Liquid monomer

As an example stereolithography is a 3-D rapid process that produces automatically simple to very complex shaped models in plastic. Basically it is a method of building successive layers across sections of pho-topolymerized plastics on top of each other until all the thin printed layers can be joined together to form a whole product. The chemical key to the process, photopolymerization, is a well established technology in which a photo initiator absorbs UV energy to form free radicals that then initiate the polymerization of the liquid monomers. The degree... 

In solution polymerization, monomers mix and react while dissolved in a suitable solvent or a liquid monomer under high pressure (as in the case of the manufacture of polypropylene). The solvent dilutes the monomers which helps control the polymerization rate through concentration effects. The solvent also acts as a heat sink and heat transfer agent which helps cool the locale in which polymerization occurs. A drawback to solution processes is that the solvent can sometimes be incorporated into the growing chain if it participates in a chain transfer reaction. Polymer engineers optimize the solvent to avoid this effect. An example of a polymer made via solution polymerization is poly(tetrafluoroethylene), which is better knoivn by its trade name Teflon . This commonly used commercial polymer utilizes water as the solvent during the polymerization process,... 

Another method of manufacturing polypropylene employs the liquid monomer as the polymerization solvent. This process, known as the liquid propylene or bulk-phase process, has a major advantage over the slurry method in that the concentration of the monomer is extremely high. The high concentration increases the rate of the reaction relative to that seen... 

An explosion in a valve in a liquid monomer line was ascribed to traces of oxides of nitrogen remaining after the valve had been passivated by treatment with nitric acid. 

Figure 2. 13C NMR spectra of the TrMPTrA liquid monomer (lower) and solid polymer (upper).

Mobil-Witco-shell A process for making poly (1-butene) by polymerizing 1-butene with a Ziegler catalyst in an excess of liquid monomer. 

The liquid monomer dimerizes to a solid upon storing at room temperature 24>. 

Owing to their liquid or semisolid nature, monomers are easy to process into polymers. For radical polymerization the use of solid AIBN for liquid monomers at room temperature and liquid MEKP for semisolid monomers or a mixture of liquid and semisolid monomers with some heating is convenient. During the course of curing at 85- 100°C for 22 h the problem of surface inhibition of free radicals by oxygen from the air can be avoided by inert-gas blanketing. 

Liquid-molding resins, based on poly(dicyclopentadiene), 20 432 Liquid monomer phase, in PVC polymerization, 25 667 Liquid NaK alloy, 20 603. See also NaK entries... 

Figure 1. Schematic drawing of two planarization processes using (A) a low molecular weight polymeric resin and (B) a low viscosity, liquid monomer.

The liquid monomer or the liquid mix is cast by simple gravity without pressure in the open or closed mould, possibly containing a reinforcement. 

Figure 24. X-ray diffraction pattern (in the inset the 2D image) of the polyethylene sample recovered by the laser-assisted high-pressure reaction in the pure liquid monomer. The two measured sharp lines nicely fit the polymer diffraction pattern having a orthorhombic cell (Pnam) defined by the lattice parameters reported in the figure.

Table 3.17. Thermodynamic parameters for the conversion of liquid monomer into solid amorphous polymer [750],...

DSC studies have shown that multifunctional monomers react quickly to form densely crosslinked networks from liquid monomer solutions. However, even a small amount of unreacted monomer can effectively plasticize a crosslinked network, rendering it more pliable. Eor this reason, mechanical analysis was combined with DSC studies to characterize the physical changes occurring in the proposed dimethacrylate system as polymerization proceeds. Static compression tests (Perkin-Elmer, DMA7e) were completed on disks (d = 11.5 mm, t = 1.7) immediately after they were irradiated for varied times. 

RIM is increasing in importance and emphasizes the production of thermoset PUs. Here, liquid monomers are mixed together under high pressure prior to injecting into the mold. Polymerization occurs within the mold. Most automotive dash panels are RIM-produced. Notice the tough surface and semiflexible underbelly of the dash. The amount of foam formation is controlled to give the finished product. 

Bulk polymerization of a liquid monomer such as methyl methacrylate is relatively simple in the absence of oxygen where small bottles or test tubes can be used as the reaction vessel. 

Initially, there was a problem casting lenses from CR-39 because there is typically shrinkage, with the polymer denser than the liquid monomer, when vinyl monomers are polymerized. In this case there was 14% shrinkage. This was not a problem when casting flat lenses since... 

Data fromBrandrup and Immergut [1989] Sawada [1976]. b AH refers to the conversion of liquid monomer to amorphous or (slightly) crystalline polymer. AS refers to the conversion of monomer (at a concentration of 1 M) to amorphous or slightly crystalline polymer. The subscripts Ic are often used with AH and AS to show the initial and final states (that is, AHic and AS ). The units of AH are kJ mol-1 of polymerized monomer the units of AS are J K-1 mol-1. 

Monomer concentration = 1 atm (gaseous) all other data are for neat liquid monomer. 

The single most important factor that determines whether a cyclic monomer can be converted to linear polymer is the thermodynamic factor, that is, the relative stabilities of the cyclic monomer and linear polymer structure [Allcock, 1970 Sawada, 1976]. Table 7-1 shows the semiempirical enthalpy, entropy, and free-energy changes for the conversion of cycloalkanes to the corresponding linear polymer (polymethylene in all cases) [Dainton and Ivin, 1958 Finke et al. 1956]. The Ic (denoting liquid-crystalline) subscripts of AH, AS, and AG indicate that the values are those for the polymerization of liquid monomer to crystalline polymer. 

---