Publication

Low stress acrylated hyperbranched polymers

Lars Schmidt
2006
EPFL thesis
Abstract

The objective of this study was to investigate the behavior of highly functional acrylates, during isothermal ultraviolet (UV) curing. The materials included a pentafunctional acrylate and two acrylated hyperbranched polymers, one with a stiff polyester core and one with a more flexible polyether core. In particular, the influence of UV intensity and reactive blend composition on structural transitions, such as gelation and vitrification, and on the dynamics of internal stress was considered. Curing kinetics were studied with photo differential scanning calorimetry. The chemical conversion was analyzed using an autocatalytic model and a criterion for identifying vitrification directly from photocalorimetric experiments was proposed. It was observed that reactive blends containing HBPs had a higher conversion at vitrification, compared to the pure penta-functional acrylate. Strong intensity dependence of the maximum conversion rate and a weak intensity dependence of the ultimate conversion were observed. The latter was found to be controlled by the conversion at vitrification. The structural transitions and the modulus build-up during UV polymerization were determined by photorheology. A refined data processing algorithm was developed, that allows monitoring the shear modulus over 5 orders of magnitude within a short experimental time scale, with millisecond time resolution. Gelation – the liquid-solid transition – was found to be below 5 % conversion for all acrylates investigated. In contrast, the conversion at vitrification was strongly dependent on the actual monomer and increased with increasing UV intensity. The results of the photo DSC and the photorheology study were synthesized in the form of timeintensity- transformation diagrams. The dynamics of internal stress and cure shrinkage were studied using beambending and an interferometry-based method, respectively. The internal stress of the acrylated HBPs was largely reduced compared to the standard highly functional acrylate monomer. Moreover, in the case of one HBP with a polyester core and a reactive blend of the HBP with the standard highly functional acrylate, the stress reduction was obtained with a combined increase of Young's modulus, which was attributed to retarded modulus build-up and a higher final conversion. It was found that curing at a lower UV intensity led to earlier vitrification, hence earlier internal stress build-up, but limited maximum conversion thus limited final stress. Curing at a higher intensity led to later stress build-up but higher final stresses. Polymer microstructures were fabricated from the different acrylates in a photolithographic process and compared to SU-8, an epoxy frequently used for this kind of application. It was shown that the shape accuracy is linked to the processinduced internal stresses: the best result for thick and high aspect ratio microstructures – as used for example for microfluidic devices – was obtained for the acrylated HBP with a polyether core.

About this result
This page is automatically generated and may contain information that is not correct, complete, up-to-date, or relevant to your search query. The same applies to every other page on this website. Please make sure to verify the information with EPFL's official sources.
Related concepts (37)
Thermoset polymer matrix
A thermoset polymer matrix is a synthetic polymer reinforcement where polymers act as binder or matrix to secure in place incorporated particulates, fibres or other reinforcements. They were first developed for structural applications, such as glass-reinforced plastic radar domes on aircraft and graphite-epoxy payload bay doors on the Space Shuttle. They were first used after World War II, and continuing research has led to an increased range of thermoset resins, polymers or plastics, as well as engineering grade thermoplastics.
Ultraviolet
Ultraviolet (UV) is a form of electromagnetic radiation with wavelength shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight, and constitutes about 10% of the total electromagnetic radiation output from the Sun. It is also produced by electric arcs; Cherenkov radiation; and specialized lights; such as mercury-vapor lamps, tanning lamps, and black lights. Although long-wavelength ultraviolet is not considered an ionizing radiation because its photons lack the energy to ionize atoms, it can cause chemical reactions and causes many substances to glow or fluoresce.
Psychological stress
In psychology, stress is a feeling of emotional strain and pressure. Stress is a type of psychological pain. Small amounts of stress may be beneficial, as it can improve athletic performance, motivation and reaction to the environment. Excessive amounts of stress, however, can increase the risk of strokes, heart attacks, ulcers, and mental illnesses such as depression and also aggravation of a pre-existing condition.
Show more
Related publications (66)

Enabling simultaneous reprocessability and fire protection via incorporation of phosphine oxide monomer in epoxy vitrimer

Véronique Michaud, Valentin Rougier

The conception of epoxy thermosets with both reprocessability and flame retardancy delineates a new horizon in polymer science, offering a material solution that is not only superior in fire safety but is also environment friendly. Herein, a flame-retardan ...
Journal Mater Sci Technol2024

Moulding and Microfluidic Wet Spinning of the Soft Polymer Optical Fibers for Sensory Applications

Khushdeep Sharma

Polymer optical fibre (POFs) based wearable sensors have attracted a lot of attention in the field of healthcare and biomedical applications. They are in particular envision as the next generation of sensors for the continuous, real-time n ...
EPFL2024

Bottlebrush Dielectric Elastomers with Improved Properties for Actuation

Yeerlan Adeli

Dielectric elastomer actuators (DEA) are elastic capacitors composed of a pair of compliant electrodes and a soft dielectric elastomer film sandwiched in between. This kind of stretchable capacitors can be actuated when charged, can generate electricity fr ...
EPFL2023
Show more
Related MOOCs (3)
Micro and Nanofabrication (MEMS)
Learn the fundamentals of microfabrication and nanofabrication by using the most effective techniques in a cleanroom environment.
Microstructure Fabrication Technologies I
Learn the fundamentals of microfabrication and nanofabrication by using the most effective techniques in a cleanroom environment.
Micro and Nanofabrication (MEMS)
Learn the fundamentals of microfabrication and nanofabrication by using the most effective techniques in a cleanroom environment.

Graph Chatbot

Chat with Graph Search

Ask any question about EPFL courses, lectures, exercises, research, news, etc. or try the example questions below.

DISCLAIMER: The Graph Chatbot is not programmed to provide explicit or categorical answers to your questions. Rather, it transforms your questions into API requests that are distributed across the various IT services officially administered by EPFL. Its purpose is solely to collect and recommend relevant references to content that you can explore to help you answer your questions.