Small-Angle Neutron Scattering from Single Arm Labeled Polybutadiene Star Polymers in Dilute Solution

Abstract

Dilute cyclohexane solutions of polybutadiene star polymers with 3, 4, 8, and 12 arms wherein one arm is perdeuterated have been investigated by small-angle neutron scattering. The scattering cross sections obtained showed a characteristic peak at finite values of the scattering vector, Q. This maximum is not a structure factor arising from intermolecular interactions but is intrinsic to the scattering law of star molecules with one arm of a different isotopic composition to the other arms. The theoretical scattering law developed for such isotopic copolymers was found to fit the observed scattering well and provided values of the radius of gyration of the labeled arm. No dependence of the radius of gyration on star polymer concentration was noted, but the radius of gyration of the labeled arm increased as the functionality of the star increased from 3 to 12, the increase in dimensions in the 12-arm star being ca. 25% greater than the radius of gyration obtained for the three-arm star. In these dilute solutions the radii of gyration were larger than obtained for the bulk melt state of the stars. The data have been compared with theoretical predictions, but generally a much stronger dependence of the radius of gyration on star functionality is observed than is predicted.

Diffusion Controlled Termination of Linear Polystyrene Radicals in Linear, 4-Arm, and 6-Arm Star Polymer Matrices in Dilute, Semidilute, and Concentrated Solution Conditions

“…This is not unexpected since the Zimm-Stockmayer expression was developed for swollen Gaussian chains. In the case of short-arm star polymers the high polymer segment densities cause congestion leading to stiffening of the star arms close to the core 22,53,[60][61][62] (see inset illustration in Figure 6). Hence, the deviation to higher ratios at lower molecular weight stars.…”

Monte Carlo Study of Heteroarm Star Copolymers in Good and Selective Solvents

“…The dependence of the radii of gyration of a single arm on the number of arms was studied by small angle neutron scattering by Hutchings et al in a system of single arm deuterated stars 57. The authors found a linear increase in the radius of gyration of one arm with increasing number of arms.…”

Comparison of Tethering of Linear and Four-Arm Poly(ethylene oxide)

“…The most notable difference between the tethering process for the two architectures was that the surface attachment density of four-arm PEO-NH 2 was about 4−5 times greater than that of linear PEO-NH 2 at all times during the tethering process, indicating a higher tethering rate for the four-arm PEO-NH 2 . In the tethering process, diffusion of the polymer molecule to the surface rather than its chemical reaction with the surface is the rate-determining step. ,,,, Since rate of diffusion through solvent is inversely proportional to R g , four-arm PEO-NH 2 , with R g = 2.63 nm, would diffuse only 18% faster than linear PEO-NH 2 , with R g = 3.10 nm . Thus, the effect of polymer architecture, i.e., four-arm vs linear, on diffusion through the solvent is relatively minor, and the explanation of the dramatic increase in rate and surface attachment density must lie elsewhere.…”

“…In the tethering process, diffusion of the polymer molecule to the surface rather than its chemical reaction with the surface is the rate-determining step. 1,2,5,6,10 Since rate of diffusion through solvent is inversely proportional to R g , four-arm PEO-NH 2 , with R g ) 2.63 nm, 11 would diffuse only 18% faster than linear PEO-NH 2 , with R g ) 3.10 nm. 12 Thus, the effect of polymer architecture, † University of Kentucky.…”