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Polymer conjugates of camptothecin (CPT) have been pursued as a solution to the difficulties present in treating cancers with CPT and its derivatives. Covalent attachment of CPT to a polymer can improve solubility, increase blood circulation time, enhance tumor uptake, and significantly improve efficacy of the drug. In this report, we describe a novel polymer conjugate of CPT using a core-functionalized, symmetrically PEGylated poly(l-lysine) (PLL) dendrimer. The PEGylated dendrimer consisted of a lysine dendrimer functionalized with aspartic acid, which was used as an attachment site for poly(ethylene glycol) (PEG) and CPT. The final conjugate had a molecular weight of 40 kDa and was loaded with 4-6 wt % CPT. Polymer-bound CPT was shown to have a long blood circulation half-life of 30.9 +/- 8.8 h and a tumor uptake of 4.2 +/- 2.3% of the injected dose/g of tissue, compared to free CPT in which less than 1% was retained in the blood after 30 min and had a tumor accumulation of 0.29 +/- 0.04% of the injected dose/g of tissue. The PEGylated PLL-CPT showed superior efficacy in murine (C26) and human colon carcinoma (HT-29) tumor models when compared with no treatment or treatment with irinotecan. In the C26 tumor model, treatment resulted in significantly prolonged survival (P0.05) for all mice treated with a single injection of PEGylated PLL-CPT. In the HT-29 tumor model, all mice treated with multiple injections of a low dose survived to the end of the study, with three mice of eight surviving tumor-free.

We describe the rational design of oligothiophene semiconductors to facilitate solution-based fabrication of environmentally stable organic field-effect transistors (OFETs). Ultrathin films of α,ω-distyryl quaterthiophene (DS4T), pentathiophene (DS5T), and sexithiophene (DS6T) were prepared via solution processing to probe the effect of styryl end groups, oligomer length, and thin film structure on air stability. These films were prepared via solution deposition and thermal annealing of precursors featuring thermally labile ester solubilizing groups. A detailed study of the thin film structure was performed using atomic force microscopy (AFM), near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, and grazing incidence X-ray diffraction (GIXD). Functional OFETs were obtained for DS5T and DS6T and have, respectively, hole mobilities of 0.051 and 0.043 cm2/(V s) and on/off ratios of 1 × 105 to 1 × 106, whereas DS4T OFETs failed to function because of poor film continuity. The effect of both short-...

Bipolar transport polymers have been developed as host materials for electroluminescent devices by incorporating both electron-transporting and hole-transporting functionalities into copolymers. Two different copolymers having the same molecular weight (Mn ∼ 30 kg/mol) and the same fraction of electron-transporting monomers (fOXA = 0.50) have been synthesized in the form of random and diblock copolymers, respectively. The effect of molecular structure and film morphology of these bipolar polymers on device performance has been studied. For the diblock copolymers, pronounced phase segregation forming different nanomorphologies has been observed by modern microscopic techniques, which is not observed for the random counterparts under the same thin film preparation conditions. The results of single-layer polymer light emitting diodes (PLEDs) show that the nanophase separation morphology of diblock copolymers has a significant effect on device performance: lowering charge transport and facilitating the hole−...

Hydrogen adsorption using a series of nanoporous synthetic polymers has been studied. Promising results were obtained during the screening of commercially available porous polymer beads; of the polymers considered, hypercrosslinked Hypersol-Macronet MN200 resin exhibited the highest adsorption capacity for hydrogen. This initial success triggered the development of our own high surface area hypercrosslinked materials. Subjecting gel-type and macroporous vinylbenzyl chloride-based precursors swollen in dichloroethane to a Friedel−Crafts reaction catalyzed by iron trichloride afforded beads with surface areas of 1 930 and 1 300 m2/g, respectively, as calculated using the BET equation. The former polymer reversibly stores up to 1.5 wt % H2 at a pressure of 0.12 MPa and a temperature of 77.3 K. The initial heat of adsorption of hydrogen molecules onto this polymer is 6.6 kJ/mol.

Symmetrical α,ω-substituted quarter-(T4), penta-(T5), sexi-(T6), and heptathiophene (T7) oligomers containing thermally removable aliphatic ester solubilizing groups were synthesized, and their UV−vis and thermal characteristics were compared. Spun-cast thin films of each oligomer were examined with atomic force microscopy and near-edge X-ray absorption fine structure spectroscopy to evaluate the ability of the material to self-assemble from a solution-based process while maintaining complete surface coverage. Films of the T5−T7 oligomers self-assemble into crystalline terraces after thermal annealing with higher temperatures required to affect this transformation as the size of the oligomers increases. A symmetrical α,ω-substituted sexithiophene (T6-acid) that reveals carboxylic acids after thermolysis was also prepared to evaluate the effect of the presence of hydrogen-bonding moieties. The charge transport properties for these materials evaluated in top-contact thin film transistor devices were found t...

The role of architecture and nanoenvironment in the catalytic properties of dendritic polymers containing 4-(dialkylamino)pyridines was investigated in the context of acylation reactions employing sterically demanding tertiary alcohols as substrates. Frechet-type benzyl ether and aliphatic ester dendrimers were prepared in a convergent manner from a common trivalent core containing three DMAP groups while a linear polymer was dendronized with aliphatic esters using a divergent growth scheme. Catalysis experiments clearly indicate that nanoenvironment plays the dominant role in determining the activity of the polymer catalysts, with the polyester platform being superior to the benzyl ether. Polymer architecture played little or no role in affecting catalysis. With respect to molecular transport and catalysis, this represents the first comparative study of the effect of architecture and nanoenvironment using structurally similar dendritic materials.

[structure: see text] A series of bridged oligothiophenes have been synthesized. Their novel molecular architecture, comprising two oligothiophenes linked together by a bridge at one alpha-extremity and one binding group at the other alpha-extremity, is expected to improve their utility as electroactive surfactants for semiconducting nanoparticles or organic electronics.

High molecular weight polymers (> 20 000 Da) have been widely used as soluble drug carriers to improve drug targeting and therapeutic efficacy. Dendritic polymers are exceptional candidates for the preparation of near monodisperse drug carriers due to their well-defined structure, multivalency, and flexibility for tailored functionalization. We evaluated various dendritic architectures composed of a polyester dendritic scaffold based on the monomer unit 2,2-bis(hydroxymethyl)propanoic acid for their suitability as drug carriers both in vitro and in vivo. These systems are both water soluble and nontoxic. In addition, the potent anticancer drug, doxorubicin, was covalently bound via a hydrazone linkage to a high molecular weight 3-arm poly(ethylene oxide)-dendrimer hybrid. Drug release was a function of pH, and the release rate was more rapid at pH < 6. The cytotoxicity of the DOX-polymer conjugate measured on multiple cancer lines in vitro was reduced but not eliminated, indicating that some active doxorubicin was released from the drug polymer conjugate under physiological conditions. Furthermore, biodistribution experiments show little accumulation of the DOX-polymer conjugate in vital organs, and the serum half-life of doxorubicin attached to an appropriate high molecular weight polymer has been significantly increased when compared to the free drug. Thus, this new macromolecular system exhibits promising characteristics for the development of new polymeric drug carriers.

Capillaries with inner diameters of 550 microm have successfully been packed with 1.5-microm octadecyl silica particles using frits made of macroporous polymers by the UV photopolymerization of a solution of glycidyl methacrylate and trimethylolpropane trimethacrylate. This type of frit is found superior to one made of low-melting point poly(styrene-co-divinylbenzene) beads. Bubble formation is not observed to occur within these capillary columns under our experimental conditions. Separations can be achieved with sample injection volumes as high as 1 microL. To demonstrate its semipreparative use, a mixture of 500 nL of taxol (20 mM) and its precursor, baccatin III (30 mM), is separated using such a column with a Tris buffer.

The synthesis of functional aromatic bis(sulfonyl chlorides) containing an acetophenone and two sulfonyl chloride groups, i.e., 3,5-bis[4-(chlorosulfonyl)phenyl]-1-acetophenone (16), 3,5-bis(chlorosulfonyl)-1-acetophenone (17), and 3,5-bis(4-(chlorosulfonyl)phenyloxy)-1-acetophenone (18) via a sequence of reactions, involving in the last step the quantitative oxidative chlorination of S-(aryl)- N,N'-diethylthiocarbamate, alkyl- or benzyl thiophenyl groups as masked nonreactive precursors to sulfonyl chlorides is described. A related sequence of reactions was used for the synthesis of the aromatic trisulfonyl chloride 1,1,1-tris(4-chlorosulfonylphenyl)ethane (24). 4-(Chlorosulfonyl)phenoxyacetic acid, 2,2-bis[[[4-(chlorosulfonyl)phenoxyacetyl]oxy]methyl]-1,3-propanediyl ester (27), 5,11,17,23-tetrakis(chlorosulfonyl)-25,26,27,28-tetrakis(ethoxycarbonylmethoxy)calix[4]arene (38), 5,11,17,23,29,35-hexakis(chlorosulfonyl)-37,38,39,40,41,42-hexakis(ethoxycarbonylmethoxy)calix[6]arene (39), 5,11,17,23,29,35,41,47-octakis(chlorosulfonyl)-49,50,51,52,53,54,55,56-octakis(ethoxycarbonylmethoxy)calix[8]arene (40), 5,11,17,23-tetrakis(tert-butyl)-25,26,27,28-tetrakis(chlorosulfonyl phenoxyacetoxy)calix[4]arene (44), 5,11,17,23,29,35-hexakis(tert-butyl)-37,38,39,40,41,42-hexakis(chlorosulfonylphenoxyacetoxy)calix[6]arene (45), and 5,11,17,23,29,35,41,47-octakis(tert-butyl)-49,40,51,52,53,54,55,56-octakis(chlorosulfonylphenoxyacetoxy)calix[8]arene (46) were synthesized by two different multistep reaction procedures, the last step of both methods consisting of the chlorosulfonation of compounds containing suitable activated aromatic positions. 2,4,6-Tris(chlorosulfonyl)aniline (47) was obtained by the chlorosulfonation of aniline. The conformation of two series of multisulfonyl chlorides i.e., 38, 39, 40 and 44, 45, 46, was investigated by (1)H NMR spectroscopy. The masked nonreactive precursor states of the functional aromatic multisulfonyl chlorides and the aromatic multisulfonyl chlorides reported here represent the main starting building blocks required in a new synthetic strategy elaborated for the preparation of dendritic and other complex organic molecules.

The highly compact and globular shape, as well as the uniform size and plurifunctionality of dendrimers make them ideal molecular building blocks for a wide range of interfacial materials involving self-assembled monolayers, Langmuir films, multilayers, and other surface-confined assemblies. Moreover, the study of the behavior of dendrimers at surfaces and interfaces provides unique insight into their chemical and physical properties. Dendritic macromolecules play an increasingly important role in the materials and surface sciences, where applications utilizing polymer thin films can benefit from their distinctive chemical and physical properties. Recent investigations have highlighted the use of dendrimers as functional surfaces and as interfacial materials for applications in membranes, adhesion, microelectronics or in chemical and biological sensing.

Natural photosynthetic systems collect sunlight using a vast array of light-harvesting chromophores that channel the absorbed energy to a single reaction center. Recently, it has been realized that dendritic macromolecules can exhibit similar properties, though on a more modest scale. The preparation of dendritic structures and assemblies composed of numerous light-collecting chromophores that transfer their energy to a single energy ‘sink’ at the core has been achieved in a number of diverse and creative ways. These novel structures are being used as model systems in light-emitting diodes, signal amplifiers, fluorescent sensors, frequency converters, and other photonic devices.

We describe a six-step synthesis to water-soluble doxorubicin (DOX)-loaded biodegradable PEGylated star-comb polymers with favorable pharmaceutical properties by atom transfer radical polymerization (ATRP) starting with a commercially available tripentaerythritol carrying eight reactive sites. The low polydispersity polymers degrade in a stepwise manner into lower molecular weight (MW) fragments by 15 days at 37 °C at either pH 5.0 or pH 7.4. The half-life of the star-comb polymers in blood is dependent upon the molecular weight; the 44 kDa star-comb has a t(1/2, β) of 30.5 ± 2.1 h, which is not significantly changed (28.6 ± 2.7 h) when 6.6 wt % of DOX is attached to it via a pH-sensitive hydrazone linker. The star-comb polymers have low accumulation in organs but a high accumulation in C26 flank tumors implanted in Balb/C mice. The hydrodynamic diameter of polymer-DOX conjugates measured by dynamic light scattering increases from 8 to 35 to 41 nm as the loading is increased from 6.6 to 8.4 to 10.2 wt %. Although there is no significant difference in the t(1/2, β) or in the accumulation of polymer-DOX in C-26 tumors, the uptake of polymer in the spleen is significantly higher for polymers with DOX loadings greater than 6.6 wt %. Polymer accumulation in other vital organs is independent of the DOX loading. The facile synthesis, biodegradability, long circulation time, and high tumor accumulation of the attached drug suggests that the water-soluble star-comb polymers have promise in therapeutic applications.

A new class of porphyrin containing hyperbranched polymers has been prepared via proton-transfer polymerisation utilising an A2 + B3 approach, thus providing an accelerated entry into the construction of branched multiporphyrin architectures.

The synthesis of functional aromatic bis(sulfonyl chlorides) containing an acetophenone and two sulfonyl chloride groups, i.e., 3,5-bis[4-(chlorosulfonyl)phenyl]-1-acetophenone (16), 3,5-bis(chlorosulfonyl)-1-acetophenone (17), and 3,5-bis(4-(chlorosulfonyl)phenyloxy)-1-acetophenone (18) via a sequence of reactions, involving in the last step the quantitative oxidative chlorination of S-(aryl)- N,N‘-diethylthiocarbamate, alkyl- or benzyl thiophenyl groups as masked nonreactive precursors to sulfonyl chlorides is described. A related sequence of reactions was used for the synthesis of the aromatic trisulfonyl chloride 1,1,1-tris(4-chlorosulfonylphenyl)ethane (24). 4-(Chlorosulfonyl)phenoxyacetic acid, 2,2-bis[[[4-(chlorosulfonyl)phenoxyacetyl]oxy]methyl]-1,3-propanediyl ester (27), 5,11,17,23-tetrakis(chlorosulfonyl)-25,26,27,28-tetrakis(ethoxycarbonylmethoxy)calix[4]arene (38), 5,11,17,23,29,35-hexakis(chlorosulfonyl)-37,38,39,40,41,42-hexakis(ethoxycarbonylmethoxy)calix[6]arene (39), 5,11,17,23,29,35,41,...

The highly compact and globular shape, as well as the uniform size and plurifunctionality of dendrimers make them ideal molecular building blocks for a wide range of interfacial materials involving self-assembled monolayers, Langmuir films, multilayers, and other surface-confined assemblies. Moreover, the study of the behavior of dendrimers at surfaces and interfaces provides unique insight into their chemical and physical properties. Dendritic macromolecules play an increasingly important role in the materials and surface sciences, where applications utilizing polymer thin films can benefit from their distinctive chemical and physical properties. Recent investigations have highlighted the use of dendrimers as functional surfaces and as interfacial materials for applications in membranes, adhesion, microelectronics or in chemical and biological sensing.

Collaborative research was conducted by the faculty known as the Lithography Network. This network brings together world class researchers over a broad set of technology areas essential to the success of maskless lithography and non-conventional patterning. The primary faculty by task is listed below: Task 1: Electron Beam Technology for Maskless Lithography, Professor R. Fabian Pease (Coordinator); Task 2: Spatial Light Modulators for Maskless lithography, Professor Olav Solgaard (Coordinator); Professor Andrew Neureuther; Task 3: Maskless Droplet-On-Demand (DoD) Systems. Professor Vivek Subramanian (Coordinator), Professor Jeffrey Bokhor; Task 4: Advanced Materials for Maskless Lithography, Professor C. Grant Willson (Coordinator), Professor Jean Frechet; Task 5: Characterization of Nanoscale Phenomena for Maskless Lithography, Professor Andrew R. Neureuther (Coordinator); Task 6: Data Compression and Path Issues for Maskless Lithography, Professor Avideh Zakhor (Coordinator).

The active sites of metalloenzymes are often deeply buried inside a hydrophobic protein sheath, which protects them from undesirable hydrolysis and polymerization reactions, allowing them to achieve their normal functions. In order to mimic the hydrophobic environment of the active sites in bacterial monooxygenases, diiron(II) compounds of the general formula [Fe2([G-3]COO)4(4-RPy)2] were prepared, where [G-3]COO− is a third-generation dendrimer-appended terphenyl carboxylate ligand and 4-RPy is a pyridine derivative. The dendrimer environment provides excellent protection for the diiron center, reducing its reactivity toward dioxygen by about 300-fold compared with analogous complexes of terphenyl carboxylate ([G-1]COO−) ligands. An FeIIFeIII intermediate was characterized by electronic, electron paramagnetic resonance, Mössbauer, and X-ray absorption spectroscopic analyses following the oxygenation of [Fe2−([G-3]COO)4(4-PPy)2], where 4-PPy is 4-pyrrolidinopyridine. The results are consistent with the formation of a superoxo species. This diiron compound, in the presence of dioxygen, can oxidize external substrates.

The synthesis of a variety of core functionalized PEGylated polyester dendrimers and their in vitro and in vivo properties are described in this report. These water-soluble dendrimers have been designed to carry eight functional groups on their dendritic core for a variety of biological applications such as drug delivery and in vivo imaging as well as eight solubilizing groups. Using a common symmetrical aliphatic ester dendritic core and trifunctional amino acid moieties, a library of dendrimers with phenols, alkyl alcohols, alkynes, ketones, and carboxylic acid functionalities has been synthesized without the need for column chromatography. The amines were PEGylated, leaving the other functionality of the amino acid available for further manipulation such as the attachment of drugs and/or labels. Radiolabeling experiments with the PEGylated dendrimers showed that they had a long circulation half-life in mice, confirming the potential of this class of dendrimers for therapeutic and/or diagnostic applications. A carboxylic acid functionalized dendrimer was elaborated to carry doxorubicin bound via a hydrazone bond. The drug-loaded carrier accumulated more in tumors and less in healthy organs than the clinically used PEGylated liposomal formulation Doxil. The efficient synthesis, high versatility, and favorable biological properties make these PEGylated polyester dendrimers promising structures for therapeutic and/or imaging applications.

The immobilization of catalytic groups onto a dendritic support either at the core or at the periphery gives rise to unique properties that affect rates of reaction, substrate activation or selectivity, etc. When advantageous, these properties can be classified as a positive dendrimer effect. Positive dendrimer effects can arise from site isolation, transition state stabilization and/or dielectric effects in the case of core-modified dendrimers, while peripherally modified dendrimers usually benefit from steric crowding or cooperativity for catalytic residues confined to the surface of the polymer. In this review, the appearance of positive dendrimer effects from the literature will be highlighted as well as prospects for future work in the field.

Using facile, highly modular synthetic approaches, a new monomer family based on a 1,2,3-triazole-4-vinyl building block has been prepared, and various functional derivatives have been obtained. Subsequent homo- and copolymerization of these novel functionalized monomers gives polymeric materials with unique physical properties, combining many attractive features of more traditional monomers, such as styrene, vinylpyridine, and meth/acrylates.

The thin film microstructure development of functionalized oligothiophenes with branched, thermally removable groups at each end of conjugated cores with five, six, and seven thiophene rings was monitored during their thermal conversion from solution processible precursors to insoluble semiconductor products. The change in end group character provides a comparison of branched vs linear end group functionalization in oligothiophenes. Near edge X-ray absorption fine structure (NEXAFS) spectroscopy confirmed that branched alpha-, omega-substitutions of the precursors strongly influenced the packing of the conjugated core. The quinque- and sexithiophene precursors oriented perpendicular to the substrate, whereas the septithiophene precursor oriented parallel to the substrate, providing one of the first examples of length dependence in oligothiophene orientation. This dependence may be due to a packing mismatch between the conjugated cores and the branched end groups. The convertible septithiophene exhibits four distinct microstructures as it converts from precursor to product that correlate strongly with its field-effect hole mobility in field-effect transistors. The extent of septithiophene order and the surface-relative orientation of its ordered phases clearly influence field-effect transistor performance.

Rigid-rod dendronized linear polymers consisting of a poly(4-hydroxystyrene) backbone and fourth-generation polyester dendrons were evaluated in vitro and in vivo to determine their suitability as drug delivery vectors. Cytotoxicity assays indicated that the polymers were well tolerated by cells in vitro. Biodistribution studies of the polymers in both nontumored and tumored mice revealed that as for random coil linear polymers, renal clearance was a function of polymer size, with significant urinary excretion observed for a 67 kDa dendronized polymer. High accumulation in organs of the reticuloendothelial system was exhibited by a dendronized polymer with a very high molecular weight (M(n) = 1740 kDa), but was not as significant for smaller polymers with M(n) = 67 kDa and M(n) = 251 kDa. The rank order for tumor accumulation of the polymers on a percent injected dose per gram tumor basis was 251 kDa approximately 1740 kDa > 67 kDa. These data will help guide the selection of highly functionalizable rigid-rod dendronized polymers with pharmacokinetic properties appropriate for use as drug carriers.

High molecular weight (MW) polymers have shown promise in terms of improving the properties and the efficacy of low MW therapeutics. However, new systems that are highly biocompatible, are biodegradable, have well-defined MW, and have multiple functional groups for drug attachment are still needed. The biological evaluation of a library of eight polyester dendrimer-poly(ethylene oxide) (PEO) bow-tie hybrids is described here. The group of evaluated polymers was designed to include a range of MWs (from 20000 to 160000) and architectures with the number of PEO arms ranging from two to eight. In vitro experiments revealed that the polymers were nontoxic to cells and were degraded to lower MW species at pH 7.4 and pH 5.0. Biodistribution studies with (125)I-radiolabeled polymers showed that the high MW carriers (40000) exhibited long circulation half-lives. Comparison of the renal clearances for the four-arm versus eight-arm polymers indicated that the more branched polymers were excreted more slowly into the urine, a result attributed to their decreased flexibility. Due to their essentially linear architecture that does not provide for good isolation of the iodinated phenolic moieties, the polymers with "two arms" were rapidly taken up by the liver. The biodistributions of two long-circulating high MW polymers in mice bearing subcutaneous B16F10 tumors were evaluated, and high levels of tumor accumulation were observed. These new carriers are therefore promising for applications in drug delivery and are also useful for improving our understanding of the effect of polymer architecture on pharmacokinetic properties.

A near-white light-emitting polymer, consisting of hole transport (HT), electron transport (ET), and phosphorescent Pt functionalities, was prepared and utilized as the emissive layer in solution-processed OLEDs. The air-stable devices had a maximum external quantum efficiency of 4.6%.

Self-assembled polyester dendritic bow-ties with various peripheral groups were prepared, and their association constants were measured by (1)H NMR in CDCl(3). The two complementary dendrons were prepared by attachment of either a bis(adamantylurea) or a glycinylurea to the focal point of the dendron. The parent self-assembled system with benzylidene acetals on one periphery and isopropylidene acetals on the other had an association constant of 520 M(-)(1). Upon deprotection of one dendron, the association constant is increased by more than an order of magnitude as the solubility of the hydroxyl-terminated dendron in CDCl(3) is decreased. In contrast, attachment of tri(ethylene oxide) units to the periphery of one dendron lowers the association constant by almost an order of magnitude. The causes of these relatively large changes in complex strength are discussed in terms of solubility, steric effects, competitive hydrogen bonding, and the structure of the dendritic scaffold.

The site isolation of two dyes capable of electronic interaction via Forster energy transfer has been studied with the two dyes coumarin 343 and pentathiophene encapsulated by dendrons containing both solubilizing and electroactive moieties. Photoluminescence studies of mixtures of the dendritic dyes show that at high dendron generation, significant site isolation is achieved with relative emission characteristics influenced by both the degree of site isolation and the emission quantum yield of the dyes. Electroluminescence studies carried out in organic light emitting diode devices confirm that color tuning may be achieved by mixing the two encapsulated dyes in a single layer. However, selective carrier trapping by one of the core component dyes can dramatically influence the effectiveness of other components in the device.

A novel porous polymer was microfabricated to serve as a porous plug for a new device, the porous plug electro-osmotic pump (pp-EOP). The plug eliminates any back pressure effects while enhances electro-osmotic flow in a channel. The pp-EOP was batch fabricated by surface micromachining on top of a silicon wafer. The pp-EOP device is driven by a periodic, zero-average injected current signal at low frequencies producing bubble-free electro-osmotic flow with reversible net movement. Testing of the device produced an average water-air interface velocity of 1.8 /spl mu/m/s at 0.8 Hz. The velocity was increased to 4.8 and to 13.9 /spl mu/m/s by necking the channel size.

Monolithic plugs of poly(N-isopropylacrylamide) cross-linked with 5% methylenebisacrylamide have been prepared by photoinitiated polymerization within the channel of a microfluidic device. The volume change associated with the polymer phase transition at its lower critical solution temperature of 32 degrees C allows both the rapid swelling and the deswelling of the monoliths enabling the polymer to close or open the channel as it functions as a nonmechanical valve. Thermoelectric elements capable of changing the temperature of the system between 17 and 57 degrees C were used to actuate the valve. Flow through the device was monitored by fluorescence measurements via the laser-triggered photobleaching of a dye contained in the liquid phase. Photobleaching occurs quickly once the flow is stopped, and the time required to open and close the valve was 3.5 and 5.0 s, respectively. No changes in function were observed even after 120 open-close cycles. Although the 2-mm-long valve was prepared from a polymerization mixture consisting of only a 5% aqueous solution of monomers, it resists pressures of up to 1.38 MPa (200 psi) without observable structural damage.

An acid catalysed rearrangement that transforms a bicyclic lactone into a phenolic carboxylic acid has been tested for potential use in chemically amplified microlithographic imaging.

Attachment of drugs to high molecular weight polymers can significantly improve both tumor targeting and therapeutic efficacy due to the enhanced permeability and retention effect observed in tumor tissue. However, the commercial availability of well-defined water-soluble polymeric systems with narrow polydispersities that are biocompatible, nontoxic, and nonimmunogenic is rather limited. To address this need, we have investigated dendritic polymers as promising scaffolds for the preparation of new soluble polymeric drug carriers due to their well-defined molecular architecture and their multiplicity of surface sites. Herein we show the design and synthesis of dendritic polyester systems based on the monomer unit 2,2-bis(hydroxymethyl)propanoic acid as a possible versatile drug carrier. The potent anticancer drug doxorubicin was attached via a pH-sensitive linkage to one of the carriers presented, demonstrating the feasibility of using these polyester dendritic structures to prepare a viable polymer-drug conjugate.

Natural photosynthetic systems collect sunlight using a vast array of light-harvesting chromophores that channel the absorbed energy to a single reaction center. Recently, it has been realized that dendritic macromolecules can exhibit similar properties, though on a more modest scale. The preparation of dendritic structures and assemblies composed of numerous light-collecting chromophores that transfer their energy to a single energy ‘sink’ at the core has been achieved in a number of diverse and creative ways. These novel structures are being used as model systems in light-emitting diodes, signal amplifiers, fluorescent sensors, frequency converters, and other photonic devices.

A novel approach to thermoresponsive polymeric membranes based on molded monolithic sheets of macroporous polymers has been demonstrated. The macroporous sheet prepared from glycidyl methacrylate ethylene dimethacrylate is functionalized either by free-radical grafting of N-isopropylacrylamide, or, better, by copolymerization of N-isopropylacrylamide onto the vinylated surface of the pores of the polymer sheet. The macroporous polymers modified with poly(N-isopropylacrylamide) were shown to be thermoresponsive. Changes in the temperature of a flow system incorporating the modified macroporous material were accompanied by significant changes in the backpressure required to effect flow. This study confirms the feasibility of thermoresponsive membranes for water purification.

A new class of porphyrin containing hyperbranched polymers has been prepared via proton-transfer polymerisation utilising an A2 + B3 approach, thus providing an accelerated entry into the construction of branched multiporphyrin architectures.

During the last years, efforts have been made to encapsulate porphyrins1 within dendrimers to tune their photophysical,2 electrochemical,3 and chemical4 properties. Work carried out in several laboratories has demonstrated the profound ability of a dendritic shell to isolate the porphyrin core moiety facilitating the design of hemeprotein mimics. Unfortunately, dendrimer synthesis is usually time-consuming, and a more rapid route to encapsulated porphyrins that preserves the architectural and functional control afforded by a dendritic shell is desired. Recent advances in the area of “living” ring opening polymerization (ROP) of -caprolactone5 have enabled the accurate construction of star-shaped polymers.6 We sought to take advantage of this methodology coupled with the space filling branching approach of dendrimer synthesis to achieve site isolation of porphyrins. Our approach is based on a highly branched porphyrin core that acts as a multisite initiator for the ROP of -caprolactone. Versatile modification of the core and the end-group functionalities renders the synthesis flexible, allowing one to tailor-design a variety of functional star polymers. Such materials may be of general applicability in the design of oxidation catalysts7 as well as energyharvesting8 and optoelectronic devices.9 Starting from tetrakis(4-hydroxyphenyl)porphyrin 1a and tetrakis(3,5-dihydroxyphenyl)porphyrin 1b, respectively, the initiators 2a,b were prepared via esterification employing acetonide-protected 2,2-bis(hydroxymethyl)-propionic acid10 followed by deprotection of the diol functionalities under acidic conditions (Scheme 1). By using the methodology developed by Trollsas and Hedrick,6a-c we obtained star polymers 3a,b possessing either 8 or 16 arms by bulk polymerization of -caprolactone with initiators 2a,b and tin(II) 2-ethylhexanoate (Sn(Oct)2) as the catalyst. By adjusting the monomer-to-initiator ratio, we could prepare polymers with varying chain lengths and low polydispersities in almost quantitative yields (Table 1). To tune the properties of these materials, we accomplished further modification of the dendritic stars by metalation of the core moiety as well as by derivatization of the hydroxyl-functional chain ends (Scheme 2). Insertion of zinc(II) into the free base porphyrin gave 4b, which is easily identified by its characteristic electronic absorption spectrum in the Q-band region11 (Figure 1a). Introduction of the dye coumarin at each of the 16 hydroxyl chain ends of 3b was easily accomplished by esterification with coumarin-3-carboxylic acid chloride affording 5b. The additivity of the individual coumarin chromophore units contributes to the large absorption in the UV region of the spectrum (Figure 1a). The proton NMR spectra of 3b and 5b (Figure 1b) reveal a significant downfield shift of the signal associated with the end groups of 3b (CH2OH) by conversion to the coumarin esters in 5b. Due to the energetic match between the emission of the coumarin donors and the absorption of the porphyrin acceptor, compounds such as 5b offer the opportunity of efficient light harvesting and resonance energy transfer.12 Further studies of these processes are currently underway. A significant advantage of the high yield processes used is that the only purification required after polymerization, metalation, (1) For an introduction to porphyrin chemistry, see: Milgrom, L. R. The Colours of Life; Oxford University Press: Oxford, U.K., 1997, and references therein. (2) (a) Jin, R.-H.; Aida, T.; Inoue S. J. Chem. Soc., Chem. Commun. 1993, 1260. (b) Tomoyose, Y.; Jiang, D.-L.; Jin, R.-H.; Aida, T.; Yamashita, T.; Horie, K.; Yashima, E.; Okamoto, Y. Macromolecules 1996, 29, 5236. (c) Sadamoto, R.; Tomioka, N.; Aida, T. J. Am. Chem. Soc. 1996, 118, 3978. (d) Pollak, K. W.; Leon, J. W.; Frechet, J. M. J.; Maskus, M.; Abruna, H. D. Chem. Mater. 1998, 10, 30. (e) Pollak, K. W.; Sanford, E. M.; Frechet, J. M. J. J. Mater. Chem. 1998, 8, 519. (f) Jiang, D.-L.; Aida, T. J. Am. Chem. Soc. 1998, 120, 10895. (3) (a) Dandliker, P. J.; Diederich, F.; Gross, M.; Knobler, C. B.; Louati, A.; Sanford, E. M. Angew. Chem., Int. Ed. Engl. 1994, 33, 1739. (b) Dandliker, P. J.; Diederich, F.; Gisselbrecht, J.-P.; Louati, A.; Gross, M. Angew. Chem., Int. Ed. Engl. 1995, 34, 2725. (c) Dandliker, P. J.; Diederich, F.; Zingg, A.; Gisselbrecht, J.-P.; Gross, M.; Louati, A.; Sanford, E. M. HelV. Chim. Acta 1997, 80, 1773. (4) (a) Jiang, D.-L.; Aida, T. Chem. Commun. 1996, 1523. (b) Collman, J. P.; Fu, L.; Zingg, A.; Diederich, F. Chem. Commun. 1997, 193. (c) Bhyrappa, P.; Young, J. K.; Moore, J. S.; Suslick, K. S. J. Am. Chem. Soc. 1996, 118, 5708. (d) Bhyrappa, P.; Vaijayanthimala, G.; Suslick, K. S. J. Am. Chem. Soc. 1999, 121, 262. (5) For a recent review, consult Lofgren, A.; Albertsson, A.-C.; Dubois, P.; Jerome, R. J. Macromol. Sci., ReV. Macromol. Chem. Phys. 1995, C35, 379. (6) (a) Trollsas, M.; Hedrick, J. L.; Mecerreyes, D.; Dubois, P.; Jerome, R.; Ihre, H.; Hult, A. Macromolecules 1997, 30, 8508. (b) Trollsas, M.; Hedrick, J. L.; Mecerreyes, D.; Dubois, P.; Jerome, R.; Ihre, H.; Hult, A. Macromolecules 1998, 31, 2756. (c) Trollsas, M.; Hedrick, J. L. J. Am. Chem. Soc. 1998, 120, 4644, and references therein. (7) Detailed review are given in (a) Sheldon, R. A., Ed. Metalloporphyrins in Catalytic Oxidations; Marcel Dekker: New York, 1994. (b) Montanari, F., Casella, L., Eds. Metalloporphyrin Catalyzed Oxidations; Kluwer: London, 1995. (8) For a recent discussion, see Freemantle, M. Chem. Eng. News 1998, (10/26), 37. (9) An enhancement of the luminescence properties of lanthanide ions using the concept of site isolation has recently been reported: Kawa, M.; Frechet, J. M. J. Chem. Mater. 1998, 10, 286. (10) Ihre, H.; Hult, A.; Frechet, J. M. J.; Gitsov, I. Macromolecules 1998, 31, 4061. (11) (a) Buchler, J. W. In The Porphyrins; Dolphin, D., Ed.; Academic Press: New York, 1978; Vol. I, Part A, p 390. (b) Smith, K. M. In Porphyrins and Metalloporphyrins; Smith, K. M., Ed.; Elsevier: New York, 1976; p 3 and appendix p 871. (12) For a related study, see Gilat, S. L.; Adronov, A.; Frechet, J. M. J. Angew. Chem., Int. Ed. Engl. 1999, 38, 1422. Scheme 1

N-(p-methylstyryl)-(1R,2S)-ephedrine is prepared by alkylation of p-chloromethylstyrene under conditions which do not favor quaternization. A series of Copolymerization reactions confirm that the new chiral monomer and styrene copolymerize in random fashion with r1=1.09 and r2=0.98. The optical rotation of the copolymers does not vary linearly with composition. Applications of the copolymer include its use as chiral ligand for asymmetric synthesis or as a separation medium.

Dialkylaminopyridines whose N -substituents bear a hydroxyl or amino group can be made economically from 4-cyanopyridine. Simple but selective alkylation of these compounds with commercial (chloromethyl) or (3-bromopropyl) polystyrene gives several new solid-phase catalysts which are highly active in promoting the acylation of hindered alcohols. Comparison of syntheses and reactivities, among these and some other heterocyclic polymers, illustrates several useful general principles of reactive polymer chemistry such as local concentration and microenvironment effects.

Crosslinked bead polymers containing vinylpyridine units were prepared by pearl copolymerization of monomer mixtures containing various percentagesof 4-vinylpyridine, styrene, and di-vinylbenzene. The polymers were functionalized by reaction with hydrogen bromide and bromine, and the resulting poly-(vinylpyridinium hydrobromide perbromide) resins, which were stable for long periods of time, were used to brominate a number of alkenes and ketones. In most cases, the brominated products were obtained in excellent yields and could be separated from the polymeric by-product by a simple filtration. The polymeric reagent could be fully regenerated after use without loss of activity.

The use of the t-BOC protecting group for the preparation of an organic soluble derivative of poly(vinyl alcohol) is reported. Poly(vinyl-t-butyl carbonate) can be obtained by free-radical polymerization of the monomer using peroxide or azo initiators at 90–120°C. The t-BOC polymer is thermolyzed cleanly to poly(vinyl alcohol) with evolution of carbon dioxide and 2-methyl-propene when heated to 210–220°C. The t-BOC polymer may be useful for imaging processes involving acid-catalyzed thermolysis.

The kinetics of phase-transfer catalysis using glycidyl methacrylate-ethylene dimethacrylate resins modified with pendant quaternary butylammonium groups have been studied. In contrast to expectations based on currently proposed mechanisms, the activity of polymeric catalysts is not improved through modifications that balance the hydrophilic and hydrophobic properties of the material. It is believed that much of the activity of the polymeric catalysts derives from the swelling of the polymer in both aqueous and organic phases. This enhances not only the rate of diffusion of both reagents to the vicinity of the catalytically active groups but also the ability of reactive groups to oscillate between the two phases. Both swelling and diffusion are restricted severely as the percentage of crosslinking is increased. This restriction is of particular importance with macroporous resins. Comparison of kinetic data obtained with various polymers suggests that gel polymers with very small bead sizes and therefore high external surface areas provide much higher reactivities than their macroporous counterparts.