Controlled Radical Mechanism Research Articles

Degree of branching of hyperbranched polystyrenes via a controlled radical mechanism of an inimer: Determination by a kinetic approach

AbstractWe studied, with a kinetic approach, the living nature and degree of branching (DB) of the formation of hyperbranched polystyrene by the free‐radical photopolymerization of 2‐(N,N‐diethyldithiocarbamyl)methylstyrene in benzene. The free‐radical polymerization proceeded with a living radical mechanism. Subsequently, we treated the kinetics of the initiation and propagation steps of the active A* and B* (side‐group) sites with model compounds. The degradation rates of two types of dithiocarbamate groups at the A and B sites agreed well with theoretical trends for CS bond dissociation energies predicted by the density functional theory for model compounds. The reactivity of the initiating B* groups was greater than that of the propagating A* groups. DB of the hyperbranched polymers was estimated to be 0.31 with both reaction rates in terms of Müller's equation. This result supported the DB value (0.39) estimated from NMR data. The hyperbranched molecules obtained in this work were not perfectly dendritic but had somewhat defective structures. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1810–1815, 2005

Controlled radical polymerization of styrene initiated by diethyldithiocarbamate‐mediated iniferters

AbstractWe demonstrated that density functional theory calculations provide a prediction of the trends in C‐S bond dissociation energies and atomic spin densities for radicals using two model compounds as diethyldithiocarbamate (DC)‐mediated iniferters. On the basis of this information, we synthesized 2‐(N,N‐diethyldithiocarbamyl)isobutylic acid (DTCA) and (4‐cyano‐4‐diethyldithiocarbamyl)pentanoic acid (CDPA) as DC‐mediated iniferters. Free‐radical polymerizations of styrene (St) were carried out in benzene initiated by DTCA or CDPA under UV irradiation. The first‐order time‐conversion plots showed the straight line for the UV irradiation system initiated by CDPA indicating the first order in monomer. The number‐average molecular weight (Mn) of the polystyrene (PSt) increased in direct proportion to monomer conversion. The molecular weight distribution (Mw/Mn) of the PSt was in the range of 1.3–1.7. It was concluded this polymerization system proceeded with a controlled radical mechanism. However, photopolymerization of styrene initiated by DTCA showed nonliving polymerization consistent with UV initiation. Theoretical predictions supported these experimental results. Methacrylic acid (MA) could also be polymerized in a living fashion with such a PSt precursor as a macroinitiator because PSt exhibited a DC group at its terminal end. This system could be applied to the architecture of block copolymers. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 413–418, 2005

Copolymerization of the macromonomer poly(ethylene oxide) with styryl end group and styrene in the presence of poly(ε‐caprolactone) with 2,2,6,6‐tetramethylpiperidinyl‐1‐oxy end group by controlled radical mechanism

AbstractA copolymerization of macromonomer poly(ethylene oxide) (PEO) with a styryl end group (PEOS) and styrene was successfully carried out in the presence of poly(ε‐caprolactone) (PCL) with 2,2,6,6‐tetramethylpiperidinyl‐1‐oxy end group (PCLT). The resulting copolymer showed a narrower molecular weight distribution and controlled molecular weight. The effect of the molecular weight and concentration of PCLT and PEOS on the copolymerization are discussed. The purity of PEOS exerted a significant effect on the copolymerization; when the diol contents of PEO macromonomer were greater than 1%, the crosslinking product was found. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2093–2099, 2004

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

AbstractPhotopolymerizations 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 (Mn) 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

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

AbstractWe 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 (Mw/Mn) 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 solution properties of alternating maleimide/styrene hyperbranched copolymers via controlled radical mechanism

AbstractCopolymerizations of (N,N‐diethyldithiocarbamyl)methylstyrene (inimer: DTCS) with maleimide (MI) were carried out under UV irradiation. DTCS monomers play an important role in this copolymerization system as an inimer that is capable of initiating radical polymerization of the vinyl group. Reactivity ratios (r1 = 0.15 and r2 = 0) were estimated by the curve‐fitting procedure (DTCS [M1]; MI[M2]). These reactivities show strong alternation, and the propagating copolymer radicals proceed with homopolymerization of 1:1 complexes formed between the donor and acceptor monomers. These alternating copolymers exhibit highly branched structure and are actually hyperbranched copolymers. The compact nature of the hyperbranched molecules was demonstrated by comparison of their dilute‐solution properties with those of the linear analogues. The hyperbranched macromolecules behave as single, well‐separated molecules (even in good solvent) and as hard spheres. Copyright © 2003 Society of Chemical Industry

Polymerisation of polar olefins promoted by organometallic cobalt complexes: free radical or coordinative process?

Organometallic cobalt(III) complexes, namely [Co(R) 2(NN) 2][X] (NN=2,2′-bipyridine, 1,10-phenanthroline and 4,7-dimethyl-1,10-phenanthroline, R=methyl, benzyl; X −=BF 4 − , PF 6 − , SbF 6 − ) have been obtained in good yield as stable orange crystalline compounds, by reduction of CoCl 2 with NaBH 4 in methanol in the presence of NN and the appropriate organic halide. The crystal structure of the complexes [Co(CH 3) 2(bipy) 2][PF 6] and [Co(CH 2Ph) 2(bipy) 2][PF 6] shows an octahedral coordination geometry for cobalt with a cis disposition of the two chelating ligands and the organic groups σ-bonded to the cobalt atom. In particular, the benzyl derivative shows stacking interactions between the phenyl ring of the benzyl groups and the planar bidentate ligands. NMR investigation confirms the cis coordination geometry in solution. Moreover, in the benzyl derivatives a restricted rotation of the phenyl group around the CC ipso bond is observed. These complexes efficiently promote the polymerisation of polar olefins, such as acrylonitrile, in the dark and with no addition of radical traps. Molecular weight and polydispersities determination suggest a catalytic controlled radical mechanism.

Kinetics on Formation of Hyperbranched Poly(ethyl methacrylate) via a Controlled Radical Mechanism of Photofunctional Inimer

We studied the living nature on the formation of hyperbranched poly(methacrylic acid ester) by free radical photopolymerization of 2-(N,N-diethyldithiocarbamyl)ethyl methacrylate (DTEM) in benzene....

Preparation of a copolymer of methyl methacrylate with a new monomer, 2,2,6,6‐tetramethyl‐4‐benzyloxyl‐piperidinyl methacrylate, and its initiation of the graft copolymerization of styrene with a controlled radical mechanism

AbstractA copolymer [P(MMA‐co‐TBPM)] was prepared by the radical polymerization of methyl methacrylate (MMA) and 2,2,6,6‐tetramethyl‐4‐benzyloxyl‐piperidinyl methacrylate (TBPM) with azobisisobutyronitrile as an initiator. TBPM was a new monomer containing an activated ester. Both the copolymer and TBPM were characterized with NMR, IR, and gel permeation chromatography in detail. It was confirmed that P(MMA‐co‐TBPM) could initiate the graft polymerization of styrene by the cleavage of the activated ester of the TBPM segment. This process was controllable, and the molecular weight of the graft chain of polystyrene increased with the increment of conversion. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4398–4403, 2002

Synthesis and Characterization of Poly(ε-CL)-block-poly(MMA-co-St)-block-poly(ε-CL) by Combination of Coordination and Controlled Radical Polymerization

The triblock copolymer poly(ϵ-caprolactone)-block-poly[(methyl methacrylate)-co-styrene]-block-poly(ϵ-caprolactone) was synthesized by a combination of coordination polymerization and controlled radical mechanism. The poly(ϵ-caprolactone) prepolymers (PCLBP) were first obtained by coordination polymerization using benzopinacol as the initiator and aluminium triisopropoxide as the promoter at room temperature. It was determined by means of UV and NMR spectroscopy that the benzopinacolate groups are left intact in the PCLBP prepolymers; no isomerization was found. The benzopinacolate groups incorporated into the poly(ϵ-caprolactone) then initiate the copolymerization of styrene (St) and methyl methacrylate (MMA) via a controlled radical mechanism at 95°C. The desired block copolymers were characterized by GPC, IR, UV and NMR spectroscopy in detail.

Preparation of a copolymer of methyl methacrylate and 2-(dimethylamino)ethyl methacrylate with pendant 4-benzyloxy-2,2,6,6-tetramethyl-1-piperidinyloxy and its initiation of the graft polymerization of styrene by a controlled radical mechanism

The macroinitiator of a copolymer (PMD BTM ) of methyl methacrylate (MMA) and 2-(dimethylamino)ethyl methacrylate (DAMA) with 4-benzyloxy-2,2,6,6-tetramethyl-1-piperidinyloxy (BTEMPO) pendant groups was prepared by the photochemical reaction of tertiary amine groups of the copolymer with benzophenone in the presence of BTEMPO. The radical copolymerization of MMA and DAMA was carried out first with azo-bis-isobutyronitrile (AIBN) as an initiator; then, the dimethylamine groups of the copolymer constituted a charge-transfer complex with benzophenone under UV irradiation, and the methylene of ternary amine and diphenyl methanol radicals were produced. The former was capped by BTEMPO, and the nitroxide (BTEMPO) was attached to the polymeric backbone. The amount of pendant BTEMPO on PMD BTM was measured by 1 H NMR. PMD BTM initiated the graft polymerization of styrene via a controlled radical mechanism, and the molecular weight of the PMD-g-polystyrene increased with the polymerization time.