Reinforcement molecular

Figure 22.8 Chemical structures of PPP derivatives 40-42 with lateral substituents, designed so as to induce specific aggregation behavior, to test polyelectrolyte theories and the concept of molecular reinforcement.

Eisenbach et al. used charged PPP-based rods such as 42, mixed with countercharged coiled macromolecules, for the purpose of molecular reinforcement [95]. The mechanical properties of these ionomeric nanocomposites was shown to depend heavily on the molecular parameters of the rod component- that is, the degree of polymerization and the rod volume fraction [96]. 

B. Schartel and J. H. Wendorff, Molecular composites for molecular reinforcement A promising concept between success and failure, Polymer Engineering and Science, vol. 39, No. 1, 128-151, January (1999). 

Self-Reinforcing Composites—Molecular Reinforcement. The idea... 

One of the most successful approaches for producing improved structural materials is reinforced polymer composite technology. Unfortunately, the limitations of fiber reinforced materials, for instance, have also produced drawbacks and necessitated the consideration of an improved materials concept. Indeed, molecular reinforcement was expected to be an innovative concept for structural materials and, what is more, one of the most promising because it relies on the well-established techniques of composite technology and it is subject to market demands. 

Molecular reinforcement is affected by the consequent translation of fiber reinforcement to the molecular level. At the same time, in composite science and technology, it is well known that the mechanical performance of a composite material depends on two main factors, namely, the aspect ratio of the reinforcing component and the adhesion quality between matrix and reinforcement. Analysis of the mechanical data, as well as the superior reachable aspect ratio of single stiff molecules, identifies single molecule fibers as the limit of materials aimed at fiber reinforcement. Lindenmeyer [1] explained the concept of molec-... 

In the excellent review by Schartel and Wendorff [30] on molecular composites, after analyzing the thermodynamic requirements for the preparation of molecular reinforced composites and stressing that blends of rigid rod-hke polymers with flexible-chain polymers are thermodynamically nonmiscible, they describe possible routes for obtaining homogeneous mixtures. Further, they draw attention to the fact that none of these approaches could avoid the dephasing completely. Therefore, better results in this respect can be obtained by a combination of various approaches. 

For systems of rigid poly diacetylenes with functional or ionic side groups and car-boxylated or sulfonated polystyrene or sulfonated polyester-urea urethanes, molecular composites could be achieved by ionic interactions [51]. The blends exhibited no microphase separation and the miscibility on a molecular length scale was proven by infrared spectroscopic, dynamic mechanical and differential scanning calorimetry analysis. The molecular reinforcement amounted to up to 1 order of magnitude in compliance with a Halpin Tsai description and was achieved by only a few weight percent of the rigid compound. 

Braun D, Hartig C, Reubold M, Soliman M and Wendorff J H (1993) Molecular reinforcement by lambda-shaped molecules, Makromol Chem Rapid Commun 14 663-668. 

Wendling J and Wendorff J H (1996) Molecular reinforcement A force field evaluation, Macromol Theory Simvl 5 381-391. 

Schartel B, Stumpflen V, Wendling J, Wendorff J H, Heitz W and Neuhaus R (1996) Rigid starshaped multipodes Molecules designed for molecular reinforcement, Coll Polym Sci 274 911-919. 

Seufert M, Fakirov C and Wegner G (1995) Ultrathin membranes of molecularly reinforced liquids on porous substrates, Adv Mater 7 52-55. 

One of the exciting concepts in the field of blend/composite materials is the reinforcement of flexible-chain polymers by highly rigid rod-like macromolecules with a persistence length Lp > lOnm. The basic principle of these blends, which are known as molecular composites , is dispersion of rigid-chain polymers in a random coil chain, ductile matrix. The basic principles, advantages, and difficulties of molecular reinforcement, and the available data on this problem were summarized... 

Thus, the blend components, PIr and Pip, were rather close in their chemical structure differing, however, by the absence or presence of oxygen hinges in the chains. This predetermined the sharply different chain rigidity and allowed one to consider these blends as the PIr/PIp molecular composites consisting of molecular reinforcing fibers and relatively ductile matrix. 

Keywords Catalysis Molecular reinforcement Nanocomposites Olefin polymerization Polymerization filling Polyolefin Reactor blends Single-site... 

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