Multifunctional macromolecule

The failure in increasing residence time of mucoadhesive systems in the human intestinal tract has led scientists to the evaluation of multifunctional mucoadhesive polymers. Research in the area of mucoadhesive drug delivery systems has shed light on other properties of some of the mucoadhesive polymers. One important class of mucoadhesive polymers, poly(acrylic acid) derivatives, has been identified as potent inhibitors of proteolytic enzymes [72-74]. The interaction between various types of mucoadhesive polymers and epithelial cells has a direct influence on the permeability of mucosal epithelia by means of changing the gating properties of the tight jrmctions. More than being only adhesives, some mucoadhesive polymers can therefore be considered as a novel class of multifunctional macromolecules with a number of desirable properties for their use as delivery adjuvants [72,75]. 

Synthesis of well defined functionalized (- telechellc or multifunctional-) macromolecules Is an Important task for polymer chemists. The polymers with P0(0R)2, - Si(0R)3, -OH, - . .. functional groupslrS. are produced In limited quantities. The need for polymeric materials possessing specific properties has led to a renewed Interest Is functional polymers, especially if the initial material Is a common hydrocarbon polymer. One of the techniques that we use in our laboratory to prepare these new molecules Is based on anionic processes. This anionic technique is best suited to control the length of the chains prepared and to obtain samples with low polydlsperslty. Although the functionalization of carbanionic sites with various deactivating reagents Is easier than with other methods because of the long lived species, It Is still necessary to carefully control the deactivation reaction to prevent secondary reactions. 

The phase-separating and assembly behavior of functional copolymer architectures with longer functional polymer segments of one kind is the base of today s high importance of self-assembly of synthetic multifunctional macromolecules and biohybrids in bionanotechnology. Functionality can be confined in specific compartments of nanometer size, and further self-assembly in specific solvents can lead to micrometer-sized objects (see further examples in Section 6.1.1.2). 

Due to this progress that has been made in the recent years and the high impact on biotechnology and biomedicine, this textbook will provide the basic synthetic tools available to tailor-make multifunctional polymers and to control their biointeractions and self-assembly, and on the other hand, it will highlight functional materials and system applications that are based on the availability of such complex and multifunctional macromolecules. 

Figure 12.5 Schematic illustration of (a) simultaneous parallel and (b) cascade reactions performed on multifunctional macromolecules using click techniques in one-pot procedure. Such reactions are possible because of orthogonality of many click techniques. (Adapted from Sumerlin and Vogt, 2010.)...

Mattice, W. L. Masses, sizes and shapes of macromolecules from multifunctional monomers in Newkome, G. R., Moorefield, C. N. and Vogtle, F. (eds), Dendritic Molecules. Concepts, Synthesis, Perspectives, Chapter I, VCH Verlag, Weinheim, Germany, 1996. 

Fig. 27. Molar mass dependence of [rj] for a fractionated comb macromolecule. The fractionation was made with a SEC/LALLS/VISC set-up. The comb macromolecule consists oi a polyimidazole backbone prepared by free radical polymerization. The imidazol side groups acted in a melt with phenylglycidylether and phthalic anhydride as multifunctional initiator for the anionic growth of polyester chains. The straight lines correspond to the behavior of unattached polyester chains and the comb polymers at low and high molar masses respectively [136]...

Covalent bonding of acrylic or methacrylic monomer to the template leads to multifunctional monomers (multimonomers).If monomer units are connected by covalent bonds within the frame of the template and polymerization proceeds according to the zip mechanism , a product with ladder-type structure can he expected. The structure of products obtained depends on the competition between the reactions proceeding on the template and the reaction between groups belonging to different macromolecules (templates). Template homopolymerization in this case can he represented by the scheme given in Figure 9.1. 

The understanding of the macromolecular properties of lignins requires information on number- and weight-average molecular weights (Mn, Mw) and their distributions (MWD). These physico-chemical parameters are very useful in the study of the hydrodynamic behavior of macromolecules in solution, as well as of their conformation and size (1). They also help in the determination of some important structural properties such as functionality, average number of multifunctional monomer units per molecule (2, 3), branching coefficients and crosslink density (4,5). 

Mathias, L.J., Warren, R.M. and Huang, S., tert-Butyl a-(hydroxymethyl)acrylateand its ether dimer multifunctional monomers giving polymers with easily cleaved ester groups, Macromolecules, 1991, 24, 2036. 

The competition between these opposite effects (increase and decrease of pendant double bond reactivity) depends on the concentration of multifunctional monomers, the length and flexibility of the primary chains, and the quality of thermodynamic interactions between monomers and macromolecules. As a rule, cyclization is more effective at the beginning of polymerization, whereas the steric excluded-volume effects are more effective at the later stages. 

Cationic synthesis of block copolymers with non-linear architectures has been reviewed recently [72]. These block copolymers have served as model materials for systematic studies on architecture/property relationships of macromolecules. (AB)n type star-block copolymers, where n represents the number of arms, have been prepared by the living cationic polymerization using three different methods (i) via multifunctional initiators, (ii) via multifunctional coupling agents, and (iii) via linking agents. 

Lichter JA, Van Vliet KJ, Rubner MF (2009) Design of antibacterial surfaces and interfaces polyelectrolyte multilayers as a multifunctional platform. Macromolecules 42 8573-8586... 

Masses, Sizes, and Shapes of Macromolecules from Multifunctional Monomers ... 

As implied by the name, one of the fundamental distinctions between macromolecules and small molecules lies in their mass, or molecular weight, M. The lower limit for the molecular weight of a macromolecule is ill defined, but it is often considered to lie in the range M = 103-104. The upper limit for the molecular weight of a macromolecule is unbounded, and for all practical purposes it can be considered to be infinite. Of course, an infinite molecular weight is unattainable with a finite amount of material. However, molecular masses in covalently bound polymeric networks are conveniently expressed in units of kg molecule-1, rather than units of kg mol-1, and they are certainly an acceptable approximation to infinite in the context of this work. These polymeric networks contain numerous branch points, either as a consequence of the use of multifunctional monomers during the polymerization or as a consequence of crosslinking reactions after polymerization has occurred. In such systems, the molecular mass is of less fundamental interest than the mass of the network chains between crosslinks. 

Sanderson IR, Walker WA (1993) Uptake and transport of macromolecules by the intestine possible role in clinical disorder (An update). Gastroenterol 104 622-629 Schneeberger EE, Lynch RD (2004) The tight junction a multifunctional complex. Am J Physiol Cell Physiol 286 1213-1228... 

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