Arborescent polymers architecture

The influence of polymer architecture on intermolecular interactions in dilute solutions was investigated by membrane osmometry in toluene (good solvent for polystyrene), cyclohexane (theta or 0 solvent), and methylcyclohexane (poor solvent Striolo et al., 2001). The osmotic second virial coefficient (B22) measured for arborescent polystyrene in toluene was lower than for homologous linear polymers, as expected due to their smaller Rg. In a 0 solvent (cyclohexane), branching lowered the 0 temperature from 34.5 °C (linear homolog) to 32.2 °C (GO polymer). The 0 temperature for the GO polystyrene sample in methylcyclohexane was likewise lowered to 36 °C, as compared to values estimated between 60 and 70 °C for linear polystyrene samples. The experimental osmotic pressure data were successfully fitted with a molecular-thermodynamic equation suitable for colloids, indicating that the behavior of arborescent polystyrene molecules in dilute solution corresponds to a perturbed (weakly interacting or interpenetrable) hard sphere. 

Puskas, J.E. et al. Effect of tbe molecular weight and architecture on the size and glass transition of arborescent polyisobutylenes, J. Polym. Sci. Chem., 44, 1770, 2006. 

Figure 1 Macromolecular architectures linear macromolecular chains (homopolymer, block-copolymer and statistical copolymer [14]), brushed-polymer (= linear chains attached to a polymer-chain brush-polymer, brush-copolymers [14]), star polymer [4], mikto-star-polymer [16], arborescent graft polymer (=repeated grafting of linear chains on a macromolecule [17,18]), dendrimer (= maximally branched, regular polymer [15])...

The effects of side chain architectures on the properties and proton conductivities of graft copolymer membranes for DMFCs were studied by Su et al. [126]. Poly(vinylidene fluoride)-g-poly(styrene sulfonic acid) (PVDF-g-PSSA) copolymers with either linear graft (LG) or arborescent graft (AG) PSSA side chains were prepared. Scheme 6.29 shows the structures of LG and AG polymers. 

Arborescent homopolymers are interesting, among others, as model compounds to study the properties of branched macromolecules beyond other systems such as star-branched polymers and microgels, due to their high branching functionalities and the extensive control achieved over the architecture (branching density, side-chain molecular weight) of the molecules. The synthesis of arborescent styrene homopolymers and some of their physical properties will be discussed first. 

The structures described include those previously discussed elsewhere (miktoarm stars, combs, grafts, rings, dendritic, hyperbranched and arborescent), as well as newly synthesized complex architectures (multicyclic, hydrogen-bonded complex architectures, structures from living alkene polymerization, ADMET and polyhomologation, as well as topological polymer chemistry). 

---