Surface segregation and bulk thermodynamics in blends of linear and branched functionalized polybutadienes

Blends of well defined polybutadienes (PBs) with three different chain ends were investigated to reveal the effect of chain ends and molecular architecture on bulk thermodynamics and surface segregation. Small Angle Neutron Scattering measurements showed that the bulk thermodynamic interaction in blends of deuterated star and hydrogenous linear PBs increased as the chain ends changed from 3-( tert-butyldimethylsiloxy)-1-propyl (SO) to hydroxypropyl (OH) to 2,2,2-trifluoroethanesulfonyloxypropyl ( CF) and as the number of arms increased from 4 to 8 to 12. The influence of chain-end functionalization was much smaller for blends of hydrogenous stars and deuterated linear chains. The bulk thermodynamic interactions in linear/linear blends of functionalized "arms" showed the same trends.;Surface tension measurements of pure linear PBs with 4 different chain ends suggested that the energy cost associated with placing end groups at the surface increased as CF < SO < BU < OH. Surface tension was low when CF ends could segregate to the surface, but OH ends were excluded from the surface. Neutron Reflectometry measurements revealed that both interfaces of star/linear blend films containing deuterated star with SO chain ends were enriched in the functionalized star and that the interfacial excesses increased with the number of star arms. In blends containing hydrogenous stars with CF chain ends, 4-arm stars were depleted from the air interface. As the number of arms increased further, an excess of stars was seen at the air interface, meaning that the point at which the isotopic labeling effect is balanced by the combined effects of architecture and CF chain ends occurs for about 8 arms.;The effect on adhesive "tack" of adding 12-arm star-branched PB to linear PB to form adhesive blends was studied using a Texture analyzer. The probe tack of a blend containing stars was always superior to that of the pure linear material. The adhesive performance was dominated by bulk dissipation during debonding and thus by the changes to the bulk loss modulus caused by adding stars.