Swell in solvent

The conventionally covalently cross-linked rubbers and plastics cannot dissolve without chemical change. They will, however, swell in solvents of similar solubility parameter, the degree of swelling decreasing with increase in cross-link density. The solution properties of the thermoelastomers which are two-phase materials are much more complex, depending on whether or not the rubber phase and the resin domains are dissolved by the solvent. 

An IPN has different properties from either a copolymer or a polymer blend. It may swell in solvents, but will not dissolve it will resist creep or flow to a greater extent than copolymers or blends. Some differences in the physical properties of IPNs compared with polymer blends can be seen in Table 10.3. The major reason for the differences in properties between polymer blends and IPNs is that the latter have greater adhesion and better mixing. 

The other main support used for solid base catalysts is polystyrene, which while it does not have a well-defined porous structure, does swell in solvents providing an accessible high surface area on which to carry out reactions. One common method of chemically attaching groups to polystyrene involves incorporation of specific amounts of styrene contain-... 

Highly cross-linked rubbers swell less in good solvents than do lightly cross-linked rubbers((188,189). For this reason, swelling in solvents is often used to determine quantitatively the degree of cross-linking. However, in... 

Only when chemical bonds between neighboring molecules are introduced is a raw elastomer converted into a rubber vulcanizate, which is essentially a three-dimensional network structure (see Figure 5.3). The process is referred to as vulcanizahon or curing, or more accurately, as cross-linking. A cross-linked elastomer, or rubber vulcanizate, is capable of large reversible deformations within a broad temperature range and does not dissolve, but only swells in solvents and other liquids. 

Flory has recently summarized the experimental evidence pertaining to local correlation and their effects on chain dimensions (49). There is experimental support for local alignment from optical properties such as stress-optical coefficients in networks (both unswelled and swelled in solvents of varying asymmetry), and from the depolarization of scattered light in the undiluted state and at infinite dilution. The results for polymers however, turn out to be not greatly different from those for asymmetric small molecule liquids. The effect of... 

Structural parameters of crosslinked polystyrene determined from tension-deformation dependence and swelling in solvents of different activity. Collection Czech. Chem. Commun. 32, 1554 (1967). 

The same authors developed a process of encapsulation of polymers swelled by halogenated solvents in which ozone is greatly soluble but not monomers to be grafted. After ozonization of polymers swelled in solvents, mixtures of mono unsaturated or di unsaturated monomers are added to the activated polymers. Then, grafting is operated by UV irradiation. Grafting is mainly located at the surface of the starting polymer what prevents the modification of its intrinsic properties. This process permits to produce hydrophilic polysiloxanes used in medical applications (contact lenses, tubes, catheters, etc.). 

At this point, the chains have not fully developed and the hard segments will have the joined chain at random lengths in the structure. This has the effect of increasing the viscosity of the mix as well as improving the compression set and swelling in solvents. This is important in very hard compounds. A trifuctional isocyanate such as Tolonate HDT (Rhone Poulenc) will do the same as TMP but with less decrease in dynamic properties. 

The various parameters can be determined from measurements of the modulus of elasticity (see 5.1) and from swelling in solvents. 

Cross-linked polystyrene (PS)-based resins are most commonly used for routine SPPS. Beads of 200 to 400 mesh size distribution (corresponding to a diameter of about 50 pm) and a loading of 0.5 to 0.8 mmol/g present good characteristics for polymer swelling in solvents such as DMF and DCM, diffusion of reactants into the polymer matrix, and accessibility of linker sites buried into the bead. For larger peptides (more than 25 amino acids) or more difficult sequences, a lower loading is required (0.1-0.2 mmol/g). 

Solid support lasoiuble. functionalized polymeric material to which library members or reagents may be attached, often via u linker, allowing them to be readily separated fmtn solvent, cxcc.ss reagent, etc. Typically, the solid support swells in. solvent. allowing reactions to occur in the interior of the bead nr oilier form. This greatly increases the available surface area for reaction. 

Hence, the more general Panyukov form [Eq. (7.70)] reduces to the Flory form [Eq. (7.69)] for swelling in -solvents. The gel modulus in a -solvent is then proportional to the 1 /3 power of concentration ... 

Polymer-supported catalysts, especially those based on polystyrene resins, have been used on many occasions but they also suffer from low thermal stability as well as high cost and a tendency to swell in solvent.147,148 Simple physisorbed supported PTCs can be prepared by the incipient wetting method. In this way, alumina-supported phosphonium compounds have been prepared and used to catalyse various halogen exchange reactions in the gas phase along with various other nucleophilic substitutions (Figure 4.24). 

Tg will be much reduced. Therefore, as low a temperature as conveniently obtainable was planned for a series of experiments, reported by Rigbi74 (It may incidentally be noted that stresses in the macromolecular network do develop on swelling in solvent, but as long as no external stress is applied, the meaning of the expression stress softening becomes debatable. Nevertheless, this semantic problem will not be discussed here). 

Undoubtedly, the condition of the hair also plays a role in the rate of reduction, especially under conditions where diffusion is rate-limiting. Permanent-waving [31] and bleaching [32] produce alterations to hair that result in increased swelling in solvents. One might also anticipate more rapid rates of reduction for hbers that have been previously bleached or... 

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