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

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.

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

“…The impact of propargyl ether cross-links observed on the α-process in the present bulk of protonated c-SCNPs is similar to that found for the melt of deuterated SCNPs synthesized following the same chemistry route [14]. In that case, an increase of 5 K was reported for the glass-transition temperature of the SCNPs with respect to the Prec counterpart.…”

“…The aim of the QENS experiments was to follow the self-atomic motions (hydrogen) in energy-resolved experiments to study the dynamical properties at local length scales when the chain topology is altered by internal cross-linkers. The results are compared with those obtained on the deuterated counterparts previously published [ 14 ] and with those reported for the melts of protonated SCNPs obtained via UV irradiation from the same precursor chains [ 13 ].…”

“…The combination of these different but complementary techniques allows also the study of the properties of SCNP melts. In recent works [ 12 , 13 , 14 ], the structure and dynamics in melts of SCNPs based on poly(tetrahydrofuran) (PTHF) synthesized via two different mechanisms have been studied applying such a methodology. The first synthesis mechanism was based on the intra-molecular azide photodecomposition process, exposed to UV irradiation procedure.…”

“…The second route was via “click” chemistry, where an external homobifunctional cross-linker was used to prepare the SCNP samples. Deuterated materials were investigated, such that the neutron scattering investigation addressed collective features [ 12 , 13 , 14 ]. In an overall view, it was found that internal cross-links do not influence the average inter-molecular distances in the melt, while they have a profound impact at intermediate length scales (length scales larger than the inter-molecular ones but not yet in the hydrodynamic regime).…”

Onco-Receptors Targeting in Lung Cancer via Application of Surface-Modified and Hybrid Nanoparticles: A Cross-Disciplinary Review

“…Using single chain technology, individual copolymer chains of different natures, compositions and molar masses have been folded intramolecularly to develop single chain nanoparticles (SCNPs). This leads to very small size polymer nanoparticles in the sub-20 nm size [174,175]. The folding is achieved by the self-assembly or crosslinking of functional groups on the precursor polymer, or rather moderated by the external cross-linker.…”