Segmented polyurethane elastomers for biomedical applications were synthesized and studied at macroscopic (by mechanical testing) and meso/nanoscopic length scales (by atomic force microscopy, AFM). The polyurethanes are composed of 4,4'‐methylenebis(phenyl isocyanate), 1,4‐butanediol and an ε‐polycaprolactone diol. The stoichiometric ratio of the isocyanate and hydroxyl groups is constant, but the polymer diol to total diol—varies from 0 to 100 %. We show the representative features of the morphology from phase separation to mixed phases, how this is related to the mechanical properties in the bulk and locally, at exposed free surfaces and at the nanoscale. We propose a morphological model considering the molecular structure, the length of hard segments, and the dimensions of both the soft and the hard phases, respectively. Understanding such structure–property relations is pivotal to establishing designer materials and controlling the performance of the final product to achieve optimal properties in polyurethane based medical devices. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 2298–2310.
The integrated application of green chemistry, life cycle thinking, and systems thinking has the potential to reduce environmental impacts related to the use and production of chemical products or materials. Life cycle and systems thinking are key perspectives needed to avoid the unintended consequences or unsubstantiated claims that inhibit development and adoption of more sustainable products. However, systems thinking is rarely taught in the chemistry curriculum. Students need experience evaluating the effects of products on societal and earth systems (i.e., using systems thinking) in order to anticipate trade-offs and make informed design decisions. To give students an immersive learning experience, we developed a sustainable product design project that brings together tools from green chemistry, life cycle thinking, and systems thinking. We found that this experiential learning approach gave students generalizable strategies for innovating and implementing sustainable practices in their current industrial positions. The project was divided into three workshops: in Workshop I they evaluated the life cycle impacts and toxicity for a material of concern, in Workshop II they measured the performance of this material and compared it to alternatives, and in Workshop III they designed a mock-product that was both high performing and environmentally friendly. We piloted this framework with master’s students evaluating polymer foams for use in an infant car seat; however, we envision this project being suitable for a range of other types of products. Moreover, we have suggested ways to adapt the duration and sophistication of the workshops to make them appropriate for a variety of course levels.
A series of segmented polycaprolactone polyurethane (PU) polymers is synthesized. One set of polymers ranges in composition from 0 to 100 wt% hard segments (HSs). The syntheses are carried out in solution and the polymers are melt‐processed by compression molding. Another subset of polymers is formed in bulk from a blocked isocyanate prepolymer. The blocked polymer's thermal and mechanical properties are compared with the melt‐processed materials. The emphasis in this paper is on the effects of varying the chemical structures of the PUs on their phase structures and physical cross‐linking due to nanocrystalline hard domains. The thermal properties indicate that nanophase separation and the formation of hard domains occur at HS contents above ≈8 wt%. Property differences resulting from varying the hard segment amounts are directly related to differences in morphology at the nanoscale. Atomic force microscopy images show that the best elastomeric mechanical properties are found when nanocrystallites are 4–5 nm in size.
This paper considers inkjet printing of optical quality 3D nano-composites from diethylene-glycol diacrylate monomer (DEGDA) containing ZrO 2 nanoparticles at varying concentrations. One application for the composites is for gradient refractive index (GRIN) lenses. The process involves printing of a nanoparticle loaded monomer "ink" onto a substrate and then photopolymerizing the monomer layer by layer using UV light. The results of the study confirm that the presence of nanoparticles favorably affects the reaction kinetics. The reaction rate and chemical conversion are enhanced considerably by the nanoparticles. A seamless interface between the layers, which are 20 m thick, may be achieved if the conversion level of the layer onto which ink is deposited is limited at 60 to 80 %. Dynamic mechanical analysis (DMA) data indicate that both the glass transition and sub Tg viscoelastic properties are influenced by the nanoparticles. When nanoparticles are introduced the Tg relaxation shifts to lower temperatures and a sub Tg relaxation appears whose intensity increases with particle concentration. These results are consistent with a molecular confinement model involving a lower crosslink density rubbery layer at the polymer-particle interfaces.
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