Polybutadienes polyblends

The commercial success of ABS polymers has led to the investigation of many other polyblend materials. In some cases properties are exhibited which are superior to those of ABS and some of the materials are commercially available. For example, the opacity of ABS has led to the development of blends in which the glassy phase is modified to give transparent polymers whilst the limited light aging has been countered by the use of rubbers other than polybutadiene. 

Water, methanol, and n-hexane do not influence the photooxidation of PVC (43), but the photodegradation is accelerated by ferric chloride (70,71) and certain other compounds containing iron (70,71,72). Purification of the polymer might be expected to enhance its photostability by removing deleterious impurities such as iron compounds that are derived from metal equipment. This type of result was obtained in one recent study (58) but not in others (30,59). In contrast, the photo-oxidative degradation of PVC should be enhanced by admixture of the polymer with materials that are unusually susceptible to photooxidation themselves. Such behavior has been observed for impact-modified PVC containing polybutadiene-based polyblends (69,73). 

In a heterogeneous polyblend of two dissimilar elastomers, such as chlorinated butyl rubber and polybutadiene, a certain interfacial bonding... 

The impact resistance of polypropylene at low temperature has been improved by polyblending with EPDM or E-P rubber to make possible the application of this material in the automotive industry. The low-temperature properties of polyamides such as nylon 6 and nylon 66 have been improved by polyblending with ethylene copolymers or specially grafted polybutadiene (45). 

Polyblends with Soft Matrix and Soft or Rigid Dispersed Phase. Polyblends in which both components are soft are mixtures of various elastomers. For example, treads of automobile tires are made of a polyblend of SBR with either natural rubber or cis-polybutadiene. 

Polyblends with Soft Matrix. Polyblends in which both phases are soft are mixtures of different rubbers. Treads of automobile tires are made of polyblends of SBR with either natural rubber or cts-polybutadiene. Co vulcanization of EPDM with various rubbers is discussed in the chapter of M. E. Woods and T. R. Mass. Relaxation behavior of blends of EVA rubber with styrene/ethylene-butylene/styrene block copolymer and of poly (ethylene oxide) with ethylene oxide/propylene oxide/ethylene oxide block copolymer were studied by M. Shen, U. Mehra, L. Toy, and K. Biliyar. 

For example, a 50 50 blend of polystyrene (a hard, glassy polymer at ordinary temperature) and polybutadiene (an elastomer) will be hard if polystyrene is the continuous phase, but soft if polystyrene is the dispersed phase. In some cases, however, an immiscible polyblend may have both components dispersed as continuous phases. Evidently, a proper control of phase morphology is of utmost importance with immiscible blends. The size of the dispersed phase should be optimized considering the final performance of the blend. 

Scientists and engineers working in the fields of polyblends and block copolymers have realized for many years that phase separation of the two components takes place, and that this is indeed important to the development of the mechanical behavior characteristic of these materials. However, it was not until the development of the electron microscope that the structure of any but the coarsest mechanical blends could be discerned, and even then lack of contrast between the two phases remained serious. This problem was solved in 1965 by Kato (1966, 1968), who discovered that osmium tetroxide preferentially stains polymer molecules containing carbon-carbon double bonds, such as in polybutadiene and polyisoprene. The osmium tetroxide also hardens the rubbery phase, allowing convenient ultramicrotoming of specimens to 500 A thickness. 

The simplest method of polyblending involves equipment such as rolls or extruders, which can effect the mechanical blending of the two polymeric components in the molten state (Matsuo, 1968). High-impact polystyrene (HiPS) is an important example of a polyblend made by this technique. Such materials commonly contain 5-20 % of rubber, usually polybutadiene, dispersed in a polystyrene matrix. As shown in Figure 3.1, electron microscopy studies on specimens stained with osmium tetroxide reveal well-defined, irregular rubber particles (1-10 fim in diameter) dispersed in the polystyrene matrix. The elastomer domains appear dark because the osmium tetroxide stains the elastomer preferentially (see Section 2.4). 

Blends of TPUs and Acrylonitrile-Polybutadiene-Styrene graft polymer (ABS) have been studied by a number of researchers [14-16]. The structures of the blends are very complex due to the complex polyblend of ABS, in which there is a rigid SAN copolymer with a rubbery graft butadiene polymer and the heterophase system of the TPU. The two polymers can benefit each other, as shown in Table 1. 

Polybutadiene based polyblends (Table 3.19) are very important plastics with industrial applications, e.g. impact resistance polymers and impact modifiers for rigid poly(vinyl chloride). These polyblends are very susceptible to photo-oxidative degradation, because of the presence of polybutadiene. Intensive studies of the photo-oxidation of the rubber modified polyblends lead to the following conclusions [761-764, 1936] ... 

A similar behaviour has been observed with polybutadiene-containing polyblends acrylonitrile-butadiene-styrene (ABS) (cf. section 3.12.13), methyl methacrylate-butadiene-styrene (MBS) and methyl methacrylate-acrylonitrile-butadiene-styrene (MABS), and the accelerated photo-oxidative effect has been found to be related to the amount of unsaturated groups present [1936]. 

Polybutadiene based polyblends such as acrylonitrile-butadiene-styrene (ABS) are known to be very sensitive to photodegradation when exposed to sunlight and also to longer wavelengths (>300nm) [1113]. 

In Figure 5 an electron micrograph of a midrange PEA (butadiene doped)/PS incompatible IPN composition is compared with a commercial graft-type polyblend, HiPS, supplied by Monsanto Company, Springfield, Mass. HiPS contains polybutadiene (stained black with osmium tetroxide) dispersed in PS. 

Surprisingly, the IPN exhibits a complex cellular structure. Similar cellular structures are evident in the polybutadiene portion of the HiPS, and in graft-type polyblends... 

Fortunately, in two of the most commercially important binary polyblends, PS/polybutadiene (PB) and PS/polyisoprene the interactive effects lead to stabilization the composition... 

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