Polymer blending, development

Although great strides have been made in the past, opportunities still exist to improve and solve numerous polymer blend problems. Research and technical innovation will continue to impact polymer blend development and production. We are confident that polymer blends will continue to contribute to the development of our modem society. 

Part 1 Polymer Blend Developments fin- Developing Opportunities. 1435... 

The formation of a polymer blend aims in achieving certain specific properties, which are difficrrlt to obtain from any one of the single components alone. Here, the certain specific properties refer to the properties of the polymers which are improved by formation of blends. Specific types of components of polymer blends modify some specific kinds of properties only. In other words, a large nttmber of polymer properties cannot be improved simrrltaneously by blending two different polymers. Blend development is far less costly and to smaller extent time-consrtming than the... 

For substrates of WORM and EOD(PCR) disks the industry in the future wants polymers that have a markedly improved resistance to heat softening compared to BPA-PC and, if possible, a lower water absorption and lower birefringence, but otherwise maintain the good characteristics in toughness, production, and cost (194). This goal is being approached in different ways further modification of BPA-PC, newly developed polymers, improvement of the processing characteristics of uv-curable cross-linked polymers, and development of special copolymers and polymer blends, eg,... 

Copolymers nd Blends of PC. Numerous co- and terpolymers as well as polymer blends of BPA-PC have been developed and their suitabihty as substrate materials for optical data storage media has been tested (Table 8) (195). From these products, three lines of development have been chosen for closer examination. 

Although the concept of polymer blends is sometimes a route for a voiding the development of new polymers, it often has been an integral part of the utiliza tion of new polymer chemistry, eg, the commercial success of PPO hinged on the advantages of its blends with PS. 

Synthetic polymers have become extremely important as materials over the past 50 years and have replaced other materials because they possess high strength-to-weight ratios, easy processabiUty, and other desirable features. Used in appHcations previously dominated by metals, ceramics, and natural fibers, polymers make up much of the sales in the automotive, durables, and clothing markets. In these appHcations, polymers possess desired attributes, often at a much lower cost than the materials they replace. The emphasis in research has shifted from developing new synthetic macromolecules toward preparation of cost-effective multicomponent systems (ie, copolymers, polymer blends, and composites) rather than preparation of new and frequendy more expensive homopolymers. These multicomponent systems can be "tuned" to achieve the desired properties (within limits, of course) much easier than through the total synthesis of new macromolecules. 

Whilst the volume production of completely new polymers which have achieved commercial viability in recent years has been small, the development of polymer blends has been highly significant. Of these the most important involve a glassy... 

K. Binder. Phase transitions in polymer blends and block copolymer melts some recent developments. Adv Polym Sci 772 181-299, 1994. 

Leibler [17] and Noolandi et al. [18,19] developed thermodynamic theories concerning the emulsification of copolymers (A-b-B) in immiscible polymer blends (A-B). 

In a fundamental sense, the miscibility, adhesion, interfacial energies, and morphology developed are all thermodynamically interrelated in a complex way to the interaction forces between the polymers. Miscibility of a polymer blend containing two polymers depends on the mutual solubility of the polymeric components. The blend is termed compatible when the solubility parameter of the two components are close to each other and show a single-phase transition temperature. However, most polymer pairs tend to be immiscible due to differences in their viscoelastic properties, surface-tensions, and intermolecular interactions. According to the terminology, the polymer pairs are incompatible and show separate glass transitions. For many purposes, miscibility in polymer blends is neither required nor de-... 

This is one of the most universal techniques for obtaining hydrogels from water-soluble polymers. Crosslinked PEO, PVA, PAAm, PAAc and its salts, as well as some polymer blends were obtained by this method. Although all polymers mentioned above have their own specific features, in most cases the gelation doses do not exceed 1-2 Mrad, i.e. they are substantially lower than for the same polymer in bulk. This is due to the fact that in aqueous media crosslinking occurs indirectly, namely because of the OH radical formation and their attack on the macromolecules. There exists a developed theory of these processes [73],... 

Since most polymers, including elastomers, are immiscible with each other, their blends undergo phase separation with poor adhesion between the matrix and dispersed phase. The properties of such blends are often poorer than the individual components. At the same time, it is often desired to combine the process and performance characteristics of two or more polymers, to develop industrially useful products. This is accomplished by compatibilizing the blend, either by adding a third component, called compatibilizer, or by chemically or mechanically enhancing the interaction of the two-component polymers. The ultimate objective is to develop a morphology that will allow smooth stress transfer from one phase to the other and allow the product to resist failure under multiple stresses. In case of elastomer blends, compatibilization is especially useful to aid uniform distribution of fillers, curatives, and plasticizers to obtain a morphologically and mechanically sound product. Compatibilization of elastomeric blends is accomplished in two ways, mechanically and chemically. 

Binder, K. Phase Transitions in Polymer Blends and Block Copolymer Melts Some Recent Developments. VoL 112, pp. 115-134. 

Huneault, M. A., Shi, Z. H., and Utracki, L. A., Development of polymer blend morphology during compounding in a twin-screw extruder. Part IV A new computational model with coalescence. Polym. Eng. Sci. 35(1), 115-127 (1995). 

Aliphatic polyesters based on monomers other than a-hydroxyalkanoic acids have also been developed and evaluated as drug delivery matrices. These include the polyhydroxybutyrate and polyhydroxy valerate homo- and copolymers developed by Imperial Chemical Industries (ICI) from a fermentation process and the polycaprolactones extensively studied by Pitt and Schindler (14,15). The homopolymers in these series of aliphatic polyesters are hydrophobic and crystalline in structure. Because of these properties, these polyesters normally have long degradation times in vivo of 1-2 years. However, the use of copolymers and in the case of polycaprolactone even polymer blends have led to materials with useful degradation times as a result of changes in the crystallinity and hydrophobicity of these polymers. An even larger family of polymers based upon hydroxyaliphatic acids has recently been prepared by bacteria fermentation processes, and it is anticipated that some of these materials may be evaluated for drug delivery as soon as they become commercially available. 

Recent developments have allowed for more detailed studies of polymer surface morphology by ESCA. Angle-resolved ESCA (ARXPS) allows for providing chemical compositions from shallower depths. By varying the angle of incidence different depths can be probed, and procedures have been developed to arrive at three-dimensional reconstruction of the surface. An example is shown in Figure 2, where a PVC/PMMA polymer blend has been analysed using such an approach [9]. 

---