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Here, we report orthogonal folding and self-assembly systems of amphiphilic/fluorous random block copolymers for double core and multicompartment micelles in water. For this, we developed the precision folding techniques of polymer chains via the selective self-assembly of the pendant groups. Typically, A/C-B/C random block copolymers were designed: Hydrophobic dodecyl groups (A) and fluorous fluorinated octyl groups (B) were introduced into the respective blocks, while hydrophilic poly(ethylene glycol) chains (C) were randomly incorporated into all the segments. By controlling the chain length and composition of the respective blocks, the copolymers induce orthogonal single-chain folding in water to form double-compartment micelles comprising hydrophobic and fluorous cores. The copolymers were site-selectively folded in a fluoroalcohol to result in tadpole unimer micelles comprising a hydrophobic A/C unimer micelle and an unfolded fluorous B/C chain. Additionally, asymmetric A/C-B/C random block copolymers with short and highly hydrophobic or fluorous segments were effective for multicompartment micelles in water.

In this report, we demonstrate the use of a thermoresponsive ligand for the ruthenium-catalyzed living radical polymerization of butyl methacrylate (BMA) in miniemulsion. A phosphine-ligand-functionalized polyethylene glycol chain (PPEG) in conjunction with a Cp*-based ruthenium complex (Cp*: pentamethylcyclopentadienyl) provided thermoresponsive character as well as catalysis for living polymerization: the complex migrated from the water phase to the oil phase for polymerization upon heating and then migrated from the oil to water phase when the temperature was decreased to quench polymerization. Consequently, simple treatment (i.e., water washing or methanol reprecipitation) yielded metal-free polymeric particles containing less than 10 μg/g (by ICP-AES) of ruthenium residue.

Two types of star polymer gels containing perfluorinated microgels were created as purification materials to separate polyfluorinated surfactants (e.g., perfluorooctanoic acid) from water. One macrogel is prepared by the radical coupling of fluorine and/or amine-functionalized microgel star polymers alone, while another is done by the radical cross-linking of the star polymers with poly(ethylene glycol) methyl ether methacrylate. Importantly, the reactive olefin remaining within the microgel cores was directly employed for both coupling and cross-linking reactions. Swelling properties of star polymer gels were effectively controlled by the latter cross-linking technique. Analyzed by small-angle X-ray scattering, a star-star coupling gel typically consists of a three-dimensional network where star polymers are sequentially connected with the microgels at the constant interval of about 20 nm. Owing to the fluorous and acid/base cooperative interaction, star polymer gels carrying fluorine/amine-functionalized microgels efficiently captured polyfluorinated surfactants in water and successfully afforded the removal from water via simple mixing and filtration.

Gradient copolymers with differential sequences linearly changing from methyl methacrylate (MMA) to dodecyl methacrylate (DMA) were efficiently synthesized by a concurrent tandem catalysis in the ruthenium-catalyzed living radical (co)polymerization coupled with the in situ transesterification of MMA with 1-dodecanol assisted by titanium isopropoxide [Ti(Oi-Pr)4]. The key is to perfectly synchronize the two reactions throughout the tandem catalysis by using molecular sieves (MSs), which facilitates the MMA transesterification into DMA by removing the resulting methanol. The MMA/DMA gradient copolymers had an extremely broad glass transition temperature range (i.e., hardly detectable by differential scanning calorimetry (DSC)), in sharp contrast to the random and the block counterparts of similar compositions.

Iterative single unit monomer radical addition with a bulky tertiary methacrylate monomer, adamantyl and isopropyl pendant methacrylate (IPAMA), under ATRP conditions was studied in detail toward the syntheses of sequence-defined oligo- or poly(methacrylate)s in higher yields. The introduction of an activated ester for the alkyl halide or the adduct was effective in improving the accuracy of the single unit addition of IPAMA without forming unfavorable products. Thus, a cycle consisting of 4 steps, “radical addition”, “transformation”, “selective cleavage”, and “active esterification”, was established to realize the circumstances for effective single unit monomer addition and the iterative process along with pendant modification. The cycle was actually repeated to synthesize 2 units of adduct in high yield.

Herein, we created amphiphilic polymers bearing hydrophilic/hydrophobic block pendants as a new class of self-assembled materials for microphase separation in the solid state and forming folded flower micelles in water. For this, we designed amphiphilic block methacrylates comprising hydrophilic poly(ethylene glycol) (PEG) and a hydrophobic dodecyl group: DPEG10MA and DPEG23MA. The DPEG10MA and DPEG23MA homopolymers induced microphase separation of the block pendants. For example, the DPEG23MA homopolymer formed lamellar structures; the hydrophilic and crystallized PEG and hydrophobic dodecyl units are alternately layered with about 14 nm domain spacing. In water, random copolymers of PEG methyl ether methacrylate and DPEG10MA folded into flower micelles with both looped and linear PEG shells, where the dodecyl groups of the incorporated DPEG10MA assembled to form hydrophobic cores. The micelles further showed thermoresponsive solubility in water. The size, aggregation number, and cloud point of the micelles were controlled by their composition and chain length.

Acrylate-selective transesterification of methacrylate/acrylate copolymers with alcohols was developed for a site-selective postfunctionalization technique of polymers without using specific monomers. Importantly, a common methyl acrylate efficiently works as a selective modification unit via transesterification coupled with a titanium alkoxide catalyst. The acrylate-selective transesterification is achieved owing to less steric hindrance of the carbonyl groups that are attached to the main chain without an α-methyl group. Typically, the acrylate pendants of dodecyl methacrylate/methyl acrylate (MA) random copolymers were selectively transesterified with benzyl alcohol (BzOH). The conversion of the pendent esters into benzyl esters proportionally increased with MA contents. Additionally, various alcohols were applicable to this MA-selective transesterification system.

Amphiphilic random copolymers comprising different hydrophilic poly(ethylene glycol) (PEG, average number of oxyethylene units = 4.5 or 8.5) and hydrophobic butyl or dodecyl pendants were designed to investigate self-folding and self-assembly behavior in water. The copolymers with controlled composition and chain length were synthesized by ruthenium-catalyzed living radical copolymerization. We revealed that the pendant design was one of the most critical factors to selectively induce intramolecular self-folding or intermolecular self-assembly. In the case of 30 mol % hydrophobic monomers, random copolymers bearing short PEG (on average 4.5 oxyethylene units) and butyl pendants intramolecularly self-folded into unimer micelles in water, independent of chain length. The size of unimer micelles thus increased with increasing chain length. In contrast, random copolymers bearing long dodecyl pendants intermolecularly self-assembled into uniform multichain micelles; the size depended on composition and PEG len...

Perfluorinated gradient copolymers comprising fluorous units and hydrophobic or hydrophilic units were created as fluorous polymer materials with unique physical properties. The gradient copolymers were efficiently synthesized via the tandem catalysis of living radical polymerization and titanium alkoxide-mediated transesterification of 1H,1H,2H,2H-perfluorooctyl methacrylate (13FOMA) with alcohols. Owing to the electron-withdrawing perfluorooctyl unit, 13FOMA was efficiently transesterified into another methacrylate (RMA) with alcohols during the copolymerization of 13FOMA and RMA to afford well-controlled 13FOMA/RMA gradient copolymers. The gradient sequence gradually changed from 13FOMA to RMA-rich composition according to monomer composition varying in the polymerization solutions. The tandem catalysis is allowed to use various alcohols including 1-dodecanol, 1-octadecanol, ethanol, and poly(ethylene glycol) methyl ether; the catalysis developed herein is thus one of the most versatile systems to prod...

We report programmed self-assembly systems of amphiphilic random copolymers bearing hydrophilic poly(ethylene glycol) (PEG) and hydrophobic alkyl pendants into size-controlled and thermoresponsive micelles in water. This system affords simultaneous and precise control of the size, aggregation numbers, and cloud point (Cp) of micelles in water by primary structure (pendant alkyl groups, composition, and chain length) that is programmed in the copolymers. Typically, random copolymers bearing PEG and alkyl pendants (butyl, octyl, dodecyl, and octadecyl groups) universally induce intermolecular self-assembly in water to produce uniform size micelles (

Fluorine-containing polymers have potential for use in medicine and other applications, but the synthesis of degradable fluorous polymers is underexplored. In this report, we present a facile route to degradable fluorinated polymers and characterize the effect of fluorous comonomer identity on the polymerization as well as the degradation kinetics of the resulting polymer. Copolymers of poly(ethylene glycol methyl ether methacrylate) (PEGMA), fluorous methacrylate (1H,1H,2H,2H-perfluorooctyl or 1H,1H,2H,2H,3H,3H-perfluoropentyl methacrylate), and cyclic ketene acetal 5,6-benzo-2-methylene-1,3-dioxepane (BMDO) were synthesized via ruthenium-catalyzed living radical polymerization. It was observed that increasing the fluorous monomer content led to enhanced BMDO incorporation in the resulting polymer. Density functional theory calculations suggest that this is due to the decreased energy gap between the singly occupied molecular orbital (SOMO) of the methacrylate radical and the highest occupied molecular o...

Iron-bearing self-folding polymers were created with amphiphilic random copolymers as active, versatile, and recyclable polymer-supported catalysts for living radical polymerization (LRP). The key is to build bis(imino)pyridine ligand cavities for iron complexes as linking units within self-folding polymers. Self-folding polymer ligands are synthesized by the intramolecular imine cross-linking of self-folded amphiphilic random copolymers bearing hydrophilic poly(ethylene glycol) (PEG), hydrophobic dodecyl, and urea/aniline pendants with 2,6-pyridinedicarboxaldehyde in water. The folding polymers efficiently formed iron complex catalysts in the cores to induce LRP and random or block copolymerization of various methacrylates. The self-folding polymer catalysts not only showed high activity and tolerance to functional groups such as acid, hydroxyl groups, and oxygen but also afforded easy product recovery and catalyst recycle thanks to hydrophilic PEG chains.

Cyclopolymerization of a divinyl monomer, where two different vinyl groups, that is, acrylate and vinyl ether, are connected via an ester bond, was performed under diluted condition with nitroxide-meditated radical polymerization (NMP). Both vinyl groups were consumed at almost same rate under suitable condition, although the inherent cross-propagation ability between the two vinyl groups are pretty low in radical copolymerization. Furthermore, the polymerization was controlled to some extent to give polymers of unimodal molecular weight distributions. The results obviously differed from copolymerization and homopolymerization with vinyl monomers that constitutes the divinyl monomer, 2-methoxyethyl acrylate and 2-acetoxyethyl vinyl ether. Structural analyses indicated formation of the cyclopolymer but the cyclo-efficiency was imperfect indicating that some units of olefinic dangling were incorporated. Eventually, the ester bonds of the cyclo units were cleaved to convert into the copolymer consisting of acrylic acid and 2-hydroxy ethyl vinyl ether and the composition ratio (DP

Herein, we clarified the ring-expansion cationic polymerization with a cyclic hemiacetal ester (HAE)-based initiator was versatile in terms of applicable vinyl ether monomers. Although there was a risk that higher reactive vinyl ethers may incur β-H elimination of the HAE-based cyclic dormant species to irreversibly give linear chains, the polymerizations were controlled to give corresponding cyclic polymers from various alkyl vinyl ethers of different reactivities. Functional vinyl ether monomers were also available, and for instance a vinyl ether monomer carrying an initiator moiety for metal-catalyzed living radical polymerization in the pendant allowed construction of ring-linear graft copolymers through the grafting-from approach. Furthermore, ring-based gel was prepared via the addition of divinyl ether at the end of the ring-expansion polymerization, where multi HAE bonds cyclic polymers or fused rings were crosslinked with each other. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017

Development of living polymerizations via reversible activation of dormant species opened the door to discovery of metal-catalyzed living radical polymerization that is now very useful for precise construction of tailor-made polymeric architectures. In this commemorative Perspective, the historical aspects as well as the prospects as a new polymerization tool are described toward advanced structural control or technological materials innovation in various fields.

Ring-driven physical properties of cyclic poly(vinyl ether)s were studied, such as thermal sensitivity in solution and glass transition temperature (Tg). The samples were precisely synthesized via ring-expansion cationic polymerization with a hemiacetal ester (HAE)-based cyclic compound as the initiator. To clarify the topology effects, linear polymers with similar molecular weights were also prepared via a conventional living cationic polymerization with the HAE-based acyclic initiator (i.e., an adduct of vinyl ether with acetic acid) for comparison. Cyclic poly(vinyl ether)s carrying bulky tricyclic alkane pendant exhibited higher Tgs than the linear counterparts of similar molecular weights. Interestingly, the Tg was not so decreased even as the molecular weight was lower, which was clearly different from linear polymers. The thermosensitivity of cyclic polymer was also studied with ethyl acetate solution of poly(dodecyl vinyl ether) showing upper critical solution temperature (UCST) at around 45 °C. T...

Amphiphilic gradient copolymers with poly(ethylene glycol) pendants were synthesized via tandem catalysis of ruthenium-catalyzed living radical polymerization (LRP) and titanium alkoxide-mediated transesterification. The gradient sequence can be catalytically controlled by tuning the kinetic balance of the two reactions. The tandem catalysis is one of the most efficient and versatile systems to produce amphiphilic gradient and sequence-controlled copolymers. Typically, methyl methacrylate (MMA) was polymerized as a starting monomer with a ruthenium catalyst and a chloride initiator in the presence of Ti(Oi-Pr)4 and molecular sieves (MS 4A) in poly(ethylene glycol) methyl ether (PEG-OH) as a solvent at 80 °C. Hydrophobic MMA was concurrently transesterified into hydrophilic PEG methacrylate (PEGMA) during LRP to give MMA/PEGMA gradient copolymers. The gradient sequence is directly determined by the instantaneous monomer composition changing from MMA alone to PEGMA-rich mixture in solution. Synchronized cat...

Imine-functionalized reversible microgel star polymers were synthesized by dynamic covalent cross-linking of hydrogen-bonding block copolymer micelles in organic media. This approach allows the precision and wide range control of molecular weight (Mw = 100–10 000 K; Mw/Mn = ∼1.1) of star polymers via preforming micelles of block copolymers. For this, a urea and aniline-functionalized methacrylate (ApUMA) was newly designed as a key monomer. The block copolymer of methyl methacrylate (MMA) and ApUMA, prepared by ruthenium-catalyzed living radical polymerization, efficiently self-assembled into micelles via hydrogen-bonding interaction of the urea pendants in dichloromethane and dichloromethane/N,N-dimethylformamide mixture. The subsequent treatment with terephthalaldehyde gave imine-cross-linked star polymers with quite narrow distribution in high yield. The molecular weight of the star polymers was successfully controlled by tuning solvents, concentration, and the block copolymer structure (PMMA arm and A...

Self-assembly of hydrophilic poly(ethylene glycol) (PEG) and hydrophobic dodecyl-graft amphiphilic copolymers in water was investigated in detail, by especially focusing on the effects of the monomer sequence and chain flexibility on the size controllability, mobility, and the thermoresponse of micelles. For this, we designed and synthesized PEG/dodecyl graft copolymers with different sequence distributions, backbones, compositions, and chain lengths via controlled or free radical copolymerization: acrylate random, methacrylate/acrylate gradient and bidirectional gradient, and methacrylate random block. Acrylate-based amphiphilic random copolymers produced uniform micelles in water, whose size was determined just by the composition. The flexible acrylate-based micelles had higher mobility of graft PEG and in-core dodecyl units than methacrylate counterparts yet effectively maintained uniform and compact size (∼10 nm) up to a high concentration. Additionally, the sequence distribution critically affected the size controllability of micelles. Gradient or random block copolymers with highly biased and/or locally accumulated hydrophobic monomer segments provided micelles with different sizes and/or broad size distributions. Thus, it was revealed that the random, statistical, and non-biased sequence distribution of hydrophilic and hydrophobic monomers is a key factor to efficiently induce composition-dependent precision self-assembly of PEG/dodecyl-graft copolymers into uniform size micelles in water.

Cyclic polymers have unique topologies that are free from terminal groups and thus have attracted attention among polymer physicists. In sharp contrast to the conventional macrocyclization approach where telechelic linear polymers depend on highly diluted conditions, “ring-expansion polymerization” is expected to become a useful methodology to construct cyclic polymers efficiently and reliably. However, synthesis of tailor-made cyclic polymers with conventional living polymerization methods are still a challenging subject, especially for addition polymerization of acyclic vinyl monomers. We have recently realized ring-expansion cationic polymerization of vinyl ethers by using a hemiacetal ester embedded cyclic initiator that is easily synthesized. Herein, the unique polymerization is reviewed along with the history of ring-expansion polymerization.

Fluorinated gradient copolymers were synthesized by the tandem catalysis of ruthenium-catalyzed living radical polymerization (LRP) and titanium alkoxide-mediated transesterification of methyl methacrylate (MMA) with fluoroalcohols. Although transesterification using less nucleophilic fluoroalcohols is generally regarded as difficult, we found that MMA was efficiently transesterified with fluoroalcohols (RFOH) into fluorinated methacrylates (RFMA) by Ti(Oi-Pr)4 catalysts (2–8 mol%) in the presence of molecular sieves 4A (MS 4A). The yield of RFMA increased with increasing the alkyl spacer (carbon number) between a hydroxyl group and a fluorinated alkyl segment in fluoroalcohols: propyl (4,4,5,5,5-pentafluoro-1-pentanol: 5FPOH) > ethyl (1H,1H,2H,2H-nonafluoro-1-hexanol: 9FHOH) > methyl (1H,1H-heptafluoro-1-butanol). Tandem polymerization of MMA was conducted with a ruthenium catalyst, a chloride initiator, and Ti(Oi-Pr)4 in toluene/fluoroalcohol mixtures (1/1, v/v) at 80 °C. Typically, in the presence of 4 mol% Ti and MS 4A, transesterification of MMA with 5FPOH or 9FHOH was efficiently synchronized with LRP to produce well-controlled MMA/5FPMA or MMA/9FHMA gradient copolymers in high yield (Conv. >95%, Mw/Mn = 1.2).

Urea and poly(ethylene glycol) (PEG)-functionalized amphiphilic random copolymers served as self-folding polymers in both water and chloroform via hydrophobic and/or hydrogen-bonding interactions. For this, a urea-bearing methacrylate (BPUMA) was newly designed as a trigger monomer. Various random, gradient, and block copolymers were synthesized by living radical copolymerization of PEG methyl ether methacrylate (PEGMA) and BPUMA to systematically survey folding/association properties. Importantly, self-folding in both water and chloroform requires the random incorporation of BPUMA along a chain and the control of its composition, while gradient or block counterparts tend to induce multichain aggregation. Typically, 30–40 mol % BPUMA random copolymers effectively fold in water to form compact globular unimer micelles with hydrophobic/hydrogen-bonding core covered by multiple PEG arm chains. The dual functionalization of polymers with hydrophilic PEG and hydrophobic/hydrogen-bonding urea units afforded sin...

Living CO2-switchable poly(methyl methacrylate) (PMMA) latexes were prepared using reverse ATRP emulsion polymerization and AGET ATRP miniemulsion polymerization. The prepared latexes can be switched between the aggregated and dispersed states using only CO2 and any nonacidic gas (e.g., argon, air, nitrogen) as triggers. AGET ATRP miniemulsion polymerizations were enabled by the design and synthesis of a CO2-switchable ATRP inisurf, 1,1-(diethylamino)undecyl 2-bromo-2-methylpropanoate (BrC11N), which can generate stable emulsions under CO2 without requiring the addition of other emulsifiers. The resulting PMMA has controlled molecular weight and low dispersity.

Polyacrylamide pseudo crown ethers with large in-chain rings (15–24 membered) were synthesized by hydrogen bond-mediated cyclopolymerization of bisacrylamides comprising poly(ethylene oxide) spacers (PEGnDAAm, ethylene oxide units: n = 3–6). The monomers undergo the intramolecular hydrogen bonding of the bisacrylamide units in halogenated solvents to dynamically place the two olefins adjacently. As a result, the bisacrylamides homogeneously allowed controlled radical cyclopolymerization without any macroscopic gelation in 1,2-dichloroethane, even at relatively high concentration of monomers (200 mM), to directly provide precision cyclopolyacrylamides and the related copolymers with high cyclization efficiency (84–98%). Owing to the in-chain ring pendants, a cyclopolyacrylamide had glass transition temperature higher than a corresponding polyacrylamide with linear pendants. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 3294–3302

Self-assembly of amphiphilic molecules in water is a cornerstone to build compartmentalized materials toward unique functions, whereas it is yet challenging to create uniform, discrete, and size-controlled nanocompartments. This paper is to report that precision random copolymers, amphiphilic with hydrophilic poly(ethylene glycol) (PEG) and hydrophobic dodecyl pendants, induce precision self-assembly and self-recognition in water to form uniform, tunable, and self-sorting nanoparticles with inner-core hydrophobic compartments covered by PEG chains; the copolymers have been obtained via living or free radical copolymerization. The nanoparticles allow the on-target and predictable control of size, molecular weight, and aggregation number by tuning the primary structure of the copolymers; even mixtures of the copolymers with different composition underwent self-sorting to provide size-controlled discrete compartments.

Multimode self-folding polymers were created via the reversible and thermoresponsive self-assembly of amphiphilic/fluorous random copolymers bearing poly(ethylene glycol) (PEG) and perfluoroalkyl pendants in water, N,N-dimethylformamide (DMF), and 2H,3H-perfluoropentane (2HPFP). The random copolymers with precision primary structure were synthesized by ruthenium-catalyzed living radical copolymerization of PEG methyl ether methacrylates and perfluoroalkyl methacrylates. Owing to three distinct properties of the hydrophobic backbone, hydrophilic PEG chains, and fluorous perfluorinated pendants, the random copolymers allowed various self-assembly modes for different folded structures by changing solvents. Namely, they form self-folding polymers of fluorous and/or hydrophobic cores in water or DMF, while they in turn provide reverse self-folding polymers of hydrophilic PEG cores in 2HPFP. The reverse folding in 2HPFP was further promoted by lower critical solution temperature-type phase separation of the PEG...

Herein we propose a new concept to control sequence for vinyl polymers. A tertiary alkyl methacrylate monomer carrying both adamantyl and isopropyl groups (IPAMA) is very unique to allow control of single unit addition with an alkyl halide initiator for metal-catalyzed living radical polymerization due to the exceptional bulkiness. After control of the single unit addition, the bulkiness can be removed via acidolysis to further convert into the ester pendant with less bulky and nontertiary alcohol. The resultant adduct can be used as an initiator for the next single unit addition of IPAMA and the terminal ester can be selectively hydrolyzed followed by esterification similar to the first process. Namely, the cycle consisting of "radical addition of IPAMA", "acidolysis of the IPAMA side group", and "esterification of resultant carboxylic acid" can be repeated to construct sequence well-defined poly(oligo-)methacrylates. In this letter, results of the cycle and the iterative process with the special methacrylate monomer are actually demonstrated as well as the scope of applicable alcohols for the esterification process toward sequence control with functional units.

We present the cationic Cp*–ruthenium complexes [Cp*Ru(CH3CN)(PPh3)2A; A–: the counteranion; abbreviated Cp*Ru+A–] as the active, cocatalyst-free, and tunable catalysts for metal-catalyzed living radical polymerization (Mt-LRP). A PF6-based cationic complex in conjunction with a alkyl halide initiator led to controlled polymerization of methyl methacrylate (MMA) giving well-controlled PMMAs with narrow molecular weight distribution (Mw/Mn 80% in 15 h), although cocatalyst was not combined. The catalytic feature was clearly different from the neutral counterpart [Cp*RuCl(PPh3)2: Cp*Ru], resulting in retarded polymerization under the cocatalyst-free condition. Interestingly, the catalytic activity was influenced by the counteranions. For example, the PF6-based complex did not afford catalysis for controlled polymerization of methyl acrylate (MA), but an Sb6-based [Cp*Ru(CH3CN)(PPh3)2SbF6: Cp*Ru+SbF6–] allowed control of the polymerization. Model reacti...

We report a novel storage technology of proteins with surface-perfluorinated poly(ethylene glycol) compartments in 2H,3H-perfluoropentane. The compartments were obtained from self-folding and self-assembly of an amphiphilic random copolymer bearing poly(ethylene glycol) and perfluoroalkyl pendants in the hydrofluorocarbon. Lysozyme and α-chymotrypsin as model proteins were efficiently encapsulated within the PEG compartments and quantitatively recovered therefrom with water. The recovered lysozyme maintained the original higher order structure without denaturation to show enzymatic activity for the hydrolysis of Micrococcus lysodeikticus as high as its original counterpart in water. The storage technology was further effective to inhibit inactivation of α-chymotrypsin.

The Hamilton receptor group (–DADDAD–; D = hydrogen donor; A = hydrogen acceptor) was periodically introduced into a polystyrene backbone, starting from the ruthenium-catalyzed living radical polymerization of styrene with the Hamilton receptor-based bifunctional initiator. The carbon–halogen bonds at both terminals of the resultant unimodal polystyrene (PSDADDAD) carrying the –DADDAD– units at the center position were activated with a ruthenium catalyst to promote the radical–radical coupling reaction between chains, and thereby –DADDAD– units were multiply introduced into the polymer backbone with regular intervals [(PSDADDAD)n]. Upon mixing of the polymer with the end-functionalized poly(methyl methacrylate) (PMMA) carrying a “complementary” hydrogen bonding site (ADADA: PMMAADADA) in CDCl3, supramolecular graft copolymers were formed through the complementary hydrogen bonding between the terminal ADADA site of the guest polymers and the DADDAD site at the periodic positions in the polystyrene backbone. The differential scanning calorimetry (DSC) analysis showed the influence of periodicity in the grafting arm positions on the enthalpic transition of the supramolecular copolymers.

In this paper, we demonstrate a convergent approach to convert “fused” ring chains obtained via ring expansion cationic polymerization of vinyl ether with a hemiacetal ester (HAE)-based ring initiator (1) into “sing” ring ones of narrow MWDs. In the ring-expansion propagation process, the propagation can be controlled without any side reactions but an intermolecular counteranion exchange reaction between HAE bonds between propagating ring polymers ineluctably occurs resulting in broad molecular weight distributions (MWDs) composed of “fused” ring chains with multiple HAE bonds as well as a “sing” ring chain with one HAE bond. Hence, after monomer conversion reached over 95%, the polymerization solution was diluted (i.e., post dilution) without deactivation of an employed Lewis acid activator (i.e., SnBr4) to induce intramolecular counteranion exchange in the fused ring chain. Size exclusion chromatography (SEC) curves of the product eventually became almost unimodal, though a small shoulder peak from the fused ring remained. Importantly, the HAE bond in ring chains still survived even after the post dilution process, which was confirmed by 1H NMR, and the retention of the ring structure was also supported by an acidolysis experiment where the apparent peak top molecular weight (Mp) was increased in SEC due to topology conversion from a ring to linear. The approach was proved to be effective even for higher molecular weight ring polymers that were prepared with a higher [monomer]/[1] ratio as well as ring block copolymers.

Poly[poly(ethylene glycol) methyl ether methacrylate]s [poly(PEGMA)s] sharply and reversibly exhibited lower critical solution temperature (LCST)-type phase separation in 2H,3H-perfluoropentane (2HPFP). The cloud points decreased from 52 to 41 °C with increasing the PEG pendant length [−(CH2CH2O)mCH3: m = 4.5, 9, 19]. The cloud point was precisely controlled via the addition of perfluoroalkanes (e.g., perfluorooctane) to the 2HPFP solution: typically, it was inversely proportional to the amount of perfluorooctane in the mixture. The unique thermoresponsive solubility further afforded the temperature-mediated micellization of a block copolymer of PEG19MA and methyl methacrylate (MMA) in 2HPFP to uniquely give a PEG-core micelle with PMMA shell. Therefore, the LCST phase separation properties in the hydrofluorocarbon would open new vistas for thermoresponsive polymeric materials.

Decamethylferrocene (FeCp*2) was found to be an effective cocatalyst for metal-catalyzed living radical polymerization with FeBr2/n-Bu4NBr as the main catalyst. For polymerization of methyl methacrylate (MMA) with a bromine-type initiator, the conversion was limited in the absence of FeCp*2, whereas the polymerization was apparently promoted up to higher conversion (∼90%) upon combination with FeCp*2. Despite the acceleration, molecular weights and its distributions (MWDs) were fairly controlled (Mw/Mn < 1.1, conversion = 90%). The “concerted” catalysis with the two iron complexes allowed superior control of the polymerization to those without FeCp*2 to give high halogen functionalities of obtained polymers. Importantly, the two iron complexes can perform the catalysis helping each other, independently of electron support from ligands (e.g., phosphine). Therefore, ligand dissociation by polar groups, i.e., “catalyst poison”, does not matter in the FeCp*2-concerted system, leading to control over (co)polym...

The dynamics of in-core perfluorinated alkyl pendants in microgel star polymers were investigated by 19F nuclear magnetic resonance spectroscopy and 19F spin–spin relaxation time (T2) measurements, to elucidate the origin of the efficient encapsulation of perfluorinated guests into the fluorous microgel cores. Fluorinated microgel star polymers were prepared by the linking reaction of chlorine-capped poly(methyl methacrylate) arms with dimethacrylate linking agents and a perfluorinated methacrylate via ruthenium-catalyzed living radical polymerization. Temperature-dependent T2 measurements revealed the reduced thermodynamic mobility of the perfluorinated pendants indicative of their accumulation and thus aggregation in the core network. Fluorinated microgel star polymers accordingly provide stable “fluorous compartments” where the encapsulation of perfluoromethylcyclohexane (PFMCH) in DMF is better attained and more efficient than that in the corresponding block copolymer micelles.

Summary Amphiphilic three-armed star random copolymers were synthesized by ruthenium-catalyzed living radical copolymerization of hydrophilic poly(ethylene glycol) methyl ether methacrylate (PEGMA) and hydrophobic dodecyl methacrylate (DMA). Their amphiphilic star random copolymers with 10-50 mol% DMA efficiently self-folded in water with intramolecular hydrophobic interaction to form compact unimolecular micelles. Owing to PEG segments, star copolymers were thermoresponsive to induce lower critical solution temperature-type phase separation in water.

Summary For the “ring-expansion” living cationic polymerization of vinyl ethers that has recently been achieved for the first time with a hemiacetal ester-embedded cyclic initiator (1), we investigated the effects of reaction conditions (Lewis acid catalysts/activators, solvents, temperature, and reagent concentration) on the selectivity and controllability for construction of ring chains. For example, the choice of the Lewis acid catalysts turned out crucial. Specifically, tin tetrabrommide (SnBr4) was suitable, with which an undisturbed ring-expansion propagation proceeded without irreversible side reactions, to selectively construct the ring topology, though accompanied by “ring fusion” into fused ring polymers of higher molelcular weights. The fusion event, however, could be suppressed by decreasing concentration of the initiator, namely, polymers to be formed therefrom. Under these optimized conditions, the propagation is controlled enough to allow sequential addition of monomers to give either chain-extended homopolymers or block copolymers. Thus, the ring-expansion cationic polymerization is potentially a powerful tool to construct ring polymer architectures with precision control similar to that for linear living polymers.

Fluorinated microgel star polymers were designed and synthesized as fluorous nanocapsules for the encapsulation and release of perfluorinated compounds. Five types of these fluorous star polymers were obtained by ruthenium-catalyzed linking reaction of chlorine-capped poly(methyl methacrylate) arms (macroinitiators) with a perfluorinated dimethacrylate linker and a perfluorinated methacrylate (RFMA), so as to tune the in-core fluorous properties depending on the latter's structure and fluorine content. 19F nuclear magnetic resonance and 19F spin–spin relaxation time (T2) measurements revealed that the mobility of the in-core perfluorinated pendants derived from RFMA decreased on increasing the number of fluorine and carbon atoms, or the pendant length. The cores effectively recognized and encapsulated perfluorinated guest compounds (e.g., perfluorooctane and perfluoromethylcyclohexane), and the encapsulation depended on the fluorous properties of the structures and fluorous nature of RFMA and the guests. For example, encapsulation was promoted by increasing the number of in-core fluorine and CF3 groups, and typically the core with perfluorodecyl pendants successfully captured perfluorinated esters and ketones. In addition, fluorinated star polymers could reversibly capture and thermo-responsively release a perfluorinated guest, indicating that the encapsulation is selective but dynamic and stimuli-responsive.

A thermoresponsive polymer-supported catalyst consisting of a ruthenium (Ru) main catalyst and a ferrocene (Fc) cocatalyst was designed to realize both high activity and efficient removal of metal residues. The supported catalyst/cocatalyst was easily prepared via ternary random free radical copolymerization of vinylferrocene (VFc), phosphine-pendant monomer (SDP), and PEG-pendant methacrylate (PEGMA), followed by mixing with a Ru precursor ([Ru(Cp*)Cl]4). The thermoresponsive feature was confirmed by visual appearance with a water/toluene binary solvent: it was preferably soluble in water at room temperature but moved to the toluene phase at high temperature for polymerization. The supported catalyst/cocatalyst showed high catalytic activity for living radical polymerization of MMA in toluene to give controlled PMMAs with narrow molecular weight distributions and a high halogen end functionality (e.g., Mw/Mn = 1.16 and 96% Cl-end of PMMA obtained at 89% conversion in 24 h). The metal residues in PMMA can almost be quantitatively removed via water washing of the resulting polymerization solution [Residual Ru: 5.7 ppm (99.8% removal), residual Fe: 89 ppm (98.5% removal), characterized by ICP-AES analysis].

Herein, amphiphilic/fluorous random copolymers bearing poly(ethylene glycol) (PEG) chains and perfluorinated alkane pendants were developed as novel non-cytotoxic polymers for protein conjugation. Three kinds of random copolymers with different initiating terminals (carboxylic acid, pyridyl disulfide, and N-hydroxysuccinimide ester) were prepared by reversible addition–fragmentation chain transfer (RAFT) copolymerization of a PEG methyl ether methacrylate and a perfluorinated alkane methacrylate with the corresponding functional chain transfer agents. All of the polymers were soluble in water to form nanostructures with perfluorinated compartments via fluorous interaction: large aggregates from the intermolecular multi-chain association and compact unimer micelles from the intramolecular single-chain folding. Such a PEGylated and perfluorinated random copolymer was non-cytotoxic to NIH 3T3 mouse embryonic fibroblast cells and human umbilical vein endothelial cells (HUVECs). Additionally, a random copolymer with a pyridyl disulfide terminal was also successfully conjugated with a thiolated lysozyme.

Chiral 1,3,5-tricarboxamide (BTA)-functionalized copolymers with gradient, bidirectional gradient, and random sequence distributions were synthesized via tandem living radical polymerization (LRP) with in situ monomer transesterification to investigate the effects of the BTA sequence on self-folding/aggregation properties in organic media. Here, 2-ethylhexyl methacrylate (EHMA) as a starting monomer was polymerized with a ruthenium catalytic system in the presence of a chiral BTA-bearing alcohol (BTA-OH) and Ti(Oi-Pr)4. By tuning the concentration and time of addition of the Ti catalyst, the transesterification rate of EHMA into a chiral BTA-functionalized methacrylate (BTAMA) was synchronized with LRP to produce EHMA/BTAMA gradient or bidirectional gradient copolymers. In contrast, faster transesterification than LRP gave the corresponding random copolymer. Circular dichroism spectroscopy and dynamic light scattering performed on solutions of all BTA-functionalized copolymers indicated that the chiral BTA pendants self-assemble helically via hydrogen-bonding interaction in 1,2-dichloroethane, methylcyclohexane (MCH), and their mixtures to form single-chain or multichain polymeric nanoparticles. The temperature-dependent self-assembly behavior of the BTA pendants was virtually independent of the sequence distribution, whereas the size of the resultant nanoparticles depended on the sequence as follows: random < gradient < bidirectional gradient in MCH.

Amphiphilic random methacrylate copolymers, consisting of poly(ethylene glycol) (PEG) and alkyl pendent groups, undergo reversible single-chain self-folding in water via intramolecular hydrophobic interaction, to generate a dynamic unimolecular hydrophobic nanospace, similar in shape but structurally different relative to micelles and microgel star polymers. These copolymers were prepared by the ruthenium-catalyzed living radical copolymerization of a PEG methacrylate (PEGMA) and an alkyl methacrylate (RMA; R, −CnH2n+1, n = 1–18), where copolymer composition, degree of polymerization, and hydrophobic R moiety were varied. Detailed structural and chain-folding characterization has revealed: single-chain folding is favored with the RMA content 20–40 mol % per chain; the hydrophobic inner compartment (or the self-folded structure) is stable even at a high polymer concentration (up to ∼6 wt %); and folded–unfolded transition occurs on addition of methanol or by elevating solution temperature, finally to phase...

This paper deals with a preliminary study in controlled radical depolymerization, that is a unimodal polymer is converted into monomer while maintaining the narrow molecular weight distribution. Thus, our effort has been directed to unzipping-type depolymerization triggered by the reversible activation of the terminal group. An indenyl-based ruthenium catalyst afforded depolymerization of a chlorine-capped poly(methyl methacrylate) (PMMA-Cl) at relatively high temperature (>100 °C). Interestingly, the SEC curve shifted to lower molecular weight as the time proceeds, and the monomer, that is MMA, definitely generated and the amount almost corresponded to the decrease in molecular weight. The depolymerization was eventually saturated due to the equilibrium monomer concentration, but evaporation of the generating monomer followed by an addition of solvent and re-heating allowed further progress of depolymerization. We have thus demonstrated four consecutive depolymerizations via the evaporation methodology resulting in the unimodal SEC curve shift to lower molecular weight.

Hydrogen bonding self-assemblies were formed in an aqueous medium from a pair of an amphiphilic ABA triblock copolymer and a hydrophobic homopolymer, both with a triple hydrogen bonding site that was complementary to each other and precisely placed at the main-chain center: (PEGMA)m–(MMA)n–ADA–(MMA)n–(PEGMA)m and (MMA)p–DAD–(MMA)p (A = hydrogen acceptor; D = hydrogen donor; PEGMA: PEG methacrylate; MMA: methyl methacrylate). The polymers were synthesized by the ruthenium-catalyzed living radial polymerization with bifunctional initiators (Br–ADA–Br and Cl–DAD–Cl) aiming at pinpoint chain center functionalization to give a symmetric segmental sequence; ADA and DAD initiators were derived from 2,6-diaminopyridine and thymine, respectively. On mixed equimolar in tetrahydrofuran (THF), both polymers spontaneously associated, and the apparently 1:1 assembly further grew into higher aggregate particles on subsequent addition of water. The aggregates in water/THF were relatively stable and uniform in size, which most likely stems from the intermolecular complementary hydrogen bond interaction at polymer chain centers. In sharp contrast, an equimolar mixture of ADA-block polymer and DAD-free poly(MMA) in water/THF resulted in larger and irregular particles, and thus short-lived to eventually collapse. These results indicate that, however structurally marginal, precise pinpoint functionalization of macromolecular chains allows stable self-assemblies via complementary hydrogen bond interaction even in aqueous media. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4498–4504