Macromolecular architecture

Aiming at modulating further their physical and chemical properties, and thereby at extending their apphcation fields, PLGAs have been incorporated into a broad variety of macromolecular architectures, including linear/grafted block copolymers and star/dendritic polymers. 

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K. B. Wagener and T. A. Davidson, Non-Conjugated and Conjugated Dienes in Acrylic Diene Metathesis (ADMET) Chemistry, in New Macromolecular Architecture and Functions. Proceedings OUMS 95, M. Kamachi and A. Nakamura (Eds.), Springer Verlag, New York, 1996. 

At the molecular level there are several important differences between polymeric fluids and small-molecule fluids. Because of these differences the flow behaviour of polymeric fluids is not similar to that of small-molecule fluids, which are satisfactorily described by Newtonian fluid dynamics. There are several salient features of macromolecular architecture that influence the flow behaviour ... 

Mecerreyes, A, Dubois, P and Jerdme, R. Novel Macromolecular Architectures Based on Aliphatic Polyesters Relevance of the Coordination-Insertion Ring-Opening Polymerization. VoL 147, pp. 1 -60. 

Polyamidoamine (PAMAM) dendrimers have drawn considerable interest in recent years due to their potential applications in medicine, nanotechnology, and catalysis (6,7). The ability to control dendrimer interior/exterior functionalities and the macromolecular architecture of PAMAM dendrimers... 

The history of dendrimer chemistry can be traced to the foundations laid down by Flory [34] over fifty years ago, particularly his studies concerning macro-molecular networks and branched polymers. More than two decades after Flory s initial groundwork (1978) Vogtle et al. [28] reported the synthesis and characterization of the first example of a cascade molecule. Michael-type addition of a primary amine to acrylonitrile (the linear monomer) afforded a tertiary amine with two arms. Subsequent reduction of the nitriles afforded a new diamine, which, upon repetition of this simple synthetic sequence, provided the desired tetraamine (1, Fig. 2) thus the advent of the iterative synthetic process and the construction of branched macromolecular architectures was at hand. Further growth of Vogtle s original dendrimer was impeded due to difficulties associated with nitrile reduction, which was later circumvented [35, 36]. This procedure eventually led to DSM s commercially available polypropylene imine) dendrimers. 

Synthesis of Copolymers with Complex Macromolecular Architectures... 

Stridsberg, K. M., Ryner, M. and Albertsson, A.-C. Controlled Ring-Opening Polymerization Polymers with Designed Macromoleculars Architecture. Vol. 157, pp. 27-51. 

Figure 1.4 Traditional macromolecular architectures organized chronologically according to their commercial introduction...

Will these emerging megameric structures of poly(dendrimers) represent a new class of macromolecular architecture with unique properties and characteristics ... 

Covalent polymer networks or (Class II) crosslinked macromolecular architecture polymers rank among the largest molecules known. Their molecular weight is given by the macroscopic size of the object for instance, a car tire made of vulcanized rubber or a crosslinked layer of protective coating can be considered one crosslinked molecule. Such networks are usually called macronetworks. On the other hand, micronetworks have dimensions of several nanometers to several micrometers (e.g. siloxane cages or microgels). 

Another type of architecture featuring a linear main chain surrounded by dendritic side-chains has emerged over the last decade [4], The highly descriptive term dendronized , coined by Schliiter [4] aptly describes this novel type of macromolecular architecture. Though three separate routes can be used to prepare such dendronized hybrids (Figure 7.8), the most successful approach to date has generally involved the polymerization of dendronized monomers. 

Nevertheless, the existence of the famed maximum in the dendrimer [>7] vs G relationship, and whether this behavior could be a characteristic fingerprint property of this type of macromolecular architecture, was questioned recently [19, 23], In fact, so was the linearity of the dependence of dendrimer molecular radii on M1/3 [19], so that whether this may be the beginning of yet another controversy, remains to be seen. Perhaps the future may bring an interesting debate on these subjects, but until new data become available, one should refrain from drawing premature conclusions because the exciting architectural beauty of idealized dendrimer structures has already proven itself to easily tempt the most astonishing hypotheses that may not be readily substantiated by reality. 

Lee, S. C. 2000. Dendrimers in nanobiological devices, in Tomalia, D. and Frechet, J. M. J. (eds). Dendritic Polymers-A New Macromolecular Architecture Based on the Dendritic State, John Wiley Sons, in press. 

Figure 6 Representation of the four major classes of macromolecular architectures...

The urge of polymer scientists to develop new materials is driven by society s wish to substitute conventional materials by plastics and thereby gain in performance. One reason for the emerging interest in hyperbranched polymers and other macromolecular architectures is their different properties compared to conventional, linear polymers. 

Tbe discussion of the semi-chlute properties remains confined mainly to the osmotic modulus which in good solvents describes the repulsive interaction among the macromolecules as a function of concentration. After scaling the concentration by the overlap concentration c = A2M.Yf) and normalizing the osmotic modulus by the molar mass, universal masteS" curves are obtained. These master curves differ characteristically for the various macromolecular architectures. The branched materials form curves which lie, as expected, in the range between hard spheres and flexible linear chains. 

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