Benzoxazine/amine-based polymer networks featuring stress-relaxation and reprocessability

Amines as additives in benzoxazines are known to beneficially affect the polymerization temperature and furthermore to allow for partially reversible reaction steps yielding however a non-dynamic polybenzoxazine network. This contribution proves that the polymerization behavior of a two-component polymer of the polyetheramine Jeffamine® ED-600 and a bisphenol-A-based benzoxazine features stress-relaxation and reprocessability usually known from vitrimers. With the aim to gain a deeper understanding of the material properties of this system and the corresponding polymer structure, the reaction mechanism of a monofunctional benzoxazine and monoamine model system was studied revealing at first primary, and then secondary amine induced opening of oxazine rings, leading at first to linear polymer chains and then to covalently crosslinked networks. Both consist of repeated phenolic benzoxazine/amine motifs with permanently incorporated polyetheramine chains that do not impact the mechanical properties, compared to pure polybenzoxazine. Thermal, spectroscopic, and extraction analyses show that the addition of Jeffamine® reduces the polymerization temperature and introduces material properties such as reprocessability at the same time. Stress-relaxation measurements support the assumption that the reprocessability point to vitrimer-like molecular processes. The material shows rapid stress-relaxation of up to 11 s, a corresponding bond-exchange activation energy of 146 kJ/mol, and a topology freezing temperature of 97°C

Highly Crosslinked Polybenzoxazines from Monobenzoxazines : The Effect of Meta-Substitution in the Phenol Ring

It is possible to control the crosslink density of polymers derived from monobenzoxazines by switching the type of substituents in the phenolic ring and their relative position with respect to the phenol group. We prepared several substituted monobenzoxazines in the para and meta positions of the phenolic ring and studied how these substituents affected the polymerization temperature of monomers and the thermal stability of the final polymers and, more extensively, how they affected the crosslink network of the final polymers. Gel content and dynamic mechanical analysis confirm that ortho- and para-orienting substituents in the meta position generate highly crosslinked materials compared to para ones. This fact can lead to the design of materials with highly crosslinked networks based on monobenzoxazines, simpler and more versatile monomers than the commercial bisbenzoxazines currently in use

The effects of manufacturing processes on the physical and mechanical properties of basalt fibre reinforced polybenzoxazine

The present work provides a comparative investigation between different methods of manufacturing basalt fibre reinforced polybenzoxazines (BFRP), including vacuum infusion, hand laminating, dynamic fluid compression moulding and autoclave curing processes. In comparison to the high pressure based autoclave-cured and compression-moulded BFRPs, vacuum-infused BFRPs showed similar or even higher mechanical properties. Despite the low pressure curing, vacuum infusion yielded BFRPs with a 10% higher tensile strength and a 24% higher strain at failure compared to its autoclave-cured counterparts. Thus, it is possible to gain BFRPs with near-zero porosity and high mechanical properties without the need of high pressure curing methods

Design of natural fiber composites utilizing interfacial crystallinity and affinity

Butanediol initiated poly(e-caprolactone) (PCL) has recently been reported as a toughening agent for cationically curing cycloaliphatic epoxides providing plasticized thermosets with excellent properties (Lützen et al., 2013). In this contribution that promising toughening approach was applied for the first time for the development of novel natural fiber composites (NFC). NFCs based on conventional brittle thermosetting polymers often suffer from poor interfacial adhesion and stress cracking. Composites made up of the novel plasticized thermosets and woven flax fiber preserved the elastomer-like properties and increased tensile strength and elongation at break up to 60 MPa and 5%, respectively. Furthermore, PCL was shown not only to toughen the epoxide but also to modulate the affinity of the matrix to the fiber. In conclusion, improved interfacial adhesion and the resulting excellent mechanical properties of cationically curable NFCs were achieved by both interfacial crystallization and affinity

Generation of multivalent peptide-polymer conjugates based on thioester-HPMA- copolymers to address biological issues in vitro and in vivo

Die Konjugation eines Wirkstoffs an ein biokompatibles Polymer generiert Systeme, die die bioaktive Substanz nicht nur zielgerichtet transportieren, sondern bei Bedarf kontrolliert abgeben können. Im Gegensatz zu ihrer freien Form verfügen polymergebundene Liganden, sowohl peptidischer als auch nicht- peptidischer Natur, über eine veränderte Pharmakokinetik und diverse Vorteile. Auf dem Gebiet der Polymertherapeutika ist Poly(N-2-Hydroxypropylmethacrylamid) (poly(HPMA)) gegenwärtig eines der aussichtsreichsten biokompatiblen Polymere, dessen Vielseitigkeit im Rahmen dieser Arbeit aufgezeigt wird. Auf Basis von poly(HPMA) wurde ein thioesterfunktionalisiertes Copolymer entwickelt, welches an die vorliegenden biochemischen und medizinischen Fragestellungen flexibel angepasst werden konnte. RAFT-vermittelte Copolymerisationen von HPMA mit einem thioesterfunktionalisierten Monomer lieferten Thioester-HPMA-Copolymere, die mit cysteinylierten Liganden in NCL-Reaktionen beladen wurden und so einen schnellen und flexiblen Zugang zu maßgeschneiderten Peptid-Polymerkonjugaten lieferten. Die zelluläre Aufnahme von Peptid-HPMA Konjugaten wurde in Abhängigkeit von ihrer Oberflächenladungen untersucht. Ausschließlich positiv geladene Peptid-Polymerkonjugate wurden in HeLa-Zellen internalisiert. Mit einer exzellenten Biokompatibiliät und effizienten zellulären Aufname, stellten argininbeladende HPMA-Konjugate eine Alternative zum toxischen Zell- penetrierenden Peptid Nonaarginin dar und könnten als effiziente Trägersysteme biologisch relevanter Liganden für intrazelluläre Studien eingesetzt werden. Die positiven Auswirkungen der Peptidkonjugation an die Thioester-HPMA- Copolymere im Hinblick auf den gezielten Transport an den Wirkort und den Schutz vor proteolytischem Abbau wurden in einem Projekt zur Früherkennung von Pankreaskrebs mit nichtinvasiven bildgebenden Verfahren genutzt. Für die Matrix-Metalloprotease 11 (MMP-11) als Biomarker für Bauchspeicheldrüsenkrebs wurden Substrat-Polymerkonjugate konzipiert, deren Umsatz bei der Spaltung durch das Enzym MMP-11 ein auf dem FRET-Effekt beruhendes Fluoreszenzsignal lieferte. Die ersten in vivo-Versuche an MIA PACA-Xenograft-Mäusen waren vielversprechend. Zur Untersuchung der amyloidbildenden Eigenschaften von Modellpeptiden in Neuroblastomzellen wurde ein photolysierbarer Cumarinlinker zwischen das zu transportierende Peptid und den polymeren Träger eingeführt, der eine kontrollierte, photoinduzierte Freisetzung des bioaktiven Liganden am Wirkort ermöglichte. Die Konjugation der fluoreszenzmarkierten Peptide an ein HPMA-Linker-System sorgte nicht nur für den Transport, den Schutz und die photoinduzierte Freisetzung, sondern maskierte zudem die amyloidbildenden Eigenschaften. Nach erfolgter Internalisierung zeigte das Modellpeptid nach Freisetzung Auswirkungen auf die Zellvitalität. Im Hinblick darauf, dass viele biologische Prozesse auf Protein-Protein-Interaktionen beruhen, stellt die Konjugation mehrerer Kopien monovalenter Liganden an ein biokompatibles Polymer einen wichtigen Zugang zu multivalenten Systemen dar. Der Einfluss der polymeren Trägersysteme poly(HPMA), hyperverzweigtes Polyglycerin und Dextran auf die Interaktion mit den Tandem WW-Domänen (tWW) des forminbindenden Proteins FBP21 wurde kalorimetrisch bestimmt und in MD-Simulationen modelliert. Die multivalente Präsentation der Erkennungssequenz resultierte für alle betrachteten Polymere in einer signifikanten Steigerung der Bindungsaffinitäten, die in Abhängigkeit vom verwendeten Polymer und der Peptidbeladungsdichte variierten. Im Rahmen dieser breit gefächerten Projekte konnte die Vielseitigkeit der HPMA-basierten Copolymere beispielsweise als Transportsystem biologisch relevanter Liganden für in vitro und in vivo Anwendungen oder als Trägersystem zur Darstellung multivalenter Liganden gezeigt werden.The conjugation of a drug on a biocompatible polymer generates drug delivery systems which transport and deliver the therapeutic agent into the tissue of interest. Polymer bound drugs of a peptidic or non-peptidic nature exhibit modified pharmacokinetics and diverse advantages compared to their free state. In the field of polymertherapeutics poly(N-2-hydroxypropylmethacrylamide) is one of the most promising biocompatible polymers. The versatile applications of poly(HPMA) will be shown within the scope of this work. A thioester functionalized copolymer was developed based on poly(HPMA) which could be adapted to particular biochemical or medical problem at hand. RAFT-mediated copolymerisation of HPMA with a thioester functionalized monomer provided thioester-HPMA copolymers that enabeled an NCL-reaction of cysteinylated ligands. Accordingly, thioester-HPMA copolymers provided fast and flexible access to tailor-made peptide-polymer conjugates. The surface charge dependence of the cellular uptake of peptide-HPMA conjugates was studied. Exclusively positively charged conjugates were internalized into HeLa cells. Arginine loaded HPMA-conjugates showed not only an efficient internalization but exhibit an excellent biocompatibility in comparison to the cell- penetrating peptide nonaarginine. Accordingly, positively charged HPMA- conjugates could be applied as transport systems for biologically relevant ligands in intracellular studies. The advantagous impact of peptide conjugation with respect to drug targeting and the stealth effect was used in pilot studies for the early diagnosis of pancreatic cancer using noninvasive imaging. The matrix-metallo-protease 11 (MMP-11) is a biomarker for pancreatic cancer. FRET based substrate-polymer conjugates have been developed that present a fluorescence signal upon enzymatic cleavage of MMP-11. Preliminary in vivo experiments on MIA PACA-xenograft mice showed promising results. Targeted delivery was instrumental for determining the amyloid forming properties of model peptides in neuroblastoma cells. Therefore, a photocleavable coumarine linker was incorporated into the peptide-polymer conjugate which enabled a controlled, photoinducable delivery of the peptide onto the site of action. The conjugation of fluorescence labeled peptides on an HPMA-linker-system provided the transport, protection and photoinduced delivery of the peptide. Additionally, the polymer conjugation disabled amyloid formation. After internalization, the delivery of the peptide affected the cell viability. As most biological processes are based on protein-protein- interactions, the conjugation of multiple copies of monovalent ligands on a biocompatible polymer provides an important access point to multivalent systems. The impact of the polymer scaffolds poly(HPMA), hyperbranched polyglycerol, and dextran on the interaction with tandem WW-domains of the formin binding proteine FBP21 was examined by isothermal calorimetry and was calculated in MD-simulations. The multivalent presentation of the recognition sequence resulted in a significant increase in the binding affinity for all polymers. The affinity varied slightly with a dependence on the polymer scaffold and the peptide loading density. In the scope of the diverse projects, the versatility of the HPMA-based copolymers as drug carriers for in vitro and in vivo applications, or as polymer scaffold for the design of multivalent ligands was shown

Verfahren zum Vernetzen eines Polymeres und vernetztes Polymer

The invention relates to a method for cross-linking a polymer, monomer or oligomer having at least two hydroxyl groups by means of a cross-linking agent that comprises at least two tricarbonyl domains or two trithiocarbonyl domains

Diastereoisomeric diversity dictates reactivity of epoxy groups in limonene dioxide polymerization

Limonene dioxide (LDO) has the potential to find a wide application as a bio-based epoxy resin. Its polymerizations by catalyzed ring-opening, and by poly addition with diamines were compared with the polymerizations of the commercial epoxy resins bisphenol-A diglycidyl ether (BADGE), and 3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexane carboxylate(ECC). Differential scanning calorimetry (DSC) studies showed that LDO polymerizations suffer in all cases studied from incomplete conversions. Nuclear magnetic resonance (NMR) studies revealed that in cis-isomers of LDO the internal epoxide rings were not reacting. The low reactivity of this epoxide group was explained by mechanistic considerations making use of the Fürst-Plattner rule, or trans-diaxial effect. Due to diastereomeric diversity approximately one-fourth of epoxide groups present in LDO could not react. Therefore, a diastereo selective epoxidation of limonene could provide a fully reactive bio-based epoxy resin

Effect of poly(ɛ-caprolactone) in polybenzoxazine blends and respective copolymers on morphology and mechanical properties

Covalent and non-covalent incorporation of poly(ɛ-caprolactone) (PCL) in a bisphenol A based benzoxazine (BA-a) yields copolymer and blend-type PCL/PBA-a polymers differing in their properties depending on their bonding state. Gel content and morphology studies revealed that in case of unbound PCL a threshold between 20 and 30 wt-% of PCL exist showing a partial miscibility below and phase separation above that critical value giving opaque and partially crystalline samples. Tosylated PCL binds to a certain extent covalently into PBA-a’s network yielding a homogenous polymer at low PCL contents, but a mixed bonding mode of copolymer and blend like structures with increasing PCL content. The polymerization behavior, thermomechanical properties and resulting morphologies of copolymers were studied and compared to analogue PCL/polybenzoxazine blends. Tensile tests proved that 10 and 20 wt-% of covalently incorporated PCL entail toughening of the brittle benzoxazine increasing ultimate tensile strength by 43% and elongation at break by 130%, simultaneously

The nature of bonding matters: Benzoxazine based shape memory polymers

A novel shape memory polymer is presented based on polybenzoxazine and poly(ε-caprolactone) (PCL). Polybenzoxazines with unbound and covalently incorporated PCL were prepared applying hydroxyl and tosyl terminated PCLs, respectively. Thermo-responsive and shape memory behavior with high shape fixity and recovery were demonstrated for samples containing a high ratio of covalently bonded PCL in a crosslinked benzoxazine structure. Samples with exclusively non-bonded PCL chains proved to be brittle, possessing a heterogeneous morphology and lacking shape memory properties. The type of bonding into benzoxazines network – covalent versus non-covalent bonding of PCL – strongly affects materials structure property relationship

Gedruckte elektronische Strukturen auf Geweben für ein Belastungsmonitoring von Faserverbundwerkstoffen

Die Technologieplattform ,,Functional Printing" ermöglicht eine Funktionalisierung von Geweben, welche zur Herstellung von z.B. funktionsintegrierten Glasfaser- und/ oder Carbonfaserverstärkten Kunststoffen (GFK, CFK) verwendet werden können. Diese Faserverbundstrukturen erlauben so eine integrierte Zustandsüberwachung, mit der Schäden in Form von Faserbrüchen, Matrixrissen und Delaminationen vor einem kompletten Bauteilversagen detektiert werden können