Sustainable Alternatives for the Development of Thermoset Composites with Low Environmental Impact

The current concerns of both society and the materials industries about the environmental impact of thermoset composites, as well as new legislation, have led the scientific sector to search for more sustainable alternatives to reduce the environmental impact of thermoset composites. Until now, to a large extent, sustainable reinforcements have been used to manufacture more sustainable composites and thus contribute to the reduction of pollutants. However, in recent years, new alternatives have been developed, such as thermosetting resins with bio-based content and/or systems such as recyclable amines and vitrimers that enable recycling/reuse. Throughout this review, some new bio-based thermoset systems as well as new recyclable systems and sustainable reinforcements are described, and a brief overview of the biocomposites market and its impact is shown. By way of conclusion, it should be noted that although significant improvements have been achieved, other alternatives ought to be researched.This research was funded by the Provincial Council of Bizkaia by its Technology Transfer Program 2021 (BIOKONP Project, Reference 6/12/TT/2021/) and by Department of Economic Development and Infrastructures of The Basque Government by its ELKARTEK 2022 Program (FRONTIERS Project, Reference KK-2022/00109)

Polyphosphazenes with stimulated degradation pathways

Degradable synthetic polymers are of great importance for many applications such as medical applications, as well as environmental reasons. Polymer degradation, based on the cleavage of covalent bonds, is nearly inevitable but it is time limited. Consequently, degradable polymers should be considered as polymers that degrade in specific conditions and within the timescale of the given application. Hence stimulated degradation pathways, in which the degradation process is initiated by an external trigger such as enzymatic, photochemical, and oxidative environments, are attractive tools to control the degradation of polymers. Poly(organo)phosphazenes are hybrid inorganic-organic polymers with a flexible backbone based on alternation of nitrogen and phosphorus atoms. The organic side groups, covalently bonded to the phosphorous atom, can protect the intrinsic hydrolytic backbone and tune the properties and degradation of the polymer. In this work a variety of degradable poly(organo)phosphazenes are described with different properties to make them water soluble but also porous cross-linked scaffolds. Moreover, pH, oxidation, and photochemical triggering systems can be applied to induce and promote the degradation of the polymers. Particularly, amino acid-based poly(organo)phosphazenes are presented with convenient hydrolytic degradation rates, making them attractive for many biomedical applications. Among the studied poly(organo)phosphazenes it has been shown that the degradation was promoted when the glycine amino acid was incorporated between the polymer backbone and the organic substituent. The work described in this thesis focuses on the synthesis of novel poly(organo)phosphazenes with triggered degradation pathways, that is, on stable polymers that degrade upon a certain stimulus. In the first part of the thesis a pH-triggered system is presented, in which degradation rates are increased at lower pH values. Then as potential stimulus also a known reactive oxygen species (ROS), H2O2 has been employed. ROS, generated in the organism as a consequence of aerobic life, can lead to various diseases when it is overproduced. Therefore, H2O2 has been used as an oxidative trigger leading to polymer degradation. As a third stimulus visible light has been applied which could be of particular interest also for many biological applications due to its mild and deeply penetrating wavelengths as well as spatial and temporal control. In the last part of the thesis degradable cross-linked scaffolds with highly interconnected pores are presented which provide special attraction for cell growth in tissue engineering applications.submitted by M.Sc. Aitziber IturmendiUniversität Linz, Dissertation, 2018Oebb(VLID)275143

Oxidation Responsive Polymers with a Triggered Degradation via Arylboronate Self-Immolative Motifs on a Polyphosphazene Backbone

Oxidation responsive polymers with triggered degradation pathways have been prepared via attachment of self-immolative moieties onto a hydrolytically unstable polyphosphazene backbone. After controlled main-chain growth, postpolymerization functionalization allows the preparation of hydrolytically stable poly­(organo)­phosphazenes decorated with a phenylboronic ester caging group. In oxidative environments, triggered cleavage of the caging group is followed by self-immolation, exposing the unstable glycine-substituted polyphosphazene which subsequently undergoes to backbone degradation to low-molecular weight molecules. As well as giving mechanistic insights, detailed GPC and ¹H and ³¹P NMR analysis reveal the polymers to be stable in aqueous solutions, but show a selective, fast degradation upon exposure to hydrogen peroxide containing solutions. Since the post-polymerization functionalization route allows simple access to polymer backbones with a broad range of molecular weights, the approach of using the inorganic backbone as a platform significantly expands the toolbox of polymers capable of stimuli-responsive degradation

CoumarinCaged Polyphosphazenes with a VisibleLight Driven OnDemand Degradation

Polymers that, upon photochemical activation with visible light, undergo rapid degradation to small molecules are described. Through functionalization of a polyphosphazene backbone with pendant coumarin groups sensitive to light, polymers which are stable in the dark could be prepared. Upon irradiation, cleavage of the coumarin moieties exposes carboxylic acid moieties along the polymer backbone. The subsequent macromolecular photoacid is found to catalyze the rapid hydrolytic degradation of the polyphosphazene backbone. Watersoluble and nonwatersoluble polymers are reported, which due to their sensitivity toward light in the visible region could be significant as photocleavable materials in biological applications.EFRE RU2EU124/1002010P 27410N28(VLID)339312

Mesoporous Silica Micromotors with a Reversible Temperature Regulated OnOff Polyphosphazene Switch

The incorporation of an extraneous onoff braking system is necessary for the effective motion control of the next generation of micrometersized motors. Here, the design and synthesis of micromotors is reported based on mesoporous silica particles containing bipyridine groups, introduced by cocondensation, for entrapping catalytic cobalt(II) ions within the mesochannels, and functionalized on the surface with silanederived temperature responsive bottlebrush polyphosphazene. Switching the polymers in a narrow temperature window of 2530 C between the swollen and collapsed state, allows the access for the fuel H2O2 contained in the dispersion medium to cobalt(II) bipyridinato catalyst sites. The decomposition of hydrogen peroxide is monitored by optical microscopy, and effectively operated by reversibly closing or opening the pores by the grafted gatelike polyphosphazene, to control on demand the oxygen bubble generation. This design represents one of the few examples using temperature as a trigger for the reversible onoff external switching of mesoporous silica micromotors.(VLID)4844452Version of recor

Polyphosphazene-Based Nanocarriers for the Release of Camptothecin and Epirubicin

The design and study of efficient polymer-based drug delivery systems for the controlled release of anticancer drugs is one of the pillars of nanomedicine. The fight against metastatic and invasive cancers demands therapeutic candidates with increased and selective toxicity towards malignant cells, long-term activity and reduced side effects. In this sense, polyphosphazene nanocarriers were synthesized for the sustained release of the anticancer drugs camptothecin (CPT) and epirubicin (EPI). Linear poly(dichloro)phosphazene was modified with lipophilic tocopherol or testosterone glycinate, with antioxidant and antitumor activity, and with hydrophilic Jeffamine M1000 to obtain different polyphosphazene nanocarriers. It allowed us to encapsulate the lipophilic CPT and the more hydrophilic EPI. The encapsulation process was carried out via solvent exchange/precipitation, attaining a 9.2–13.6 wt% of CPT and 0.3–2.4 wt% of EPI. CPT-loaded polyphosphazenes formed 140–200 nm aggregates in simulated body physiological conditions (PBS, pH 7.4), resulting in an 80–100-fold increase of CPT solubility. EPI-loaded polyphosphazenes formed 250 nm aggregates in an aqueous medium. CPT and EPI release (PBS, pH 7.4, 37 °C) was monitored for 202 h, being almost linear during the first 8 h. The slow release of testosterone and tocopherol was also sustained for 150 h in PBS (pH 7.4 and 6.0) at 37 °C. The co-delivery of testosterone or tocopherol and the anticancer drugs from the nanocarriers was expected. Cells of the human breast cancer cell line MCF-7 demonstrated good uptake of anticancer-drug-loaded nanocarriers after 6 h. Similarly, MCF-7 spheroids showed good uptake of the anticancer-drug-loaded aggregates after 72 h. Almost all anticancer-drug-loaded polyphosphazenes exhibited similar or superior toxicity against MCF-7 cells and spheroids when compared to raw anticancer drugs. Additionally, cell-cycle arrest in the G2/M phase was increased in response to the drug-loaded nanocarriers. Almost no toxicity of anticancer-drug-loaded aggregates against primary human lung fibroblasts was observed. Furthermore, the aggregates displayed no hemolytic activity, which is in contrast to the parent anticancer drugs. Consequently, synthesized polyphosphazene-based nanocarriers might be potential nanomedicines for chemotherapy

Dynamic Supramolecular RutheniumBased Gels Responsive to Visible/NIR Light and Heat

A simple supramolecular crosslinked gel is reported with a photosensitive ruthenium bipyridine complex functioning as a crosslinker and poly(4vinylpyridine) (P4VP) as a macromolecular ligand. Irradiation of the organogels in H2O/MeOH with visible and NIR light (in a multiphoton process) leads to cleavage of pyridine moieties from the ruthenium complex breaking the crosslinks and causing degelation and hence solubilization of the P4VP chains. Realtime (RT) photorheology experiments of thin films showed a rapid degelation in several seconds, whereas larger bulk samples could also be photocleaved. Furthermore, the gels could be reformed or healed by simple heating of the system and restoration of the metalligand crosslinks. The relatively simple dynamic system with a high sensitivity towards light in the visible and NIR region make them interesting positive photoresists for nano/micropatterning applications, as was demonstrated by writing, erasing, and rewriting of the gels by single and multiphoton lithography.FWF P27410-N28(VLID)434853

Degradable, Dendritic Polyols on a Branched Polyphosphazene Backbone

Herein, we present the design, synthesis, and characterization of fully degradable, hybrid, star-branched dendritic polyols. First multiarmed polyphosphazenes were prepared as a star-branched scaffold which upon functionalization produced globular branched hydroxyl-functionalized polymers with over 1700 peripheral functional end groups. These polyols with unique branched architectures could be prepared with controlled molecular weights and relatively narrow dispersities. Furthermore, the polymers are shown to undergo hydrolytic degradation to low molecular weight degradation products, the rate of which could be controlled through postpolymerization functionalization of the phosphazene backbone