Polybutene sealants

Butyl mbber, a copolymer of isobutjiene with 0.5—2.5% isoprene to make vulcanization possible, is the most important commercial polymer made by cationic polymerization (see Elastomers, synthetic-butyl rubber). The polymerization is initiated by water in conjunction with AlCl and carried out at low temperature (—90 to —100° C) to prevent chain transfer that limits the molecular weight (1). Another important commercial appHcation of cationic polymerization is the manufacture of polybutenes, low molecular weight copolymers of isobutylene and a smaller amount of other butenes (1) used in adhesives, sealants, lubricants, viscosity improvers, etc. 

Polyisobutylene is produced ia a range of mol wts, and has found a host of uses. The low mol wt Hquid polybutenes have appHcations as adhesives, sealants, coatings, lubricants, and plasticizers, and for the impregnation of electrical cables (7). Moderate mol wt polyisobutylene was one of the first viscosity-iadex modifiers for lubricants (8). High mol wt polyisobutylene is used to make uncured mbbery compounds, and as an impact additive for thermoplastics. 

Polybutenes enjoy extensive use as adhesives, caulks, sealants, and glaring compounds. They are used as plasticizers in mbber formulations with butyl mbber, SBR, and natural mbber. In linear low density polyethylene (LLDPE) blends they induce cling to stretch-wrap films. Polybutenes when modified at their unsaturated end groups with polar fiinctionahty are widely employed in lubricants as dispersants. Blends of polybutene with polyolefins produce semisoHd gels that can be used as potting and electrical cable filling materials. 

Actipol . [Amoco] Activated polybutene used in adhesives, sealants, coatings, unsat. polyesters, elec, conqpds., foams, andottor qridics. 

Amoco Polybutene. [Amoco] Polybutene tackifier, sttengthener, tmider in adhesives, as plasticizer for rubber, as vehicle and binder for coatings, as cling additive for LLDFE stretch wrap films, as reactive intermediaie for specialty chemicals, in caulks, sealants, and gazing com. ... 

Polybutenes have heen used for almost a century and while they are still used, most of this type sealant contains butyl rubber, which is a copolymer of butene and isoprene. Most building specifications, including Federal Specification, TT-S-001637, require solutions of butyl rubber instead of oil-based caulking compositions. Self curing butyl rubber sealants may contain phenolic resins,IS. resorcinol and hexamethylenetetramine. ... 

PB base polymers are semicrystalUne isotactic thermoplastic polyolefins. They are derived from the polymerization of butene-1 monomer with or without other alpha-olefin monomers utilizing a Ziegler-Natta type of catalyst. Their unique crystallization behavior means longer open times of adhesive and sealant formulations compared to other commonly used polymers such as polyethylene and ethylene-vinyl acetate copolymer (EVA). Polybutylene (PB), also called polybutene-1 or poly-1-butene, is different from polybutene or polyisobutylene (PIB). PIB is amorphous and rubbery, and comes in the form of a viscous liquid or big, hard block (6 in. in length and width or could be larger). PB base polymers are sup-pUed in the form of small pellets (about 0.25 in. in diameter) or nibs. 

The C4 olefins go into three types of sealants polybutenes, butyl rubber, and polyisobutylene. Polybutenes are largely linear, low molecular weight homopolymers of butene-1, used in sealants either as prime vehicles or as modifying polymers. They are relatively low cost, nondrying, tacky polymers. They are used in the formulation of three types of compounds ... 

Table 7. Polybutene-Based Sealant (Rope Caulk).

Poly isobutylene, PIB, is a homopolymer of high molecular weight. The butyl elastomers are copolymers of isobutylene with sufficient isoprene (0.5-2.5%) to permit crosslinking. Most butyl compositions are one-component, e.g., tapes or liquid gun-grade caulks. They may be modified with plasticizers such as polybutene, or tackifiers and fillers such as calcium carbonate and fibrous talc. Two-component, curing butyl sealants are also available. 

Two-Component Sealants.Two-component butyl sealants are room temperature vulcanized materials. Low in moisture vapor transmission and easy working because of low molecular weight and semi-liquid form, these sealants are filled with calcium carbonate and titanium dioxide, plasticized with polybutene, and may be modified with epoxy and silane adhesion promoters. The cure system is p-qui-none dioxime activated with a peroxide. 

Preformed Tapes. Preformed tapes of butyl, usually vulcanized, are extruded semisolid sections with pressure-sensitive adhesion. Since they are 100% solid, there are no problems of shrinkage or solvent evaporation. Sold in rolls interlined with release paper, they are often used together with liquid sealants or solid spacers, shims, etc. They vary from low cost, highly polybutene-extended tapes for trailers and mobile homes, to partially or fully vulcanized butyl rubbers with little polybutene content for high-rise glazing and automotive windshield sealants. 

Low Movement Seaiants (Caulks). These include polybutene, polyisobutene, and oil and resin-based caulks. These low cost sealants have an approximate joint movement capacity of only 5%, a slow rate of cure (120 days), a low Shore A hardness, a relatively short service life (approximately 6 or 7 years on average), and only modest weather or chemical resistance. Therefore, low movement sealants are primarily utilized in static joints having minimal exterior exposure. 

Talc applications include caulking compounds, sealants, auto putties, mastics, and joint compoimds based on polybutene, polyisoprene, butyl rubber, polyurethane, and polyvinyl acrylate. 

A variety of plasticizers can be used in adhesives and sealants as to their primary resin type. Paraffinic oils, phthalate esters, and polybutenes are typical plasticizers (Dostal 1990). Plasticizers for natural rubber adhesives, such as mineral oil or lanolin, are used to reduce the cost of the adhesive mass, and have a depressing effect on the peel adhesion (Satas 1999). Phthalates, chlorinated hydrocarbons, and aliphatic hydrocarbons are commonly used as plasticizers in urethane sealants (Dostal 1990). Most of sealants, except for silicones, contain plasticizers in their formulations. Silicone sealants can be plasticized only by low molecular weight silicone oils (Petrie 2000). 

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