The polymerization of isoprene was initiated with 3-(tert- butyldimethylsilyloxy)-1-propyllithium (TBDMSPrLi), which contained a silyl-protected hydroxyl functionality. Living poly(isoprenyllithium) with controlled molecular weight and narrow molecular weight distribution coupled efficiently with divinylbenzene to form well-defined star-shaped polymers. Both linear and star-shaped polymers were subsequently hydrogenated to poly(ethylene-co-propylene) and deprotected quantitatively to yield terminal primary hydroxyl functionality. High conversions of hydroxyl functionality to the 2-ureido-4[1H]-pyrimidinone (UPy) quadruple hydrogen-bonding group were achieved using isocyanate coupling and subsequent reaction with 6-methylisocytosine. Nonfunctionalized and UPy-functionalized linear and star-shaped poly(ethylene-co-propylene)s were characterized using 1H NMR spectroscopy, dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), tensile testing, and melt rheology. The observed glass transition temperatures were independent of molecular architecture for the UPy-functionalized polymers and nonfunctionalized analogues using both DSC and DMA. Tensile testing revealed the UPy-functionalized star polymers (UPy-Star) exhibited a higher Young's modulus and lower percent elongation at failure compared to the UPy-telechelic polymers with M n of 24 000 g/mol (UPy-24K-T) analogues. UPy-Star polymer exhibited a rubbery plateau region over a well-defined frequency range, and in contrast, the UPy-functionalized linear polymers were in the terminal flow regime, which suggested greater association for the star-shaped polymers. In addition, complex viscosity data revealed a non-Newtonian behavior for the star-shaped polymers in contrast to linear analogues, which is also consistent with a highly associated structure.
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