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In this study, a carbon fiber/vinyl ester‐polyurethane interpenetrating polymer network (IPN) laminate composite was fabricated and characterized for the first time. The IPN matrix, consisting of a commercially available vinyl ester and polyurethane, was synthesized via a sequential method with vinyl ester as the rigid phase and polyurethane as the flexible phase. Good compatibility between the two phases in the matrix was achieved and confirmed via differential scanning calorimetry and dynamic mechanical analysis. The thermomechanical response of the IPN matrix was compared with that of an unmodified vinyl ester resin. The presence of the more ductile polyurethane in the IPN matrix depressed the glass transition temperature (from 94 to 84°C), but also served to improve damping response at all frequencies studied. Tensile and flexural tests were performed on the carbon fiber/IPN and carbon fiber/vinyl ester composites to determine their mechanical response. The IPN composite exhibited lower tensile properties than the vinyl ester composite. However, its flexural properties were on par with those of the vinyl ester composite.

Graft semi-interpenetrating polymer networks (IPNs) out of poly(ethylene glycol), PEG8000-based polyurethane, and acrylic copolymers were synthesized for phase change applications. The chemical structure of the IPN samples was checked with Fourier transform infrared spectroscopy. Thermal properties of the IPNs were studied using differential scanning calorimetry and thermogravimetric analysis. A scanning electron microscope was used to study the surface morphology of the IPN samples. Moreover, polarized optical microscopy and X-ray diffraction were utilized to examine the crystallization properties of the IPNs. The cycling stability of the IPNs was studied as well. Overall, graft-IPN samples show high thermal and cycling stability with excellent shape solidity and no change in crystallization properties compared to the pristine PEG8000. The results confirm the enormous potential of IPNs in a wide variety of phase change applications.

The stress relaxation behavior of acrylic-polyurethane (PU)-based graftinterpenetrating polymer networks (IPNs) was characterized via dynamic mechanical analysis (DMA) and modeled using finite element method (FEM) analysis. Stress relaxation of glassy IPN specimens was experimentally studied under flexural testing, while rubbery IPN specimens were tested in tension. The effects of varying the styrene content in the acrylic copolymer phase, compatibility of the two phases in IPNs, and changing the concentration of acrylic copolymer and PU were studied. A higher percentage of styrene content resulted in higher homogeneity of IPN specimens, and decrease in initial modulus for acrylic copolymer specimens. Additionally, glassy IPN specimens with 90% styrene shows resistance to relaxation as high as acrylic copolymer samples. Experimental results were used to develop a numerical model to study stress relaxation response of specimens. While polymer systems have been

Electroactive polymers that exhibit controlled deformation under an applied electric field, either in liquid or air, have great potential as soft robotic actuators. However, materials for soft robotics currently face challenges, including slow response, high actuation potential, and a lack of underlying mechanistic understanding. Additionally, fabrication of soft robotic actuators with complex design features has historically been restricted by two-dimensional fabrication methods. In this work, we investigate cross-linked poly­(acrylic acid)-based actuators prepared utilizing digital light projection (DLP), an additive manufacturing technique that enables fabrication of actuators with complex geometries. A series of photopolymerizable inks are prepared incorporating acrylic acid (monomer), trimethylolpropane trimethacrylate (cross-linker), and phenylbis­(2,4,6-trimethylbenzoyl)­phosphine oxide (photoinitiator). Soft actuators are 3D-printed utilizing a commercial DLP 3D printer operating under 405 nm UV light. These 3D-printed actuators exhibit large deformation (up to 43°), high actuation speed (up to 1.08°/s), and stable actuation performance for bending cycles under relatively low actuation voltage (4–6 V). Factors such as acrylic acid content, cross-linker concentration, actuator thicknesses, and electric field strength are varied, and their impact on the 3D-printed actuators are evaluated and discussed. Lastly, a membrane valve actuator is fabricated, and its ability to open and close under applied potential is demonstrated.

A library of polyester-based A(BA′) n asymmetric miktoarm star polymers was synthesized with A, A′ = poly(L-lactide) (PLLA) as the semicrystalline hard blocks and B = poly(4-methylcaprolactone) (PMCL) as the soft segment using a graftingthrough platform known as μSTAR. The synthetic versatility of μSTAR enabled a systematic investigation of architectural design parameters, in particular the number of BA′ arms (n), while holding the A, A′, and B block lengths constant. The value of n has a pronounced impact on the mechanical properties of these high-molecular-weight miktoarm materials. Tensile toughness increases with n, an effect likely related to bridging, as the modulus drops because the hard-block volume fraction decreases. These insights expand our understanding of architecture effects in sustainable thermoplastic elastomers.

Transparent materials with robust mechanical properties are essential for numerous applications and require careful manipulation of polymer chemistry. Here, polyurethane (PU) and acrylic-based copolymers out of styrene were utilized to synthesize transparent PU-acrylic graft-interpenetrating polymer networks (graft-IPNs) for the first time. In these materials, PU imparts greater flexibility, while the acrylic copolymer increases rigidity and glass transition temperature of the graft-IPNs. Kinetics of the graft-IPN synthesis was monitored using Fourier transform infrared spectroscopy and 1 H NMR spectroscopy through the conversion of the isocyanate group. System compatibility, degree of phase separation and material transparency were evaluated using transmission electron microscopy and UV-visible spectroscopy. Overall, higher compatibility is observed at a higher percentage of styrene in the acrylate copolymer. The thermomechanical properties of the IPNs were quantified using dynamic mechanical analysis to assess the effect of the acrylic copolymer content on fracture toughness of the resulting graft-IPNs. The high fracture toughness of the graft-IPNs, coupled with excellent transparency, demonstrates the potential of these systems for high-performance applications.