Some aspects of the orientational order distribution of flexible chains in a diblock mesophase

Abstract

The segmental motions of flexible chains in the lamellar structure of a strongly segregated poly(styrene)-poly(dimethylsiloxane) (PS-PDMS) diblock were investigated over a time scale of a few tens of microseconds. (2)H NMR experiments were performed on the PDMS block, selectively perdeuterated. Transverse relaxation measurements show that the main part of the PDMS repeat units display anisotropic reorientational motions within the diblock lamellae and such a segmental ordering essentially results from interchain steric repulsions. (2)H double quantum-based experiments evidenced a non-uniform local stretching of PDMS chains and enabled the underlying distribution of the orientational order parameter to be determined quantitatively. Besides, a fraction of the PDMS chain segments, about 14%, were found to display isotropic - or nearly isotropic - reorientations, which could be assigned to repeat units located within a thin sublayer (about 1-2 nm) at the lamellae midplane, but also deeper in the lamellae, close to folded parts of the chains. These experimental results were confronted to theoretical descriptions of opposing polymer brushes and, in particular, to the strong-stretching theory (SST) including the entropic contribution of free chain ends.

Multiscale Structural Characterization of Biobased Diallyl–Eugenol Polymer Networks

“…This technique has been proven successful to characterize the intrinsic morphology of crosslinked elastomeric-like materials such as natural and synthetic rubbers, PDMS and other elastomers, as well as the influence of chemical modifications, variation of crosslink density and aging on such materials. [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34] Recently, this technique was successfully used in combination with DMA measurements to study the relationship between the structure of Poly(trimethylene carbonate) (PTMC) and their macroscopic thermomechanical behavior. 35 This robust combination of multiscale techniques has opened the perspective of obtaining a fine characterization of crosslinked polymeric networks with different chemical structures.…”

Multiscale Structural Characterization of Biocompatible Poly(trimethylene carbonate) Photoreticulated Networks

“…[28][29][30][31][32][33][34][35] In particular, Double-Quantum DQ 1 H sequences have been successfully used in elastomeric-like polymer networks (i.e. natural & synthetic rubbers and PDMS 36,37 ) and, through a careful data treatment, have allowed the fine study of the networks structure and dynamics, namely the polymers' molecular mobility, crosslink density v C , and chain defects concentration w def , [36][37][38][39][40][41][42][43][44][45][46][47] as well as the evolution of such network properties with temperature, 48,49 chemical modification [50][51][52] and thermal ageing. 53,54 The common basis of these approaches is their potential ability to discriminate dynamical and structural effects, which allows semi-local structural features of networks to be retrieved from local dynamical measurements.…”

Synthesis and Structural NMR Characterization of Novel PPG/PCL Conetworks Based upon Heterocomplementary Coupling Reactions

“…This distribution function does not have a separate width parameter, as its width depends on its average D av , restricting its general use. Therefore, following a first demonstration of Lorthioir et al for the special case of 2 H DQ buildup in a copoly mer block, [35] this study here advocates the use of a lognormal distribution of D res in terms of ln(D res )…”

“…This distribution function does not have a separate width parameter, as its width depends on its average D av , restricting its general use. Therefore, following a first demonstration of Lorthioir et al for the special case of 2 H DQ buildup in a copolymer block, this study here advocates the use of a log‐normal distribution of D res in terms of ln( D res )which depends on the median D med and the standard deviation σ ln. Notably, σ ln as defined on the ln( D res ) scale is dimensionless, and one can show that 1.023σ ln is equal to the full width at half‐maximum of the distribution after converting to a log( D res ) scale.…”