Rubbery materials swelling

Stokes was the first person to prepare a polymeric form of these species. He reported that any of the small-molecule cyclic chlorophosphazene compounds, when heated, were transformed into a rubbery material that was later called inorganic rubber. 11 This material swelled in organic solvents such as benzene but it did not dissolve. Stokes also described how inorganic rubber decomposed to reform the cyclic compounds when heated to high temperatures under reduced pressure. His accomplishments at that time are all the more remarkable because these compounds are sensitive to a moist atmosphere in which they are hydrolyzed to ammonium phosphate and hydrochloric acid. 

Functional properties and stability of rubbery materials Chapters 1, 3, 4, 7, 12 and 13, give examples of applications of spectroscopic techniques for the characterisation of thermal stability and degradation, kinetics of thermal decomposition, ageing, oxidation and weathering, self-diffusion of small molecules in rubbery materials, adhesion of rubbers to metals, fluid adsorption and swelling. 

The polymer has a low cohesive energy density (the solubility parameter 8 is about 16.1 MPaU2) and would be expected to be resistant to solvents of solubility parameter greater than 18.5 MPa1/2 (Chapter 4). Since polyethylene is a crystalline hydrocarbon polymer incapable of specific interaction, there are no solvents at room temperature. Materials of similar solubility parameters and low molecular weight will however cause swelling, the more so in low-density polymers. LDPE has a gas permeability in the range normally expected with rubbery materials. HDPE has a permeability of about one-fifth that of LDPE. 

LR-NMR also permits network structure analysis in rubbery materials [217,228a]. Cross-link densities for EPDM, PB and other rubbers can be determined. LR-NMR has also replaced the swell-index measurement of the cross-link density in the rubbery phase of ABS powder. Cross-link density of a TPE grade showed good correlation with data from swelling tests. 

There are many uses of solvents in polymer compounds. Soluble hydrocarbon oils are widely used with natural and synthetic rubber to gain the advantages of higher molecular weight. Polyvinyl chloride, which has a low level of crystallinity, swells extensively in polar solvents to become a rubbery material known as plasticized polyvinyl chloride . 

Equation (2.79) expresses the driving force in pervaporation in terms of the vapor pressure. The driving force could equally well have been expressed in terms of concentration differences, as in Equation (2.83). However, in practice, the vapor pressure expression provides much more useful results and clearly shows the connection between pervaporation and gas separation, Equation (2.60). Also, the gas phase coefficient, is much less dependent on temperature than P L. The reliability of Equation (2.79) has been amply demonstrated experimentally [17,18], Figure 2.13, for example, shows data for the pervaporation of water as a function of permeate pressure. As the permeate pressure (p,e) increases, the water flux falls, reaching zero flux when the permeate pressure is equal to the feed-liquid vapor pressure (pIsal) at the temperature of the experiment. The straight lines in Figure 2.13 indicate that the permeability coefficient d f ) of water in silicone rubber is constant, as expected in this and similar systems in which the membrane material is a rubbery polymer and the permeant swells the polymer only moderately. 

Creep, Swelling, and Extraction Studies. Additional indications of component interaction were found in the results of creep experiments with the xl series shown in Tables VI and VII. Creep in the xl series is fully recoverable, i. e. there is no permanent set, consistent with a PUx continuous phase. The increase in recoverable compliance, however, indicates a reduction in apparent crosslink density with increasing delay time before irradiation. This result is reinforced by the data in Table VII Ci and Cg are the material constants in the Mooney-Rivlin equation. The rubbery plateau modulus and the crosslink density of PUx prepared in BHA, which mimics xl formation, is less than that of PU prepared neat. 

Bulk CROP of a soy-based 2-oxazoline (SoyOx) monomer has been performed using a scientific microwave unit, with methyl tosylate (MeOTs) serving as an initiator (Scheme 3.9). Full conversion was achieved within 8 min, leaving the double bonds of the fatty acids side chains unaffected and thus available for further cross-linking by UV irradiation. Statistical copolymers of SoyOx with 2-ethyl-2-oxazoline were also prepared. Rubbery cross-linked materials showing shape-persistent swelling upon absorption of water from the air could be prepared with as little as 13 wt% (5 mol%) of SoyOx. ... 

White [25] investigated the transport properties of a series of asymmetric poly-imide OSN membranes with normal and branched alkanes, and aromatic compounds. His experimental results were consistent with the solution-diffusion model presented in [35]. Since polyimides are reported to swell by less than 15%, and usually considerably less, in common solvents this simple solution-diffusion model is appropriate. However, the solution-diffusion model assumes a discontinuity in pressure profile at the downstream side of the separating layer. When the separating layer is not a rubbery polymer coated onto a support material, but is a dense top layer formed by phase inversion, as in the polyi-mide membranes reported by White, it is not clear where this discontinuity is located, or whether it wiU actually exist The fact that the model is based on an abstract representation of the membrane that may not correspond well to the physical reality should be borne in mind when using either modelling approach. 

B-stage—An intermediate stage in the reaction of certain thermosetting resins in which the material softens when heated to a rubbery state and swells when in contact with certain liquids, hut may not entirely fuse or dissolve in some of the solvents which will dissolve resins in the A-stage. The resin in an uncured thermosetting adhesive is usually in this stage. Sometimes referred to as Resitol. 

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