Monomers viscosity

All of the eommereial alkyl eyanoaerylate monomers are low-viseosity liquids, and for some applications this can be an advantage. However, there are instances where a viseous liquid or a gel adhesive would be preferred, sueh as for application to a vertical surface or on porous substrates. A variety of viscosity control agents, depending upon the desired properties, have been added to increase the viscosity of instant adhesives [21]. The materials, which have been utilized, include polymethyl methacrylate, hydrophobic silica, hydrophobic alumina, treated quartz, polyethyl cyanoacrylate, cellulose esters, polycarbonates, and carbon black. For example, the addition of 5-10% of amorphous, non-crystalline, fumed silica to ethyl cyanoacrylate changes the monomer viscosity from a 2-cps liquid to a gelled material [22]. Because of the sensitivity of cyanoacrylate esters to basic materials, some additives require treatment with an acid to prevent premature gelation of the product. 

According to O Driscoll, / (rei) should increase with pressure in the cases discussed, the counteracting effects of viscosity changes in monomer viscosity and polymeric coil dimensions are very pronounced. 

In these equations jy, = tiltjQ is the relative bulk viscosity, with t o referring to the pure monomer viscosity at identical p and T. The terms and kp refer to the termination and propagation rate coefficients at very low conversion, respectively. Also from SP-PLP experiments, these two quantities are found to be ... 

As the polymerization proceeds with further consumption of the monomers, viscosity of the reaction mixture dramatically increases, thus additionally restricting the mobility of the growing chain s ends. For this reason, even at a high conversion of monomers, a certain part of pendant vinyl groups miss the chance of meeting a growing macroradical and remain unreacted in the final material. Thus, approximately 30% of DVB units have been found incorporated in a styrene—8% DVB network by one double bond only [32]. Even in the copolymer with l%p-DVB obtained at 70°C, 40% of DVB vinyl groups remained unreacted. This quantity dropped to 16% when the polymerization was finished at 95°C [33]. 

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As we can see, in accordance with obtained estimations (Table 5.1) the constant rate of the heterophaseous process 2 practically does not depend on nature of the di(meth)acrylate, whereas the constant rate of homophaseous process k] increases with molecular mass and decreasing monomer viscosity. 

In situ polymerization of PA12 is also very common. Here the monomer viscosity can be reduced to 3 Pa s before polymerization. Another well known material for in situ polymerization is PA6. Furthermore, to increase the toughness of the laminate, in situ polymerization can be combined with nanoparticles or carbon nanotubes. 

This experimental observation can also be correlated with the pressure dependency of the viscosity. The reaction medium tends to be more viscous at higher reaction pressures, thus slowing the rate of termination ie, the activation volume of the termination rate coefficient is very close to the corresponding activation volume that characterizes the pressure dependence of the inverse of the monomer viscosity (356). It is important to note that the pressure dependencies of the termination and propagation rate coefficients display opposite behavior, ie allowing for increased rates of polymerization at elevated pressures. 

In order to study poly(n-butyl acrylate) fronts, Pojman et al. added ultrafine silica gel to increase the monomer viscosity (74). To determine the inherent molecular weight distribution (MWD) of poly(n-butyl acrylate) produced frontally, it was necessary to perform a front without silica gel. Because of the Rayleigh-Taylor instability, the only way to accomplish this with a thermoplastic-forming monomer such as n-butyl acrylate is to eliminate the driving force for the collapse of the more dense polymer layer, i.e., eliminate the force of gravity. An experiment was launched on the 1996 Conquest / rocket... 

One way to minimize the effects of g-jitter is to increase the monomer viscosity. We did this by dissolving poly(hexyl acrylate) in the hexyl acrylate. This increased the viscosity of the monomer sufficiently to damp the effects of g-jitter. It also lowered the front temperature. Lowering the front temperature... 

V acrylate the bulk monomer viscosity of the acrylate. Equation 4.15 is an approximation as the diffusion coefficient of a diffusing entity does not only depend upon the viscosity of the medium, but also on the charateristics of the dififusant itself At 50°C, the monomer diffusion coeficient of MMA is relatively well determined and has been found to be equal to 4.11TO m s [36]. The viscosities of MMA, MA, EA and BA, that are needed to estimate a diffusion coefficient for these monomers on the basis of equation 4.15, were calculated according to [37] ... 

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