Radially layered copolymeric

In some applications it is useful to have hydrophilicity in the bulk of the polymer instead of just at the surface. One way of doing this is by simultaneously end linking hydrophilic poly(ethylene glycol) (PEG) chains and hydrophobic PDMS chains. Another way is to make a PDMS network with a trifunctional organosilane R Si(OR)3 end linker that contains a hydrophilic R side chain, such as a polyoxide. Treating only the surfaces is another possibility, for example, by adding hydrophilic brushes by vapor deposition/hydrolysis cycles.Such hydrophilic polysiloxanes can also serve as surfactants. It has also been possible to make radially layered copolymeric dendrimers with hydrophilic polyamidoamine interiors and hydrophobic organosilicon exteriors. " ... 

Radially layered copolymeric PAMAMOS dendrimers and their networks described in this chapter represent truly unique new materials which can be prepared in a variety of different chemical compositions. They consist of hydrophilic PAMAM and hydrophobic (i.e., oleophilic) OS nanoscopic domains, the sizes of which can be precisely controlled by the selection of the reagents used for the dendrimer synthesis and by the chemistry involved. Hence, this synthetic strategy is highly versatile and it enables close control of the resulting structure(s), permiting precise tailor-making of these unique new materials. 

Dvornic, P. R., de Leuze-Jallouli, A. M., Owen, M. J. and Perz, S. V. Radially layered poly(amidoamine-organosilicon) (PAMAMOS) copolymeric dendrimers in Clarson, S. J., Owen, M. J., Fitzgerald, J. J., Smith, S. D. (eds.), Silicones and Silicone-Modified Materials, ACS Symposium Series, Vol. 729, American Chemical Society, Washington, DC, 2000, pp. 241-269. 

Radially Layered Poly(amidoamine-organosilicon) Copolymeric Dendrimers and Their Networks Containing Controlled Hydrophilic and Hydrophobic Nanoscopic Domains... 

Figure 1 Schematic representation of homopolymeric (A) and two types or ordered copolymeric dendrimers radially layered (B) and segmented (C) ones. Small circles denote the branch junctures, larger circles represent the branch cells, while numerals indicate dendrimer generation layers and each Z is an end-group. Note that copolymeric dendrimers are composed of at least two different compositional types of branch cells (1 and 2).

The synthesis of radially layered poly(amidoamine-organosilicon) (PAMAMOS) copolymeric dendrimers starts from amine terminated PAMAM dendrimers, which, in turn, are obtained by a well-known excess-reagent divergent growth method that involves a reiterative sequence of (a) Michael addition reactions of methyl acrylate (MA) to primary amines, and (b) amidation of the resulting methyl ester intermediates with ethylenediamine (EDA), as shown in Reaction Scheme 1 (39-41). These PAMAM dendrimers are commercially obtained from Dendritech Inc., (Midland, MI) and they can be used for PAMAMOS preparation without any further purification. The synthesis then involves another Michael addition reaction, this time of a silylated acryl ester, such as (3-acryloxypropyl)dimethoxymethylsilane, as shown in Reaction Scheme 2 (4). 

By copolymerizing the monomers of two highly crystalline homopolymers it is possible to create a series of less crystalline copolymers with reduced levels of stiffness, elastic modulus and crystallinity depending on the blend level of the two monomers. This has been demonstrated by Soo H5nm Kim and coworkers at KIST, who have been able to synthesize a series of elastomeric (or rubbery) resorbable poly(L-lactide-co-e-caprolactone) copolymers. Because of their superior elastic behavior they have been used to prepare tubular scaffolds for vascular smooth muscle cell (SMC) culture under dynamic pulsatile conditions. We have melt spun and electrospun the 50/50 copolymer to fabricate a two-layer small-caliber vascular prosthesis prototype with radial elongation at break in excess of 300% (Fig. 15.33). " ... 

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