Radical Polymerization Of N-butyl Acrylate Research Articles

Interfacial and ion-pairing catalysis for oxygen-tolerant large-scale ATRP in ab initio emulsion

A cooperative interfacial and ion-pairing catalysis, coupled with a molecular oxygen reduction reaction (ORR), to scale up an Atom Transfer Radical Polymerization of n-butyl acrylate (BA) from 20 mL to 10 L (scale-up factor = 500) in ab initio emulsion conditions is introduced. The polymerization is driven by the regeneration of [CuIL]+ through CuII/Cu0 comproportionation. [CuIL]+ simultaneously converts O2 to H2O2 (which is then degraded by sodium pyruvate) and drives the polymerization of butyl acrylate. The anionic surfactant sodium dodecyl sulfate (SDS) facilitates catalyst transport inside and outside the micelles by ion-pairing catalysis. n-Butyl acrylate polymerizations are investigated on a small scale with Cu0 wire and on a larger scale with Cu0 powder. On a 10 L scale, the polymerization yielded controlled PBA-Br (Mn = 32.3 × 103; Ð = 1.39, ∼1.64 kg) after 9 h. Chain extension of PBA-Br macroinitiators proved their livingness. An on-line electrochemical monitoring was also introduced to determine the instantaneous CuI and CuII concentrations at the Cu0 wire surface during the polymerization.

Computational and Experimental Confirmation of the Diradical Character of para-Quinonedimethide.

The ground-state structure of the parent para-quinonedimethide (p-QDM) molecule is generally represented in its closed shell form, i.e., as a cyclic, nonaromatic, through-conjugated/cross-conjugated hybrid comprising four C═C bonds. Nonetheless, p-QDM has been theorized to contain a contribution from its open-shell aromatic singlet diradical form. VBSCF calculations identify an open-shell contribution of 29% to the structure, while CASPT2(16,16)/def2-TZVP and ωB97XD/aug-cc-pVTZ calculations predict that dimerization proceeds along an open-shell singlet diradical pathway with a low (77 kJ/mol) barrier toward dimerization, which occurs by way of C-C bond formation between the exocyclic methylene carbons. A similar low (98 kJ/mol) barrier exists toward the reaction between a p-QDM molecule and the radical trap TEMPO. These predictions are verified experimentally through the isolation of bis-TEMPO-trapped p-QDM, its C-C coupled dimer, and by demonstrating that a mixture of p-QDM and TEMPO can initiate the radical polymerization of n-butyl acrylate at ambient temperature. In contrast to p-QDM, tetracyanoquinone (TCNQ) neither dimerizes nor reacts with TEMPO, despite having a similar diradical character to p-QDM. This lack of reactivity is consistent with both a higher kinetic barrier and a thermodynamically unfavorable process, which is ascribed to destabilizing steric clashes and polar effects.

Deterministic modeling of non-adiabatic solution radical polymerization of n-butyl acrylate in light of runaway prevention

Acrylate polymerizations with high exothermicity exhibit strongly non-isothermal characteristics. The presence of side reactions involved in the polymerization mechanisms makes process safety as well as polymer properties more sensitive to operation parameters. In this study, a deterministic moment-based modeling approach combining with the divergence criterion was developed to investigate the non-isothermality of acrylate polymerization process. In silico design of non-adiabatic processes was achieved by the modeling approach involving reaction mechanism, energy balance, and mass balance. The safe and unsafe states of the reactor under a wide range of process operating conditions were identified by a divergence criterion. From the perspective of process intensification, optimization of operating parameters was carried out. Afterwards, the pseudo-isothermal operation was mimicked by using stepwise jacket temperature profiles to investigate the effects of temperature and monomer content on molecular properties. The simulation results provide a safe operating window for the polymerization reactor under the given feed schemes and process conditions. Additionally, a pseudo-isothermal process is more suitable to tune the molecular properties of the resulting polymers during polymerization. The current work puts forward deterministic simulations in terms of both process safety and molecular properties control compared to the previous works.

Jacket temperature regulation allowing well-defined non-adiabatic lab-scale solution free radical polymerization of acrylates

Conventional batch solution free radical polymerization of n-butyl acrylate with thermal initiators such as AIBN is known to be strongly exothermic and influenced by highly activated side reactions such as backbiting and β-scission.

Dispersion polymerization of n-butylacrylate under the action of acrylic acid and N-isopropylacrylamide copolymers

The regularities of dispersion radical polymerization of n-butylacrylate in water-alcohol medium under the action of polymer tritiocarbonates based on copolymers of acrylic acid and N-isopropylacrylamide have been investigated. The conditions for the formation of a block copolymer with controlled molecular weight and high yield have been found. The conditions of formation of stable suspensions of block copolymers with unimodal particle size distribution have been determined.

Cu(0)-mediated reversible-deactivation radical polymerization of n-butyl acrylate in suspension

Cu(0)-mediated reversible-deactivation radical polymerization of n-butyl acrylate was performed in suspension without the use of an organic solvent. In all cases, a 5 v% organic phase (monomer, initiator, and ligand) was used with respect to 95 v% aqueous phase. Polyvinyl alcohol (PVA) as a suspension stabilizer has been shown to be able to control the polymerization for the degree of polymerizations of 222 and higher. The polymerization reaction showed linear first-order kinetics for a PVA concentration range of 1–10 wt%, leading to polymers with dispersities from 1.22 to 1.43. Conversions as high as 96% were obtained in 55 min. Scanning electron microscopy analysis of the suspensions confirmed the formation of micron-sized polymer particles dispersed in aqueous media, and that the size of the particles decreased with increasing PVA concentration. Rheometry measurements of the aqueous phase containing PVA before and after polymerization demonstrated the increase in the viscosity of the reaction mixture after polymerization. The difference between the viscosity of the PVA solution in water and the same solution after polymerization decreased as the PVA decreased, which indicates smaller particle sizes formed with increasing PVA content. All suspensions were stable over a period of three months storage at room temperature without any precipitation or sedimentation. The maximum copper species concentration in the reaction medium and water can be as low as 7 ppm. This Cu(0)-mediated reversible-deactivation radical polymerization in suspension has the potential for industrial use, especially for paint and adhesives.

Mid-Chain Radical Migration in the Radical Polymerization of n-Butyl Acrylate.

The occurrence of intramolecular transfer to polymer in the radical polymerization of acrylic monomers has been extensively documented in the literature. Whilst it has been largely assumed that intramolecular transfer to polymer leads to short chain branches, there has been some speculation over whether the mid-chain radical can migrate. Herein, by the matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) mass spectrometry (MS) of poly(n-butyl acrylate) synthesized by solution polymerization under a range of conditions, it is shown that this mid-chain radical migration does occur in the radical polymerization of acrylates conducted at high temperatures, as is evident from the shape of the molecular weight distribution. Using a mathematical model, an initial approximation of the rate at which migration occurs is made and the distribution of branching lengths formed in this scenario is explored. It is shown that the polymerizations carried out under a low monomer concentration and at high temperatures are particularly prone to radical migration reactions, which may affect the rheological properties of the polymer.

Multifunctional block copolymer nanocarriers for co-delivery of silver nanoparticles and curcumin: Synthesis and enhanced efficacy against tumor cells

Functional multilayer polymeric micelles were obtained by self-assembly of a poly(ethylene oxide)-b-poly(n-butyl acrylate)-b-poly(acrylic acid) (PEO113-b-PnBA235-b-PAA14) triblock terpolymer and exploited as template for the synthesis of silver nanoparticles and loading of anti-cancer agents. The terpolymer was synthesized by atom transfer radical polymerization of n-butyl acrylate and tert-butyl acrylate (tBA), initiated by a PEO-based macroinitiator. Then, PtBA blocks were converted into PAA by selective hydrolysis. PEO113-b-PnBA235-b-PAA14 terpolymer formed nano-sized spherical micelles in the concentration range from 1 to 10mgmL−1 as confirmed by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The presence of PAA chains in the middle micellar layer allowed loading of silver ions and subsequent UV-induced synthesis of silver nanoparticles within the micelles. After that, the anti-cancer drug curcumin was loaded in the hydrophobic PnBA micellar cores. The effect of combination of two anti-cancer agents, spontaneously released from the micelles, on the vitality of acute myeloid leukemia (HL-60), its multidrug-resistant subline HL-60/DOX and human urinary bladder carcinoma (EJ) cells was assessed. The in vitro experiments revealed enhanced efficacy in regard to the cytotoxic activity of silver nanoparticles and curcumin.

Phase transfer catalyst aided radical polymerization of n-butyl acrylate in two-phase system: a kinetic study

The kinetics of radical polymerization of butyl acrylate initiated by potassium peroxydisulphate and cetyltrimethylammonium bromide as phase transfer catalyst (PTC) was carried out under inert and unstirred conditions at constant temperature of 60 ± 2 °C in ethyl acetate–water biphase media. The polymerization reactions were relatively fast in the two-phase systems with phase transfer agent whereas extremely sluggish in the system without PTC. Use of PTC accelerates the reaction effectively if the reactants located in two phase. The effects of rate of polymerization (R p) on various experimental conditions such as different concentrations of monomer, initiator, phase transfer catalyst, temperature, and different ionic strength of the medium were explored. The order with respect to monomer, initiator and phase transfer catalyst was found to be unity. The R p is independent of ionic strength and pH of the medium. However, an increase in the polarity of solvent has slightly increased the R p value. Based on the results obtained, a plausible mechanism has been proposed for the polymerization reaction. The obtained polymer was confirmed by FT-IR analysis.

Analyzing the discrepancies in the activation energies of the backbiting and β-scission reactions in the radical polymerization of n-butyl acrylate

Activaton energies for backbiting and β-scission reactions for the polymerization of n-BA were determined by fitting experimental data to a mathematical model. The activation energy for backbiting was higher and that for β-scission lower than those accepted in the literature.

Electrochemically mediated atom transfer radical polymerization of n-butyl acrylate on non-platinum cathodes

Inexpensive metals and metal alloys were used as cathodes in well-controlled, electrochemically mediated ATRP ofn-butyl acrylate in DMF with the ppm level of catalysts.

Homophase and heterophase polymerizations of butyl acrylate mediated by poly(acrylic acid) as a reversible addition–fragmentation chain-transfer agent

The radical polymerization of n-butyl acrylate in organic, aqueous, and water–alcohol media in the presence of poly(acrylic acid) containing a trithiocarbonate group within the chain is studied for the first time. It is shown that in nonselective solvents (1,4-dioxane and DMF) poly(acrylic acid) serves as a reversible addition–fragmentation chain-transfer agent and the triblock copolymer poly(acrylic acid)–block–poly(n-butyl acrylate)-–block-poly(acrylic acid) is formed. In aqueous and aqueous–organic media (under conditions of emulsion, dispersion, and miniemulsion polymerizations as well as polymerization-induced selfassembly), the block copolymer being formed additionally serves as a stabilizer of polymer–monomer particles. The sizes of these particles and the molecular-mass characteristics of the resulting polymers may be controlled via variation in the concentration ratio of the components. It is found that, during polymerization in aqueous media, there is the formation of spherical polymer particles that preserve their morphology in thin films prepared via precipitation of the synthesized dispersion.

Synthesis of Vinylic Macromolecular Rotaxane Cross-Linkers Endowing Network Polymers with Toughness.

Macromolecular rotaxane cross-linkers having two radically polymerizable vinyl groups (RCs) were first synthesized and used to prepare network polymers. A crown ether/sec-ammonium-type pseudorotaxane initiator having an OH terminal-containing axle and a crown ether wheel with a vinyl group was subjected to the living ring-opening polymerization of δ-valerolactone followed by end-capping with a bulky isocyanate to yield a polyester axle-tethering macromolecular [2]rotaxane cross-linker (RC). Rotaxane cross-linked polymers (RCPs) were prepared by the radical polymerization of n-butyl acrylate in the presence of RCs (0.25, 0.50 mol %). The properties of the RCPs and covalently cross-linked polymers (CCPs) were characterized mainly by mechanical properties. Both fracture stress and strain values of RCPs were much higher than those of CCPs, probably owing to the increased network homogeneity by the rotaxane cross-link. The hybrid-type RCPs obtained from a mixture of RC and covalently connected cross-linker (CC) showed poorer mechanical properties similar to that of CCPs, indicating the importance of RCs in increasing the toughness of the network polymers.

Synthesis of Bulky Nitroxides, Characterization, and Their Application in Controlled Radical Polymerization

This paper describes the synthesis of several highly sterical hindered alkoxyamines based on 6-membered cyclic nitroxides and their application as initiators/regulators in the controlled nitroxide-mediated radical polymerization of n-butyl acrylate and styrene. Rate constant kd and activation energy Ea of the C–O bond of the novel alkoxyamines are reported. Conformational studies on the new nitroxides are performed by X-ray analysis and by DFT calculations. The polymerization of n-butyl acrylate can be conducted at 60 °C showing that these hindered nitroxides are highly valuable to conduct nitroxide-mediated acrylate polymerization (NMP). In addition, low temperature (50 °C) styrene polymerizations are disclosed.

Formation and Possible Reactions of Organometallic Intermediates with Active Copper(I) Catalysts in ATRP

The CuI complex obtained in situ from CuI and tris((4-methoxy-3,5-dimethylpyridin-2-yl)methyl)amine (TPMA*) is currently the most reducing and the most active catalyst for atom transfer radical polymerizations (ATRP). The complex has a high affinity for alkyl halides (ATRP pathway) but also has sufficient affinity toward organic radicals to potentially participate in organometallic-mediated radical polymerization (OMRP). Thus, the radical polymerization of n-butyl acrylate initiated by AIBN (azobisisobutyronitrile) was significantly retarded, and the molecular weights decreased in the presence of the CuI/TPMA* complex. These results suggest the presence of a Cu-mediated termination processes, even after the amount of radicals generated from AIBN exceeded the initial amount of CuI/TPMA*. Nevertheless, in the presence of alkyl bromides, which act as ATRP initiators for acrylates, control was gained through metal-mediated halogen atom transfer, i.e., ATRP, not OMRP.

Synthetic and mechanistic inputs of photochemistry into the bis-acetylacetonatocobalt-mediated radical polymerization of n-butyl acrylate and vinyl acetate

The input of photochemistry to the Co(acac)2 mediated radical polymerization (CMRP) of n-butyl acrylate and vinyl acetate is investigated for the first time. Upon UV irradiation, photoinitiators are able to initiate the n-butyl acrylate polymerization that remains controlled up to very high molar masses (>4 × 106 g mol−1) with low polydispersities. The photoinitiator as well as the irradiation time must be appropriately chosen to reach acceptable initiator efficiencies while maintaining an optimal control over the polymerization. Laser flash photolysis experiments were then carried out to evidence the addition of alkyl and phosphonyl radicals onto Co(acac)2 and to determine the rate constants (kdeact) of these addition reactions that were still lacking. Finally, both kinetics of polymerization and spin-trapping experiments have evidenced that the C–Co bond at the extremity of the dormant polymer chains can be easily photocleaved. UV irradiation can therefore be considered as an additional lever for tuning the reactivity of the CMRP process mediated by Co(acac)2.

Synthesis, characterization, and rheological properties of hybrid titanium star‐shaped poly(n‐butyl acrylate)

AbstractThe synthesis of hybrid star‐shaped polymers was carried out by atom transfer radical polymerization of n‐butyl acrylate from a well‐defined multifunctional titanium‐oxo‐cluster initiator. Conditions were identified to prevent possible side reactions among monomer, polymer, and the titanium‐oxo‐cluster ligands. Polymerizations provided linear first‐order kinetics and the evolution of the experimental molecular weight is also linear with the conversion. 1H DOSY NMR and cleavage of the polymeric branches from the multifunctional initiator by hydrolysis were used to (i) prove the star‐shaped structure of the polymer, and (ii) demonstrate that the shoulder observed on size exclusion chromatograms is not due to a noncontrolled polymerization but to ungrafting of polymeric branches during analysis. Rheological properties of the hybrid star‐shaped poly(n‐butyl acrylate) were studied in the linear regime and show that the Ti‐oxo‐cluster not only increases significantly the viscosity of the polymer relative to its ungrafted arm but has a rheological signature which is qualitatively different from that of stars with organic cores suggesting that the Ti cluster reduces significantly the molecular mobility of the star. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Stable free radical polymerization of n-butyl acrylate in the presence of high-temperature initiators

Living radical polymerizations of acrylate are known to be difficult to achieve using TEMPO as a mediator. The stable free radical polymerization (SFRP) of acrylate tends to stop at low monomer conversion due to the accumulation of TEMPO in the medium as a result of unavoidable bimolecular termination. Rather than solving this problem by destroying the excess nitroxide using ascorbic acid or glyceraldehyde associated with pyridine as reported recently, high temperature initiators were used to slowly and continuously generate new radicals throughout the polymerization to consume the excess TEMPO molecules. Polymerizations of n-butyl acrylate initiated by the alkoxyamine unimer (1-benzoyloxy)-2-phenyl-2-(2′,2′,6′,6′-tetramethyl-1′-piperidinyloxy)ethane (BST) were performed between 130 °C and 134 °C in the presence of a series of high temperature peroxide and azo initiators. The best results in this study were obtained by the continuous addition of small amounts of di- tert-amyl peroxide throughout the polymerization. Under these conditions, the acrylate polymerizations fulfilled the criteria of a controlled polymerization process although the molecular weight distributions were slightly broad ( M w/ M n ∼ 1.5).

Effect of Ligand and n-Butyl Acrylate on Cobalt-Mediated Radical Polymerization of Vinyl Acetate

The electron-withdrawing effect of the ligand in the cobalt complex was studied in cobalt-mediated radical polymerization of vinyl acetate (VOAc) initiated by 2,2‘-azobis(4-methoxy-2,4-dimethylvaleronitrile) (V-70). The polymerization of VOAc with V-70 and a series of bis(acetylacetonate)cobalt derivatives, Co(R1COCHCOR2)2 (R1 = R2 = CH3 (1), R1 = CF3, R2 = CH3 (2), R1 = R2 = CF3 (3)), was conducted under the same conditions. Complexes 1 and 2 successfully mediated the radical polymerization of VOAc, resulting in poly(VOAc) with predetermined Mn and low polydispersity. In contrast, complex 3 did not control the radical polymerization of VOAc, resulting in poly(VOAc) with higher molecular weight and higher polydispersity. While complex 1 was not able to control the radical polymerization of n-butyl acrylate (nBA), the copolymerization of nBA with various amounts of VOAc (9%, 23%, and 50%) in the presence of V-70 and 1 showed that Mn and Mw/Mn of copolymers decreased with increasing VOAc ratio. This indicat...

Living Radical Polymerization: Use of an Excess of Nitroxide as a Rate Moderator

The kinetics of the living radical polymerization of n-butyl acrylate (BuA) in the presence of an excess of N-tert-butyl-N-(1-diethylphosphono-2,2-dimethylpropyl)-N-oxyl (DEPN) as a rate moderator has been studied in the temperature range 115−125 °C. The equilibrium rate constant K = kd/kc between dormant and active chains was determined experimentally from the slope of ln([BuA]0/[BuA]) vs time. It obeys the following Arrhenius relation: K = 4.93 × 105 exp(−119.3 kJ mol-1/RT), i.e., K = 1.09 × 10-10 mol L-1 at 125 °C. Some straightforward analytical kinetic equations that only depend on the excess of DEPN as the experimental parameter were established. These equations were successfully applied to simulate the DEPN-mediated polymerization of n-butyl acrylate initiated by either a styryl-DEPN alkoxyamine or an AIBN/DEPN bicomponent system. Last, the slow degradation of DEPN was considered in order to account for the upward deviation of the kinetics when a great excess of DEPN was used.