Controlling Volume Shrinkage in Soft Lithography through Heat-Induced Cross-Linking of Patterned Nanofibers

Self-polymerization of Meldrum's acid-amine compounds: an effective route to polyamides

Meldrum's acid-amine compounds are effective monomers for the synthesis of linear and hyperbranched polyamides in a short reaction time under mild reaction conditions.

Self-crosslinkable polymers from furan-functionalized Meldrum's acid and maleimides as effective precursors of free-standing and flexible crosslinked polymer films showing low dielectric constants

The integration of Michael addition and Diels–Alder reaction in the synthesis of reactive polymers for self-standing and flexible crosslinked polymer films.

Polymerization of Meldrum's Acid and Diisocyanate: An Effective Approach for Preparation of Reactive Polyamides and Polyurethanes

Meldrum's acid (MA) is utilized as a monomer to polymerize with diisocyanates to result in polyamides, containing MA moieties at polymer chains. This reaction is also employed to prepare isocyanate-terminated polyamide segments which are utilized as a precursor for preparation of MA-containing polyurethanes. Based on the thermolysis reaction of MA groups, followed by ketene dimerization reaction, the reactive polyamides and polyurethanes show self-cross-linkable features. The cross-linked polyurethanes exhibit good film formability, thermal stability, and mechanical properties. A new MA-based polymerization method and a novel synthesis route for preparation of reactive polyamides and polyurethanes are demonstrated.

The Michael addition reaction of Meldrum's acid (MA): an effective route for the preparation of reactive precursors for MA-based thermosetting resins

Reactive monomers and polymers possessing Meldrum's acid groups from the Michael addition reaction are demonstrated.

Cyclopolymerizations: Synthetic Tools for the Precision Synthesis of Macromolecular Architectures

Monomers possessing two functionalities suitable for polymerization are often designed and utilized in syntheses directed to the formation of cross-linked macromolecules. In this review, we give an account of recent developments related to the use of such monomers in cyclopolymerization processes, in order to form linear, soluble macromolecules. These processes can be activated by means of radical, ionic, or transition-metal mediated chain-growth polymerization mechanisms, to achieve cyclic moieties of variable ring size which are embedded within the polymer backbone, driving and tuning peculiar physical properties of the resulting macromolecules. The two functionalities are covalently linked by a "tether", which can be appropriately designed in order to "imprint" elements of chemical information into the polymer backbone during the synthesis and, in some cases, be removed by postpolymerization reactions. The two functionalities can possess identical or even very different reactivities toward the polymerization mechanism involved; in the latter case, consequences and outcomes related to the sequence-controlled, precision synthesis of macromolecules have been demonstrated. Recent advances in new initiating systems and polymerization catalysts enabled the precision syntheses of polymers with regulated cyclic structures by highly regio- and/or stereoselective cyclopolymerization. Cyclopolymerizations involving double cyclization, ring-opening, or isomerization have been also developed, generating unique repeating structures, which can hardly be obtained by conventional polymerization methods.

Effective Synthesis Route for Linear and Cross-Linked Biodegradable Polyesters Using Aliphatic Meldrum's Acid Derivatives as Monomers

On the basis of the reaction between ketene and alcohol groups to result in an ester linkage and Meldrum's acid as an effective precursor of ketene group, a bifunctional aliphatic Meldrum's acid compound (BisMA) is synthesized and used as a monomer to react with ethylene glycol and glycerol for the preparation of linear and cross-linked aliphatic polyesters, respectively. A 62 and 35 wt % of biodegradation fraction have been recorded on the linear and cross-linked aliphatic polyesters after an 8 week biodegradation test, respectively, to demonstrate the good biodegradability of the synthesized polyesters. In addition to conventional linear biodegradable polyesters, this synthetic route also provides a new and convenient method for preparation of cross-linked biodegradable polyesters. The types of the required monomers and reaction methods for preparation of the cross-linked biodegradable polyesters are similar to those used for conventional thermosetting resins. An integration of biodegradable polymers and thermosetting resins in polymer chemistry has been demonstrated.

Fabrication of Silicon Nanobelts and Nanopillars by Soft Lithography for Hydrophobic and Hydrophilic Photonic Surfaces

Soft lithography allows for the simple and low-cost fabrication of nanopatterns with different shapes and sizes over large areas. However, the resolution and the aspect ratio of the nanostructures fabricated by soft lithography are limited by the depth and the physical properties of the stamp. In this work, silicon nanobelts and nanostructures were achieved by combining soft nanolithography patterning with optimized reactive ion etching (RIE) in silicon. Using polymethylmethacrylate (PMMA) nanopatterned layers with thicknesses ranging between 14 and 50 nm, we obtained silicon nanobelts in areas of square centimeters with aspect ratios up to ~1.6 and linewidths of 225 nm. The soft lithographic process was assisted by a thin film of SiO_x (less than 15 nm) used as a hard mask and RIE. This simple patterning method was also used to fabricate 2D nanostructures (nanopillars) with aspect ratios of ~2.7 and diameters of ~200 nm. We demonstrate that large areas patterned with silicon nanobelts exhibit a high reflectivity peak in the ultraviolet C (UVC) spectral region (280 nm) where some aminoacids and peptides have a strong absorption. We also demonstrated how to tailor the aspect ratio and the wettability of these photonic surfaces (contact angles ranging from 8.1 to 96.2°) by changing the RIE power applied during the fabrication process.

Olefin Polymerization Catalyzed by Double-Decker Dipalladium Complexes: Low Branched Poly(α-Olefin)s by Selective Insertion of the Monomer Molecule

Dipalladium complexes of a cyclic bis(diimine) ligand with a double-decker structure catalyze polymerization of ethylene and α-olefins and copolymerization of ethylene with 1-hexene. The polymerization of 1-hexene yields a polymer that is mainly composed of the hexamethylene unit formed by 2,1-insertion of the monomer into the palladium-carbon bond, followed by chain-walking (6,1-insertion). The polymerization of 4-methyl-1-pentene proceeds by 2,1-insertion with a selectivity of 92-97 %, and affords the polymer with methyl and 2-methylhexyl branches. 2,1-Insertion occurs selectively in all of the polymerization reactions of α-olefins catalyzed by the dipalladium complexes. Ethylene polymerization with the catalyst at 100 °C lasts over 24 h, whereas the monopalladium-diimine catalyst loses its activity within 8 h at 60 °C. Polyethylene obtained by the dipalladium catalyst is less-branched and has a higher molecular weight compared to that of the monopalladium catalyst under the same conditions. Copolymerization of ethylene with 1-hexene affords solid products with melting points and molecular weights that vary depending on the polymerization time, suggesting formation of a block and/or gradient copolymer.

Thermosetting resins with high fractions of free volume and inherently low dielectric constants

A new class of thermosetting resins are developed through the ketene chemistry with in situ formation of cavities in the resins so as to reduce the dielectric constants of the resins to about 2.0.

Chiral Lewis acid catalyzed asymmetric cycloadditions of disubstituted ketenes for the synthesis of β-lactones and δ-lactones

Highly diastereo- and enantioselective [2 + 2]- and [4 + 2]-cycloadditions of disubstituted ketenes were realized by chiral Lewis acid catalysis. A series of arylalkylketenes underwent the reaction smoothly with isatins and β,γ-unsaturated α-ketoesters, providing optically active β-lactones and δ-lactones with vicinal chiral centers in excellent yields (up to 99%) and enantioselectivities (up to 99% ee), as well as exclusively high diastereoselectivities under 0.2-2 mol % catalyst loading.

Ketene-Based Route to rigid Cyclobutanediol Monomers for the Replacement of BPA in High Performance Polyesters

Recently, polyesters based on the diol monomer 2,2,4,4-tetramethyl-1,3-cyclobutanediol (TMCBDO) have been shown to exhibit excellent thermal stability, mechanical properties, and optical clarity. In particular, the ability of TMCBDO to replace bisphenol A as a diol monomer in polycarbonates and polyesters has resulted in significant commercial and academic interest in these types of monomers. Herein, we report a versatile synthetic strategy based on the dimerization of ketenes derived from the thermal treatment of Meldrum's acid for the synthesis of structurally diverse cyclobutanediol (CBDO) monomers. This strategy allows a library of CBDO monomers amenable to standard polyester polymerization procedures to be prepared and the structural diversity of these CBDO monomers provides polymers with tunable physical properties, such as glass transition temperature ranging from 120 to 230 °C. The versatility and modularity of this Meldrum's acid-based approach to substituted cyclobutanediols, combined with the ease of synthesis, will be important for the further development of high-performance polyester materials that are not based on bisphenol A.

Cyclopolymerization To Synthesize Conjugated Polymers Containing Meldrum's Acid as a Precursor for Ketene Functionality

Recently, the importance of Meldrum's acid has been reinvestigated because it serves as a great precursor for ketene generation by thermolysis. In this study, we synthesized conjugated polymers containing Meldrum's acid via controlled cyclopolymerization using a third-generation Grubbs catalyst. To avoid the solubility issue, copolymerization with soluble monomers was successfully used to provide various random and block copolymers containing Meldrum's acid in the conjugated backbone. Interestingly, when a polyacetylene derivative containing Meldrum's acid was incorporated into the second block of the diblock copolymers, highly stable core-shell supramolecules spontaneously formed during the polymerization via in situ nanoparticlization of conjugated polymer. This direct fabrication of nanostructures without requiring any post-treatments was due to the strong π-π interactions and the insolubility of the polyacetylene segment leading to the formation of core in situ. Moreover, thermolysis of Meldrum's acid to generate ketene in the conjugated polymer core was monitored by IR, and its consecutive cycloaddition to afford the cross-linked core improved the stability of the supramolecules.

Fabrication of ultra-fine nanostructures using edge transfer printing

The exploration of new methods and techniques for application in diverse fields, such as photonics, microfluidics, biotechnology and flexible electronics is of increasing scientific and technical interest for multiple uses over distance of 10-100 nm. This article discusses edge transfer printing--a series of unconventional methods derived from soft lithography for nanofabrication. It possesses the advantages of easy fabrication, low-cost and great serviceability. In this paper, we show how to produce exposed edges and use various materials for edge transfer printing, while nanoskiving, nanotransfer edge printing and tunable cracking for nanogaps are introduced. Besides this, different functional materials, such as metals, inorganic semiconductors and polymers, as well as localised heating and charge patterning, are described here as unconventional "inks" for printing. Edge transfer printing, which can effectively produce sub-100 nm scale ultra-fine structures, has broad applications, including metallic nanowires as nanoelectrodes, semiconductor nanowires for chemical sensors, heterostructures of organic semiconductors, plasmonic devices and so forth.