Solid-state polymerization low-temperature

Simultaneous evaporation of metal with organic and inorganic substances followed by vapor deposition on a substrate allows the production of composite films containing M nanoparticles stabilized in various dielectric matrices [2, 28]. The use of monomer molecules in this process polymerizing during deposition or as a result of the subsequent reactions yields polymeric nanocomposite films with metal inclusions [2, 3, 28, 37]. The new low-temperature synthesis of polymeric nanocomposite films has been elaborated recently. This synthesis is based on the deposition of M/SC and monomers vapors at temperature 80 K followed by low-temperature solid-state polymerization of obtained films in conditions of frozen thermal movement of molecules (cryochemical synthesis) [2], This synthesis has important features, which will be considered further. 

As mentioned above, the new method of cryochemical synthesis of polymer nanocomposite films has been developed based on co-deposition of M/ SC and monomer vapors at temperature 80K and subsequent low-temperature solid-state polymerization of monomer matrix ([2] and works cited herein). It has been established that a number of monomers (acrylonitrile, formaldehyde, /i-xylylene and its derivatives) polymerize in solid state in absence of thermal movement of molecules owing to own specific supra-molecular structure. When reaction is initiated by y- or UV-radiation the formation of a polymer matrix occurs even at the temperatures close to temperature of liquid helium [66-69]. 

Inorganic nanoparticles such as metal/semiconductors (M/SC) immobilized in polymer matrices have attracted considerable interest in recent years due to their distinct individualistic and cooperative properties [84]. Although the control of size and shape of M/SC nanoparticles has been widely investigated, the fundamental mechanism of nanostructural formation and evolution is still poorly understood. A novel cryochemical solid-state synthesis technique has been developed to produce M/SC nanocomposites [85]. This method is based on the low-temperature cocondensation of M/SC and monomer vapors, followed by the low-temperature solid-state polymerization of the cocondensates. As a result of the method of stabilizing the metal particle without requiring any specific coordination bonds between the particle surface and the polymer matrix, generated nanoparticles (Ag-nanocrystal mean size 50 A) were embedded in the polymer matrix with well-controlled shapes and a narrow size distribution [86]. 

Nylon-4,6. This nylon is produced from diaminobutane and adipic acid. The process is similar to that for nylon-6,6, but the amine has a high tendency to cyclize and the temperatures are therefore kept low. This results in a low molecular weight polymer, which is subsequendy increased in viscosity by solid-state polymerization. 

A low degree of tacticity is obtained because these monomer-orienting forces are quite weak. Thus, polymer stereoregularity is achieved only with certain suitable monomers and at low temperatures. Increased tacticity can be achieved in some cases by using monomer-orienting forces other than the catalyst or the polymer end groups, but these have rather limited utility (canal complexes, solid state polymerizations, etc.). Simple polymerization systems fall outside the scope of this review and are not discussed further. 

Pofy-l-vinyluradl (poly-VUr, 10) was also obtained by a free-radical polymerization6). In this case, it should be noted that the formation of substituted dihydrouradl rings occurred via a cydopolymerization mechanism11). y-Ray induced solid-state polymerization of the monomer (9) in high concentration and at low temperature excluded cydopolymerization completely12). Poly-VUr was also prepared by a free-radical polymerization of 2-ethoxy-4-l-vinyl-pyrimidone (ii)8) or 4-ethoxy-l-vinyl-2-pyrimidone (13)iy> followed by acid hydrolysis of the resulting polymers (12) or (14) (Scheme 2). 

Solid-state polymerization involves first-step production of low molecular weight polymer or oligomer via melt or interfacial process. The low molecular weight material is then crystallized in acetone. Basic catalyst is added and the material is heated above Tg but below crystalline melting temperature (Tm) to polymerize, and phenol is removed. The resulting polymer is melt-processed to remove crystallinity and form amorphous... 

In a solid state polymerization reaction monomer crystals of diacetylene molecules (R-CiC-C=C-R) are converted to polydiacetylene crystals (1,2). The primary photochemical processes during the low-temperature photopolymerization reaction have been investigated by ESR (3,4) and optical absorption spectroscopy (5,6). A review ofthe spectroscopy of the intermediate states has been given by Sixl (V. A simple reaction scheme is shown in Figure 1. The reaction is characterized by the uv-photolnitiation of dira-dlcal dimer molecules. Chain propagation is performed by thermal addition of monomer molecules. Thus trimer, tetra-mer, pentamer etc. molecules are obtained. 

A continuous process for polymerization of nylon 6,6 in which a fluidized bed solid state polymerization reactor is used as the high polymerizer is represented schematically in Figure 3 (26). In this process the low molecular weight polymer is produced in a filled pipe reactor located just upstream of the spray drier. The liquid product of this step is then sprayed into a hot inert gas atmosphere where the water is flashed off and a fine powder is produced. This powder is fed into an opposed-flow, fluidized bed reactor at 200 °C where the high molecular weight polymer powder is generated at temperatures well below the 255 °C melting point of nylon 6,6. The powder is then melted in the extruder and converted into fiber or chip. 

Although solid-state polymerizations of polyamides and polyesters (which are crystalline polymers), have been known since 1939 and 1962 (13,14), until now, it has been considered impossible to produce polycarbonate by solid-state polymerization, because polycarbonates are amorphous polymers and become molten at the temperatures necessary to effect polymerization. The key technology in solid-state polymerization of polycarbonate is the crystallization of the amorphous piepolymer. It has been found that the low molecular weight amorphous prepolymer is easily crystallized, and the obtained crystallized prepolymer retains its solid-state when it is heated to the temperatures necessary for polymerization. 

The first report of ADMET polymerization in the solid state [171] was in 2003 by Wagener and coworkers, who polymerized a variety of dienes with both [Ru] 1 and [Ru]2. Their data proved that solid-state polymerization did occur, even at relatively low temperatures (30 °C), and produced polymers with number average molecular weight as high as 3.1 X lO gmol , a 20-fold increase over the prepolymer molecular weight. A series of rigid-rod polymers were also produced [172]. 

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