Living ring-opening polymerization of cyclic thiocarbonate

This work deals with the cationic ring-opening polymerization of a cyclic thiocarbonate, 5,5-dimethyl-1,3-dioxane-2-thione (1). The polymerization was carried out with 2 mol% of trifluoromethanesulfonic acid, methyl trifluoromethanesulfonate, boron trifluoride etherate, or triethyloxonium tetrafluoroborate as an initiator to afford the polythiocarbonate with the narrow molecular weight distribution (M_n = 11200-31000, M_w/M_n = 1.04-1.15). The molecular weight of the obtained polymer could be controlled by the feed ratio of the monomer to the initiator and increased when the second monomer was added to the polymerization mixture after quantitative consumption of 1 in the first stage, supporting that the cationic ring-opening polymerization of 1 proceeded via a living process.     

Polymers of carbonic acid. XXVII. Macrocyclic polymerization of trimethylene carbonate

2,2-Dibutyl-2-stanna-1,3-dioxepane (DSDOP) was used as cyclic initiator for the polymerization of trimethylene carbonate (TMC). The polymerizations were either conducted in concentrated chlorobenzene solution at 50 and 80°C or in bulk at 60 and 120°C. With monomer/initiator ratios ≤100 the conversion was complete within 2 h at 80°C and within 12 h at 50°C. Variation of the reaction time revealed that the rapid polymerization is followed by a relatively rapid (backbiting) degradation even at 80°C. The polymerizations in bulk at 60°C were somewhat slower than those at 80°C in solution, but the influence of degradation reactions was less pronounced. With optimized reaction time the number average molecular weight (M_n) roughly parallels the monomer/initiator ratio and M_n's up to 100,000 were obtained. In contrast to a classical living polymerization broader polydispersities (1.5–1.7) were found. In the case of 5,5-dimethyltrimethylene carbonate rapid degradation and chain transfer reactions prevented the formation of high molecular weight polymers. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2179–2189, 1999     

Iron‐mediated atom transfer radical polymerization of styrene with tris(3,6‐dioxaheptyl) amine as a ligand

The atom transfer radical bulk polymerization of styrene with FeX₂ (X = Br or Cl)/tris(3,6‐dioxaheptyl) amine as the catalyst system was successfully implemented at 110 °C. The number‐average molecular weight of the polymers with a narrow molecular weight distribution (weight‐average molecular weight/number‐average molecular weight = 1.2–1.5) increased linearly with the monomer conversion and matched the predicted molecular weight. The polymerization rate, initiation efficiency, and molecular weight distribution were influenced by the selection of the initiator and iron halide. The high functionality of the halide end group in the obtained polymers was confirmed by both ¹H NMR and a chain‐extension reaction. Because of its water solubility, the iron complexes could be removed easily from the reaction mixture through the washing of the polymerization mixture with water. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 483–489, 2006     

Investigation of catalyst‐transfer condensation polymerization for synthesis of poly(p‐phenylenevinylene)

Kumada‐Tamao coupling polymerization of 1,4‐dialkoxy‐2‐bromo‐5‐(2‐chloromagnesiovinyl)benzene ( 1 ) and 1,4‐dialkoxy‐2‐(2‐bromovinyl)‐5‐chloromagnesiobenzene ( 2 ) with a Ni catalyst and Suzuki‐Miyaura coupling polymerization of 2‐{2‐[(2,5‐dialkoxy‐4‐iodophenyl)]vinyl}‐4,4,5,5‐tetramethyl‐1,3,2‐dioxaborolane ( 3 ), its bromo counterpart 4 , and 2,5‐dialkoxy‐4‐(2‐bromovinyl)phenylboronic acid ( 5 ) with a Pd initiator were investigated under catalyst‐transfer condensation polymerization conditions for the synthesis of well‐defined poly(p‐phenylenevinylene) (PPV). The Kumada‐Tamao polymerization of vinyl Grignard‐type monomer 1 with Ni(dppp)Cl₂ at room temperature did not proceed, whereas aryl Grignard‐type monomer 2 afforded oligomers of low molecular weight. Matrix‐assisted laser desorption ionization time‐of‐flight (MALDI‐TOF) mass spectra of the polymer obtained from 2 implied that the Grignard end group reacted with tetrahydrofuran to terminate polymerization. On the other hand, Suzuki‐Miyaura polymerization of vinyl boronic acid ester type monomers 3 and 4 and phenylboronic acid type monomer 5 with a Pd initiator and aqueous KOH at ?20 °C to room temperature yielded the corresponding PPV with high molecular weight within a few minutes. However, the molecular weight distribution was broad, and MALDI‐TOF mass spectra showed the peaks of polymers bearing no initiator unit at the chain end, as well as those of polymers with the initiator unit. These results indicated that intermolecular chain transfer of the Pd catalyst occurred. Dehalogenation and disproportionation of the growing end also took place as side reactions. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2643‐2653     

Cationic polymerization with p-substituted benzyl p-hydroxyphenyl methyl sulfonium salts: Effect of substituents and mechanistic aspects of initiation reaction

Various p-substituted benzyl p-hydroxyphenyl methyl sulfonium salts ( 2 ) were synthesized and their initiator activities were evaluated in bulk polymerization of glycidyl phenyl ether (PGE). The order of the activity was found to be 2b (X = CH₃) > 2a (X = H) ≈ 2c (X = Cl) > 2d (X = NO₂), indicating that the introduction of an electron-donating group enhanced the activity. In Hammett's plots, the logarithm of the ratio of the polymerization rates (log k_x/k_H) was correlated with σ⁺_ρ better than with σ_p and a negative ρ⁺ value (-1.18) was obtained. Reaction of 2a with benzyl mercaptan mainly gave dibenzyl sulfide and p-hydroxyphenyl methyl sulfide. The obtained results seemed to demonstrate that the OH group of the aryl group yielded no proton as initiator for the polymerization, whereas the benzyl group caused the polymerization, which was initiated by the corresponding benzyl cation formed by C? S bond cleavage. © 1993 John Wiley & Sons, Inc.     

In situ atom transfer radical polymerization of styrene with a tetraethylthiuram disulfide/copper bromide/2,2′‐bipyridine initiating system

The living radical polymerization of styrene in bulk was successfully performed with a tetraethylthiuram disulfide/copper bromide/2,2′‐bipyridine (bpy) initiating system. The initiator Et₂NCS₂Br and the catalyst cuprous bromide (CuBr) were produced from the reactants in the system through in situ atom transfer radical polymerization (ATRP). A plot of natural logarithm of the ratio of original monomer concentration to monomer concentration at present, ln([M]₀/[M]) versus time gave a straight line, indicating that the kinetics was first‐order. The number‐average molecular weight from gel permeation chromatography (GPC) of obtained polystyrenes did not agree well with the calculated number‐average molecular weight but did correspond to a 0.5 initiator efficiency. The polydispersity index (i.e., the weight‐average molecular weight divided by the number‐average molecular weight) of obtained polymers was as low as 1.30. The resulting polystyrene with α‐diethyldithiocarbamate and ω‐Br end groups could initiate methyl methacrylate polymerization in the presence of CuBr/bpy or cuprous chloride/bpy complex catalyst through a conventional ATRP process. The block polymer was characterized with GPC, ¹H NMR, and differential scanning calorimetry. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 4001–4008, 2001     

End-Functionalized polymers by living cationic polymerization. IV. Poly(vinyl ethers) with acidic or basic terminal groups by functional initiator method

Carboxylic acid or primary amine-terminated poly(isobutyl vinyl ethers) were synthesized by living cationic polymerizations with functionalized initiators (CH₃CHIO? CH₂CH₂ ? X; X: that are the adducts of the corresponding vinyl ethers (CH₂ ? CH ? OCH₂CH₂? X) with hydrogen iodide. In the presence of iodine, these initiators induced living cationic polymerization of isobutyl vinyl ether to give polymers with the α-end group of X originating from the initiators. The polymer molecular weights were regulated by the monomer to initiator feed ratio and the molecular weight distributions were very narrow (M _w/M _n ≤ 1.15). Subsequent deprotection of the terminal group X led to polymers with a terminal carboxylic acid or primary amine. ¹H- and ¹³C-NMR analyses showed that the end functionalities of these polymers were all close to unity.     

Acidic peroxo salts: A new class of initiators for vinyl polymerization. III. Kinetics of polymerization of methyl methacrylate initiated by potassium monopersulfate catalyzed by Co(II)

Kinetics of the polymerization of methyl methacrylate by an acidic peroxo salt like potassium monopersulfate catalyzed by Co(II) have been investigated in aqueous medium, over the range of 35–50°C. The rates of polymerization (R_p) have been studied at various concentrations of monomer and initiator. The efficiencies of various metal salts in catalyzing the polymerization have been evaluated from the observed value of R_p. The effects of catalyst (CoSO₄), initiator, monomer, and various concentrations of FeCl₃ on R_p and percentage conversion have been studied. The end groups of the recovered polymers have been studied using standard methods. From the observed end groups and kinetic results, a reaction scheme has been proposed involving initiation by S O₄· or OH· radicals, generated by the interaction of the initiator with cobalt sulfate and termination of the polymer chains by mutual combination.     

Electrochemical polymerization to a controlled molecular weight distribution

Living polyanions were generated by the passage of electrolytic current through solutions in tetrahydrofuran (THF). The concentration of living polyanions was controlled by the current and could be increased by further electrolysis or decreased by electrolysis with reversal of polarity. Inasmuch as the living end (LE) concentration determines the molecular weight at a given monomer concentration it was possible to program a molecular weight distribution. Model distributions were attempted by (1) indirect methods in which an electrolytic formation of initiating dianions was followed by monomer addition, polymerization, current reversal and further polymerization and (2) direct methods in which monomer was present throughout the electrolysis. The molecular weight distributions were obtained by gel-permeation chromatography and corresponded closely to the values calculated from the simple kinetic model of anionic polymerization. For styrene a sharp low molecular weight fraction and a clear binodal high molecular weight fraction were obtained. The binodal character was attributed to the growth of active single-ended and double-ended polyanions. The yields of high and low molecular weight material, the ratios of molecular weights obtained, and the values of the molecular weights were in agreement with expectation. The direct electrochemical polymerization methods were employed for α-methylstyrene, but the high k_p for styrene thwarted efforts to apply the direct technique with this monomer.     

SET‐LRP of acrylonitrile catalyzed by tin powder

Sn(0)‐mediated single electron transfer‐living radical polymerization (SET‐LRP) of acrylonitrile (AN) with carbon tetrachloride (CCl₄) as initiator and hexamethylenetetramine (HMTA) as ligand in N, N‐dimethylformamide (DMF) was studied. The polymerization obeyed first order kinetic. The molecular weight of polyacrylonitrile (PAN) increased linearly with monomer conversion and PAN exhibited narrow molecular weight distributions. Increasing the content of Sn(0) resulted in an increase in the molecular weight and the molecular weight distribution. Effects of ligand and initiator were also investigated. The block copolymer PAN‐b‐polymethyl methacrylate with molecular weight at 126,130 and polydispersity at 1.36 was successfully obtained. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Polymerization of styrene with tetramethylthiuram disulfide as an initiator in the presence of 2,2,6,6‐tetramethyl‐1‐piperidinyloxy

The bulk polymerization of styrene was investigated with tetramethylthiuram disulfide (TMTD) as an initiator in the presence of 2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO) at 123 °C. The polymerization proceeded in a controlled/living way; that is, the polymerization rate was first‐order with respect to the monomer concentration, and the molecular weight increased linearly with conversion. The molecular weights of the polymers obtained were close to the theoretical values, and the molecular weight distributions were relatively low (weight‐average molecular weight/number‐average molecular weight = 1.1–1.3). The rate of polymerization with TMTD as an initiator was faster than that with benzoyl peroxide, and the rate was independent of the initial concentration of TMTD in the presence of TEMPO. The obtained polystyrene was functionalized with ultraviolet‐light‐sensitive ? SC(S)N(CH₃)₂ groups, which was characterized with ¹H NMR spectroscopy. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 543–551, 2005     

Living radical polymerization of acrylonitrile catalyzed by copper with a high concentration of radical initiator and its application in removal of Ag(I) after modification

In this study, we reported the synthesis of polyacrylonitrile (PAN) via living radical polymerization in N, N‐dimethylformamide using carbon tetrachloride as initiator, copper(II) chloride (CuCl₂)/hexamethylenetetramine as catalyst system, and 2,2‐azobisisobutyronitrile as a high concentration of thermal radical initiator. The polymerization proceeded in controlled/living manner as indicated by first‐order kinetics of the polymerization with respect to the monomer concentration, linear increase of the molecular weight with monomer conversion and narrow polydispersity. Higher polymerization rate and narrower molecular weight distributions were observed with CuCl₂ less than 50 ppm. The rate of polymerization showed a trend of increase along with temperature. The modified PAN containing amidoxime group was used for extraction of Ag(I) ions from aqueous solutions. The adsorption kinetics data indicated that the adsorption process followed pseudo‐second‐order rate model. The isotherm adsorption process could be described by the Freundlich isotherm model. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

RAFT synthesis of a water‐soluble triblock copolymer of poly(styrenesulfonate)‐b‐poly(ethylene glycol)‐b‐poly(styrenesulfonate) using a macromolecular chain transfer agent in aqueous solution

Triblock copolymers of poly(styrenesulfonate)‐b‐poly(ethylene glycol)‐b‐poly(styrenesulfonate) with narrow molecular weight distribution (M_w/M_n = 1.28–1.40) and well‐defined structure have been synthesized in aqueous solution at 70 °C via reversible addition‐fragmentation chain transfer polymerization. Poly(ethylene glycol) (PEG) capped with 4‐cyanopentanoic acid dithiobenzoate end groups was used as the macro chain transfer agent (PEG macro‐CTA) for sole monomer sodium 4‐styrenesulfonate. The reaction was controllable and displayed living polymerization characteristics and the triblock copolymer had designed molecular weight. The reaction rate depended strongly on the CTA and initiator concentration ratio [CTA]₀/[ACPA]₀: an increase in [CTA]₀/[ACPA]₀ from 1.0 to 5.0 slowed down the polymerization rate and improved the molecular weight distribution with a prolonged induction time. The polymerization proceeded, following first‐order kinetics when [CTA]₀/[ACPA]₀ = 2.5 and 5.0. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3698–3706, 2007     

MALDI‐TOF‐MS analysis of living cationic polymerization of vinyl ethers. II. Living nature of growing end and side reactions

Matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry analysis revealed that the HCl–vinyl ether adduct/SnCl₄/n‐Bu₄NCl initiating system induced living cationic polymerization of isobutyl vinyl ether in CH₂Cl₂ at ?78 °C, that is, the well‐resolved spectra demonstrated that the produced polymers consist of only one series of polymers carrying one initiator fragment at the α end and one methoxy group originated from quenching with methanol at the ω end. The polymer molecular weight as well as the terminal structure were unchanged even when the reaction mixtures were kept unquenched at ?78 °C for an interval of more than five times longer than the reaction period after complete consumption of monomer, which indicates the long lifetime of the living end even under such starved conditions. In contrast, the polymers obtained at a higher temperature, ?15 °C, showed an additional minor series of polymers formed via proton initiation, originating from adventitious water. Under the starved conditions, other side reactions occurred to generate minor series of polymers with an aldehyde ω end or a diisobutyl acetal ω end. Rather surprisingly, however, unsaturated C?C end groups were not detected, which means the absence of β‐proton elimination under these conditions. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1249–1257, 2001     

Controlled radical polymerization of 2‐hydroxyethyl methacrylate initiated by photofunctional 2‐(N,N‐diethyldithiocarbamyl)isobutyric acid

We demonstrated that density functional theory calculations provide a reliable and quantitative prediction of the trends in C? S bond dissociation energies using several model compounds as photoinitiator. On the basis of this information, we designed a possible photofunctional initiator for the polymerization of hydrophilic vinyl monomers. Photopolymerization of 2‐hydroxyethyl methacrylate (HEMA) hydrophilic monomer was carried out in ethanol initiated by 2‐(N,N‐diethyldithiocarbamyl)isobutyric acid (DTCA) under UV irradiation. We performed the first‐order time‐conversion plots in this polymerization system, and the straight line in the semilogarithmic coordinates indicated first order in monomer. The molecular weight of the poly(2‐hydroxyethyl methacrylate) (PHEMA) increased with increasing conversion. The molecular weight distribution (M_w/M_n) of the PHEMA was about 1.5. Methyl methacrylate (MMA) could also be polymerized in a living fashion with such a PHEMA precursor as a macroinitiator because PHEMA exhibited a dithiocarbamate (DC) group at its terminal end. This system could be applied to the architecture of amphiphilic block copolymers. It was concluded that these polymerization systems proceeded with controlled radical mechanism. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 76–82, 2004     

Synthesis and kinetic analysis of DPE controlled radical polymerization of MMA

The 1,1‐diphenylethene (DPE) controlled radical polymerization of methyl methacrylate was performed at 80 °C by using AIBN as an initiator and DPE as a control agent. It was found that the molecular weight of polymer remained constant with monomer conversion throughout the polymerization regardless of the amounts of DPE and initiator in formulation. To understand the result of constant molecular weight of living polymers in DPE controlled radical polymerization, a living kinetic model was established in this research to evaluate all the rate constants involved in the DPE mechanism. The rate constant k₂, corresponding to the reactivation reaction of the DPE capped dormant chains, was found to be very small at 80 °C (1 × 10^?5 s^?1), that accounted for the result of constant molecular weight of polymers throughout the polymerization, analogous to a traditional free radical polymerization system that polymer chains were terminated by chain transfer. The polydispersity index (PDI) of living polymers was well controlled <1.5. The low PDI of obtained living polymers was due to the fact that the rate of growing chains capped by DPE was comparable with the rate of propagation. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009     

Living carbocationic polymerization. IV. Living polymerization of isobutylene

Truly living polymerization of isobutylene (IB) has been achieved for the first time by the use of new initiating systems comprising organic acetate-BCl₃ complexes under conventional laboratory conditions in various solvents from ?10 to ?50°C. The overall rates of polymerization are very high, which necessitated the development of the incremental monomer addition (IMA) technique to demonstrate living systems. The living nature of the polymerizations was demonstrated by linear M _n versus grams polyisobutylene (PIB) formed plots starting at the origin and horizontal number of polymer molecules formed versus amount of polymer formed plots. DP _n obeys [IB]/[CH₃COOR^t · BCl₃]. Molecular weight distributions (MWD) are very narrow in homogeneous systems (M _w/M _n = 1.2–1.3) whereas somewhat broader values are obtained when the polymer precipitates out of solution (M _w/M _n = 1.4–3.0). The MWDs tend to narrow with increasing molecular weights, i.e., with the accumulation of precipitated polymer in the reactor. Traces of moisture do not affect the outcome of living polymerizations. In the presence of monomer both first and second order chain transfer to monomer are avoided even at ?10°C. The diagnosis of first and second order chain transfer has been accomplished, and the first order process seems to dominate. Forced termination can be effected either by thermally decomposing the propagating complexes or by nucleophiles. In either case the end groups will be tertiary chlorides. The living polymerization of isobutylene initiated by ester. BCl₃ complexes most likely proceeds by a two-component group transfer polymerization.     

Synthesis of polymers by template polymerization. I. Template polymerization of poly(methacrylic acid) with β‐cyclodextrin

A novel template monomer with multiple methacryloyl groups was synthesized with β‐cyclodextrin by the acetylation of primary hydroxyl groups and the esterification of secondary hydroxyl groups with methacrylic acid anhydride. The average number of methacryloyl groups in the monomer was 11. The radical polymerization of the monomer was carried out with the following initiators: α,α′‐azobisisobutylonitrile, H₂O₂? Fe²⁺ redox initiator, p‐xylyl‐N,N‐dimethyldithiocarbamate (XDC), and α‐bromo‐p‐xylyl‐N,N‐dimethyldithiocarbamate (BXDC). When the concentration of the monomer was less than 4.12 × 10^?3 M, polymerization was limited inside the molecule, and gelation of the system was hindered. For controlled radical photopolymerization with XDC and BXDC, the methacryloyl groups of the monomer were homogeneously polymerized, and poly(methacrylic acid) with a narrow molecular weight distribution was obtained by the hydrolysis of the polymerized products. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3539–3546, 2001     

Radical polymerization behavior of ethyl ortho-formylphenyl fumarate involving intramolecular hydrogen abstraction

The radical polymerization behavior of ethyl ortho-formyl-phenyl fumarate (EFPF) using dimethyl 2,2′-azobisisobutyrate (MAIB) as initiator was studied in benzene kinetically and ESR spectroscopically. The polymerization rate (R_p) at 60°C was given by R_p = k[MAIB]^0.76[EFPF]^0.56. The number-average molecular weight of poly(EFPF) was in the range of 1600–2900. EFPF was also easily photopolymerized at room temperature without any photosensitizer probably because of the photosensitivity of the formyl group of monomer. Analysis of ¹H? and ¹³C-NMR spectra of the resulting polymer revealed that the radical polymerization of EFPF proceeds in a complicated manner involving vinyl addition and intramolecular hydrogen-abstraction. The polymerization system was found to involve ESR-observable poly(EFPF) radicals under the actual polymerization conditions. ESR-determined rate constant (2.4–4.0 L/mol s) of propagation at 60°C increased with decreasing monomer concentration, which is mainly responsible for the observed low de-pendency of R_p on the EFPF concentration. Copolymerizations of EFPF with some vinyl monomers were also examined. © 1995 John Wiley & Sons, Inc.     

Living cationic polymerization of cis- and trans-ethyl propenyl ethers and synthesis of block copolymers with isobutyl vinyl ether

The cationic polymerization of cis- and trans-ethyl propenyl ethers (EPE, CH₃? CH?CH? O? C₂H₅), initiated by a mixture of hydrogen iodide and iodine (HI/I₂ initiator) at ?40°C in nonpolar media (toluene and n-hexane), led to living polymers of controlled molecular weights and a narrow molecular weight distribution (MWD) (M?_w/M?_n = 1.2–1.3). The geometrical isomerism of the monomer did not affect the living character of the polymerization. ¹³C NMR stereochemical analysis of the polymers showed that the living propagating end is sterically less crowded than nonliving counterparts generated by conventional Lewis acids (e.g., BF₃OEt₂). New block copolymers between EPE (cis or trans) and isobutyl vinyl ether were also prepared by sequential living polymerization of the two monomers.