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A series of shape amphiphiles based on functionalized polyhedral oligomeric silsesquioxane (POSS) head tethered with two polymeric tails of symmetric or asymmetric compositions was designed and synthesized using sequential "grafting-from" and "click" surface functionalization. The monofunctionalization of octavinylPOSS was performed using thiol-ene chemistry to afford a dihydroxyl-functionalized POSS that was further derived into precisely defined homo- and heterobifunctional macroinitiators. Polymer tails, such as polycaprolactone and polystyrene, could then be grown from these POSS-based macroinitiators with controlled molecular weight via ring-opening polymerization and atom transfer radical polymerization (ATRP). The vinyl groups on POSS were found to be compatible with ATRP conditions. These macromolecular precursors were further modified by thiol-ene chemistry to install surface functionalities onto the POSS cage. The polymer chain composition and POSS surface chemistry can thus be tuned separately in a modular and efficient way.

Anionic polymerization, especially alkyllithium-initiated polymerization of styrenes and dienes, is a truly living polymerization that proceeds in the absence of the kinetic steps of chain termination and chain transfer. The major discoveries in the science and technology of anionic polymerization are chronicled herein. My introduction to this fascinating science is also described. This includes research and training at Phillips Petroleum Company (1974) with Dr. Henry Hsieh and a sabbatical leave at The University of Akron (1976–1977) with Professors Maurice Morton and Lewis J. Fetters. Also detailed is the initiation of my formal anionic polymerization research career at Midland Macromolecular Institute (MMI) in 1979 with outstanding colleagues Drs. Dale Meier, Karl Solc, and Hans Georg Elias. At MMI, I started research on the use of living, alkyllithium-initiated polymerization to prepare chain-end functionalized polymers. This developed into one of my most important research areas. Based on my research experience and publications at MMI, I was appointed Professor of Polymer Science at The University of Akron in 1983. This was the most significant development in my professional career. The University of Akron offered a graduate polymer research program with outstanding, world-class colleagues and facilities; excellent graduate students; a moderate, primarily graduate teaching responsibility; a supportive university administration; and an international reputation in polymer research and education. As described herein, at The University of Akron I was able to develop a comprehensive research program on anionic polymerization, especially in the area of functionalized elastomers, which was the basis for the American Chemical Society Rubber Division Award of the Goodyear Medal to me. A summary of the many research contributions of my outstanding graduate students, visiting scientists, and postdoctoral associates is included.

This research paper describes a general method to synthesize functional polymers using a combination of atom transfer radical polymerization and hydrosilation. Methyl methacrylate (MMA) was copolymerized with (4-vinylphenyl)dimethylsilane (VPDS) in toluene via atom transfer radical polymerization (ATRP). The presence of a silyl hydride bond was proven using MALDI-ToF, NMR and IR spectra. The ability of the copolymer to undergo hydrosilation reaction was confirmed by reacting it with allyl alcohol. The expected molecular weight increase of the final polymer after functionalization was in agreement with the observed molecular weight. This method can be used to control both the type and quantity of functionalization by varying the amount of VPDS in the monomer feed.

An efficient method for synthesis of well-defined, well-characterized, tadpole-shaped polystyrene with a single atom junction point that is optimal for the study of dynamics has been developed using anionic polymerization, silicon chloride linking chemistry, and metathesis ring closure. The difunctional macromolecular linking agent, ω-methyldichlorosilylpolystyrene, was formed by reacting sec-butyllithium-initiated poly(styryl)lithium with excess (30×) methyltrichlorosilane to eliminate formation of linear dimer and three-arm star polystyrene. The asymmetric, three-arm, star precursor was formed by linking excess α-4-pentenylpoly(styryl)lithium (α-PSLi) with the macromolecular linking agent, and the excess α-PSLi functionalized with ethylene oxide before termination with methanol to facilitate chromatographic separation. Cyclization of the three-arm, star precursor to form tadpole-shaped polystyrene was effected in methylene chloride at high dilution using the Grubbs first generation catalyst, bis(tricycl...

A methodology to efficiently synthesize well-defined, 8-shaped polystyrene using anionic polymerization, silicon chloride linking chemistry, and metathesis ring closure has been developed, and the 8-shaped architecture was ascertained using the fragmentation pattern of the corresponding Ag+ adduct, acquired with tandem mass spectrometry. The 4-arm star precursor, 4-star-α-4-pentenylpolystyrene, was formed by linking α-4-pentenylpoly(styryl)lithium (PSLi) with 1,2-bis(methyldichlorosilyl)ethane and reacting the excess PSLi with 1,2-epoxybutane to facilitate purification. Ring closure of 4-star-α-4-pentenylpolystyrene was carried out in dichloromethane under mild conditions using a Grubbs metathesis catalyst, bis(tricyclohexylphosphine)benzylidine ruthenium(IV) chloride. Both the 4-arm star precursor and resulting 8-shaped polystyrene were characterized using SEC, NMR, and MALDI-ToF mass spectrometry (MS). Tandem mass spectrometry (MS2) was used for the first time to study the fragmentation pattern of 8-sha...

An efficient method for the synthesis of well-defined cyclic polystyrenes using anionic polymerization, silicon chloride linking chemistry, and metathesis ring closure has been developed. The macrocycle precursor, α,ω-bis(4-pentenyl)polystyrene, was formed by 4-pentenyllithium-initiated polymerization of styrene, coupling of α-pentenylpoly(styryl)lithium (PLi) with dimethyldichlorosilane to form α,ω-bis(4-pentenyl)polystyrene (Mn = 4600 g mol−1) and reaction of excess PLi with ethylene oxide to facilitate purification. Cyclization of the purified α,ω-bis(4-pentenyl)polystyrene was performed in dichloromethane under mild conditions using a Grubbs catalyst, bis(tricyclohexylphosphine)benzylidine ruthenium(IV) chloride, as a metathesis ring-closure agent. In contrast to prior work, no fractionation is required to obtain the pure product. Both the divinyl precursor and resulting macrocycle were characterized by SEC, MALDI-TOF mass spectrometry (MS) and NMR. The macrocycle was unambiguously distinguished from its precursor using the fragmentation patterns from tandem mass spectrometry (MS2) experiments. The results show that the macrocyclic precursor, α,ω-bis(4-pentenyl)polystyrene, was of high purity and that the cyclization was highly efficient.

Polyisobutylene was synthesized using 2-chloro-2,4,4-trimethylpentane (TMPCl) as an initiator and TiCl4 as a coinitiator. After taking a base sample, the living cation was reacted with 5 equivalents of (4-vinylphenyl)dimethylsilane (VPDMSi). It was observed that the cation preferred reduction by hydride elimination from VPDMSi compared to electrophilic addition of even a single vinyl group. It was postulated that the reduction of the cation in presence of strong Lewis acid such as TiCl4 occurs readily before addition of cation to vinyl group. Thus saturated polyisobutylene was obtained with a terminal hydrogen group instead of chlorine group which is produced by conventional cationic polymerization.

We explored a new synthetic strategy for ultra-high molecular weight long-chain branched (LCB) polymers with equal spacing between adjacent branch points. This method can synthesize LCB polystyrene (LCB-PS) with total molecular weight of 4.9 million g/mole, 16 branches of 140 kg/mole and polydispersity index of 1.5. The introduction of multiple branch points with long side chains allows the LCB-PS to resist the elastic-driven decohesion. Even after a large step extension of stretching ratio λ = 7.4, the specimen would not undergo elastic breakup that occurs in linear PS even at λ = 2.7. These LCB-PSs are also extraordinarily more stretchable during startup uniaxial extension, with the maximum engineering stress emerging at stretching ratio λ max ≈ 4 M bb / M e , where Mbb is the molecular weight of backbone and Me is the molecular weight between entanglements.

A new general anionic functionalization method (GFM) for preparing α-chain-end functionalized polymers utilizes the initiator formed from sec-butyllithium and dimethyl[4-(1-phenylvinyl)-phenyl]silane (DPESiH) followed by hydrosilation with substituted alkenes. α-(4-dimethylsilyl hydride)phenyl-functionalized polystyrene and poly(methyl methacrylate) were synthesized in quantitative yield by living anionic polymerization. These α-silyl hydride-functionalized polymers were further functionalized by reaction with tridecafluorooctene in the present of Karstedt's hydrosilation catalyst. These tridecafluorooctane-functionalized polymers were characterized by SEC, FTIR, 1H-, 13C- and 19F-NMR spectroscopy.

A new general functionalization method (GFM) of synthesizing α-functionalized polymers has been developed. α-Vinyl-functionalized polystyrene was obtained by anionic polymerization of styrene using 4-pentenyllithium as an initiator. Chloromethyldimethylsilane-functionalized polystyrene was successfully synthesized from vinyl-functionalized polystyrene by hydrosilation using Karstedt's catalyst. Nucleophilic substitution of this polymer was carried out in presence of pyrrolidine to obtain α-pyrrolidine-functionalized polystyrene. α-Triethoxysilylpolystyrene was obtained by hydrosilation of a-4-pentenylpolystyrene with triethoxysilane using Karstedt's catalyst.

“Click chemistry” is, by definition, a general functionalization methodology (GFM) and its marriage with living anionic polymerization is particularly powerful in precise macromolecular synthesis. This paper reports the synthesis of a “clickable” middle-chain azide-functionalized polystyrene (mPS-N3) by anionic polymerization and its application in the preparation of novel shape amphiphiles based on polyhedral oligomeric silsesquioxane (POSS). The mPS-N3 was synthesized by coupling living poly(styryl)lithium chains (PSLi) with 3-chloropropylmethyldichlorosilane and subsequent nucleophilic substitution of the chloro group in the presence of sodium azide. Excess PSLi was end-capped with ethylene oxide to facilitate its removal by flash chromatography. The mPS-N3 was then derived into a giant lipid-like shape amphiphile in two steps following a sequential “click” strategy. The copper(I)-catalyzed azide-alkyne cycloaddition between mPS-N3 and alkyne-functionalized vinyl-substituted POSS derivative (VPOSS-alkyne) ensured quantitative ligation to give polystyrene with VPOSS tethered at the middle of the chain (mPS-VPOSS). The thiol-ene reaction with 1-thioglycerol transforms the vinyl groups on the POSS periphery to hydroxyls, resulting in an amphiphilic shape amphiphile, mPS-DPOSS. This synthetic approach is highly efficient and modular. It demonstrates the “click” philosophy of facile complex molecule construction from a library of simple building blocks and also suggests that mPS-N3 can be used as a versatile “clickable” motif in polymer science for the precise synthesis of complex macromolecules.

A combination of living anionic polymerization and thiol–ene “click” chemistry provides an efficient and convenient method for synthesis of well-defined comb polystyrenes with precisely controlled architecture details and a wide selection of functionalities. ω-(p-Vinylbenzyl)polystyrene macromonomer was synthesized by sec-butyllithium-initiated polymerization of styrene followed by termination with 4-vinylbenzyl chloride (VBC). For the synthesis of α-4-pentenyl-ω-(p-vinylbenzyl)polystyrene macromonomer, an unsaturated initiator, 4-pentenyllithium, was used followed by termination with VBC. To ensure successful living anionic polymerization of macromonomers, impurities present in the macromonomers and glass reactors were readily removed by titration with excess sec-butyllithium initiator right before initiation, resulting in polymacromonomers with controlled Mn (74 000, 130 000 g/mol) and narrow Mw/Mn. Living anionic copolymerization of mixtures of both types of macromonomers yielded a well-defined comb-sh...

A new approach has been developed for the preparation of well-defined, eight-arm star polymers via the addition of poly(styryl)lithium to octavinylPOSS in benzene. The reaction proceeds rapidly to completion (within 5 min for molecular weight of each arm up to 33 kg/mol), forming predominantly eight-arm star polymers. The products were purified by fractionation and fully characterized by 1H NMR, 13C NMR, 29Si NMR, FT-IR, MALDI-TOF mass spectrometry, and size exclusion chromatography. Compared to conventional coupling approaches, this process is found to be less sensitive to the stoichiometry of the reactants and the molecular weight of each arm. A mechanism based on cross-association and intra-aggregate addition is invoked to account for this unusual observation. As evidence, when a polar solvent, tetrahydrofuran, or a strongly coordinating and disassociating Lewis base, tetramethylethylenediamine, was used to dissociate the living polymer chains, star polymers with lower average arm numbers than those of...

The model reaction of n-butyllithium with excess (11 M equivalents) 1,1-diphenylethylene (DPE) was reinvestigated using modern characterization techniques including SEC, one dimensional and two dimensional nuclear magnetic resonance (1D and 2D NMR) spectroscopy and electrospray ionization mass spectrometry (ESI MS). The products were the monoadduct, 1,1-diphenylhexane (nBuDPEH), and the diadduct, 1,1,3,3-tetraphenyloctane [nBu(DPE)2H], formed in 62 mol% and 38 mol% yields, respectively, as determined by SEC and 1H NMR spectroscopy. The 1H NMR spectrum of 1,1,3,3-tetraphenyloctane exhibited a terminal methine triplet resonance at δ 3.71 ppm that was uniquely coupled to the adjacent methylene doublet resonance at δ 3.09 ppm, located between the two carbons, each bonded to two phenyl groups [–C(C6H5)2-CH2-CH(C6H5)2. All of the characteristic 1H and 13C NMR resonances for both adducts were assigned using 2D NMR spectroscopic methods. The diadduct, nBu(DPE)2H, exhibited unique 13C NMR resonances at δ 50.79 ppm for the quaternary carbon resonance [CH2-C(C6H5)2−CH2], and at δ 43.74 ppm for the methylene group isolated between the two carbons, each bonded to two phenyl groups [–C(C6H5)2-CH2-CH(C6H5)2].

A series of [60]fullerene (C60)-containing poly(ethylene oxide)-block-polystyrene (PEO-b-PS) with various numbers and different locations of C60 along the polymer chains were designed and synthesized via a combination of “click” chemistry and living/controlled polymerization techniques such as anionic polymerization, atom transfer radical polymerization, and reversible addition–fragmentation chain transfer polymerization. One C60 was tethered either to the end of a PS block (PEO-b-PS-C60) or at the junction point between PS and PEO blocks [PEO-(C60)-PS]; while multiple C60s could be attached randomly along the PS block (PEO-b-PS/C60). The reaction conditions were carefully controlled to ensure a quantitative C60 functionality at precise locations in the case of PEO-b-PS-C60 and PEO-(C60)-PS and to avoid crosslinking in the synthesis of PEO-b-PS/C60. The results have implications in the precision synthesis of fullerene polymers in general. These C60-containing diblock copolymers possess different composition, diverse architecture, and high fullerene functionality. They can serve as model “shape amphiphiles” for the construction of complex hierarchical structures via the interplay between C60–C60 aggregation and block copolymer self-assembly/micro-phase separation.

Summary: The possible oligomerization of 1,1-diphenylethylene (DPE) in the end-capping reaction of poly(styryl)lithium (PSLi) was studied in hydrocarbon solvents using excess DPE (≤16 mol-eq); the effect of addition of THF (30 mol-eq Lewis base) and extended times of reaction (8-24 h) were also investigated. The characterization of the polymers was made by size exclusion chromatography (SEC), proton nuclear magnetic resonance spectroscopy (1H NMR) and matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS). MALDI- TOF mass spectrometric results revealed the absence of DPE oligomerization under the reaction conditions used in this study.

A combination of living anionic polymerization and metathesis ring-closure provides an efficient method for synthesis of well-defined, macrocyclic polymers over a broad molecular weight range. A series of well-defined, α,ω-divinylpolystyrene precursors (Mn = 2800, 8600, 17000, and 38000 g/mol) were synthesized by 4-pentenyllithium-initiated polymerization of styrene followed by termination with 4-chloromethylstyrene. Efficient cyclization of these α,ω-divinylpolystyrene precursors was effected in CH2Cl2 and CH2Cl2/cyclohexane mixtures using a Grubb’s catalyst, bis(tricyclohexylphosphine)benzylidine ruthenium(IV) chloride. As the precursor Mn increased, more cyclohexane was added and the concentration of the precursor was decreased from 1.41 × 10–4 to 2.15 × 10–6 M. The macrocyclic polymers were uniquely characterized by MALDI–TOF mass spectrometry in terms of peaks that appeared characteristically 28 m/z units lower than those of the corresponding open-chain precursor peaks, corresponding to the loss of a...

To understand the formation mechanism of nonflat polymer single crystals, two types of triblock copolymers with a middle crystalline block and two amorphous, immiscible end-blocks were designed and synthesized. Specifically, polystyrene-block-poly(ethylene oxide)-block-poly(1-butene oxide) and polystyrene-block-poly(ethylene oxide)-block-polydimethylsiloxane were examined. When the end-blocks possess different volumes and are microphase separated onto the opposite sides of the single crystal lamella formed by the middle crystalline block, unbalanced surface stress can be generated. As a result, large scrolled single crystals (∼80 μm) were grown from dilute solution using the self-seeding procedure at low supercoolings. The scrolling direction was identified to be along the (120) planes based on transmission electron microscopy (TEM) observations of the sedimented scrolled single crystals, which is in line with the fact that the scrolling occurs along the planes with the highest coefficient of thermal expa...

For the first time, the scope of Fisher esterification has been extended to fullerene derivatives to improve the synthesis of alkyne-functionalized fullerenes (fullerynes) using 1-chloronaphthalene as a solvent and a specially-designed, home-made reactor to promote high yield. The design allows for higher solubility of fullerene derivatives and a continuous azeotropic distillation for the removal of water to drive the reaction to completion with yields >90%. Both fullerynes (Fulleryne01 and Fulleryne02) were found to “click” to polymers, such as azide-functionalized poly(ɛ-caprolactone) (PCL-N 3 ), in high efficiency without the need for fractionation. As evidenced by 1 H NMR, 13 C NMR, size exclusion chromatography, and matrix assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry, the fullerene polymers thus obtained possess well-defined structure, narrow polydispersity (∼1.01 by MALDI-TOF mass spectrometry; ∼1.03 by size exclusion chromatography), and high fullerene functionality (∼100%). They can serve as model compounds for the investigations of polymer structures and dynamics.

A series of precisely defined, mono- and heterotelechelic polystyrenes have been facilely synthesized by combining living anionic polymerization with other efficient chemical transformations, such ...

This paper reports a facile, modular, and efficient approach to the synthesis of shape amphiphiles with a hydrophobic polymer chain as the tail and a polar, compact, functional polyhedral oligomeric silsequioxane (POSS) nanoparticle as the headgroup. A poly(l-lactide) (PLLA) chain was grown from monohydroxyl-functionalized heptavinyl POSS (VPOSS−OH) with controlled molecular weight and narrow polydispersity by stannous octoate-mediated ring-opening polymerization of l-lactide. To impart tunable polarity and functionality to the headgroup, various functional groups, such as carboxylic acids, hydroxyl groups, and sugars, were attached to the POSS cage in high efficiency by thiol−ene “click” chemistry, which provides a straightforward and effective approach to synthesize shape amphiphiles with diverse head surface chemistry. The polymers have been fully characterized by 1H NMR, 13C NMR, FT-IR spectroscopy, MALDI-TOF mass spectrometry, and size exclusion chromatography. These functional POSS can serve as vers...

This work aims to elucidate how molecular parameters dictate the occurrence of inhomogeneous cohesive failure during step strain and large amplitude oscillatory shear (LAOS) respectively in entangled polymer mixtures. Based on three well-entangled polybutadiene (PB) mixtures, we perform simultaneous rheometric and particle-tracking velocimetric (PTV) measurements to illustrate how the slip length controls the degree of shear banding. Specifically, the PB mixtures were prepared using the same parent polymer (M w ∼ 106 g/mol) at 10 wt.% concentration in respective polybutadiene solvents (PBS) of three different molecular weights 1.5, 10, and 46 kg/mol. After step strain, the entangled PB mixture with PBS-1.5 K displayed interfacial failure whereas the PB mixture with PBS-10 K showed bulk failure, demonstrating the effectiveness of our strategy to suppress wall slip by controlling PBS’ molecular weight. Remarkably, the PBS-46K actually allows the elastic yielding to occur homogeneously so that no appreciable macroscopic motions were observed upon shear cessation. PBS is found to play a similar role in LAOS of these three PB mixtures. Finally, we demonstrate that in case of the slip-prone mixture based on PBS-1.5 K the interfacial failure could be drastically reduced by use of shearing plates with considerable surface roughness.

A novel giant surfactant possessing a well-defined hydrophilic head and a hydrophobic polymeric tail, polystyrene-(carboxylic acid-functionalized polyhedral oligomeric silsesquioxane) conjugate (PS-APOSS), has been designed and synthesized via living anionic polymerization, hydrosilylation, and thiol-ene "click" chemistry. PS-APOSS forms micelles in selective solvents, and the micellar morphology can be tuned from vesicles to wormlike cylinders and further to spheres by increasing the degree of ionization of the carboxylic acid. The effect of APOSS-APOSS interactions was proven to be essential in the morphological transformation of the micelles. The PS tails in these micellar cores were found to be highly stretched in comparison with those in traditional amphiphilic block copolymers, and this can be explained in terms of minimization of free energy. This novel class of giant surfactants expands the scope of macromolecular amphiphiles and provides a platform for the study of the basic physical principles of their self-assembly behavior.

4 páginas, 4 figuras, 1 esquema.-- et al., In this communication, we present first results on the dielectric response of various end-functionalized polystyrenes (PS). The functional polymers have been prepared by using a combination of anionic polymerization techniques and hydrosilation chemistry that gives well-defined polymers where the functional group can be placed with flexibility and high precision. The data show that for rather large functional groups, the overall polymer matrix properties are altered giving rise to a decrease in the glass transition temperature. The trend can be rationalized in terms of free volume effects caused by the bulky functional groups. However, for cyano-functionalized PS, i.e. PS with a CN group at the chain end, the inclusion of the group does not affect the matrix properties. We show that by taking advantage of the strong dipole moment of the CN group, we can obtain a strong dielectric signal that can be used to selectively study the specific dynamics where the group is located. In other words, by appropriately attaching cyano groups at different part of the chains, these can be used as dielectric probes that allow specific contributions to the alpha relaxation.

In this study, we systematically investigated the effects of confined dimension (the thickness of PEO layer) and reduced tethering density (σPEO, defined by σπRg2, where σ is the tethered chain density and Rg is the radius of gyration of the tethered PEO chain in its end-free state in the melt) on the PEO crystal orientation change within a 1D nanoscale confinement. We realized this confinement by utilizing two symmetric polystyrene-block-poly(ethylene oxide) (PS-b-PEO) diblock copolymer single crystals grown at different crystallization temperatures (Tx) in dilute solution via the self-seeding technique. After these single crystals were collected as mats, the thicknesses of both the PEO single crystal (dPEO) and PS glassy layer were measured using small-angle X-ray scattering (SAXS) coupled to the 1D correlation function. Because TgPS is higher than TmPEO in those PS-b-PEO single crystal mats, 1D confinements having different dPEO and σPEO values can be prepared by changing Tx values. The PEO block sin...

A new general anionic functionalization methodology is described based on (a) the quantitative silyl hydride functionalization of well-defined polymeric organolithium compounds with either dimethylchlorosilane (ω-chain end functionalization) or dichloromethylsilane (in-chain functionalization) and (b) reaction of the silyl hydride-functionalized polymer with a functionalized alkene using Karstedt's Pt(o) hydrosilylation catalyst.

ω-Cyano-functionalized polystyrene has been prepared in 87% isolated yield using the general functionalization methodology based on anionic polymerization, silyl hydride functionalization, and hydr...

Utilizing crystalline−amorphous block copolymers, such as in the case of polystyrene-block-poly(ethylene oxide) (PS-b-PEO), under a large amplitude shear process provides an opportunity for investigating crystal growth and orientation within nanoconfinements at different supercoolings. However, the internal stress generated during the shearing process and the structural defects embedded in the phase-separated morphology inevitably play roles in affecting the confinement effect on the crystallization of the crystalline blocks. In this study, we designed a one-dimensional (1D), defect-free confinement constructed by PS-b-PEO single crystal mats collected in dilute solution. Each single crystal possessed a square-shaped, “sandwiched” lamellar structure, and it consisted of a PEO single crystal layer between two PS nanolayers formed by the tethered PS blocks on the PEO single crystal top and bottom fold surfaces. Furthermore, in these single crystal mats the glass transition temperature of the PS blocks is hi...

A new approach was designed to study polymer crystallization in a one-dimensional (1D), defect-free, nanoscale confinement utilizing single crystals of poly(ethylene oxide)-block-polystyrene (PEO-b...

Velocity profiles of six entangled polybutadiene solutions (PBD) have been determined during startup shear using a particle tracking velocimetric (PTV) technique, where the number Z of entanglements per chain in these solutions varies from 13 to 119, depending on the PBD molecular weight and solution concentration. Flow behavior of these solutions at various rates in the stress plateau region has been investigated in both parallel-disk and cone−plate cells. For the least entangled solution with Z = 13, homogeneous shear was observed under all flow conditions. The solution with Z = 27 displayed inhomogeneous shear after the stress maximum before returning to a linear velocity profile at long times. For solutions with Z ≥ 40, shear banding was observed in both transient and steady states for a range of shear rates in the stress plateau region. At sufficiently high rates, shear homogeneity returns in steady state for these solutions (Z ≥ 40) after initial banding.

A new general functionalization methodology (GFM) is applied to the synthesis of trimethoxysilyl-functionalized polymers. This GFM involves (a) the preparation of a well-defined polymeric organolithium compound (PLi) using alkyllithium-initiated anionic polymerization; (b) quantitative silyl hydride-functionalization of PLi with chlorodimethylsilane to form PSi(CH3)2H; (c) hydrosilation of PSi(CH3)2H with vinyltrimethoxysilane in the presence of Karstedt's catalyst. The desired PSi(OCH3)3 was obtained in > 80% yield. The product was characterized by SEC, 1H and 13C NMR and MALDI-TOF mass spectrometry.

The Ag(+) adducts of polystyrene (PS) oligomers with different sizes (6-19 repeat units) and initiating (alpha) or terminating (omega) end groups mainly decompose via free radical chemistry pathways upon collisionally activated dissociation. This reactivity is observed for ions formed by matrix-assisted laser desorption/ionization as well as electrospray ionization. With end groups lacking weak bonds (robust end groups), dissociation starts with random homolytic C-C bond cleavages along the PS chain, which lead to primary and benzylic radical ions containing either of the chain ends. The primary radical ions mainly depolymerize by successive beta C-C bond scissions. For the benzylic radical ions, two major pathways are in competition, namely, depolymerization by successive beta C-C bond scissions and backbiting via 1,5-H rearrangement followed by beta C-C bond scissions. The extent of backbiting decreases with internal energy. With short PS chains, the primary radical ions also undergo backbiting involving 1,4- and 1,6-H rearrangements; however, this process becomes negligible with longer chains. If the polystyrene contains a labile substituent at a chain end, this substituent is eliminated easily and, thus, not contained in the majority of observed fragments. Changes in the PS backbone structure can have a dramatic effect on the resulting dissociation chemistry. This is demonstrated for poly(alpha-methylstyrene), in which backbiting is obstructed due to the lack of benzylic H atoms; instead, this backbone connectivity promotes 1,2-phenyl shifts in the primary radical ions formed after initial C-C bond homolyses as well as H atom transfers between the incipient primary and benzylic radicals emerging from these homolyses.

Poly(styryl)lithiums (Mn = 1500−2200 g/mol) in benzene were reacted with propylene sulfide (1.3−3 equiv) to prepare the corresponding thiol chain-end-functionalized polymers. The resulting polymers were characterized by thin layer chromatography, elemental analysis, 1H, 13C, and DEPT NMR spectroscopy, and MALDI-TOF mass spectrometry. Analysis of the resulting polymers by MALDI-TOF mass spectrometry indicates that reaction occurs by a ring-opening mechanism, in contrast to precedents showing that the reaction of organolithium compounds with propylene sulfide occurs by a sulfur extrusion mechanism. Poly(styryl)lithium was also reacted with 1.3 equiv of ethylene sulfide. The results from MALDI-TOF mass spectrometry show that the structure of the polymer corresponds to the product resulting from a ring-opening mechanism analogous to the reaction of propylene sulfide with poly(styryl)lithium. More oligomerization was observed for functionalizations with 1.3 equiv of ethylene sulfide (34.6%) compared to propyle...

A poly(ethylene oxide)-block-polystyrene (PEO-b-PS) diblock copolymer with number-average molecular weights of 7.7k g/mol for the PS block and 21.4k g/mol for the PEO block was used to study the PEO crystal orientation changes at different crystallization temperatures (Tx) via small- and wide-angle X-ray scattering techniques. For this diblock copolymer, an inverse hexagonal cylinder (IHC) phase morphology was identified with PS cylinders hexagonally packed within the PEO matrix. In this IHC morphology, the PEO blocks were tethered on the convex interfaces of the PS domains, and the crystallization of PEO blocks was outside of the cylinders. The crystal orientation of the PEO blocks (the c-axis of the PEO crystals) after crystallization among the PS cylinders was, for the first time, found to change with respect to the long cylinder axis, â, depending solely on Tx. At very low Tx's, when the samples were quenched into liquid nitrogen, the crystals possessed a random orientation. When −30 °C ≤ Tx ≤ 5 °C, P...

The reaction of excess poly(styryl)lithium mass spectrometry. The DEPT 13 C NMR spectrum showed (Mn = 1 400g · mol -1 ) with 1,3-butene diepoxide proceeds that a disecondary 1,2-diol unit was present, consistent with efficiently to produce a coupled product with two in-chain attack of PSLi on the least-substituted, methylene carbons of hydroxyl groups. The pure coupled, functionalization pro- 1,3-butadiene diepoxide. The MALDI-TOF mass spectrum duct was isolated in quantitative yield by silica gel column of the purified product exhibited only one distribution with chromatography. This product was characterized by 'H and monoisotopic peaks corresponding to the coupled, dihydroxyMALDI-TOF mass spectrum of the purified, in-chain, hydroxyl-functionalized polystyrene and the reaction of PSLi with 1,3-butadiene diepoxide.

A poly(ethylene oxide)-b-polystyrene (PEO-b-PS) diblock copolymer with a number average molecular weight of PEO blocks, M n PEO =8.8 kg/mol, and a number average molecular weight of PS blocks, M n PS =24.5 kg/mol, (volume fraction of the PEO blocks, fPEO, was 0.26) exhibited a hexagonal cylinder (HC) phase structure. Small angle X-ray scattering results showed that the PEO cylinder diameter was 13.3 nm, and the hexagonal lattice was a=25.1 nm. The cylinder diameter of this HC phase structure was virtually the same as that in the blend system constructed by a PEO-b-PS diblock copolymer ( M n PEO =8.7 kg/mol and M n PS =9.2 kg/mol) and a PS homo-polymer ( M n PS =4.6 kg/mol) in which the fPEO was 0.32. The cylinder diameter in this blend sample was 13.7 nm and the hexagonal lattice was a=23.1 nm. Comparing crystal orientation and crystallization behaviors of this PEO-b-PS copolymer with the blend, it was found that the crystal orientation change with respect to crystallization temperature was almost identical. This is attributed to the fact that in both cases the PEO block tethering densities and confinement sizes are very similar. This indicates that when the M n PS of PS homo-polymer is lower than the PS blocks, the PS homo-polymer is located inside of the PS matrix rather than at the interface between the PEO and PS in the HC phase structure. On the other hand, a substantial difference of crystallization behaviors was observed between these two samples. The PEO-b-PS copolymer exhibited much more retarded crystallization kinetics than that of the blend. Based on the small angle X-ray scattering results, it was found that in the blend sample, the HC phase structure was not as regularly ordered as that in the PEO-b-PS copolymer, and thus, the HC phase structure contained more defects in the blend. This led to a suggestion that the primary nucleation process in the confined crystallization is a defect-controlled process. The mean crystallite sizes were estimated by the Scherer equation, and the PEO crystal sizes are on the scale of the confined size.

We have investigated the self-assembly behavior of an amphiphilic diblock copolymer, polystyrene-block-poly(ethylene oxide) (PS-b-PEO), in N,N-dimethylformamide (DMF)/water and DMF/acetonitrile. In...

The direct functionalization of poly(styryl)lithium (Mn ≈ 2000 g/mol) with p-vinylbenzyl chloride (VBC) has been investigated in hydrocarbon solvent. With a 9-fold excess of VBC and normal addition, the predominant product (55% yield) was the corresponding head-to-head dimer; the macromonomer was formed in only 20% yield as determined by 1H NMR analysis. MALDI-TOF MS analysis of the products showed that the other major side reaction products resulted from addition of PSLi to the vinyl group of VBC. However, in the presence of excess lithium halides (LiCl, LiBr) the amount of dimer formation was reduced (30%), but the yield of macromonomer was increased only slightly (27%). The principal impurity was the corresponding nonfunctional polystyrene attributed to hydrogen abstraction from VBC by PSLi. A high yield (≥98%) of ω-(p-vinylbenzyl)polystyrene macromonomer was obtained when the functionalization was effected in the presence of 10 equiv of lithium 2,3-dimethyl-3-pentoxide. No dimer formation was observed...

We report the formation of a highly entangled and interconnected, self-assembled, wormlike-cylinder network of polystyrene-block-poly(ethylene oxide) in N, N-dimethylformamide/water. In this system, N,N-dimethylformamide was a common solvent and water was a selective solvent for the poly(ethylene oxide) blocks. The degrees of polymerization of the polystyrene and poly(ethylene oxide) blocks were 962 and 227, respectively. The network was formed at copolymer concentrations higher than 0.4 wt % and consisted of self-assembled, wormlike cylinders that were interconnected by Y-shaped, T-shaped, and multiple junctions. The network morphology was visualized with transmission electron microscopy. Capillary viscometry measurements revealed an order-of-magnitude increase in the inherent viscosity of the colloidal system upon the formation of the network. A similar effort to obtain a wormlike-cylinder network in an N,N-dimethylformamide/acetonitrile system, in which acetonitrile was a selective solvent for the poly(ethylene oxide) blocks, was unsuccessful even at high copolymer concentrations; instead, the wormlike cylinders showed a tendency to align. The viscosity measurements also did not show a substantial increase in the inherent viscosity. Thus, the solvent played a critical role in determining the formation of the self-assembled, wormlike-cylinder network. This formation of the network resulted from an interplay between the end-capping energy, bending energy (curvature), and configurational entropy of the self-assembled, wormlike-cylinder micelles that minimized the free energy. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3605–3611, 2006

Hydroxyl chain-end functionalizations of polymeric organolithium compounds with oxetane (trimethylene oxide) were studied in benzene at 25 °C. Functionalizations of poly(styryl)lithium and polystyrene-oligo-butadienyllithium proceed efficiently to form the corresponding ω-hydroxypropyl-functionalized polymers in 98 and 97% isolated yields, respectively. No nonfunctional polymer (≤1–2%) was detected by thin layer chromatography (TLC) analysis for either polymer. All functionalized polymers were characterized by 13C and 1H NMR analyses; no evidence for oxetane oligomerization at the chain end was observed. The MALDI-TOF mass spectrum of ω-hydroxypropylpolystyrene was consistent with the expected structure without any detectable oligomerization of oxetane. A small, but detectable series of peaks corresponding to nonfunctional polystyrene was also observed in the MALDI-TOF mass spectrum. The functionalization of the adduct of 1,1-diphenylethylene and PSLi produced the corresponding ω-hydroxypropyl-functionalized polymer in only 86% isolated yield. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2684–2693, 2006

Lamellar single crystals grown in dilute solutions can be used as templates for tethered chain analysis. Two series of diblock copolymers, poly(ethylene oxide)-block-polystyrene (PEO-b-PS) and poly...

The regiochemistry of the nickel-catalyzed polymerization of 2,5-dichlorobenzophenone in the presence of excess zinc and triphenylphosphine with (PBP-B) and without added coligand, 2,2′-bipyridine (PBP-A), has been re-examined. The carbonyl region of the 13 C NMR spectra have been interpreted by analysis of dimeric models for the H–T, H–H and T–T units in the polymer, i.e. 2,3′-bisbenzophenone, 2,2′-bisbenzophenone and 3,3′-bisbenzophenone. Based on the NMR spectral assignments for these model compounds, it has been concluded that PBP-B has few if any H–H units, whereas these units are present in significant amounts in PBP-A. Based on these results, it is proposed that what determines the conjugation length in the UV-vis spectra of PBPs is the occurrence of H–H units along the polymer backbone and not the percentage of H–T units in the chains.

A general anionic ω-chain-end functionalization methodology is described and illustrated by the synthesis of ω-primary amine functionalized polystyrenes. First, the quantitative ω-silyl hydride functionalization of well-defined poly(styryl)lithium (Mn = 2200 and 14 100 g/mol) was effected with dimethylchlorosilane in hydrocarbon solution at room temperature. In the second step, involving amination by hydrosilation, the silyl hydride functionalized polystyrene was added quantitatively to 3-[N,N-bis(trimethylsilylamino]-1-propene, a protected amine, using Karstedt's Pt(0) hydrosilation catalyst in benzene. One of the principal advantages of this method is the fact that it is not necessary to use protecting groups for many functional groups, as illustrated by the quantitative primary amine functionalization of ω-silyl hydride functionalized poly(styryl)lithium with allylamine using the Karstedt's hydrosilation catalyst. The silyl hydride and amine functionalized polystyrenes were characterized by SEC, FTIR, ...

A series of well-defined, long-branched polystyrenes (PS) of various architectures, but the same overall molecular weight, suited to the systematic study of branching effects, have been synthesized by anionic polymerization and characterized. Three end-branched, star-branched polystyrenes with 6, 9, and 13 end branches were synthesized with a trifunctional organolithium initiator; the synthesis of the 13-end molecule required a recently developed methoxysilyl functionalization and precipitation procedure to remove excess linking agent. In these architectures the number of branch points was fixed at four, while the number of chain ends varied. A 6-end, pom-pom (dumbbell-shaped) PS with two branch points was synthesized with a difunctional organolithium initiator. A regular 6-arm star polystyrene having one branch point was included to provide a comparison among three polymers, each having 6 ends, but having the number of branch points equal to 1, 2, or 4. The intrinsic viscosities and infinite dilution dif...

The reaction of poly(styryl)lithium (PSLi) with styrene oxide (SO) in benzene solution has been investigated. In addition to the functionalized polymer (83.5 wt %) the product mixture consisted of unfunctionalized polymer (9 wt %) and a dimeric product (5.6 wt %). The structure of the dimeric product was determined to be the head-to-head dimer. The regiochemistry of the addition reaction was unselective: 53 mol % addition to the methylene carbon and 47 mol % corresponding to addition to the hindered, methine carbon. Based on the formation of the dimer and the lack of regioselectivity, a pathway involving electron transfer from PSLi to SO was proposed. To further investigate the propensity to react via this electron-transfer mechanism, the SO functionalization of the adduct of PSLi with 1,1-diphenylethylene was investigated as well as the functionalization of PSLi with 1,1-diphenylethylene oxide.

Matrix-assisted laser desorption ionization (MALDI) time-of-flight (TOF) mass spectrometry (MS) is applied to examine the products arising upon the preparation of chain-end functional polymers via living anionic polymerization techniques. Both post-polymerization functionalizations as well as the use of functionalized initiators are investigated. MALDI-TOF MS is shown to be a sensitive probe for the qualitative analysis of the major and minor oligomers from novel functionalization reactions whose mechanisms are not yet well established. The method is particularly valuable for the identification of the end groups of the minor, and often unexpected, distributions that may be undetectable by other analytical means. Complete characterization of all oligomers generated during functionalization reactions provides an essential tool to the synthetic chemist for understanding the corresponding mechanisms. This insight is necessary for selecting alternative routes or making modifications to the reaction conditions. It is demonstrated that MALDI-TOF MS can convey quantitative information about the yields of the chain-end groups introduced during functionalization. From the cases presented it is evident that post-polymerization reactions allow for better control of chain-end functionality and molecular weight than functionalization with the limited number of currently available protected functionalized initiators.

The functionalization of poly(styryl)lithium with styrene oxide as a route to functional polymers was investigated. When the reaction was performed in benzene at room temperature, analysis of the products by SEC and column chromatography indicated the presence of functional polymer (83.5 wt %), along with unfunctionalized polymer (9.0 wt %), dimeric product (5.6 wt %), and trimeric product (0.1 wt %). The structure of the dimeric product was determined to be head-to-head dimer from both 13C NMR analysis and MALDI−TOF MS and was proposed to result from an electron-transfer mechanism. The dimeric product was eliminated when the functionalization was effected in the presence of tetrahydrofuran (>15 mol equiv). Under these conditions >99 wt % functionalized polymer was obtained as determined by column chromatography and MALDI−TOF MS. Addition of PSLi to the epoxide can occur by addition to the least hindered carbon or by addition to the most hindered carbon. Analysis of the regiochemistry of the chain end was...