Miscible Reactive Polymer Blends

As far as the stereoregularity is concerned, studies of various types of initiation show that methacrylates could be polymerized to give as well as isotaetie, syndiotaetie atactic polymers. Numerous physical properties are tacticity dependent for example, the rate of water absorption is higher for syndiotaetie than for isotactic polymer [97], the transition temperatures of liquid crystalline methacrylic polymers can be specifically influenced [160-162], and the miscibility of polymer blends is changed [163-165]. In general, the stereoregularity depends on the solvent used, the initiator, and the reaction temperature. Reviews have provided an overview concerning analysis, properties and reactivities of polymers with respect to their tacticity [97,166,167]. 

In this example of model reactive polymer processing of two immiscible blend components, as with Example 11.1, we have three characteristic process times tD,, and the time to increase the interfacial area, all affecting the RME results. This example of stacked miscible layers is appealing because of the simple and direct connection between the interfacial layer and the stress required to stretch the multilayer sample. In Example 11.1 the initially segregated samples do create with time at 270°C an interfacial layer around each PET particulate, but the torsional dynamic steady deformation torques can not be simply related to the thickness of the interfacial layer, <5/. However, the initially segregated morphology of the powder samples of Example 11.1 are more representative of real particulate blend reaction systems. 

The problems and challenges Inherent to developing useful materials with optimal morphologies and properties from an Immiscible or partially miscible polymer blend are not trivial and have spawned considerable Industrial and academic research. Work on polymer miscibility, compatibilizing agents, reactive systems, and the Influence of flow on the structure and properties of blends Is described in later chapters. 

The understanding of the formation of miscible and immiscible polymer blends requires the application of the principles of phase chemistry. A miscible blend may be regarded as a solution of one polymer in the other. The thermodynamic criteria for the miscibility of liquids are well known and may be applied to polymers as a first approximation. The added complexity comes from the long-chain nature of polymers. In addition to the entropic factors there are kinetic factors to be considered. Since in reactive processing the reactions are occurring within a short time, they will very often be a long way from equilibrium. 

The second case we describe here is the polymerization of styrene to polystyrene in the presence of polyphenylene oxide. Poly-2,6-dimethyl-l,4-phenylene oxide (PPE) is an orange-red polymer with a glass transition temperature of 220°C and it is completely miscible with PS. Although strictly speaking the system consists of two components, the mutual complete miscibility of all components (monomer as well as both polymers) permits to treat this polymerization as a one-component reactive extrusion process. From product point of view the addition of PPE to PS results in a polymer blend with a higher glass transition temperature (6) than polystyrene. From process point of view the increased viscosity of PPO... 

Polymer alloys are commercial polymer blends with improvanent in property balance with the use of compatibilizers. Texas A M University [1] has patented a com-patibilizer that can result in a product with high impact resistance as well as scratch resistance. The blend is composed of HIPS or polypropylene (PP) and a compati-bilizer made of a triblock copolymer of styrene-ethylene-propylene. Udipi [2] discovered that polymer blends composed of PC, a copolyester of PETG, and nitrile rubber exhibit a superior balance of properties. Reactive compatibilization of PC/ SAN blends at various AN compositions were conducted by Wildes et al. [3] using a SAN-amine compatibilizer. PC and SAN were found to be miscible over a range of AN composition by Mendelson [5]. Nylon/ABS blends can be compatibilized by use of SAN-maleic acid (Lavengood et al. [6]). Styrene-GMA copolymers can be used as compatibilizers for PS/PA, PS/PBT, PS/PET, and PPO/PBT blends. 

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