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1.
Dimethyl sulfoxide has been used as a solvent in the polymerization of methyl methacrylate and styrene. The chain-transfer coefficients of the solvent and the values of δ [i.e., (2kt)1/2/kp] in solvent-monomer mixtures of various compositions were determined. δ was observed to be dependent on the solvent concentration in the case of methyl methacrylate but remained constant in case of styrene. The lowering of the values of δ with increasing solvent concentration in case of methyl methacrylate has been attributed to an interaction between the solvent and poly(methyl methacrylate) radical resulting in lower termination rate.  相似文献   

2.
Various kinds of NCA's were polymerized in dimethyl sulfoxide (DMSO). DL -Alanine NCA polymerized at a fast rate without initiator, the rate being represented by Rp1 = k[M]1/2. When the polymerization was carried out in chloroform in the presence of DMSO, the rate was represented by the equation, Rp2 = K2[M][DMSO]1/2. Glycine NCA and DL -α-amino-n-butyric acid NCA also polymerized at a fast rate in DMSO without initiator. On the other hand, N-methylglycine NCA, DL - and L -valine NCA and DL - and L -leucine NCA did not polymerize in DMSO without initiator.  相似文献   

3.
The rates of photochemical polymerization of styrene (St), p-chlorostyrene (Cl-St), methyl methacrylate (MMA), and butyl methacrylate (BMA) with polymethylphenylsilane (PMPS) as an initiator were measured. Polymethylphenylsilane is photodegrated to form silyl radicals that may initiate polymerization of vinyl monomers. Rate constants kp and kt have been determined for these systems. A good correlation (log P = α + βμ) of the resonance stabilization (P) of the chain radicals and the dipole moment (μ) of the monomers is observed for these polymerization systems. This equation may be used to estimate the resonance stabilization (P) of a monomer and the polymerization rate constant (kp). © 1996 John Wiley & Sons, Inc.  相似文献   

4.
The propagation and termination rate constants kp and kt for the radical polymerization of butyl acrylate initiated by biacetyl have been measured by using the rotating-sector method, in various solvents at 30°C. The value of kp and initiation rate Ri varied with solvents, while the value of kt did not change with solvents except for benzonitrile. The variation of kp with aromatic solvents has a trend against Hammett σp of the solvent substituents similar to that for methyl methacrylate or phenyl methacrylate except for the value in benzonitrile, when it is larger than the variation for methyl methacrylate or phenyl methacrylate. The larger variation of kp for butyl acrylate is compatible with the view that the origin of the solvent effect lies in complex formation between the propagating radical and aromatic solvent molecules. The exceptional decrease in kp and kt in benzonitrile is explained by a contraction of the poly(butyl acrylate) chain in the poor solvent.  相似文献   

5.
The separate rate constants kp and kt for propagation and termination of radical template polymerization of methyl methacrylate along isotactic poly(methyl methacrylate) as a polymer template have been determined. The polymerizations were carried out in the strongly complexing solvent dimethylformamide at 5°C. For the evaluation of k/kt from stationary kinetic experiments, the rates of initiation were determined by employing a scavenger method. The nonstationary experiments yielding kp/kt were performed by means of the rotating sector technique. As the template rate effects increased with decreasing initiator concentration, the rotating sector curves were corrected for variation in light intensity. It appeared that the radical lifetime increases from 8.4 sec for normal or blank polymerization to 64 sec for template polymerization. The calculated values of kp are 26.6 and 5.9 l./mole-sec and of kt 140 × 104 and 1.7 × 104 l./mole-sec for blank and template polymerization, respectively. The changes in kp and kt, due to the presence of template polymer, are explained in terms of an extra loss of activation entropy in the stereoselective propagation step and a strong hindrance of segmental diffusion for the termination reaction of the chains growing along the polymer template.  相似文献   

6.
Polymerization of methyl methacrylate with some cobalt (III) complexes was carried out in various solvents and in mixed solvents of acetone and water or alcohols. Sodium hexanitrocobaltate(III) was found to be an effective initiator in mixed solvent of water and acetone. The kinetic study on the polymerization of methyl methacrylate with Na3[Co(NO2)6] in a water-acetone mixed solvent gave the following over-all rate equation: Rp = 8.04 × 104 exp{ ?13,500/RT} [I]1/2[M]2 (mol/1.?sec). The effects of various additives on polymerization rate and the copolymerization curve with styrene suggest that polymerization proceeds via a radical mechanism. The dependence of the polymerization rate on the square of monomer concentration and the spectroscopic data were indicative of the formation of a complex between initiator and monomer.  相似文献   

7.
Radical polymerizations of styrene and methyl methacrylate in the presence of phenylacetylene and five of its p-substituted derivatives were carried out with the use of 2,2′-azobisisobutyronitrile as the initiator at 60°C. The initial overall rates of the polymerizations of styrene and methyl methacrylate in the presence of phenylacetylene were not proportional to the square root of the initiator concentration under the experimental conditions employed. The relationship between the overall polymerization rate and the concentration of the phenylacetylenes could be expressed by the Kice equation for the rate of a radical polymerization in the presence of a terminator. From this relationship the rate constant (ks) of the reaction of a growing polymer radical with the phenylacetylenes and the constant Cs = (ks/kp), where kp is the propagation rate constant of vinyl monomers, were determined. The Cs value thus obtained agree well with that derived from the relationship between the number-average degree of polymerization and the molar ratio of the phenylacetylenes to the vinyl monomer. Therefore the mechanism of the reaction may be considered as being one in which the growing radical reacts with the ethynyl group of the phenylacetylenes to yield a comparatively stable radical which terminates mainly by reaction with the growing radical, and so apparently the phenylacetylenes retard the vinyl polymerization. The substituent effects on the reaction were discussed on the basis of the following modified Hammett equation proposed by Yamamoto and Otsu: log [Cs(p-sub. PA)/Cs(PA)] = ρσ + γER where PA represents phenylacetylene, σ and ER are the Hammett polar substituent constant and resonance substituent constant, respectively, and both ρ and γ are reaction constants. The γ value for the polymerization of both styrene and methyl methacrylate was 1.7. The ρ value was 1.0 for the polymerization of styrene and approximately zero for that of methyl methacrylate. These results demonstrate that the reactivity of the phenylacetylenes with the growing chain is influenced by both polar and resonance effects of their p-substituents in the degradative copolymerization of styrene and only by the resonance effect in that of methyl methacrylate.  相似文献   

8.
The kinetics of the emulsion polymerization of methyl methacrylate at 50°C have been studied in seeded systems using both chemical initiation and γ-radiolysis initiation. Both steady-state rates and (for γ-radiolysis) the relaxation from the steady state were observed. The average number of free radicals per particle was quite high (e.g., ~0.7 for 10?3 mol dm?3 S2O28 initiator). The data are quantitatively interpreted using a generalized Smith–Ewart–Harkins model, allowing for free radical entry, exit, biomolecular termination within the latex particles, and aqueous phase hetero-termination and re-entry. From this treatment, there results (i) the dependence of the termination rate coefficient (kt) on the weight fraction of polymer (wp), (ii) lower bounds for the dependence of the entry rate coefficient on initiator concentration, and (iii) the conclusion that most exited free radicals undergo subsequent re-entry into particles rather than hetero-termination. The results for kt(wp) are consistent with diffusion control at temperatures below the glass transition point. Comparisons are presented of the behavior of methyl methacrylate, butyl methacrylate, and styrene in emulsion polymerization systems.  相似文献   

9.
Several kinetics aspects of the methyl methacrylate (MMA) polymerization using 4-dimethylamino-4'-isopropylbenzophenone (PI) as photoinitiator have been studied. The order of the polymerization reaction with respect to monomer and initiator concentrations have been investigated, as well as the polymerization behavior under well-stirred and unstirred conditions; values of initiation quantum yield (?i) and kp/kt1/2 have also been determined. It has been found that the nature of the polymerization-initiating radicals depends on the type of solvent and the photoinitiator concentration ([PI]). In cyclohexane solution and at low [PI] (< 5 x 10-5M), the cyclohexyl radical is practically the only polymerization initiating radical, while at higher [PI] both radicals, cyclohexyl and the aminoalkyl derived from PI, participate in the initiation step, increasing the participation of the later as the [PI] increases. When benzene is used as solvent both phenyl and aminoalkyl radicals participate in the initiation step at any [PI] employed. Efficiencies of the radicals derived from solvent and photoinitiator have been determined.  相似文献   

10.
Polymerization of MMA was carried out in presence of visible light (440 nm), quinoline-bromine charge-transfer complex being used as the photoinitiator. The initiator exponent was observed to be 0.5 up to 0.014 M initiator concentration; when chloroform was used as the solvent, the monomer exponent was found to be unity. The polymerization was inhibited in presence of hydroquinone but little inhibitory effect was observed in the presence of air. An average value of k2p/kt for this photopolymerization system was found to be (1.08 ± 0.22) × 10-2. Kinetic and other evidence indicates that the overall polymerization takes place by a radical mechanism.  相似文献   

11.
Methyl methacrylate and styrene were polymerized by using 2,2′-azobis(2,4-dimethyl valeronitrile) as initiator in various solvents. When a poor solvent is used, the dependence of polymerization rate Rp on initiator concentration [C] is small and can be treated by equations for the analysis of the polymerization with primary radical termination. With a good solvent, the dependence of Rp on [C] is so large that such equations are not applicable. Thus, the [C] dependence in a good solvent is explained qualitatively through the molecular weight dependence of rate for termination between polymer radicals, based on the excluded volume effect.  相似文献   

12.
Summary: The analysis of the influence of ionic liquids (ILs) in polymer synthesis as an alternative for common organic solvents is still an active field of research. 1 Using ILs as solvents for free radical polymerizations implies a significant increase in polymerization rates and molecular weights which can be observed. In this work we examined the copolymerization behaviour of styrene (S) and methyl methacrylate (MMA), glycidyl methacrylate (GMA) and 2-hydroxypropyl methacrylate (HPMA) with acrylonitrile (AN) in 1-etyhl-3-methylimidazolium ethylsulfate ([EMIM]EtSO4). ILs are liquids with comparable high polarities and viscosities. These two characteristic properties are strongly correlated with the rate coefficients of propagation kp and termination kt. 2 - 4 The rate constant of termination kt decreases when the IL concentration and therefore the viscosity of the reaction mixture is increased, whereas the propagation rate coefficient kp increases with increasing IL content. The viscosity of the IL can be varied by either working with mixtures of IL with conventional organic solvents – here the IL [EMIM]EtSO4 was mixed with DMF – or by variation of the temperature. The influence of the viscosity of the IL ([EMIM]EtSO4) on polymerization kinetics of methyl methacrylate (MMA) and styrene/acrylonitrile (S/AN) was investigated.  相似文献   

13.
A variety of conditions, including catalysts [CuCl, CuI, Cu2O, and Cu(0)], ligands [2,2′‐bipyridine (bpy), tris(2‐dimethylaminoethyl)amine (Me6‐TREN), polyethyleneimine, and hexamethyl triethylenetetramine], initiators [CH3CHClI, CH2I2, CHI3, and F(CF2)8I], solvents [diphenyl ether, toluene, tetrahydrofuran, dimethyl sulfoxide (DMSO), dimethylformamide, ethylene carbonate, dimethylacetamide, and cyclohexanone], and temperatures [90, 25, and 0 °C] were studied to assess previous methods for poly(methyl methacrylate)‐b‐poly(vinyl chloride)‐b‐poly(methyl methacrylate) (PMMA‐b‐PVC‐b‐PMMA) synthesis by the living radical block copolymerization of methyl methacrylate (MMA) initiated with α,ω‐di(iodo)poly(vinyl chloride). CH3CHClI was used as a model for α,ω‐di(iodo)poly(vinyl chloride) employed as a macroinitiator in the living radical block copolymerization of MMA. Two groups of methods evolved. The first involved CuCl/bpy or Me6‐TREN at 90 °C, whereas the second involved Cu(0)/Me6‐TREN in DMSO at 25 or 0 °C. Related ligands were used in both methods. The highest initiator efficiency and rate of polymerization were obtained with Cu(0)/Me6‐TREN in DMSO at 25 °C. This demonstrated that the ultrafast block copolymerization reported previously is the most efficient with respect to the rate of polymerization and precision of the PMMA‐b‐PVC‐b‐PMMA architecture. Moreover, Cu(0)/Me6‐TREN‐catalyzed polymerization exhibits an external first order of reaction in DMSO, and so this solvent has a catalytic effect in this living radical polymerization (LRP). This polymerization can be performed between 90 and 0 °C and provides access to controlled poly(methyl methacrylate) tacticity by LRP and block copolymerization. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1935–1947, 2005  相似文献   

14.
1,4-Bis(p-tert-butylphenylselenomethyl)benzene was used as a bifunctional photoiniferter for the polymerization of methyl methacrylate (MMA). Both the polymer yields and the number average of molecular weights ([Mbar]n) of polymers increased with the polymerization time and the [Mbar]n linearly increased with polymer yield. The addition of MMA to the poly(MMA) with irradiation increased the [Mbar]n of the polymer. Photoirradiation of telechelic polystyrene having phenylseleno groups at both ends as polymeric photoiniferter in the presence of MMA or p-chloromethylstyrene afforded effectively corresponding to the ABA type triblock copolymers. On the other hand, photopolymerization of p-methylstyrene with ABA type triblock copolymer of styrene and p-chloromethylstyrene as polymeric photoiniferter afforded to multiblock copolymer of styrene and p-substituted styrenes.  相似文献   

15.
The kinetics of solution polymerization of methyl methacrylate using trioctylmethylammonium persulfate (aliquat persulfate) at 60°C has been studied in t-butyl alcohol, N,N-dimethyl formamide, acetonitrile, dioxane, acetone, and methyl ethyl ketone. The rate of polymerization depends markedly on the solvent used. The initiator exponent is close to 0.5 in the first three solvents but larger than this value in the other three solvents. The overall activation energy of the polymerization has been determined in all the solvents. The rate constants and activation parameters for the primary decomposition of the initiator have been determined in the first three solvents where ideal polymerization conditions prevail. The activation parameters for the decomposition of AQ2S2O8 in the organic solvents depend on the type of solvent. They are very different from those of the free S2O2?8 ion in water. These differences have been explained taking into consideration the various ionic forms in which the initiator exists in the studied solvents using a previously postulated model of the activated state.  相似文献   

16.
The propagation rate coefficient (kp) of methyl methacrylate has been measured in miniemulsions. The molecular weight distributions show many higher order peaks, which seems to be specific for pulsed initiation polymerization in compartmentalized liquids. The kp values are very similar to bulk values although a frequency dependence is observed. This frequency dependence, which was overlooked in earlier research, is also present in pulsed laser experiments in bulk.  相似文献   

17.
The polymerization of methylated β‐cyclodextrin (m‐β‐CD) 1 : 1 host‐guest compounds of methyl methacrylate (MMA) ( 1 ) or styrene ( 2 ) is described. The polymerization of complexes 1 a and 2 a was carried out in water with potassium peroxodisulfate (K2S2O8)/sodium hydrogensulfite (NaHSO3) as radical redox initiator at 60°C. Unthreading of m‐β‐CD during the polymerization led to water‐insoluble poly(methyl methacrylate) (PMMA) ( 3 ) and polystyrene ( 4 ). By comparison, analogously prepared polymers from uncomplexed monomers 1 and 2 in ethanol as organic solvent with 2,2′‐azoisobutyronitrile (AIBN) as radical initiator showed significantly lower molecular weights and were obtained in lower yields in all cases. Polymerization of m‐β‐CD complexed MMA in water, initiated with 2,2′‐azobis(N,N ′‐dimethyleneisobutyroamidine) dihydrochloride, occurred much faster than the polymerization of uncomplexed MMA in methanol under similar conditions. Furthermore, it was shown, that the precipitation polymerization of complexed MMA from homogeneous aqueous solution can be described by equations (Pn–1 ∝ lsqb;Irsqb;0.5) similar to those for classical polymerization in solution.  相似文献   

18.
Solvent effect on homo- and copolymerization of di-2-[2-(methoxyethoxy)ethoxy]ethyl itaconate (DMEI) was studied at 50 °C using dimethyl 2,2-azobisisobutyrate as radical initiator. The polymerization rate (Rp) highly depended on the kind of solvent; 19 solvents were used. The highest Rp (in 1-tetradecanol) is 13 times the smallest (in chloroform). On the other hand, the solvents did not exert as great an effect on the molecular weight of the resulting polymers. The propagation rate constant (kp) was determined in 15 different solvents by means of ESR spectroscopy. The highest kp (4.5 l/mol s in toluene) is 5.6 times the lowest (0.8 l/mol s in chloroform). A noticeable solvent effect was also observed in the copolymerization of DMEI (M1) and styrene (M2), where nine solvents were used. The highest r1 (0.46 in 1-butanol) is about 6 times the lowest (0.08 in methanol). The r2 value falls in the range of 0.2 (dimethyl sulfoxide) and 0.52 (benzene). The solvent effects thus observed were analyzed according to the linear solvation energy relationship proposed by Taft and co workers.  相似文献   

19.
Photopolymerization of methyl methacrylate in bulk and in solution at 40 °C using monochloroacetic acid –dimethyl aniline (MCAA–DMA) combination as photoinitiator was studied kinetically. The apparent activation energy was found to be 4.39 kcal/mol (18.37 kJ/mol) while the kinetic parameter kp2/kt was 1.27 × 10−2 1/mol/sec. The kinetic data indicated that polymerization followed a radical mechanism. The initiator order was found to be 0.25, indicating significant deviation from the square root dependence for normal free radical kinetics. The non‐ideality in the kinetics can be explained on the basis of significant initiator‐dependent termination through primary radicals or degradative initiator transfer. The observed monomer order was significantly less than unity (i.e. nonideal behavior) for use of carbon tetrachloride, chloroform, methylethyl ketone and acetic acid as diluents, but it was unity (i.e. ideal behavior) for use of benzene as the diluent. Solvents other than benzene contributed to enhancement of rate of polymerization by influencing the radical generation step. End‐group analysis indicated the incorporation of DMA and MCAA moieties as end‐groups in the polymers. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

20.
Propagation rate coefficients, kp, of methyl methacrylate (MMA) and glycidyl methacrylate (GMA) homopolymerizations were measured at ambient pressure in four ionic liquids (ILs): 1‐ethyl‐3‐methylimidazolium ([emim]) ethyl sulfate and [emim] hexyl sulfate as well as butyl‐3‐methylimidazolium ([bmim]) hexafluorophosphate and [bmim] tetrafluoroborate via the pulsed‐laser polymerization size‐exclusion chromatography technique. In passing from bulk polymerization at 40 °C polymerization in IL solution containing 20 vol % monomer, kp is enhanced by up to a factor of 4 with MMA and by a factor of 2 with GMA. This enhancement of kp primarily results from a lowering of activation energy upon partial replacement of monomer by ionic liquid species. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1460–1469, 2008  相似文献   

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