Polymer blends graft copolymers

Chain functionalized polymers or graft copolymers are of great technological importance. They are used as compatibilizing agents for immiscible polymer blends (8) and adhesive layers between polymer-polymer co-extruded surfaces (8). Currently, of all polymers sold, about 30% are in the form of compatibilized immiscible blends (9-12). Next we discuss a few examples of chain functionalization. 

A random co-polymer or a blend of compatible polymers will have a single glass transition temperature intermediate between those of the two homopolymers. An example is shown in Figure 14 for nitrile-butadiene-rubber (22). The specific weight percents shown are those of commercial interest for NBR. In contrast, most polymer blends, graft and block copolymers, and interpenetrating polymer networks (IPN s) are phase separated (5) and exhibit two separate glass transitions from the two separate phases. Phase separated systems will not be considered here. 

Kuhn R (1983) Characterization of polymer blends, block copolymers, and graft copolymers by fractionation procedures using demixing solvents. Polym Sci Technol 20 45-58. 

This part of the monograph will examine systems containing mixtures of two distinguishable kinds of polymer molecules. Such mixtures, known as polymer blends, polyblends, or simply blends, include mechanical blends, graft copolymers, block copolymers, and interpenetrating polymer networks. 

Most of the polymer blends, grafts, and blocks examined in the preceding chapters formed two amorphous phases. When one phase was plastic and stiff, and the other rubbery and soft, we observed that toughened materials resulted. In this chapter we examine several types of block copolymers in which one or both components crystallize in particular we consider three possible combinations of such blocks ... 

L. H. Sperling, Isomeric Graft Copolymers and Interpenetrating Polymer Networks. Current Status of Nomenclature Schemes, in Chemistry and Properties of CrosslinkedPolymers, S. S. Labana, ed., Academic, New York (1977). Group theory concepts applied to polymer blends, grafts, blocks, and IPNs. Nomenclature scheme. 

The precursor polymer blend can be made out of (1) linear block copolymers, (2) AB block copolymers, (3) ABA block copolymers, (4) ABC block copolymers, (5) multiblock copolymers, (6) symmetrical and asymmetrical star block copolymers, (7) blends of polymers, (8) graft copolymers, (9) multibranched copolymers, (10) hyperbranched or dendritic block copolymers, and (11) novel brush copolymers. 

J. P. Kennedy, "An Introduction to the Synthesis of Block and Graft Copolymers", in Recent Advances in Polymer Blends, Grafts and Blocks", L. H. Sperling, ed.. Plenum Press, New York, 1974, p. 47. 

NEXAFS spectroscopy can be applied for quantitative analyses of the chemical composition of polymer blends and copolymers [9]. An interesting application concerns NEXAFS microscopy (see Section 6.3). Moreover, the application of NEXAFS spectroscopy to surface studies -and in particular to studies related to the adsorption of organic molecules onto the surfaces of metals and polymers - is of particular interest. For example, the NEXAFS spectra of a monolayer of poly-3-methylthiophene, electrochemically grafted onto Pt, revealed that the aromatic rings in the polymeric layer are Jt-bonded to the Pt(lll) surface [16]. In addition, NEXAFS spectroscopy provides answers to questions such as Flow do molecules interact with surfaces or How do molecules orient on surfaces ... 

Many important advances have been made in the nomenclature of polymer blends, grafts, blocks and IPN s. These include a nomenclature document recently published by the lUPAC Nomenclature Committee and one now under consideration. Briefly, two advances were made that relate to IPN s. The first was the use of the prefix cross- to indicate a crosslinked polymer. Thus, cross-poly-butadiene is distinguished from the linear product, written polybutadiene. The second advance was the introduction of the symbol -inter-, which means interpenetrating. Thus, cross-poly-(ethyl acrylate)-mtcr-cross-polystyrene (1) represents the IPN based on poly(ethyl acrylate) and polystyrene. The symbol -inter- has exactly the equivalent meaning as -block- and -graft- possess for block and graft copolymers, respectively. 

Fig. 6. Illustration of (a) compatibiLization of immiscible blends of polymers and B by block or graft copolymers and (b) the subsequent modification of...

Because graft copolymers are much "easier" to obtain synthetically than heterogeneous diblock or triblock copolymers, they have also been used as compatibiUzers ia polymer blends. Theoretically, they are not as efficient as the diblocks (60), but they are successhilly and economically used ia a number of commercial systems (61). 

Two commercially significant graft copolymers are acrylonitrile—butadiene—styrene (ABS) resins and impact polystyrene (IPS) plastics. Both of these families of materials were once simple mechanical polymer blends, but today such compositions are generally graft copolymers or blends of graft copolymers and homopolymers. 

The relative U.S. production of styrene homopolymer and copolymer resins is also noteworthy (103) (Fig. 6). The impact polystyrene (graft and polymer blend) copolymers are produced in nearly the same quantities as styrene homopolymers. The ABS resins are synthesized in lesser, yet significant, quantities. 

Copolymer technology is progressing along two "fronts." First, new appHcations for copolymers are being found to increase the volume of materials that are already commercially available. One example of this is the rapid growth of styrenic block copolymers sold as asphalt (qv) and polymer modifiers over the past 10 years (Fig. 7). Another is the increased interest in graft and block copolymers as compatihilizers for polymer blends and alloys. Of particular interest are compatihilizers for recycled polymer scrap. 

Polypropylene block and graft copolymers are efficient blend compatibilizers. These materials allow the formation of alloys, for example, isotactic polypropylene with styrene-acrylonitrile polymer or polyamides, by enhancing the dispersion of incompatible polymers and improving their interfacial adhesion. Polyolefinic materials of such types afford property synergisms such as improved stiffness combined with greater toughness. 

In contrast to two-phase physical blends, the two-phase block and graft copolymer systems have covalent bonds between the phases, which considerably improve their mechanical strengths. If the domains of the dispersed phase are small enough, such products can be transparent. The thermal behavior of both block and graft two-phase systems is similar to that of physical blends. They can act as emulsifiers for mixtures of the two polymers from which they have been formed. 

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