Polymerization in the Solid State

The following discussion is confined to solid-state polymerizations started by high- or low-energy irradiation. 

Various indications suggest that high-energy irradiation polymerizations are started at crystal defects. If a crystal is scratched, the polymer chains will start to grow at this point. In addition, the points where polymerizations begin are randomly distributed. Because of the density difference between polymer and monomer, polymerizations in monomer crystals lead to the buildup of stresses which produce further crystal defects. New polymerizations can be started at these new defects sites. Electron 

It is usually difficult to establish whether the polymerization is free radical or ionic in initiations by irradiation. Electron spin resonance measurements often give signals, but this does not prove that the free radicals responsible for these signals actually start the polymerization. Chemical experience is used in many cases If a monomer polymerizes cationically only in solution, then the polymerization in the crystal cannot be free radical, and vice versa. 

Similarly, the action of inhibitors does not unambiguously prove the existence or absence of a free radical mechanism. An addition of 5 % benzoquinone, for example, lowers the rate of polymerization of acrylonitrile by half, but the same effect is brought about by 5 % toluene. Definite evidence can only be produced with inhibitors when these are isomorphous with the monomer, do not alter the concentration of crystal defect sites, and are present at high concentrations. The same is true for copolymerizations as a criterion for the mechanism (see Chapter 22). 

There are other phenomena that do not present unconditional proof of the mechanism. The activation energies of polymerizations in the solid state are often unusually low (see below). Since no activation energy is needed with a radiation-induced start reaction, these low activation energies can also be due to the special conditions in the crystal. The same applies to solid-state polymerizations of monomers that can only be polymerized ionically in the fluid phase. 

Commercial 1,3,5-trioxane is purified by sublimation under normal pressure at 50 °C, followed by recrystallization of 60 g from 500 ml of dry cyclohexane (yield about 36 g). Especially well-formed crystalline needles are obtained which, after filtering off the solvent, can be used without further drying. 

20 g of 1,3,5-trioxane are placed in a 300 ml conical flask that is then flushed with nitrogen and sealed with a polyethylene film. 10 ml of BF3 gas are injected through the film. 

After a short time the trioxane crystals which initially have a glassy appearance, become cloudy. After 1 min the polymerization has advanced so far that a sample is nearly totally insoluble in methanol.The conical flask is kept for another hour at 80 °C to allow the polymerization to die away.The product can be worked up and treated further as described under a). Yield 50%. 

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Isoindoles are reactive toward oxidizing agents, and precautions usually advocated in the preparation of these compounds to prevent their oxidation merit careful consideration. The end products of oxidation are most often colored, resinous materials of indeterminate structure. The oxidative reactions appear to be accelerated by light and occur much more rapidly in solution than in the solid state. In a separate but possibly related process, certain isoindoles undergo polymerization in the solid state to give resins which, according to... 

Nakase, Y., Kurijama, I. and Odajima, A. Analysis of the Fine Structure of Poly(Oxyme-thylene) Prepared by Radiation-Induced Polymerization in the Solid State. Vol. 65, pp. 79-134. 

Bis(but-3-enoato)zinc, a two-dimensional coordination polymer, has been polymerized in the solid state by irradiation of a crystalline sample resulting in isotactic zinc poly(but-3-enoate).393... 

Oligomerization of nucleobases can be advantageous to reinforce the H-bonding supramolecular motifs when supramacromolecular polymers are desired. Moreover the different interconverting outputs that may form by oligomerization define a dynamic polyfunctional diversity which may be extracted selectively under the intrinsic stability of the system or by interaction with external factors by polymerization in the solid state. 

We first discuss the materials research which includes monomer synthesis, growth of monomer crystalline structures and polymerization in the solid state, yielding the requisite polymer structures. Next, the nonlinear optical experimental research is discussed which includes a novel experimental technique to measure x (w). Linear and nonlinear optical data obtained for the polydiacetylene films is subsequently presented. Detailed theoretical analysis relating the data to x (< >) and subsequently to its molecular basis will be discussed in a later publication. 

In contrast, the sodium complex [Na(AsPh2)(dioxane)]x is polymeric in the solid state [Na-As = 2.962(4), 2.937(4) A] (25). This complex was synthesized by the rather unusual method of sodium reduction of a diarsine ... 

Fig. 17 Schematic diagram showing the molecular packing and topochemical polymerization of diacetylenes [30] in crystals. There are two idealized packing arrangements either (a), (b) or (c), (d) in crystals and each has two modes of polymerization. The polymerization in the solid state is said to occur smoothly when, v = 240 400 pm and y = 45° (Baughman, 1974 Baughman and Yee, 1978).

The solubility of polyoxymethylene is very poor so that the ring-opening polymerization of 1,3,5-trioxane proceeds heterogeneously both in bulk (melt) and in solution. 1,3,5-Trioxane can also be readily polymerized in the solid state this polymerization can be initiated both by high-energy radiation and by cationic initiators (see Example 3-24). 

Polymerization of diacetylene (Fig. 8.13) is one of the most elegant examples of the topochemical principle. Wegner (1971, 1979) showed that diacetylene monomers, R—C = C—C = C— R, polymerize in the solid state by a 1,4-addition reaction at the diacetylene group to produce a polymer that can be represented by the mesomeric structures ... 

Complexes (66 R = H and n = 2) were five-coordinate square pyramidal monomers in py, six-coordinate species form.728 Compound (66 R1 = R2 = R = H), polymeric in the solid state (Figure 30), was considered to break down to five-coordinate monomers in CHCI3 and six-coordinate. in py. Changes in the spectrum of (66 R1 = R2 = R = H, n = 9) in CHC13 on dilution indicate that the complexes with n 4 are not monomers. Compounds (66 R = 3-MeO) were five-coordinate monomers except when R1 = R2 and n = 3.557 Compounds (66 R = 5-C1) tend to be polymeric solids. Complexes with (74) appear monomeric in the solid state except when n = 3. 

The Mo04+ core structure is found in MoVI chemistry in a relatively small number of authenticated structures and in a few suggested examples shown in Table 3. The simplest set of complexes which potentially contains the Mo04+ core is MoOX4(X = F, Cl, Br). While a square pyramidal structure seems probable for the chloro and bromo complexes,232 the fluoro complex is polymeric in the solid state and in solution as well.233-235... 

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