Using copper chloride as catalyst, we have achieved telomerization of butadiene with several different halogenated compounds as telogens. These telogens must have a CCl3 group to be active as transfer agents. There is a linear relationship between log (telogen reactivity) and the σ1 Taft constant of the R group. Using this relation, we have determined the values of the σ1 constants for some halogenated substances. The reactivities of the telogens can be measured by this means. The results confirm those obtained earlier with styrene. 相似文献
The molecular mass distributions (MMD) of perfluorinated oligomers in products of tetra-fluoroethylene (TFE) radical polymerization in various solvents (telogens) were determined from an analysis of differential thermogravimetric curves and data of gel permeation chromatography and mass spectrometry. Radiolysis of the telogens generates radicals initiating polymer chain growth. The choice of the solvent and TFE concentration makes it possible to obtain oligomers with the controlled average chain length from 4 for 40 CF2 fragments and specified terminal groups. The polymerization of TFE in THF and propylene oxide affords oligomers with cyclic terminal groups capable of further polymerization due to ring opening. The appearance of two MMD maxima (low-molecular-weight at n1 ~6–8 and high-molecular-weight at n2 > 10 shifting towards high n with an increase in the TFE concentration) is caused by the formation of colloidal solutions of oligomers. 相似文献
A method for the direct computation of the chain length distribution in a bulk polymerization is developed, based on the discretization procedure introduced by Kumar and Ramkrishna (Chem. Eng. Sci. 1996 , 51, 1311) in the context of particle size distribution. The overall distribution of chain lengths is partitioned into a finite number of classes which are supposed to be concentrated at some appropriate pivotal chain lengths. Several of the involved reactions lead to the formation of chain whose length differs from the pivotal values. Rules have been introduced in order to share chains between two contiguous classes, which have been designed so as to preserve two well‐defined properties of the distribution, such as, for example, two of its moments. The method has been applied to a polymerization system including propagation, bimolecular terminations and two different chain branching mechanisms: chain transfer to polymer and crosslinking. In addition, complex systems such as one with chain length‐dependent kinetic constants or a two‐dimensional distribution of chain length and number of branches have been considered. 相似文献
Radical polymerizations of methyl methacrylate (MMA) and styrene (St) in bulk at low conversion were carried out in the presence of pentadienic chain transfer agents (CTA), 5-bromo-1,3-pentadiene (1), 5-benzenesulphonyl-1,3-pentadiene (2) and methyl 2-bromomethyl-4-methyl-2,4-pentadienoate (3), to produce conjugated diene-end capped macromonomers by a addition-fragmentation mechanism. The chain-transfer constants (Cir) of 1, 2 and 3 for MMA polymerization were obtained from the Mayo equation, respectively. Correction to zero conversion afforded an accurate value of the chain transfer constant for 1. The chain transfer was found to be degradative. The pentadienyl group formed by fragmentation of the macroradical abduct is quantitatively introduced at the ω-end of the polymer. 相似文献
Abstract The kinetics of the copolymerization of alpha‐methyl styrene (AMS) and butyl acrylate (BA) have been revised to include both the bulk and solution systems. Reactivity ratios and other kinetic parameter estimates based upon a copolymerization model developed by Kruger have been ascertained for a range of temperatures (60–140°C) and at a single solvent level (23?wt%). Full conversion range studies have been completed at two different solvent levels to determine the effects of feed composition, solvent, and chain transfer agent (CTA) on the rate of polymerization, copolymer composition, and the resulting molecular weight. 相似文献
Abstract The most usual procedure to estimate the chain transfer ratio in vinyl polymerization is to use a Mayo plot. This plot can only be applied directly when the polymerization rate is not modified by the chain transfer agent. In spite of this, the equation has been applied to several systems where this condition is not fulfilled. In the present work we present a slightly modified equation that can be employed irrespective of the changes in rate. This equation is applied to several systems reported in the literature. The improvement in the interpretation of the results in these systems is discussed. 相似文献
N-alkyl phosphoranimines were synthesized via the Staudinger reaction of four different alkyl azides with tris(2,2,2-trifluoroethyl) phosphite. N-adamantyl, N-benzyl, N-t-butyl, and N-trityl phosphoranimines were thoroughly characterized and evaluated as chain-capping compounds in the anionic polymerization of P-tris(2,2,2-trifluoroethoxy)-N-trimethylsilyl phosphoranimine monomer. All four compounds reacted with the active chain ends in a bulk polymerization, and the alkyl end groups were identified by 1H-NMR spectroscopy. These compounds effectively controlled the molecular weight of the resulting polyphosphazenes. The chain transfer constants for the monomer and N-benzyl phosphoranimine were determined using Mayo equation. 相似文献
A method is proposed for analysing the problems associated with non-ideal polymerizations reflected mainly in the variability of Rp/[I]0·5[M] where Rp is the rate of polymerization and [I] and [M] are the initiator and monomer concentrations, respectively. Primary radical termination and degradative chain transfer are treated jointly and the entirely different mathematical natures of the two processes are described. The method could dispense with the need to use the uninhibited rate of polymerization which does not lend itself to reliable measurements for many systems. It is found to be efficient in detecting the active species in a polymerization system that leads to non-ideality due to degradative chain transfer.This method is applied to vinyl chloride polymerization data from the literature, the values of constants obtained therefrom are found to agree well with the existing values. 相似文献
Pulsed‐laser polymerization (PLP) has been adopted by IUPAC as the method of choice for the determination of propagation rate constants (kp). However, the method has failed in the polymerization of alkyl acrylates at temperatures above 30 °C. In this work, the PLP experiments were analyzed by simulation using a Monte Carlo algorithm. It was found that the experimental difficulties encountered to accurately determine kp at temperatures above 30 °C were caused by extensive intramolecular chain transfer. This mechanism is not operative at lower temperatures because of its high activation energy.
Pulsed‐laser polymerization of BA in bulk at temperatures between −41 and +40 °C: Simulated MWD trace. 相似文献
In quasiliving polymerizations with reversible chain transfer (QL0R systems), polymers with narrow molecular weight distribution can be obtained, It has been shown that while in true living systems (L00) R = 1, and in quasiliving systems with irreversible chain transfer (QL01) R = 2 is the limiting value of polydispersity, in QL0R systems r = 4/3 is the polydispersity to which the distribution of the polymer tends with increasing polymerization time. This limit is independent of the rate of reinitiation; the course of the R vs t curves is, however, determined by the various rate constants. 相似文献
Detailed kinetic analysis of AIBN-initiated polymerization of methylmethacrylate in presence of p-benzoquinone has been reported. Primary radical transfer, whereby a primary radical transfers its radical reactivity to a transfer agent, has been considered along with macroradical transfer. It is found that the former process is quite appreciable in the system and must be allowed for to arrive at accurate values of transfer constants. Values of transfer constants for both primary radicals and macroradicals towards benzoquinone, and characteristic constants for degradative chain transfer and primary radical transfer have been evaluated applying the mathematical treatment developed previously. The mode of termination of macroradicals by fairly stable microradicals formed as a result of transfer has also been discussed. 相似文献
Abstract The course of the isothermal bulk polymerization of methacrylic acid and some methacrylic acid esters differing in the length of the ester group was studied by differential scanning calorimetry at different temperatures. The enthalpies of polymerization, the residual monomer content, the overall reaction rate constants, and the overall activation energies were calculated. The molecular weight averages of the synthesized polymers before and after the gel effect were measured by gel permeation chromatography. 相似文献
The role of monomer in catalytic chain transfer polymerization was studied by determination of the chain transfer constants of the tetraphenyl derivative of cobaloxime boron fluoride (COPhBF) in methyl methacrylate at 60°C varying the monomer concentration instead of the COPhBF concentration as is common practice. Toluene and tert‐butyl acetate were used as diluents in these studies and it was found that the chain transfer constants obtained in the present studies were not significantly different from those observed in conventional experiments. These results suggest the absence of a direct participation of monomer molecules in the hydrogen abstraction step in catalytic chain transfer. 相似文献
Abstract The reversible addition fragmentation chain transfer (RAFT) bulk polymerization of isobutyl methacrylate (i‐BMA) has been studied using 2‐cyanoprop‐2‐yl dithionaphthalate (CPDN) as RAFT agent in the presence of 2,2′‐azobisisobutyronitrile (AIBN). The results of polymerizations of i‐BMA show that i‐BMA can polymerize in a controlled way by RAFT polymerization using CPDN as RAFT agent; i.e., the polymerization rate is first order with respect to monomer concentration, molecular weight increases linearly with monomer conversion, and polydispersities are relatively low (PDI?<?1.2). The structure of the polymer was characterized by 1H‐NMR. A chain‐extension experiment of the resulting polymer was successfully carried out. The influences of [i‐BMA]0/[CPDN]0/[AIBN]0 molar ratio and reaction temperature were investigated. 相似文献