Polybutene structure

The polybutene structure also contains one carbon-carbon double bond at the end of the polymer chain [40]. The nature of this double bond is important in defining the ease with which it will undergo chemical modification. Normally it is found as the CIS- and franx-trisubstituted group, but polybutenes having the more reactive disubstituted vinylidene structure are now available. Fig. 2.2. Polybutenes have good stability as lubricant components, even whilst containing the residual unsaturation. It is possible to react the double bond to produce products such as lubricant dispersants, see Chapter 7, but the reaction is achieved only under certain controlled conditions. 

Examples of reversible breakdown of structure have been reported for procaine penicillin dispersions (7), for model systems of calcium carbonate in polybutene ( ), and for numerous other systems. During shear the particles are forced into contact with each other with sufficient kinetic energy to overcome any natural barrier against their displacement of a lyosphere around each individual particle. A dispersion which is inherently stable can thus be forced by shear into a condition of instability. 

Incompatible Mixtures. Even at very low levels, many of the poly-ether additives led to incompatible mixtures. These blends were not successfully milled to a smooth sheet under any conditions tried. Instead, a mass of crumbs was obtained. These crumbs could be molded into a coherent mass, but the physical properties were poor. For example, addition of 8.75 parts of polybutene-1 oxide to Masterbatch B for CPVC alone gave a brittle, free-flowing material with these properties notched Izod impact strength, 0.7 lb/in notch, flow rate 452 g/10 min. This is a particularly interesting result, since PBO has the same chemical formula as PTHF but structurally is a substituted ethylene oxide polymer rather than a linear homopolymer. No further studies were made of such blends. 

Chemical degradation can be avoided by using closed structures, which may have protective covers or which may be fully hermetic, as well as by using unreactive metals. Barrier coatings are effective in some cases, and polyethylene—polybutene grease (8) is used in some splicing connectors for telecommunications cable. 

Several conclusions have to be drawn. The first is related to the obvious gap between the empiricism and even archaism of most of industrial cationic polymerization processes and the level of fundamental science devoted for decades to these reactions. Previous chapters in this volume clearly illustrate the situation. This feature was pointed out in the early book of Kennedy and Marechal [1], and the explanation based on the very favorable price/performances characteristics of the products is still realistic. Nevertheless it is noteworthy that recent improvements or new processes based on more scientific approaches led to a better control of the polymerization, of polymer structure, and to high-performance commercial products which will increasingly occupy the market. This is the case for the recently marketed reactive BF3-based polybutenes with high content of exomethylenic chain ends, for the strongly developing pure monomer hydrocarbon resins ( + 8% in 1994), or for the new benzyl halide-based halobutyl rubber, and it is revealing that these products represent the three families of cationically prepared industrial polymers... 

Differential thermal analysis has been used for the measurement of crystallinity of random and block ethylene-methacrylate copolymers [30] and of polybutene [31], PET, 1,4-cyclohexanedimethyl terephthalate, and polypropylene (PP) [32, 33] and in the examination of morphologically different structures of PE ionomers [34]. 

Finally, a few comments about the uniqueness of polymer crystal structures and phase space localization are warranted. Almost all crystallizable polymers exhibit polymorphism, the ability to form different crystal structures as a result of changes in thermodynamic conditions (e.g., temperature or pressure) or process history (e.g., crystallization conditions) [12]. Two or more polymorphs of a given polymer result when their crystal structures are nearly iso-energetic, such that small changes in thermodynamic conditions or kinetic factors cause one or another, or both, to form. Polymorphism may arise as a result of competitive conformations of the chain, as in the case of syndiotactic polystyrene, or as a result of competitive packing modes of molecules with similar conformations, as in the case of isotactic polypropylene. In some instances, the conformational change may be quite subtle isotactic polybutene, for example, exhibits... 

The IR spectrum of amorphous alternating polybutene-1-ethylene copolymer shows absorptions at 13.3 pm (characteristic of methylene sequences of two units) and at 9 pm (characteristic of the structure). 

ESR spectroscopy has been applied to studies of unsaturation and other structural features in a wide range of homopolymers including polyethylene [101-110], polypropylene [111-121], polybutenes [115], polystyrene [122-124], PVC [125,126], polyvinylidene chloride [127], polymethylmethacrylate [128-137], polyethylene glycol polycarbonates [137-140], polyacrylic acid [136-139, 141, 142], polyphenylenes [143], polyphenylene oxides [143], polybutadiene [144], conjugated dienes [145,146], polyester resins [146], cellophane [143,147] and also to various copolymers including styrene grafted polypropylene [148], ethylene-acroline [149], butadiene-isobutylene [150], vinyl acetate copolymers [151] and vinyl chloride-propylene. 

The polymer we are concerned with is PB-1. In the past this polymer has been referred to as polybutylene, PB, PB-1, and polybutene, as well as its chemically correct name, PB-1. PB-1 is obtained by polymerization of butene-1 with a stereo-specific Z-N catalyst to create a linear, high molecular, isotactic, semicrystalline polymer. PB-1 combines the typical properties of conventional polyolefins with some characteristics of technical polymers. In chemical structure PB-ldiffers from polyethylene and polypropylene only by the number of carbon atoms in Ae monomer molecule, as in Fig. 2.22. 

The difi actograms of nascent copolymer samples clearly show that dififaction reflections shift to smaller diffraction angles. For statistical propylene-1-butene copol5miers, this effect was repeatedly observed for various catalytic systems.This outcome may be explained by the fact that, even after replacement of a certain amount of propylene units with 1-butene units, copol5mier macromolecules continue formation of the crystalline component of a-PP but have other imit-cell parameters. In fact, in the case of isotactic PP, a macromolecule occurs in the conformation of the 3/1 helix with a cross-sectional area of 0.34 nm and an identity period of 0.65 mn for all polymorphic structures. Although isotactic polybutene exhibits the conformational type of polymorphism, it has polymorphic stmcture, in which macromolecules assiune the conformation of the 3/1 helix with a cross-sectional area of 0.44 mn and an identity period of 0.65... 

Both isotactic poly(propylene-co-butene) [81, 82] and syndiotactic poly(propylene-co-butene) [83] statistical copolymers exhibit isodimorphic behavior when crystallized. In isotactic poly(propylene-co-butene), the copolymer was found to crystallize over the entire range of butene content. A transition in crystal unit cell structure was observed at about 50 mol% butene, where below this composition, the crystalline phase resembled that for polypropylene and above this composition, the copolymer was essentially polybutene with propylene defect units [81]. The observed isodimorphic behavior can be explained by the similar helical chain structures exhibited by both polypropylene and polybutene in the crystal, which results in a relatively small free energy penalty for co-crystallization [42, 81-83],... 

In the Raman spectra of conformationally disordered polyethylene, the D-LAM mode found at a frequency (near 200 cm ) that is proportional to the concentration of gauche bonds [74]. This D-LAM mode is also observed in other molten vinyl polymers including polypropylene, polybutene and polystyrene. The presence of this Raman line in these polymers suggests a common structural basis although the chains themselves have different side chains [75]. In the vinyl polymers the band may appear as a doublet. For polypropylene, for example, there is a line near 200 cm and 400 cm and it is suggested that these two components are associated with the conformationally ordered (gt)4 polypropylene. 

In actual fact a considerable yield of ethylene is obtained from polybutene-1, whereas the production of propylene is much smaller because this can only emanate from the principal chain. The complicated structure of polybutene-1, as compared with the structures of PE and polypropylene, gives rise to the formation of a markedly larger number of structurally isomeric degradation products. Theoretically with a maximum molecular size of Cg, 37 different hydrocarbon decomposition products should be obtainable from polybntene-1 and, in fact, Voigt [68] was able to identify, or indicate the probable existence of 33 compounds for polybutene-1. 

Polybutene-1 is a polyolefin with unique characteristics which distinguish it from PE and PP. They include low heat of fusion, shear thinning, creep resistance and an intriguing polymorphic structure. Compatibility of PB-1 with PP and immiscibility with PE are often exploited to create convenient packaging which is easily opened by the consumer. This paper will review examples of the use of PB-1 in such applications and in the modification of the sealing initiation temperature of films. 

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