Solid-state polymer reactions

A unique characteristic of polyesters is their ability to undergo additional condensation reactions during processing or when in the solid state. These reactions redistribute the molecular weight of the polymer until a dynamic equilibrium is established. Water, when present at high temperatures in polyester melts, can depolymerize polyesters via a hydrolysis reaction. For this reason, manufacturers must carefully dry the polymer before processing. 

However, the chemical changes observed in low molecular weight compounds can be quite misleading as models for polymers. Difficulties include the high concentration of end groups, e.g. COOH in N-acetyl amino acids, which can dominate the radiation chemistry of the models. Low molecular weight compounds are usually crystalline in the solid state and reactions such as crosslinking may be inhibited or severely retarded. 

We have previously reported the results of careful investigations of the solution carbonation (8) and oxidation (9) of polymeric organolithium compounds. These studies have been extended to the investigation of solid-state carbonation reactions and these results are reported herein. In addition, a new method has been developed for the synthesis of telechelic polymers with primary amine end-group... 

Although the SOFC community has generally maintained an empirical approach to the three-phase boundary longer than the aqueous and polymer literature, the last 20 years have seen a similar transformation of our understanding of SOFC cathode kinetics. Few examples remain today of solid-state electrochemical reactions that are not known to be at least partially limited by solid-state or surface diffusion processes or chemical catalytic processes remote from the electrochemical—kinetic interface. 

The smallest subimit of these fullerene polymers is the C j2o dimer [368], Synthesis and examination of the properties of this molecule are, therefore, of considerable interest. Beside the solid-state mechanochemical reaction of with KCN -described in Section 3.2.3 -the dimer Cj2o can be synthesized at 5 GPa and 200 °C in good yields from a bis(ethylene-difhio)TTF-C5Q complex [369]. Cj2o is a dark brown solid that is almost insoluble in most organic solvents. 1 ts solubility decreases with increasing purity of the sample this behavior is also known for pristine C q. 

Fig. 17 The solid-state photopolymerization reaction of DSP (shown at top), (a) Crystal structure of the polymeric product phase obtained directly from the solid-state photopolymerization reaction of DSP, viewed along the i)-axis (for clarity, only half the unit cell is shown along the direction of view), and (b) overlay of the monomer (green) and polymer (orange) in their crystal structures...

Basilevsky et al. [1982] proposed a mechanism of ionic polymerization in crystalline formaldehyde that was based on Semenov s assumption [Semenov, 1960] that solid-state chain reactions are possible only when the products of each chain step prepare a configuration of reactants that is suitable for the next step. Monomer crystals for which low-temperature polymerization has been observed fulfill this condition. In the initial equilibrium state the monomer molecules are located in lattice sites and the creation of a chemical bond requires surmounting a high barrier. However, upon creation of the primary cation (protonated formaldehyde), the active center shifts toward another monomer, and the barrier for addition of the next link diminishes. Likewise, subsequent polymerization steps involve motion of the cationic end of the polymer toward a neighboring monomer, which results in a low barrier to formation of the next C-0 bond. Since the covalent bond lengths in the polymer are much shorter than the van der Waals distances of the monomer crystal, this polymerization process cannot take place in a strictly linear fashion. It is believed that this difference is made up at least in part by rotation of each CH20 link as it is incorporated into the chain. 

The biphasic kinetics curve for the reactions of polymers is very typical and is found frequently in the polymer literature. Daglen and Tyler showed62 that equation 27 gave excellent fit to these systems as well, which suggests the presence of reaction spheres is common in the mechanism of solid-state polymer photodegradation. 

In addition, mechanistic studies of the photochemical reactions are necessary to determine whether similar processes occur in the solid state. Polymer chain scission is usually the predominant process in the solid state, although cross-linking reactions become more important in the presence of pendant unsaturation. However, little is known about the nature of the intermediates produced in the solid state. Information of this type is important, because most of the applications of polysilane derivatives require the materials as solid films. 

This contribution gives a review of recent spectroscopic investigations concerning the photophysical and photochemical primary and secondary processes of the solid state polymerization reaction in diacetylene single crystals. It will be shown, that diacetylenes are an unique model system for the study of the reaction mechanism of a solid state chemical reaction which is characterized by a variety of reaction intermediates. The polymerization reaction in these crystals is of special importance, due to the resulting polymer single crystals, which exhibit extraordinary anisotropic physical properties. 

Fig. 1. Schematical representation of the solid state polymerization reaction at room temperature. The partially polymerized monomer crystal contains long polymer filaments...

Ca—O = 2.30 A). The closeness of the molecules help explains why under irradiation with 7-rays from °Co, a solid-state cyclodimerization reaction in induced, producing cis,trans-TO.epe. ic acid, one of four possible diastereomers. Related radiation-induced chemistry is displayed by aquated (3-butenoato)calcium, Ca(CH2=CHCH2C02)2(H20), synthesized from 3-butenoic acid and calcium carbonate. The carboxylate is a two-dimensional coordination polymer with nearly parallel vinyl groups and short -C=C—C=C- contacts of 3.73 A and 3.90 A (see Figure 63). ... 

Solids can be classified according to their organizational structure and, in the context of photochemical reactions, be classified as glasses, polymers, and crystals. Furthermore, a solid-state photochemical reaction only takes place in a thin layer of the solid surface, while in a dilute solution all the molecules are equally exposed to the radiation. In a tablet, the radiation has been estimated to reach a penetration depth of 0.03 cm, and the faded layer apparently does not increase upon further exposure (Carstensen, 1974). A study of nifedipine in the solid state demonstrated that the degradation rate was inversely proportional to the thickness of the powder bed (Marciniec and Rychcik, 1994). 

A polymeric pinacol,poly[3-methyl-2-(4-vinylphenyl)-2,3-butanediol],has been prepared by radical polymerization of the styrenic diol monomer and shown to be cleanly and quantitatively converted to a non-conjugated ketone in the solid state by reaction with a photochemically-generated acid [151,348, 350]. The rearrangement reaction can be readily monitored by IR spectroscopy as the disappearance of the hydroxyl OH absorption is accompanied by appearance of a new ketone carbonyl absorption (Fig. 116). Since a polar alcohol (isopropanol) dissolves the polar diol polymer in the unexposed regions but cannot dissolve the less polar ketone polymer produced in the exposed regions, the resist functions as a negative system with alcohol as a developer. The diol polymer is stable thermally to 225 °C in the absence of acid. 

Mashukov, N. I. Temiraev, K. B. Shustov, G. B. Kozlov, G. V Modelling of solid state polymer properties at the stage of synthesis fractal analysis. Chapters of 6th International Chaptershop of Polymer Reaction Engng. Berlin, 5-7 October, 1998,134, 429 38. 

H. Sixl, Spectroscopy of the Intermediate State of the Solid-State Polymerization Reaction in Diacetylene Crystals, Adv. Polym. 

As discussed earlier, solid-state polymerization reactions are used to increase the degree of polymerization in the production of nylon-6 and nylon-6,6. The solid-state polymerization process has been studied by process simulation. Mallon and Ray [208] developed a comprehensive model to handle the reactions in polymers undergoing polycondensation reactions in the solid state. The polymer crystalline fraction is modeled as containing only repeat units,... 

In the solid state such reactions may or may not proceed but, depending on the conformation of the affected segment of the polyester chain, it is assumed that a PET melt exhibits no order and that the necessary positioning of the atoms in the chain will occur through random motions of a freely rotating polymer chain. Reactions may thus be posited to occur as follows ... 

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