Nitroxide-mediated Radical Copolymerization Research Articles

Kinetics of Polymer Network Formation by Nitroxide-Mediated Radical Copolymerization of Styrene/Divinylbenzene in Supercritical Carbon Dioxide

The kinetics of nitroxide-mediated dispersion copolymerization with crosslinking of styrene (STY) and divinylbenzene (DVB) in supercritical carbon dioxide (scCO2) is addressed experimentally. 2,2,6,6-Tetramethylpiperidinyl-1-oxy (TEMPO) and dibenzoyl peroxide (BPO) were used as nitroxide controller and initiator, respectively. A high-pressure cell with lateral sapphire windows at 120 °C and 207 bar was used to carry out the polymerizations. The nitroxide-mediated homopolymerization (NMP) of STY, as well as the conventional radical copolymerization (FRC) of STY/DVB, at the same conditions were also carried out as reference and for comparison purposes. The effect of nitroxide content on polymerization rate, evolution of molecular weight averages, gel fraction, and swelling index was studied.

Insights into the Network Structure of Cross-Linked Polymers Synthesized via Miniemulsion Nitroxide-Mediated Radical Polymerization

The effect of reversible-deactivation radical polymerization on the structure of the network formed by copolymerization of mono- and divinyl monomers is studied. The nitroxide-mediated radical copolymerization (NMP) of butyl methacrylate and ethylene glycol dimethacrylate, initiated with the alkoxyamine 3-(((2-cyanopropan-2-yl)oxy)cyclohexylamino)-2,2-dimethyl-3-phenylpropanenitrile (Dispolreg 007) in an aqueous miniemulsion was used as a case study. Combination of asymmetric-flow field-flow fractionation and small-angle X-ray scattering clearly showed that NMP led to a more homogeneous network structure formed by regions of relatively open networks connected with short polymer chain segments, whereas that of the polymer formed by free radical polymerization consists of densely cross-linked regions linked by long polymer chain portions.

Quantitative study on the homogeneity of networks synthesized by nitroxide-mediated radical copolymerization of styrene and divinylbenzene

The nitroxide-mediated radical copolymerization (NMRP) of styrene and divinylbenzene was studied using a Monte Carlo simulation. The model predictions were validated by comparing to experimental results gathered from literature. Polymer network microstructure was studied through complete molar mass distribution (including the gel part) of the polymer and by quantitative representation of the homogeneity of the network, i.e. the broadness of the distribution of the molar mass between crosslinking points (Mc). The nitroxide mediated radical polymerization led to a narrower Mc distribution compared to free radical polymerization, and the average Mc did not change significantly through the reaction. The narrower Mc distribution is an indicator of more homogenous network and clarifies many conflicting statements in the literature on homogeneity of the network obtained by controlled radical polymerization.

Synthesis and characterization of graft copolymers by photoinduced CuAAC click chemistry

Well-defined graft copolymers were synthesized by a simple photoinduced copper(I) catalyzed 1,3-dipolar cycloaddition click reaction of alkyne-terminated poly(epsilon-caprolactone) (PCL) either side-chain azide-functional polystyrene (PSt) or poly(vinyl chloride) (PVC). The alkyne-terminated PCL was prepared by ring-opening polymerization of epsilon-caprolactone in bulk using Sn(Oct)2 as a catalyst and propargyl alcohol as an initiator. Whereas, the halide groups of PVC and poly(styrene-co-chloromethylstyrene) prepared by nitroxide mediated radical copolymerization were transformed to side chain azide-functional PVC or PSt via nucleophilic substitution reaction using sodium azide. Subsequently, the resulting alkyne and azide functional polymers were mixed in DMF with Cu(II)Br2/PMDETA ligand and 2, 2-dimethoxy-2-phenyl acetophenone and irradiated by UV light to form corresponding graft copolymers. The FT-IR, 1H NMR, GPC and DSC analyzes clearly pointed out an efficient photoinduced CuAAC click reactions between azide- and alkyne-functional precursor polymers.

Crosslinking nitroxide-mediated radical copolymerization of styrene with divinylbenzene

Results from the crosslinking kinetics of nitroxide-mediated radical polymerization (NMRP) of styrene (STY) in the presence of a small amount of divinylbenzene (DVB) are presented. The performance of styrene polymerization with N-tert-butyl-N-(2-methyl-1-phenylpropyl)-O-(1-phenylethyl) hydroxylamine (referred to as TIPNO-based alkoxyamine or I-TIPNO) is first examined to see if the system exhibits controlled behavior. Then, typical profiles for crosslinking NMRP of STY/DVB in the presence of this alkoxyamine (as controller) are presented and contrasted with crosslinking under regular free radical polymerization, and NMRP of styrene (in the absence of crosslinker). Subsequently, the performance of crosslinking NMRP is evaluated based on rate of polymerization, molecular weights, polydispersity values and gel content under different operating conditions (different crosslinker and nitroxide concentrations). Finally, prediction profiles from a mathematical model are contrasted with experimental data to check the validity of the developed model with respect to both NMRP and crosslinking NMRP of STY/DVB with this TIPNO-based alkoxyamine.

Macromol. Theory Simul. 5/2012

Cover: Polymers may contain several active, dead, and dormant radical centers at the same time, which results in a multidimensional modeling problem. A model of the network formation kinetics during the nitroxide-mediated radical copolymerization of vinyl/divinyl monomers is presented in this work using a multifunctional macromolecule approach. The predictions of this model are then compared with experimental data. Further details can be found in the article by J. C. Hernández-Ortiz, E. Vivaldo-Lima,* and A. Penlidis on page 302.

Modeling of Network Formation in Nitroxide‐Mediated Radical Copolymerization of Vinyl/Divinyl Monomers Using a Multifunctional Polymer Molecule Approach

AbstractA mathematical model for the kinetics of copolymerization with crosslinking of vinyl/divinyl monomers in the presence of stable nitroxyl radicals is presented. A reaction scheme considering multifunctional polymer molecules is proposed. The Flory‐Stockmayer theory is used for the post‐gelation period. Average crosslink and cyclization densities are calculated using two different approaches. Good agreement between predicted profiles and experimental data from our and other groups is observed in all cases. Overall monomer concentration, controller/initiator ratio, and crosslinker initial concentration are found to be the governing factors for the development of average crosslink and cyclization densities and therefore for the homogeneity of the resulting polymer network. magnified image

Nitroxide-mediated radical copolymerization of methyl methacrylate controlled with a minimal amount of 9-(4-vinylbenzyl)-9H-carbazole

The controlled nitroxide-mediated homopolymerization of 9-(4-vinylbenzyl)-9H-carbazole (VBK) and the copolymerization of methyl methacrylate (MMA) with varying amounts of VBK were accomplished by using 10 mol % {tert-butyl[1-(diethoxyphosphoryl)-2,2-dimethylpropyl]amino} nitroxide relative to 2-({tert-butyl[1-(diethoxyphosphoryl)-2,2-dimethylpropyl]amino}oxy)-2-methylpropionic acid (BlocBuilder™) in dimethylformamide at temperatures from 80 to 125 °C. As little as 1 mol % of VBK in the feed was required to obtain a controlled copolymerization of an MMA/VBK mixture, resulting in a linear increase in molecular weight versus conversion with a narrow molecular weight distribution (Mw/Mn ≈ 1.3). Preferential incorporation of VBK into the copolymer was indicated by the MMA/VBK reactivity ratios determined: rVBK = 2.7 ± 1.5 and rMMA = 0.24 ± 0.14. The copolymers were found significantly “living” by performing subsequent chain extensions with a fresh batch of VBK and by 31P NMR spectroscopy analysis. VBK was found to be an effective controlling comonomer for NMP of MMA, and such low levels of VBK comonomer ensured transparency in the final copolymer. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Living Radical Polymerization of Styrene Derivatives Containing Trialkylmetal Groups

Fourteenth group oganometallic styrene derivatives were synthesised by nitroxide-mediated controlled radical polymerization using di-tert butyl nitroxide (A-T) as initiator. This is the first time that nitroxide-controlled radical polymerization has been successfully adapted for the synthesis of new polystyrenes bearing organometallic species with controlled molecular weights and narrow polydispersities. Monomer reactivity ratios were determined in controlled nitroxide-mediated radical copolymerization between styrene and substituted styrene. All experiments permitted the synthesis of new organometallic polymers that will be used for the development of a polymer capsule for Inertial Confinement Fusion Experiments.

Nitroxide-mediated radical copolymerization of styrene and divinylbenzene: increased polymerization rate by using TBEC as initiator

Nitroxide-mediated radical copolymerizations of styrene and divinylbenzene using 2,2,6,6-tetramethyl-1-piperidinoxyl (TEMPO) as controller were performed to produce crosslinked polymers. Tert-butylperoxy 2-ethylhexyl carbonate (TBEC) was used instead of conventional initiators such as benzoyl peroxide (BPO) in order to enhance the polymerization rate while trying to keep the controlled characteristics of the system. The effect of temperature, initial concentration of initiator, and ratio of TEMPO to initiator on conversion, molecular weight averages, and polydispersity was investigated. It was observed that, when using TBEC, it was possible to produce controlled copolymer in a faster rate when compared to conventional initiators, like BPO.

Effects of the oil–water interface on network formation in nanogel synthesis using nitroxide-mediated radical copolymerization of styrene/divinylbenzene in miniemulsion

Nitroxide-mediated radical copolymerization of styrene (99mol%)/divinylbenzene (1mol%) employing the nitroxide 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO) in aqueous miniemulsion using sodium dodecylbenzenesulfonate as surfactant has been carried out at 125°C. At a given styrene conversion, the degree of crosslinking increases with decreasing polystyrene–TEMPO macroinitiator concentration in excess of what is predicted based on the increase in primary chain length assuming an ideal controlled/living process. This discrepancy is mainly a result of the oil–water interface effect on the deactivation reaction between propagating radicals and TEMPO. This interface effect causes a marked increase in primary chain length, and therefore an accompanying increase in the number of crosslinks per primary chain. Polymerizations in the presence of free TEMPO minimizes the interface effect, and one then obtains molecular weight distributions and well-defined networks conducive with a controlled/living process.

Comprehensive Modeling Study of Nitroxide-Mediated Controlled/Living Radical Copolymerization of Methyl Methacrylate with a Small Amount of Styrene

This article presents a comprehensive kinetic study of the SG1 nitroxide-mediated copolymerization of methyl methacrylate with a small percentage of styrene using the PREDICI software. The aim of this study was to confirm the results from a previous publication showing that a living polymerization can be achieved for this system. The PREDICI simulations based on the penultimate unit effect model were also able to give a better insight into the complex mechanism of nitroxide-mediated controlled radical copolymerization. The model showed the copolymerization kinetics and the evolution of the number average molar mass, the fraction of living and dead chains, and the concentration of the four types of alkoxyamines and propagating radicals with monomer conversion. It was applied for different initial percentages of styrene and different initiator concentrations.

Network formation in nitroxide-mediated radical copolymerization of styrene and divinylbenzene in miniemulsion: Effect of macroinitiator hydrophilicity

Nitroxide-mediated crosslinking radical copolymerizations of styrene and divinylbenzene have been carried out in aqueous miniemulsion with Dowfax 8390 as surfactant at 125°C employing TEMPO-based macroinitiators of various hydrophilicities (random copolymers comprising styrene and methyl acrylate). The pendant conversion (i.e. the degree of crosslinking) increased with increasing macroinitiator hydrophilicity and with decreasing particle size. It is proposed that a concentration gradient is generated within the particle such that the macroinitiator concentration tends to be higher near the oil–water interface than in the particle interior. The macroinitiators are surface active and are thus preferentially adsorbed at/located near the oil–water interface. This in turn leads to an increase in the ratio [pendant unsaturation]/[monomer] in the vicinity of propagating radicals, which are generated from the macroinitiators, and thus an increase in pendant conversion. This effect is enhanced by an increase in macroinitiator hydrophilicity and a decrease in particle size. The present approach offers novel means of controlling network formation in dispersed systems.

Synthesis of star-like random copolymers from resorcinarene-based octa-functional alkoxyamine initiatorvia nitroxide mediated free radical polymerization

An octa-functional alkoxyamine initiator, with the 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) free radical, was synthesized based on resorcinarene, with its efficiency to initiate the nitroxide-mediated free radical copolymerization of styrene and methyl methacrylate (MMA) described. A difunctional analogue of this initiator was also synthesized, using resorcinol as the core molecule. The structures of the resulting initiators were confirmed by homolysis studies based on electron spin resonance spectroscopy and molecular modeling. The polymerization behavior and characteristics of the polymers obtained using these two initiators were also compared. Well-defined star-shaped and linear random copolymers, with low polydispersities and controlled molecular weights, were prepared. The efficiencies of these initiators towards copolymerization, as well as the parameters permitting the formation of well-defined polymers, were also investigated. The reactivity ratios werer a = 0.42 (a = styrene) andr b = 0.33 (b = MMA) for the octa-functional initiator system andr a = 0.45 andr b = 0.39 for the difunctional initiator system.

Gel formation and primary chain lengths in nitroxide-mediated radical copolymerization of styrene and divinylbenzene in miniemulsion

Gelation in 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO)-mediated cross-linking copolymerization of styrene and divinylbenzene (8.2 mol%) in aqueous miniemulsion at 125 °C has been investigated. The rate of gel formation relative to monomer conversion was the same in miniemulsion and the corresponding solution polymerization when the organic phase contained 6 vol% tetradecane (TD; hydrophobe) and 48 vol% toluene. However, at 54 vol% TD and no toluene (the same total monomer concentration), the conversion at the gel point was lower in miniemulsion than in solution, consistent with our previous results describing enhanced apparent pendant reactivity related to the presence of TD in the present system. The primary chain lengths were higher in miniemulsion with 54 vol% TD than in miniemulsion with 6 vol% TD and in solution (6 and 54 vol% TD). It was deduced via application of Flory–Stockmayer gelation theory that this difference in primary chain lengths, although significant with regards to gelation, was insufficient to explain the rapid gel formation in the miniemulsion containing 54 vol% TD, which is speculated to be related to specific effects of the heterogeneity of the miniemulsion system.

Network Formation in Nitroxide-Mediated Radical Copolymerization of Styrene and Divinylbenzene in Miniemulsion

Polymer network formation in controlled/living radical crosslinking copolymerization of S/DVB initiated by a poly(S)-TEMPO macroinitiator in aqueous miniemulsion at 125 °C is investigated. The crosslinking proceeded differently in miniemulsion (heterogeneous systems) and in bulk/ solution (homogeneous systems), with markedly lower apparent pendant reactivity in miniemulsion. The relative rate of DVB consumption was lower in miniemulsion than in bulk/solution. It is proposed that the interface between the particle (monomer droplet at time = 0) and the aqueous phase may play an important role during the crosslinking process. The presence of tetradecane as a hydrophobe in the monomer droplets strongly influenced both the pendant reactivity and the molecular weight distributions in miniemulsion, whereas only small effects were observed in the corresponding bulk/ solution polymerizations. It is believed that this is related to previous results of the hydrophobe promoting migration of poly(DVB) to the interface of toluene droplets in aqueous emulsion. The results suggest novel approaches towards control of polymer network development in crosslinking radical polymerizations.

A Concept for Quasiliving Nitroxide-Mediated Radical Copolymerization

A principle conception for quasiliving TEMPO-mediated radical copolymerization was advanced. It was concluded that TEMPO-mediated copolymerization of styrene with other monomers (which are not able...