2-Methylpropane, molecular model

Copolymers with sites for association in aqueous solutions were pre-pared by copolymerizing acrylamide with N-alkylacrylamides or with the ampholytic monomer pairs sodium 2-acrylamido 2 methylpro-panesulfonate (NaAMPS) and 2-acrylamido-2-methylpropane-dimethylammonium chloride (AMPDAC). The copolymers were characterized by elemental analysis, NMR and Fourier transform infrared spectroscopy, and lowhangle laser and quasielastic lightscattering measurements. Rheological properties were studied as a function of microstructure, molecular weight, polymer concentration, electrolyte concentration, and shear rate. On the basis of those results, a conceptual model that is based on microheterogeneous domain formation in aqueous solutions is proposed. 

Butane and 2-methylpropane, whose space-filling models are shown at the top of the next column, are both nonpolar and have the same molecular formula, C4H10, yet butane has the higher boiling point (—0.5 °C compared to — 11.7 °C). Explain. 

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