Solvents, polymers dissolved

Once placed in a solvent, polymers dissolve in several steps. First, the solvent must wet the polymer. Second, the solvent diffuses into the polymer, swelling it. For polymers of high molecular weight, this process may take several hours or longer, depending on sample size, temperature, and so on. Contrary to many low molecular weight substances, the polymer does not initially diffuse into the solvent. 

A good solvent is the technical as well as descriptive term used to identify a solvent which tends to increase coil dimensions. Since this is a consequence of thermodynamically favorable polymer-solvent interactions, good solvents also dissolve polymers more readily in the first place. 

The polymers dissolve in l,l,l,3,3,3-hexafluoro-2-propanol [920-66-1/, hot phenols, and /V, /V- dim ethyl form am i de [68-12-2] near its boiling point. The excellent solvent resistance notwithstanding, solvents suitable for measurement of intrinsic viscosity, useflil for estimation of molecular weight, are known (13,15). 

Similarly, polymers dissolve when a solvent penetrates the mass and replaces the interchain secondary bonds with chain-solvent secondary bonds, separating the individual chains. This cannot happen when the chains are held together by primary covalent cross-links. Thus, linear and branched polymers dissolve in appropriate solvents, whereas cross-linked polymers are insoluble, although they may be swelled considerably by absorbed solvent. 

Reaction and Heat-Transfer Solvents. Many industrial production processes use solvents as reaction media. Ethylene and propylene are polymerized in hydrocarbon solvents, which dissolves the gaseous reactant and also removes the heat of reaction. Because the polymer is not soluble in the hydrocarbon solvent, polymer recovery is a simple physical operation. Ethylene oxide production is exothermic and the catalyst-filled reaction tubes are surrounded by hydrocarbon heat-transfer duid. 

Although waterborne systems were developed in the 1960s, the form of this chemistry that dominates the industry utilizes end-functional, high molecular weight base polymers dissolved in organic solvents. Work on solventless condensation systems continues, but has not yet become commonplace [45,47]. Solvent-borne condensation cure systems are convenient for their ease of pro-... 

As previously discussed, solvents that dissolve cellulose by derivatization may be employed for further functionahzation, e.g., esterification. Thus, cellulose has been dissolved in paraformaldehyde/DMSO and esterified, e.g., by acetic, butyric, and phthalic anhydride, as well as by unsaturated methacrylic and maleic anhydride, in the presence of pyridine, or an acetate catalyst. DS values from 0.2 to 2.0 were obtained, being higher, 2.5 for cellulose acetate. H and NMR spectroscopy have indicated that the hydroxyl group of the methy-lol chains are preferably esterified with the anhydrides. Treatment of celliflose with this solvent system, at 90 °C, with methylene diacetate or ethylene diacetate, in the presence of potassium acetate, led to cellulose acetate with a DS of 1.5. Interestingly, the reaction with acetyl chloride or activated acid is less convenient DMAc or DMF can be substituted for DMSO [215-219]. In another set of experiments, polymer with high o -celliflose content was esterified with trimethylacetic anhydride, 1,2,4-benzenetricarboylic anhydride, trimellitic anhydride, phthalic anhydride, and a pyridine catalyst. The esters were isolated after 8h of reaction at 80-100°C, or Ih at room temperature (trimellitic anhydride). These are versatile compounds with interesting elastomeric and thermoplastic properties, and can be cast as films and membranes [220]. 

The general principle of solubility is that like dissolves like. Hence polar polymers dissolve most readily in polar solvents, aromatic polymers in aromatic solvents, and so on. This is reflected in the thermodynamics of dissolution. 

A mixed-mode method called liquid chromatography under limited conditions of adsorption has been described and applied to analyzing co-polymer composition of poly(styrene)-co-(methylmethacrylate).41 The polymer, dissolved in a good solvent, was injected onto a GPC column and eluted with a poor solvent. The polymer partially adsorbed to the column, allowing the plug of injection solvent to catch up with the adsorbed polymer and desorb it. 

In this context, liquid specimens are polymers dissolved in solvent, in dispersion, or of very low molecular weight. The specimen may contain pigments and additives. If the specimen contains obvious colour and turbidity, then it must be prepared for complete... 

Define the main weak solvent (that dissolves the additives but not the polymer). 

The expansion of a polymer coil is determined by its interaction with the solvent. The more favorable the interaction between the polymer segments and the solvent molecules (good solvent), the better the polymer dissolves and the more the coil expands. 

The bond additivity approximation (BAA) appears to work for polymers dissolved in isotropically polarizable nonpolar solvents. However in the gas phase, BAA has been shown to be incorrect by Ward and coworkers (11). It has been speculated that the solvent provides a symmetrical environment in which local electric fields at a given bond caused by adjoining bonds, are cancelled by fields due to solvent molecules. Thus assuming the correctness of the RIS and BAA models, the configurational average over all internal degrees of freedom r is given by... 

C). The polymer dissolves in solvents such as dimethyl formamide, dimethylsulphoxide, etc. It is difficult to work with it as on heating it turns yellow and red due to linking of nitrile groups ... 

Dry spinning. The polymer, dissolved in a suitable solvent and filtered, is pressed through spinnerettes and, in an oxygen-free atmosphere, pulled by vacuum through a heated shaft, where the polymer solidifies as the solvent evaporates. The requirements of this process regarding the heat stability of pigments are much less... 

The slurry phase, the traditional route to PP, uses Ziegler-Natta type catalyst, a hydrocarbon solvent like hexane or heptane and polymer grade propylene (99.5%). Like the stringent requirements for polyethylene plant feeds, propylene must be high purity. Water, oxygen, carbon monoxide, or carbon dioxide will poison the catalyst. The reaction takes place in the liquid phase at 150—160°C and 100—400 psi. When the isotactic polymer particles form, they remain suspended in the diluent as slurry. The atactic polymers dissolve in the diluent. 

Polymer electrolytes intended for applications in lithium-based cells could be roughly divided into two major classifications (1) those based on neat high polymers, which serve as both solvent to dissolve lithium salts and mechanical matrix to support... 

---