Alternating vs. random amphiphilic polydisulfides: aggregation, enzyme activity inhibition and redox-responsive guest release

Herein, we report the synthesis of an alternating copolymer (ACP) with a bio-reducible amphiphilic polydisulfide backbone and highlight the impact of the alternating monomer connectivity on the self-assembly, morphology, chain-exchange dynamics, drug-release kinetics, and enzyme activity inhibition. Condensation polymerization between hydrophobic 1,10-bis(pyridin-2-yldisulfaneyl)decane and hydrophilic 2,3-mercaptosuccinic acid (1.04 : 1.00 ratio) generated amphiphilic ACP P1 (Mw = 8450 g mol-1, Đ = 1.3), which exhibited self-assembly in water, leading to the formation of an ultra-thin (height <5.0 nm) entangled fibrillar network. In contrast, structurally similar amphiphilic random copolymer P2 exhibited a truncated irregular disc-like morphology under the same conditions. It is postulated that due to the perfect alternating sequence of the hydrophobic and hydrophilic segments in P1, its immiscibility-driven aggregation in water leads to a pleated structure, which further assembles and forms the observed long fibrillar structures, similar to crystallization-driven self-assembly. In fact, wide-angle X-ray diffraction (WXRD) analysis of a lyophilized P1 sample showed sharp peaks, indicating its crystalline nature (approximately 37% crystallinity), and these were completely missing for P2. The effect of such distinct self-assembly on the chain-exchange dynamics was probed by fluorescence resonance energy transfer (FRET) using 3,3'-dioctadecyloxacarbocyanine perchlorate (DiO) and 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI) as the FRET-donor and -acceptor, respectively. For DiI- and DiO-entrapped solutions of P1, when mixed, no prominent FRET appeared even after 24 h. In sharp contrast, for P2, intense FRET emission occurred, and the FRET ratio (approximately 0.9) reached saturation in approximately 15 h, indicating the greatly enhanced kinetic stability of P1 aggregates. Glutathione-induced release of encapsulated Nile red showed much slower kinetics for P1 compared to that of P2, which was corroborated by the observed slow chain-exchange dynamics of the highly stable alternating copolymer assembly. Furthermore, the well-ordered assembly of P1 exhibited an excellent surface-functional group display (zeta potential of -32 mV compared to -14 mV for P2), which resulted in the effective recognition of the α-chymotrypsin (Cht) protein surface by electrostatic interaction. Consequently, P1 significantly (>70%) suppressed the enzymatic activity of Cht, while in the presence of P2, the enzyme was still active with >70% efficacy.

Recent Applications of Amphiphilic Copolymers in Drug Release Systems for Skin Treatment

Amphiphilic copolymers (ACs) are versatile systems with self-assembling and aggregating properties, enabling the formation of nanomaterials (NMs) such as micelles, vesicles, nanocapsules, and nanogels. These materials have been extensively explored for the delivery of various drugs and active compounds, enhancing the solubility and permeation of poorly water-soluble drugs into skin tissue. This improvement facilitates the treatment of skin diseases, including chronic conditions like cancer, as well as infections caused by bacteria, fungi, and viruses. This review summarizes recent applications of ACs in skin treatment, with a particular focus on their use in anti-cancer drug therapy. It covers the synthesis, classification, and characterization of ACs using various experimental techniques. Additionally, it discusses recent research on different drug delivery pathways using ACs, including encapsulation efficiency, release behavior, characteristics, applications, and responses to various chemical and physical stimuli (both in vivo and in vitro). Furthermore, this review provides a comprehensive analysis of the effects of ACs NMs on several skin diseases, highlighting their potential as alternative treatments.

Alternating Graft Copolymer Carrying PLA Graft Chains at Every Other Unit: Sequence Impacts on Crystallization Behaviors

Alternating graft copolymers were precisely synthesized via selective cyclopolymerization of pendant-transformable divinyl monomer (1), post-polymerization modification via aminolysis with alkylamine, and ring-opening polymerization of l-lactide (LLA) from the hydroxy pendant group in alternating sequence. The poly(LLA) (PLLA) graft chain on the alternating copolymer gave a higher crystallization degree on the isothermal treatment than that on the random counterpart likely because of the periodic sequence. The comonomer pendant group from alkylamine in the aminolysis reaction in the alternating sequence affected the crystallization behaviors, and the oligoethylene glycol (OEG) group promoted the crystallization thanks to the larger free volume effect. As for the stereocomplex formation of the racemic mixture of enantiomeric PLLA and poly(d-lactide) (PDLA) chains, the alternating graft copolymer gave a higher degree of stereocomplex crystallization in the mixture with the enantiomer homopolymer than the random analogue.

Radical Stitching Polymerization and Its Alternating Copolymerization

Polymers possessing saturated fused polycycles in the main chain repeating unit have been underexplored despite their potential utility based on their expected properties such as high rigidity, chemical resistance, transparency, and thermal stability. In this regard, herein, we developed a radical stitching polymerization of styryl vinyl ketones for the synthesis of polyketones possessing saturated fused bicyclic repeating units. The polymerization proceeded smoothly with a high degree of stitching efficiency in a chain-growth manner under free radical conditions. This method was further extended to the alternating copolymerization of styryl vinyl ketones and 1-styryl-2-vinylbenzenes, representing the first alternating stitching copolymerization of two different monomers. The obtained polymers were found to show promising thermal properties and high transparency in the visible light region.

Ultrasmall Single-Chain Nanoparticles Derived from Amphiphilic Alternating Copolymers

The collapse or folding of an individual polymer chain into a nanoscale particle gives rise to single-chain nanoparticles (SCNPs), which share a soft nature with biological protein particles. The precise control of their properties, including morphology, internal structure, size, and deformability, are a long-standing and challenging pursuit. Herein, a new strategy based on amphiphilic alternating copolymers for producing SCNPs with ultrasmall size and uniform structure is presented. SCNPs are obtained by folding the designed alternating copolymer in N,N-dimethylformamide (DMF) and fixing it through a photocatalyzed cycloaddition reaction of anthracene units. Molecular dynamics simulation confirms the solvophilic outer corona and solvophobic inner core structure of SCNPs. Furthermore, by adjusting the length of PEG units, precise control over the mean size of SCNPs is achieved within the range of 2.8 to 3.9 nm. These findings highlight a new synthetic strategy that enables enhanced control over morphology and internal structure while achieving ultrasmall and uniform size for SCNPs.

Radical Homopolymerization of Linear α-Olefins Enabled by 1,4-Cyano Group Migration

α-Olefins are valued and abundant building blocks from fossil resources. They are widely used to provide small-molecule or polymeric products. Despite numerous advantages of radical polymerization, it has been well-documented as textbook knowledge that α-olefins and their functionalized derivatives cannot be radically homopolymerized because of the degradative chain transfer side reactions. Herein, we report our studies on the homopolymerization of thiocyanate functionalized α-olefins enabled by 1,4-cyano group migration under radical conditions. By this approach, a library of ABC sequence-controlled polymers with high molecular weights can be prepared. We can also extend this strategy to the homopolymerization of α-substituted styrenic and acylate monomers which are known to be challenging to achieve. Overall, the demonstrated functional group migration radical polymerization could provide new possibilities to synthesize polymers with unprecedented main chain sequences and structures. These polymers are promising candidates for novel polymeric materials.

Design of sec-Benzyl Vinyl Ethers toward the Synthesis of Alternating Copolymers Composed of Vinyl Alcohol and Vinyl Ether Units

In this work, we designed benzyl vinyl ethers carrying alkyl substituents at the benzyl position (i.e., sec-BnVEs) as bulky, reactive, and transformable monomers to realize the alternating cationic copolymerization with an alkyl vinyl ether (VE). In particular, the isopropyl substitution caused not only the bulkiness to suppress the successive propagation but also an enhancement of the vinyl group reactivity to promote crossover propagation with a less bulky VE comonomer. The isopropyl-substituted BnVE (iPr-BnVE) underwent living cationic alternating copolymerization with n-butyl VE (nBVE), and the alternating propagation was strongly suggested by the reactivity ratios. The subsequent deprotection of the sec-benzyl pendant afforded the vinyl alcohol (VA)-nBVE alternating copolymer, and the corresponding statistical copolymer was also synthesized by using the nonsubstituted monomer (BnVE) instead of iPr-BnVE. The alternating copolymer exhibited a higher glass transition temperature, which likely stems from the uniform and efficient hydrogen-bonding formation due to the periodic sequence.

Antibacterial activity of hydrophobicity modulated cationic polymers with enzyme and pH-responsiveness

The membrane lipid compositions of prokaryotic and eukaryotic cells are inherently different in many aspects, although some similarities exist in their structure and composition. Therefore, selective targeting of membrane lipids with a compound of therapeutic value, such as an antibacterial copolymer, is often challenging. Hence, developing an ideal copolymer with antibacterial properties demands hydrophobicity/hydrophilicity balance with a high biosafety profile. To integrate hydrophobic/hydrophilic balance and cationic charge in an alternating antibacterial copolymer with enzyme and pH-responsiveness, a lysine appended styrenic monomer was copolymerized with a fatty acid (octanoic acid (OA) or myristic acid (MA)) tethered maleimide monomer via reversible addition-fragmentation chain transfer (RAFT) polymerization. A range of microscopic analyses, including dynamic light scattering (DLS), confirmed the formation of nanoaggregates (size ∼30-40 nm) by these polymers in aqueous solution with positive zeta potential (cationic surface charge). Hydrophobic Nile red (NR) dye was successfully encapsulated in the nanoaggregates, and the in vitro release kinetics of the NR dye were monitored at different pHs and in the presence or absence of esterase/lipase. The in vitro release kinetics of NR revealed ∼85% dye release in the presence of pH 5.5 and lipase, suggesting their suitability for pH/enzyme-triggered therapeutic payload delivery. The standard broth microdilution assay showed significant bactericidal activity against both Gram-positive (Bacillus subtilis) and Gram-negative (Escherichia coli) bacteria with an MIC50 value <30 μg mL-1. The effect of polymeric nanoaggregates on bacterial morphology and in vitro survival was further confirmed by field emission scanning electron microscopy (FESEM), agar gel disk diffusion assay, and bacterial live/dead cell count. The significantly low hemolytic activity against red blood cells (RBCs) (HC50 >103 μg mL-1) and nontoxic effect on human intestinal epithelial cells (INT 407) (EC50 >500 μg mL-1) ensure that the polymer nanoaggregates are safe for in vivo use and can serve as a potent antibacterial polymer.

Synthesis of High-Molecular-Weight Poly(ether-alt-ester) by Selective Double Ring-Opening Polymerization of Spiroorthoesters

We report the selective double ring-opening polymerization of presequenced spiroorthoester monomers to form high-molecular-weight (≈90 kDa) poly(ether-alt-ester)s with a simple cationic alkyl gallium catalyst. The selective formation of double ring-opened polymer units was confirmed by NMR and IR spectroscopies. Thermal and rheological properties of homo- and copolymers were further characterized by differential scanning calorimetry, thermogravimetric analysis, and stress-controlled rotational rheometry. Linear viscoelastic moduli show that these systems are well entangled (plateau modulus), thereby possessing nearly terminal relaxation at long time scales (low frequencies) and Rouse segmental dynamics at short time scales (high frequencies) with characteristic slopes. These are the highest-molecular-weight poly(ether-alt-ester)s reported to date.

Umpolung Isomerization in Radical Copolymerization of Benzyl Vinyl Ether with Pentafluorophenylacrylate Leading to Degradable AAB Periodic Copolymers

This study revealed that benzyl vinyl ether (BnVE) shows a peculiar isomerization propagation in its radical copolymerization with an electron-deficient acrylate carrying a pentafluorophenyl group (PFA). The co-monomer pair inherently exhibits the cross-over propagation feature due to the large difference in the electron density. However, the radical species of PFA was found to undergo a backward isomerization to the penultimate BnVE pendant giving a benzyl radical species prior to propagation with BnVE. The isomerization brings a drastic change in the character of the growing radical species from electrophilic to nucleophilic, and thus the isomerized benzyl radial species propagates with PFA. Consequently, the two monomers were consumed in the order AAB (A: PFA; B: BnVE) and the unique periodic consumption was confirmed by the pseudo-reactivity ratios calculated by the penultimate model: r11 =0.174 and r21 =6600 for PFA (M1 ) with BnVE (M2 ). The pentafluorophenyl ester groups of the resulting copolymers are transformed into ester and amide groups by post-polymerization alcoholysis and aminolysis modifications. The unique isomerization in the AAB sequence allowed the periodic introduction of a benzyl ether structure in the backbone leading to efficient degradation under acid conditions.

A General Strategy To Access Alternating Styrene/Substituted Styrene Copolymers by Using a Traceless Controlling Group

We herein report a synthetic strategy for alternating copolymers of styrene and substituted styrenes by utilizing α-styryl boronate pinacol ester (StBpin) as the co-monomer through radical alternating copolymerization followed by protodeboronation. The excellent alternating polymerization behavior of the StBpin co-monomer in such a radical polymerization system is considered to be attributed to the steric hindrance and radical stabilization exerted by the Bpin group. This strategy is effective with a wide range of substituted styrene co-monomers regardless of the electronic nature of the substituents, and the protodeboronation of the alternating Bpin-containing polymers is highly efficient without polymer backbone alternation. RAFT living polymerization was also compatible with this approach. Thus, this strategy provides a way to build-up alternating copolymers consisting of similar styrene-type co-monomers, which has been inaccessible by conventional synthetic methods.

A Transformable and Bulky Methacrylate Monomer That Enables the Synthesis of an MMA-nBA Alternating Copolymer: Sequence-Dependent Self-Healing Properties

In this study, we designed a methacrylate molecule with an alkyl-substituted trichloro salicylic acid pendant as a transformable bulky monomer to enable the synthesis of an alternating copolymer of methyl methacrylate (MMA) and n-butyl acrylate (nBA). The adamantyl-substituted methacrylate monomer (1-Ad) showed very low homopolymerization propensity in radical polymerizations, but afforded the alternating copolymer with nBA via copolymerization. The 1-Ad units in the resultant copolymer were quantitatively and selectively transformed into MMA via transesterification with methanol to yield the alternating copolymer of MMA and nBA. Its alternating sequence was clearly demonstrated by a structural analysis via ¹³ C NMR spectroscopy as well as the low reactivity ratios for the 1-Ad and nBA pair. Finally, we verified the superior self-healing ability of the alternating copolymer compared to that of the corresponding 1 : 1 statistical copolymer.

The Fluorocarbene Exploit: Enforcing Alternation in Ring-Opening Metathesis Polymerization

Fluoroalkenes are known to be notoriously reluctant substrates for olefin metathesis due to the generation of thermodynamically stable Fischer-type fluorocarbene intermediates, which invariably fail to undergo further reaction. In the present disclosure, we find that fluorine substitution on the sp² carbon also strictly suppresses homopolymerization of norbornene derivatives (NBEs), and this can be harnessed to achieve alternating ring-opening metathesis polymerization (ROMP) with an appropriately electron-rich comonomer. Dihydrofuran (DHF) is thereby shown to undergo alternating ROMP with fluorinated norbornenes, the perfectly alternating structure of the resulting copolymer having been unambiguously elucidated by ¹H, ¹⁹F, and ¹³C NMR analyses. Furthermore, we find that the degradability of the resultant copolymers in acidic media via hydrolysis of enol ether moieties in the backbone can be predictably modulated by the number of fluorine atoms present in the NBE comonomer, affording an opportunity to engage with the desirable physical properties of fluorinated polymers while limiting their attendant environmental degradability issues.

Alternating Terpolymers through Cyclopolymerization and Subsequent Orthogonal Functionalization

A method for the synthesis of functionalized alternating copolymers by reversible deactivation radical polymerization was developed. Copolymerization by reversible addition-fragmentation chain transfer of hexenyl vinyl ether with a novel fluorinated divinyl monomer yields alternating cyclopolymers that can be chemoselectively modified by three distinct orthogonal functionalization reactions. Along the thiol-ene click reaction and amidation, a third functionalization was achieved via NHC-catalyzed transesterification or acylation resulting in a small library of ABC-type alternating terpolymers.

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.

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.

Temperature triggered alternating copolymerization of epoxides and lactones via pre-sequenced spiroorthoester intermediates

We report the alternating copolymerization of caprolactone and epoxide through the in situ formation of pre-sequenced spiroorthoester monomer. The reaction is catalyzed by the temperature triggered, bifunctional cationic indium complex (±)-[(NN_iO_tBu)In(CH₂SiMe₃)][B(C₆F₅)₄] (1). 1 can catalyze the coupling of epoxide and lactone to form spiroorthoester at 60 °C and its double ring-opening polymerization at 110 °C to form poly(ether-alt-ester). The post-polymerization modification and degradation of the poly(ether-alt-ester) are further investigated.

We report the alternating copolymerization of caprolactone and epoxide through the in situ formation of pre-sequenced spiroorthoester monomer.

Unraveling Sequence Effect on Glass Transition Temperatures of Discrete Unconjugated Oligomers

Sequence plays a critical role in enabling unique properties and functions of natural biomolecules, which has promoted the rapid advancement of synthetic sequence-defined polymers in recent decades. Particularly, investigation of short chain sequence-defined oligomers (also called discrete oligomers) on their properties has become a hot topic. However, most studies have focused on discrete oligomers with conjugated structures. In contrast, unconjugated oligomers remain relatively underexplored. In this study, three pairs of discrete oligomers with the same composition but different sequence for each pair are employed for investigating their glass transition temperatures (T_g s). The resultant T_g s of sequenced oligomers in each pair are found to be significantly different (up to 11.6 °C), attributable to variations in molecular packing as demonstrated by molecular dynamics and density function theory simulations. Intermolecular interaction is demonstrated to have less impact on T_g s than intramolecular interaction. The mechanistic investigation into two model dimers suggests that monomer sequence caused the difference in intramolecular rotational flexibility of the sequenced oligomers. In addition, despite having different monomer sequence and T_g s, the oligomers have very similar solubility parameters, which supports their potential use as effective oligomeric plasticizers to tune the T_g s of bulk polymer materials.

Lewis Pair Catalyzed Regioselective Polymerization of (E,E)-Alkyl Sorbates for the Synthesis of (AB)n Sequenced Polymers

In this contribution, Lewis pairs (LPs) composed of N-heterocyclic olefins (NHOs) with different steric hindrance and nucleophilicity as Lewis bases (LBs) and Al-based compounds with comparable acidity but different steric hindrance as Lewis acids (LAs) were applied for 1,4-selective polymerization of (E,E)-methyl sorbate (MS) and (E,E)-ethyl sorbate (ES). The effects of steric hindrance, electron-donating ability, and acidity of LPs on MS and ES polymerization were systematically investigated. High catalytic activity and high initiation efficiency can be achieved, leading to the formation of PMS with 100 % 1,4-selectivity, tunable molecular weight (M_w up to 333 kg mol^-1 ), and narrow molecular weight distribution (MWD). Block copolymerization of ES and methyl methacrylate (MMA) was also realized. Meanwhile, this system can be applied to other homologous conjugated diene substrates. Furthermore, simple chemical reactions can efficiently convert PMS to different polymers with strict (AB)_n sequence structures, such as poly(sorbic acid), poly(propylene-alt-methyl acrylate), poly(propylene-alt-acrylic acid), poly(propylene-alt-allyl alcohol), and poly(ethylene-alt-2-butylene).

Ouzo phase occurrence with alternating lipo/hydrophilic copolymers in water

Selection of monomer couples, ensuring reactivity ratios close to zero, is an effective strategy to induce spontaneous copolymerization into an alternating sequence. In addition, monomer design and customisation of the solvent-monomer interactions open the way to functional copolymers showing molecular self-assembly relevant to their regular amphipathic structure. In this work, we show that the design of comonomers with adequate reactivities and interactions can be used to direct copolymer self-assembly on a mesoscopic scale. We investigate spontaneous formation of nanoparticles through solvent/non-solvent interactions using the so-called "ouzo effect". In this way, an ouzo diagram was built to determine the operation window for the self-assembly, in aqueous suspensions, of alternating copolymers consisting of vinyl phenol and maleimide units carrying long alkyl-pendant groups (C₁₂H₂₅ or C₁₈H₃₇). Also, investigations were pursued to account for the influence of the lateral lipophilic pendant units on the size and structure of the nanoaggregates formed during one-shot water addition. Structure characterisation by light scattering techniques (DLS and SLS), small-angle neutron scattering (SANS) and transmission electron microscopy (cryo-TEM and TEM) confirmed the self-assembly of copolymer chains into nanoparticles (size range: 60-300 nm), the size of which is affected by the lipophilicity of the alternating copolymers, solvent-water affinity and the solvent diffusion in water. Altogether, we present here the spontaneous ouzo effect as a simple method to produce stable alternating copolymer nanoparticles in water without the addition of stabilizing agents.

Substituent Effects Provide Access to Tetrasubstituted Ring-Opening Olefin Metathesis of Bicyclo[4.2.0]oct-6-enes

Herein, we report the origin of unexpected reactivity of bicyclo[4.2.0]oct-6-ene substrates containing an α,β-unsaturated amide moiety in ruthenium-catalyzed alternating ring-opening metathesis polymerization reactions. Specifically, compared with control substrates bearing an ester, alkyl ketone, nitrile, or tertiary amide substituent, α,β-unsaturated substrates with a weakly acidic proton showed increased rates of ring-opening metathesis mediated by Grubbs-type ruthenium catalysts. ¹H NMR and IR spectral analyses indicated that deprotonation of the α,β-unsaturated amide substrates resulted in stronger coordination of the carbonyl group to the ruthenium metal center. Principal component analysis identified ring strain and the electron density on the carbonyl oxygen (based on structures optimized by means of ωB97X-D/6311+G(2df,2p) calculations) as the two key contributors to fast ring-opening metathesis of the bicyclo[4.2.0]oct-6-enes; whereas the dipole moment, conjugation, and energy of the highest occupied molecular orbital had little to no effect on the reaction rate. We conclude that alternating ring-opening metathesis polymerization reactions of bicyclo[4.2.0]oct-6-enes with unstrained cycloalkenes require an ionizable proton for efficient generation of alternating polymers.

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.

Reduction-Induced Crystallization-Driven Self-Assembly of Main-Chain-Type Alternating Copolymers: Transformation from 1D Lines to 2D Platelets

In recent years, crystalline-driven self-assembly (CDSA) has received enormous attention, but almost only for block copolymers (BCPs). Herein, we introduced perfluorocarbon chains into main-chain-type liquid crystalline alternating copolymers (ACPs) to obtain perfluoroalkane-containing ACPs with periodic C-I bonds in polymer backbones via step transfer-addition and radical-termination (START) polymerization, followed by an iodine reduction reaction of C-I bonds to induce CDSA of ACPs and put forward a novel concept of "reduction-induced crystallization-driven self-assembly" (RI-CDSA) of main-chain-type ACPs for the first time. Finally, we proposed the folded-chain model and mechanism to explain the novel RI-CDSA behavior, and its rationality has been proved by the corresponding experimental results.

Perfluoroalkylated alternating copolymer possessing solubility in fluorous liquids and imaging capabilities under high energy radiation

A highly fluorinated alternating polymer, P(RFMi-St), possessing improved thermal properties and patterning capabilities over perfluoroalkyl polymethacrylates under high energy radiation was achieved with semi-perfluorododecyl maleimide (RFMi) and styrene (St). RFMi could be synthesised efficiently via a Mitsunobu reaction condition and copolymerised with St by free radical and reversible-deactivation radical polymerisation protocols. P(RFMi-St) showed a satisfactory glass-transition temperature (108 °C) and intermolecular cross-linking behaviour under electron-beam and commercially more important extreme UV (λ = 13.5 nm) irradiation. The exposed regions lost their solubility, resulting in the successful formation of mechanically non-deteriorated negative-tone images down to 50 nm. In addition, P(RFMi-St) could be solution-processed with chemically non-damaging fluorous liquids, which enabled the polymer to be applied effectively on top of an organic semiconductor layer as a dielectric material (dielectric constant 2.7) for the organic field-effect transistor fabrication.

Dependence of the liquid crystalline properties on the exactly controlled single-site functionalized density of mesogens focused on the alternating copolymer model

Fluorinated liquid crystal polymers (FLCPs) with an alternating sequence of mesogenic moieties within their backbones were precisely constructed.

Information-Based Design of Polymeric Drug Formulation Additives

Tailor-made copolymers are designed based on a peptide-poly(ethylene glycol) (QFFLFFQ-PEG) conjugate as a blueprint, to solubilize the photosensitizer meta-tetra(hydroxyphenyl)chlorin (m-THPC). The relevant functionalities of the parent peptide-PEG are mimicked by employing monomer pairs that copolymerize in a strictly alternating manner. While styrene (S) or 4-vinylbenzyl-phthalimide (VBP) provide aromatic moieties like Phe, the aliphatic isobutyl side chain of Leu4 is mimicked by maleic anhydride (MA) that reacts after polymerization with isobutylamine to give the isobutylamide-carboxyl functional unit (iBuMA). A set of copolymer-PEG solubilizers is synthesized by controlled radical polymerization, systematically altering the length of the functional segment (DP_n = 2, 4, 6) and the side chain functionalization (iBuMA, iPrMA, MeMA). The m-THPC hosting and release properties of P[S-alt-iBuMA]₆-PEG reached higher payload capacities and more favored release rates than the parent peptide-PEG conjugate. Interestingly, P[S-alt-RMA]_n-PEG mimics the sensitivity of the peptide-PEG solubilizer well, where the exchange of Leu4 residue by Val and Ala significantly reduces the drug loading by 92%. A similar trend is found with P[S-alt-RMA]_n-PEG as the exchange of iBu → iPr → Me reduces the payload capacity up to 78%.

Synthesis of Well-Defined Alternating Copolymer Composed of Ethylmaleimide and Hydroxy-Functionalized Vinyl Ether by RAFT Polymerization and Their Thermoresponsive Properties

Here we report the controlled synthesis of alternating copolymers by reversible addition-fragmentation chain transfer (RAFT) polymerization of hydroxy-functionalized vinyl ether (DEGV) and ethylmaleimide (EtMI) using dithiocarbonate derivative (CPDB) as the RAFT reagent. The resulting alternating copolymer poly[ethylmaleimide-alt-(diethylene glycol mono vinyl ether)] (poly(MalMI-alt-DEGV)) had a relatively narrow molecular weight distribution (M_w/M_n < 1.4). These polymers are fully soluble in cold water (5 °C) and an aqueous solution of poly(MalMI-alt-DEGV) became turbid upon heating (using an incident wavelength of 600 nm and 1.0 mg mL⁻¹ (0.1 wt %) polymer concentration), indicating phase separation above the cloud point temperature (T_cp). The T_cp of the polymer solution ranged from 15–35 °C, depending on the molecular weight and molecular weight distribution of the polymer.

Telodendrimers: Promising Architectural Polymers for Drug Delivery

Architectural complexity has played a key role in enhancing the efficacy of nanocarriers for a variety of applications, including those in the biomedical field. With the continued evolution in designing macromolecules-based nanoparticles for drug delivery, the combination approach of using important features of linear polymers with dendrimers has offered an advantageous and viable platform. Such nanostructures, which are commonly referred to as telodendrimers, are hybrids of linear polymers covalently linked with different dendrimer generations and backbones. There is considerable variety in selection from widely studied linear polymers and dendrimers, which can help tune the overall composition of the resulting hybrid structures. This review highlights the advances in articulating syntheses of these macromolecules, and the contributions these are making in facilitating therapeutic administration. Limited progress has been made in the design and synthesis of these hybrid macromolecules, and it is through an understanding of their physicochemical properties and aqueous self-assembly that one can expect to fully exploit their potential in drug delivery.

Saccharin-pendant methacrylamide as a unique monomer in radical copolymerization: peculiar alternating copolymerization with styrene

A saccharin metharylamide was found to uniquely induce alternating copolymerization with styrene.