Starburst amine

EDA and other alkylene amines react readily with acrylonitrile or acrylate esters. EDA reacts with acrylonitrile to give tetrakis(2-cyanoeth5i)-ethylenediamine which is reduced over Raney nickel to give tetralds(3-anainoprop5i)-ethyl-enediainine (52). With methyl acrylate and EDA under controlled conditions, a new class of starburst dendritic macromolecules forms (53,54). 

The addition of ammonia to excess methyl acrylate (a linear monomer), followed by amidation with excess ethylenediamine afforded the resultant cascade molecule, and thus Tomalia [37] created the commercially available PAMAM starburst series of dendrimers (2, Fig. 2). Related core molecules such as ethylenediamine and aminoalcohols and other functionalizable groups such as thiol moieties were used to prepare similar dendrimers [38]. This methodology is applicable to most primary amines, resulting in a 1 —> 2 branching pattern. Recently, examples of related Si-, [39] P-, [40] and metallo systems [41], which follow this linear monomer protocol have been reported. 

More complex bulky amines, especially dendrimers, have been developed to enhance the properties of the HTL materials. These include starburst products such as ST638 and componnds with spiro structures (Spiro-TAD) from Covion. These are shown in Figure 3.34. 

Figure 14.1 Common commercially available dendrimers. Top left Polypropylene imine) dendrimer (G5). Top right Poly(amido amine) dendrimer (G3). Bottom Poly(amido amine) ( Starburst ) dendrimer (G5). Each generation is marked with a circle (reproduced by permission of The Royal Society of Chemistry).

Starburst PAMAM dendrimers (Fig. 1), a specific class of commercially available dendrimers that have repeating amine/amide branching units, have drawn considerable interest in recent years due to their potential applications in medicine, nanotechnology, and catalysis [3-7]. These dendrimers are readily functionalized to terminate in diverse moieties such as primary amines, carboxylates, hydroxyls, or hydrophobic alkyl chains. Because dendrimer size and end groups can be varied, they are typically named by their generation (Gl, G2, etc.) and exterior functionality (- NH2, - OH). 

Poly(amidoamine)-(PAMAM-Starburst)-Monodendrons Among the first Starburst (Cascade) syntheses we performed in the early 1980s [83] involved partially masked (differentiated) initiator cores. For example dodecyl-amine, hydroxyalkyl amines or partially protected alkylene diamines were used as initiator cores and submitted to sequential (a) Michael addition with methyl acrylate followed by (b) reaction with an excess of ethylene diamine to give in situ branch cell construction in a divergent manner. The resulting products were core functionalized monodendrons as shown below ... 

Starburst polyamidoamine (PAMAM) synthesis [2, 77-81, 83] may begin with either a nucleophilic or an electrophilic core. In the case of nucleophilic cores such as ammonia or amine, step A in Scheme 21 involves exhaustive Michael addition to methyl acrylate. This addition occurs very rapidly and in high yield with essentially complete selectively and no amidation at room temperature. Step B requires addition of this triester intermediate to a large excess of ethylenediamine at room temperature to produce the terminal triamine core cell shown in Fig. 2 and Scheme 21. Repeating the sequence of steps A and B leads, via a hexaester... 

As early as 1983, de Gennes and Hervet [85] proposed a simple equation derived from fundamental principles, to predict the Starburst limited or dense-packed generation mt for PAM AM dendrimers. Based on ideal dendrimer growth, with tertiary amine branch junctures connected by linear, flexible branch cell segments P, this equation relates m, to the branch cell segment length 1 or P ... 

Reaction of various primary amine-terminated dendrimers with either inorganic or organic acids allows the preparation of a wide variety of crystalline derivatives. One such intermediate was implicated in the development of lyotropic phases [156] when octanoic acid was combined with Starburst poly(ethylenimine) (generation-3). 

Nitrobenzene starburst polymers were also prepared by reacting amine-termini intermi-nates with 4-fluoro-nitrobenzene. Thereafter the nitro component was reduced using 5% palladium on carbon and is described by the author. 

Figure 1.20. Synthesis of an amine-terminated polyamide dendrimer by a divergent route (the Starburst PAMAM system). Adapted from Frechet and Hawker (1996).

---