Some aspects of the n-vinylcarbazole polymerization initiated by iodine

The polymerization of N-vinylcarbazole initiated by iodine in dichloroethane solution, shows some interesting features, particularly the unusual trend of the conversion-time curves: in all cases a very fast initial reaction is followed by a much slower process. Molecular weights of the polymers decrease noticeably with increasing conversion and with increasing initial monomer concentration. The system is very complex and the data indicate that two different mechanisms are operating.     

Radical polymerization of allylbiguanide

Monoallyl compounds are not readily homopolymerized by a conventional free‐radical mechanism. However, we successfully performed the radical polymerization of allylbiguanide hydrochloride in a concentrated acid solution (hydrochloric acid or phosphoric acid) in the presence of a radical initiator at 50 °C. The polymer product was precipitated from the reaction solution through the addition of an excess amount of acetone. The precipitated crude polymer [polyallylbiguanide (PAB)] was then purified by dialysis. PAB was confirmed by elemental analysis, infrared spectroscopy, and ¹H NMR. The molecular weight range of PAB was 10,340–113,200, and PAB exhibited a low polydispersity (weight‐average molecular weight/number‐average molecular weight = 1.04–1.68) by multi‐angle laser light scattering. The polymerization of allylbiguanide was quite sensitive to the protonic concentration of the inorganic acid. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1707–1711, 2004     

Atom transfer radical polymerization of n-octyl acrylate under microwave irradiation

The atom transfer radical polymerization (ATRP) of n-octyl acrylate (OA) was successfully carried out using ethyl-2-bromobutyrate as an initiator, and CuBr/2,2^′-bipyridine (bpy) as a catalyst under microwave irradiation (MI) at 76.8 °C. The polymerization of n-octyl acrylate under MI showed linear first-order rate plots, a linear increase of the number-average molecular weight M_n with conversion, and low polydispersities, 1.1<M_w/M_n<1.4, where M_w is weight-average molecular weight. The ATRP of n-octyl acrylate is well controlled. Under the same experimental conditions, the apparent rate constant, k_p^app, under MI is larger apparently than that under conventional heating. In addition, the effects of concentration of catalyst and other factors on polymerization are reported.     

Radical polymerization in biosensing

This review briefly summarizes recently published work on radical polymerization in biosensor-related applications. Advancements in surface modification aimed at improving sensor biocompatibility and reducing nonspecific background noises are discussed. Direct applications of polymers as one of the key sensing elements in which they are used either as detection probes for the biomolecular binding events or as signal transducers to amplify sensing signals are detailed. Initial applications of radical polymerization reactions in biosensing are evident and appear promising.     

Radical polymerization behavior of hydroxystyrenes

Homopolymerizations of m- and p-hydroxystyrene and their copolymerizations with styrene and methyl methacrylate by use of azobisisobutyronitrile as initiator were investigated, and the results were compared with those obtained previously o-hydroxystyrene. Intrinsic viscosities of m- and p-hydroxystyrene polymers obtained by bulk and solution polymerizations were ca. 2 to 3 times larger than those of o-hydroxystyrene polymers obtained by the similar conditions. The structures of the polymers thus produced were investigated by infrared and ultraviolet spectroscopy. These studies suggested that all of the homopolymers consisted mainly of structures of normal vinyl type polymer. R_p was proportional to [I]^0.52 for m-hydroxystyrene and to [I]^0.50 for p-hydroxystyrene, for o-hydroxystyrene R_p was proportional to [I]^0.72. A reasonable chain transfer mechanism for these monomers was postulated. The apparent activation energies of polymerization for m- and p-hydroxystyrene were found to be 20.1, and 18.0 kcal/mole, respectively, compared to the value of 21.5 kcal/mole for o-hydroxystyrene. Monomer reactivity ratios and Q ? e values for m- and p-hydroxystyrene were determined, and the results were also compared with the case of o-hydroxystyrene. Copolymerization generally gave a polymer with relatively high intrinsic viscosity, even in the case of o-hydroxystyrene.     

Radical polymerization behavior of trimethoxyvinylsilane

Trimethoxyvinylsilane (TMVS) was quantitatively polymerized at 130 °C in bulk, using dicumyl peroxide (DCPO) as initiator. The polymerization of TMVS with DCPO was kinetically studied in dioxane by Fourier transform near‐infrared spectroscopy. The overall activation energy of the bulk polymerization was estimated to be 112 kJ/mol. The initial polymerization rate (R_p) was expressed by R_p = k[DCPO]^0.6[TMVS]^1.0 at 120 °C, being closely similar to that of the conventional radical polymerization involving bimolecular termination. The polymerization system involved electron spin resonance (ESR) spectroscopically observable polymer radicals under the actual polymerization conditions. ESR‐determined apparent rate constants of propagation and termination were 13 L/mol s and 3.1 × 10⁴ L/mol s at 120 °C, respectively. The molecular weight of the resulting poly(TMVS)s was low (M_n = 2.0–4.4 × 10³), because of the high chain transfer constant (C_mtr = 4.2 × 10^?2 at 120 °C) to the monomer. The bulk copolymerization of TMVS (M₁) and vinyl acetate (M₂) at 120 °C gave the following copolymerization parameters: r_l = 1.4, r₂ = 0.24, Q₁ = 0.084, and e₁ = +0.80. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5864–5871, 2005     

Radical polymerization behavior of N-vinylsaccharin

Synthesis and radical polymerization behavior of N-vinylsaccharin (1) are described. Radical homopolymerization of 1 was carried out in the presence of a radical initiator for 24 h to afford the polymer containing a saccharin moiety in the side group, which was insoluble in common organic solvents. Among the copolymers of 1 with various vinyl monomers such as vinyl acetate (VAc), methyl acrylate (MA), acrylonitrile (AN), and styrene (St), only the copolymer [copoly(1-St)] obtained from 1 and St was soluble in common organic solvents. In the copolymerization of 1 and St, the Q and e values of 1 were estimated to be 0.10 and −1.60, respectively. These values are similar to those of N-vinylphthalimide (Q = 0.36, e = −1.52). The reaction of copoly(1-St) with LiAlH₄ was carried out in THF for 24 h to convert the saccharin moiety into the ring-opened structure bearing hydroxy and sulfonamide groups. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3419–3426, 1999     

Synthesis of para-substituted styrenes

Using double Stille cross-coupling reaction bromo (or chloro)benzylbromide is easily transformed into substituted styrene monomers bearing a wide range of substituents in para position     

Anionic polymerization of methacrylonitrile—I. Polymerization with n-butyllithium as initiator

The anionic polymerization of methacrylonitrile has been studied at ?75° in toluene and with n-butyllithium as initiator. The kinetics of the polymerization were investigated considering the consumption of both monomer and initiator. BuLi disappears relatively slowly and about 50–60% remains unreacted. A simple kinetic scheme cannot therefore be put forward. All possible side reactions have also been examined. The molecular weight study establishes the living character of this system and gives an initiator efficiency of about 0.2. The contribution of low molecular weight products, typical of the polymerization of polar monomers, is also taken into account. In order to obtain a better understanding of the mechanism of this polymerization, in which unreacted initiator is probably engaged in very stable and inactive mixed associated particles, small amounts of THF (known frequently to break down such aggregates) were added to the system. A rather unexpected slow but complete disappearance of the initiator occurs; the conversion at which the rate of monomer consumption levels off depends on the THF concentration.     

Vibrational analysis of n-butyl, n-pentyl,and n-hexyl fluorides

Infrared spectra were obtained for n-butyl, n-pentyl, and n-hexyl fluorides in the liquid and solid states, and liquid-state Raman spectra were obtained for the first two of these. Normal coordinate calculations were carried out and twenty force constants of the C-CH₂F group were refined to provide the best fit for the 114 assigned frequencies of trans-n-propyl, gauche-n-propyl, TT-n-butyl, and TG-n-butyl fluorides. The resulting force constants were used to calculate the frequencies of the GT- and GG conformations of n-butyl fluoride and the two conformations for each of n-pentyl and n-hexyl fluoride that have coplanar carbon chains. The presence of all four conformers of n-butyl fluoride in the liquid state is indicated, but only the TG-conformer is present in the solid. The existence of the two conformations of n-pentyl and n-hexyl fluorides for which calculations were made is supported by comparison of the observed and calculated frequencies. Additional conformations seem to be present. The simplest solid-state spectrum is due only to the conformer that has a coplanar chain of carbons and the fluorine atom in the gauche position. Previous tentative conclusions about the relation between C-F stretching frequency and configuration have been revised.     

Radical desorption in emulsion polymerization

The derivation of a radical desorption coefficient in emulsion polymerization is presented, which takes into account the possible reactions of the desorbed radical in the aqueous phase as well as the competition between desorption and termination in polymer particles containing more than one radical. This model overcomes some important limitations of the previous models and is able to explain previously reported experimental results that the other models were unable to explain.     

Stereocontrol during the free‐radical polymerization of methacrylamides in the presence of Lewis acids

The effects of Lewis acids, that is, rare earth metal trifluoromethanesulfonates, on the free‐radical polymerization of N‐methylmethacrylamide (MMAM), N‐isopropylmethacrylamide (IPMAM), N‐tert‐butylmethacrylamide (tBMAM), N‐phenylmethacrylamide (PMAM), and methacrylamide were examined under various conditions. A catalytic amount of Yb(OSO₂CF₃)₃ significantly affected the stereochemistry during the radical polymerization. Polymerization solvents strongly influenced the effect of the Lewis acids. Methanol was the best solvent for increasing the isotactic specificity during the polymerization of MMAM and IPMAM, whereas tetrahydrofuran was more effective for the tBMAM and PMAM polymerizations. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1027–1033, 2003     

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).     

Radical polymerization behavior of vinyl phenylsufonylacetate

Vinyl phenylsulfonylacetate (VPSA) was prepared by the reaction of vinyl chloroacetate with sodium benzenesulfinate in acetone in the presence of a phase-transfer catalyst. VPSA showed a high radical homopolymerizability similar to vinyl acetate in spite of the fact that VPSA carries a phenyl group. The polymerization of VPSA with 2,2^′-azobisisobutyrate (MAIB) was kinetically investigated in acetone. The overall activation energy of the polymerization was 27.6 kcal/mol. The polymerization rate (R_p) at 50 °C was expressed by R_p=k[MAIB]^0.67[VPSA]^1.1. Poly(VPSA) showed exothermic (27 °C) and endothermic (57 °C) peaks in its DCS curve, corresponding to crystallization and melting. The tacticity of poly(VPSA) was estimated to be rr=29, mr=49, and mm=22.     

Radical polymerization of ethyl acrylate with dead end polymerization conditions

The radical polymerization of ethyl acrylate (EA) with 4,4^′-azobis(4-cyanovaleric)acid as initiator was investigated in propionitrile at 363 K in order to obtain carboxy-telechelic oligo(ethyl acrylate). The results of functionality and molecular weights showed that a transfer reaction had occurred. A molecular weight study was performed in order to show the importance of transfer to solvent due to the high reactivity of the EA radical. Finally, the radical polymerization was investigated at very low temperature (253-273 K), using a redox system initiation. A behavior of dead end polymerization was observed but the activation energy of propagation for EA is still high and does not allow the synthesis of a telechelic oligomer.     

Regio-controlled synthesis of N-substituted imidazoles

A regio-specific synthesis of N-substituted imidazoles is described. Readily available α-amino acids are converted to α-aminocarbonyl derivatives and reacted with various isothiocyanates to give N-substituted cyclic thioureas. Oxidative or reductive desulfurization of the cyclic thioureas affords structurally diversified imidazoles in good to excellent yields.