Search

Polymerization‐induced self‐assembly (PISA) is conducted in a non‐polar medium (n‐dodecane) via reversible complexation‐mediated polymerization (RCMP). Stearyl methacrylate (SMA) is used to synthesize a macroinitiator, and subsequent block polymerization of benzyl methacrylate (BzMA) from the macroinitiator in n‐dodecane afforded a PSMA–PBzMA block copolymer, where PSMA is poly(stearyl methacrylate) and PBzMA is poly(benzyl methacrylate). Because PSMA is soluble but PBzMA is insoluble in n‐dodecane, the block copolymer formed a self‐assembly during the block polymerization (PISA). Spherical micelles, worms, and vesicles are obtained, depending on the degrees of polymerization of PSMA and PBzMA. "One‐pot" PISA is also attained; namely, BzMA is directly added to the reaction mixture of the macroinitiator synthesis, and PISA is conducted in the same pot without purification of the macroinitiator. The spherical micelle and vesicle structures are also fixed using a crosslinkable monomer during PISA. RCMP‐PISA is highly attractive as it is odorless and metal‐free. The "one‐pot" synthesis does not require the purification of the macroinitiator. RCMP‐PISA can provide a practical approach to synthesize self‐assemblies in non‐polar media. [ABSTRACT FROM AUTHOR]

Biomimetic actuators are critical components of bionics research and have found applications in the fields of biomedical devices, soft robotics, and smart biosensors. This paper reports the first study of nanoassembly topology‐dependent actuation and shape memory programming in biomimetic 4D printing. Multi‐responsive flower‐like block copolymer nanoassemblies (vesicles) are utilized as photocurable printing materials for digital light processing (DLP) 4D printing. The flower‐like nanoassemblies enhance thermal stability, attributed to their surface loop structures on the shell surfaces. Actuators prepared from these nanoassemblies display topology‐dependent bending in response to pH and temperature‐programmable shape memory properties. Biomimetic octopus‐like soft actuators are programmed with multiple actuation patterns, large bending angles (≈500°), excellent weight‐to‐lift ratios (≈60), and moderate response time (≈5 min). Thus, nanoassembly topology‐dependent and shape‐programmable intelligent materials are successfully developed for biomimetic 4D printing. [ABSTRACT FROM AUTHOR]

This work reports the first use of organic chloride salts as catalysts for reversible complexation mediated living radical polymerization. Owing to the strong halogen‐bond forming ability of Cl−, the studied four tetraalkylammonium chloride catalysts (R4N+Cl−) successfully control the polymerizations of methyl methacrylate, yielding polymers with low dispersities up to high monomer conversion (>90%). Benzyldodecyldimethylammonium chloride is further exploited to other methacrylates and yields low‐dispersity block copolymers. The advantages of the chloride salt catalysts are wide monomer scope, good livingness, accessibility to block copolymers, and good solubility in organic media. Because of the good solubility, the use of the chloride salt catalysts can prevent agglomeration of catalysts on reactor walls in organic media, which is an industrially attractive feature. Among halide anions, chloride anion is the most abundant and least expensive halide anion, and therefore, the use of the chloride salt catalysts may lower the cost of the polymerization. [ABSTRACT FROM AUTHOR]

Organocatalyzed living radical polymerizations of itaconates are studied, yielding low‐dispersity linear and star polymers (Đ = Mw/Mn = 1.28−1.46) up to Mn = 20 000 and monomer conversion = 62%, where Mn and Mw are the number‐ and weight‐average molar masses, respectively. The block polymerization with functional methacrylates, an acrylate, and styrene yields various rod−coil block copolymers. Linear A−B diblock, linear B−A−B triblock, and 3‐arm star A−B diblock copolymers generate spherical micelles (nanoparticles) and vesicles (nanocapsules), depending on the polymer structures. Itaconates can be derived from bioresources, and thus the obtained polymers may serve as green polymers. Because of the biocompatibility of polyitaconates, the assemblies may serve as biocompatible nanocarriers. [ABSTRACT FROM AUTHOR]

A temperature‐directed micellar morphological transformation was developed using CABC multi‐block copolymers with a hydrophobic block A, a hydrophilic block B, and a thermally responsive block C with a lower critical solution temperature (LCST). The micellar structure was switched from a star (below LCST) to a flower (above LCST). The transition temperature was tunable in a wide range (11–90 °C) by varying the C monomer composition. The large difference in the loading capacity between the star and flower enabled efficient encapsulation and controlled release of external molecules. Unlike conventional systems, the present star‐to‐flower transformation keeps micellar structures and hence does not liberate polymers but only external molecules selectively. Another application is a hidden functional segment. A functional segment is hidden (shielded) below the LCST and exposed to interact with external molecules or surfaces above the LCST. [ABSTRACT FROM AUTHOR]

An effective method to synthesize azido‐end polymethacrylates from tetrabutylammonium azide (BNN3) in a nonpolar solvent (toluene) was developed. Several low‐mass alkyl halides were reacted with BNN3 in toluene as model reactions and the rate constants of these reactions were determined, to confirm fast BNN3 azidation for tertiary and secondary halides. The end‐group transformation of halide‐end polymethacrylates was effective and nearly quantitative. Notably, the combination of organocatalyzed living (or reversible deactivation) radical polymerization and BNN3 azidation enabled the metal‐free synthesis of azido‐end polymethacrylates, including single‐azido‐end and multi‐azido‐end functional homopolymers and block copolymers. The rapid and quantitative reaction without the requirement for a large excess of BNN3, metal‐free and polar‐solvent‐free nature, and broad polymer scope are attractive features of this azidation. [ABSTRACT FROM AUTHOR]

Molecular weight distribution of polymers, termed dispersity (Đ), is a fundamental parameter for determining polymer material properties. This paper reports a novel approach for controlling Đ by exploiting a temperature‐selective radical generation in organocatalyzed living radical polymerization. The polymers with tailored Đ were synthesized in a batch system without the assistance of an external pump. A unique aspect of this approach is that Đ was tuneable from 1.11 to 1.50 in any segment in diblock, triblock, and multiblock copolymers and in any form of star and brush polymer without segmental or topological restriction. This approach is amenable to various monomers and free from metals and thus attractive for applications. The approach also generated polymer brushes on surfaces with tailored Đ. An interesting finding was that the polymer brushes exhibited unique interaction with external molecules, depending on the Đ value. Brush up: A novel approach for modulating polymer dispersity was developed. It is based on temperature‐selective organocatalyzed living radical polymerization and enabled dispersity modulation in any segment in linear and branched block copolymers as well as polymer brushes. A dispersity‐dependent size‐exclusion effect to external molecules was observed for the polymer brushes. [ABSTRACT FROM AUTHOR]

Abstract: Photocontrolled surface‐initiated reversible complexation mediated polymerization (photo‐SI‐RCMP) was successfully applied to fabricate concentrated polymer brushes with complex patterning structures. Positive‐type patterned polymer brushes were obtained by photo‐SI‐RCMP under visible light (550(±50) nm) using photomasks. A particularly interesting finding was that negative‐type patterned polymer brushes were also obtainable in a facile manner. A nonspecial UV light (250–385 nm) enabled the preparation of pre‐patterned initiator surfaces in a remarkably short time (1 min), leading to negative‐type patterned polymer brushes. Based on this unique selectivity between visible and UV light, the combination of two patterning techniques enabled the preparation of complex patterned brushes, including diblock copolymers, binary polymers, and functional binary polymers, without multistep immobilization of one or more initiators on the surfaces. [ABSTRACT FROM AUTHOR]

Abstract: Temperature‐selective radical generation from a newly designed alkyl diiodide (I−R2−R1−I) was studied. R1−I and I−R2 had different reactivities for generating alkyl radicals in the presence of a tetraoctylammonium iodide (ONI) catalyst. Taking advantage of the temperature selectivity, we used the alkyl diiodide as a dual initiator in ONI‐catalyzed living radical polymerization to uniquely synthesize CABC non‐symmetric multi‐block copolymers. Because of their non‐symmetric structure, CABC multi‐block copolymers form unique assemblies, that is, Janus‐type particles with hetero‐segment coronas and flower‐like particles with hetero‐segment petals. [ABSTRACT FROM AUTHOR]

A new method of producing carbon-centered radicals was discovered through the reaction of an alkyl iodide (R-I) with organic salts to reversibly generate the corresponding alkyl radical (R•). Via this new reaction, the organic salts were used as new and highly efficient organic catalysts in living radical polymerization. The catalysts included common and inexpensive compounds such as tetrabutylammonium iodide and methyltributylphosphonium iodide. Notably, the catalysts were highly reactive. They enabled the synthesis of high-molecular-weight polymers (up to Mn = 140?000) and the control of acrylate polymerization, which had been difficult with other organic catalysts. The organic salt catalysts were highly versatile, reacting with methacrylate, acrylate, styrene, acrylonitrile, and functional methacrylate monomers. Well-defined block copolymers were also prepared by using this method. A kinetic study quantitatively confirmed the high reactivity of these catalysts. Attractive features of this system include its low cost, its ease of operation, and its ability to access a wide range of polymer designs. [ABSTRACT FROM AUTHOR]

Abstract: This article introduces the new family of living radical polymerizations with germanium (Ge), tin (Sn), phosphorus (P), and nitrogen (N) catalysts which we recently developed. The polymerizations are based on a new reversible activation mechanism, Reversible chain Transfer (RT) catalysis. Low-polydispersity polymers are obtained in the homopolymerizations and random and block copolymerizations of styrene, methyl methacrylate, and functional methacrylates. The background, performance, and kinetic features of the polymerizations are described. Attractive features of the catalysts include their high reactivity, low toxicity (Ge, P, and N), low cost (P and N), and ease of handling (robustness). [Copyright &y& Elsevier]

Abstract: The degenerative (exchange) chain transfer constant C ex was determined for the dithioacetate-mediated living radical block and random copolymerizations of styrene (St) and methyl methacrylate (MMA) at 40°C. The addition of the polystyrene (PSt) radical to a polymer–dithioacetate adduct (P–X) to form the intermediate radical (PSt–(X )–P) was (about twice) faster than that of the poly(methyl methacrylate) (PMMA) radical to form the intermediate radical PMMA–(X )–P. The fragmentation (release) of the PMMA radical from the PSt–(X )–PMMA intermediate formed at the initiating stage of block copolymerization was much (about 100 times) faster than the release of the PSt radical, explaining why the block copolymerization of MMA from a PSt–dithiocarbonate adduct is not so satisfactory as that of St from a PMMA–dithiocarbonate adduct. In the random copolymerization, there was implicit penultimate unit effect on the exchange chain transfer process, which appeared in the addition process but not in the fragmentation process. [Copyright &y& Elsevier]

Linear and miktoarm star-shaped diblock copolymers consistingofsingle-stranded DNA and poly(N-isopropylacrylamide)(PNIPAAm) with various compositions were synthesized via atom transferradical polymerization and click chemistry. The temperature-responsivephase transition behavior, micellization, was systematically examinedusing UV–vis spectrometry, high-sensitivity differential scanningcalorimetry, dynamic light scattering, and small-angle X-ray scattering.The lower critical solution temperature (LCST) increased, and itsenthalpy decreased with decreasing PNIPAAm content. The copolymersself-assembled into well-defined nanoparticles having a core composedof PNIPAAm and a coronal layer of DNA above LCST. The particle sizeand micellar aggregation number of copolymer chains depended on themacromolecular composition and chain architecture. On the other hand,regardless of their factors, the surface area occupied by one DNAstrand was found to be almost unchanged. The hybridization of DNAon the nanoparticles with fully complementary one induced the aggregationof the particles in a non-cross-linking configuration. The nanoparticlecomposed of miktoarm star copolymer showed a quicker DNA-hybridizationresponse in this non-cross-linking aggregation compared with the caseof a linear analogue. [ABSTRACT FROM AUTHOR]

Abstract: Diblock and miktoarm star-shaped thermoresponsive copolymers composed of single-stranded DNA (ssDNA) and poly(N-isopropylacrylamide) were successfully synthesized with combination of atom transfer radical polymerization (ATRP) and click chemistry. This approach should be generalizable to other DNA-functionalized copolymers. Such copolymers self-assemble into spherical micelles with ssDNA corona in aqueous solution above the lower critical solution temperature. The micellar size can be tuned from the macromolecular architecture. These DNA-encoded micellar particles are able to encapsulate and release hydrophobic guest molecules upon changing temperature. [Copyright &y& Elsevier]