Structural Isomers of PiPAAm

The structural isomers of PiPAAm with corresponding literature values of Tip are given in Table 5. 

To the best of our knowledge, the last two structural isomers of PiPAAm are not soluble in water (PLeu [144, 441, 442] and PLLeu [144]). Urry defined Leu as a more hydrophobic residue than iLeu [144]. Small rearrangement of the methyl group from Leu to iLeu results in a 5°C rise on the hydrophobicity scale. PLeu and PiLeu are crystalline polymers. PLeu forms a-helical structures, the so called leucine zippers, consisting of two parallel a-helices. PLLeu forms fewer a-helices, favouring the formation of P-structures (Fig. 4) [144,443]. 

PnPAAm vs. PiPAAm and PLeu vs. PiLeu the solubility is higher (i.e. higher 

PNEMAAm vs. PNNEMAAm methyl group in the main chain causes higher solubility. 

PViBAm vs. PiPAAm reversed amide linkage (NH group linked to the main chain in the case of PViBAm, vs. C=0 for PiPAAm) results in better solubility. 

---

Structural isomer of PiPAAm (reversed amide linkage) differences in the properties have been analysed using microcalorimetry [314], pressure-dependent solubility analysis [315] and light scattering [316] Tip= 35-39°C [310, 313]... 

Structural isomer of PiPAAm (reversed amide linkage with N in the main chain and propyl instead of isopropyl pendant)... 

Structural differences, together with differences in the synthesis, result in considerable variations of the physical properties of the PiPAAm structural isomers. Thus, PiPOz is a crystalline polymer [389] and is able to crystallize from water as a fibrous material when its solution is annealed for 24 h above Tip = 65°C [373, 387]. Coagulated PiPOz particles exhibit hierarchical structures with two levels of ordering that are micron-sized spherical particles consisting of fibrils wifh a cross-sectional diameter of about 30-50 nm and a length of several microns [373]. The densely packed microspheres formed in dilute solutions are uniform in size and shape and resemble a ball made of rattan. 

---