Effect of acrylic acid neutralization on ‘livingness’ of poly[styrene‐ran‐(acrylic acid)] macro‐initiators for nitroxide‐mediated polymerization of styrene

BACKGROUND: The effect of acrylic acid neutralization on the degradation of alkoxyamine initiators for nitroxide‐mediated polymerization (NMP) was studied using styrene/acrylic acid and styrene/sodium acrylate random copolymers (20 mol% initial acrylate feed concentration) as macro‐initiators. The random copolymers were re‐initiated with fresh styrene in 1,4‐dioxane at 110 °C at SG1 mediator/BlocBuilder^® unimolecular initiator ratios of 5 and 10 mol%. RESULTS: The value of k_pK (k_p = propagation rate constant, K = equilibrium constant) was not significantly different for styrene/acrylic acid and styrene/sodium acrylate compositions at 110 °C (k_pK = 2.4 × 10^?6–4.6 × 10^?6 s^?1) and agreed closely with that for styrene homopolymerization at the same conditions (k_pK = 2.7 × 10^?6–3.0 × 10^?6 s^?1). All random copolymers had monomodal, narrow molecular weight distributions (polydispersity index M?_w/M?_n = 1.10–1.22) with similar number‐average molecular weights M?_n = 19.3–22.1 kg mol^?1. Re‐initiation of styrene/acrylic acid random copolymers with styrene resulted in block copolymers with broader molecular weight distributions (M?_w/M?_n = 1.37–2.04) compared to chains re‐initiated by styrene/sodium acrylate random copolymers (M?_w/M?_n = 1.33). CONCLUSIONS: Acrylic acid degradation of the alkoxyamines was prevented by neutralization of acrylic acid and allowed more SG1‐terminated chains to re‐initiate the polymerization of a second styrenic block by NMP. Copyright © 2008 Society of Chemical Industry     

Mechanistic and kinetic studies on the polymerization of styrene initiated by dimethyl sulfonium 2-pyridyl carbonyl methylide

Dimethyl sulfonium 2-pyridyl carbonyl methylide (Y_py-s) initiated radical polymerization of styrene in dimethyl sulfoxide at 85±0.1°C for 6 h under a nitrogen blanket using dilatometric techniques has been studied. The initiator and monomer exponent values were calculated to be 0.5 and 1.2, respectively. The system follows ideal radical kinetics with bimolecular termination. The higher monomer exponent value is ascribed to significant solvent effects on the initiation rate. The overall activation energy and average value of k²_p/k_t are 52.0 kJ mol^?1 and 1.0 × 10^?3 litre mol^?1 s^?1, respectively. The polymerization was retarded in the presence of hydroquinone or benzene; dimethylformamide, however, enhanced the rate of polymerization. Kinetic data and ESR studies indicate that the overall polymerization takes place via triplet carbene formation which acts as a source of free radicals.     

Kinetics of ylide-initiated radical copolymerization of 4-vinylpyridine and methyl methacrylate

The ylide-initiated radical copolymerization of 4-vinylpyridine (4-VP) with methyl methacrylate (MMA) at 60°C using carbon tetrachloride as inert solvent yields non-alternating copolymers. The kinetic parameters, average rate of polymerization (R_p) and orders of reaction with respect to monomers and initiator, have been evaluated and the kinetic equation is found to be R_pα[ylide]^0.94 [MMA]^1.0 [4-VP]^1.5. The values of the energy of activation and k_p²/k_t are 48 kJ mol^?1 and 6.6 × 10^?5 litre mol^?1s^?1, respectively. The copolymers have been characterized by IR and NMR spectroscopy.     

Determination of Free-Radical Propagation Rate Coefficient of N-Vinylindole by the Pulsed-Laser Polymerization Method

Summary The pulsed-laser polymerization method was applied to determine the propagation rate constant k_p of N-vinylindole (VI), and the Arrhenius parameters were evaluated in the range of 30-70 °C. One of the characteristics of the VI monomer was its low activation energy (17.5 kJ mol^-1) compared with other vinyl monomers, indicating that the propagating radical has a high reactivity. Although the reaction rate constant k_p = 86 L mol^-1 s^-1 at 30 °C was relatively small and similar to that of styrene, the Q-value and the products of photochemical reactions suggested again that it has a higher reactivity than styrene monomer. This property of VI radical probably gives rise to high termination probability and the cyclic structure at the chain end of the linear polymer.     

Using 1H‐NMR spectroscopy for the kinetic study of the in situ solution free‐radical copolymerization of styrene and ethyl acrylate

The free‐radical copolymerization of styrene and ethyl acrylate in benzene‐d₆ as the solvent in the presence of benzoyl peroxide as an initiator at 70°C was studied by online ¹H‐NMR spectroscopy. The chemical composition of the copolymer at different reaction times was calculated from the conversion of the monomers to the copolymer, and then the reactivity ratios of styrene and ethyl acrylate were determined at both low and high conversions. Data for the overall monomer conversion versus the time were used to estimate the ratio k_pk_t^?0.5 for different compositions of the initial feed (k_p is the propagation rate constant, and k_t is the termination rate constant). k_pk increased with an increasing molar fraction of ethyl acrylate in the initial feed. The monomer mixture and copolymer compositions versus the overall monomer conversion were calculated with the data of ¹H‐NMR spectra. The incorporation of the styrene monomer into the copolymer structure was more favored than that of the ethyl acrylate monomer. Reducing the molar fraction of styrene in the initial feed intensified this. Drawing the molar fraction of styrene (or ethyl acrylate) in the copolymer chains versus that in the initial feed showed a tendency of the system toward random copolymerization. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Miniemulsion copolymerizations of styrene and methyl methacrylate in the presence of reactive costabilizer

Miniemulsion stability of three‐component disperse phase systems comprising styrene [ST (1)], methyl methacrylate [MMA (2)], and stearyl methacrylate [SMA (3)] was investigated. The Ostwald ripening rate (ω) increases with increasing MMA content in the monomer mixture. The empirical equation 1 /ω = k(φ₁/ω₁ + φ₂/ω₂) + φ₃/ω₃ was proposed to adequately predict the miniemulsion stability data. The empirical parameter k was determined to be 555.77, and the Ostwald ripening rate (ω₃) and water solubility of SMA were estimated to be 8.77 × 10^?21 cm³/s and 1.90 × 10^?9 mL/mL, respectively. A water‐insoluble dye was used as a molecular probe to study particle nucleation mechanisms in the miniemulsion copolymerizations. In addition to the primary monomer droplet nucleation, homogeneous nucleation also plays an important role in the formation of particle nuclei, and this mechanism becomes more important for the polymerization systems with higher MMA contents as a result of the enhanced aqueous phase polymer reactions. The polymer composition data suggest that, during the early stage of polymerization, MMA is consumed more rapidly by free radical polymerization compared with ST. The final latex particle surface potential data also support this conclusion. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis,characterization and kinetics of terpolymerization of acrylonitrile,N-vinyl pyrrolidone and styrene

Synthesis of a series of novel terpolymers, consisting of two electron-donating monomers, viz. N-vinyl pyrrolidone (N-VP) (heterocyclic polar monomer) and styrene (Sty) (non-polar monomer), with one electron-accepting polar monomer, i.e. acrylonitrile (AN), using α,α'-azobisisobutyronitrile as radical initiator and benzene as diluent at 60°C, has been extensively surveyed. Besides the synthesis, an attempt has been made to study the kinetics and various properties of the terpolymers, such as softening temperature and chemical resistance. The system follows non-ideal kinetics and the kinetic equation for the present system can be written as This non-ideality can be explained on the basis of significant initiator-dependent termination through primary radicals and degradative chain transfer to acrylonitrile monomer. The overall energy of activation is 72.4 kJ mol^?1 and k_p²/k_t is 0.26 × 10^?3 litre mol^?1 s^?1. The effects of various additives such as imidazolium-p-chlorophenacylide (ICPY) and ZnCl₂ were also studied. ICPY functions as a chain transfer agent (C^tr = 0.43 × 10^?4), whereas ZnCl₂ accelerates the rate of reaction. IR spectroscopy was used to confirm the structure of the terpolymers.     

Copolymerization of methylmethacrylate with styrene using triphenylbismuthoniumylide as radical initiator

Bismuthoniumylide‐initiated radical copolymerization of methylmethacrylate with styrene at 60 ± 0.2°C using dioxane as an inert solvent, follows ideal kinetics (R_p ∝ [ylide]^0.5 [MMA]^1.0 [sty]^1.0), and yields alternating copolymer as evident from NMR spectroscopy. The values of reactivity ratios r₁ and r₂, calculated from Finemann–Ross method are 0.48 and 0.45, respectively. The system follows ternary molecular complex mechanism. The radical mode of polymerization has been confirmed by ESR spectroscopy and the effect of hydroquinone. The value of activation energy and k/k_t are 65.0 KJ mol^?1 and 2.5 × 10^?5 l mole^?1 s^?1, respectively. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2774–2781, 2001     

Linear segmented polyurethanes: I. A kinetics study

This work investigates the two‐step polymerization between methylene diphenyl diisocyanate (MDI), two different poly(tetramethylene oxide) macrodiols, and 1,4‐butanediol (BD) as chain extender. At the end of the prepolymerization, the reaction mixture contains MDI in excess and a prepolymer with isocyanate end group. Then, BD and a solvent (tetrahydrofuran) were added to start the finishing stage under nominal stoichiometric equilibrium. The reaction was analyzed by Fourier transform infrared spectroscopy, hydrogen nuclear magnetic resonance (¹H‐NMR), and size exclusion chromatography. ¹H‐NMR was employed to follow global concentrations of unreacted isocyanate end groups and internal urethane groups. This information enabled to estimate the following “effective” rate constants: k₁ = 1.07 × 10^?3 L mol^?1 s^?1 for the prepolymerization; and k₂ = 1.94 × 10^?4 L mol^?1 s^?1 for the finishing stage. These values are subject to errors caused by biases introduced in the recipe, in the measurements, in the reaction conditions, in the quality of reagents, and in the reaction mechanism assumptions. Such errors also explain the dispersion of the published rate constants values. The ¹H‐NMR measurements also enabled to estimate the evolution (with extent of reaction) of the number‐average number of structural units along the prepolymerization and finishing stages; and such estimates reasonably verify Flory's classical expressions. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45747.     

Synthesis and characterization of a synthetic heme‐based oxygen carrier

We have prepared a novel oxygen carrier composed of Starburst dendrimer 3 hematoporphyrin iron(III) di‐1‐(3‐aminopropyl)imidazole di‐succinic acid (SDHAPI). This compound has a molecular weight of ～12.7 kD. O₂ and CO binding to SDHAPI was demonstrated by UV‐vis spectroscopy. Oxygenated SDHAPI had an estimated auto‐oxidation half‐life of 24 min. The oxygen stoichiometry (～6 mol of O₂ mol^?1 SDHAPI) and the k_obs(on+off) of 0.084 s^?1 and k_obs(off) of 0.009 s^?1 were estimated with an oxygen electrode. Copyright © 2005 Society of Chemical Industry     

Synthesis and kinetics of ascorbic acid initiated graft copolymerized delignified cellulosic fiber

Graft copolymerization of delignified Grewia optiva fiber with methyl methacrylate (MMA) as vinyl monomer was attempted using ascorbic acid/H₂O₂ as redox initiator. Different reaction conditions affecting the grafting percentage (P_g) were optimized to get the maximum P_g (32.56%) of MMA onto delignified Grewia optiva fibers. Grafted and ungrafted fibers were subsequently subjected to evaluation of physico‐chemical properties such as swelling behavior and acid and alkali resistance. The rate expression for the grafting reaction (R_g = k [ASC]^0.12 [H₂O₂]^0.53 [MMA]^0.05) was evaluated and a suitable mechanism for grafting was suggested. The overall activation energy of the copolymerization reaction was found as 11.97 kJ mol^?1 at temperature range 25–65°C. Further, morphological and structural analysis of raw, delignified, and grafted Grewia optiva‐g‐poly(MMA) were studied by using Fourier‐transform Infrared spectroscopy, scanning electron microscopy, X‐ray diffraction, and thermogravimetric analysis.The tensile properties of grafted and ungrafted fiber samples were also reported. POLYM. ENG. SCI., 55:474–484, 2015. © 2014 Society of Plastics Engineers     

Flash photolysis investigation on primary processes of the sensitized polymerization of vinylmonomers. III. Photoreactions of benzoin compounds and stationary polymerization experiments

Benzoin (B), benzoinacetate (BA), benzoinmethylether (BME) and benzoinisopropylether (BIPE) were irradiated at room temperature in benzene solution in the presence of styrene (St), methyl methacrylate (MMA), vinylacetate (VAc) or acrylonitrile (AN). Flash photolysis experiments at λ=347 nm yielded (a) rate constants k_q (in 1 mol^-1s^-1) of the reaction between excited sensitizers and monomers: 8·10⁹ (B/St), 5·10⁸ (B/MMA), 5·10⁹ (BA/St), 8·10⁸ (BA/MMA); (b) rate constants K^R.+M (in 1mol^-1 s^-1) of the reaction between sensitizer radicals and monomers: about 1.5·10⁵ (BME/St, BME/VAc, BA/VAc, B/VAc), 9· 10⁴ (BME/MMA), 2·10⁴ (BME/AN). The reaction R·+M caused in certain cases (B/St, B/VAc, BME/St) the formation of an additional optical absorption after the flash. Stationary irradiations at λ>320 nm of monomer solutions (5mol/1) showed that BA is least effective. Rates of polymerization increased in the series BA<B<BIPE<BME. For the systems containing St or MMA it was found that ?_i=_i+0.6α_R (?_i=quantum yield for the initiation of kinetic chains, α_R =fraction of triplets converted to radicals). The fraction of radicals starting kinetic chains is ca. 0.3 in these cases.     

Radical terpolymerization of zincacrylate,acrylonitrile, and styrene initiated by As2S3-styrene complex

Terpolymerization was investigated by dilatometry for zincacrylate (ZnA₂), acrylonitrile (AN), and styrene (St), radically initiated by a As₂S₃-styrene complex (I) in dimethyl sulphoxide (DMSO), at 90 ± 0.1°C for 1 h under inert atmosphere. The system follows non-ideal kinetics, due to primary radical termination as well as a degradative chain transfer reaction. The kinetic expression for the system is R_pα(I)^0.27 (St)^0.31 (AN) ^0.22[ZnA₂]^0.12. The value for the activation energy and k/k_t are 55 kJ mol^?1 and 1.87 × 10^?7 1 mol^?1 s^?1 respectively. The terpolymer has been characterized by IR and NMR spectroscopy. The thermal stability and solubility of the terpolymer have also been studied.     

Ceric ion‐induced graft copolymerization of acrylamide on cationic guar gum at low temperature

The solution polymerization of acrylamide (AM) on cationic guar gum (CGG) under nitrogen atmosphere using ceric ammonium sulfate (CAS) as the initiator has been realized. The effects of monomer concentration and reaction temperature on grafting conversion, grafting ratio, and grafting efficiency (GE) have been studied. The optimal conditions such as 1.3 mol of AM monomer and 2.2 × 10^?4 mol of CAS have been adopted to produce grafted copolymer (CGG1‐g‐PAM) of high GE of more than 95% at 10°C. The rates of polymerization (R_p) and rates of graft copolymerization (R_g) are enhanced with increase in temperature (<35°C).The R_p is enhanced from 0.43 × 10^?4 mol L^?1 s^?1 for GG‐g‐PAM to 2.53 × 10^?4 mol L^?1 s^?1 for CGG1‐g‐PAM (CGG1, degree of substitute (DS) = 0.007), and R_g from 0.42 × 10^?4 to 2.00 × 10^?4 mol L^?1 s^?1 at 10°C. The apparent activation energy is decreased from 32.27 kJ mol^?1 for GG‐g‐PAM to 8.09 kJ mol^?1 for CGG1‐g‐PAM, which indicates CGG has higher reactivity than unmodified GG ranging from 10 to 50°C. Increase of DS of CGG will lead to slow improvement of the polymerization rates and a hypothetical mechanism is put forward. The grafted copolymer has been characterized by infrared spectroscopy, thermal analysis, and scanning electron microscopy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 3715–3722, 2007     

Polymerization of some oxiranes using the diphenylzinc-butanone system in benzene at 60°C

The diphenylzinc-butanone system was used as polymerization catalyst for some oxiranes in benzene solution at 60°C. This system is greatly influenced by the molar ratio of butanone to diphenylzinc, and the maximum catalytic activity for propylene oxide and ethylene oxide was found for a ratio of unity. GPC results strongly suggest the presence of more than one active species for the system. ¹³C NMR analysis indicates that the resulting poly(propylene oxide) has a head-to-tail arrangement. For the polymerization of propylene oxide with butanone/diphenylzinc = 1, after an initial induction period, the reaction was first-order with respect to monomer with k = 2·51 × 10^?5 s^?1. Ethylene oxide polymerizations using butanone/diphenylzinc = 1 and 5 were also first-order with respect to monomer after an initial induction period with k = 7·80 × 10^?6 s^?1 and k = 5·71 × 10^?6 s^?1, respectively. The diphenylzinc-butanone system was not an effective catalyst for styrene oxide polymerization.     

Radiation-induced graft copolymerization of styrene to cellulose

The radiation-induced graft copolymerization of styrene to cellulose has been studied in vacuo at 30°C and at dose rates from (0.37 to 8.73) × 10^?2 W/kg. Dioxan was used as solvent for monomer and polystyrene homopolymer, and water (2% total volume) was incorporated as swelling agent for cellulose. The concentration of styrene in the bulk medium was varied from 0.432 to 3.46 moles/l., and the rates of both grafting and homopolymerization were shown to be proportional to [monomer] · [intensity]^1/2. The value of 3.3 × 10^?4 l. mole^?1 sec^?1 derived for k_p²/k_t in homopolymerization is similar to that for normal free-radical polymerization of styrene. However, reduced termination during grafting yielded a much higher value (58 l. moles^?1 sec^?1). Degradation of cellulose in the absence of monomer was followed viscometrically, and values of 13.5 and 24.6 were derived for G (scission) in vacuo and in air, respectively.     

Studies on β-picolinium-p-chlorophenacylide initiated copolymerization of methyl methacrylate with styrene

The alternating copolymerization of methyl methacrylate (MMA) with styrene (S) using β-picolinium-p-chlorophenacylide (β-PCPY) as radical initiator at 55, 60, and 65°C for 3 h has been kinetically investigated. The copolymerization rate (R_p) is proportional to the square root of [β-PCPY] and indicates bimolecular termination. The average degree of polymerization decreases as [β-PCPY] increases. The values of k_p²/k_t and energy of activation have been evaluated as 1.43 · 10^-3 l mol^-1 s^-1 and 87 kJ mol^-1, respectively. The NMR spectroscopy has been used to determine the structure, composition, and stereochemistry of copolymers.     

On the primary processes of sensitized photopolymerization of vinylmonomers. Laser flash photolysis studies and stationary polymerization experiments

The absorption spectra of the triplets of aromatic ketones used as photosensitizers for the polymerization of unsaturated compounds — benzophenone (BP), 3,3′,4,4′-tetramethoxycarbonylbenzophenone (TMCB) and 3,3′,4,4′-benzophenone tetracarboxylic dianhydride (BTDA) — were recorded after irradiation of benzene or acetone solutions of the ketones with 25 ns flashes from a frequency doubled ruby laser (λ = 347,1 nm) at room temperature. Furthermore, the spectra of the respective ketyl radicals were measured. Rate constants of the reaction of triplets with various monomers were measured. Very high rate constants (> 10⁹ 1 · mol^?1 s^?1) were found for styrene (St) and N-vinylpyrrolidone (VP). The triplet energy E_T of these monomers is smaller than E_T of the sensitizers, except the case BP/VP. Other monomers — vinylacetate (VAc), methylmethacrylate (MMA), acrylonitrile (AN) — react relatively slowly with sensitizer triplets (5 × 10⁶ to 1.4 × 10⁸ l · mol^?1 s^?1). It is assumed that these monomers have E_T values higher than the E_T values of the sensitizers. The rate of polymerization v was determined in tetrahydrofuran solutions containing monomer (5 mol/1) and sensitizer (6–7 × 10⁴ mol/1) from stationary experiments with irradiation of light with λ > 320 nm. The probabilities, α_R, for the initiation of polymerization derived from the rate constants of triplet quenching by the monomers were correlated with the measured rates of polymerization. In accordance with expectation it was found that St and VP did not polymerize and that in the cases of VAc, MMA and AN a significant polymerization takes place (in the absence of sensitizer the rates v were negligibly small). For MMA v is proportional to α.     

Synthesis and characterization of novel rod–coil diblock copolymers of poly(methyl methacrylate) and liquid crystalline segments of poly(2,5‐bis[(4‐methoxyphenyl)oxycarbonyl] styrene)

Liquid crystalline diblock copolymers with different molecular weights and low polydispersities were synthesized by atom transfer radical polymerization of methyl methacrylate (MMA) and 2,5‐bis[(4‐methoxyphenyl)oxycarbonyl]styrene (MPCS) monomers. The block architecture (coil‐conformation of MMA segment and rigid‐rod of MPCS segment) of the copolymer was experimentally confirmed by a combination of ¹H nuclear magnetic resonance and gel permeation chromatograph techniques. The liquid crystalline behaviour of the copolymer was studied using differential scanning calorimetry and polarized optical microscope. It was found that the liquid crystalline behaviour was dependent on the number average molecular weight of the rigid segment. Only those copolymers with M_n(GPC) of the rigid block above 9200 g mol^?1 could form liquid crystalline phases higher than the glass transition temperature of the rigid block. The random copolymers MPCS‐co‐MMA were also synthesized by conventional free radical polymerization. The molar content of MPCS in MPCS‐co‐MMA had to be higher than 71% to maintain liquid crystalline behaviour. © 2003 Society of Chemical Industry