Copolymers and Interpenetrating Networks

As already mentioned, the sequential coupling of functionally terminated chains of different chemical structure can be used to make block copolymers,59,354,355 including those in which one or more of the blocks is a polysiloxane.74,115,356 If the blocks are relatively long, separation into a two-phase system almost invariably occurs. Frequently, one type of block will be in a continuous phase and the other will be dispersed in it in domains having an average size the order of a few hundred angstroms. Such materials can have unique mechanical properties not available from either species when present simply in homopolymeric form. Sometimes similar properties can be obtained by the simple blending of two or more polymers.357 

In this type of material, two networks are formed, either simultaneously or sequentially, in such a way as to interpenetrate one another. They thus communicate with one another through interchain interactions, including entanglements, rather than through 

In the case of controlled drug-delivery systems, the goal is to have the drug released at a relatively constant rate (zero-order kinetics) at a concentration within the therapeutic range. It is obviously important to minimize the amount of time the concentration is in 

CONTROLLED DRUG DELIVERY SYSTEMS SILICONE IMPLANTS 

RATE CONTROLLING MECHANISM - MEMBRANE DOW CORNING Silicone Tubing Elastomers 

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The highest sonic damping is obtained in transition zones. The glass transition can be used for this purpose if cross-linked polymers are applied, with a rubbery solid state until far above Tg. Very interesting work in this field was done by Sperling and his coworkers (1987,1988) who studied the damping behaviour of homopolymers, statistical copolymers and interpenetrating networks (IPNs) of polyacrylics, polyvinyls and polystyrenes. 

This chapter on applications of PAB s focuses on polymer systems giving synergistic and generally high performance properties. Low performance PAB s of commodity plastics, rubber toughened plastics, copolymers, and interpenetrating networks are excluded. Some of the more common PAB s are described elsewhere in this book. 

Multiphase or multicomponent polymers can clearly be more complex structurally than single phase materials, for there is the distribution of the various phases to describe as well as their internal structure. Most polymer blends, block and graft copolymers and interpenetrating networks are multiphase systems. A major commercial set of multiphase polymer systems are the toughened, high impact or impact modified polymers. These are combinations of polymers with dispersed elastomer (rubber) particles in a continuous matrix. Most commonly the matrix is a glassy amorphous thermoplastic, but it can also be crystalline or a thermoset. The impact modified materials may be blends, block or graft copolymers or even all of these at once. 

Mazurek, M. Silicone Copolymer Networks and Interpenetrating Networks. In Silicon-Containing Polymers. The Science and Technology of Their Synthesis and Applications-, Jones, R. G., Ando, W., Chojnowski, J., Eds. Kluwer Dordrecht, 2000 pp 113-137. 

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. 

Network Copolymers and Interpenetrating Polymer Networks Polyblends... 

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. 

Blends and interpenetrating networks are physical mixtures of constitutionally and/or configurationally different homo- or copolymers. They are produced in order to improve certain final use of processing properties so that the property spectrum of bulk plastics can approach that of engineering plastics in an economically viable way. 

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. 

L. H. Sperling and K. B. Ferguson, Isomeric Graft Copolymers and Interpenetrating Polymer Networks. Possible Arrangements and Nomenclature, Macromolecules 8(6), 69 (1975). Graft copolymer and IPN nomenclature scheme. Application of group theory concepts. 

Most polymer blends, as well as their related graft and block copolymers and interpenetrating polymer networks, are phase-separated (122) (see Section 4.3). In this case each phase will exhibit its own Tg. Rgure 8.29 (123,124) illustrates two glass transitions appearing in a series of triblock copolymers of different over l compositions, lie intensity of the transition, especially in the loss spectra "), is indicative of the mass fraction of that phase. 

Phase separations, blends, and related subjects (57-64) covered at the symposium involved binodal and spinodal phase separations (Viers), block copolymers (Weber, McGrath, Yilgor, Gravier), blends (Talmon, Krenceski, Singh, Yilgor, Pearce), and interpenetrating networks (65) (Boileau, Wengrovius) (26). 

Interpenetrating networks have been made by co-curing polychloroprene with copolymers of 1-chloro-1,3-butadiene [627-22-5]. The 1-chloro-1,3-butadiene serves as a cure site monomer, providing a cure site similar to that already in polychloroprene. The butadiene copolymer with 1-chloro-1,3-butadiene (44) and an octyl acrylate copolymer (45) improved the low temperature brittieness of polychloroprene. The acrylate also improved oil resistance and heat resistance. 

Another area of recent interest is covulcanization in block copolymers, thermoplastic rubbers, and elasto-plastic blends by developing an interpenetrating network (IPN). A classical example for IPN formation is in polyurethane elastomer blended acrylic copolymers [7]. 

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