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The effect of dispersity on block polymer self-assembly was studied in the monodisperse limit using a combination of synthetic chemistry, matrix-assisted laser desorption ionization spectroscopy, and small-angle X-ray scattering. Oligo(methyl methacrylate) (oligoMMA) and oligo(dimethylsiloxane) (oligoDMS) homopolymers were synthesized by conventional polymerization techniques and purified to generate an array of discrete, semidiscrete, and disperse building blocks. Coupling reactions afforded oligo(DMS–MMA) block polymers with precisely tailored molar mass distributions spanning single molecular systems (Đ = 1.0) to low-dispersity mixtures (Đ ≈ 1.05). Discrete materials exhibit a pronounced decrease in domain spacing and sharper scattering reflections relative to disperse analogues. The order–disorder transition temperature (TODT) also decreases with increasing dispersity, suggesting stabilization of the disordered phase, presumably due to the strengthening of composition fluctuations at the low molar mas...

A facile, highly efficient, and metal-free synthesis of well-defined polyester-based core cross-linked star (CCS) polymers with yields of up to 96 % was achieved via an organic catalyst (i.e., methanesulfonic acid) mediated ring-opening polymerization (ROP) at room temperature, through either a two-pot or a one-pot, two-step strategy. CCS polymers with narrow molecular weight distributions (PDI ≤ 1.3) and macroinitiator (MI) conversions of 90−96% were prepared using poly(ε- caprolactone) (PCL) MIs with molecular weights ranging from 9.9 to 36.2 kDa and [4,4′-bioxepane]-7,7′-dione (BOD) as the cross-linker. Furthermore, transesterification was identified as being responsible for the small percentage of unincorporated low molecular weight polymer remaining and star−star couplings in the star formation. Compared to CCS polymers synthesized via the methanesulfonic acidmediated ROP, CCS polymers prepared via ROP mediated by high transesterification rate catalysts (i.e., stannous octoate (Sn(Oct)2)) suffer from much lower star purity (ca. 70%) and star−star coupled products due to more prominent transesterification side-reactions. Refereed/Peer-reviewed

Regulating the aqueous polymerization of acrylic acid (AA) is a major opportunity for future materials design, requiring the development of scalable, industry‐oriented procedures that afford modest molar mass and dispersity control without long reaction times and environmentally demanding conditions. To address these challenges, this report presents the rapid copolymerization of aqueous mixtures of AA and sodium acrylate using an inexpensive and scalable protocol based on alkyl iodides/sodium iodide as mediators in water.

The utilization of sodium iodide, potassium persulfate, and a thermal radical initiator enables facile access to PAA via the direct reverse iodine transfer polymerization of acrylic acid. This polymerization proceeds rapidly in aqueous media using inexpensive and commercially available reagents.

Metal-free hydrosilylation using tris(pentafluorophenyl)borane (B(C6F5)3) as a catalyst enables the rapid polymerization of α-diketone and bis(silane) monomers under ambient conditions to give high molecular weight poly(silyl ether)s (PSEs). A wide selection of commercially available monomers bearing different backbone and side-chain functional groups are shown to be compatible with these metal-free conditions. Significantly, the thermal properties of these poly(silyl ether)s are highly tunable, with novel semicrystalline materials being obtained in a variety of cases. These poly(silyl ether) materials serve as a versatile platform for materials with designed degradation profiles and crystallinity.

The grafting-through copolymerization of two distinct macromonomers via ring-opening metathesis polymerization is typically used to form statistical or diblock bottlebrush polymers with large total backbone degrees of polymerization (NBB) relative to that of the side-chains (NSC). Here, we demonstrate that Grubbs-type chemistry in the opposite limit, namely NBB ≪ NSC, produces well-defined materials with excellent control over ensemble-averaged properties, including molar mass, dispersity, composition, and number of branch points. The dependence of self-assembly on these molecular design parameters was systematically probed using small-angle X-ray scattering and self-consistent field theoretic simulations. Our analysis supports the notion that two-component bottlebrush copolymers with small NBB behave like miktoarm star polymers. The star-to-bottlebrush transition is quantifiable for both statistical and diblock sequences by unique signatures in the experimental scaling of domain spacing and simulated dis...

Inspired by nanotechnologies based on DNA strand displacement, herein we demonstrate that synthetic helical strand exchange can be achieved through tuning of poly(methyl methacrylate) (PMMA) triple-helix stereocomplexes. To evaluate the utility and robustness of helical strand exchange, stereoregular PMMA/polyethylene glycol (PEG) block copolymers capable of undergoing crystallization driven self-assembly via stereocomplex formation were prepared. Micelles with spherical or wormlike morphologies were formed by varying the molecular weight composition of the assembling components. Significantly, PMMA strand exchange was demonstrated and utilized to reversibly switch the micelles between different morphologies. This concept of strand exchange with PMMA-based triple-helix stereocomplexes offers new opportunities to program dynamic behaviors of polymeric materials, leading to scalable synthesis of "smart" nanosystems.

An efficient and scalable strategy to prepare libraries of discrete conjugated oligomers (Đ = 1.0) using the combination of controlled polymerization and automated flash chromatography is reported. From this two-step process, a series of discrete conjugated materials from dimers to tetradecamers could be isolated in high yield with excellent structural control. Facile and scalable access to monodisperse libraries of different conjugated oligomers opens pathways to designer mixtures with precise composition and monomer sequence, allowing exquisite control over their physical, optical, and electronic properties.

A versatile strategy is reported for the multigram synthesis of discrete oligomers from commercially available monomer families, e.g., acrylates, styrenics, and siloxanes. Central to this strategy is the identification of reproducible procedures for the separation of oligomer mixtures using automated flash chromatography systems with the effectiveness of this approach demonstrated through the multigram preparation of discrete oligomer libraries (Đ = 1.0). Synthetic availability, coupled with accurate structural control, allows these functional building blocks to be harnessed for both fundamental studies as well as targeted technological applications.

A reduced copper metal–organic framework (rCu-MOF) containing CuI ions was prepared by reducing raw MOFs (Cu-BTC). A series of polymer functionalizations and coupling reactions could subsequently be achieved via CuAAC click chemistry, thus demonstrating the high activity, facile recyclability and good structural stability of rCu-MOFs for catalytic applications.

The triple-helix stereocomplex of poly(methyl methacrylate) (PMMA) is a unique example of a multistranded synthetic helix that has significant utility and promise in materials science and nanotechnology. To gain a fundamental understanding of the underlying assembly process, discrete stereoregular oligomer libraries were prepared by combining stereospecific polymerization techniques with automated flash chromatography purification. Stereocomplex assembly of these discrete building blocks enabled the identification of (1) the minimum degree of polymerization required for the stereocomplex formation and (2) the dependence of the helix crystallization mode on the length of assembling precursors. More significantly, our experiments resolved binding selectivity between helical strands with similar molecular weights. This presents new opportunities for the development of next-generation polymeric materials based on a triple-helix motif.

© 2018 American Chemical Society. Inspired by marine siderophores that exhibit a morphological shift upon metal coordination, hybrid peptide-polymer conjugates that assemble into different morphologies based on the nature of the metal ion coordination have been designed. Coupling of a peptide chelator, hexahistidine, with hydrophobic oligostyrene allows a modular strategy to be established for the efficient synthesis and purification of these tunable amphiphiles (oSt(His)6). Remarkably, in the presence of different divalent transition metal ions (Mn, Co, Ni, Cu, Zn, and Cd) a variety of morphologies were observed. Zinc(II), cobalt(II), and copper(II) led to aggregated micelles. Nickel(II) and cadmium(II) produced micelles, and multilamellar vesicles were obtained in the presence of manganese(II). This work highlights the significant potential for transition metal ion coordination as a tool for directing the assembly of synthetic nanomaterials.

Core cross-linked star (CCS) polymers with radiating arms composed of high-order multiblock copolymers have been synthesized in a one-pot system via iterative copper-mediated radical polymerization. The employed "arm-first" technique ensures the multiblock sequence of the macroinitiator is carried through to the star structure with no arm defects. The versatility of this approach is demonstrated by the synthesis of three distinct star polymers with differing arm compositions, two with an alternating ABABAB block sequence and one with six different block units (i.e. ABCDEF). Owing to the star architecture, CCS polymers in which the arm composition consists of alternating hydrophilic-hydrophobic (ABABAB) segments undergo supramolecular self-assembly in selective solvents, whereas linear polymers with the same block sequence did not yield self-assembled structures, as evidenced by DLS analysis. The combination of microstructural and topological control in CCS polymers offers exciting possibilities for the development of tailor-made nanoparticles with spatially defined regions of functionality.

Surface-confined ultra-thin polyrotaxane (PRX)-based films with tunable composition, surface topology and swelling characteristics were prepared by solid-state continuous assembly of polymers (ssCAP). The PRX-based films supported cell attachment, and their degradation in biological media could be tuned. This study provides a versatile nano-coating technology with potential applications in biomedicine, including tissue engineering and medical devices. Refereed/Peer-reviewed

Macromolecular architecture is a key factor determining the materials properties of polymers. Exploration of novel structural arrangements has become a viable means to develop advanced functional nanomaterials. Recent developments in polymer chemistry have forged robust synthetic platforms for innovative polymeric materials with highly regulated structures, functionalities, and compositions. This review summarizes the latest synthetic strategies for well-defined polymer architectures through covalent chemistry, with the focus on four main types of well-defined macromolecular constructs.

Recent advances in controlled/living polymerization techniques and highly efficient coupling chemistries have enabled the facile synthesis of complex polymer architectures with controlled dimensions and functionality. As an example, star polymers consist of many linear polymers fused at a central point with a large number of chain end functionalities. Owing to this exclusive structure, star polymers exhibit some remarkable characteristics and properties unattainable by simple linear polymers. Hence, they constitute a unique class of technologically important nanomaterials that have been utilized or are currently under audition for many applications in life sciences and nanotechnologies. This article first provides a comprehensive summary of synthetic strategies towards star polymers, then reviews the latest developments in the synthesis and characterization methods of star macromolecules, and lastly outlines emerging applications and current commercial use of star-shaped polymers. The aim of this work is to promote star polymer research, generate new avenues of scientific investigation, and provide contemporary perspectives on chemical innovation that may expedite the commercialization of new star nanomaterials. We envision in the not-too-distant future star polymers will play an increasingly important role in materials science and nanotechnology in both academic and industrial settings.

This study presents the development of a novel solid state photocatalyst for the photoinduced controlled radical polymerization of methacrylates under mild UV irradiation (λmax ≈ 365 nm) in the absence of conventional photoinitiators, metal-catalysts or dye sensitizers. The photocatalyst design was based on our previous finding that organic amines can act in a synergistic photochemical reaction with thiocarbonylthio compounds to afford well controlled polymethacrylates under UV irradiation. Therefore, in the current contribution an amine-rich polymer was covalently grafted onto a solid substrate, thus creating a heterogeneous catalyst that would allow for facile removal, recovery and recyclability when employed for such photopolymerization reactions. Importantly, the polymethacrylates synthesized using the solid state photocatalyst (ssPC) show similarly excellent chemical and structural integrity as those catalysed by free amines. Moreover, the ssPC could be readily recovered and re-used, with multiple cycles of polymerization showing minimal effect on the integrity of the catalyst. Finally, the ssPC was employed in various photo-“click” reactions, permitting high yielding conjugations under photochemical control.

Burst release of a payload from polymeric particles upon photoirradiation was engineered by altering the cross-linking density. This was achieved via a dual cross-linking concept whereby noncovalent cross-linking was provided by cyclodextrin host-guest interactions, and irreversible covalent cross-linking was mediated by continuous assembly of polymers (CAP). The dual cross-linked particles (DCPs) were efficiently infiltrated (∼80-93%) by the biomacromolecule dextran (molecular weight up to 500 kDa) to provide high loadings (70-75%). Upon short exposure (5 s) to UV light, the noncovalent cross-links were disrupted resulting in increased permeability and burst release of the cargo (50 mol % within 1 s) as visualized by time-lapse fluorescence microscopy. As sunlight contains UV light at low intensities, the particles can potentially be incorporated into systems used in agriculture, environmental control, and food packaging, whereby sunlight could control the release of nutrients and antimicrobial agents. Refereed/Peer-reviewed

The first example of core cross-linked star (CCS) polyrotaxane was prepared using the poly(ϵ-caprolactone) (PCL) CCS three-dimensional (3D) scaffold. The 3D CCS polymer was firstly prepared through the "arm-first" approach. Then, the "arms" of the resultant PCL CCS polymer were threaded with α-cyclodextrins (α-CDs). The threaded α-CDs were permanently locked by the "click" reaction of terminal alkyne functionalities of the star polymers with the azide-functionalized end caps to afford the CCS polyrotaxanes. All analytical results confirm the formation of the CCS polyrotaxanes and reveal their characteristics, including fluorescence under UV, a channel-type crystalline structure, a two-step thermal decomposition, and a unique core-shell structure in great contrast to the polymer precursors.

Poly(e-caprolactone) (PCL) macromonomers (MMs) with norbornenyl end groups were synthesized viaring-opening polymerization (ROP) of e-caprolactone using stannous 2-ethylhexanoate (Sn(Oct)2) as catalyst. Then ring-opening metathesis polymerization (ROMP) of these MMs was carried out using the highly active, fast-initiating ruthenium olefin metathesis catalyst (H2IMes)(pyr)2(Cl)2RuCHPh to form high molecular weight (Mn = 420–1346 kDa) and high density PCL bottlebrush polymers. The inclusion complexation of the prepared PCL bottlebrush polymers and α-cyclodextrins (α-CDs) afforded the novel bottlebrush polypseudorotaxanes with a length of 350 ± 50 nm and a width of 50 ± 10 nm. The formation of bottlebrush polypseudorotaxane was confirmed by nuclear magnetic resonance (NMR) spectroscopic analysis, X-ray diffractogram analysis and dynamic light scattering (DLS) measurements. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) showed that the bottlebrush polypseudorotaxane displays higher thermal stability and weaker melting and crystallization behavior in comparison to its PCL bottlebrush precursor. Transmission electron microscopy (TEM) revealed that the resultant bottlebrush polypseudorotaxanes possess a unique elongated cylindrical morphology.

An efficient and versatile synthetic route toward highly functionalized core cross-linked star (CCS) polymers with interesting structures and properties is presented using an alkyne CCS polymer as scaffold. The alkyne CCS polymer scaffold was initially prepared via an improved arm-first approach, through ring-opening polymerization (ROP) of 4,40- bioxepanyl-7,70-dione (BOD) with a poly(caprolactone-b-propargyl methacrylate) macroinitiator and stannous triflate (Sn(OTf)2) catalyst. Highly functionalized fluorescent, saccharide and amphiphilic CCS polymers were synthesized by grafting the alkyne CCS polymer with the corresponding azido substituted compounds via copper catalyzed 1,3-dipolar azide alkyne cycloaddition (CuAAC), 'click' chemistry. The resulting coronafunctionalized CCS polymers were characterized via GPC, 1H NMR spectroscopic analysis and DLS. 1H NMR spectroscopic analysis revealed that the grafting efficiency (i.e., click efficiency) ranged from 10 to >99%and was highly dependent on the structure and functionality of the azido compounds. This equates to the grafting of 45 to 450 functional compounds onto the CCS polymer scaffolds corona. The results indicate that the click functionalization efficiency is closely related to the molecular size of the azido compounds. Other than size, factors including molecular structure, compatibility and synergistic driving forces, such as the formation of potential inclusion complexes, are also found to affect the functionalization efficiencies. Refereed/Peer-reviewed

A simple and straightforward method of self-assembling grafted copolymers was developed to fabricate cross-linked polymer vesicles, which could conjugate anticancer drug cis-platinum and possess the capability of a high drug loading content, and a steady release rate.

Using all-atom classical molecular dynamics simulations, we have determined the structure of stereocomplexes composed of double-stranded helices of linear isotactic and cyclic syndiotactic poly(methyl methacrylate) in agreement with experimental X-ray diffraction data.

A series of novel amphiphilic diblock copolymers composed of hydrophilic linear poly(ethylene glycol) (PEG) and linear brush hydrophobic polydimethylsiloxane (PDMS) were synthesized. Three different molecular weights of monomethyl ether PEG were initially functionalized with 2-bromoisobutyryl bromide to afford macroinitiators suitable for atom-transfer radical polymerization. The macroinitiators were characterized by gel permeation chromatography, 1 H and 13 C nuclear mag- netic resonance spectroscopic analysis and matrix-assisted laser desorption ionization time-of-flight mass spectroscopy. The three different molecular weight macroinitiators were then chain extended with monomethacryloxypropyl-terminated PDMS and photoactive 2-(methylacyloyloxy)ethyl anthracene-9- carboxylate in different molar ratios to afford a series of photo- responsive amphiphilic diblock copolymers with high conver- sions. Self-assembly of these linear-linear brush diblock copolymers in N,N-dimethylformamide afforded nanoparticles with hydrodynamic diameters (dH) ranging from 41 to 268 nm, as determined by dynamic light scattering analysis. Crosslink- ing and stabilization of the nanoparticles was achieved via (414) photodimerization of the anthracene moieties upon exposure to UV radiation at 365 nm with the reverse reaction studied at a wavelength of 254 nm. Transmission electron microscopy revealed that the self-assembled nanoparticles and their crosslinked derivatives had spherical morphologies. V C 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 00, 000-000

Water-soluble poly(2-hydroxyethyl acrylate) (PHEA)-based core cross-linked star polymers were efficiently synthesised with high macroinitiator-to-star-conversion (>95 %) in a one-pot system via single electron transfer-living radical polymerisation. The star polymers display excellent water solubility and the pendant hydroxyl groups provide a platform for facile post-functionalisation with various molecules. In demonstrating this, a photo-isomerisable molecule, 4-(phenylazo)benzoic acid was conjugated onto the preformed stars through partial esterification of the available hydroxyl groups (5-20 %). The azobenzene functionalised stars were subsequently employed to form reversible inclusion complexes with α-cyclodextrin. Refereed/Peer-reviewed

Clinical studies demonstrate that estrogen replacement therapy in postmenopausal women may enhance cognitive function and reduce neurodegeneration associated with Alzheimer's disease and stroke, This study assesses whether physiologic levels of estradiol prevent brain injury in an in vivo model of permanent focal ischemia. Sprague-Dawley rats were ovariectomized; they then were implanted, immediately or at the onset of ischemia, with capsules that produced physiologically low or physiologically high 17β-estradiol levels in serum (10 or 60 pg/mL, respectively), One week after ovariectomy, ischemia was induced. Estradiol pretreatment significantly reduced overall infarct volume compared with oil-pretreated controls (mean ± SD: oil = 241 ± 88; low = 139 ± 91; high = 132 ±88 mm3); this protective effect was regionally specific to the cortex, since no protection was observed in the striatum. Baseline and ischemic regional CBF did not differ between oil and estradiol pretreated rats, as measured by laser Doppler flowmetry. Acute estradiol treatment did not protect against ischemic injury. Our finding that estradiol pretreatment reduces injury demonstrates that physiologic levels of estradiol can protect against neurodegeneration.