Effects of crosslinker on the morphology and properties of microgels containing N-vinylformamide, glycidylmethacrylate and vinylamine

AbstractMicrogels are swollen crosslinked polymer colloid particles. We used non-aqueous dispersion polymerisation to prepare new water-swellable microgels containing N-vinylformamide (NVF), glycidylmethacrylate (GMA) and an alkali-stable crosslinker, 2-(N-vinylformamido)ethyl ether (NVE). The microgel particles had a core that was rich in NVF. The shell contained GMA and NVF. In order to expose the amine functionality, alkaline hydrolysis was used, transforming the NVF groups in the shell to vinylamine (VAM) while leaving most NVF in the core untouched. The hydrolysed microgels (H-NVF–GMA–NVE) were cationic at low pH and were shown to have polyampholyte behaviour. Inclusion of NVE had the beneficial effects of preventing microphase separation at the microgel surface and stabilising the polyampholyte structure against excessive fragmentation during hydrolysis. These new water-swellable core–shell microgels were prepared using scalable methods and may enable future preparation of functionalised core–shell microgels and composites

One-Step Preparation of Uniform Cane-Ball Shaped Water-Swellable Microgels Containing Poly(N-vinyl formamide)

In this study we report the preparation of a new family of core shell microgels that are water-swellable and have a morphology that is controllable by particle composition. Here, nearly monodisperse core shell PNVF-xGMA [poly(N-vinylformamide-co-glycidyl methacrylate)] particles (where x is the weight fraction of GMA used) were prepared via nonaqueous dispersion (NAD) polymerization in one step. The shells were PGMA-rich and were cross-linked by reaction of epoxide groups (from GMA) with amide groups (from NVF). The core of the particles was PNVF-rich. A bifunctional cross-linking monomer was not required to prepare these new microgels. The particles had a remarkable "cane-ball"-like morphology with interconnected ridges, and this could be controlled by the value for x. The particle size was tunable over the range 0.8-1.8 mu m Alkaline hydrolysis was used to hydrolyze the PNVF segments to poly(vinylamine), PVAM. The high swelling pressure of the cationic cores caused shell fragmentation and release of some of the core polymer when the hydrolyzed particles were dispersed in pure water. The extent to which this occurred was controllable by x. Remarkably, the PGMA-rich shells could be detached from the hydrolyzed particles by dispersion in water followed by drying. The hydrolyzed PNVF-0.4GMA particles contained both positively and negatively charged regions and the dispersions appeared to exhibit charge-patch aggregation at low ionic strengths. The new cross-linking strategy used here to prepare the PNVF-xGMA particles should be generally applicable for amide-containing monomers and may enable the preparation of a range of new water-swellable microgels

Highly Ordered Thermoplastic Polyurethane/Aramid Nanofiber Conductive Foams Modulated by Kevlar Polyanion for Piezoresistive Sensing and Electromagnetic Interference Shielding

Abstract Highly ordered and uniformly porous structure of conductive foams is a vital issue for various functional purposes such as piezoresistive sensing and electromagnetic interference (EMI) shielding. With the aids of Kevlar polyanionic chains, thermoplastic polyurethane (TPU) foams reinforced by aramid nanofibers (ANF) with adjustable pore-size distribution were successfully obtained via a non-solvent-induced phase separation. In this regard, the most outstanding result is the in situ formation of ANF in TPU foams after protonation of Kevlar polyanion during the NIPS process. Furthermore, in situ growth of copper nanoparticles (Cu NPs) on TPU/ANF foams was performed according to the electroless deposition by using the tiny amount of pre-blended Ti3C2Tx MXene as reducing agents. Particularly, the existence of Cu NPs layers significantly promoted the storage modulus in 2,932% increments, and the well-designed TPU/ANF/Ti3C2Tx MXene (PAM-Cu) composite foams showed distinguished compressive cycle stability. Taking virtues of the highly ordered and elastic porous architectures, the PAM-Cu foams were utilized as piezoresistive sensor exhibiting board compressive interval of 0–344.5 kPa (50% strain) with good sensitivity at 0.46 kPa−1. Meanwhile, the PAM-Cu foams displayed remarkable EMI shielding effectiveness at 79.09 dB in X band. This work provides an ideal strategy to fabricate highly ordered TPU foams with outstanding elastic recovery and excellent EMI shielding performance, which can be used as a promising candidate in integration of satisfactory piezoresistive sensor and EMI shielding applications for human–machine interfaces. Graphical Abstrac

One-Step Preparation of Uniform Cane-Ball Shaped Water-Swellable Microgels Containing Poly(<i>N</i>-vinyl formamide)

In this study we report the preparation of a new family of core–shell microgels that are water-swellable and have a morphology that is controllable by particle composition. Here, nearly monodisperse core–shell PNVF-<i>x</i>GMA [poly­(<i>N</i>-vinylformamide-<i>co</i>-glycidyl methacrylate)] particles (where <i>x</i> is the weight fraction of GMA used) were prepared via nonaqueous dispersion (NAD) polymerization in one step. The shells were PGMA-rich and were cross-linked by reaction of epoxide groups (from GMA) with amide groups (from NVF). The core of the particles was PNVF-rich. A bifunctional cross-linking monomer was not required to prepare these new microgels. The particles had a remarkable “cane-ball”-like morphology with interconnected ridges, and this could be controlled by the value for <i>x</i>. The particle size was tunable over the range 0.8–1.8 μm. Alkaline hydrolysis was used to hydrolyze the PNVF segments to poly­(vinylamine), PVAM. The high swelling pressure of the cationic cores caused shell fragmentation and release of some of the core polymer when the hydrolyzed particles were dispersed in pure water. The extent to which this occurred was controllable by <i>x</i>. Remarkably, the PGMA-rich shells could be detached from the hydrolyzed particles by dispersion in water followed by drying. The hydrolyzed PNVF-0.4GMA particles contained both positively and negatively charged regions and the dispersions appeared to exhibit charge-patch aggregation at low ionic strengths. The new cross-linking strategy used here to prepare the PNVF-<i>x</i>GMA particles should be generally applicable for amide-containing monomers and may enable the preparation of a range of new water-swellable microgels

Hollow Colloidosomes Prepared Using Accelerated Solvent Evaporation

We demonstrate a new, scalable, simple, and generally applicable two-step method to prepare hollow colloidosomes. First, a high volume fraction oil-in-water emulsion was prepared. The oil phase consisted of CH₂Cl₂ containing a hydrophobic structural polymer, such as polycaprolactone (PCL) or polystyrene (PS), which was fed into the water phase. The water phase contained poly­(vinylalcohol), poly­(<i>N</i>-isopropylacrylamide), or a range of cationic graft copolymer surfactants. The emulsion was rotary evaporated to rapidly remove CH₂Cl₂. This caused precipitation of PCL or PS particles which became kinetically trapped at the periphery of the droplets and formed the shell of the hollow colloidosomes. Interestingly, the PCL colloidosomes were birefringent. The colloidosome yield increased and the polydispersity decreased when the preparation scale was increased. One example colloidosome system consisted of hollow PCL colloidosomes stabilized by PVA. This system should have potential biomaterial applications due to the known biocompatibility of PCL and PVA

Poly(vinylamine) microgels : pH-responsive particles with high primary amine contents

pH-responsive microgels are crosslinked polymer colloid particles that swell when the pH approaches the pK(a) of the polybase or polyacid chains. Poly(vinylamine) (PVAM) has the highest primary amine content of all amine-containing polymers. Despite much effort the preparation of colloidally stable PVAM microgels is still elusive. Here, we introduce a simple and scalable, two-step method for preparation of pH-responsive PVAM microgels. First, non-aqueous dispersion (NAD) polymerization was used to prepare new monodisperse water-swellable poly(N-vinylformamide-co-2-(N-vinylformamido) ethyl ether microgels (PNVF-xNVEE). Here, x is the mol% of the alkali-stable crosslinker (NVEE) used. Alkali-hydrolysis of the PNVF-xNVEE microgels in water gave colloidally stable poly(vinylamine-co-bis(ethyl vinylamine)ether) (PVAM-xBEVAME) microgel dispersions. SEM images showed that both the PNVF-9NVEE and PVAM-9BEVAME microgel particles had cluster-like morphologies. The PVAM-xBEVAME particles were positively charged at pH values less than 12. The hydrodynamic diameters and electrophoretic mobilities increased strongly as the pH decreased. In order to demonstrate that primary amines could be used as chemical handles for conjugation, pyrene carboxylic acid was coupled using N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide (EDC) chemistry and its presence confirmed by fluorescence microscopy. Because this new family of colloidally stable microgels has very high primary amine contents and was prepared by a scalable synthetic method there should be potential applications in a wide range of areas from surface coatings and new hybrid particles to delivery