Polyisobutylene, high-molecular weight

The low molecular weight materials produced by this process are used as lubricants, whereas the high molecular weight materials, the polyisobutylenes, are used as VI improvers and thickeners. Polybutenes that are used as lubricating oils have viscosity indexes of 70—110, fair lubricating properties, and can be manufactured to have excellent dielectric properties. Above their decomposition temperature (ca 288°C) the products decompose completely to gaseous materials. 

Polymers account for about 3—4% of the total butylene consumption and about 30% of nonfuels use. Homopolymerization of butylene isomers is relatively unimportant commercially. Only stereoregular poly(l-butene) [9003-29-6] and a small volume of polyisobutylene [25038-49-7] are produced in this manner. High molecular weight polyisobutylenes have found limited use because they cannot be vulcanized. To overcome this deficiency a butyl mbber copolymer of isobutylene with isoprene has been developed. Low molecular weight viscous Hquid polymers of isobutylene are not manufactured because of the high price of purified isobutylene. Copolymerization from relatively inexpensive refinery butane—butylene fractions containing all the butylene isomers yields a range of viscous polymers that satisfy most commercial needs (see Olefin polymers Elastomers, synthetic-butylrubber). 

Cohesive strength of these adhesives can be modified by blending butyl rubber and polyisobutylene. Higher strength is obtained by using high molecular weight PIB or butyl rubber. On the other hand, blends of butyl rubber or PIB with chlorinated butyl rubber show improved cure properties. 

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. 

Fig. 143.—The intrinsic viscosity of a polyisobutylene fraction of high molecular weight plotted against temperature in four solvents cyclohexane, diisobutylene (DIB), toluene and benzene. The lines shown have been calculated according to theory. (Fox and Flory. )...

In the absence of substantial unsaturation and of active groups on the chain for either polymer, only linear block copolymers are formed, according to the initiation Reactions 1 and 4. Low density polyethylene and high molecular weight polyisobutylene are typical of polymers which form block copolymer fractions on intensive mechanical working. The composition of block copolymers is related also to the relative rates of reaction, (Reactions 2 and 3) which is determined by the relative radical reactivity. 

Like dissolves like, and this is true with both polymers and smaller molecules. Thus linear amorphous polymers with nonpolar groups are typically soluble in nonpolar solvents with solubility parameter values within 1.8 H of that of the polymer. Thus polyisobutylene (PIB) is soluble in hot lubricating oils, and small amounts of high-molecular-weight PIB are used as viscosity improvers. 

Schremp,F. W., Ferry, J.D., Evans, W. W. Mechanical properties of substances of high molecular weight. IX. Non-Newtonian flow and stress relaxation in concentrated polyisobutylene and polystyrene solutions. J. Appl. Phys. 22,711-717 (1951). 

The question immediately raised is would this technique portray an opposite or negative adhesion response if applied to a polymer blended system where no interfacial bonding could be present Such a system would be cis-polybutadiene and high molecular weight polyisobutylene restricted to that portion of the blend system where polyisobutylene is the minor dispersed phase in cis-polybutadiene. A high molecular weight polyisobutylene [L-300 Vistanex (Enjay Chemical Co.)] was compounded with zinc oxide, sulfur, and TMTDS and then dissolved in hexane. cis-Polybutadiene (Phillips Chemical Co.) was also mixed with... 

Figure 6. High molecular weight polyisobutylene in cis-poly butadiene. Differential swelling in styrene at —25°C. Blends cured 30 minutes at 300° F.

Three classes of PSAs used most widely in transdermal systems are polyisobutylene (PIB), polyacrylate, and polydimethylsiloxane (silicone). More recently, hydrophilic adhesive compositions, hydrogels composed of high-molecular-weight polyvinylpyrrolidon (PVP) and oligometric polyethylene oxide (PEO), have been shown to be compatible with a broad range of drugs and are used in several commercial products.60... 

Our goal in this work has been the development of a terminally bifunctional liquid rubber. Carboxy-terminated polyisobutylene (CTPIB) approaches a terminally bifunctional polymer. It is made by the ozoniza-tion in the presence of pyridine of a high molecular weight, low unsaturation piperylene-isobutylene copolymer as shown in Reaction 1. 

The terminally bifunctional prepolymer, carboxy-terminated polyisobutylene, is prepared by the pyridine-modified ozonization of a copolymer of piperylene (2-4% ) and isobutylene. Figure 1 shows a block diagram of the process. The high molecular weight elastomer can be prepared by the conventional techniques of isobutylene-diene copoly-... 

Within the family of polyolefins there are many individual families that include low density polyethylenes, linear low density polyethylenes, very low polyethylenes, ultra low polyethylenes, high molecular weight polyethylenes, ultra high molecular weight polyethylenes, polyethylene terephthalates, ethylene-vinyl acetate polyethylenes, chlorinated polyethylenes, crosslinked polyethylenes, polypropylenes, polybutylenes, polyisobutylene, ionomers, polymethylpentene, thermoplastic polyolefin elastomers (polyolefin elastomers, TP), and many others. 

Polyisobutylene is a synthetic polymer. Low-molecular-weight grades are soft and gummy high-molecular-weight... 

Using 2-chloro-2,4,4,-trimethylpentane as the initiator and ethylaluminum dichloride as the Lewis acid, McDonald [5] and Shaffer [6] prepared high molecular weight polyisobutylene with perfluorinated alkanes as polymerization solvents. 

High molecular weight polyisobutylene (M =1.2-10 ) was formed in 36% yield after 11 days at —78° in bulk by using this method. Also polystyrene of an unusually high (for the cationic process) molecular weight (M = 1.7 -10 ) was obtained, however, in 4% yield only after 27 days at 0°. 

Subsequent to his discovery that alkylaluminum compounds in conjunction with suitable alkyl halides are effective initiator systems for synthesizing high molecular weight polyisobutylene (/), Kennedy in 1970 (6) studied the reaction between alkyl and aryl halides with tri-methylaluminum using methyl chloride solvent at —78° C. The results... 

Because high-molecular weight polyisobutylene is an inert hydrocarbon polymer, a very small amount of major tackifiers and oils can be dissolved in polyisobutylene. Consequently, a common polyisobutylene adhesive is composed of both high- and low-molecular weight polyisobutylene, which is also the major reason for the relatively low tack and adhesion of polyisobutylene-based adhesives. 

---