Scientific and Technical Achievements
Work Package 1 – Synthesis
Researchers successfully synthesized a broad range of vitrimer systems, including amorphous, semi-crystalline, and copolymer-based materials. Amorphous vitrimers (e.g. PS, PEHMA, PMMA, and PnBMA) were produced with tunable crosslink densities and molecular weights. Semi-crystalline polyolefin vitrimers were obtained via hydrogenation and reactive extrusion, maintaining stability and demonstrating potential as compatibilizers for recycled HDPE. In addition, PS–PMMA copolymers were synthesized by controlled RAFT polymerization to act as model compatibilizers, to be compared with vitrimer. These samples were distributed to the consortium.
Work Package 2 – Structure and Local Dynamics
Structural studies revealed that vitrimer incorporation into HDPE reduces crystallinity, increases chain mobility, and alters lamellar organization. These effects improve flexibility and tunability for recycled polyethylene. In amorphous PnBMA vitrimers, the addition of exchangeable crosslinks restricted segmental mobility. For PS-based vitrimers, increasing crosslink density led to higher stiffness and more brittle fracture behavior. These findings establish a link between crosslink chemistry and large-scale polymer dynamics.
Work Package 3 – Rheology and Flow
A new Rheo-DLS setup was developed to study polymer dynamics under shear, validated against commercial instruments. Experiments confirmed the slow relaxation dynamics of vitrimer systems. Rheological analysis of degraded HDPE showed that small vitrimer additions (as low as 5%) could restore strain hardening and mechanical strength. Crosslinker chemistry was found to determine flow behavior—fast exchangers improved processability, while slow exchangers enhanced rigidity. Molecular simulations confirmed these macroscopic trends by showing that bond-exchange rates directly govern vitrimer relaxation and stress dissipation.
Depending on the nature of the vitrimer, microphase separation of the functional groups may take place. This leads to materials characterized by a very long annealing time. It is thus important to account for this microphase separation in the response of the vitrimers.
Work Package 4 – Mechanical and Adhesion Properties
Preliminary adhesion tests demonstrated that optimized PS/PMMA bilayer systems can be reliably produced for vitrimer-based adhesion studies. The incorporation of vitrimers is expected to significantly enhance interfacial strength through dynamic covalent bonding. The methodology developed during this phase establishes the foundation for quantitative adhesion measurements in future work.
Work Package 5 – Modelling
Theoretical and computational models were developed to predict vitrimer–polymer blend stability and viscoelastic properties. A modified Semenov–Rubinstein–Dobrynin model showed that vitrimer addition can lead to microphase separation depending on crosslink density and concentration. Experimental rheology supported this, revealing separate relaxation plateaus. A tube-based model for telechelic vitrimers was also validated, showing how molecular weight and entanglement affect mechanical relaxation, providing predictive tools for designing recyclable materials.
Work Package 6 – Processing and Applications
Processing studies on PS-based vitrimer blends demonstrated high thermal stability, good compatibility with homopolymers, and improved mechanical resistance at moderate vitrimer contents. At higher concentrations, vitrimer aggregates were observed but did not impair processability. Parallel work on dual-network vitrimer elastomers achieved the synthesis of both static (ACM) and dynamic (boronic ester) components, establishing a foundation for recyclable elastomeric materials with tunable crosslink ratios.
Work Package 7 – Management
During the reporting period, effective coordination and governance structures were implemented to support the timely execution of the scientific work packages. Transparent recruitment procedures enabled the successful selection and contracting of the doctoral candidates, ensuring that all research activities could start as planned. Supervisory mechanisms, Personal Career Development Plans, data management procedures aligned with FAIR principles, and intellectual property protocols were established to support the structured development of the research projects and future scientific outputs.
Work Package 8 – Training
Doctoral candidates have participated in an interdisciplinary training programme designed to build the skills required for the network’s scientific objectives. Advanced local courses, network-wide lectures, and thematic summer schools provided foundational expertise in polymer synthesis, physical chemistry, and structure–property relationships in dynamic polymer networks.
Work Package 9 – Industrial exposure
Industrial partners have contributed to the network through participation to the meetings, workshops, site visits, and the first secondment, allowing doctoral candidates to gain insight into industrial research and development. These early interactions helped identify application-relevant challenges, and align experimental approaches with practical industrial needs.
Work Package 10 – Scientific dissemination
Scientific dissemination activities have started, focusing on sharing preliminary results and methodological developments. Doctoral candidates have presented early findings at conferences and workshops, and several manuscripts integrating experimental and modelling approaches are in preparation. Communication towards a broader community is also encouraged through our website and social networks.
