Sequence-controlled Copolymers Research Articles

Heteroatom Substitution Strategy Modulates Thermodynamics Towards Chemically Recyclable Polyesters and Monomeric Unit Sequence by Temperature Switching.

In this paper, we proposed a heteroatom substitution strategy (HSS) in the δ-valerolactone (VL) system to modulate thermodynamics toward chemically recyclable polyesters. Three VL-based monomers containing different heteroatoms (M1 (N), M2 (S), and M3 (O)), instead of C-5 carbon, were designed and synthesized to verify our proposed HSS. All three monomers undergo organocatalytic living/controlled ROP and controllable depolymerization. Impressively, the resulting P(M1) achieved over 99 % monomer recovery under both mild solution depolymerization and high vacuum pyrolysis conditions without any side reactions, and the recycled monomers can be polymerized again forming new polymers. The systematic study of the relationship between heteroatom substitution and recyclability shows that introducing heteroatoms does change the thermodynamics of the monomers (ΔHp o, ΔSp o and Tc values), thereby adjusting the polymerizability and depolymerizability. DFT calculations found that the introduction of heteroatoms adjusts the ring strain by changing the angular strain of the monomers, and the order of their angular strain (M2>M1>M3) is consistent with the order of the experimentally obtained enthalpy change. Notably, the one-pot/one-step copolymerization of two of each of the three monomers enables the synthesis of sequence-controlled copolymers from gradient to random to block structures, by simply switching the copolymerization temperature.

Tailoring Hierarchical Structure and Rare Earth Affinity of Compositionally Identical Polymers via Sequence Control.

Macromolecule sequence, structure, and function are inherently intertwined. While well-established relationships exist in proteins, they are more challenging to define for synthetic polymer nanoparticles due to their molecular weight, sequence, and conformational dispersities. To explore the impact of sequence on nanoparticle structure, we synthesized a set of 16 compositionally identical, sequence-controlled polymers with distinct monomer patterning of dimethyl acrylamide and a bioinspired, structure-driving di(phenylalanine) acrylamide (FF). Sequence control was achieved through multiblock polymerizations, yielding unique ensembles of polymer sequences which were simulated by kinetic Monte Carlo simulations. Systematic analysis of the global (tertiary- and quaternary-like) structure in this amphiphilic copolymer series revealed the effect of multiple sequence descriptors: the number of domains, the hydropathy of terminal domains, and the patchiness (density) of FF within a domain, each of which impacted both chain collapse and the distribution of single- and multichain assemblies. Furthermore, both the conformational freedom of chain segments and local-scale, β-sheet-like interactions were sensitive to the patchiness of FF. To connect sequence, structure, and target function, we evaluated an additional series of nine sequence-controlled copolymers as sequestrants for rare earth elements (REEs) by incorporating a functional acrylic acid monomer into select polymer scaffolds. We identified key sequence variables that influence the binding affinity, capacity, and selectivity of the polymers for REEs. Collectively, these results highlight the potential of and boundaries of sequence control via multiblock polymerizations to drive primary sequence ensembles hierarchical structures, and ultimately the functionality of compositionally identical polymeric materials.

Click Chemistry for Linker-Free BAMO-Based Energetic Sequence-Controlled Copolymers

Click Chemistry for Linker-Free BAMO-Based Energetic Sequence-Controlled Copolymers

Sequence-Controlled Polymer Synthesis Derived from Alcohols, Cyclic Enol Ethers, and Vinyl Ethers: Selective Generation of 2-Alkoxy Cyclic Ethers Followed by Living Cationic Alternating Copolymerization by the One-Pot Process

Syntheses of sequence-controlled copolymers with controllable molecular weights and chain ends composed of alcohols, cyclic enol ethers, and vinyl ethers (VEs) were demonstrated using an approach consisting of selective monomer generation and subsequent alternating copolymerization. Acid-catalyzed additions of alcohols to 2,3-dihydrofuran or 3,4-dihydro-2H-pyran proceeded quantitatively to yield 2-alkoxy cyclic ethers (2-ACEs). Subsequent cationic alternating copolymerization of the 2-ACE and a VE proceeded successfully via concurrent ring-opening and vinyl-addition mechanisms, yielding copolymers with periodically arranged alcohol-derived side chain-containing cyclic enol ether and VE moieties in the repeating units. Complete degradation of the obtained copolymers into a single compound by alcoholysis confirmed the alternating sequences. The use of 2-propanol, (−)-menthol, and (1R)-endo-(+)-fenchyl alcohol was effective for the syntheses of well-defined polymers, whereas the use of methanol resulted in oligomers. The bulkiness of the alkoxy groups of the 2-ACEs likely contributed to the preference for propagation rather than chain transfer.

Controlling Rheology of Fluid Interfaces through Microblock Length of Sequence-Controlled Amphiphilic Copolymers.

Previous studies have demonstrated that films of sequence-controlled amphiphilic copolymers display contact angles that depend on microblock size. This suggests that microblock length may provide a means of tuning surface and interfacial properties. In this work, the interfacial rheology of a series of sequence-controlled copolymers, prepared through the addition of bicyclo[4.2.0]oct-1(8)-ene-8-carboxamide (monomer A) and cyclohexene (monomer B) to generate sequences up to 24 monomeric units composed of (A m B n ) i microblocks, where m, n, and i range from 1 to 6. Interfacial rheometry is used to measure the mechanical properties of an air-water interface with these copolymers. As the microblock size increases, the interfacial storage modulus, G', increases, which may be due to an increase in the size of interfacial hydrophobic domains. Small-angle X-ray scattering shows that the copolymers have a similar conformation in solution, suggesting that any variations in the mechanics of the interface are due to assembly at the interface, and not on solution association or bulk rheological properties. This is the first study demonstrating that microblock size can be used to control interfacial rheology of amphiphilic copolymers. Thus, the results provide a new strategy for controlling the dynamics of fluid interfaces through precision sequence-controlled polymers.

Self-assembly of sequence-regulated amphiphilic copolymers with alternating rod and coil pendants.

We conducted a computational study on the self-assembly behavior of sequence-controlled amphiphilic copolymers with alternating rod and coil pendants. Complex self-assembled morphologies, such as onion-like vesicles with two layers, can be generated by introducing rod pendants. The amphiphilic alternating copolymers self-assemble into onion-like vesicles through a fusion process of tiny micelles and a bending operation of disk-like micelles with double layers. A stimuli-responsive simulation shows that the cylindrical vesicles can transform into onion-like vesicles by a rod-to-coil conformation transition of rigid pendants. Inspired by this finding, we conducted a drug-loading simulation by adding two reactive drugs at different stages and found that the onion-like vesicles can almost completely isolate two drugs. This work provides theoretical guidance on the self-assembly of amphiphilic alternating copolymers with rod and coil pendants for future experimental design.

Isotactic-Alternating, Heterotactic-Alternating, and ABAA-Type Sequence-Controlled Copolyester Syntheses via Highly Stereoselective and Regioselective Ring-Opening Polymerization of Cyclic Diesters.

Synthesizing different types of sequence-controlled copolyesters can enrich the diversity of copolyesters and modify their properties more precisely, but it is still a challenge to synthesize a complicated sequence-controlled copolyester using different hydroxy acids in a living polymerization manner. In this work, a highly regioselective and stereoselective catalytic system was developed to synthesize biorenewable and biodegradable copolyesters of mandelic acid and lactic acid with isotactic-alternating, heterotactic-alternating, and ABAA-type precise and complicated sequences. Because of the regular incorporation of mandelic acid into polylactide, these sequence-controlled copolymers of mandelic acid and lactic acid show higher glass-transition temperatures than polylactide and a random copolymer. A stereocomplexation interaction between two opposite enantiomeric isotactic polymer chains was also discovered in the isotactic-alternating copolymer.

2,5-Dimethylfuran/Acrylonitrile as Latent Monomer for Sequence-Controlled Copolymer and Sequence-Dependent Thermo-Responsivity.

Sequence control has attracted increasing attention for its ability of regulating polymer property and performance. Herein, the sequence-controlled polymer containing acrylonitrile (AN) is achieved by using 2,5-dimethylfuran/acrylonitrile adduct as a latent monomer. The temperature-dependent retro Diels-Alder reaction is engaged in controlling the release of AN during RAFT polymerization, that is, regulating the instant AN concentration via a non-invasive and in situ manner. Such control over the instant AN concentration and particularly the molar ratio of comonomer pair leads to the simultaneous change of monomer units in "living" polymeric chain, thus resulting in the sequence-controlled polymeric structures. By delicately manipulating the polymerization temperature, diverse sequence-on-demand structures of AN-containing copolymers, such as poly(AN/methyl methacrylate), poly(AN/styrene), poly(AN/butyl acrylate), poly(AN/N,N-dimethylacrylamide), and poly(AN/N-isopropylacrylamide) are created. Meanwhile, this study presents an initial attempt in tuning the thermal responsivity of poly(AN/N-isopropylacrylamide), which is closely correlated to the sequence of polymer structure. More importantly, the polymer with averagely distributed AN units results in the higher thermal sensitivity. Therefore, the synthetic strategy proposed in this work offers a promising platform for accessing the sequence-controlled copolymers containing AN structures, thus expanding the investigation on the relationship between the polymer structures and correlated properties.

Elucidating the effect of sequence and degree of polymerization on antimicrobial properties for block copolymers

Sequence-controlled copolymers have recently attracted great interest in a variety of applications, including antimicrobial materials.

Highly Regioselective Ring-Opening Polymerization of Cyclic Diester for Alternating Sequence-Controlled Copolymer Synthesis of Mandelic Acid and Glycolic Acid

To control the monomer sequence in copolymers of different hydroxyl acids remains a big challenge so far, which is valuable for tuning the properties of copolyesters. In this work, the perfectly al...

Role of N-substituents of maleimides on penultimate unit effect for sequence control during radical copolymerization

Radical copolymerization of N-substituted maleimides (RMIs) and olefins provides AAB sequence-controlled copolymers by penultimate unit (PU) control. In this study, we investigated the steric, resonance, and polar effects of N-substituents on sequence control during copolymerization of RMIs as the M2 monomer with diisobutene (DIB) and d-limonene (Lim) as the M1 monomer in chloroform at 60 °C. The monomer reactivity ratios (i.e., r2 (= k22/k21), r12 (= k122/k121), and r22 (= k222/k221)) were determined based on the terminal and PU models using a nonlinear least-squares method. For the copolymerization of RMIs with DIB, the introduction of a bulky N-alkyl group suppressed the PU effect and led to the formation of alternating copolymers. The copolymerization of N-phenylmaleimides with o- and p-substituents was also investigated to reveal the steric, resonance, and polar effects of the substituents. In conclusion, less bulky and more electron-donating substituents effectively induced the PU effect during the radical copolymerization of RMIs and olefins. Radical copolymerization of N-substituted maleimides and olefins provides AAB sequence-controlled copolymers by penultimate unit control. In this study, we investigated the steric, resonance, and polar effects of N-substituents on sequence control during copolymerization of various N-substituted maleimides with diisobutene and limonene in chloroform at 60 °C, and concluded that less bulky and more electron-donating substituents effectively induced the penultimate unit effect. We also demonstrated that 2:1 sequence-controlled maleimide copolymers was efficiently produced during radical copolymerization of limonene and N-phenylmaleimides with an electron-donating substituent.

Synthesis of sequence-controlled polymers via sequential thiol-ene and amino-yne click reactions in one pot

Sequence-controlled polymers are prepared by the combination of thiol-ene click reaction and amino-yne click reaction. Due to the high selectivity of the amine unit and thiol unit toward thiolactone, methacrylate, propiolate, etc., the sequence of the resulting polymers can be easily controlled by monomer-addition sequence. Moreover, thiol-ene click reaction and amino-yne click reaction can be carried out under mild conditions without need of any catalyst. Different kinds of sequence-controlled copolymers have been prepared by the combination of thiol-ene click reaction and amino-yne click reaction in one pot. NMR spectra and GPC traces confirmed the formation of polymers with high molecular weight and controlled sequence structure. Therefore, we provide a new method for the preparation of functional polymers with well-controlled sequences.

Regenerable-Catalyst-Aided, Opened to Air and Sunlight-Driven "CuAAC&ATRP" Concurrent Reaction for Sequence-Controlled Copolymer.

An ideal stimuli-responsive controlled/living radical polymerization should have the ability to manipulate the reaction through spatiotemporal "on/off" controls, achieving the polymerization under fully open conditions and allowing for precise control over macromolecular architecture with defined molecular weights and monomer sequence. In this contribution, the photo (sunlight)-induced electron transfer atom transfer radical-polymerization (PET-ATRP) can be realized to be reversibly activated and deactivated under fully open conditions utilizing one-component copper(II) thioxanthone carboxylate as multifunctional photocatalyst and oxygen scavenger. The polymerization behaviors are investigated, presenting controlled features with first-order kinetics and linear relationships between molecular weights and monomer conversions. More importantly, "CuAAC&ATRP" concurrent reaction combining PET-ATRP, photodriven deoxygenation, and photoactivated CuAAC click reaction is successfully employed to synthesize the sequence-defined multiblock functional copolymers, in which the iterative monomer additions can be easily manipulated under fully open conditions.

Amphiphilic PEG-Functionalized Gradient Copolymers via Tandem Catalysis of Living Radical Polymerization and Transesterification

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...

シークエンス制御したマレイミド共重合体の合成と耐熱透明ポリマー材料設計への応用

シークエンス制御したマレイミド共重合体の合成と耐熱透明ポリマー材料設計への応用

Aperiodic Copolymers.

Current polymer terminology only describes very simple copolymer structures such as block, graft, alternating periodic, or statistical copolymers. This restricted vocabulary implies that copolymers exhibit either segregated (i.e., block and graft), regular (i.e., alternating and periodic), or uncontrolled (i.e., statistical or random) comonomer sequence distributions. This standard classification does not include many new types of sequence-controlled copolymers that have been reported in recent years. In this context, the present viewpoint describes a new category of copolymers: aperiodic copolymers. Such structures can be defined as copolymers in which monomer sequence distribution is not regular but follows the same arrangement in all chains. The term aperiodic can be used to describe encoded comonomer sequences in monodisperse sequence-defined copolymers but also the block sequence of some multiblock copolymers. These new types of copolymers open up very interesting perspectives for the design of complex materials. Some recent relevant literature on the topic is discussed herein.

On the synthesis of sequence-controlled poly(vinyl benzyl amine-co-N-substituted maleimides) copolymers

The sequence-controlled copolymerization of donor and acceptor comonomers was studied for the synthesis of primary amine-containing copolymers with precisely controlled functional microstructures. For this, a large excess of phthalimide-protected vinylbenzylamine was copolymerized with discrete amounts of N-substituted maleimides, namely N-benzylmaleimide, N-(n-propyl)maleimide, 4-(N-maleimido)-azobenzene and triisopropylsilyl-protected N-propargyl maleimide, in the presence of the commercial alkoxyamine BlocBuilder MA®. The formed copolymers were characterized by 1HNMR and size exclusion chromatography, and exhibited controlled chain-length, molecular weight distribution and comonomer sequence distribution. After copolymerization, the phthalimide protecting groups were removed by treatment with hydrazine monohydrate to afford vinyl benzyl amine-based copolymers. 1H and 13CNMR characterization of the deprotected samples indicated that the functional N-substituted succinimide moieties were preserved in the copolymers after hydrazine monohydrate treatment. Moreover, the obtained sequence-controlled copolymers were readily soluble in acidic water.

Functional spaces in star and single-chain polymers via living radical polymerization

This article reviews recent advances in the creation of functional spaces with core-functionalized star polymers and single-chain folding/crosslinked polymers via living radical polymerization. Various core-functionalized star polymers were efficiently prepared with functional linking agents and monomers to perform unique functions. For example, they can serve as nanoreactors for active and robust catalysis in organic reactions and polymerization and as nanocapsules for selective and stimuli-responsive molecular recognition. Single-chain folding polymers were obtained from the self-folding of amphiphilic random copolymers bearing hydrophilic poly(ethylene glycol) chains and hydrophobic alkyl pendants in water, resulting in unimer micelles with dynamic hydrophobic domains. The folded structure could be further fixed via the intramolecular crosslinking of the hydrophobic interior. In addition, cation template-assisted cyclopolymerization and concurrent tandem living radical polymerization with in situ monomer transesterification were also developed for the one-pot synthesis of cyclopolymers with large in-chain cavities and gradient and sequence-controlled copolymers.

Sequence-controlled copolymers of 2,3,4,5-pentafluorostyrene: mechanistic insight and application to organocatalysis

A number of copolymers between styrene (St) or 4-azidomethylstyrene (N3St) and 2,3,4,5,6-pentafluorostyrene (FSt) have been prepared by atom-transfer radical polymerization (ATRP) and conventional free radical polymerization (FRP). The mode of monomer alternation in copolymers has been established unambiguously using heteronuclear multiple bond correlation (HMBC) NMR. The degree and nature of monomer alternation was found to be strongly dependent on both the solvent (or lack thereof) and the polymerization initiator. These results are in contrast to previously published studies, which rely primarily on classic analysis of monomer reactivity ratios. We proceeded to independently functionalize the N3St and FSt moieties using orthogonal “click” chemistries: copper-catalyzed azide–alkyne cycloaddition (CuAAC) and fluoroarene–thiol coupling (FTC). An alternating copolymer bearing –NH2 and –SO3− functional groups was found to be a competent organocatalyst for a Henry reaction between benzaldehyde and nitromethane.

Sequence-Regulated Copolymers via Tandem Catalysis of Living Radical Polymerization and In Situ Transesterification

Sequence regulation of monomers is undoubtedly a challenging issue as an ultimate goal in polymer science. To efficiently produce sequence-controlled copolymers, we herein developed the versatile tandem catalysis, which concurrently and/or sequentially involved ruthenium-catalyzed living radical polymerization and in situ transesterification of methacrylates (monomers: RMA) with metal alkoxides (catalysts) and alcohols (ROH). Typically, gradient copolymers were directly obtained from the synchronization of the two reactions: the instantaneous monomer composition in feed gradually changed via the transesterification of R(1)MA into R(2)MA in the presence of R(2)OH during living polymerization to give R(1)MA/R(2)MA gradient copolymers. The gradient sequence of monomers along a chain was catalytically controlled by the reaction conditions such as temperature, concentration and/or species of catalysts, alcohols, and monomers. The sequence regulation of multimonomer units was also successfully achieved in one-pot by monomer-selective transesterification in concurrent tandem catalysis and iterative tandem catalysis, providing random-gradient copolymers and gradient-block counterparts, respectively. In contrast, sequential tandem catalysis via the variable initiation of either polymerization or in situ transesterification led to random or block copolymers. Due to the versatile adaptability of common and commercially available reagents (monomers, alcohols, catalysts), this tandem catalysis is one of the most efficient, convenient, and powerful tools to design tailor-made sequence-regulated copolymers.