of water into the polymerization solution resulted in a monomer concentration gradient, leading to varied polymerization rates along the substrate, and finally polymer thin film gradients. Poly(ethylene glycol) methacrylate (PEGMA) gr...

Parallel Synthesis of Polymer Libraries Using Atom Transfer Radical Polymerization (ATRP)

AbstractParallel atom transfer radical polymerization (ATRP) of styrene and t‐butyl acrylate (t‐BA) was investigated. A series of ATRP polymerizations were carried out in parallel with varying targeted molecular weight ($\overline M _{\rm n}$) and showed excellent reproducibility of $\overline M _{\rm n}$, polydispersity, and conversion. In addition, polymerizations were done to determine the effect of inhibitor on styrene polymerization, yielding similar results. In synthesizing a library of polymers having varying $\overline M _{\rm n}$ using ATRP, polymers having lower $\overline M _{\rm n}$ reach their target values earlier and the others continue to react under heating, resulting in peak broadening for the low $\overline M _{\rm n}$ polymers. Reinitiation experiments indicated that termination reactions were taking place resulting in “dead” polymer chains which were unable to reinitiate polymerization.magnified image

Synergistic Interaction Between ATRP and RAFT: Taking the Best of Each World

This review covers recent developments on the combination of atom transfer radical polymerization (ATRP) and reversible addition–fragmentation chain transfer (RAFT) polymerization to produce well controlled (co)polymers. This review discusses the relative reactivity of the R group in ATRP and RAFT, provides a comparison of dithiocarbamate (DC), trithiocarbonate (TTC), dithioester (DTE), and xanthate versus bromine or chlorine, and an optimization of catalyst/ligand selection. The level of control in iniferter polymerization with DC was greatly improved by the addition of a copper complex. New TTC inifers with bromopropionate and bromoisobutyrate groups have been prepared to conduct, concurrently or sequentially, ATRP from Br-end groups, ATRP from the TTC moiety, and RAFT polymerization from the TTC moiety, depending on the combination of monomer and catalyst employed in the reaction. The use of concurrent ATRP/RAFT (or copper-catalyzed RAFT polymerization or ATRP with dithioester leaving groups), resulted in improved control over the synthesis of homo- and block (co)polymers and allowed preparation of well-defined high-molecular-weight polymers exceeding 1 million. Block copolymers that could not be prepared previously have been synthesized by sequential ATRP and RAFT polymerization using a bromoxanthate inifer. A simple, versatile, and one-step method involving atom-transfer radical addition–fragmentation (ATRAF) for the preparation of various chain transfer agents (including DC, DTE, and xanthate) in high purity is discussed and a one-pot, two-step polymerization starting with a RAFT agent synthesized by ATRAF, followed by polymerization, is demonstrated.

Synthesis of Well-Defined Poly(vinyl acetate)-b-Polystyrene by Combination of ATRP and RAFT Polymerization

The synthesis of well-defined poly(vinyl acetate)-b-polystyrene (PVAc-b-PSt) by combination of atom transfer radical polymerization (ATRP) and reversible addition-fragmentation chain transfer (RAFT) polymerization was described. Two difunctional compounds, S-(2-chloropropionoxyethoxycarbonylmethyl) O-ethyl xanthate (2) and S-(2-bromo-2-methylpropionoxyethoxycarbonylmethyl) O-ethyl xanthate (3), with an activated halide group and a xanthate group in the molecule were synthesized. The activated halide group was used as an ATRP initiator to initiate polymerization of St, and the xanthate group was used as a RAFT agent to mediate polymerization of VAc. Thus, 2 was first used to mediate the radical polymerization of VAc, followed by ATRP of St, while 3 was used first to initiate the ATRP of St, followed by the RAFT polymerization of VAc. Both approaches indicate that either the radical polymerization of St or that of VAc is controlled, and well-defined PVAc-b-PSt is obtained as confirmed by gel permeation chromatography and NMR measurements.

Synthesis of poly(tert‐butyl acrylate‐block‐vinyl acetate) copolymers by combining ATRP and RAFT polymerizations

AbstractThe synthesis of poly(tert‐butyl acrylate‐block‐vinyl acetate) copolymers using a combination of two living radical polymerization techniques, atom transfer radical polymerization (ATRP) and reversible addition‐fragmentation chain transfer (RAFT) polymerization, is reported. The use of two methods is due to the disparity in reactivity of the two monomers, viz. vinyl acetate is difficult to polymerize via ATRP, and a suitable RAFT agent that can control the polymerization of vinyl acetate is typically unable to control the polymerization of tert‐butyl acrylate. Thus, ATRP was performed to make poly(tert‐butyl acrylate) containing a bromine end group. This end group was subsequently substituted with a xanthate moiety. Various spectroscopic methods were used to confirm the substitution. The poly(tert‐butyl acrylate) macro‐RAFT agent was then used to produce (tert‐butyl acrylate‐block‐vinyl acetate). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7200–7206, 2008

Novel Biodegradable Adaptive Hydrogels: Controlled Synthesis and Full Characterization of the Amphiphilic Co-Networks

Adaptive and amphiphilic poly(N,N-dimethylamino-2-ethyl methacrylate-graft-poly[epsilon-caprolactone]) co-networks (netP(DMAEMA-g-PCL)) were synthesized from a combination of controlled polymerization techniques. Firstly, PCL cross-linkers were produced by ring-opening polymerization (ROP) of epsilon-CL initiated by 1,4-butane-diol and catalyzed by tin(II) 2-ethylhexanoate ([Sn(Oct)2]), followed by the quantitative esterification reaction of terminal hydroxyl end-groups with methacrylic anhydride. Then, PCL cross-linkers were copolymerized to DMAEMA monomers by atom-transfer radical polymerization (ATRP) in THF at 60 degrees C using CuBr complexed by 1,1,4,7,10,10-hexamethyltriethylenetetramine (HMTETA) and 2-ethyl isobutyrylbromide (EiBBr) as catalytic complex and initiator, respectively. A comprehensive study of gel formation was carried out by employing dynamic light scattering (DLS) to determine the gel point as a function of several parameters and to characterize the viscous solutions obtained before the gel point was reached. The evolution of the mean diameters was compared to a model previously developed by Fukuda and these attest to the living formation of the polymer co-network. Furthermore, we also demonstrated the reliability of ATRP for producing well-defined and homogeneous polymer co-networks by the smaller deviation from Flory's theory in terms of cross-linking density. For sake of clarity, the impact of polymerization techniques over the final structure and, therefore, properties was highlighted by comparing two samples of similar composition, but that were produced by either ATRP or thermal-initiated free-radical polymerization (FRP).

Synthesis of Surface-Initiated Stimuli-Responsive Diblock Copolymer Brushes Utilizing a Combination of ATRP and RAFT Polymerization Techniques

The synthesis of diblock copolymer brushes, including poly(styrene) (PSty)-b-PSty, PSty-b-poly(acrylic acid), PSty-b-poly(N-isopropylacrylamide), and poly(methyl acrylate)-b-poly(N,N-(dimethylamino)ethyl acrylate), was achieved utilizing a combination of surface-mediated atom transfer radical polymerization (ATRP) and reversible addition−fragmentation chain transfer (RAFT) polymerization techniques. Conversion of bromine end groups of homopolymer brushes formed by ATRP via a modified atom transfer addition reaction to a RAFT agent and diblock extension via RAFT polymerization allowed the direct formation of well-defined stimuli-responsive diblock copolymer brushes. The addition of sacrificial initiator and/or chain transfer agent permitted formation of well-defined diblock copolymer brushes and free polymer chains in solution. The free polymer chains were isolated and used to estimate the molecular weights and polydispersity index of chains attached to the surface. Ellipsometry, contact angle measurements...

Synthesis of poly(glycidol)‐block‐poly(N‐isopropylacrylamide) copolymers using new hydrophilic poly(glycidol) macroinitiator

AbstractNew, water soluble poly(glycidol) (PGl) macroinitiators for atom transfer radical polymerization (ATRP) were synthesized. This new class of macroinitiators were prepared in a three‐step process. First, series of well‐defined ω‐hydroxyl functional poly(glycidol acetal)s with different molecular weights was synthesized via anionic polymerization followed by quantitative termination of anionically growing active sites. End capping was achieved by treatment of living chain ends with water. The living nature of the system and termination reaction is discussed. In the second stage, monofunctional poly(glycidol acetal)s were functionalized by esterification with 2‐chloropropionyl chloride. Finally, selective deprotection (hydrolysis) of acetal protective groups was performed. As simultaneous partial cleavage of ester bond of attached ATRP moieties was unavoidable, the final functionality of macroinitiator calculated from 1H NMR varied in the range 85–95%. The obtained (2‐chloropropionyl) poly(glycidol) macroinitiator with DP = 55 and 90% functionality was successfully used in ATRP polymerization of N‐isopropylacrylamide (NIPAAm) at room temperature in the DMF/water mixture. Linear block copolymers with relatively narrow molecular weight distribution and controlled composition were obtained and characterized with 1H NMR and SEC‐MALLS measurements. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2488–2499, 2008

Controlled synthesis of amphiphilic block copolymers based on polyester and poly(amino methacrylate): Comprehensive study of reaction mechanisms

The synthesis of amphiphilic and adaptative block copolymers has been envisioned following a commutative two-step strategy involving atom transfer radical polymerization (ATRP) and the Huisgen-1,3-dipolar cycloaddition techniques. The reliability of this strategy is based on the use of an azido-containing ATRP initiator, the 2-(2-azidoethoxy)ethylbromoisobutyrate (N 3E i BBr), able to be “clicked” to an alkyne-terminated derivative and to promote the ATRP polymerization from the active site. In the context of this work, an alkyne-terminated poly(ε-caprolactone) produced by ring-opening polymerization (ROP) of CL was employed as hydrophobic “clickable” segment. The N 3E i BBr initiator was obtained by nucleophilic substitution of the chloride atom from 2-(2-chloroethoxy)ethanol by an azide function and followed by the esterification of the hydroxy function by bromoisobutyryl bromide. This initiator was employed in polymerization of N, N-dimethylamino-2-ethyl methacrylate (DMAEMA) monomer by ATRP in THF at 60 °C using CuBr complexed by 1,1,4,7,10,10-hexamethyltriethylenetetramine (HMTETA) as catalytic complex. Low initiation efficiencies were obtained and they were ascribed to intramolecular cyclization during the polymerization as evidenced by ESI-MS and 2D NMR spectroscopy. The “Click” coupling reaction was performed in THF at r.t. and was found to be efficient when using CuBr complexed by 2,2′-bipyridine ligand. To circumvent the low initiation efficiency, the N 3E i BBr could be “clicked” in a first step to PCL precursors before initiating the polymerization of DMAEMA monomer by ATRP. In this context, various catalytic complexes in different composition ratio were employed to optimize the “click” coupling step. Moreover, this strategy was found to be suitable to produce well-defined PCL-b-PDMAEMA block copolymers, characterized by narrow polydispersity indices. Since ATRP and the Huisgen-1,3-dipolar cycloaddition both require the use of a copper(I)-based catalyst, the two first strategies were merged in a “one-pot” process in order to obtain in one step a well-defined block copolymer characterized by a narrow polydispersity index and predictable composition and block lengths.

Synthesis and characterization of novel functional inorganic–organic hybrid material with macromolecule–metal complex by atom transfer radical polymerization

AbstractThe hydrophilic homopolymer brushes of poly(acrylamide) (PAAM) and poly(2‐hydroxyethyl methacrylate) (PHEMA) were prepared by means of atom transfer radical polymerization (ATRP) on the modified silicon gel by the initiator that was prepared by vapor method. The block copolymer brushes consisting of PAAM and PHEMA blocks were obtained by using the homopolymer brush as the macroinitiator for the second ATRP polymerization of another monomer. The structures of the homopolymer brushes and the block copolymer brushes were characterized by IR and X‐ray photoelectron spectroscopy (XPS). XPS revealed that the first polymer layer of the surface was partly covered with the second polymer layer after being block‐copolymerized with the second monomer. SEM showed that the silicon gel particles with polymer brushes were made up of the silicon gel particles as the core and the polymer as the shell. Under appropriate conditions, the copper or cadmium ion was introduced into the silicon gel with the homopolymer brushes and the block copolymer brushes to form the inorganic–organic hybrid material. TGA analysis showed that the inorganic–organic hybrid material is more stable. The results of ESR indicated that the inorganic–organic hybrid material with the polymer metal complex basing on the silicon gel particle possessed well paramagnetism. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Mixed Molecular Brushes with PLLA and PS Side Chains Prepared by AGET ATRP and Ring-Opening Polymerization

Brush macromolecules having poly(l-lactide) (PLLA) and poly(styrene) (PS) side chains were prepared on the backbone of partially esterified poly(2-hydroxyethyl methacrylate) (PHEMA) by using a combination of atom transfer radical polymerization (ATRP) and ring-opening polymerization. The number-average degrees of polymerization of PLLA side chains and PS side chains were determined by 1H NMR spectroscopy, and the apparent molecular weights of the brush molecules were measured by gel permeation chromatography. The relationship between the crystallization of PLLA with PLLA and PS side chain lengths was investigated. Inside a brush molecule due to the unfavorable interaction between PLLA and PS two phases were formed. Brush molecules adsorbed on mica tend to make a starlike conformation; however, they change to a globular conformation after thermal treatment.

Dynamic Monte Carlo Simulation of Atom‐Transfer Radical Polymerization

AbstractSummary: A dynamic Monte Carlo model was developed to simulate atom‐transfer radical polymerization (ATRP). The algorithm used to describe the polymerization includes activation, deactivation, propagation, chain transfer, and termination by combination and disproportionation reactions. Model probabilities are calculated from polymerization kinetic parameters and reactor conditions. The model was used to predict monomer conversion, average molecular weight, polydispersity and the complete molecular weight distribution at any polymerization time or monomer conversion. The model was validated with experimental results for styrene polymerization and compared with simulation results from a mathematical model that uses population balances and the method of moments. The simulations agree well with experimental and theoretical results reported in the literature. We also investigated the control volume size and number of iterations to reduce computation time while keeping an acceptable noise level in the Monte Carlo results.Comparison of the chain length distribution of polystyrene made with ATRP and conventional free radical (CFR) polymerization at 50% conversion. The initiator to monomer ratios are 1:100 (ATRP left peak), 1:500 (ATRP right peak), and 1:1000 (CFR).magnified imageComparison of the chain length distribution of polystyrene made with ATRP and conventional free radical (CFR) polymerization at 50% conversion. The initiator to monomer ratios are 1:100 (ATRP left peak), 1:500 (ATRP right peak), and 1:1000 (CFR).

Living free‐radical polymerization of sterically hindered monomers: Improving the understanding of 1,1‐disubstituted monomer systems

AbstractThe sterically hindered, 1,1‐disubstituted monomers di‐n‐butyl itaconate (DBI), dicyclohexyl itaconate (DCHI), and dimethyl itaconate (DMI) were polymerized with reversible addition–fragmentation chain transfer (RAFT) free‐radical polymerization and atom transfer radical polymerization (ATRP). Cumyl dithiobenzoate, cumyl phenyl dithioacetate, 2‐cyanoprop‐2‐yl dithiobenzoate, 4‐cyanopentanoic acid dithiobenzoate, and S‐methoxycarbonylphenylmethyl dithiobenzoate were employed as RAFT agents to mediate a series of polymerizations at 60 °C yielding polymers ranging in their number‐average molecular weight from 4500 to 60,000 g mol−1. The RAFT polymerizations of these hindered monomers displayed hybrid living behavior (between conventional and living free‐radical polymerization) of various degrees depending on the molecular structure of the initial RAFT agent. In addition, DCHI was polymerized via ATRP with a CuCl/methyl benzoate/N,N,N′,N″,N″‐pentamethyldiethylenetriamine/cyclohexanone system at 60 °C. Both the ATRP and RAFT polymerization of the hindered monomers displayed living characteristics; however, broader than expected molecular weight distributions were observed for the RAFT systems (polydispersity index = 1.15–3.35). To assess the cause of this broadness, chain‐transfer‐to‐monomer constants for DMI, DBI, and DCHI were determined (1.4 × 10−3, 1.3 × 10−3, and 1.0 × 10−3, respectively) at 60 °C. Simulations carried out with the PREDICI program package suggested that chain transfer to monomer contributed to the broadening process. In addition, the experimental results indicated that viscosity had a pronounced effect on the broadness of the molecular weight distributions. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3692–3710, 2006

Studies on the self-assembly behavior of the amphiphilic block copolymer of PSt-b-PAA in apolar solvents with polar fluorescent probe

The block copolymer of polystyrene-b-poly(butyl acrylate) (PSt-b-PBA) with a well-defined structure was synthesized by atom transfer radical polymerization (ATRP); its structure was characterized, and the living polymerization was also validated by gel permeation chromatography, Fourier transform infrared, and 1H NMR measurements. Then, the amphiphilic block copolymer of polystyrene-b-poly(acrylic acid) (PSt-b-PAA) has been prepared by hydrolysis of PSt-b-PBA, and copolymers of PSt-b-PAA with longer PSt blocks and shorter PAA blocks were obtained by controlling the conditions of ATRP polymerization. The reversed micelle solution of PSt-b-PAA in toluene was prepared by using the single-solvent dissolving method, and the reverse micellization behavior of PSt-b-PAA in toluene was mainly investigated in this paper. The fluorescent probe technique was used by using polar fluorescence compound N-(1-Naphthyl)ethylenediamine dihydrochloride (NEAH) as a polar fluorescent probe to study the reverse micellization behavior of PSt-b-PAA. It was found that the reverse micellization behaviors of PSt-b-PAA in toluene can be clearly revealed by using NEAH as a polar fluorescence probe, and the critical micelle concentrations (cmcs) can be well displayed. The experimental results showed that the self-assembling behavior of PSt-b-PAA in toluene depends apparently on the microstructure of the macromolecules and is also influenced by the temperature. For the copolymers of PSt-b-PAA with the same length of hydrophobic PSt blocks, the copolymer with a longer hydrophilic block PAA has lower cmc, and at higher temperature, the copolymer has lower cmc.

Isotope Effects and the Mechanism of Atom Transfer Radical Polymerization

The mechanism of free-radical polymerization and atom transfer radical polymerization (ATRP) of methyl methacrylate was studied by a combination of 13C kinetic isotope effects and theoretical calculations. Free-radical polymerization initiated by AIBN and ATRP initiated by 1:2:1 CuBr:2,2‘-bipyridine:ethyl 2-bromoisobutyrate exhibit statistically indistinguishable 13C isotope effects. This supports identical chain-propagation steps in ATRP and free-radical polymerization. The free-radical additions leading to these isotope effects were modeled in DFT calculations of transition structures for the addition of 2-methoxycarbonyl-2-propyl radical to methyl methacrylate. Comparison of predicted isotope effects with the experimental values supports the approximate accuracy of the DFT transition structures vs the physical transition state but suggests that the predicted transition structures are slightly too early. This suggestion is supported by comparison of DFT predictions with high-level ab initio predictions ...

Properties of poly(n-butyl methacrylate) prepared by reverse atom transfer radical polymerization in an aqueous dispersed system

Reverse atom transfer radical polymerization (ATRP) of n-butyl methacrylate (BMA) in waterborne media using Cu(II) complexes with azo initiators (i.e., reverse ATRP) was conducted. The influence of several factors, such as surfactant, catalyst, and reaction time, on the stability of the emulsion, the particle size, the morphology of the emulsion particles, and the control of the polymerization was investigated. The results showed great differences between ATRP and conventional emulsion polymerization, especially the nucleation mechanism and the kinetics. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1542–1547, 2003

Stereoblock copolymers and tacticity control in controlled/living radical polymerization.

Three controlled/living radical polymerization processes, atom transfer radical polymerization (ATRP), reversible addition-fragmentation transfer (RAFT) polymerization, and nitroxide-mediated polymerization (NMP), were investigated for the polymerization of N,N-dimethylacrylamide in the presence of Lewis acids known to enhance isotacticity, such as yttrium trifluoromethanesulfonate (Y(OTf)(3)) and ytterbium trifluoromethanesulfonate (Yb(OTf)(3)). Poly(N,N-dimethylacrylamide) with controlled molecular weight, low polydispersity (M(w)/M(n) < 1.2), and a high proportion of meso dyads ( approximately 85%) was prepared by ATRP (with initiating system methyl 2-chloropropionate/CuCl/Me(6)TREN) and RAFT (with cumyl dithiobenzoate transfer agent) in the presence of Y(OTf)(3). The combination of NMP (using N-tert-butyl-1-diethylphosphono-2,2-dimethylpropyl nitroxide, SG1) and a Lewis acid complexation technique led to less precise control over chain architecture and microstructure ( approximately 65% meso dyads), as compared to RAFT/Y(OTf)(3) or ATRP/Y(OTf)(3). The latter two systems were used for the first one-pot synthesis of stereoblock copolymers by radical polymerization. Well-defined stereoblock copolymers, atactic-b-isotactic poly(N,N-dimethylacrylamides), were obtained by adding Y(OTf)(3) at a given time to either RAFT or ATRP polymerizations, initially started without the presence of the Lewis acid.

Structural Control of Poly(Methyl Methacrylate)-g-poly(Lactic Acid) Graft Copolymers by Atom Transfer Radical Polymerization (ATRP)

Atom transfer radical copolymerization of methyl methacrylate (MMA) and (meth)acrylate-terminated poly(lactic acid) (PLA) macromonomers was investigated. The relative reactivity of methacrylate-terminated macromonomer (1/rMMA = 1.75) and acrylate-terminated macromonomer (1/rMMA = 0.61) was close to that of 2-hydroxyethyl methacrylate and 2-hydroxyethyl acrylate, respectively. The difference in reactivity in ATRP and conventional radical polymerization is discussed in terms of the diffusion control effect. A mixture of methacrylate-terminated macromonomer and acrylate-terminated macromonomer was copolymerized with MMA by ATRP to give a homogeneously branched PMMA-g-PLA graft copolymer with low polydispersity (Mw/Mn = 1.15).