Influence of Architecture on Arm Dimensions and Interaction Parameters in Polybutadiene Star Polymers

Abstract

Star branched polymers of polybutadiene with 3, 4, 8, and 12 arms have been synthesized with one arm perdeuterated. Small-angle neutron scattering data have been collected for each of the star polymers and for the four-arm star polymer mixed with hydrogenous linear polybutadiene of the same molecular weight either as a single arm or of the whole star. The labeled four-arm star polymer has also been mixed with the equivalent hydrogenous star polybutadiene. For the pure labeled star polymer the scattering is dominated by a peak located at a scattering vector determined by the radius of gyration of the arm. As the labeled star polymer is diluted by adding hydrogenous polymer, the peak declines in amplitude and the maximum scattered intensity shifts to zero scattering vector. The scattered intensity for each sample has been fitted with expressions based on random phase approximation theory and the radius of gyration of the labeled arm was obtained. Two interaction parameters were needed to obtain acceptable fits of the theoretical expressions to the data. Indisputable evidence for increased stretching of the labeled arm as the number of arms in the star polymer increases has been obtained, and the stretching factor has been compared to predictions of a liquid state theory of star polymers. The interaction parameters obtained are considered to be reflections of the differential screening of core and corona segments of the star molecules, an integral aspect of the liquid state theory, rather than true Flory−Huggins-type interaction parameters.

Soft Character of Star-Like Polymer Melts: From Linear-Like Chains to Impenetrable Nanoparticles

“…The W intra would be an analogy of the experimental scattering function obtained for stars in a melt with labeled arms. 15 Here, W intra intensities are identical for all stars of the same polymer type within the obtained accuracy. The decay of W inter is more abrupt for (PS) f than for (PEO) f , which agrees with a tighter packing of PS arms reported recently.…”

“…Concerning the intensity drop at intermediate length scales, we decomposed W ( q ) into the scattering contributions coming from the same-arm, W intra , and interarm, W inter , correlations in Figure b. The W intra would be an analogy of the experimental scattering function obtained for stars in a melt with labeled arms . Here, W intra intensities are identical for all stars of the same polymer type within the obtained accuracy.…”

“…Also, elaborate experimental practices, such as scattering techniques, are necessary to get basic characteristics like the star radius of gyration R g . 15,16 Recently, a two-layer model has been presented for grafted nanoparticles in a melt, which divides the space around nanoparticles into an impenetrable core and an interpenetration layer, 17 similarly to the work on hyperstar polymers. 18 Both grafted nanoparticles and hyperstar polymers, resemble polymer brushes, in which the chains have one end anchored to a substrate or a polymer backbone and, due to their high grafting density, tend to pack closely, forming "dry" impenetrable regions of a given brush thickness.…”

“…The experimental investigation of the internal star morphology is nontrivial, and one has to rely on computational and theoretical models when interpreting results; the latter ones typically involve several approximations. ,− A melt state is particularly laborious to study because many-body interactions are usually not accounted for in single-molecule models. Also, elaborate experimental practices, such as scattering techniques, are necessary to get basic characteristics like the star radius of gyration R g . , …”

Macromolecular engineering: a synthetic perspective

“…30 In a similar vein, isotopic mikto arm star branched polymers of polybutadiene with three, four, eight and 12 arms have been synthesised with one arm perdeuterated. 31,32 Small angle neutron scattering was used to probe the stretching of the arms (by obtaining radius of gyration (R g ) values for the deuterated arm) in star polymers and it was clearly demonstrated that the degree of stretching of the arms increases with the number of arms. A plot of R g /M 1=2 w versus the number of arms (Fig.…”