Insolubility of polymer

The importance of crosslinked polymers, since the discovery of cured phenolic formaldehyde resins and vulcanized rubber, has significantly grown. Simultaneously, the understanding of the mechanism of network formation, the chemical structure of crosslinked systems and the motional properties at the molecular level, which are responsible for the macroscopic physical and mechanical properties, did not accompany the rapid growth of their commercial production. The insolubility of polymer networks made impossible the structural analysis by NMR techniques, although some studies had been made on the swollen crosslinked polymers. 

Johnson et al. (15) reported the first attempt to synthesize PEEK by polycondensation of bisphenolate with activated dihalides using DMSO as a solvent and NaOH as a base. High molecular weight polymers were difficult to obtain due to the crystallinity and the resulting insolubility of polymers in DMSO. To circumvent the solubility problem, Attwood and Rose (16) used diphenyl sulfone as a solvent, and the polymerization was carried out close to the melting point. Victrex PEEK was commercialized by the British company ICI in 1982 using this method. Since its commercialization, this thermoplastic polymer has been used in a wide range of applications, from medicine to the electronic, telecommunications and transport industries (automobile, aeronautic and aerospace) (17,18). 

Bulk polymerization can be divided into two types polymerization in the solid phase and in the molten phase. Bulk polymerization is interesting for the following reasons (1) polymerization of crystalline monomer may lead to crystalline and stereoregular polymers, and (2) impurities, such as solvent, catalyst, and initiator, may be avoided. However, only the second reason is realistic since polymer obtained by solid-state polymerization is amorphous and shows no tendency to crystallize. The crystalline matrix is unable to exert any appreciable steric control. Further investigations have shown that propagation takes place at the polymer-monomer interface, controlled by local strains and defects in the crystal. Polymerization in the molten monomer soon becomes heterogeneous because of insolubility of polymer in its own monomer. 

Polymers in Solution. Polyacrylamide is soluble in water at all concentrations, temperatures, and pH values. An extrapolated theta temperature in water is approximately —40° C (17). Insoluble gel fractions are sometimes obtained owing to cross-link formation between chains or to the formation of imide groups along the polymer chains (18). In very dilute solution, polyacrylamide exists as unassociated coils which can have an eUipsoidal or beanlike stmcture (19). Large aggregates of polymer chains have been observed in hydrolyzed polyacrylamides (20) and in copolymers containing a small amount of hydrophobic groups (21). 

Bulk Polymerization. The bulk polymerization of acryUc monomers is characterized by a rapid acceleration in the rate and the formation of a cross-linked insoluble network polymer at low conversion (90,91). Such network polymers are thought to form by a chain-transfer mechanism involving abstraction of the hydrogen alpha to the ester carbonyl in a polymer chain followed by growth of a branch radical. Ultimately, two of these branch radicals combine (91). Commercially, the bulk polymerization of acryUc monomers is of limited importance. 

Emulsion polymerizations of vinyl acetate in the presence of ethylene oxide- or propylene oxide-based surfactants and protective coUoids also are characterized by the formation of graft copolymers of vinyl acetate on these materials. This was also observed in mixed systems of hydroxyethyl cellulose and nonylphenol ethoxylates. The oxyethylene chain groups supply the specific site of transfer (111). The concentration of insoluble (grafted) polymer decreases with increase in surfactant ratio, and (max) is observed at an ethoxylation degree of 8 (112). 

An interesting development of this research is the preparation of polymer-supported FITS reagent from bis(trifluoroacetoxy)iodoperfluoroalkanes and Nafion-H [145]. FITS-Nafion reacts with organic substrates that react to usual FITS reagents, but the products of the perfluoroalkylation reaction can be separated easily from the insoluble resin by filtration [145]... 

Shodex AT-800, HT-800, and UT-800 series are designed for use at high temperature of up to 140, 140, and 210°C, respectively. These columns are suited for the analysis of polymers such as polyolefins, which are insoluble at room temperature. The UT-800 series is recommended if the sample contains ultrahigh molecular weight components (Table 6.3). 

Obtain free -poly(L-malic acid) after passage over Amberlite IR 120 (H -form) (20 ml bed volume/1 g of polymer salt). Lyophylize, dissolve powder in acetone, remove insoluble material by centrifugation, and evaporate acetone from the supernatant. 

Unsubstituted poly(/ -phenylene) PPP 1 as a parent system of a whole class of polymers is an insoluble and intractable material, available by a variety of synthetic methods [3, 4]. The lack of solubility and fusibility hinders both unequivocal characterization and the processing of PPP 1. Moreover, the intractability of unsubstituted PPP materials has thwarted any serious commercial development of the polymer. 

Hard, attrition-resistant, insoluble synthetic polymers (typically a copolymer of styrene with divinylbenzene). The resins are manufactured in a spherical bead shape that contain either exchangeable anion or cation portions, capable of exchanging with other anions or cations and usually in an aqueous medium. Typically cation resins for water softening will have a practical operating capacity of 20,000 gpg (at 6 lb NaCl per cu ft) rising to 30,000 gpg (at 15 lb NaCl per cu ft). 

Mohanty et al. were the first to introduce pendent r-butyl groups in die polymer backbones. The resulting material was quite soluble in aprotic dipolar solvents.83 The PEEK precursors were prepared under a mild reaction condition at 170°C. The polymer precursor can be converted to PEEK in die presence of Lewis acid catalyst A1C13 via a retro Friedel-Crafts alkylation. Approximately 50% of die rerr-butyl substitutes were removed due to die insolubility of the product in die solvent used. Later, Risse et al. showed diat complete cleavage of f< rf-butyl substitutes could be achieved using a strong Lewis acid CF3SO3H as both die catalyst and the reaction medium (Scheme 6.15).84... 

Another class of silicon-containing polymers that have great potential to be extremely useful precursor materials are poly(chlorocarbosilanes).14f 46 Poly (chlorocarbosilanes) are not useful without modification because of the rapid hydrolysis of Si—Cl bonds, forming HC1 and an insoluble crosslinked polymer network. However, nucleophilic substitution of these Si—Cl bonds with various reagents produces materials widi a broad range of properties that are determined by the nature of the nucleophile used.47 Poly(chlorocarbosilanes) can be easily synthesized by ADMET (Fig. 8.18) without any detrimental side reactions, since the Si—Cl bond is inert to both catalysts 12 and 14. Early studies produced a polymer with Mn = 3000.14f... 

The yield of polymer is assumed to be the sum of the insoluble and soluble polypropylene. The basis for this simple formulation of the yield and rate is grounded in the following relationship ... 

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