Modified Breath Figure Methods for the Pore-Selective Functionalization of Honeycomb-Patterned Porous Polymer Films

Recent developments in the field of the breath figure (BF) method have led to renewed interest from researchers in the pore-selective functionalization of honeycomb-patterned (HCP) films. The pore-selective functionalization of the HCP film gives unique properties to the film which can be used for specific applications such as protein recognition, catalysis, selective cell culturing, and drug delivery. There are several comprehensive reviews available for the pore-selective functionalization by the self-assembly process. However, considerable progress in preparation technologies and incorporation of new materials inside the pore surface for exact applications have emerged, thus warranting a review. In this review, we have focused on the pore-selective functionalization of the HCP films by the modified BF method, in which the self-assembly process is accompanied by an interfacial reaction. We review the importance of pore-selective functionalization, its applications, present limitations, and future perspectives.

Steric Hindrance Drives the Boron-Initiated Polymerization of Dienyltriphenylarsonium Ylides to Photoluminescent C5-Polymers

A series of alkyl-subsituted dienyltriphenylarsonium ylides were synthesized and used as monomers in borane-initiated polymerization to obtain practically pure C5-polymers (main-chain grows by five carbon atoms at a time). The impact of triethylborane (Et3 B), tributylborane (Bu3 B), tri-sec-butylborane (s-Bu3 B), and triphenylborane (Ph3 B) initiators on C5 polymerization was studied. Based on NMR and SEC results, we have shown that all synthesized polymers have C5 units with a unique unsaturated backbone where two conjugated double bonds are separated by one methylene. The synthesized C5-polymers possess predictable molecular weights and narrow molecular weight distributions (Mn,NMR =2.8 -11.9 kg mol-1 , Ð=1.04-1.24). It has been found that increasing the steric hindrance of both the monomer and the initiator can facilitate the formation of more C5 repeating units, thus driving the polymerization to almost pure C5-polymer (up to 95.8 %). The polymerization mechanism was studied by 11 B NMR and confirmed by DFT calculations. The synthesized C5-polymers are amorphous with tunable glass-transition temperatures by adjusting the substituents of monomers, ranging from +30.1 °C to -38.4 °C. Furthermore, they possess blue photoluminescence that changes to yellow illuminating the polymers for 5 days with UV radiation of 365 nm (IIE, isomerization induced emission).

Boron-Catalyzed Polymerization of Dienyltriphenylarsonium Ylides: On the Way to Pure C5 Polymerization

The first C5 polymerization is reported, where the main-chain is growing by five carbon atoms of the monomer at a time. Three dienyltriphenylarsonium ylide monomers were synthesized and polymerized with triethylborane as an initiator, leading to random terpolymers (C1, C3, C5) with mainly C5 repeating units (up to 84.1 %). It has been found that the methyl group (electron-donating substituent) on the conjugated double bond of the ylides facilitates the formation of C5 segments. A mechanism was proposed based on NMR characterization and DFT calculations. The high C5 content ensures that things are on the right track for pure C5 homopolymerization.

Terpolymers from Borane-Initiated Copolymerization of Triphenyl Arsonium and Sulfoxonium Ylides: An Unexpected Light Emission

The first synthesis of well-defined poly[(phenylmethylene-co-methylpropenylene)-b-methylene, [(C1-co-C3)-b-C1], terpolymers was achieved by one-pot borane-initiated random copolymerization of ω-methylallyl (C3 units, chain is growing by three carbon atoms at a time) and benzyltriphenylarsonium (C1 units, chain is growing by one carbon atom at a time) ylides, followed by polymerization of sulfoxonium methylide (C1 units). Other substituted arsonium ylides, such as prenyltriphenyl, propyltriphenyl and (4-fluorobenzyl)triphenyl can also be used instead of benzyltriphenylarsonium. The obtained terpolymers are well-defined, possess a predictable molecular weight and low polydispersity (Mn,NMR =1.83-9.68×103  g mol-1 , Đ=1.09-1.22). An unexpected light emission phenomenon was discovered in these non-conjugated terpolymers, as confirmed by fluorescence and NMR spectroscopy. This phenomenon can be explained by the isomerization of the double bonds of allylic monomeric units along the chain of the terpolymers (isomerization-induced light emission).

Synthesis of novel guanidine-based ABA triblock copolymers and their antimicrobial honeycomb films

Novel antimicrobial poly(methacryl guanidine hydrochloride)-block-polystyrene-block-poly(methacryl guanidine hydrochloride) triblock copolymers were synthesizedviaRAFT polymerization and fabricated into antimicrobial honeycomb films.

Dry Etching with Nanoparticles: Formation of High Aspect-Ratio Pores and Channels Using Magnetic Gold Nanoclusters

Methods for generating nanopores in substrates typically involve one or more wet-etching steps. Here a fundamentally different approach to produce nanopores in sheet substrates under dry, ambient conditions, using nanosecond-pulsed laser irradiation and magnetic gold nanoclusters (MGNCs) as the etching agents is described. Thermoplastic films (50-75 µm thickness) are coated with MGNCs then exposed to laser pulses with a coaxial magnetic field gradient, resulting in high-aspect ratio channels with tapered cross sections as characterized by confocal fluorescence tomography. The dry-etching process is applicable to a wide variety of substrates ranging from fluoropolymers to borosilicate glass, with etch rates in excess of 1 µm s^-1 . Finite-element modeling suggests that the absorption of laser pulses by MGNCs can produce temperature spikes of nearly 1000 °C, which is sufficient for generating photoacoustic responses that can drive particles into the medium, guided by magnetomotive force.

Supramolecular Host-Guest Interaction-Enhanced Adjustable Drug Release Based on β-Cyclodextrin-Functionalized Thermoresponsive Porous Polymer Films

Drug delivery systems based on stimuli-responsive porous polymer films (PPFs) have been extensively investigated because of their many advantages. However, the ability to adjust the drug release from PPFs is not always perfect, and at times, it cannot satisfy real-world requirements. In this paper, supramolecular host-guest interactions were harnessed to overcome the difficulties associated with adjustable release from these systems by incorporating host molecules into the pore walls of thermoresponsive PPFs. β-Cyclodextrin-functionalized porous amphiphilic block copolymer films (β-CD-PBCPFs) with controllable pore parameters, high homogeneity, and large areas were prepared by combining the self-assembly and breath-figure methods. Drug-loaded β-CD-PBCPFs displayed thermoresponsive release behavior, which could be tuned by increasing the β-CD content in phosphate-buffered saline. The release was governed by the host-guest interactions of the β-CD moieties and drug molecules. The concept of host-guest interaction-enhanced adjustable release could be applied to different drug molecules, such as doxorubicin and metronidazole.

Well-defined triblock copolymers of polyethylene with polycaprolactone or polystyrene using a novel difunctional polyhomologation initiator

α,ω-Dihydroxy polyethylene, valuable precursor for the synthesis of polyethylene-based terpolymers with polar blocks, was synthesized by polyhomologation of dimethylsulfoxonium methylide with 9-thexyl-9-BBN, a novel difunctional initiator with two active and one blocked sites.

C1 polymerization: a unique tool towards polyethylene-based complex macromolecular architectures

The recent developments in organoborane initiated C1 polymerization of ylides open unique horizons towards perfectly linear polymethylenes (equivalent to PE) and PE-based complex structures. This review summarizes research on conventional and newly discovered initiators/ylides, as well as initial efforts on C3 polymerization.

Allyl borates: a novel class of polyhomologation initiators

Allyl borates, a new class of monofunctional polyhomologation initiators, are reported. Upon increasing the ratio [ylide]/[B] the PM molecular weight increases correspondingly. The initiation mechanism was elucidated by¹H and¹¹B NMR.

Boron-Catalyzed C3-Polymerization of ω-2-Methyl Allylarsonium Ylide and Its C3/C1 Copolymers with Dimethylsulfoxonium Methylide

A novel arsonium ylide, ω-2-methylallylarsonium ylide, was synthesized and used as monomer for polyhomologation with triethyborane as initiator. It was found that the terminal methyl group leads to C3 polymerization. Furthermore, the copolyhomologation of arsonium ylide with dimethylsulfoxonium methylide is reported for the first time.

New synthetic strategy targeting well-defined α,ω-telechelic polymethylenes with hetero bi-/tri-functionalities via polyhomologation of ylides initiated by new organic boranes based on catecholborane and post functionalization

Diverse well-defined α,ω-telechelic polymethylenes with hetero bi-/tri-functionalities were synthesized by a tandem strategy combining polyhomologation with post functionalization using end-capping reagents and esterification.

Well-defined 4-arm stars with hydroxy-terminated polyethylene, polyethylene-b-polycaprolactone and polyethylene-b-(polymethyl methacrylate)2 arms

Bis-boron-thexyl-silaboracycle was used to initiate the polyhomologation of dimethylsulfoxonium methylide to afford well-defined hydroxy-terminated 4-arm polyethylene (PE) stars, which served as precursors for the synthesis of PE-based starblock copolymers.

Synthesis of well-defined α-fluorinated alkyl ester, ω-carboxyltelechelic polystyrenes and fabrication of their hydrophobic highly ordered porous films and microspheres

Porous films and microspheres of α-fluorinated alkyl ester, ω-carboxyl telechelic polystyrenes synthesized via combining aminolysis of RAFT-polystyrene with thiol–ene “click” reaction.

Polyhomologation based on in situ generated boron-thexyl-silaboracyclic initiating sites: a novel strategy towards the synthesis of polyethylene-based complex architectures

Polyhomologation of dimethylsulfoxonium methylide using the in situ generated boron-thexyl-silaboracyclic initiating sites allows the synthesis of polyethylene-based complex macromolecular architectures.

Cooling-induced formation of honeycomb patterns on pre-cast PMMA films at low temperatures

Surface patterns formed on pre-cast PMMA films. A typical AFM image shows the hexagon network.

New polymethylene-based AB2 star copolymers synthesized via a combination of polyhomologation of ylides and atom transfer radical polymerization

Polymethylene-based AB₂ star copolymers were synthesized. PM-b-(PS)₂ porous films and particles were fabricated via static breath-figure process and electrospraying, respectively.

Multiple interfaces in self-assembled breath figures

Progress in the breath figure method is reviewed by emphasizing the role of the multiple interfaces and the applications of honeycomb films in separation, biocatalysis, biosensing, templating, stimuli-responsive surfaces and adhesive surfaces.

Synthesis of amphiphilic diblock copolymers derived from renewable dextran by nitroxide mediated polymerization: towards hierarchically structured honeycomb porous films

A novel dextran-SG1 macro-alkoxyamine was designed to afford amphiphilic linear block copolymers synthesized by nitroxide mediated polymerization toward the formation of hierarchically structured bio-resourced honeycomb films.

Honeycomb films of cellulose azide: molecular structure and formation of porous films

Development of value-added micropatterned porous materials from naturally abundant polymers, such as cellulose, are of growing interest. In this paper, regioselectively modified amphiphilic cellulose azide, 3-O-azidopropoxypoly(ethylene glycol)-2,6-di-O-thexyldimethylsilyl cellulose, with different degrees of substitution (DS) and degrees of polymerization (DP) of the poly(ethylene glycol) (PEG) side chain, was synthesized and employed in the formation of honeycomb-patterned films. With the variation of the DP and/or DS, the amphiphilicity of the polymer and the pore size of the formed films changed accordingly. It was found that amphiphilicity of the cellulose azide played a significant role in the formation of honeycomb films. Balanced amphiphilicity was of particular importance in the formation of uniform honeycomb films. Via the Cu(I)-catalyzed alkyne-azide [2 + 3] cycloaddition reaction, fluorescent avidin and quantum dots were attached to the films. By means of confocal microscopy, it was confirmed that the functional azido group was preferentially allocated inside the pores. This provides a platform for the development of advanced honeycomb materials with site-specific functionalities, such as biosensors.

Polyhomologation. A living C1 polymerization

The physical properties of synthetic macromolecules are strongly coupled to their molecular weight (MW), topology, and polydispersity index (PDI). Factors that contribute to their utility include the control of functionality at the macromolecule termini and copolymer composition. Conventional polymerization reactions that produce carbon backbone polymers (ionic, free radical, and coordination) provide little opportunity for controlling these variables. Living polymerizations, sometimes referred to as controlled polymerizations, have provided the means for achieving these goals. Not surprisingly, these reactions have had a profound impact on polymer and materials science. Three basic reaction types are used for the synthesis of most carbon backbone polymers. The first examples of "living" polymerizations were developed for ionic polymerizations (cationic and anionic). These reactions, which can be technically challenging to perform, can yield excellent control of molecular weight with very low polydispersity. The second reaction type, free radical polymerization, is one of the most widely used polymerizations for the commercial production of high molecular weight carbon backbone polymers. Nitroxide mediated polymerization (NMP), reversible addition-fragmentation chain transfer polymerization (RAFT), and atom transfer radical polymerization (ATRP) have emerged as three of the more successful approaches for controlling these reactions. The third type, transition metal mediated coordination polymerization, is the most important method for large-scale commercial polyolefin production. Simple nonfunctional hydrocarbon polymers such as polyethylene (PE), polypropylene, poly-α-olefins, and their copolymers are synthesized by high pressure-high temperature free radical polymerization, Ziegler-Natta or metallocene catalysts. Although these catalysts of exceptional efficiency that produce polymers on a huge scale are in common use, control that approaches a "living polymerization" is rare. Although the controlled synthesis of linear "polyethylene" described in this Account is not competitive with existing commercial processes for bulk polymer production, they can provide quantities of specialized materials for the study of structure-property relationships. This information can guide the production of polymers for new commercial applications. We initiated a search for novel polymerization reactions that would produce simple hydrocarbon polymers with the potential for molecular weight and topological control. Our research focused on polymerization reactions that employ nonolefin monomers, more specifically the polymerization of ylides and diazoalkanes. In this reaction, the carbon backbone is built one carbon at a time (C1 polymerization). These studies draw upon earlier investigations of the Lewis acid catalyzed polymerization of diazoalkanes and build upon our discovery of the trialkylborane initiated living polymerization of dimethylsulfoxonium methylide 1.