Therefore we have established the photopolymerization chemistry with vinylesters, vinylcarbonates and other enes that show significantly lower toxicity.

Diseases of the cardiovascular system are principal causes for morbidity and mortality in all western countries. The total direct and indirect costs of cardiovascular diseases (CVD) and stroke for 2010 were estimated at $503.2 billion for the United States alone. Electrospinning (ES) has attracted the interest of biomedical research as it is possible to manufacture seamless, non-woven, nanofibrous tubes with high (>20 m²/g) surface areas which mimic the extracellular matrix (ECM) and are potentially suitable as vascular grafts. Unfortunately, currently used materials show low compliancy (ePTFE) and/or are non-degradable (Thermoplastic polyurethane elastomers (TPUs)). Therefore degradable TPUs are of high interest.

The number of patients with minor and major accidents coming into accident and emergency care is steadily rising due to increasing life spans and the aging of our society. The fixation and adhesion between tissues, implants or scaffolds have to be refined, but the number and versatility of biomimetic and biocompatible adhesives that can be used for such purpose is limited. Up to now, adhesives based on cyanoacrylates, polyurethanes, epoxy resins or poly(methyl methacrylates) still bear several drawbacks ranging from possible allergic response, lack of mechanical strength to toxic side products. Therefore, new biomimetic glues for bonding of tissue-tissue and tissue-implant interfaces are urgently needed.

The extracellular matrix (ECM) forms the mechanical framework for living tissue and controls many functions including tissue morphogenesis, regulation of cell differentiation and proliferation, and processes for regeneration after injuries and is therefore a central consideration in the field of tissue engineering and regenerative medicine. To replace the damaged tissue artificial hydrogels are required with low cytotoxicity. Multiphoton Polymerization is a suitable tool to structure such hydrogels including the placement of signals to stimulate and guide cell differentiation.

As far as the aspect of sustainability is concerned, renewable raw materials play a key role in polymer technology. The use of recoverable raw materials is especially efficient if benefits in synthesis provided by nature are fully exploited, i.e. if only few physical, chemical or biotechnological modification steps are necessary to obtain industrially utilizable materials and products. Research topics at the institute are e.g. the synthesis of reactive carbohydrate and protein derivatives, usable as components for water-borne UV-curable resins , and the synthesis of so-called glycopolymers from saccharide-based (glucose, sucrose, glucamine..) monomers. Application of poly-functional carbohydrate monomers or addition of commercially available cross-linkers yields hydrophilic cross-linked polymers , which are tested as polymer supports in e.g. biomedicine. Printability and wettability of polypropylene can be significantly improved by photochemical immobilization of carbohydrates on the polymer surface. Other main fields of research are the functionalization of polysaccharides such as cellulose and starch and we are also engaged in the modification of wood and lignin.

During the last 25 years research of the PCT group has focused on radical photoinititiators. Besides water-soluble and covalently linked photoinitiators, new chromophores were aimed. With Ivocerin^(c) a milestone for dental composites has been created. Besides this Ge-based compounds also Si and Sn-based long wavelength initiators have been explored. As migration of uncunsumed copounds is always an issue, self-initiating monomers and non-aromatic photoinitiators have been developed.

Oxygen inhibition in radical photopolymerization is a major drawback as it leads to tacky surfaces and frequently requires expensive nitrogen inertization. Beside such physical methods there are a large variety of chemical methods available that try to circumvent these disadvantages. However, a recent study that compares most of the strategies known from literature shows that there is up to now only a moderate improvement possible and no general strategy available.

Cationic photopolymerization offers not only wide range of polymerizeable monomers (e.g. epoxides, oxetanes, vinyl ether) but also a clear advantage compared to the classical free radical photopolymerization, which is the independence of the process from oxygen. The state of the art cationic photoinitiators (so called photo acids) are usually iodonium or sulfonium salts of fluorometallate anions (e.g. BF^4-; PF^6-; AsF^6-; SbF^6-) or [BAr₄F]--anions. These anions suffer from different drawbacks like toxicity, hydrolysis or tough synthesis.

Very recently we have developed a new class of cationic photoinitiators (sulphonium as well as iodonium salt) based on a fluorinated alkoxyaluminate with a low toxicity, high stability and outstanding reactivity. Excellent activity has been demonstrated for epoxides and ring opening monomers like oxazolines, cyclic carbonates, cyclic orthoesters etc. Based on that success the cation and anion has been widely changes to give new high performance photoacids

Generally, in Multi Photon Induced Photopolymerization (MPIP, also called Two Photon induced Polymerization) a resin, that contains mainly a multifunctional monomer (typically acrylate-based) and a photoinitiator, is cured inside the focal point of a fs pulsed near infrared laser beam to produce a desired 3D shape with a resolution down to 100 nm. As usual single photon initiators have only limited two photon absorption properties specialized molecules have to be desinged containing a long planar π-system and strong electron donor and or acceptor groups are required. Initiators known from literature have the disadvantages of deactivation of the excited singlet state by fluoreszenz and cis-trans isomerization of the double bonds.

Besides classical D-π-A-π-D Systems, we have developed water soluble and for the first time cleavable initiators.

With the use of vinylcyclopropanes, cyclopolymerizable monomers or Addition Fragmentation Chain Transfer Reagents one is able to have a modified polymer architecture and a reduced shrinkage process.

Thiol-Ene polymerization is known since the 50’s of the last century and has gained tremendously increasing interest during the last decade, thanks to the rediscovery by Hoyle and recent efforts by Bowman. Advantages such as low oxygen inhibition and shrinkage and the formation of uniform networks in a click chemistry style are accompanied by up to now unsolved disadvantages such as unpleasant odour, poor storage stability and low modulus materials.

We have demonstrated that this chemistry could speed up low toxic vinylester and vinylcarbonate polymerization and also the suitability in the formation of hydrogels in the field of tissue engineering.

Azide grafting chemistry is another field of high importance which is now applied in the high resolution multiphoton chemistry for site selective surface modification of hydrogels

We have demonstrated that frontal polymerization of classical acrylate systems is also possible in water. Furthermore, a new system for radical induced cationic polymerization of epoxides has been established that allows the curing of composite materials

In cooperation with the Institute of Materials Sciences and Technology from the TU Wien and different companies new materials are developed for Light based Additive Manufacturing including Ceramic 3D Printing (Lithoz), the Hot Lithography technology (Cubicure) and Multiphoton Polymerization (UpNano). Toughening of Photopolymers, Biomaterials or High Resolution Structuring are the principle aims.

Since more than 20 years there is a continous industry cooperation with a dental company. The main aims are to develop new efficient photoinitiators the have good solubility in aqueous dental primer formulations and especialy long wavelength absorption for excellent cure depth of highly filled composites. In the later case, a milestone in dental photoinitiators has been brought to market, Ivocerin^(c) . Another ongoing topic is shrinkage stress of dental filling composites. Here the Addition Fragementation Chain Transfer concept has been introduced to the market due to its low retardation, excellent shrinkage reduction and surprsing improvement of toughness. Furthermore, cyclopolymerizable monomers and vinylcyclopropane were used to counteract shrinkage.

Photopolymerizable glues and cements that offer debonding on demand (DoD) through an external stimulus are of great interest for the fields of recycling and repair. State-of-the-art DoD solutions often require a high-energy impulse (e.g., >200 °C, strong force), which is due to the typical glassy nature of such photopolymer networks. We have developed some DoD solutions for methacrylate-based monomers in the field of dentistry.

Polymer characterization includes the determination of molecular weight and molecular weight distribution, molecular structure, conformation of the polymer in solution, thermal properties and mechanical properties. The monomer and oligomer characterization according to type, purity and additives is also regularly carried out in our laboratory.

RT-NIR/MIR-Photorheometry is a world wide unique equipment in our group. It allows to follow photocuring reaction under simulateous evaluation of the rheological and mechanical properties, chemical information on the monomer conversion and shrinkage behaviour.

Our group is well equipt with numerous tools to follow photopolymerization reactions and characterize the formed materials: