Conformational Behavior of Guest Polymer Chains in Uniaxially Stretched Polydiethylsiloxane Elastomers: 2H NMR and SANS

Published

October 12, 2021

Author(s)

A Batra, R C. Hedden, P Schofield, A Barnes, C Cohen, T M. Duncan

Abstract

2H nuclear magnetic resonance (NMR) and small angle neutron scattering (SANS) data are reported for deuterated guest chains of polydiethysiloxane (PDES) in end-linked optimal PDES networks as a function of the relative molecular weight of guest chains to network elastic chains. We exploit the ability of PDES networks to form a strain-induced mesophase to demonstrate the tendency of longer guest chains to phase separate or partition selectively to the amorphous phase and the tendency of smaller guest chains to be retained in the mesophase. When the molar mass Mn of the guest chains is comparable to the molar mass Mn of the precursor network chains, the guest chains act as perfect probes; they show the same segmental orientation as the elastic network chains. As the network is uniaxially stretched into the mesophase, these probe chains are also incorporated into the mesophase. However, when the molar mass of the guest chains is much larger than that of the elastic chains, the guest chains partition to the amorphous phase and are excluded from the mesophase. From analysis of the segmental orientation of the guest chains measured via 2H NMR peak splitting, the guest chain segments show an enthalpic orientational coupling in the amorphous state similar to that observed for elastic chains. SANS results show that the radius of gyration of guest chains in the unstretched and the stretched networks remains essentially unchanged from that in the melt state. The scattering intensity from SANS patterns for networks with guest chains of any size has a peak in the direction parallel to the stretch direction that reflects the domain spacing of the lamellae in the mesophase.

Citation

Macromolecules

Pub Type

Journals

Keywords

elastomers, mesophase, poly(diethylsiloxane), SANS, solid-state NMR spectroscopy

Citation

Batra, A. , Hedden, R. , Schofield, P. , Barnes, A. , Cohen, C. and Duncan, T. (2021), Conformational Behavior of Guest Polymer Chains in Uniaxially Stretched Polydiethylsiloxane Elastomers: ²H NMR and SANS, Macromolecules (Accessed April 25, 2024)