Well-defined Molecular Weight Research Articles

Nanoelectronic detection of breast cancer biomarker

There is a fundamental need for semiconductor-based ultrasensitive nanosensors for detecting heterogeneous biomarkers associated with cancer, which do not have a well-defined molecular weight. Here we show that a nanoscale gated biological field effect transistor can be used for detecting the breast cancer serum biomarker protein CA15.3 down to levels of concentration less than 20 units/ml, relevant for clinical use. Our work extends the capability of nanowire sensors to a class of mucin-based heterogeneous protein biomarkers that are of fundamental importance to modern cancer detection.

High Crystallinity and Nature of Crystal−Crystal Phase Transformations in Regioregular Poly(3-hexylthiophene)

Molecular weight and stereoregularity affect the morphology and the crystallinity of conjugated polymers and are thus of pivotal relevance for the mobility of charge carriers in electro-optical device applications. Currently, poly(3-akylthiophenes) are discussed as one of the most promising classes of materials for photovoltaic applications. Here, we use 13C solid-state NMR to determine the crystallinity and details on crystal−crystal phase transformations in regioregular head-to-tail poly(3-hexylthiophene) of well-defined molecular weight and demonstrate that the crystallinity was previously severely underestimated. Typical crystallinities are at least around 37% for the lowest molecular weights and as high as about 64% upon increasing MW, corresponding to a corrected maximum value for the reference melting enthalpy of ΔHm∞ ≈ 37 J/g for use in DSC experiments. Using 1D 13C spectra and 2D experiments that measure the strength of 13C−1H dipolar couplings, we observe that the crystal−crystal phase transitio...

Molecular structures for the oligomeric constituents of petroleum pitch

Individual dimer, trimer, and tetramer constituents that comprise the higher molecular weight (mol wt), mesophase-forming fraction of M-50 petroleum pitch were characterized in terms of polycyclic aromatic hydrocarbon (PAH) backbone structure, the extent of alkylation, and the nature of the bonds connecting the monomeric “building blocks” comprising the oligomeric species. Isolation of individual oligomeric constituents for subsequent analysis and identification was made possible by applying our two-step, sequential fractionation technique of dense-gas/supercritical extraction (DGE) followed by prep-scale gel permeation chromatography (GPC). MALDI and MALDI-post source decay (PSD) mass spectrometry of the narrow mol wt fractions obtained indicate that the major oligomeric constituents are grouped in terms of well-defined molecular weight distributions, with each composed of base monomer PAH backbone structure(s) (e.g., pyrene, triphenylene, benzopyrenes, chrysene, and benz[a]anthracene) possessing various degrees (typically 1–4/monomer unit) of methylation. UV–Vis analysis indicates that the oligomerization process occurs via a condensation reaction, with the loss of four hydrogens as a nonalternant, 5-membered PAH ring forms to join the reacting monomer units. FT-IR spectroscopy indicates that this reaction results in relatively uncondensed structures over the entire range of oligomers investigated. Analogous results to those given above were obtained for the thermal polymerization of an anthracene pitch.

Further Studies on the Anionic Copolymerization of Styrene and Glycidyl Methacrylate in Toluene

Sequential anionic copolymerization of styrene and glycidyl methacrylate (GMA) was performed with the protection of argon under normal pressure, where styrene, GMA, toluene, THF, n-butyllithium and a small amount of lithium chloride (LiCl) were used as first monomer, second monomer, solvent, polar reagent, initiator and additive, respectively. Polystyrene-b-poly(glycidyl methacrylate) diblock copolymers (PS-b-PGMA) with well-defined structure and narrow molecular weight distribution were prepared by the copolymerization reaction of poly(styryl)lithium with GMA under certain temperatures. The copolymers were characterized using gel permeation chromatography (GPC), 1H-NMR, 13C-NMR, thin layer chromatography (TLC) and hydrochloric acid-dioxane argentimetric methods. The effects of additives, copolymerization temperature and THF dosage on the copolymerization were studied. No chain transfer reaction of anionic polymerization of styrene in toluene was observed. Slightly broader molecular weight distribution of PS-b-PGMA was observed with the increase the GMA repeat units. Using THF/toluene blend solvent could reduce the polydispersity index (M w /M n ) and dissolve the copolymer better than toluene alone. Lower temperature (< -40°C) and LiCl are required to prepare PS-b-PGMA with narrower molecular weight distribution.

Temperature and Molecular Weight Dependent Hierarchical Equilibrium Structures in Semiconducting Poly(3-hexylthiophene)

We report on structural investigations of a series of regioregular poly(3-hexylthiophene) with well-defined molecular weight (5−19 kg/mol) using DSC, small angle and wide-angle X-ray scattering, and AFM. With increasing temperature, we identify three ordered phases, namely 3D crystalline, 2D crystalline with disordered side chains, and a layered phase of smectic symmetry, followed by complete melting. Although all samples crystallize in extended chain conformation, the lower molecular weight material exhibits a lower crystallinity, most likely caused by noncrystallizable end groups. The crystallinity increases strongly with increasing molecular weight, which could be a possible explanation for the known dependence of charge transport properties on molecular weight.

Effect of Molecular Structure on Thermoresponsive Behaviors of Pyrrolidone-Based Water-Soluble Polymers

This paper describes the molecular structure dependent thermoresponsive behaviors of pyrrolidone-based water-soluble polymers. A series of well-defined poly[N-(2-methacryloyloxyethyl)pyrrolidone] (PNMEP), poly[N-(3-acryloyloxypropyl)pyrrolidone] (PNAPP), and poly[N-(3-methacryloyloxypropyl)pyrrolidone] (PNMPP) were synthesized via visible light activating RAFT polymerization at 25 °C. Kinetic studies indicate a rapid and well-controlled behavior of this polymerization. Gel permeation chromatography (GPC) and 1H NMR analysis confirm their intact molecular structure, well-defined molecular weight, and narrow distribution. Laser light scattering and temperature-variable 1H NMR analyses demonstrate that the cloud point of a PNMEP sample at a degree of polymerization (DP) of 96 is 1.5 °C lower than that of PNAPP at a DP = 104. Additional backbone methyl groups in PNMPP lead to a dramatic cloud point lowering, e.g., cloud point of PNMPP at a DP = 100 is 37 °C lower than that of PNAPP at a DP = 104. This is cont...

Living cationic polymerization of an azide-containing vinyl ether toward addressable functionalization of polymers

We first achieved the living cationic polymerization of azide-containing monomer, 2-azidoethyl vinyl ether (AzVE), with SnCl4 as a catalyst (activator) in conjunction with the HCl adduct of a vinyl ether [H-CH2CH(OR)-Cl; R  CH2CH2Cl, CH2CH(CH3)2]. Despite the potentially poisoning azide group, the produced polymers possessed controlled molecular weights and fairly narrow distributions (Mw/Mn ∼ 1.2) and gave block polymers with 2-chloroethyl vinyl ether. The pendent azide groups are easily converted into various functional groups via mild and selective reactions, such as the Staudinger reduction and copper-catalyzed azide-alkyne 1,3-cycloaddition (CuAAC; a “click” reaction). These reactions led to quantitative pendent functionalization into primary amine (NH2), hydroxy (OH), and carboxyl (COOH) groups, at room temperature and without any acidic or basic treatment. Thus, poly(AzVE) is a versatile precursor for a wide variety of functional vinyl ether polymers with well-defined structures and molecular weights. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1449–1455, 2010

Nanoreactors for Polymerizations and Organic Reactions

The aim of this Perspective is to use the knowledge of the underpinning kinetic and thermodynamic precepts that govern free-radical and “living” radical water-based heterogeneous polymerizations and apply this to small molecule organic reactions in nanoreactors. The difficulty in applying “living” radical polymerization to water-based heterogeneous systems has led to such an understanding, including partitioning of agents between the phases, nucleation of particles, and other phenomena including superswelling. This knowledge has allowed us to prepare polymers in heterogeneous systems with well-defined molecular weight distributions and particle size distributions. However, to overcome the physical chemistry constraints, researchers had to develop complex nanoreactor systems. For the field of small molecule organic reactions in heterogeneous systems to be industrially relevant and to grow rapidly, such physical chemistry precepts should be more greatly developed.

Functional Star Polymers with a Cholic Acid Core and their Thermosensitive Properties

Star polymers derived from cholic acid with poly(allyl glycidyl ether) arms have been prepared via anionic polymerization, yielding polymers with well-defined molecular weight and low polydispersity. The double bonds of the allyl groups on the polymer are used to introduce either amine or carboxylic acid groups to obtain amphiphilic polymers with cationic and anionic groups, respectively. The polymers can aggregate in water above a certain critical concentration, which was found to vary with the arm length of the star polymers. The star polymers bearing amino groups showed interesting thermosensitivity, which also depends on the pH of the media. A simple acetylation of the amine groups can sharpen the transition and vary the cloud point from 15 to 48 degrees C, depending on the degree of acetylation. Such polymers offer useful alternatives to the existing thermosensitive polymers.

Controlled Synthesis of High Molecular Weight Polyacrylates Having a Dumbbell Topology

Well-defined high molecular weight (MW) (Mn ∼ 500 000, Mw/Mn < 1.2) dumbbell-shaped copolymers based on butyl acrylates (BA) were synthesized by atom transfer radical polymerization (ATRP) in acetone. The synthesis was carried out by polymerization of BA initiated by a difunctional ATRP initiator. The resulting difunctional bromine end-functionalized PBA was used to initiate a small amount of hydroxyethyl acrylate (HEA). The resulting ABA type copolymer containing two short poly(hydroxyethyl acrylate) end blocks was reacted with α-bromoisobutyryl bromide. The resulting ABA polymer was used to reinitiate additional BA end arms to afford the desired dumbbell PBA. All polymer intermediates and the final polymer were characterized by NMR and multiangle laser light scattering size exclusion chromatography (SEC-MALLS). SEC analysis of the low-MW polymers obtained by base hydrolysis of the intended structure confirmed the successful BA polymerization at the A blocks. Hydrolysis gave the expected number and MWs o...

Tailor-Made Poly(methyl acrylate) bearing Amantadine Functionality (Amino Adamantyl) via Atom Transfer Radical Polymerization (ATRP). A Precursor of a Supramolecular Cross-Linked Polymer

Poly(methyl acrylate)s bearing an amino adamantyl group were prepared via atom transfer radical polymerization (ATRP). The amino adamantyl (amantadine) group was incorporated into the polymer by homopolymerization as well as by copolymerization of acrylate bearing amantadine functional group. The rate of ATRP was slow compared to the rate of ATRP of methyl acrylate or adamantyl containing acrylate. It is due to the interaction of amine group of amantadine with Cu catalyst. 1H NMR, matrix assisted laser desorption ionization time-of-flight mass spectrometry (MALDI−TOF−MS) and gel permeation chromatography (GPC) analysis showed that the polymers had well-defined molecular weight and amino adamantyl functional group. Interestingly, this amine group was further reacted with epoxy group of the tailor-made poly(glycidyl methacrylate) (PGMA) to produce hydrogen-bonded polymers having porous network structure. It was evidenced by field-emission scanning electron microscopy (FESEM) analysis, differential scanning ...

Size of Bicelle Defects Probed via Diffusion Nuclear Magnetic Resonance of PEG

Diffusion of various poly(ethylene glycol) (PEG) tracers of well-defined molecular weight and narrow polydispersity confined within the aqueous interstices between positively magnetically aligned bicelles was measured using pulsed-field-gradient 1H nuclear magnetic resonance. The bicelles consisted of mixtures of dimyristoylphosphatidylcholine (DMPC), dimyristoylphosphatidylglycerol (DMPG), and dihexanoylphosphatidylcholine (DHPC) in the molar ratios q = [100 DMPC +5 DMPG]/[DHPC] = 3.5, 4.5, and 5.5, to which Yb3+ had been added in the ratio 1:75 Yb3+/phospholipid. The field gradients were applied such that diffusion was measured in the direction parallel to the normal to the bicelles' planar regions, thereby rendering the experiment sensitive to the ability of PEG to traverse lamellar defects within the bicelles. The pulsed-field-gradient nuclear magnetic resonance diffusive intensity decays were diffusion-time-independent in all cases, with diffusive displacements corresponding to many hundreds of bicellar lamellae. This permitted a description of such diffusive decays in terms of a mean behavior involving a combination of straight obstruction effects common to all PEG, with hindrance to diffusion proportional to the relative size of a given PEG with respect to the size of the lamellar defects. Across the range of PEG molecular weights (200–4600) and bicelle compositions examined, the apparent radial dimension of the lamellar defects decreased from 165 Å with q = 3.5 to 125 Å with q = 5.5. This is opposite to the trend predicted from static geometric models of either bicelle disks or perforated lamellae. Qualitatively, the observed trend suggests that mobility of the obstructions to diffusion will need to be considered to reconcile these differences.

Zwitterionic Polymerization: A Kinetic Strategy for the Controlled Synthesis of Cyclic Polylactide

The zwitterionic ring-opening polymerization of lactide initiated by N-heterocyclic carbenes generates cyclic polylactides with well-defined molecular weights between M(n) = 5000 and 30,000 g/mol with narrow polydispersities (M(w)/M(n) < or = 1.31). These zwitterionic polymerizations are extremely rapid (k(p) = 48.7 M(-1) s(-1)), but also exhibit exceptional control of molecular weight and molecular weight distribution. The unusual kinetic features of these zwitterionic polymerizations are illuminated with kinetic and mechanistic investigations, which implicate a mechanism that involves a slow initiation step (second order in [M]), a propagation step (first order in [M]) that is much faster than initiation (k(i) = 0.274 M(-2) s(-1)), cyclization (k(c) = 0.0575 s(-1)), and depropagation (k(d) = 0.208 s(-1)). Numerical and stochastic simulations of the kinetic data provide a kinetic rationale for the evolution of molecular weight with monomer conversion: the molecular weights increase with increasing monomer conversion, exhibit a nonzero intercept near 0% monomer conversion, and are relatively insensitive to the initial monomer-to-initiator ratio. The observed narrow molecular weight distributions are due to a high rate of propagation relative to cyclization and chain transfer. Kinetic simulations define the kinetic criteria under which the active zwitterions remain in solution; these simulations were substantiated by chain-extension experiments, which provide experimental evidence for chain extension of the zwitterions and reinitiation by the N-heterocyclic carbenes liberated upon macrocyclization. The kinetic model rationalizes some of the unique features of zwitterionic ring-opening polymerization and provides a useful mechanistic framework to optimize these polymerizations as a strategy to generate well-defined cyclic polyesters.

SYNTHESIS AND CHARACTERIZATION OF POLY(PHTHALAZINONE ETHER NITRILE)-POLYDIMETHYLSILOXANE BLOCK COPOLYMERS

High molecular weight block copolymers with different backbone compositions were synthesized from eugenol end-capped polydimethylsiloxane(PDMS)and fluorophenyl-terminated poly(phthalizinone ether nitrile)(PPEN)oligomers.These oligomers of PPEN were prepared via S_NAr step-growth polymerization from 4-(4-hydroxylphenyl)(2H)-phthalazin-1-one(DHPZ)and 2,6-difluoro-benzonitrile(DFBN)using DMSO as solvent at 180℃.The oligomers with well-defined fluoro-terminated and various quantitative molecular weights were obtained by using an excess of DFBN.The number-average molecular weight(M_n)values of PPEN oligomers ranged from 3100 to 10500.The eugenol terminated PDMS oligomers were prepared by reacting silane terminated PDMS with eugenol in toluene via the well-known Pt-catalysed hydrosilation reaction.The phenol-group of eugenol was protected by trimethylchlorosilane in the hydrosilation to avoid side reactions and loss of functional group,and the aryl-trimethylsilyl ethers can be cleaved by refluxing in aqueous methanol.The M_n values of PDMS oligomers were 4550 and 7220,respectively.The block polycondensation was carried out in the presence of dimethyl sulfoxide/o-dichlorobenzene and K_2CO_3 as solvents and catalyst at 180℃ by the S_NAr reaction.The M_n values of block copolymers ranged from 19400 to 25100.The results of GPC indicated that reaction of two oligomers occurred and then the higher molecular weight copolymers were obtained.It further suggested that the new synthesis method is an effective and convenient approach to prepare similar PDMS based block copolymers.The structure of copolymers obtained was characterized by FTIR and 1H-NMR.Differential scanning calorimetry analysis indicated that the block copolymers showed two glass-transition temperatures(T_g) at-98～-90℃ and 255～287℃,respectively.The distinct two T_g's in the block copolymers suggested that microphase separation occurred in the block copolymer.The copolymer also showed a high thermal stability with 10% weight-loss temperatures in excess of 450℃ in nitrogen according to thermogravimetric analysis.The migration of PDMS segments to the copolymer surface was observed directly by atomic force microscope(AFM) and transmission electron microscope(TEM).PDMS expanded to the continuous phase on the surface,suggesting that PDMS segments were rich on the surface.The PPEN phase as the particle cavities was dispersed in copolymer surfaces with diameters of 0.1～0.3 nm.

Semiconductor Block Copolymer Nanocomposites with Lamellar Morphology via Self-Organization

Novel semiconductor block copolymers were synthesized using nitroxide-mediated radical polymerization (NMRP). They are comprised of a hole conductor block carrying tetraphenylbenzidine pendant units (PVDMTPD) and a second poly(4-vinylpyridine) (P4VP) block suitable for the preferential incorporation of n-type semiconductor nanocrystals. The conditions of NMRP for both monomers were optimized in order to get macroinitiators with well-defined molecular weights and very low polydispersity (<1.2). The resulting block polymers exhibit a lamellar morphology due to microphase separation. Furthermore, semiconductor nanocomposites were prepared using these diblock copolymers and light harvesting CdSe:Te nanocrystals, and their bulk morphologies were characterized by TEM. This new hybrid nanocomposite material maintains the original lamellar structure in which the hole conductor domains are separated from electron conducting/light harvesting nanocrystals that are confined in the P4VP domains. Thus, the challenging ...

Theory of Polydisperse Block Copolymer Melts: Beyond the Schulz−Zimm Distribution

Block copolymers are renowned for self-assembling intoperiodic morphologies with long-range order, and for their richselection of interesting behaviors and potential applications.There has been a general feeling that this high degree of orderrequires the block copolymers to have well-defined molecularweights with small polydispersities.

Well-Defined Acetylene-Functionalized Oxanorbornene Polymers and Block Copolymers

Well-defined and high molecular weight acetylene-functionalized poly(oxanorbornenes) were synthesized using ring-opening metathesis polymerization (ROMP) of cobalt-functionalized exo-oxanorbornene monomer 2a. Dicobalt hexacarbonyl, Co2(CO)6, was used as a protecting group for the acetylene moiety. This protecting group was found to be compatible with third-generation Grubbs’ catalyst, offering well-defined homopolymers and block copolymers in high yields (up to 97%). Equally important, it was removed (>99%) by treating the polymers with ceric(IV) ammonium nitrate (CAN), under mild conditions, with no observable unwanted side reactions. This approach yields high fidelity polymers containing the acetylene functionality which is incompatible with Ru-based catalysis. The explosion of click chemistry makes these polymers attractive starting macromolecules for postpolymerization chemistry.

Current Patents of Dendrimers and Hyperbranched Polymers in Membranes

Dendrimers or other hyperbranched polymers are a new class of artificial polymers with unique properties, such as high degree of branching units, high density of surface functional groups, nano-scaled size, well-defined molecular weight and low-dispersity. These features make them attractive materials in the field of membrane science. This review is a short survey of patents on dendrimers and other hyperbranched polymers in membrane fields such as proton exchange membranes, bipolar membranes, gas separation membranes, and solid-liquid separation membranes, etc. Keywords: Dendritic polymer, dendrimer, hyperbranched polymer, membrane

Reversible Addition Fragmentation Chain Transfer (RAFT) Polymerization in Undergraduate Polymer Science Lab

This 8-hour experiment (spread over two 4-hour sessions) is designed to equip students with essential skills in polymer synthesis, particularly in synthesizing polymers of well-defined molecular weight. The experiment involves the synthesis and characterization of poly(vinyl neodecanoate) via living free radical polymerization, specifically the reversible addition fragmentation chain transfer (RAFT) process. The commercial availability of the RAFT agent employed (ethylxanthogenacetic acid) enables an efficient laboratory practice without recourse to extensive synthetic chemistry. Through the current experiment, undergraduate students gain invaluable laboratory experience in one of the living free radical polymerization techniques that has revolutionized contemporary polymer science.

Synthesis of Biomimetic Poly(hydroxybutyrate): Alkoxy- and Carboxytriazolines as Latent Ionic Initiator

A well-defined high molecular weight poly(3-hydroxybutyrate) was synthesized by “living”/controlled ring-opening polymerization (ROP) of β-butyrolactone (BL) using a metal-free catalytic system. The ROP was initiated from either primary alcohol or carboxylic acid added with 1 equiv of a stable carbene, i.e., 1,3,4-triphenyl-4,5-dihydro-1H-1,2,4-triazol-5-ylidene carbene, 1. Interestingly, perfect control over molecular weight (Mn up to 32 000 g·mol-1), molecular weight distribution (Mw/Mn ∼ 1.1 − 1.3) and end group fidelity was attained using t-BuOH as the only polymerization solvent at 80 °C. Structural and kinetics studies highlighted an anionic polymerization mechanism where the protonated 1 (1-H) played the role of associated counterion. Attesting for the control of the ROP, amphiphilic block copolymers were further synthesized by polymerization of BL from poly(ethylene oxide) α-methoxy, ω-carboxylic acid macroinitiator while their tensioactive properties were evidenced by the pendant drop method.