Fabrication of Double-Stranded Vinyl Polymers Mediated by Coordination Nanochannels.

Although double-stranded structures are commonly found in biopolymers, a general and versatile methodology for fabricating double-stranded synthetic polymers has not yet been developed. Here, we report a new approach for synthesizing double-stranded polymers composed of polystyrene and poly(methyl methacrylate). We conducted crosslinking radical polymerization inside a metal-organic framework (MOF), which had one-dimensional channels with diameters similar to the thickness of two polymer chains. Effective spatial constraint within the MOF pores facilitated highly regulated crosslinking reactions between two polymer chains with extended conformations. Remarkably, the obtained double-stranded polymers were soluble in many organic solvents, even at a high crosslinking ratio (20%), unlike conventional crosslinked polymers. Notably, this stable duplex topology, which was inaccessible using previous methods, endowed the double-stranded vinyl polymers with unusual properties in the solution and bulk states. By designing the properties of the MOF nanochannels, the proposed technique can contribute to the development of a wide range of synthetic polymer duplexes.

Homopolymer-block-Alternating Copolymers Composed of Acrylamide Units: Design of Transformable Divinyl Monomers and Sequence-Specific Thermoresponsive Properties.

In this work, we synthesized an acrylamide-based terpolymer that is a block copolymer composed of an AB alternating copolymer and a C homopolymer. The key to the unprecedented achievement is rational design of an acrylate-acrylamide divinyl monomer carrying CF3-substituted salicylic acid ester bonds (AAm-CF3) to realize the efficient and selective cyclopolymerization as well as the quantitative transformation of the resultant cyclorepeating units. The selectivity in the cyclopolymerization and the pendant transformation ability were evaluated through reactivity ratios of the corresponding model monomers and quantitative aminolysis reactions of the model compound. The cyclopolymerization via the photoinduced electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT) process with a macrochain-transfer agent and subsequent aminolysis reaction afforded the homopolymer-block-alternating copolymer. The sequence-controlled terpolymer exhibited a very unique thermal response behavior in water that was strikingly different from the corresponding sequence-uncontrolled terpolymers, such as homopolymer-block-statistical copolymers and all statistical terpolymers, despite the fact that the structure cannot be distinguished by 1H NMR.

One-Pot Preparation of Methacrylate/Styrene Alternating Copolymers via Radical Copolymerization and Alcoholysis Modification: Sequence Impacts on Glass Transition Temperature.

A series of methacrylate/styrene alternating copolymers were efficiently and systematically synthesized via alternating copolymerization of saccharin methacrylamide (1) with styrene and subsequent one-pot alcoholysis transformation with alcohols. The saccharin amide bond in 1 was stable enough that 1 was used as a bench-stable monomer, but the bond became reactive toward alcohols after the copolymerization. Thanks to the specific feature, the postpolymerization modification could be performed under mild conditions despite easy handling of the monomer. The quantitative transformation as well as the alternating sequence were certainly supported by 1H NMR and MALDI-TOF-MS analyses. The alternating copolymers carrying relatively short alkyl pendants expressed lower glass transition temperatures than those of the statistical counterparts. Moreover, the alternating copolymerization was controlled via a RAFT polymerization system, affording a unique block copolymer composed of alternating copolymer segments.

Unprecedented Sequence Control and Sequence-Driven Properties in a Series of AB-Alternating Copolymers Consisting Solely of Acrylamide Units.

Herein, we report a method to synthesize a series of alternating copolymers that consist exclusively of acrylamide units. Crucial to realizing this polymer synthesis is the design of a divinyl monomer that contains acrylate and acrylamide moieties connected by two activated ester bonds. This design, which is based on the reactivity ratio of the embedded vinyl groups, allows a "selective" cyclopolymerization, wherein the intramolecular and intermolecular propagation are repeated alternately under dilute conditions. The addition of an amine to the resulting cyclopolymers afforded two different acryl amide units, i.e., an amine-substituted acryl amide and a 2-hydroxy-ethyl-substituted acryl amide in alternating sequence. Using this method, we could furnish ten types of alternating copolymers; some of these exhibit unique properties in solution and in the bulk, which are different from those of the corresponding random copolymers, and we attributed the differences to the alternating sequence.

Control of the Alternating Sequence for N-Isopropylacrylamide (NIPAM) and Methacrylic Acid Units in a Copolymer by Cyclopolymerization and Transformation of the Cyclopendant Group.

An alternating copolymer of methacrylic acid and N-isopropyl acrylamide (NIPAM) was synthesized by selective cyclopolymerization of a special divinyl monomer and transformation of repeating cyclo-units in the resultant cyclopolymer. Crucial to the breakthrough is the monomer design in view of two types of cleavable bonds (3° ester and activated ester) in the pendant group of the monomer and the lower reactivity ratio of the two double bonds (methacrylate and electron-poor acrylate) for the polymerizable groups. The thus-obtained cyclopolymer was transformed into the alternating copolymer by transformation of the activated ester into amide by isopropyl amine and cleavage of the 3° ester by trifluoroacetic acid. The resultant copolymer showed thermal and pH response in aqueous solution that was different from the 1:1 random copolymer as well as the homopolymers.

Cyclopolymerization of Cleavable Acrylate-Vinyl Ether Divinyl Monomer via Nitroxide-Mediated Radical Polymerization: Copolymer beyond Reactivity Ratio.

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 (DPacryl/DPVE) was 55:45. The copolymer showed higher glass transition temperature than that estimated from the composition ratio and Tg values of the homopolymers, which is likely due to the formation of quasi-cyclopolymer between carboxylic acid and hydroxy groups aligned in alternating fashion.