Physically crosslinked polyacrylates by quadruple hydrogen bonding side chains.

Dynamic polymer materials can be obtained by introducing supramolecular interactions between the polymer chains. Here we report on the preparation and mechanical properties of poly(methyl acrylate) (PMA) and poly(-butyl acrylate) (PBA) funcionalized with ureidopyrimidinone (UPy) in the side chains. In contrast to the traditional UPy with a methyl group, the selected UPy motif contained a branched alkyl side chain, which enhances solubility, compatibility with the polymer matrix and potentially prevents stacking of UPy dimers.

Low , strongly segregated, ABA triblock copolymers: a rheological and structural study.

ABA triblock copolymers can form microphase separated structures where the B blocks form bridges between A domains, leading to reversible networks interesting for a variety of applications such as pressure sensitive adhesives or thermoplastic elastomers. However, a major drawback of these systems is their rapid loss of mechanical properties upon temperature increase. A potential way to circumvent this limitation would be to design ABA triblock copolymers that keep their microphase separation at high temperatures.

Constraint Release Rouse Mechanisms in Bidisperse Linear Polymers: Investigation of the Release Time of a Short-Long Entanglement.

Despite a wide set of experimental data and a large number of studies, the quantitative description of the relaxation mechanisms involved in the disorientation process of bidisperse blends is still under discussion. In particular, while it has been shown that the relaxation of self-unentangled long chains diluted in a short chain matrix is well approximated by a Constraint Release Rouse (CRR) mechanism, there is no consensus on the value of the average release time of their entanglements, τobs, which fixes the timescale of the CRR relaxation. Therefore, the first objective of the present work is to discuss the different approaches proposed to determine this time and compare them to a large set of experimental viscoelastic data, either newly measured (poly(methyl-)methacrylate and 1,4-polybutadiene blends) or coming from the literature (polystyrene and polyisoprene blends).

Characterising different molecular landscapes in dynamic covalent networks.

Dynamic covalent networks present a unique opportunity to exert molecular-level control on macroscopic material properties, by linking their thermal behaviour to the thermodynamics and kinetics of the underlying chemistry. Yet, existing methods do not allow for the extraction and analysis of the influence of local differences in chemical reactivity caused by available reactants, catalysts, or additives. In this context, we present a rheological paradigm that allows us to correlate the composition of a reactive polymer segment to a faster or slower rate of network rearrangement.

Supramolecular Polymer Brushes: Influence of Molecular Weight and Cross-Linking on Linear Viscoelastic Behavior.

The origin of unique rheological response in supramolecular brush polymers is investigated using different polymer chemistries (poly(methyl acrylate) (PmA) and poly(ethylene glycol) (PEG)), topologies (linear or star), and molecular weights. A recently developed hydrogen-bonding moiety (1-(6-isocyanatohexyl)-3-(7-oxo-7,8-dihydro-1,8-naphthyridin-2-yl)-urea) (ODIN) was coupled to PmAs and PEGs to form supramolecular brush polymers, the backbone of which is formed by the associated moieties. At low molecular weights of monofunctionalized polymers (both PmA and PEG), the formed brushes are mostly composed of a thick backbone (with very short arms) and are surrounded by other similar brush polymers, which prevent them from diffusing and relaxing.

Supramolecular Mimic for Bottlebrush Polymers in Bulk.

A series of poly(tetrahydrofuran)s with molecular weights above entanglement molecular weight were synthesized, and one of their end-groups was functionalized with a supramolecular entity so that the corresponding polymers form a brushlike structure suitable for comparison with conventional irreversible bottlebrush polymers. To compare their relaxation mechanisms, linear rheology was employed and showed that a hierarchical relaxation, which is usually observed in bottlebrush polymers, occurs in these materials, too. The polymer chain segments close to the supramolecular backbone are highly immobilized due to strong association in the center of polymer brush and cannot relax via reptation mechanism, which is mainly responsible for linear entangled polymer relaxations.

Synthesis and characterisation of redox hydrogels based on stable nitroxide radicals.

The principle of encapsulation/release of a guest molecule from stimuli responsive hydrogels (SRHs) is mainly realised with pH, temperature or light stimuli. However, only a limited number of redox responsive hydrogels have been investigated so far. We report here the development of a SRH that can release its guest molecule upon a redox stimulus.

Comparative Analysis of Different Tube Models for Linear Rheology of Monodisperse Linear Entangled Polymers.

The aim of the present paper is to analyse the differences between tube-based models which are widely used for predicting the linear viscoelasticity of monodisperse linear polymers, in comparison to a large set of experimental data. The following models are examined: Milner-McLeish, Likhtman-McLeish, the Hierarchical model proposed by the group of Larson, the BoB model of Das and Read, and the TMA model proposed by the group of van Ruymbeke. This comparison allows us to highlight and discuss important questions related to the relaxation of entangled polymers, such as the importance of the contour-length fluctuations (CLF) process and how it affects the reptation mechanism, or the contribution of the constraint release (CR) process on the motion of the chains.

Linear Viscoelasticity of Weakly Hydrogen-Bonded Polymers near and below the Sol-Gel Transition.

Supramolecular polymers bearing weak hydrogen bonds (sticker) can express outstanding dynamic properties due to their labile association. Studying the linear viscoelasticity (LVE) of this type of polymer can provide us with sufficient knowledge to design polymeric materials for applications that need dynamic properties such as self-healing. Using different compositions of flexible weak stickers, LVE analysis showed scalings corresponding to a transition from a linear precursor to a cluster.

A novel fibrin-based artificial ovary prototype resembling human ovarian tissue in terms of architecture and rigidity.

Purpose: The aim of this study is to optimize fibrin matrix composition in order to mimic human ovarian tissue architecture for human ovarian follicle encapsulation and grafting.

Methods: Ultrastructure of fresh human ovarian cortex in age-related women (n = 3) and different fibrin formulations (F12.5/T1, F30/T50, F50/T50, F75/T75), rheology of fibrin matrices and histology of isolated and encapsulated human ovarian follicles in these matrices.

Closer insight into the structure of moderate to densely branched comb polymers by combining modelling and linear rheological measurements.

Synthesis of combs with well-entangled backbones and long branches with high densities has always been a challenge. Steric hindrance frequently leads to coupling of chains and structural imperfections that cannot be easily distinguished by traditional characterization methods. Research studies have therefore tried to use a combination of different methods to obtain more information on the actual microstructures.