Gelation period

In this paper, the pseudo-kinetic rate constant method in which the kinetic treatment of a multicomponent polymerization reduces to that of a hcmopolymerization is extensively applied for the statistical copolymerization of vinyl/divinyl monomers and applications to the pre- and post-gelation periods are illustrated. 

Now the post-gelation period of the copolymerization of divinyl/vinyl monomers in the presence of a good solvent as a diluent will be considered. Let Qv(x) be the equilibrium volume swelling ratio of the gel formed at conversion x, and Q°(x) its degree of dilution in the reaction system, i.e.,... 

Promoters, If needed, may be added during the gelation period. Alternatively. they may be deposited, using the same methods described later for active components. 

Zhu and Hamielec [94] studied the FRC of vinyl monomers with chain transfer to polymer and the copolymerization of vinyl/divinyl monomers using a multiradical approach. They used the method of moments and focused on the pre-gelation period. They concluded that... 

Run 2 was conducted by Injecting two fracture pore volumes of sodium orthosilicate and HCI solution at a pH of 9.4. This was followed by a CO injection. The CO2 injection rate was slow (20 ml/hr) and a total volume of 90ml was injected. During gel and CO2 injection, the core was left intact overnight. The same procedure was used for Runs 2 through 10. For Run 2 this gelation period was followed by a waterflood. The injected water salinity was the same as the... 

A low gelation temperature is used to minimise the thermal expansion of the rubber part of the mould and so avoid undue pressure on the composite during the critical gelation period. Accelerator DY 062 was selected to achieve a long useable life at 30 C, while giving a relatively short gelation period at 60°C. 

Formation of floccules is interpreted theoretically within the frameworks of the gelation period concept [137] (the indicated concept is stated in more detail in Chapter 3). The authors of paper [138] explained the formation of floccules within the frameworks of synergetics and fractal analysis in the example of sulfur-containing epoxy polymers (SCE) cured by aromatic diamines (4,4 -diaminodiphenylsulfone (SCE-DADPS) and 4,4 -diaminodiphenylmethane (SCE-DADPM)) and iso-methyltetrahydrophthalic anhydride (SCE-IMTHPhA) [139]. 

At the formation of the structure of crosslinked polymers one can observe the formation of dissipative structures (DS) of two levels - micro- and macro-DS. Micro-DS are local order domains (clusters) and their formation is due to the high viscosity of the reactive medium in the gelation period. As it is known [47], this results in turbulence of viscous media and subsequent formation of ordered regions. 

The free radicals initially formed are neutralized by the quinone stabilizers, temporarily delaying the cross-linking reaction between the styrene and the fumarate sites in the polyester polymer. This temporary induction period between catalysis and the change to a semisoHd gelatinous mass is referred to as gelation time and can be controUed precisely between 1—60 min by varying stabilizer and catalyst levels. 

The commercial polymers are of comparatively low molecular weight (M = 25 000-60 000) and whilst being essentially linear may contain a few branches or cross-links arising out of thermal oxidation. Exposure to ultraviolet light causes a rapid increase in gel content, whilst heating in an oven at 125°C causes gelation only after an induction period of about 1000 hours. Eor outdoor applications it is necessary to incorporate carbon black. The polymers, however, exhibit very good hydrolytic stability. 

In random bond percolation, which is most widely used to describe gelation, monomers, occupy sites of a periodic lattice. The network formation is simulated by the formation of bonds (with a certain probability, p) between nearest neighbors of lattice sites, Fig. 7b. Since these bonds are randomly placed between the lattice nodes, intramolecular reactions are allowed. Other types of percolation are, for example, random site percolation (sites on a regular lattice are randomly occupied with a probability p) or random random percolation (also known as continuum percolation the sites do not form a periodic lattice but are distributed randomly throughout the percolation space). While the... 

Porous asymmetric CA membranes were prepared from all the solutions listed in Tables 1 and 2. Temperature of the casting solutions was 25°C except in one case which is later thoroughly discussed. The glass plate on which the solution was cast was kept at the same temperature as the casting dope. Temperature of the casting atmosphere was 20-25°C and the relative humidity was 60-65%. If not otherwise specified the evaporation period was as short as possible, i.e. the cast solution was immersed immediately into a gelation bath consisting of ice-cold water. 

Control of crosslinking is critical for processing thermoset plastics, both the reaction prior to the gel point and that subsequent to the gel point. The period after the gel point is usually referred to as the curing period. Too slow or too rapid crosslinking can be detrimental to the properties of a desired product. Thus, in the production of a thermoset foamed product, the foam structure may collapse if gelation occurs too slowly. On the other hand, for reinforced and laminated products the bond strength of the components may be low if crosslinking occurs too quickly. 

An increase in curing temperature resulted in UPE gelation, which restricted the secondary phase separation and the coalescence of spinodal decomposition. To be specific the longer the demixing period, the larger or the more interconnected the dispersed phase became. Min et al. [20,21] observed the dual phase morphology at 15wt% polysulfone... 

According to Claude Bernard the action of anesthetics is very general. They react not only with animals but also with plants. Bose has found that plants anesthetized with ether go through a preliminary period of increased irritability or stimulation. A dilute alcohol solution acted as a stimulant, whereas a concentrated alcohol solution acted as a depressant. Nichols applied chloroform to the wall of an intemode of Nitella by means of a capillary pipette. An area of non-motile protoplasm was produced at the point of application of the anesthetic. This area of non-motile protoplasm resumed its movements later, so the process appears to be a reversible one. Nichols considers the effect to be due to gelation, thus providing us with a case of reversible coagulation in plants accompanied by anesthesia of the part affected. 

The number indicates the evaporation period (mini. Film is specified in reference 6. dThe first, second, and third numbers indicate acetyl content, volume percent of ethanol in gelation bath, and shrinkage temperature, respectively. A zero as the third number means no shrinkage. 

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