Polymerization crystallization

Molecular Optics Nonlinear Optical Properties of Organic and Polymeric Crystals... 

The linear and nonlinear optical properties of the conjugated polymeric crystals are reviewed. It is shown that the dimensionality of the rr-electron distribution and electron-phonon interaction drastically influence the order of magnitude and time response of these properties. The one-dimensional conjugated crystals show the strongest nonlinearities their response time is determined by the diffusion time of the intrinsic conjugation defects whose dynamics are described within the soliton picture. 

It is also shown that the electron-phonon interaction is operative in the polymerization process of the one-dimensional conjugated polymeric crystals a simple dynamical model for the polymerisation in polydiacetylenes is presented that accounts for the existing observations. 

The orthogonal projection of the epitaxial poly(DMDA) could not be indexed using the unit cell data for the bulk polymerized crystal (8). However, poly(DMDA) cannot usually be polymerized to completion or to high crystallinity in the bulk due to cross-linking. The use of an epitaxial substrate may have controlled the polymerization process that led to oriented single crystals. 

Note The aging of a gel can involve polymerization, crystallization, aggregation, syneresis, phase changes, formation of branch points and junction points as well as scission and chemical changes to constitutional units of network chains. 

Previous work has shown that the presence of Calcofluor or Tinopal could dramatically increase A. xylinum cellulose synthesis. This observation was the basis for the hypothesis that cellulose polymerization can be uncoupled from a slower sequential crystallization step (2-5). We believe the hypothesis is not consistent with our observations. At the very least, the presence of an ordered and crystal-like submicrofibril produced in the presence of 0.25 mM Tinopal would relegate Tinopal s or Calcofluor s effects to an event occurring after the initial cellulose polymerization-crystallization step or steps. 

Later, Tieke reported the UV- and y-irradiation polymerization of butadiene derivatives crystallized in perovskite-type layer structures [21,22]. He reported the solid-state polymerization of butadienes containing aminomethyl groups as pendant substituents that form layered perovskite halide salts to yield erythro-diisotactic 1,4-trans polymers. Interestingly, Tieke and his coworker determined the crystal structure of the polymerized compounds of some derivatives by X-ray diffraction [23,24]. From comparative X-ray studies of monomeric and polymeric crystals, a contraction of the lattice constant parallel to the polymer chain direction by approximately 8% is evident. Both the carboxylic acid and aminomethyl substituent groups are in an isotactic arrangement, resulting in diisotactic polymer chains. He also referred to the y-radiation polymerization of molecular crystals of the sorbic acid derivatives with a long alkyl chain as the N-substituent [25]. More recently, Schlitter and Beck reported the solid-state polymerization of lithium sorbate [26]. However, the details of topochemical polymerization of 1,3-diene monomers were not revealed until very recently. 

The novel species obtained from the reaction of zinc(II) salts with thiophenol have been further investigated and complexes of formula [Zn4(SPh)8(ROH)] have been isolated from the interaction of Zn[C03] and PhSH in ROH. A crystallographic study of these species has shown that they should be formulated cflte -( -SPh) ( -SPh) n4(ROH)(SPh) and that they form one-dimensional polymeric crystals with one intercluster bridging PhS unit. A crystal structure of the complex [Me4N] [ClZn4( -SPh)i2(ZnSPh)4], formed from Zn(N03)2, PhSH, Pr3N and [Me4N]Cl, has also been reported.823... 

Polyphenylene formed from simultaneously doped and polymerized crystals of terphenyl has the form of a macroscopic slab. The final conductivity with AsF5 doping is 60 S cm-1 along the chains and 40 S cm-1 perpendicular to the chains, less of a difference than would be expected on a simple chain conduction model61). 

Stockmayer and Hecht (1953) have developed an additional mathematical theory of the heat capacity of chain polymeric crystals. Their theory is based on the concept of strong valence forces between atoms in the polymeric chain and of weak (non-zero) coupling between chains. This model corresponds to that also proposed by Tarassov (1952). There are not many low temperature specific heat data on polymers, but the Stockmayer-Hecht theory can be tested by calculating the Tm constant... 

The manufacture of products by reactive molding results in the superposition of interrelated chemical and physical phenomena. These include polymerization, crystallization, vitrification, heat transfer, rheokinetic effects, changes in the physical properties and volume of a material injected into a mold. It is quite natural that special experimental methods are required to study and control the complex processes which take place in molds. 

Again, detailed structural studies have been carried out on polymerized single crystals. Moret et al. [82] polymerized crystals under hydrostatic conditions... 

The geometrical parameters of equilibrium configurations of small fullerenes isolated molecules C , their dimers (Cn)2 and cuban-like clusters(Cn)8 are obtained for n = 20, 24, 28, 32. The Cuban like clusters can be considered as fragments of polymerized crystal structures with simple cubic symmetry. Total energy, heat of formation, energies of HOMO and LUMO orbitals, density of one-electron states (DOS) are determined for equilibrium configurations of all these objects. All the computations are performed by help of pocket PC Gamess in frames of optimized semi-empirical PM3-basis [4-5],... 

The polyacetaldehyde thus prepared has the same properties and structure as Letort s polyacetaldehyde which was obtained by crystallization polymerization. This indicates that crystallization polymerization, the only previously known method of acetaldehyde polymerization, is only a special case of acid-initiated or cationic acetaldehyde polymerization. We feel that Letort s proposal (29) that the peroxide-induced acetaldehyde polymerization (crystallization polymerization) as a radical polymerization can now be reinterpreted in the following way The initiating species, which is prepared by reacting acetaldehyde with a controlled amount of oxygen, is obtained via a... 

Fig. 12. (a) Micrographs of monomer and partially polymerized crystals of DSP, (b) micrographs of monomer and partially polymerized crystals of p-CPA nPr, (c) micrographs of m-PDA Me crystals and oligomer, (source Ref. 61)... 

Similar results have been obtained by measuring the Raman spectra of partially polymerized crystals and by other spectroscopic techniques. Here, the vibrational frequency of the polymer chain can be used as a probe for the lattice strain in the vicinity of the dispersed macromolecules It should be noted that monomer and polymer are not strictly isomorphous. The mismatch between monomer stacking and polymer repeat of 0.2 A per addition step has to be accounted for by the monomer matrix. The raman frequencies shift accordingly to the lattice changes (cf. Fig. 11) in agreement with the random chain distribution. 

A deeper insight into the reaction mechanism may elucidate the conversion dependence of the molecular weight and its distribution. Owing to the extreme insolubility of the better investigated polydiacetylenes like PTS, however, only very limited experimental data have been available until recently from indirect determinations, e.g. from mechanical properties or diffuse scattering of partially polymerized crystals. 

In calculating the Avrami exponent from DSC data, it was observed that fractional Avrami exponents are obtained, and not whole numbers, as is observed for the application of the equation to metal melts for which the theory was developed or in the majority of cases for polymeric crystallization from melts. In certain instances the practice of rounding off the Avrami exponent value could lead to ambiguity, especially where rounding off intermediate values between two integers, e.g., where exponents of 2.45 or 2.48 are obtained. 

The reactivity of the DSP crystal was thoroughly interpreted in terms of the topochemical concept proposed by Schmidt, in which potentially reactive double bonds are oriented parallel to each other and separated by approximately 3.5-4.2 A. The reaction proceeds with a minimum of atomic and molecular motion (2 ). The reactive double bonds in most of the topochemically polymeric crystals thus far found are related to the center of symmetry (centrosymmetric ct-type crystal) and dimerize to give highly crystalline polymers containing cyclobutanes with a 1,3-trans configuration in the main chain. 

Figure 11. Polymeric crystal of after exposure to a y-ray dose of 30 Hrad.

Solid-State Polymerization, Crystal Optics, and Conformational Itansitions... 

---