Dynamic Processes and Mechanisms Involved in Relaxations of Single-Chain Nano-Particle Melts.

Jon Maiz,Arantxa Arbe,Bernhard Frick,José A Pomposo,Paula Malo De Molina,Juan Colmenero,Ester Verde-Sesto,Isabel Asenjo-Sanz

doi:10.3390/polym13142316

Abstract

We present a combined study by quasielastic neutron scattering (QENS), dielectric and mechanical spectroscopy, calorimetry and wide-angle X-ray diffraction on single-chain nano-particles (SCNPs), using the corresponding linear precursor chains as reference, to elucidate the impact of internal bonds involving bulky cross-links on the properties of polymer melts. Internal cross-links do not appreciably alter local properties and fast dynamics. This is the case of the average inter-molecular distances, the β-relaxation and the extent of the atomic displacements at timescales faster than some picoseconds. Contrarily, the α-relaxation is slowed down with respect to the linear precursor, as detected by DSC, dielectric spectroscopy and QENS. QENS has also resolved broader response functions and stronger deviations from Gaussian behavior in the SCNPs melt, hinting at additional heterogeneities. The rheological properties are also clearly affected by internal cross-links. We discuss these results together with those previously reported on the deuterated counterpart samples and on SCNPs obtained through a different synthesis route to discern the effect of the nature of the cross-links on the modification of the diverse properties of the melts.

Highlights

Over the last years, new synthesis strategies have been developed in order to obtain new polymers with properties similar to those of folded biomolecules
In this work we present a combined study by different experimental techniques, including calorimetry, mechanical analysis, dielectric spectroscopy and quasielastic neutron scattering on bulk samples consisting of protonated single chain polymer nano-particles (SCNPs) synthesized from poly(tetrahydrofuran)based linear precursors (Prec) via copper “click” chemistry mechanism, as shown in Scheme 1
In order to confirm the successful formation of Click Single-Chain Nano-Particles (c-SCNPs) from Prec via a “click” chemistry reaction prior to melt sample preparation, we show in Figure 1 how the c-SCNPs obtained have longer retention time at the SEC peak maximum compared to their precursor

Summary

Introduction

New synthesis strategies have been developed in order to obtain new polymers with properties similar to those of folded biomolecules. A new family of macromolecular objects based on purely intra-molecular bonding of single polymer chains emerges as promising. The so-called single chain polymer nano-particles (SCNPs) have attracted significant attention due to their potential applications and special characteristics such as their small size, softness and internal segmentation [1,2,3,4,5,6,7]. SCNPs are unimolecular nano-objects obtained by intra-molecular cross-link of individual macromolecular chains (functionalized linear polymers called “precursors”). Polymer melts are complex systems where the relevant dynamic processes depend on the length scale of observation [8,9].

Methods

Results

Discussion

Conclusion