No abstract

Polymers containing hydrogen-bonding side groups (HBGs) can form transient supramolecular networks that exhibit technologically useful viscoelastic properties. Here, we investigate how dynamic behavior of functional poly(nbutyl acrylate) melts and cross-linked networks is influenced by different HBGs. Random copolymers containing weak and strong HBGs were synthesized and subjected to thermal and dynamic mechanical analysis. The glass transition temperature (T g ) increased nearly linearly with the HBG concentration, and this effect was similar for both weak and strong binding groups. Copolymers containing weak HBGs behaved as unentangled melts and exhibited higher storage and loss modulus with increasing amounts of binding group. In contrast, copolymers containing strong HBGs behaved like entangled networks. Flow activation energies increased linearly with comonomer content; and, for weak hydrogen-bonding groups, they depended only on the departure from T g . Similar behavior was observed in cross-linked films. Differences between weak and strong HBGs were also apparent from shape memory cycles.

Abstract. In Antarctica, uncertainties in mass input and output translate directly into uncertainty in glacier mass balance and thus in sea level impact. While remotely sensed observations of ice velocity and thickness over the major outlet glaciers have improved our understanding of ice loss to the ocean, snow accumulation over the vast Antarctic interior remains largely unmeasured. Here, we show that an airborne radar system, combined with ice-core glaciochemical analysis, provide the means necessary to measure the accumulation rate at the catchment-scale along the Amundsen Sea coast of West Antarctica. We used along-track radarderived accumulation to generate a 1985-2009 average accumulation grid that resolves moderate-to large-scale features (> 25 km) over the Pine Island-Thwaites glacier drainage system. Comparisons with estimates from atmospheric models and gridded climatologies generally show our results as having less accumulation in the lower-elevation coastal zone but greater accumulation in the interior. Ice discharge, measured over discrete time intervals between 1994 and 2012, combined with our catchment-wide accumulation rates provide an 18-year mass balance history for the sector. While Thwaites Glacier lost the most ice in the mid-1990s, Pine Island Glacier's losses increased substantially by 2006, overtaking Thwaites as the largest regional contributor to sealevel rise. The trend of increasing discharge for both glaciers, however, appears to have leveled off since 2008.