Core Cross-linked Star Polymers Research Articles

A synthetic optimization study on thermoresponsive core cross-linked starpolymers (CCSs)

The well-defined starpolymers can offer a precise stimuli-responsive drug delivery system (SDDS). For this, core cross-linked starpolymers (CCSs) using the poly(N-isopropylacrylamide)-b-poly(n-butyl acrylate) (PNB) linear arm chain and ethylene glycol diacrylate (EGDA) cross-linker were designed and synthesized by the reversible addition-fragmentation chain transfer (RAFT) system. The important synthetic parameters, including reaction time, radical concentration, and cross-linker concentration, were varied to optimize the reaction conditions for highly uniform PNiPAM-based amphiphilic starpolymers (PNBA). The reaction was monitored by GPC, resulting in the sharp monomodal PNBA GPC curve with an almost degraded original curve corresponding to the PNB linear chain. The PNBA revealed a dramatic size increase from 150 nm to 15,000 nm when the temperature increased up to 40 °C. Notably, the uniform CCS structure gives rise to a particular phase transformation system, which can be helpful in biomedical and catalytic applications with enhanced performance.

Poly(2-oxazoline)-based core cross-linked star polymers: synthesis and drug delivery applications.

Poly(2-oxazoline)s (POxs) are promising platforms for drug delivery applications due to their biocompatibility and stealth properties. In addition, the use of core cross-linked star (CCS) polymers based on POxs is expected to enhance drug encapsulation and release performances. In this study, we employed the "arm-first" strategy to synthesize a series of amphiphilic CCS [poly(2-methyl-2-oxazoline)]n-block-poly(2,2'-(1,4-phenylene)bis-2-oxazoline)-cross-link/copolymer-(2-n-butyl-2-oxazoline)s (PMeOx)n-b-P(PhBisOx-cl/co-ButOx)s by using microwave-assisted cationic ring-opening polymerization (CROP). First, PMeOx, as the hydrophilic arm, was synthesized by CROP of MeOx using methyl tosylate as the initiator. Subsequently, the living PMeOx was used as the macroinitiator to initiate the copolymerization/core-crosslinking reaction of ButOx and PhBisOx to form CCS POxs having a hydrophobic core. The molecular structures of the resulting CCS POxs were characterized by size exclusion chromatography and nuclear magnetic resonance spectroscopy. The CCS POxs were loaded with the anti-cancer drug doxorubicin (DOX), and the loading was detected by UV-vis spectrometry, dynamic light scattering, and transmission electron microscopy. In vitro studies showed that DOX release at pH 5.2 was faster than that at pH 7.1. The in vitro cytotoxicity study using HeLa cells revealed that the neat CCS POxs are compatible with the cells. In contrast, the DOX-loaded CCS POxs exhibited a cytotoxic effect in a concentration-dependent manner in HeLa cells, which strongly supports that the CSS POxs are potential candidates for drug delivery applications.

Alkyne-Palladium(II)-Catalyzed Living Polymerization of Isocyanides: An Exploration of Diverse Structures and Functions.

Inspired by the perfect helical structures and the resulting exquisite functions of biomacromolecules, helical polymers have attracted increasing attention in recent years. Polyisocyanide is well known for its distinctive rodlike helical structure and various applications in chiral recognition, enantiomer separation, circularly polarized luminescence, liquid crystallization, and other fields. Although various methods and catalysts for isocyanide polymerization have been reported, the precise synthesis of helical polyisocyanides with controlled molecular weight, low dispersity, and high tacticity remains a formidable challenge. Owing to a limited synthesis strategy, the controlled synthesis of topological polyisocyanides has barely been realized. This Accounts highlights our recent endeavors to explore novel catalysts for the living polymerization of isocyanides. Fortunately, we discovered that alkyne-Pd(II) catalysts could initiate the living polymerization of isocyanides, resulting in helical polyisocyanides with controlled structures, high tacticity, and tunable compositions. These catalysts are applicable to various isocyanide monomers, including alkyl isocyanides, aryl isocyanides, and diisocyanobenzene derivatives. Incorporating chiral bidentate phosphine ligands onto alkyne-Pd(II) complexes formed chiral Pd(II) catalysts, which promoted the asymmetric living polymerization of achiral isocyanide, yielding single left- and right-handed helices with highly optical activities.Using alkyne-Pd(II) catalysts, various topological polyisocyanides have been facilely prepared, including hybrid block copolymers, bottlebrush polymers, core cross-linked star polymers, and organic/inorganic nanoparticles. For instance, various hybrid block polyisocyanides were easily produced by coupling alkyne-Pd(II)-catalyzed living isocyanide polymerization with controlled radical polymerization and ring-opening polymerization (ROP). Combining the ring-opening metathesis polymerization (ROMP) of norbornene with Pd(II)-catalyzed isocyanide polymerization, bottlebrush polyisocyanides and core cross-linked star polymers were easily prepared. Pd(II)-catalyzed living polymerization of poly(lactic acid)s with isocyanide termini resulted in densely grafted bottlebrush polyisocyanides with closely packed side chains. Moreover, the surface-initiated living polymerization of isocyanides produced a family of polyisocyanide-grafted organic/inorganic hybrid nanoparticles using nanoparticles with alkyne-Pd(II) catalysts anchored on the surfaces. Surprisingly, the nanoparticles and star polymers with helical polyisocyanide arms performed exceptionally well in terms of chiral recognition and resolution. Incorporated organocatalysts such as proline and prolinol units onto the pendants of optically active helical polyisocyanides, a family of polymer-based chiral organocatalysts, were generated, which showed significantly improved stereoselectivity for the asymmetric Aldol reaction and Michael addition and can be easily recycled.Using a chiral alkyne-Pd(II) catalyst, single-handed helical polyisocyanides bearing naphthalene and pyrene probes were produced from achiral isocyanide monomers. These polymers showed excellent self-sorting properties as revealed using a fluorescence resonance energy transfer (FRET) investigation and were self-assembled into two-dimensional (2D) smectic nanostructures driven by both helicity and chain length. Incorporating helical poly(phenyl isocyanide) (PPI) onto semiconducting poly(3-hexylthiophene) (P3HT) induced the asymmetric assembly of the resulting P3HT-b-PPI copolymers into single-handed cylindrical micelles with controlled dimensions and tunable photoluminescence.

Folding of Sequence-Controlled Graft Copolymers to Subdomain-Defined Single-Chain Nanoparticles

We developed a methodology, inspired by the folding of proteins, for the precision synthesis of hairy polymer nanoparticles. High-molar mass and narrowly dispersed graft copolymers were synthesized by graft-through ring opening metathesis polymerization, to incorporate a designated number of side chains and dimerizable cinnamic acid groups. Intrachain photodimerization collapsed the backbone and arrested it into a compact globular conformation, resulting in hairy nanoparticles topologically equivalent to a core cross-linked star polymer. The single-chain collapse process translates the molecular information written on the 1D graft copolymer into the 3D globular polymer nanoparticle, like protein folding. Unprecedented control over structural parameters was achieved, including the length, number, and composition of the side chains as well as cross-linking density. Different side chains formed distinct subdomains in the sterically congested nanoparticle state and further self-assembled into micellar aggregates in a selective solvent. Both experimental observations and computational simulations indicated that preorganization of the side chains in the block sequence produces subdomains which primarily follow the backbone length scale, while random sequences showed side chain-dependent scaling. Polymer nanoparticles with discrete multiple subdomains were produced by folding of the ternary block graft copolymers. Drastic differences in the self-assembly behavior of ABC- and ACB-sequenced nanoparticles indicate that the spatial organization of subdomains can be achieved by sequence control.

Synthesis of ultra‐high molecular weight core cross‐linked star (CCS) polymer using high molecular weight spherical nanoparticles and arm‐first method

AbstractP (N,N‐Dimethylacrylamide) ‐b‐P (2‐methoxyethyl acrylate) (PDMA‐b‐PMEA) and Poly (poly (ethylene glycol) methyl ether methacrylate) ‐b‐P (2‐methoxyethyl acrylate) (PPEGMA‐b‐PMEA) di‐block copolymer nanoparticles are prepared by RAFT dispersion polymerization in water at 35°C. By changing the degree of polymerization (DP) of PMEA and the solid content of the reaction solution, only spherical nanoparticles are obtained. Using PDMA and PPEGMA as macromolecular chain transfer agents (Macro‐CTA), the actual DP of PMEA block can be up to 11,520 and 17,000, respectively, the size of the obtained spherical nanoparticles can be close to 600 nm, and the molecular weight of the block copolymer can reach 106. Such large spheres may serve as model sterically stabilized particles for analytical centrifugation studies. In the mixed solvent of ethanol and water (1:1, v/v), we synthesize ultra‐high molecular weight CCS polymer by the arm‐first method. Star polymer with such high molecular weight and small particle size can be used for emulsification.

Amphiphilic Core Cross-Linked Star Polymers for the Delivery of Hydrophilic Drugs from Hydrophobic Matrices.

The delivery of hydrophilic drugs from hydrophobic polymers is a long-standing challenge in the biomaterials field due to the limited solubility of the therapeutic agent within the polymer matrix. In this work, we develop a drug delivery mechanism that enables the impregnation and subsequent elution of hydrophilic drugs from a hydrophobic polymer material. This was achieved by synthesizing core cross-linked star polymer amphiphiles with hydrophilic cores and hydrophobic coronas. While significant work has been done to create nanocarriers for hydrophilic drugs, this work is distinct from previous work in that it designs amphiphilic and core cross-linked particles for controlled release from hydrophobic matrices. Ultraviolet-mediated atom transfer radical polymerization was used to synthesize the poly(ethylene glycol) (PEG)-based hydrophilic cores of the star polymers, and hydrophobic coronas of poly(caprolactone) (PCL) were then built onto the stars using ring-opening polymerization. We illustrated the cytocompatibility of PCL loaded with these star polymers through human endothelial cell adhesion and proliferation for up to 7 days, with star loadings of up to 40 wt %. We demonstrated successful loading of the hydrophilic drug heparin into the star polymer core, achieving a loading efficiency and content of 50 and 5%, respectively. Finally, the heparin-loaded star polymers were incorporated into a PCL matrix and sustained release of heparin was illustrated for over 40 days. These results support the use of core cross-linked star polymer amphiphiles for the delivery of hydrophilic drugs from hydrophobic polymer matrices. These materials were developed for application as drug-eluting and biodegradable coronary artery stents, but this flexible drug delivery platform could have impact in a broad range of medical applications.

Intravenous anti-VEGF agents with RGD peptide-targeted core cross-linked star (CCS) polymers modified with indocyanine green for imaging and treatment of laser-induced choroidal neovascularization.

Age-related macular degeneration (AMD) is a leading cause of irreversible visual loss among elderly persons, of which wet AMD is characterized by choroidal neovascularization (CNV). We herein developed nanoparticles with good biosafety for effective treatment of choroidal neovascularization (CNV). S-PEG-ICG-RGD-RBZ NPs were synthesized and characterized by ZP, DLS, UV-Vis, TEM and Coomassie Brilliant Blue staining analyses. In our study, the S-PEG-ICG-RGD-RBZ NPs exhibited good biocompatibility in vitro and in vivo. There was no cellular toxicity, dead cells, apoptosis or genotoxicity in the studied concentration range in vitro; meanwhile, intravenous injection of the designed NPs did not cause histological damage or apoptosis in the organs in vivo, including the heart, liver, spleen, lung, kidneys and brain. The designed NPs inhibited VEGF-induced proliferation, cell migration, tube formation and expression of CD31 and VEGF in vitro. Meanwhile, in vivo studies also indicated the inhibition of CNV development by NPs. What's more, the CNV area was imaged after intravenous injection of NPs modified with indocyanine green. The NPs were mainly targeted to CNV areas and did not remain in the other organs. In summary, S-PEG modified with RGD was designed as a powerful carrier to deliver anti-VEGF agents to CNV areas. The smart NPs, which have good cellular compatibility, hold great potential for drug delivery in CNV treatment.

Synthetic route-dependent intramolecular segregation in heteroarm core cross-linked star polymers as Janus-like nanoobjects

Polymerization-induced intramolecular segregation can be realized during the “in–out” synthesis of heteroarm core cross-linked star polymers to facilitate well-defined microphase separation.

Gold nanoparticles for smart and recoverable catalyst using thermo-responsive core-crosslinked star polymer as the nanoreactor

In this work, a novel kind of temperature-responsive core cross-linked star (CCS) polymer, composing of poly(methoxypolyethylene glycol-co-di(ethylene glycol) ethyl ether acrylate) (P(PEGA-DEGA)) as thermo-responsive arm and poly(2-(dimethylamino)ethyl methacrylate) as functional core, was developed as nanoreactor for immobilizing gold nanoparticles for smart catalyst with facile recovery. The protonated imino groups in CCS polymer core could capture AuCl4- and simultaneously reduce it to Au NPs in aqueous solution, leading to the formation of P(PEGA-DEGA) CCS@Au composite. The whole procedure was carried out in aqueous media without using any toxic reducing agent, which is facile, efficient and green. The as-prepared CCS@Au composite exhibit a superior high catalytic activity for the reduction of 4-nitrophenol (4-NP), owing to that the soluble polymeric arms of the CCS polymers provides a homogeneous reaction system with fast mass transfer and thus facilitates interactions between Au NPs in the core and 4-NP. In addition, temperature-responsive catalyzing behavior was observed for the CCS@Au composite: the reaction rate enhanced with the elevation of the reaction temperature at first, but decreased when the temperature increased close to the LCSTs of the CCS@Au catalysts.

Novel Organic/Inorganic Hybrid Star Polymer Surface-Crosslinked with Polyhedral Oligomeric Silsesquioxane

Novel organic/inorganic hybrid star polymer was prepared dually crosslinked within inner-core via divinylbenzene (DVB) and outer-surface via octafunctional polyhedral oligomeric silsesquioxane (POSS). Core cross-linked star polymers bearing dialkynyl-terminated polystyrene arms, (dialkynyl-PS)n-CCL, were synthesized at first by the atom transfer radical polymerization (ATRP) of DVB using α,α-dialkynyl-terminated PS macroinitiator, followed by the subsequent fractionation. Under high dilution conditions, (dialkynyl-PS)n-CCL was subjected to surface cross-linking with octa(3-azidopropyl) polyhedral oligomeric silsesquioxane, POSS-(N3)8, via click reaction, affording POSS-functionalized hybrid polymer doubly cross-linked within core and surface regions, SCL-(PS)n-CCL. FT-IR, 1H NMR, GPC, and elemental analysis results revealed that on average, the obtained hybrid polymer possesses a cross-linked PDVB inner core, ∼14 linear PS arms (the Mw per arm of 5.1 kDa), and ∼4-5 POSS moieties at outer surface. Differential scanning calorimetry (DSC) thermograms and thermogravimetric analysis (TGA) revealed that after surface cross-linking the thermal stability of SCL-(PS)n-CCL is considerably improved. This work provides a proof-of-concept example for the preparation of dually cross-linked hybrid star polymer, which represents a novel category of organic/inorganic composite materials with unique chain architectures.

Microwave-Assisted Synthesis of Core-Crosslinked Star Polymers with Benzophenone Derivatives in the Core

Core-crosslinked star polymers, which have polyethylene oxide (PEO) as a shell and cross-linked poly(2-{4′-iodobenzoyloxy}-ethyl methacrylate) (PIEMA) with benzophenone derivatives as a core, have been successfully synthesized by an “arm-first” method. PEO-b-PIEMA was prepared via atom transfer radical polymerization (ATRP) of 2-{4′-iodobenzoyloxy}-ethyl methacrylate (4-IEMA) with preformed PEO-Br as a macroinitiator. Core-crosslinked star polymers (CCSP) were efficiently synthesized by ultrafast carbonylation reactions under air by flash microwave irradiation in the presence of dicobalt octacarbonyl in 6 min. Gel permeation chromatography (GPC) trace of CCSP showed a drastic shift to a higher molecular weight when compared to precursor polymer, PEO-b-PIEMA diblock copolymer, indicating that the carbonylation reaction was fully progressed. The CCSP with benzophenone was successfully immobilized on a silicon wafer through a photochemical reaction under UV irradiation.

A Temperature-Responsive Boronate Core Cross-Linked Star (CCS) Polymer for Fast and Highly Efficient Enrichment of Glycoproteins.

Fast and highly efficient enrichment and separation of glycoproteins is essential in many biological applications, but the lack of materials with high capture capacity, fast, and efficient enrichment/separation makes it a challenge. Here, a temperature-responsive core cross-linked star (CCS) polymer with boronate affinity is reported for fast and efficient enriching and separating of glycoproteins from biological samples. The temperature-responsive CCS polymers containing boronic acid in its polymeric arms and poly(N-isopropyl acrylamide) in its cross-linked core are prepared using reversible addition-fragmentation chain transfer polymerization via an "arm-first" methodology. The soluble boronate polymeric arms of the CCS polymers provide a homogeneous reaction system and facilitate interactions between boronic acid and glycoproteins, which leads to a fast binding/desorption speed and high capture capacity. Maximum binding capacity of the prepared CCS polymer for horseradish peroxidase is determined to be 210 mg g-1 , which can be achieved within 20 min. More interestingly, the temperature-responsive CCS polymers exhibit rapid reversible thermal-induced volume phase transition by increasing the temperature from 15 to 30 °C, resulting in a facile and convenient sample collection and recovery for the target glycoproteins. Finally, the temperature-responsive CCS polymer is successfully applied to enrichment of low abundant glycoproteins.

Surface charge of well-defined polymeric nano-stars regulates non-invasive fluorescence imaging of lymph node

Accurate identification of sentinel lymph node (SLN) is crucial for clinical SLN biopsy surgery. Herein, we developed an innovative nanoprobe based on well-defined core crosslinked star (CCS) polymers for non-invasive fluorescence imaging of SLN. A well-defined biodegradable CCS polymer comprising multiple polyethylene glycol (PEG) arms and carboxyl terminal groups (denoted as CCS-COOH) was synthesized successfully by reversible addition-fragmentation chain transfer polymerization with a disulfide-based crosslinker reagent. Besides, CCS-COOH was coupled by tert-butyl carbazate to produce the CCS derivative with neutral butoxycarbonyl (Boc) terminal groups (denoted as CCS-Boc). By the removal of Boc groups, another CCS derivative with positive primary amino terminal groups (denoted as CCS-NH2) was also yielded. These CCS polymers had similar particle size but different surface charge. For SLN fluorescence imaging, the CCS polymers labeled by CY7, a near-infrared probe, exhibited superior in vitro photo-stability to CY7 alone. After intradermal injection of the CY7-labeled CCS polymers in a mouse model, they could efficiently accumulate in the lymph node of the mouse. CY7-labeled CCS-COOH having negatively-charged surface displayed longer duration time and higher fluorescence intensity in the lymph node as compared to its counterparts with neutral or positive charge surface. In vitro and in vivo toxicity tests supported low cytotoxicity of these CCS polymers against cell lines and low systemic toxicity. The results of this work highlight the potential of negatively-charged near-infrared-emitting CCS polymer as a new nanoprobe for safe and efficient SLN imaging.

Continuous flow synthesis of core cross-linked star polymers via photo-induced copper mediated polymerization

A convenient method to synthesize core cross-linked star polymers via a continuous flow photopolymerization process is developed.

Synthesis of bioreducible core crosslinked star polymers with N,N′-bis(acryloyl)cystamine crosslinker via aqueous ethanol dispersion RAFT polymerization

The aim of this study is to synthesize well-defined bioreducible core crosslinked star (CCS) polymers via heterogeneous reversible addition-fragmentation transfer (RAFT) polymerization in aqueous ethanol solutions. To this end, water-soluble linear arm polymers, poly (poly (ethylene glycol) methyl ether methacrylate) (PPEGMA), poly (2-(dimethylamino)ethyl methacrylate) (PDMAEMA) and poly (N,N-dimethylacrylamide) (PDMA), were prepared respectively. Next, heterogenous RAFT polymerization of the polymers with N,N′-bis(acryloyl)cystamine (BAC) as a crosslinker was systemically investigated in an aqueous ethanol solvent. It was found that these bioreducible CCS polymers with crosslinked BAC core could be prepared successfully depending on polymerization parameters. The formation of PPEGMA-based CCS polymers was affected by water volume fraction (Vw) of water-ethanol solution, reaction time, arm polymer concentration, and spacing monomer. Besides, at an optimal Vw of 80% (i.e. the molar concentration of water is 44.44 M) and arm polymer concentration of 10% (w/v), PPEGMA-based CCS polymers at >90% yield could be achieved within 1 h. By the same Vw and reaction time, PDMAEMA- and PDMA-based CCS polymers could also be prepared with high yield (>75%). The mechanism underlying the formation of the CCS polymers was ascribed to enhanced driving force of polymerization-induced self-assembly at an optimal Vw. These CCS polymers were degradable in thiol-containing dithiothreitol, suggesting their potential application for drug release in a reductive intracellular environment.

On-Demand Cascade Release of Hydrophobic Chemotherapeutics from a Multicomponent Hydrogel System.

A multicomponent hydrogel drug-delivery platform with covalent incorporation of core-cross-linked star (CCS) polymers has been fabricated through dual cross-linking reactions. The presence of amphiphilic CCS polymers enhances the mechanical stability of the network and allows for immobilization of hydrophobic chemotherapeutics (e.g., doxorubicin: DOX) within a hydrophilic matrix. Thanks to thiol-responsive disulfide segments, the hybrid network is selectively degradable upon exposure to the glutathione-rich tumor environment, leading to an on-demand cascade release of payloads in a prolonged manner. After network degradation, the integrity of the therapeutic cargos is still well-protected by the CCS polymeric carriers. A cellular study demonstrated efficient internalization of released drug-containing CCS polymers by HeLa cells, intracellular delivery of encapsulated drugs following pH-mediated erosion of the CCS containers, and excellent cytocompatibility of this hydrogel system.

Arm-First Approach toward Cross-Linked Polymers with Hydrophobic Domains via Hypervalent Iodine-Mediated Click Chemistry.

In this work, synthesis of two cross-linked polymeric systems through isoxazoline ring formation using nitrile oxide–acrylate click chemistry has been described. In the first system, styrenic block copolymer with oxime-functionalized middle block was synthesized using S,S′-bis(α,α′-dimethyl-α″-acetic acid)trithiocarbonate as chain-transfer agent using reversible addition fragmentation chain-transfer technique. This block copolymer was further utilized to prepare core cross-linked star polymers by reacting with a four-arm acrylic cross-linker by employing environment-friendly, nontoxic PhI(OAc)2-mediated “click reaction” via the formation of isoxazoline ring. In the second system, two linear styrenic block copolymers, one containing oxime and another containing acrylate group, were reacted to form a cross-linked (CS) polymeric system. Formation of cross-linked polymers and isoxazoline ring was confirmed by Fourier transform infrared spectroscopy, gel permeation chromatography, NMR spectroscopy, and dynamic light scattering studies. Later, we also demonstrated that in aqueous medium these CS polymers produced polymeric nanoparticles (NPs), which can be used as potential carriers of hydrophobic drug molecules. The loading capacity of the hydrophobic domains has been investigated using coumarin dyes with varying hydrophobicity through steady-state and time-resolved spectroscopy studies. The polymeric NPs were also shown to successfully encapsulate a hydrophobic drug doxorubicin.

Linker chemistry dictates the delivery of a phototoxic organometallic rhenium(i) complex to human cervical cancer cells from core crosslinked star polymer nanoparticles.

We have investigated core-crosslinked star polymer nanoparticles designed with tunable release chemistries as potential nanocarriers for a photoactive Re(i) organometallic complex. The nanoparticles consisted of a brush poly(oligo-ethylene glycol)methyl ether acrylate (POEGA) corona and a cross-linked core of non-biodegradable N,N'-methylenebis(acrylamide) (MBAA) and either pentafluorophenyl acrylate (PFPA), 3-vinyl benzaldehyde (VBA) or diacetone acrylamide (DAAM). Each star was modified with an amine functionalized photodynamic agent (i.e. a rhenium(i) organometallic complex) resulting in the formation of either a stable amide bond (POEGA-star-PFPA), or hydrolytically labile aldimine (POEGA-star-VBA) or ketimine bonds (POEGA-star-DAAM). These materials revealed linker dependent photo- and cytotoxicity when tested in vitro against non-cancerous lung fibroblast MRC-5 cells and HeLa human cervical cancer cells: the toxicity results correlated with final intracellular Re concentrations.

Synthesis of core cross-linked star polymers carrying helical poly(phenyl isocyanide) arms via “core-first” strategy and their surface chiral recognition ability

A norbornene functionalized alkyne-Pd(II) complex was designed and synthesized, which copolymerized with a bisnorbornene cross linker via ring-opening metathesis polymerization (ROMP) afforded a cross-linked Pd(II) macroinitiator. Living polymerization of phenyl isocyanides with the Pd(II) macroinitiator lead to the formation of well-defined core cross-linked star polymer carrying helical poly(phenyl isocyanide)s arms. Because of the living nature of Pd(II)-initiated phenyl isocyanide polymerization, a series of star polymers with controlled structure and tunable compositions was readily prepared. Optically active star polymers with excess of one handed helical arms were obtained by using enantiopure phenyl isocyanide monomers. Such star polymer exhibited excellent chiral recognition ability. The contact angle of the star polymer is strongly dependent on the chirality of the D/L-phenylglycinol droplets. The enantioselective surface recognition can be further applied to the chiral resolution of racemic D/L-phenylglycinol. The enantiomeric excess (ee) of the isolated enantiomer is up to 75%. The chiral star polymers can also be used to induce enantioselectively crystallization of racemic Boc-alanine. The ee value of the induced enantiomer can be up to 91%.

Porous Polystyrene Monoliths and Microparticles Prepared from Core Cross-linked Star (CCS) Polymers-Stabilized Emulsions

A hydrophobic CCS polymer of poly(benzyl methacrylate) (PBzMA) was prepared in toluene by reversible addition-fragmentation chain transfer (RAFT)-mediated dispersion polymerization. The CCS polymer, with poly(benzyl methacrylate) as the arm and crosslinked N, N′-bis(acryloyl)cystamine (BAC) as the core, was confirmed by characterization with gel permeation chromatography (GPC) and nuclear magnetic resonance (NMR) spectroscopy. Three kinds of oils (toluene, anisole and styrene) were chosen to study the emulsification properties of PBzMA CCS polymer. The oils can be emulsified by CCS polymer to form water-in-oil (w/o) emulsions. Moreover, w/o high internal phase emulsions (HIPEs) can be obtained with the increase of toluene and styrene volume fractions from 75% to 80%. Porous polystyrene monolith and microparticles were prepared from the emulsion templates and characterized by the scanning electronic microscopy (SEM). With the internal phase volume fraction increased, open-pore porous monolith was obtained.