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1.
The polymerization of vinyl monomer initiated by poly-p-vinylphenol (PVPh) in NaOH aqueous solution was carried out at 85°C with shaking. Methyl methacrylate (MMA) was polymerized, whereas styrene and acrylonitrile were not. PVPh, which is dissociated into phenolate form (PVPh?Na+) in NaOH aqueous solution, was effective for the polymerization. The effects of the amounts of MMA, PVPh, NaOH, and H2O on the conversion of MMA were studied. The rate of polymerization of MMA increased with an increase in the molecular weight of PVPh-Na. The overall activation energy was estimated as 54 kJ mol?1. The polymerization proceeded through a radical mechanism. The addition of tetra-n-butylammonium bromide increased the rate of polymerization.  相似文献   

2.
The first example of organostibine mediated controlled/living random copolymerization of styrene (St) and methyl methacrylate (MMA) was achieved by heating a solution of St/MMA/organostibine mediator at 100 °C or St/MMA/organostibine mediator/AIBN with various monomer feed ratios at 60 °C. The addition of AIBN significantly decreased the reaction temperature and enhanced the rate of copolymerization. The structure of poly(St-co-MMA) was verified by 1H NMR. The reactivity ratios at 60 °C were determined by the extended Kelen-Tüd?s method to be γSt = 0.40 and γMMA = 0.44. The ln([M]0/[M]) increased linearly with increasing reaction time. The number-average molecular weights of poly(St-co-MMA) increased linearly with conversion. Poly(St-co-MMA) with expected number-average molecular weight and low polydispersity index was formed. The living characteristic was further confirmed by chain-extension of poly(St-co-MMA) to form poly(St-co-MMA)-b-PMMA.  相似文献   

3.
The effect of fullerene (C60) on the radical polymerization of methyl methacrylate (MMA) in benzene was studied kinetically and by means of ESR, where dimethyl 2,2′-azobis(isobutyrate) (MAIB) was used as initiator. The polymerization rate (Rp) and the molecular weight of resulting poly(MMA) decreased with increasing C60 concentration ((0–2.11) × 10−4 mol/L). The molecular weight of polymer tended to increase with time at higher C60 concentrations. Rp at 50°C in the presence of C60 (7.0 × 10−5 mol/L) was expressed by Rp = k[MAIB]0.5[MMA]1.25. The overall activation energy of polymerization at 7.0 × 10−5 mol/L of C60 concentration was calculated to be 23.2 kcal/mol. Persistent fullerene radicals were observed by ESR in the polymerization system. The concentration of fullerene radicals was found to increase linearly with time and then be saturated. The rate of fullerene radical formation increased with MAIB concentration. Thermal polymerization of styrene (St) in the presence of resulting poly(MMA) seemed to yield a starlike copolymer carrying poly(MMA) and poly(St) arms. The results (r1 = 0.53, r2 = 0.56) of copolymerization of MMA and St with MAIB at 60°C in the presence of C60 (7.15 × 10−5 mol/L) were similar to those (r1 = 0.46, r2 = 0.52) in the absence of C60. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2905–2912, 1998  相似文献   

4.
The emulsion polymerization of methyl methacrylate (MMA) and styrene (St) were investigated with using polyamidoamine (PAMAM) dendrimer as seed, potassium persulfate as initiator and sodium dodecyl sulfate as emulsifier. The effects of 4.0GPAMAM dendrimer concentration, initiator concentration, emulsifier concentration, monomer concentration, and polymerization temperature on the monomer conversion and polymerization rate were investigated. At the same time, the influence of the generation of PAMAM dendrimer on latex particle size was studied also. The results showed that the monomer conversion and polymerization rate increased with increasing initiator concentration, emulsifier concentration, monomer concentration, and polymerization temperature. But polymerization rate increased firstly with an increase in the 4.0GPAMAM dendrimer from 0.03 g to 0.09 g and then decreased with further increase to 0.12 g. When the concentration of 4.0GPAMAM dendrimer less than 1.449 × 10?4 mol/L, the kinetic equation can be expressed by Rp∝[4.0GPAMAM]0.772[SDS]0.562[KPS]0.589[M]0.697, and the activation energy (Ea) of emulsion polymerization is 62.56kJ/mol. In additional, the copolymer latex particle size decreased and possessed monodispersity with increasing the generation of PAMAM dendrimer. According to FT-IR spectrum analysis, PAMAM dendrimer is successfully incorporated into the poly(PAMAM-St–MMA) latex particles.  相似文献   

5.
Propagation rate constants for the free radical polymerization of methacrylonitrile (MAN) have been obtained by pulsed laser photolysis (PLP). The temperature dependence of the propagation rate constants indicates a frequency factor of 10(6,43 ± 0,26) L · mol−1 · s−1 and an activation energy of 29,7 ± 1,5 kJ · mol−1. These parameters suggest that the relatively slow rate of propagation in MAN polymerization in relation to other common monomers (methyl methacrylate, styrene) can be attributed to the relative steric bulk and stability of the propagation species.  相似文献   

6.
The effects of triphenyl phosphite (TPP) on the radical polymerization of styrene (St) and methyl methacrylate (MMA) initiated with α,α,-azobisisobutyronitrile (AIBN) was investigated at 50°C. The rate of polymerization of St and MMA at a constant concentration of TPP was found to be proportional to the monomer concentration and the square root of the initiator concentration. The rate of polymerization and the degree of polymerization of both St and MMA increased with increasing TPP concentration. The accelerating effect was shown to be due to the decrease of the termination rate constant kt with an increase in the viscosity of the polymerization systems. The chain transfer constant Ctr of TPP in St and MMA systems was determined from the degree of polymerization system. The Ctr of TPP was almost zero in the St system and 6.5 × 10?5 in the MMA system.  相似文献   

7.
For a temperature range of −11.8–92.6°C, the propagation rate constant kp of styrene has been determined with the use of pulsed-laser polymerization (PLP). The temperature dependency of the obtained kp data was evaluated using the Arrhenius equation. The NLLS error-in-variables method (EVM) is recommended for this fit. The resulting activation energy is 32.6 kJ mol−1 and the pre-exponential factor is 107.66 dm3 mol−1 s−1. A joint confidence interval for these parameters is given. © 1996 John Wiley & Sons, Inc.  相似文献   

8.
A new chain transfer agent, ethyl 2-[1-(1-n-butoxyethylperoxy) ethyl] propenoate (EBEPEP) was used in the free radical polymerization of methyl methacrylate (MMA), styrene (St), and butyl acrylate (BA) to produce end-functional polymers by a radical addition–substitution–fragmentation mechanism. The chain transfer constants (Ctr) for EBEPEP in the three monomers polymerization at 60°C were determined from measurements of the degrees of polymerization. The Ctr were determined to be 0.086, 0.91, and 0.63 in MMA, St, and BA, respectively. EBEPEP behaves nearly as an “azeotropic” transfer agent for styrene at 60°C. The activation energy, Eatr, for the chain transfer reaction of EBEPEP with PMMA radicals was determined to be 29.5 kJ/mol. Thermal stability of peroxyketal EBEPEP in the polymerization medium was estimated from the DSC measurements of the activation energy, Eath = 133.5 kJ/mol, and the rate constants, kth, of the thermolysis to various temperature. © 1994 John Wiley & Sons, Inc.  相似文献   

9.
The free-radical copolymerization of methyl methacrylate (MMA) with styrene (St) in the presence of 2-mercaptoethanol (ME) was investigated in order to obtain ω-hydroxy oligomers with random copolymer-type chains of various compositions and molecular weights. Polymerizations at three different MMA/St molar ratios were carried out, while keeping constant the ME/monomer ratio. Monomer mixtures richer in MMA than in St were employed in order to attempt preparing lower polydispersity oligomers with monomodal molecular weight distribution (MWD). The molecular weights of the resulting oligomers increased with both conversion and MMA fraction in the feed, while polydispersities increased with conversion and decreased with MMA concentration in the initial monomer mixture. For the lower MMA fractions in the monomer feed, bimodal MWDs resulted beyond a certain conversion due to the faster relative consumption of ME than of monomer. Based on the pseudo-kinetic rate constant method, apparent chain transfer constants corresponding to the three different compositions of the monomer feed were estimated. The values obtained were in good agreement with the evolution of molecular weights and polydispersities with conversion and MMA fraction in the monomer feed. The co-oligomers prepared displayed functionalities around unity, making them suitable for the synthesis of macromonomers.  相似文献   

10.
《Thermochimica Acta》1987,122(1):143-152
Enthalpies and temperatures of fusion have been measured by differential scanning calorimetry for urea and a number of its mono- and di-alkyl derivatives. Enthalpies obtained are: urea, 14.79 kj mol−1; monomethylurea, 15.75 kJ mol−1 ; monoethylurea, 13.94 kJ mol−1 ; monopropylurea, 14.63 kJ mol−1 ; monoisopropylurea, 17.40 kJ mol−1 ; monobutylurea, 14.55 kJ mol−1 ; monotertbutylurea, 33.13 kJ mol−1 ; dimethyl-1,1 urea, 29.61 kJ mol−1 ; dimethyl-1,3 urea, 13.62 kJ mol−1; diethyl-1,1 urea, 16/78 kJ mol−1 ; diethyl-1,3 urea, 12.46 kJ mol−1 ; dibutyl-1,3 urea, 14.87 kJ mol−1; trimethyl-1,1,3 urea, 14.30 kJ mol−1. Entropies of fusion have been derived from the experimental results.By temperature scanning starting from r.t. some solid-to-solid transitions for four alkylureas have also been detected, all hitherto unreported. Temperatures and enthalpies of transition are: for monoisopropylurea, 375.5 K and 2.31 kJ mol −1 ; for monobutylurea (two transitions), 313.1 K and 7.02 kJ mol−1 , 344.9 K and 0.88 kJ mol−1 ; for diethyl-1,3 urea, 339.4 K and 1.87 kJ mol−1 ; for dibutyl-1,3 urea, 311.5 K and 11.10 kJ mol−1.  相似文献   

11.
The kinetics of the atomization process of selenium with prereduced and unreduced palladium nitrate modifiers were investigated. It was found that stabilization, in both forms, occurred by principally physical processes, as opposed to compound formation. For the unreduced modifier, it was shown that higher pyrolysis temperatures resulted in a higher activation energy of atomization and that the selenium vapour-surface interaction was increased. The importance of the second high temperature step in the stabilization mechanism was stressed, and an additional conditioning step in the furnace program was proposed for the unreduced palladium modifier. The reaction order for the unreduced modifier was near first order (1.29) with an activation energy of 330 kJ mol−1 and a frequency factor in the order of 1 × 109. For the reduced palladium modifier, a reduction temperature of 500°C–700°C was shown to be most effective. The reduced palladium modifier showed second order kinetics and the activation energy of 500 kJ mol−1, was nearly 50% higher than that of the unreduced form. This and the large frequency factor (ca. 1 × 1015) indicated strong surface interactions, thus providing an explanation to the better stabilization properties observed for the reduced form of the modifier.  相似文献   

12.
2‐Phenylethanol, racemic 1‐phenyl‐2‐propanol, and 2‐methyl‐1‐phenyl‐2‐propanol have been pyrolyzed in a static system over the temperature range 449.3–490.6°C and pressure range 65–198 torr. The decomposition reactions of these alcohols in seasoned vessels are homogeneous, unimolecular, and follow a first‐order rate law. The Arrhenius equations for the overall decomposition and partial rates of products formation were found as follows: for 2‐phenylethanol, overall rate log k1(s−1)=12.43−228.1 kJ mol−1 (2.303 RT)−1, toluene formation log k1(s−1)=12.97−249.2 kJ mol−1 (2.303 RT)−1, styrene formation log k1(s−1)=12.40−229.2 kJ mol−1(2.303 RT)−1, ethylbenzene formation log k1(s−1)=12.96−253.2 kJ mol−1(2.303 RT)−1; for 1‐phenyl‐2‐propanol, overall rate log k1(s−1)=13.03−233.5 kJ mol−1(2.303 RT)−1, toluene formation log k1(s−1)=13.04−240.1 kJ mol−1(2.303 RT)−1, unsaturated hydrocarbons+indene formation log k1(s−1)=12.19−224.3 kJ mol−1(2.303 RT)−1; for 2‐methyl‐1‐phenyl‐2‐propanol, overall rate log k1(s−1)=12.68−222.1 kJ mol−1(2.303 RT)−1, toluene formation log k1(s−1)=12.65−222.9 kJ mol−1(2.303 RT)−1, phenylpropenes formation log k1(s−1)=12.27−226.2 kJ mol−1(2.303 RT)−1. The overall decomposition rates of the 2‐hydroxyalkylbenzenes show a small but significant increase from primary to tertiary alcohol reactant. Two competitive eliminations are shown by each of the substrates: the dehydration process tends to decrease in relative importance from the primary to the tertiary alcohol substrate, while toluene formation increases. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 401–407, 1999  相似文献   

13.
《Thermochimica Acta》1987,122(1):189-195
The sublimation enthalpies of monophenylurea (MPhU) and diphenyl-1,3 urea (1,3-DPhU) have been derived from the dependence of their vapour pressures on temperature, as measured by the torsion-effusion method. Values obtained are: 136 kj mol−1 for MPhU and 152 kJ mol−1 for 1,3-DPhU, where the estimated errors are comprised within 6 kJ mol−1Enthalpies and temperatures of fusion have been measured by differential scanning calorimetry, leading to 23.7 kJ mol−1 and 420.6 K for MPhU, and 34.6 kJ mol−1 and 512 K for 1,3-DPhU. Poor reproducibility of results for 1,3-DPhU seems be due to the beginning of decomposition. No solid-to-solid transitions have been revealed from r.t. to fusion for both compounds.  相似文献   

14.
In this paper, the kinetics and mechanism of gold nanoparticles formation during the redox reaction between [AuCl4]− complex and l ‐ascorbic acid under different conditions were described. It was also shown that reagent concentration, chloride ions, and pH influence kinetics of nucleation and growth. To establish rate constants of these stages, the model of Finke and Watzky was applied. From Arrhenius and Eyring dependencies, the values of activation energy (22.5 kJ mol−1 for the nucleation step and 30.3 kJ mol−1 for the growth step), entropy (about −228 J K−1 mol−1 for the nucleation step and −128 J K−1 mol−1 for the growth step), and enthalpy (19.8 kJ mol−1 for nucleation and 27.8 kJ mol−1 for particles growth) were determined. It was also shown that the disproporationation reaction had influence on the rate of nanoparticles formation and may have impact on final particles morphology.  相似文献   

15.
2‐[(Diphenylphosphino)methyl]pyridine (DPPMP) was successfully used as a bidentate ligand in the iron‐mediated atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) with various initiators and solvents. The effect of the catalytic system on ATRP was studied systematically. Most of the polymerizations with DPPMP ligand were well controlled with a linear increase in the number‐average molecular weights (Mn) versus conversion and relatively low molecular weight distributions (Mw/Mn = 1.10–1.3) being observed throughout the reactions, and the measured molecular weights matched the predicted values. Initially added iron(III) bromide improved the controllability of the polymerization reactions in terms of molecular weight control. The ratio of ligand to metal influenced the controllability of ATRP system, and the optimum ratio was found to be 2:1. It was shown that ATRP of MMA with FeX2/DPPMP catalytic system (X = Cl, Br) initiated by 2‐bromopropionitrile (BPN) was controlled more effectively in toluene than in polar solvents. The rate of polymerization increased with increasing the polymerization temperature and the apparent activation energy was calculated to be 56.7 KJ mol?1. In addition, reverse ATRP of MMA was able to be successfully carried out using AIBN in toluene at 80 °C. Polymerization of styrene (St) was found to be controlled well by using the PEBr/FeBr2/DPPMP system in DMF at 110 °C. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2922–2935, 2008  相似文献   

16.
The kinetic of D,L-lactide polymerization in presence of biocompatible zirconium acetylacetonate initiator was studied by differential scanning calorimetry in isothermal mode at various temperatures and initiator concentrations. The enthalpy of D,L-lactide polymerization measured directly in DSC cell was found to be ΔH=−17.8±1.4 kJ mol−1. Kinetic curves of D,L-lactide polymerization and propagation rate constants were determined for polymerization with zirconium acetylacetonate at concentrations of 250–1000 ppm and temperature of 160–220 °C. Using model or reversible polymerization the following kinetic and thermodynamic parameters were calculated: activation energy Ea=44.51±5.35 kJ mol−1, preexponential constant lnA=15.47±1.38, entropy of polymerization ΔS=−25.14 J mol−1 K−1. The effect of reaction conditions on the molecular weight of poly(D,L-lactide) was shown.  相似文献   

17.
The free‐radical copolymerization of itaconic acid (IA) and styrene in solutions of dimethylformamide and d6‐dimethyl sulfoxide (50 wt %) has been studied by 1H NMR kinetic experiments. Monomer conversion versus time data were used to estimate the ratio kp · kt−0.5 for various comonomer mixture compositions. The ratio kp · kt−0.5 varies from 5.2 · 10−2 for pure styrene to 2.0 · 10−2 mol0.5 L−0.5 s−0.5 for pure IA, indicating a significant decrease in the rate of polymerization. Individual monomer conversion versus time traces were used to map out the comonomer mixture–composition drift up to overall monomer conversions of 60%. Within this conversion range, a slight but significant depletion of styrene in the monomer feed can be observed. This depletion becomes more pronounced at higher levels of IA in the initial comonomer mixture. The kinetic information is supplemented by molecular weight data for IA/styrene copolymers obtained by variation of the comonomer mixture composition. A significant decrease in molecular weight of a factor of 2 can be observed when increasing the mole fraction of IA in the initial reaction mixture from 0 to 0.5. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 656–664, 2001  相似文献   

18.
The Langmuir–Hinshelwood–Hougen–Watson (LHHW) kinetic model was developed for acetylation of glycerol over highly stable and active 2 M SO42−/γ‐Al2O3 catalyst. The apparent reaction rate constants were determined by numerically solving the differential rate equations using ode23 tool in MATLAB coupled with the genetic algorithm optimization technique. The estimated rate constants were used to obtain the activation energy and pre‐exponential factor by using the Arrhenius equation. The estimated activation energy for direct acetylation of glycerol to monoacetylglycerol and diacetylglycerol was 7.2 kJ mol−1, for acetylation of monoacetylglycerol to diacetylglycerol was 37.1 kJ mol−1, and for acetylation of diacetylglycerol to triacetylglycerol was 26.6 kJ mol−1, respectively.  相似文献   

19.
The electrochemical behaviour of molybdenum(VI) in sulphuric acid solutions was investigated by cyclic voltammetry. In the reduction of Mo(VI) to Mo(III) a dimerization reaction of Mo(V) is involved; the rate constant for the reaction was estimated to be 2.79×102 M−1 s−1 and the activation energy was ca. 35 kJ mol−1 in 0.1 M H2O4. Oxidation of the monomer and dimer Mo(V) species take place at −0.31 and +0.18 V (vs. SCE), respectively.  相似文献   

20.
A new highly active rare earth coordination catalyst composed of rare earth phosphonate, di-n-butylmagnesium (MgBu), and hexamethyl phosphoramide (HMPA) for the polymerization of styrene has been developed for the first time. High molecular weight polystyrene (ν = 50–70 × 104) in 100% conversion could be prepared at following conditions: [Nd] = 6–8 × 10−4 mol/L, [St] = 3.0 mol/L, Mg/Nd = 11, and HMPA/Mg = 1–1.5 (molar ratio). The catalytic activity of this new catalyst is 3530 g PSt/g Nd. Kinetics study shows that the polymerization rate is of first order with respect to both monomer concentration and catalyst concentration, and activation energy of the polymerization is 40.1 kJ/mol. © 1996 John Wiley & Sons, Inc.  相似文献   

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