Multicomponent polymers, preparation

In a previous publication [8] we described a systematic screening of the binary interactions between 36 polyanions and 40 polycations. As a result of this study it became clear that capsules prepared from simple binary polymer complexes would not be mechanically adequate and multicomponent polymer systems would offer advantages. The rationale for capsule improvement, and for the use of a multicomponent system, has been presented in the Introduction. We have elected to investigate the methods outlined in Sects. 1.2.7 and 1.2.8 (polymer... 

S. Bose, A.R. Bhattacharyya, R.A. Khare, S.S Kamath, and A.R. Kulkarni, The role of molecular interactions and selective localization of multiwall carbon nanotubes on the electrical conductivity and phase morphology of multicomponent polymer blends (manuscript in preparation). 

For many years polymeric membranes have been utilized widely for material separation without detailed characterization of the pore size and the pore size distribution. Most of the commercially available membranes are prepared by either a dry or a wet phase-inversion process. These membranes are formed by the phase separation of multicomponent polymer-solvent systems, the underlying principle being phase separation of the polymer solution. 

The composition of the structural material and the choice of the fabrication process are important in the preparation of controlled-release systems. Over the past decades, great advances have been made in the engineering of multicomponent, polymer-based, structural materials. These materials were designed to release active substances by different mechanisms (ref. 1) including diffusion, chemical control (polymer degradation) and solvent activation (swelling or osmotic pressure). In some cases, combinations of such mechanisms have been used. Experimental methods and theoretical analysis of mass transport phenomena in these materials have been developed (refs. 2,3). 

The field of IPNs is simultaneously one of the oldest in multicomponent polymer literature, and one of its newest and fastest growing fields. With IPNs, it is relatively easy to prepare very small domain sizes and/or materials with dual phase continuity. IPNs can be made via a multitude of ways sequential, simultaneous, latex, gradient, and thermoplastic, to name some of the more prominent materials. 

In principle, the broad range of functional monomers eurrently available makes it possible to design an MIP specific for any type of stable ehemical compound. Currently the selection of the best monomers for polymer preparation is one of the most crucial issues in molecular imprinting. Thermodynamic calculations and combinatorial screening approaches olfer possible solutions, and have already been used successfully for predicting polymer properties and for the optimization of polymer compositions (see Ref. 9,57,58, and Chapter 8), however, in practical terms, application of these methods is not trivial. The problem lies in the technical difiiculty of performing detailed thermodynamic calculations on multicomponent systems and the amount of time and resources required for the combinatorial screening of polymers. To check a simple two-component combination of 100 monomers, for example, one has to synthesize and test more than 5000 polymers, a very difiicult task. This task will be further complicated by the possibility that these monomers could be used in monomer mixtures in dilferent ratios. 

Kakihana, M. Yoshimura, M. (1999). Synthesis and Characteristics of Complex Multicomponent Oxides Prepared by Polymer Complex Method. Bulletin of the Chemical Society of Japan, Vol. 72, No. 7, (1999), pp. 1427-1443, ISSN 0009-2673... 

Michler [2] has nicely summarized and realized practical examples of some of the modern tools of microscopy used to study the morphology and microstructure of polymers and polymer-based materials. The most frequently employed microscopic tool remains the scanning electron microscope. It is the fastest and allows one to reach interesting dimensions in multicomponent polymer blends and composites. Transmission electron microscopy can be ranked in the second position, whereas the optical microscope is usually used as a "first-check tool" before deeper investigation. It is nevertheless the strategic tool employed in life science (biomedical, Wlogics, etc.). In all these cases the sample preparation step is crucial before investigating the material s microstructure. 

Kakihana M., Yoshimura M. Synthesis and characteristics of complex multicomponent oxides prepared by polymer complex method. Bull. Chem. Soc. Jpn. 1999a 72 1427-1443 Kakihana M., Arima M., Nakamura Y., Yashima M., Yoshimura M. Spectroscopic characterization of precursors used in the Pechini-type polymerizable complex processing of barium titanate. Chem. Mater. 1999b 11 438-450... 

If solubility or miscibility are the properties used to separate components in a multicomponent polymer, one cannot expect the separations to be very effective. The relative differences between the neighboring chain lengths are extremely small, and so are the differences in the property used. Nevertheless, procedures have been developed that still permit the isolation of reasonably sharp fraction distributions, and are in use, particularly to prepare large-size polyolefin fractions. We discuss these procedures briefly they are fractionation by liquid liquid phase separation, and fractionation by crystallization from solution. 

Alkyne-based MCPs are rarely reported, despite the rich chemistry of alkynes. Compared with traditional polymers, polymers prepared from alkyne monomers generally contain a conjugated polymer backbone and hence possess optoelectronic properties, enabling advanced functionalities of the polymer materials. However, their rigid structure can lead to poor solubility and limit the exploration of efficient polymerization methods [20]. In this review, the most up-to-date progress in the development of alkyne-based MCPs is introduced, including MCPs of alkynes, aldehydes, and amines MCPs of alkynes, azides, and amines/alcohols and multicomponent tandem polymerization of alkynes, carbonyl chloride, and thiols. 

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. 

Conducting Polymer Blends, Composites, and Colloids. Incorporation of conducting polymers into multicomponent systems allows the preparation of materials that are electroactive and also possess specific properties contributed by the other components. Dispersion of a conducting polymer into an insulating matrix can be accompHshed as either a miscible or phase-separated blend, a heterogeneous composite, or a coUoidaHy dispersed latex. When the conductor is present in sufftcientiy high composition, electron transport is possible. 

There are several approaches to the preparation of multicomponent materials, and the method utilized depends largely on the nature of the conductor used. In the case of polyacetylene blends, in situ polymerization of acetylene into a polymeric matrix has been a successful technique. A film of the matrix polymer is initially swelled in a solution of a typical Ziegler-Natta type initiator and, after washing, the impregnated swollen matrix is exposed to acetylene gas. Polymerization occurs as acetylene diffuses into the membrane. The composite material is then oxidatively doped to form a conductor. Low density polyethylene (136,137) and polybutadiene (138) have both been used in this manner. 

Numerous kinds of gels are prepared by precipitation from supersaturated solutions. Then, the gel structure is three-dimensional and contains multicomponent branched polymers distributed by weight. 

The concept of combining two or more unique polymers to prepare new material systems with the desirable features of their constituents is widely practiced in the polymer industry (1-5). The primary issue confronting the design of such polymer systems involves guaranteeing good stress transfer between all components of the multicomponent system. This is the only way to ensure that the components individual physical properties are efficiently utilized to produce mixtures with the desired performance characteristics. 

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