Polymerization in solid state

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]. 

Similar aluminum-arsenic dimeric, 66, and trimeric, 67, [R2AlAsR R"]rt (n = 2 and 3) supermolecules have been reported. Thus, [Me2AlAsMe2] is polymeric in solid state and trimeric in solution [160]. 

Table 11. Influence of microwave irradiation on PET polymerization in solid state. Reprinted from (1998) J Appl Polym Sci 69 1203 [89] with permission ...

Probably polymeric in solid state. Air-sensitive white solid + iCeHe (C6H6). 

Polymeric in solid state, monomeric in soln. Long white needles by subl. at r.t. Mp 28.5°. Bpi6 53-6°. 

Many factors may affect the organization of monomer units during polymerization. For example, polymerization in solid state proceeds when molecules of monomer are surrounded by molecules already organized in a crystal lattice. A specific type of polymerization occurs on the surface of solids. Montmotillonite, especially, can be used for polymerization of amino add derivatives. This is connected with the fact that montmotillonite binds proteins so strongly that they cannot be washed out without being destroyed. 

When the polymer was prepared by the suspension polymerization technique, the product was crosslinked beads of unusually uniform size (see Fig. 16 for SEM picture of the beads) with hydrophobic surface characteristics. This shows that cardanyl acrylate/methacry-late can be used as comonomers-cum-cross-linking agents in vinyl polymerizations. This further gives rise to more opportunities to prepare polymer supports for synthesis particularly for experiments in solid-state peptide synthesis. Polymer supports based on activated acrylates have recently been reported to be useful in supported organic reactions, metal ion separation, etc. [198,199]. Copolymers are expected to give better performance and, hence, coplymers of CA and CM A with methyl methacrylate (MMA), styrene (St), and acrylonitrile (AN) were prepared and characterized [196,197]. 

High-molecular-weight polymers can easily be obtained by solid-state polymerization carried out just below the melting temperature of the polymer.2 5 6 8-28-41-42 In solid-state polymerization... 

Conjugated polymers are generally poor conductors unless they have been doped (oxidized or reduced) to generate mobile charge carriers. This can be explained by the schematic band diagrams shown in Fig. I.23 Polymerization causes the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the monomer to split into n and n bands. In solid-state terminology these are the valence and conduction bands, respectively. In the neutral forms shown in Structures 1-4, the valence band is filled, the conduction band is empty, and the band gap (Eg) is typically 2-3 eV.24 There is therefore little intrinsic conductivity. 

Consider alternative polymerization processes in solid state, inducing the polymerization reaction of N3P3CI6 thermally [40-42],photochemically [61, 67,68],y-radiolytically [66,210], using X-rays [74,75,90] or electron irra-... 

Solid-state synthesis of /J-nitrostyrenes has been reported by Varma et al. in a process that uses readily available styrene and its substituted derivatives and inexpensive clay-supported nitrate salts, clayfen and clayan (Scheme 6.50) [170], In a simple experiment, admixed styrene with clayfen or clayan is irradiated in a MW oven (-100-110 °C, 3 min) or heated in an oil bath (-100-110 °C, 15 min). For clayan intermittent heating is recommended with 30-s intervals to maintain the temperature below 60-70 °C. Remarkably, the reaction proceeds only in solid state and leads to the formation of polymeric products in organic solvent. 

An unusual synthetic approach to PF copolymers was demonstrated by Bunz and coworkers [370], who prepared poly(fluorene ethynylene) 281a-e by metathesis polymerization reaction (Scheme 2.44) [370], The aggregation of polymers 281 in concentrated solutions and in solid state is manifested in slight (up to 10-20 nm) red shift of the absorbance and emission peaks, although solutions and films emit pure blue light. 

In the 40 years since Olah s original publications, an impressive body of work has appeared studying carbocations under what are frequently termed stable ion conditions. Problems such as local overheating and polymerization that were encountered in some of the initial studies were eliminated by improvements introduced by Ahlberg and Ek and Saunders et al. In addition to the solution-phase studies in superacids, Myhre and Yannoni have been able to obtain NMR spectra of carbocations at very low temperatures (down to 5 K) in solid-state matrices of antimony pentafluoride. Sunko et al. employed a similar matrix deposition technique to obtain low-temperature IR spectra. It is probably fair to say that nowadays most common carbocations that one could imagine have been studied. The structures shown below are a hmited set of examples. Included are aromatically stabilized cations, vinyl cations, acylium ions, halonium ions, and dications. There is even a recent report of the very unstable phenyl cation (CellJ)... 

The complexes exhibited different behavior in solution. The gold-thallium derivative showed a shift of the emission to 536 nm when the measurement was carried out in frozen solution. This was explained by a higher aggregation of [Aull(MTP)2] units in the solid state compared to the situation in solution. In the case of the Au-Pb compound, the emission spectrum showed a strong dependence on the aggregation state and temperature. Thus, the emission band in TH F solution, which appeared at 555 nm (298 K) (x = 57 ns), was shifted to 480 nm in frozen solution (x = 2.3 ps) or appeared at 752 nm in solid state (x = 22 ns). As with the thallium complex, the shift to high energy in solution may have been related to the polymeric structure of the complex in the solid state that was not reproduced in solution. 

Topochemical Polymerization The chiral crystalline environment of a monomer itself can be a source of asymmetric induction in solid-state polymerization [69-72], Prochiral monomers such as 37 give enantiomorphic crystals, one of which can be preferentially formed by recrystallization with a trace amount of optically active compounds. Photoir-... 

FIGURE 16. Equilibrium between the monomeric Pd2(dmb)2U2 complex in solution and the polymeric Pd2(dmb)2X2 in solid state. 

The EHM was initially applied to the geometries (including conformations) and relative energies of hydrocarbons [56a], but the calculation of these two basic chemical parameters is now much better handled by semiempirical methods like AMI and PM3 (Chapter 6) and by ab initio (Chapter 5) and DFT (Chapter 7) methods. The main use of the EHM nowadays is to study large, extended systems [62] like polymers, solids and surfaces. Indeed, of four papers by Hoffmann and coworkers in the Journal of the American Chemical Society in 1995, using the EHM, three applied it to such polymeric systems [63], The ability of the method to illuminate problems in solid-state science makes it useful to physicists. Even when not applied to polymeric systems, the EHM is frequently used to study large,... 

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