Polymers polyisobutylene

E7.12 The following table gives the osmotic pressures as a function of concentration for the polymer polyisobutylene dissolved in benzene at 298.15 K. 

The photo-cross-linkability of a polymer depends not only on its chemical structure, but also on its molecular weight and the ordering of the polymer segments. Vinyl polymers, such as PE, PP, polystyrene, polyacrylates, and PVC, predominantly cross-link, whereas vinylidene polymers (polyisobutylene, poly-2-methylstyrene, polymethacrylates, and poly vinylidene chloride) tend to degrade. Likewise, polymers formed from diene monomers and linear condensation products, such as polyesters and polyamides, cross-link easily, whereas cellulose and cellulose derivatives degrade easily. ... 

Bulyk. Butyl-based materials are sold in the form of preformed tapes, thermoplastic hot melts, and one-part solvent-releasing sealants. Butyl polymers are made by the copolymerization of 97-98 mol % isobutylene with 2-3% isoprene. Another butyl-based polymer, polyisobutylene, is produced by the polymerization of isobutylene. Formulations of butyl-based sealants also include plasticizer, filler, and lackifier resins. Poly butenes are common plasticizers for butyl sealants. Solvents, such as mineral spirits, are used for the one-part solvent-releasing formulations. As the solvent leaves the typical one-part butyl, the sealant hardens and loses its elastomeric ability. This limits the use of solvents to low movement applications where durability is not of high concern. 

To describe the effects of steric restrictions in another polymer, polyisobutylene, consider the Newman projections of the staggered conformations of two adjacent carbons in its repeat unit, as shown in Fig. 2.6. Here the chain substituent on the rear carbon shown is either between a methyl group and polymer chain or between two methyl groups on the front carbon. There is no significant energy difference between the conformers. Since no conformation is favored, polyisobutylene will tend to spiral into a helix (gauche conformers) as well to form into a zigzag (If),... 

We have a dilemma we need a high-quality solvent to insure that the polymer remains in solution when it is formed but we need a solvent whose quality can be easily adjusted to induce the polymer to drop out of solution. How can we resolve it First, we need to know the thermodynamic variables that cause the occurrence of an LCST (chapter 3). The key variable in this instance is the chemical nature of the solvent or, to a first approximation, the critical properties of the solvent. Decreasing the solvent quality shifts the LCST curve to lower temperatures, and it is this variable that we wish to manipulate to force the polymer out of solution. To demonstrate the effect of solvent quality on the location of the LCST curve, consider the difference in LCST behavior for the same polymer, polyisobutylene, in two different solvents, n-pentane and cyclooctane. The LCST curve for the polyisobutylene-rt-pentane system begins at 70°C, while for the polyisobutylene-cyclooctane system it begins at 300°C (Bardin and Patterson, 1969). Cyclooctane, which has a critical temperature near 300°C, is a much better solvent than n-pentane, which has a critical temperature near 200°C, probably because cyclooctane has a greater cohesive energy density that translates into a lower thermal expansion coefficient, or equivalently, a lower free volume. Numerous examples of LCST behavior of polymer-solvent mixtures are available in the literature, demonstrating the effect of solvent quality on the location of the LCST (Freeman and Rowlinson, 1960 Baker et al., 1966 Zeman and Patterson, 1972 Zeman et al., 1972 Allen and Baker, 1965 Saeki et al., 1973, 1974 Cowie and McEwen, 1974). 

The polymer polyisobutylene (—C(CH3)2—C—) presents a case where G(cl) = 0. This polymer is entirely amorphous (except on stretching, when it crystallizes) and the linear increase of /My (D) with dose has been established over a wide range of initial molecular weights. From these results it has been concluded that the scissions take place at random positions. ... 

Viscosity. Supercritical carbon dioxide is more effective than most liquid solvents in decreasing the viscosity of a polymer. A comparison of the viscosity-reducing potential of carbon dioxide versus tetrahydrofuran is shown in Figure 10 for the polymer, polyisobutylene. As indicated by the figure, when the weight percentage of polymer is fixed, carbon dioxide will create a mixture viscosity much lower than that created by tetrahydrofuran. 

The relative solvent power (HMPA > TMSO > MP) agrees with solution-temperature measurements. The characteristic ratio Coo is about 8 1, which is slightly larger than that of a similar polymer, polyisobutylene. 

The Henry s law constant for a given polymer can be correlated with the e/ k factor (see Table 5-4). Such correlations are shown in Figs. 5-12 and 5-13. A more generalized correlation is shown in Fig. 5-14, where the Henry s law constant is correlated with the gas critical temperature for thermally softened polymers (polyisobutylene, polystyrene, and polymethyl methacrylate). Figure 5-14 offers the possibility of estimating a Henry s law constant for a polymer for which there are no data. 

Polymer polyisobutylene plasticizer ortho-nilrophenyloc-tylether organic salt tetraoctylammoniumbromide... 

It is notable that, with two exceptions, 10 dynes-sec/cm is the dividing line between polymers with disubstituted backbone chain atoms (methacrylate polymers, polyisobutylene) and those with monosubstituted backbone atoms. The presence of two substituents on the same chain atom probably introduces substantial steric hindrances to internal rotation, as can be inferred from molecular models. (A striking exception is poly(dimethyl siloxane), which is in a class by itself at the bottom of the order.) There does not seem to be any particular correlation with the... 

Polyimide. see High-temperature polymers Polyisobutylene, see Polyolefins Polymer melts 44 Polymethyl methacrylate... 

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