G> polyisobutylenes

Puskas J.E. and Kaszas G., Polyisobutylene-based thermoplastic elastomers A review. Rubber Chem. Technol., 69, 462, 1996. 

Suppose we have a piece of rubber (e.g., polyisobutylene), lA cm lA cm x 4 cm, and a piece of plastic (e.g., polystyrene) of the same dimensions. The experiment to be performed consists of suspending a weight (applying a force) of, say 1 kg, from each sample as shown in Figure 1-1. 

Depolymerization (or reversion) occurs essentially at high temperatures, only in linear polymers having weak monomer-monomer bonds, or in tridimensional polymers having weak cross-link junctions (see Table 12.2). These are linear polymers containing the weakest aliphatic C-C bonds, i.e. involving tetrasubstituted carbon atoms, e.g. polyisobutylene (PIB), poly(methyl methacrylate) (PMMA), poly(or-methyl styrene) (PorMS), etc. These are also linear polymers containing heteroatoms, e.g. poly(oxy methylene) (POM), poly(ethylene terephthalate) (PET), poly(vinyl chloride) (PVC), etc., but also sulphur vulcanized elastomers. Cross-linking predominates mainly in unsaturated linear polymers, i.e. essentially polybutadiene and its... 

Polyisobutylene and similar copolymers appear to "pack" well (density of 0.917 g/cm ) (86) and have fractional free volumes of 0.026 (vs 0.071 for polydimethylsiloxane). The efficient packing in PIB is attributed to the unoccupied volume in the system being largely at the intermolecular interfaces, and thus a polymer chain surface phenomenon. The thicker cross section of PIB chains results in less surface area per carbon atom. 

All grades of regular butyl rubber are tacky, rubbery and contain less unsaturation than natural rubber or styrene-butadiene rubber. On the other hand, low molecular weight grades of polyisobutylene are permanently tacky and are clear white semi-liquids, so they can be used as permanent tackifiers for cements, PSAs, hot-melt adhesives and sealants. Low molecular weight polyisobutylenes also provide softness and flexibility, and act as an adhesion promoter for difficult to adhere surfaces (e.g. polyolefins). 

Membranes are applied directly to the metal or concrete surface to protect from corrosion by any liquor that penetrates the brick lining through pores and cracks. Membranes consist of sheet material bonded to the metal or concrete, e.g., flexible PVC sheet, or it may be formed in situ (e.g., polyester resin reinforced with glass fiber, or synthetic rubber sheet, lead, polyisobutylene, polyethylene and asphalt). 

Further, while conventional Friedel-Crafts halides produce high molecular weight polyisobutylenes or polyisobutylene copolymers (e.g., butyl rubbers, HR) only at relatively low ( —100 °C) temperatures, alkylaluminum-based initiator systems produce high molecular weight materials at much higher ( —40 °C) temperatures. 

Kennedy J.P., Fenyvesi G., and Keszler B., Three arm star composition of matter having diblock arms based on polyisobutylene and method of preparation, US Patent 6228945, May 8, 2001. 

Deak G. and Kennedy J.P., Copolyesters containing polyisobutylene soft segments and polybutylene terephthalate as crystalline segments, MacrolmoL Rep., A33(Suppls 7 8), 439, 1996. 

FIGURE 7.16 polyisobutylene (PIB)-PpMeSt block copolymers precipitated into acetone (a) and methanol (b). (Adapted from Puskas, J.E., Dos Santos, L., and Kaszas, G., J. Polym. Sci. Chem. A., 44, 6494, 2006. With permission.)... 

Sui, C., McKenna, G.B., and Puskas, J.E. Nonlinear viscoelastic response of dendritic (arborescent) polyisobutylenes in single- and reversing double-step shearing flows, J. Rheol, 51, 1143, 2007. 

Puskas, J.E., Brister, L.B., Michef A J., I-anzenddrfer, M.G., Jamieson, D., and Pattern, W.G. Novel substituted epoxide initiators for the carbocationic pol3mierization of isobutylene, 7. Polym. Set, 38,444-451, 2000. Puskas, J.E. and Michel, A.J. New epoxy initiators for the controlled synthesis of functionalized polyisobutylenes, Makromol. Chem., Macromol. Symp., 161, 141-148, 2000. 

Foreman, E.A., Puskas, J.E., and Kaszas, G., Synthesis and characterization of Arborescent (hyper-branched) polyisobutylenes from the 4-(l,2-oxirane-isopropyl) styrene inimer. J. Polym. Set Polym. Chem., 45, 5847, 2007. 

Some polymers like PE and NR get cross-linked on exposure to radiation while others like those based on vinylidene polymers, e.g., polymethylmethacrylate (PMMA), polyisobutylene, degrade. Certain other types of polymer stmctures (high aromatic content or thermoset) resist degradation by high-energy radiation. Coating polymers usually contain acrylic, methacryUc, or fumaric vinyl unsaturation along or attached to the backbone. 

Fig. 38.—Plots of w/c against c for a series of polyisobutylene fractions M =38,000 to 720,000) in cyclohexane ( ) and in benzene (O), both at 30°C. The osmotic pressure tz is expressed in g./cm. and c in g./lOO cc. Curves have been calculated according to Eq. (13). (Krigbaum. )...

Postpolymerization of difunctional monomers to effect star branching has been successfully applied in cationic polymerization, e.g. in the case of polyisobutylene initiated with 2-chloro-2,4,4,-trimethylpentane/TiCl4. Addition of divinylbenzene leads to star polymers [104], Vinyl ethers, when polymerized with HI/ZnI2 in toluene at — 40°C, can be copolymerized with divinylether... 

Sulfonated polystyrene-b-(isobutylene)-l7-sulfonated polystyrene (S-SIBS) with lEC between 0.5 and 1.0 mmol/g also exhibits approximately 5-10 times higher selectivity than Nafion llZ o The increased selectivity is thought to be due to lower MeOH and water solubility in polyisobutylene, the major... 

Isobutylene is polymerized under conditions where chain transfer to monomer is the predominant chain-breaking reaction. A 4.0-g sample of the polymer was found to decolorize 6.0 mL of an 0.01 M solution of bromine in carbon tetrachloride. Calculate the number-average molecular weight of the polyisobutylene. 

The interactions between solvent and polymer depend not only on the nature of the polymer and type of solvent but also on the temperature. Increasing temperature usually favors solvation of the macromolecule by the solvent (the coil expands further and a becomes larger), while with decreasing temperature the association of like species, i.e., between segments of the polymer chains and between solvent molecules, is preferred. In principle, for a given polymer there is a temperature for every solvent at which the two sets of forces (solvation and association) are equally strong this is designated the theta temperature. At this temperature the dissolved polymer exists in solution in the form of a nonexpanded coil, i.e., the exponent a has the value 0.5. This situation is found for numerous polymers e.g., the theta temperature is 34 °C for polystyrene in cyclohexane, and 14 °C for polyisobutylene in benzene. 

---