Collective Motions and Mechanical Response of a Bulk of Single-Chain Nano-Particles Synthesized by Click-Chemistry.

Jon Maiz,Ester Verde-Sesto,Arantxa Arbe,Isabel Asenjo-Sanz,José A Pomposo,Juan Colmenero,Peter Fouquet,Paula Malo De Molina,Lionel Porcar

doi:10.3390/polym13010050

Abstract

We investigate the effect of intra-molecular cross-links on the properties of polymer bulks. To do this, we apply a combination of thermal, rheological, diffraction, and neutron spin echo experiments covering the inter-molecular as well as the intermediate length scales to melts of single-chain nano-particles (SCNPs) obtained through ‘click’ chemistry. The comparison with the results obtained in a bulk of the corresponding linear precursor chains (prior to intra-molecular reaction) and in a bulk of SCNPs obtained through azide photodecomposition process shows that internal cross-links do not influence the average inter-molecular distances in the melt, but have a profound impact at intermediate length scales. This manifests in the structure, through the emergence of heterogeneities at nanometric scale, and also in the dynamics, leading to a more complex relaxation behavior including processes that allow relaxation of the internal domains. The influence of the nature of the internal bonds is reflected in the structural relaxation that is slowed down if bulky cross-linking agents are used. We also found that any residual amount of cross-links is critical for the rheological behavior, which can vary from an almost entanglement-free polymer bulk to a gel. The presence of such inter-molecular cross-links additionally hinders the decay of density fluctuations at intermediate length scales.

Highlights

A new field starts emerging during the last years on the family of macromolecular objects based on purely intra-molecular bonding of single polymer chains
Before presenting the results on the bulk systems, we show in Figure 1 the successful formation of c-singlechain nano-particles (SCNPs) from Prec via a “click” chemistry reaction prior to melt sample preparation
The Tg value of the precursor melt determined by DSC was 202 K, while in the click-deuterated single-chain nanoparticles (c-SCNPs) melt this value increases by 5 K, up to 207 K

Summary

Introduction

A new field starts emerging during the last years on the family of macromolecular objects based on purely intra-molecular bonding of single polymer chains. The potential folding/collapse of individual polymer chains through pendant groups via covalent or non-covalent bonds into so-called single chain polymer nanoparticles (SCNPs) has attracted significant interest due to their potential applications in catalysis, biosensors, nanoreactors, protein mimicry, drug delivery and in nanomedicine in general [1,2]. SCNPs are attractive systems [1,3,4,5] These SCNPs are unimolecular nano-objects obtained by intra-molecular cross-link of individual macromolecular chains (functionalized linear polymers called ‘precursors’). The formation of these nanoparticles implies three steps: (i) synthesis of a precursor polymer, (ii) functionalization of the precursor polymer, and iii) folding/collapse of the functionalized precursor polymer via intra-chain interactions [5]

Methods

Results

Discussion

Conclusion