Taking a Tailored Approach to Material Design: A Mechanistic Study of the Selective Localization of Phase-Separated Graphene Microdomains

To achieve multifunctional properties using nanocomposites, selectively locating nanofillers in specific areas by tailoring a mixture of two immiscible polymers has been widely investigated. Forming a phase-separated structure from entirely miscible molecules is rarely reported, and the related mechanisms to govern the formation of assemblies from molecules have not been fully resolved. In this work, a novel method and the underlying mechanism to fabricate self-assembling, bicontinuous, biphasic structures with localized domains made up of amine-functionalized graphene nanoplatelets are presented, involving the tailoring of compositions in a liquid processable multicomponent epoxy blend. Kinetics studies were carried out to investigate the differences in reactivity of various epoxy-hardener pairs. Molecular dynamics simulations and in situ optical photothermal infrared spectroscopy measurements revealed the trajectories of different components during the early stages of polymerization, supporting the migration (phase behavior) of each component during the curing process. Confirmed by the phase structure and the correlated chemical maps down to the submicrometer level, it is believed that the bicontinuous phase separation is driven by the change of the miscibility between various building blocks forming during polymerization, leading to the formation of nanofiller domains. The proposed morphology evolution mechanism is based on combining solubility parameter calculations with kinetics studies, and preliminary experiments are performed to validate the applicability of the mechanism of selectively locating nanofillers in the phase-separated structure. This provides a simple yet sophisticated engineering model and a roadmap to a mechanism for fabricating phase-separated structures with nanofiller domains in nanocomposite films.

Interfacial energy as an approach to designing amphipathic surfaces during photopolymerization curing

Photopolymerization induced phase separation (PIPS) is a platform capable of creating heterogeneous materials from initially miscible resin solutions, where both the reaction's governing thermodynamics and kinetics significantly influence the resulting phase composition and morphology. Here, PIPS is used to develop materials in a single photopolymerization step that are hydrophobic on one face and hydrophilic on the other. These two faces possess a water contact angle difference of 50°, bridged by a bulk-scale chemical gradient. The impact of the PIPS-triggering inert additive is investigated by increasing the loading of poly(methyl methacrylate) (PMMA) in an acrylonitrile/1,6-hexanediol diacrylate comonomer resin. The extent of phase separation in the sample network depends on this loading, with increasing PMMA corresponding to macroscale domains that are more chemically and mechanically distinct. A significant period between the onsets of phase separation and reaction deceleration, determined using in situ FT-IR, facilitates this enhanced phase segregation in PMMA-modified samples. Spatially directed domain formation can be further promoted using multiple interface types in the sample mold, here, glass and stainless steel. With multiple interface types, interfacial rearrangements to minimize surface energy during resin photopolymerization result in a hydrophobic face that is nitrile-rich and a hydrophilic face that is nitrile-poor (e.g., acrylate-rich). Using this strategy, patterned wettability on a single face can also be engineered. This study illustrates the capabilities of PIPS for complex surface design and in applications requiring stark differences in surface character without sharp interfaces.

Review on the Accelerated and Low-Temperature Polymerization of Benzoxazine Resins: Addition Polymerizable Sustainable Polymers

Due to their outstanding and versatile properties, polybenzoxazines have quickly occupied a great niche of applications. Developing the ability to polymerize benzoxazine resin at lower temperatures than the current capability is essential in taking advantage of these exceptional properties and remains to be most challenging subject in the field. The current review is classified into several parts to achieve this goal. In this review, fundamentals on the synthesis and evolution of structure, which led to classification of PBz in different generations, are discussed. Classifications of PBzs are defined depending on building block as well as how structure is evolved and property obtained. Progress on the utility of biobased feedstocks from various bio-/waste-mass is also discussed and compared, wherever possible. The second part of review discusses the probable polymerization mechanism proposed for the ring-opening reactions. This is complementary to the third section, where the effect of catalysts/initiators has on triggering polymerization at low temperature is discussed extensively. The role of additional functionalities in influencing the temperature of polymerization is also discussed. There has been a shift in paradigm beyond the lowering of ring-opening polymerization (ROP) temperature and other areas of interest, such as adaptation of molecular functionality with simultaneous improvement of properties.

PU/PMMA composites synthesized by reaction-induced phase separation: a general approach to achieve a shape memory effect

We report a study on the triple-shape memory polymer composition of polyurethane/polymethyl methacrylate (PU/PMMA) synthesized using reaction-induced phase separation.

Modification of benzoxazine with aryl-ether-ether-ketone diphenol: preparation and characterization

A modified benzoxazine resin system with “high strength, high modulus and high toughness” was prepared by introducing an efficient modifier (m-DHPBP) with high catalytic activity and an aryl-ether-ether-ketone (PEEK) structure.

A novel benzoxazine/cyanate ester blend with sea-island phase structures

A novel C-BOZ/BADCy blend with sea-island phase structures was successfully prepared via reaction-induced phase separation.