Diffusion‐controlled vinyl polymerization. II. Limitations on the gel effect

Soh, S. K.; Sundberg, Donald C.

doi:10.1002/pol.1982.170200514

Cited by 109 publications

(61 citation statements)

References 7 publications

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“…In free radical polymerizations at low conversions, the termination is a diffusion-controlled process, with the rate determined by the segmental diffusion of the chaincarrying radical end-group [16][17][18] . The rate of this process is proportional to the reciprocal of the medium viscosity.…”

Section: Solvent Effect On Propagation and Termination Stepsmentioning

confidence: 99%

Solvent effects on the rate of polymerization of 2-hydroxyethyl methacrylate photoinitiated with aliphatic azo compounds

Alvarez

Encinas²,

Lissi

1999

Macromol. Chem. Phys.

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SUMMARY: The rate of polymerization (R p ) of 2-hydroxyethyl methacrylate, at low conversion, using aliphatic azo compounds as photoinitiators is considerably faster in water than in acetonitrile as a solvent. Active radical production in different solvents was analysed in detail. The quantum yield of active radicals showed only a minor dependence on the medium properties. These differences are due to changes in primary radical recombination reactions and they are unrelated to changes of R p observed in different media. By employing intermittent illumination techniques, it is shown that the increased R p in aqueous solution is due to a reduced rate of termination. Similar propagation rate constants were obtained in acetonitrile and water, whereas the termination rate constant increases by one order of magnitude when acetonitrile is employed instead of water. These results are discussed in terms of the effect of the cosolvent on the medium viscosity and the macroradical conformation.

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Section: Solvent Effect On Propagation and Termination Stepsmentioning

confidence: 99%

Solvent effects on the rate of polymerization of 2-hydroxyethyl methacrylate photoinitiated with aliphatic azo compounds

Alvarez

Encinas²,

Lissi

1999

Macromol. Chem. Phys.

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show abstract

“…Soh et al pointed out that the entanglement of a linear polymer chain, like polyisoprene, also occurred without cross linking as the polymer concentration and/or molecular weight increased. [26][27][28][29] They also explained the occurrence of an entanglement of a polymer chain whose molecular weight was more than ca. 10 4 , large enough to cause a transient network structure.…”

Section: Temperature Dependence Of T1 and T2mentioning

confidence: 98%

Pulsed NMR Study of the Curing Process of Epoxy Resin

et al. 2008

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“…Soh et al pointed out that in a bulk polymerization of MMA, the entanglement of polymer chains occurred as the polymer concentration and/or molecular weight increased. [16][17][18][19] They also explained that the gel effect is closely related to a change of the free volume and the occurrence of the entanglement of a polymer chain whose molecular weight is more than ca. 10 4 .…”

Section: Reaction Time Dependence Of the Spin-spin Relaxation Timesmentioning

confidence: 99%

Pulsed NMR Study of Network Formation in the Course of Bulk Polymerization of Methyl Acrylate

et al. 2005

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Pulsed NMR can be used to elucidate certain aspects of the polymer structure and those properties that are affected by the molecular mobility. The spin-spin relaxation time (T2), which is primarily determined by the relatively slow motion of the polymer chain in the fluid state, was found to be useful for investigating the polymer structural order, chain entanglement and their presence as permanent cross-links. 1-3 Short polymer chains in a liquid state or at high temperature in the molten state will give rise to a single exponential T2 decay. When the molecular weight exceeds a critical value, the spin-spin relaxation deviates from the single exponential behavior. This is explained by the presence of higher molecular weights of molecular entanglements sufficient in number to provide a three dimensional network. 4 The entanglement of a polymer chain restricts the chain mobility. Since this long-range chain motion affects the NMR relaxation times, the studying T2 can provide a sensitive probe with which to investigate the effect of intermolecular coupling on the mobility.Most of molecular motion studies, however, have focused on polymers in a static state, such as cross-linked rubbers, 5 polymer melts with non-disperse molecular weight. 3 From a molecular motional point of view, bulk polymerization is also one of the most interesting targets for pulsed NMR spectroscopy. The reaction is followed by a liquid-to-solid transition accompanied by a change in the polymer structure, the molecular weight distribution and the density. The molecular motion during the course of the reaction is, therefore, continuously influenced particularly by the propagation process, where the entanglement occurs along with a rapid increase in the degree of polymerization. Under such circumstances, samples consist of a mixture of high-polymer, low-molecular weight polymer, oligomers, and a residual monomer where high molecular weight entangled (network structure) molecules co-exist with low molecular weight "free molecules". The constituents' fractions also continuously change during the reaction. In terms of the molecular motion, studying the network formation by a pulsed NMR method in a kinetic process, such as bulk polymerization, is therefore of interest and worth investigating as well as that by the gravimetric method, 6-9 because the pulsed NMR method provides such a different perspective on the kinetic process of the reaction in real time.In the present work, the proton spin-spin relaxation time of poly(methyl acrylate) (PMA) was measured in order to study network formation as a function of the reaction time at various temperatures by the pulsed NMR method. The results were considered in conjunction with that of 13 C DD/MAS NMR measurements and the polymer yield. ExperimentalPulsed NMR measurements were carried out with a JEOL Mu-25 spectrometer operating at a frequency of 25 MHz. The proton spin-spin relaxation time (T2) was obtained from the free induction decay (FID), which follows a 90˚ pulse. 10 The pulse interval time was 10 s...

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Diffusion‐controlled vinyl polymerization. II. Limitations on the gel effect

Cited by 109 publications

References 7 publications

Solvent effects on the rate of polymerization of 2-hydroxyethyl methacrylate photoinitiated with aliphatic azo compounds

Solvent effects on the rate of polymerization of 2-hydroxyethyl methacrylate photoinitiated with aliphatic azo compounds

Pulsed NMR Study of the Curing Process of Epoxy Resin

Pulsed NMR Study of Network Formation in the Course of Bulk Polymerization of Methyl Acrylate

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