Synthetic Polypeptide–Polyester PolyHIPEs Prepared by Thiol–Ene Photopolymerization

Mechanism of Interconnected Pore Formation in High Internal Phase Emulsion-Templated Polymer

High internal phase emulsion-templated polymer, named polyHIPE, has received widespread attention due to its great potential applications in many fields, such as separation, adsorption, heterogeneous catalysis, and sound absorption. The broad applicability is largely dependent on its adjustable opening structure. However, the question of why polyHIPE has an interconnected pore network structure is still to be discussed. Herein, different types (w/o, o/w, and o/o) of HIPEs are prepared and subsequently detected with laser scanning confocal microscopy (LSCM), and the polyHIPEs obtained by curing the HIPEs are characterized by SEM. The observations suggest that the interconnected pore formation is primarily due to the presence of the surfactant-rich phase in the film between the neighboring droplets in HIPE. The interconnected pores are generated by removal of the surfactant-rich domains in the postcuring procedure, and their sizes would be enlarged if the solubility of the surfactant in the continuous phase decreases in the curing stage.

Effects of Secondary Structures and pH on the Self-Assembly of Poly(ethylene glycol)-b-polytyrosine

Different from conventional synthetic polymers, polypeptides exhibit a distinguishing characteristic of adopting specific secondary structures, including random coils, α-helixes, and β-sheets. The conformation determines the rigidity and solubility of polypeptide chains, which further direct the self-assembly and morphology of the nanostructures. We studied the effect of distinct secondary structures on the self-assembly behavior of polytyrosine (PTyr)-derived amphiphilic copolymers. Two block copolymers of enantiopure poly(ethylene glycol)-b-poly(l-tyrosine) (PEG-b-P(l-Tyr)) and racemic poly(ethylene glycol)-b-poly(dl-tyrosine) (PEG-b-P(dl-Tyr)) were synthesized through the ring-opening polymerization of l-tyrosine N-thiocarboxyanhydride (l-Tyr-NTA) and dl-tyrosine N-thiocarboxyanhydride (dl-Tyr-NTA), respectively, by using poly(ethylene glycol) amine as the initiator. PEG44-b-P(l-Tyr)10 adopts a β-sheet conformation and self-assembles into rectangular nanosheets in aqueous solutions, while PEG44-b-P(dl-Tyr)9 is primarily in a random coil conformation with a tiny content of β-sheet structures, which self-assembles into sheaf-like nanofibrils. A pH increase results in the ionization of phenolic hydroxyl groups, which decreases the β-sheet content and increases the random coil content of the PTyr segments. Accordingly, PEG44-b-P(l-Tyr)10 and PEG44-b-P(dl-Tyr)9 self-assemble to form slender nanobelts and twisted nanoribbons, respectively, in alkaline aqueous solutions. The secondary structure-driven self-assembly of PTyr-derived copolymers is promising to construct filamentous nanostructures, which have potential for applications in controlled drug release.

Unique Crystallization Characteristics of Pickering High Internal Phase Emulsion Templated Porous Constructs

To study the crystallization behavior of polymeric chains under the influence of porosity, the thermal properties of various nonporous and porous poly(ε-caprolactone) (PCL) based constructs were investigated. Porous cross-linked PCL nanocomposite constructs were fabricated utilizing in situ polymerization of CL-based surfactant-free Pickering high internal phase emulsions (HIPEs), stabilized using modified fumed silica nanoparticles (mSiNP) at a minimal concentration of 0.6 wt %. The corresponding nanocomposite constructs exhibited polyhedral pore morphology with significant pore roughness due to the presence of mSiNP. DSC thermograms of nonporous constructs illustrated diminished crystallization temperature and kinetics upon cross-linking and inclusion of mSiNP which confirmed suppressed mobility of polymer chains. Further introduction of porosity led to substantial supercooling, resulting in crystallization temperatures as low as -24 °C. Changes in the crystal structure of various nonporous and porous constructs were also studied using XRD. The crystallization behavior of porous constructs was finally evaluated using Jeziorny, Ozawa, and Mo theories under nonisothermal conditions. Significant deviation from the theoretical model, as observed in the case of porous constructs, implied a complex crystallization mechanism that eventually was not only controlled by the chain immobility due to cross-linking but also heterogeneity present in the wall thickness of the constructs. The unique melting-crystallization phenomenon observed in such constructs may further be expanded to other systems of high heat capacity for utilization as energy storage materials.

Polyurethane/n-Octadecane Phase-Change Microcapsules via Emulsion Interfacial Polymerization: The Effect of Paraffin Loading on Capsule Shell Formation and Latent Heat Storage Properties

Organic phase-change materials (PCMs) hold promise in developing advanced thermoregulation and responsive energy systems owing to their high latent heat capacity and thermal reliability. However, organic PCMs are prone to leakages in the liquid state and, thus, are hardly applicable in their pristine form. Herein, we encapsulated organic PCM n-Octadecane into polyurethane capsules via polymerization of commercially available polymethylene polyphenylene isocyanate and polyethylene glycol at the interface oil-in-water emulsion and studied how various n-Octadecane feeding affected the shell formation, capsule structure, and latent heat storage properties. The successful shell polymerization and encapsulation of n-Octadecane dissolved in the oil core was verified by confocal microscopy and Fourier-transform infrared spectroscopy. The mean capsule size varied from 9.4 to 16.7 µm while the shell was found to reduce in thickness from 460 to 220 nm as the n-Octadecane feeding increased. Conversely, the latent heat storage capacity increased from 50 to 132 J/g corresponding to the growth in actual n-Octadecane content from 25% to 67% as revealed by differential scanning calorimetry. The actual n-Octadecane content increased non-linearly along with the n-Octadecane feeding and reached a plateau at 66-67% corresponded to 3.44-3.69 core-to-monomer ratio. Finally, the capsules with the reasonable combination of structural and thermal properties were evaluated as a thermoregulating additive to a commercially available paint.

Synthesis of Polymer Nanoweb via a Lipid Template

We report a generalized platform for synthesizing a polymer nanoweb with a high specific surface area via a bicellar template, composed of 1,2-dipalmitoyl phosphocholine (DPPC), 1,2-dihexanoyl phosphocholine (DHPC), and 1,2-dipalmitoyl phosphoglycerol (DPPG). The pristine bicelle (in the absence of monomer or polymer) yields a variety of well-defined structures, including disc, vesicle, and perforated lamella. The addition of styrene monomers in the mixture causes bicelles to transform into lamellae. Monomers are miscible with DPPC and DPPG initially, while polymerization drives polymers to the DHPC-rich domain, resulting in a polymer nanoweb supported by the outcomes of small angle neutron scattering, differential scanning calorimetry, and transmission electron microscopy.

Synthesis and Applications of Elastomeric Polymerized High Internal Phase Emulsions (PolyHIPEs)

Polymer foams (PFs) are among the most industrially produced polymeric materials, and they are found in applications including aerospace, packaging, textiles, and biomaterials. PFs are predominantly prepared using gas-blowing techniques, but PFs can also be prepared from templating techniques such as polymerized high internal phase emulsions (polyHIPEs). PolyHIPEs have many experimental design variables which control the physical, mechanical, and chemical properties of the resulting PFs. Both rigid and elastic polyHIPEs can be prepared, but while elastomeric polyHIPEs are less commonly reported than hard polyHIPEs, elastomeric polyHIPEs are instrumental in the realization of new materials in applications including flexible separation membranes, energy storage in soft robotics, and 3D-printed soft tissue engineering scaffolds. Furthermore, there are few limitations to the types of polymers and polymerization methods that have been used to prepare elastic polyHIPEs due to the wide range of polymerization conditions that are compatible with the polyHIPE method. In this review, an overview of the chemistry used to prepare elastic polyHIPEs from early reports to modern polymerization methods is provided, focusing on the applications that flexible polyHIPEs are used in. The review consists of four sections organized around polymer classes used in the preparation of polyHIPEs: (meth)acrylics and (meth)acrylamides, silicones, polyesters and polyurethanes, and naturally occurring polymers. Within each section, the common properties, current challenges, and an outlook is suggested on where elastomeric polyHIPEs can be expected to continue to make broad, positive impacts on materials and technology for the future.