Controlled free radical photopolymerization of styrene initiated by trithiocarbonate

Density functional theory calculations are reported for prediction of the trends in C S bond dissociation energies and atomic spin densities for radicals using S,S′‐bis(α,α′‐dimethyl‐α‐acetic acid) trithiocarbonate (TTCA) and bis(2‐oxo‐2‐phenylethyl) trithiocarbonate (TTCB) as reversible addition fragmentation chain transfer (RAFT) reagents. The calculations predict that the value of the C S bond length (1.865 Å) of TTCA is longer than that (1.826 Å) of TTCB, and TTCA is more effective for the polymerization of styrene (St) compared to TTCB as predicted by density functional theory. In photopolymerizations, pseudo‐first‐order kinetics were confirmed for TTCB‐mediated photopolymerization of St due to the linear increase of ln([M]₀/[M]) up to about 28% conversion, suggesting the living characteristics behavior of the photopolymerization of St in the presence of TTCB. For both TTCA and TTCB the polydispersities change with increasing conversion in the range 1.10–1.45, typical for RAFT‐prepared (co)polymers and well below the theoretical lower limit of 1.50 for a normal free radical polymerization. In addition, the triblock copolymer polystyrene‐block‐poly(butyl acrylate)‐block‐polystyrene (PS PBA PS) was successfully prepared, with very good control over molecular weight and narrow polydispersity (M_w/M_n = 1.45), using PS S C(S) S PS as macro‐photoinitiator under UV irradiation at room temperature. This indicated that this reversible and valid strategy led to a better controlled block copolymer with defined structures. Copyright © 2007 Society of Chemical Industry     

A replicated investigation of nitroxide‐mediated radical polymerization of styrene over a range of reaction conditions

A comprehensive experimental investigation of nitroxide‐mediated radical polymerization (NMRP) of styrene using 2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO) as controller is presented. Polymerizations with a bimolecular initiator (benzoyl peroxide; BPO) were carried out at 120 and 130°C, with TEMPO/BPO molar ratios ranging from 0.9 to 1.5. Results indicate that increasing temperature increases the rate of polymerization while the decrease in molecular weights is only slight. It was also observed that increasing the ratio of TEMPO/BPO decreased both the rate of polymerization and molecular weights. Probably for the first time in the history of such investigations, the paper contains a comprehensive database, appropriate for parameter estimation in aid of future modelling studies, since it comes from a systematic data collection containing independent replication.     

Substituent effects on trithiocarbonates‐mediated polymerization of styrene

In the present work, the effectiveness of five trithiocarbonates (TTCs) as mediating agents in the reversible addition fragmentation chain transfer (RAFT) polymerization and photopolymerization of styrene (St) were investigated. The five TTCs including S,S′‐bis(α, α′‐dimethyl‐α″‐acetic acid) trithiocarbonate (TTC1), bis(2‐oxo‐2‐phenyl‐ethyl) trithiocarbonate (TTC2), 3‐(2‐carboxyethylsulfanylthiocarbonylsulfanyl)‐propionic acid (TTC3), 2‐(2‐carboxyethylsulfanylthiocarbonylsulfanyl)propionic acid (TTC4), and 2‐(2‐carboxyethylsulfanylthiocarbonylsulfanyl)‐2‐methylpropionic acid (TTC5) were synthesized, in which the substitution patterns (groups Z and R) of the TTCs were varied. The dynamic behavior of TTC1, TTC2, TTC4, and TTC5‐mediated polymerization of St was well described by pseudo first‐order kinetics. In the presence of TTC1, TTC2, TTC4, and TTC5, the polydispersity indices changed with increasing conversion in the range of 1.10–1.25 typical for RAFT‐prepared (co)polymers, and were well below the theoretical lower limit of 1.50 for a normal free radical polymerization. Transfer coefficients of TTCs in St polymerization at 70°C were estimated by using the Mayo method. Density functional theory calculations successfully predicted the effect of the structure of TTCs on the activity of RAFT agents in a qualitative manner. The calculated results for RAFT agents agreed well with the experimental results. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Controlled radical polymerization of N‐isopropylacrylamide initiated by photofunctional 2‐(N,N‐diethyldithiocarbamyl)isobutyric acid sodium salt in aqueous medium

Photopolymerizations of N‐isopropylacrylamide (NIPAAm) were carried out in water, initiated by 2‐(N,N‐diethyldithiocarbamyl)isobutyric acid sodium salt (DTCA‐Na) as water‐soluble initiator under UV irradiation. The first‐order time‐conversion plots showed slowly decreasing slopes indicating a slow decrease of the active radical concentration. The number‐average molecular weight (M_n) of the obtained poly(N‐isopropylacrylamide) (PNIPAAm) increased in direct proportion, roughly, to monomer conversion. Until ca. 60% of conversion, the polydispersity was relatively narrow (ca. 1.6). 1‐Vinyl‐2‐pyrrolidone (VP) could also be polymerized in living fashion with such PNIPAAm precursor as a macroinitiator, because PNIPAAm exhibited dithiocarbamate (DC) groups at terminal ends. It was concluded that the polymerization of NIPAAm proceeded via a controlled radical mechanism in the range ～60% of conversion. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3233–3238, 2004     

Benzotriazinyl‐mediated controlled radical polymerization of styrene

The stable free radical polymerization (SFRP) process based on (1,3‐diphenyl‐1,4‐dihydro‐1,2,4‐benzotriazin‐4‐yl), the so‐called ‘Blatter radical’, and several C‐7 substituted derivatives is introduced for the first time for the polymerization of styrene. Polystyrenes characterized by polydispersity indices in the 1.05 ? 1.27 range were obtained in the presence of the Blatter radical and its derivatives containing CF₃, Ph, Fur‐2‐yl and 4‐PhC₆H₄ substituents, while polymerization proceeded either in a non‐controlled manner or in very low polymerization yields in the presence of derivatives containing halogen (Cl, Br, I) substituents. This preliminary investigation, demonstrating the potential use of the Blatter radical and its derivatives in mediated SFRP, creates new opportunities to design and develop radicals to optimize performance in such polymerization processes. © 2013 Society of Chemical Industry     

Controlled radical polymerization of poly(methyl methacrylate‐g‐epichlorohydrin) using N,N‐dithiocarbamate‐mediated iniferters

Poly(epichlorohydrin) (PECH) with pendent N,N‐diethyl dithiocarbamate groups (PECH‐DDC) was prepared by reaction of PECH with sodium N,N‐diethyl dithiocarbamate (DDC) in anhydrous ethanol, before being used as a macrophotoinitiator for the graft polymerization of methyl methacrylate. Photopolymerization was carried out in a photochemical reactor at a wavelength greater than 300 nm. Controlled radical polymerization was confirmed by the linear increase of the molecular weight of polymers with conversion. The polydispersity remained at 1.4–1.6 during polymerization. The formation of PMMA‐g‐PECH copolymer was characterized by GPC, ¹H‐NMR, FTIR spectroscopy, and DSC. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Radical polymerization of styrene by a hexa‐substituted‐ethane type thermal iniferter

The bulk polymerization of styrene (St) initiated with a hexa‐substituted‐ethane type initiator, diethyl 2,3‐dicyano‐2,3‐diphenylsuccinate (DCDPS), was investigated. It was found that DCDPS served as a thermal iniferter for polymerization of St and the polymerization had some characteristics in common with living radical polymerization, ie, both the yield and the molecular weight of the resulting polymers increased with increasing reaction time. The resultant polystyrene can act as a macroinitiator for chain‐extension polymerization of St or for radical polymerization of methyl methacrylate to give a block copolymer. © 2001 Society of Chemical Industry     

Synthesis of two‐end‐functionalized copolymer of styrene and methyl methacrylate via living radical polymerization

The random copolymers (HO‐P(St‐r‐MMA)‐COOH) of styrene (St) and methyl methacrylate (MMA) with hydroxyl group at one end and carboxyl group at another end were synthesized by nitroxide‐mediated living radical polymerization initiated by 4,4′‐azobis(4‐cyanovaleric acid) (ACVA) and 4‐hydroxyl‐2,2,6,6–tetramethylpiperidineoxyl (TEMPO‐OH). The experimental results have shown that all synthesized copolymers have narrow molecular weight distribution. The conversion of monomers and the molecular weight of copolymer increase with polymerization time. Thus, a copolymerization mechanism containing living radical polymerization is suggested. The use of this method permits the copolymer with two functional chain ends and controllable molecular weight as well as low molecular weight distribution. X‐ray photoelectron spectroscopy result shows that the synthesized copolymers can be tethered on the surface of silicon wafer through the reaction between the hydroxyl end of the copolymer and native oxide layer on the wafer. In addition, an organic/inorganic hybrid surface has achieved by treating copolymer tethered Si‐substrates with SiCl₄ vapor. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3118–3122, 2006     

Nitroxide‐mediated polymerization of styrene initiated from the surface of montmorillonite clay platelets

Polymer‐grafted montmorillonite (MMT) hybrid composites which possess a hard backbone of MMT and a soft shell of brush‐like polystyrene (PSt) were prepared via “grafting from” strategy based on nitroxide‐mediated radical polymerization (NMRP) using 2,2,6,6‐tetramethylpiperidine‐N‐oxyl (TEMPO) as mediator. Three steps were used to graft PSt chains to the surface of MMT: anchoring of methacrylatoethyl trimethyl ammonium chloride (DMC) onto the surface of MMT by ion exchange reaction first. And then, the surface alkoxyamine initiator was produced in a one‐step process by reacting simultaneously TEMPO, BPO, and DMC in the presence of MMT. Next, PSt chains with controlled molecular weights and polydispersities were grown from the alkoxyamine functionalized MMT surface. The prepared PSt‐g‐MMT hybrid particles have been extensively characterized by FTIR, XPS, XRD, TGA, TEM, respectively. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Organometallic mediated radical polymerization

Controlled radical polymerization has become increasingly important over the past decade and a half, allowing for the facile synthesis of specific macromolecular architectures with excellent control over the chemical and physical properties. This article presents an organized and detailed review of one particular CRP technique, organometallic mediated radical polymerization (OMRP), focusing on the individual catalysts developed, their efficacy and monomer scope. Rhodium, cobalt, molybdenum, osmium, iron, palladium, titanium, chromium and vanadium mediated radical polymerizations are presented alongside organo-main group mediated reactions. A separate section reviews the types of copolymers which have been synthesized using OMRP techniques. An attempt is made to unify the many disparate names which have previously been used for OMRP by virtue of the common mechanistic aspects displayed by the different catalyst systems. A mechanistic discussion highlights the similarities and differences between these systems and examines the interplay between reversible termination and degenerative transfer OMRP and competing 1-electron redox processes.     

Synthesis of hydroxyl‐terminated copolymer of styrene and 4‐vinylpyridine via nitroxide‐mediated living radical polymerization

The random copolymers of styrene (St) and 4‐vinylpyridine (4‐VP) with hydroxyl end group and low polydispersities were synthesized by nitroxide‐mediated living radical polymerization initiated by azobisisobutyronitrile (AIBN) and 4‐hydroxyl‐2,2,6,6–tetramethylpiperidine‐oxyl (TEMPO‐OH). The experimental results have shown that all synthesized copolymers have narrow molecular weight distribution. The conversion of monomers and the molecular weight of copolymer increased with polymerization time. The copolymerization rate is affected by molar ratios of HTEMPO to AIBN. ¹H‐Nuclear magnetic resonance spectra shows that one end of copolymers was capped by TEMPO‐OH moiety. The use of this method permits the copolymer with hydroxyl chain end and controllable molecular weight and molecular weight distribution. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1842–1847, 2004     

Radical thermo‐ and sonopolymerization of methyl methacrylate initiated by iodobenzene 1,1‐diacetate

The efficiency of iodobenzene 1,1‐diacetate or (diacetoxyiodo)benzene (DAIB) as a thermo‐ and sono‐initiator of methyl methacrylate (MMA) in radical bulk polymerization is tested. The polymerization kinetics and molecular‐mass characteristics support an assumption for a combined polymerization mechanism including a classical bimolecular termination with chain transfer reaction and iniferter quasi‐living polymerization. In addition to the equilibrium formation and degradation of the ‘dormant’ polymer ends, other possible decomposition reactions of the hypervalent iodine bond are the probable reason for the deviation of this polymerization from the iniferter polymerization mechanism. These reactions bear some similarity to the two‐step addition–fragmentation chain transfer mechanism of controlled radical polymerization. The application of the poly(MMA) obtained as a macroinitiator is evidence of ‘dormant’ chain end formation. © 2001 Society of Chemical Industry     

Synthesis and reactivity of functionalized alkoxyamine initiators for nitroxide‐mediated radical polymerization of styrene

The synthesis and examination of different functionalized (2,2,6,6‐tetramethyl‐1‐piperidinyloxy free radical) TEMPO‐containing alkoxyamine initiators for nitroxide‐mediated radical polymerization of styrene are reported. Initiators with ester and carbonate functional groups were synthesized by a low‐temperature radical‐abstraction reaction of the functionalized ethylbenzene in the presence of TEMPO to introduce the functional groups onto the initiating chain‐end of polystyrene. An initiator with two alkoxyamine groups symmetrically located at each end of a carbonate bond was also synthesized and used for nitroxide‐mediated styrene polymerization. Styrene polymerization using these initiators followed first‐order kinetics up to approximately 60 min at 140 °C or 30% monomer conversion. Alkoxyamines bearing an acetoxy or tert‐butylcarbonate group at the p‐position of 1‐(2,2,6,6‐tetramethyl‐1‐piperidinyloxy)ethylbenzene behave in a similar way to the unfunctionalized initiator. With an initiator containing two alkoxyamine groups, the resulting polymer molecular weight was twice that of the polymer obtained from initiators with only one alkoxyamine group, as expected from propagation from both chain‐ends. Upon hydrolysis of the carbonate bond, it was revealed that equivalent polymer chain growth occurred from each alkoxyamine site in the difunctional initiator. Copyright © 2003 Society of Chemical Industry     

Surface‐initiated atom transfer radical polymerization (ATRP) of styrene from silica nanoparticles under UV irradiation

Diethyldithiocarbamyl‐modified silica nanoparticles were prepared and used as macroinitiator for the surface‐initiated atom transfer radical polymerization (SI‐ATRP) of styrene under UV irradiation. Well‐defined polymer chains were grown from the nanoparticle surfaces to yield particles composed of a silica core and a well‐defined, densely grafted outer PS layer with a mass ratio of styrene to silica, or percentage grafting, of 276.3% after an UV irradiation time of 5 h. Copyright © 2004 Society of Chemical Industry     

The architecture of hydroxy‐functionalized aPS‐b‐random copolymer‐b‐PE via one‐pot strategy combining living free radical polymerization with coordination polymerization

The copolymerization of styrene with ethylene was promoted by CpTiCl₃/BDGE/Zn/MAO catalyst system combining free radical polymerization with coordination polymerization via sequential monomer addition strategy in one‐pot. The effect of polymerization conditions such as temperature, time, ethylene pressure, and Al/Ti molar ratio on the polymerization performance was investigated. The hydroxy‐functionalized aPS‐b‐random copolymer‐b‐PE triblock copolymer was obtained by solvent extraction and determined by GPC, DSC, WAXD, and ¹³C‐NMR. The DSC result indicated that the aPS‐b‐random copolymer‐b‐PE had a T_g at 87°C and a T_m at 119°C which attributed to the T_g of aPS segment and the T_m of PE segment, respectively. The microstructure of the hydroxy‐functionalized aPS‐b‐random copolymer‐b‐PE was further confirmed by WAXD, ¹³C‐NMR, and ¹H‐NMR analysis; and these results demonstrated that the obtained block copolymer consisted of aPS segment, S‐E random copolymer segment, and crystalline PE segment. The connection polymerization of the hydroxy‐functionalized aPS with random copolymer‐b‐PE was revealed by GPC results. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis of new open‐chain alkoxyamines and their evaluation for nitroxide‐mediated radical polymerization

New readily available open‐chain alkoxyamines have been synthesized and evaluated as unimolecular initiators for nitroxide‐mediated radical polymerization of styrene and n‐butyl acrylate. The observed moderate control of polymerization is explained by the low thermostability of the parent nitroxide. Copyright © 2004 Society of Chemical Industry     

One‐step synthesis of star‐block copolymers via simultaneous free radical polymerization of styrene and ring opening polymerization of ε‐caprolacton using tetrafunctional iniferter

Star‐block copolymers comprised of poly(styrene) (S) core and four poly(ε‐caprolacton) (ε‐CL) arms were synthesized by the combination of free radical polymerization (FRP) of S and ring opening polymerization (ROP) of ε‐CL in one‐step in the presence of tetrafunctional ineferter. The block copolymers were characterized by ¹H‐NMR and FTIR spectroscopy, gel permeation chromatography (GPC), and fractional precipitation method. ¹H ‐NMR and FTIR spectroscopy and GPC studies of the obtained polymers indicate that star‐block copolymers easily formed as result of combination FRP and ROP in one‐step. The γ values (solvent/precipitant volume ratio) were observed between 1.04–2.72 (mL/mL) from fractional measurements. The results show that when the initial S feed increased, the molecular weights of the star‐block copolymers also increased and the polydispersities of the polymers decreased. M_w/M_n values of the products were measured between 1.4 and 2.86 from GPC. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis of poly(cyclohexene oxide)‐block‐polystyrene by combination of radical‐promoted cationic polymerization,atom transfer radical polymerization and click chemistry

The combination of radical‐promoted cationic polymerization, atom transfer radical polymerization (ATRP) and click chemistry was employed for the efficient preparation of poly(cyclohexene oxide)‐block‐polystyrene (PCHO‐b‐PSt). Alkyne end‐functionalized poly(cyclohexene oxide) (PCHO‐alkyne) was prepared by radical‐promoted cationic polymerization of cyclohexene oxide monomer in the presence of 1,2‐diphenyl‐2‐(2‐propynyloxy)‐1‐ethanone (B‐alkyne) and an onium salt, namely 1‐ethoxy‐2‐methylpyridinium hexafluorophosphate, as the initiating system. The B‐alkyne compound was synthesized using benzoin photoinitiator and propargyl bromide. Well‐defined bromine‐terminated polystyrene (PSt‐Br) was prepared by ATRP using 2‐oxo‐1,2‐diphenylethyl‐2‐bromopropanoate as initiator. Subsequently, the bromine chain end of PSt‐Br was converted to an azide group to obtain PSt‐N₃ by a simple nucleophilic substitution reaction. Then the coupling reaction between the azide end group in PSt‐N₃ and PCHO‐alkyne was performed with Cu(I) catalysis in order to obtain the PCHO‐b‐PSt block copolymer. The structures of all polymers were determined. Copyright © 2010 Society of Chemical Industry