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A novel hydrocarbon-soluble trifunctional organolithium initiator, with no polar-additive requirements, has been synthesized for use in anionic polymerization. The complete synthesis of the unsaturated tri-diphenylethylene compound, 4,4,4-(ethane-1,1,1-triyl)tris(((3-(1-phenylvinyl)benzyl)oxy)benzene) (I), is described and the efficiency of the new initiator is evaluated using 1H NMR and Nano-assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (NALDI-TOF MS). Activation of precursor I, was performed in situ using stoichiometric amounts of sec-BuLi in benzene. Three-arm polystyrene and polyisoprene stars with narrow molecular weight distributions were obtained in the case of relatively high total anion concentration, [sec-BuLi]0 > 3.8 × 10-3 mol L-1 (3 × [I]0). At low total anion concentrations, uncontrolled molecular weight and broad/bimodal distributions were obtained, plausibly attributed to the presence of partially solvated aggregation dynamics complicating the propagation. The 'living' nature of the polymerization was confirmed by the sequential polymerization of styrene, and isoprene. The viscometric branching factor g′ values of the final branched polymers were measured and compared to g′ values of three-arm stars reported in the literature. © 2016 The Royal Society of Chemistry.

We have synthesized linear ABC triblock terpolymers containing poly(1,3-cyclohexadiene), PCHD, as an end block and characterized their morphologies in the melt. Specifically, we have studied terpolymers containing polystyrene (PS), polybutadiene (PB), and polyisoprene (PI) as the other blocks. Systematically varying the ratio of 1,2- /1,4-microstructures of poly(1,3-cyclohexadiene), we have studied the effects of conformational asymmetry among the three blocks on the morphologies using transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), and self-consistent field theory (SCFT) performed with PolySwift++. Our work reveals that the triblock terpolymer melts containing a high percentage of 1,2-microstructures in the PCHD block are disordered at 110 C for all the samples, independent of sequence and volume fraction of the blocks. In contrast, the triblock terpolymer melts containing a high percentage of 1,4-microstructure form regular morphologies known from the literature. The accuracy of the SCFT calculations depends on calculating the χ parameters that quantify the repulsive interactions between different monomers. Simulations using χ values obtained from solubility parameters and group contribution methods are unable to reproduce the morphologies as seen in the experiments. However, SCFT calculations accounting for the enhancement of the χ parameter with an increase in the conformational asymmetry lead to an excellent agreement between theory and experiments. These results highlight the importance of conformational asymmetry in tuning the χ parameter and, in turn, morphologies in block copolymers. © 2012 American Chemical Society.

Concerted experimental and theoretical investigations have been carried out to understand the microphase separation in diblock copolymer melts containing poly (1,3-cyclohexadiene), PCHD, as one of the constituents. In particular, we have studied diblock copolymer melts containing polystyrene (PS), polybutadiene (PB), and polyisoprene (PI) as the second block. We have systematically varied the ratio of 1,2-/1,4-microstructures of poly (1,3-cyclohexadiene) to tune the conformational asymmetry between the two blocks and characterized the effects of these changes on the morphologies using transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS). Our experimental investigations reveal that the melts of PCHD-b-PB, PCHD-b-PS and PCHD-b-PI containing nearly equal fractions of each component and high percentage of 1,4-microstructures in the PCHD block form cylindrical rather than lamellar morphologies as expected in symmetric diblock copolymers. In contrast, the morphologies of PCHD-b-PB, PCHD-b-PS and PCHD-b-PI containing PCHD block with higher 1,2-microstructure are found to be disordered at 110 °C. The change in the morphological behavior is in good agreement with our numerical calculations using the random phase approximation and self-consistent field theory for conformationally asymmetric diblock copolymer melts. Also, the effects of composition fluctuations are studied by extending the Brazovskii-Leibler-Fredrickson-Helfand (J. Chem. Phys. 87, 697 (1987)) theory to conformationally asymmetric diblock copolymer melts. These results allow the understanding of the underlying self-assembly process that highlights the importance of the conformational asymmetry in tuning the morphologies in block copolymers. © 2012 Elsevier Ltd. All rights reserved.

The molecular orientation behavior and structural graft copolymers based on polystyrene (PS) and polyisoprene changes of morphology at high strains for multigraft and block (PI) were investigated during uniaxial monotonic loading via FT-IR and synchrotron SAXS. Results from FT-IR revealed specific orientations of PS and PI segments depending on molecular architecture and on the morphology, while structural investigations revealed a typical decrease in long-range order with increasing strain. This decrease was interpreted as strain-induced dissolution of the glass), blocks in the soft matrix, which is assumed to affect an additional enthalpic contribution (strain-induced mixing of polymer chains) and stronger retracting forces of the network chains during elongation. Our interpretation is supported by FT-IR measurements showing similar orientation of rubbery and glassy segments up to high strains. It also points to highly deformable PS domains. By synchrotron SAXS, we observed in the neo-Hookean region an approach of glassy domains, while at higher elongations the intensity of the primary reflection peak was significantly decreasing. The latter clearly verifies the assumption that the glassy chains are pulled out from the domains and are partly mixed in the PI matrix. Results obtained by applying models of rubber elasticity to stress strain and hysteresis data revealed similar correlations between the softening behavior and molecular and morphological parameters. Further, an influence of the network modality was observed (random grafted branches). For sphere forming multigraft copolymers the domain functionality was found to be less important to achieve improved mechanical properties but rather size and distribution of the domains.

The molecular orientation behavior and structural changes of morphology at high strains for multigraft and block-graft copolymers based on polystyrene (PS) and polyisoprene (PI) were investigated during uniaxial monotonic loading via FT-IR and synchrotron SAXS. Results from FT-IR revealed specific orientations of PS and PI segments depending on molecular architecture and on the morphology, while structural investigations revealed a typical decrease in long-range order with increasing strain. This decrease was interpreted as strain-induced dissolution of the glassy blocks in the soft matrix, which is assumed to affect an additional enthalpic contribution (strain-induced mixing of polymer chains) and stronger retracting forces of the network chains during elongation. Our interpretation is supported by FT-IR measurements showing similar orientation of rubbery and glassy segments up to high strains. It also points to highly deformable PS domains. By synchrotron SAXS, we observed in the neo-Hookean region an approach of glassy domains, while at higher elongations the intensity of the primary reflection peak was significantly decreasing. The latter clearly verifies the assumption that the glassy chains are pulled out from the domains and are partly mixed in the PI matrix. Results obtained by applying models of rubber elasticity to stress-strain and hysteresis data revealed similar correlations between the softening behavior and molecular and morphological parameters. Further, an influence of the network modality was observed (random grafted branches). For sphere forming multigraft copolymers the domain functionality was found to be less important to achieve improved mechanical properties but rather size and distribution of the domains. © 2011 American Chemical Society.

Two novel anionic acetylene-functionalized initiators, 5-trimethylsilyl-4- pentynyllithium (TMSPLi) and 5-triethylsilyl-4-pentynyllithium (TESPLi), were synthesized and characterized by 1H NMR, 13C NMR, and GC-MS. TMSPLi was successfully used for the polymerization of styrene, but not for the polymerization of isoprene and butadiene. On the other hand, TESPLi exhibited all characteristics of an anionic initiator for the (co)polymerization of styrene, isoprene, and butadiene. TESPLi is ideal for the synthesis of living well-defined (co)polymers with acetylene end groups, perfect candidates for "click" reactions and at the same time possessing all the potential of living anionic polymerization for the synthesis of well-defined complex macromolecular architectures. © 2011 American Chemical Society.

Diels-Alder cycloaddition reactions were used to functionalize multiwalled carbon nanotubes (MWNTs) with 1-benzocyloobutene-1′-phenylethylene (BCB-PE) or 4-hydroxy-ethylbenzocyolobutene (BCB-EO). The covalent functionalization of the nanotubes with these initiator precursors was verified by FTIR and thermogravimetric analysis (TGA). After appropriate transformations/additions, the functionalized MWNTs were used for surface initiated anionic and ring opening polymerizations of ethylene oxide and ε-caprolactone ε-CL), respectively. The OH-end groups were transformed to isopropylbromide groups by reaction with 2-bromoisobutyryl bromide, for subsequent atom transfer radical polymerization of styrene or 2-dimethylaminoethyl methacrylate to afford the final diblock copolymers. 1H NMR, differential scanning calorimetry (DSC), TGA, and transmission electron microscopy (TEM) were used for the characterization of the nanocomposite materials. TEM images showed the presence of a polymer layer around the MWNTs as well as the dissociation of MWNT bundles. Consequently, this general methodology, employing combinations of different polymerization techniques, Increases the diversity of diblocks that can be grafted from MWNTs. © 2010 Wiley Periodicals, Inc.

We describe a novel and facile strategy to modify the surface of carbon nanotubes (CNTs) with two chemically different polymer brushes utilizing the 'grafting from' technique. A [4 + 2] Diels-Alder cycloaddition reaction was used to functionalize multi-walled carbon nanotubes (MWNTs) with two different precursor initiators, one for ring opening polymerization (ROP) and one for atom transfer radical polymerization (ATRP). The binary functionalized MWNTs were used for the simultaneous surface initiated polymerizations of different monomers resulting in polymer grafted MWNTs that can form Janus type structures under appropriate conditions. 1H NMR, FTIR and Raman spectra showed that the precursor initiators were successfully synthesized and covalently attached on the CNT surface. Thermogravimetric analysis (TGA) revealed that the grafted polymer content varies when different monomer ratios and polymerization times are used. The presence of an organic layer around the CNTs was observed through transmission electron microscopy (TEM). Differential scanning calorimetry (DSC) proved that the glass transition (Tg) and melting (Tm) temperatures of the grafted polymers are affected by the presence of the CNTs, while circular dichroism (CD) spectra indicated that the PLLA α-helix conformation remains intact. © 2009 The Royal Society of Chemistry.

Single (SWNTs) and multiwalled (MWNTs) carbon nanotubes were functionalized with a titanium alkoxide catalyst through a Diels-Alder cycloaddition reaction. The catalyst-functionalized carbon nanotubes (CNTs) were used for the surface initiated titanium-mediated coordination polymerizations of L-lactide (L-LA), ε-caprolactone (ε-CL) and n-hexyl isocyanate (HIC) employing the "grafting from" technique. 1H NMR, IR and Raman spectra showed that the precursor catalyst was successfully synthesized and covalently attached on the CNTs surface. Thermogravimetric analysis (TGA) revealed that the grafted poly(L-lactide) (PLLA) content could be controlled with time. The final polymer-grafted CNTs were readily dissolved in organic solvents as compared to the insoluble pristine and catalyst-functionalized CNTs. The presence of thick layers of polymers around the CNTs was observed through transmission electron microscopy (TEM). Differential scanning calorimetry (DSC) proved that the glass transition (T g) and melting (T m) temperatures of the PLLA are affected by the presence of the CNTs, while PLLA α-helix conformation remains intact, as revealed by the circular dichroism (CD) spectra. © 2009 American Chemical Society.

Morphology and deformation mechanisms and tensile properties of tetrafunctional multi-graft (MG) polystrene-g-polyisoprene (PS-g-PI) copolymers were investigated dependent on PS volume fraction and number of branch points. The combination of various methods such as TEM, real time synchrotron SAXS, rheo-optical FTIR, and tensile tests provides comprehensive information at different dimension levels. TEM and SAXS studies revealed that the number of branch points has no obvious influence on the microphase-separated morphology of tetrafunction MG copolymers with 16 wt % PS. But for tetrafunctional MG copolymers with 25 wt % PS, the size and integrity of PS microdomains decrease with increasing number of branch point. The deformation mechanisms of MG copolymers are highly related to the morphology. Dependent on the microphase-separated morphology and integrity of the PS phase, the strain-induced orientation of the PS phase is at different size scales. Polarized FT-IR spectra analysis reveals that, for all investigated MG copolymers, the PI phase shows strain-induced orientation along SD at molecular scale. The proportion of the PI block effectively bridging PS domains controls the tensile properties of the MG copolymers at high strain, while the stress - strain behavior in the low-mediate strain region is controlled by the continuity of PS microdomains. The special molecular architecture, which leads to the higher effective functionality of PS domains and the higher possibility for an individual PI backbone being tethered with a large number of PS domains, is proposed to be the origin of the superelasticity for MG copolymers. © 2009 American Chemical Society.

Surface-functionalized polymeric nanoparticles were prepared by: a) self-assembly of poly(4-vinylbenzocyclobutene-b-butadiene) diblock copolymer (PVBCB-b-PB) to form spherical micelles (diameter: 15-48 nm) in decane, a selective solvent for PB, b) crosslinking of the PVBCB core through thermal dimerization at 200-240 °C, and c) cleavage of the PB corona via ozonolysis and addition of dimethyl sulfide to afford aldehyde-functionalized nanoparticles (diameter: ∼16-20 nm), along with agglomerated nanoparticles ranging from ∼30 to ∼100 nm in diameter. The characterization of the diblock copolymer precursors, the intermediate micelles and the final surface-functionalized crosslinked nanoparticles was carried out by a combination of size exclusion chromatography, static and dynamic light scattering, viscometry, thermogravimetric analysis, 1H NMR and FTIR spectroscopy and transmission electron microscopy.

Hysteresis behaviour of highly elastic multigraft copolymers with a polyisoprene (PI) backbone and branched polystyrene (PS) arms has been interpreted by applying the extended non-affine tube model of filler reinforced rubber elasticity (dynamic flocculation model), which takes into account that conformational fluctuations in bulk networks are strongly suppressed by packing effects. Originally, this model was developed to describe hyperelasticity of unfilled networks, and later, stress softening and hysteresis of filler reinforced elastomer materials like carbon black and silica filled rubbers. The evaluation of stress softening is obtained via pre-strain dependent hydrodynamic amplification of the rubber matrix by a fraction of rigid filler clusters with virgin filler-filler bonds. The filler-induced hysteresis is described by a cyclic breakdown and re-aggregation of the residual fraction of more soft filler clusters with already broken filler-filler bonds. We show, for the first time that the developed concept is in fair agreement with experimental stress-strain data of superelastic PI-PS multigraft copolymers. Depending on the PS-content and their functionality multigraft copolymers form microphase separated structures according to the constituting block copolymer concept, where the PS arms act as multi-domains in a PI matrix. The adaptation of the model is based on the assumption that the PS-domains are acting similar to filler clusters. The obtained microscopic material parameters appear reasonable for the description of the structure and mechanical properties of multigraft copolymers. © 2008 Elsevier Ltd. All rights reserved.

Deformation behavior of sphere-forming trifunctional micrograft (MG) copolymer by synchrotron SAXS and rheo-optical FT-IR, on nanometer size scales and molecular level, was studied. The sample polymer films with gauge dimensions of 7×4 mm2 and a thickness of 30-40 mm were uniaxially stretched at constant strain rate of 3.2 mm/min. The presence of single first-order scattering at 0% strain indicates the presence of phase-separated spherical morphology. The molecular architecture of tri- and tetrafunctional MG copolymers determines the difference of their deformation. The results also show that the MG copolymer has a heterogeneous phase-separated structure with spherical morphology and the collective deformation from the heterogeneous phases is characterized by observing the selective orientation in the individual phases.

A controlled covalent functionalization of multiwalled carbon nanotubes was reported through Diels-Alder cycloaddition of various substituted benzocyclobutenes and the extent of control over the functionalization at different temperatures was investigated. The quality of MWNT attached to the surfaces was determined from thermogravimetric analysis (TGA), which showed two distinct weight losses at 200 to 480 °C and the other at 590 to 625 °C. The FT-IR spectrum of various substituted MWNTs reveals characteristic vibrations of aromatic and CH modes along with the characteristic vibration modes for the substitutional group. The decomposition of MWNTs is clearly seen at 568 °C while the weight increase is attributed to the reaction of residual pendant MWNT groups of the polymer with oxygen present in the furnace.

Living anionic polymerization of 4-vinylbenzocylobutene was performed in benzene at room temperature using sec-butyllithium as the initiator. Results of the kinetic studies indicated the termination- and transfer-free nature of the polymerization. Homopolymers with predictable molecular weights and narrow molecular weight distributions were produced, excluding the interference of the cyclobutene rings during initiation and propagation. Thermogravimetric analysis of poly(4-vinylbenzocyclobutene) in air showed a small weight gain at ∼200 °C, a rapid decomposition at ∼455 °C, and a gradual decomposition at ∼566 °C. This behavior was attributed to the formation of radicals from the pendent benzocyclobutene functionality through o-quinodimethane intermediates and simultaneous decomposition/cross-linking reactions at high temperature. The living nature of the polymerization was also examined via sequential copolymerization with butadiene to form diblock copolymers. © 2006 American Chemical Society.

Living anionic surface-initiated polymerization on flat gold substrates has been conducted to create uniform homopolymer and diblock copolymer brushes. A 1,1-diphenylethylene (DPE) self-assembled monolayer was used as the immobilized precursor initiator. n-BuLi was used to activate the DPE in tetrahydrofuran at -78 °C to initiate the polymerization of different monomers (styrene, isoprene, ethylene oxide, and methyl methacrylate). Poly(styrene) (PS) and poly(ethylene oxide) (PEO) in particular were first investigated as grafted homopolymers, followed by their copolymers, including poly(isoprene)-b- poly(methylmethacrylate) (PI-b-PMMA). A combined approach of spectroscopic (Fourier transform infrared spectroscopy, surface plasmon spectroscopy, ellipsometry, X-ray photoelectron spectroscopy) and microscopic (atomic force microscopy) surface analysis was used to investigate the formation of the polymer brushes in polar solvent media. The chemical nature of the outermost layer of these brushes was studied by water contact angle measurements. The effect of the experimental conditions (solvent, temperature, initiator concentration) on the surface properties of the polymer brushes was also investigated. © 2005 Wiley Periodicals, Inc.

The effect of the macromolecular architecture and composition of block copolymer additives on the reduction of the interfacial tension between two immiscible homopolymers is investigated. A series of (polyisoprene)2(polystyrene), I2S, graft copolymers with constant molecular weight and varying composition are utilized as additives in polystyrene/polyisoprene blends. The interfacial tension decreases with the addition of small amounts of copolymer and reaches a plateau at higher copolymer concentration. The interfacial tension at interfacial saturation depends on copolymer composition exhibiting a minimum, which is lower than that using a symmetric diblock with the same molecular weight. Moreover, the interfacial tension at saturation depends on the side of the interface the copolymer is introduced; adding it to the polyisoprene phase is much more efficient than adding it to polystyrene. This is due to the asymmetric architecture of the copolymer and points to the fact that a local equilibrium can only be attained in such systems: the copolymer reaching the interface from one homopolymer phase probably does not diffuse to the other phase. The fact that this behavior is not a kinetic effect is verified using (polystyrene)2(polysoprene), S2I, grafts, which show the mirror image behavior. The effectiveness of the interfacial modifiers is, thus, controlled by the unfavorable interactions, which drive the additive toward the interface, and the possibility of micelle formation, which hinders its activity.

The following linear block co-, ter-, and quaterpolymers of 1,3-cyclohexadiene (CHD) with styrene (S), isoprene (I), and butadiene (B) were synthesized by sequential anionic polymerization: PS-b-PCHD, PI-b-PCHD, PB-b-PCHD, PS-b-PB-b-PCHD, PB-b-PS-b-PCHD, PB-b-PI-b-PCHD, and PS-b-PB-b-PI-b-PCHD. sec-Butyllithium with either N,N,N′,N′'-tetramethylethylenediamine (TMEDA) or 1,4-diazobicyclo[2.2.2]octane (DABCO) was used as the initiating system. In all cases CHD was the last monomer added. The polar additive (TMEDA or DABCO) was always introduced to the polymerization solution prior to the addition of CHD and isoprene. The microstructures of the polydienes obtained in the different environments were determined by NMR spectroscopy. Thorough characterization by size exclusion chromatography coupled with multiangle laser light scattering, laser differential refractometry, osmometry, and NMR spectroscopy revealed that the synthesized polymeric materials exhibit high molecular and compositional homogeneity.

This work is part of an extensive study of model nonlinear block copolymer/homopolymer blends. Effects of graft molecular architecture on the morphology of block copolymer/homopolymer blends have been examined. The single graft Y-shaped block copolymers used in the study are I2S block copolymers, which have two low polydispersity (PDI) polyisoprene arms and one low PDI polystyrene arm joint at a single junction point. Previously reported linear diblock copolymer/homopolymer blend systems showed that the order-order transitions (OOTs) occur at about the same volume fractions as in pure linear diblock copolymers. The OOT occurs at the same volume fraction regardless of the direction from which it is approached, i.e., blending homopolymer A with a diblock which forms A cylinders in a B matrix to push it toward lamella or blending B homopolymer with a lamellar diblock to push it back toward cylinders. This study shows that when a homopolymer is blended with an I2S block copolymer, the OOTs split so that they occur at different volume fractions depending up whether they are approached by blending homopolymer into the two-arm or the one-arm side of the block copolymer interface. A perforated lamellar morphology is obtained in a blend of homopolystyrene (hPS) and a lamella forming single graft block copolymer, and it is found to be stable to thermal annealing.

Photon correlation spectroscopy has been used to investigate the dynamics of composition fluctuations in disordered semidilute solutions of (polyisoprene)2(polystyrene) (I2S) graft copolymers in toluene. Four different relaxation mechanisms were identified with different concentration and wavevector dependencies: Three are the well-known processes in diblock copolymer solutions (cooperative diffusion, internal mode, and polydispersity diffusive mode), whereas the fourth is an extra process between the internal and the polydispersity modes that appears near the disorder-to-order transition. The latter displays similar characteristics to a process recently observed for inverse starblock copolymers also in the ordering region, and should be related to the macromolecular architecture.

The synthesis and bulk and solution properties of block copolymers having nonlinear architectures are reviewed. These materials include star-block copolymers, graft copolymers, miktoarm star copolymers, and complex architectures such as umbrella polymers and certain dendritic macromolecules. Emphasis is placed on the synthesis of well-defined, well-characterized materials. Such polymers serve as model materials for understanding the effects of architecture on block copolymer self-assembly, in bulk and in solution.

The morphologies formed by block copolymers with a double-graft, π or (S,I)I′(S,I) architecture were investigated using transmission electron microscopy (TEM) and small angle neutron scattering (SANS). Here S and I represent blocks of polystyrene and polyisoprene, respectively. These materials were synthesized using anionic polymerization and chlorosilane linking, and they were characterized using size exclusion chromatography, membrane osmometry, and low-angle laser light scattering. This characterization work confirmed the desired molecular architectures and narrow molecular weight distributions. The results of morphological characterization indicate that one can understand complex grafting architectures by decomposing them into fundamental building blocks, which are taken as the component single-graft structures out of which the larger structure is constructed. We propose rules for dividing structures into these components, which we call constituting block copolymers. For the π double-graft architecture, the constituting block copolymer is an asymmetric single-graft block copolymer. The morphological behaviour of the more complex double-graft architecture is approximately equivalent to that of the constituting single-graft block copolymer. Through the use of the constituting block copolymers we map the experimentally determined morphological behaviour of eight materials with π architecture onto the morphology diagram calculated by Milner for miktoarm stars. As in our previous study of asymmetric single-graft block copolymers, the asymmetry of the graft location along the backbone requires a generalization of the molecular asymmetry parameter, ε, used in the calculated morphology diagram.

The kinetics of formation of a chlorosilane-linked polystyrene six-arm star is reported. The precursor arm material (Mn = 88,000) was made using anionic polymerization in benzene. Prior to addition to the 1,2-bis(trichlorosilyl) ethane linking agent, the anions were endcapped with about five units of isoprene. Size exclusion chromatography using multiangle laser light scattering and viscosity detectors was utilized for characterization. This technique has allowed the molecular weights, radii of gyration, and intrinsic viscosities to be measured for star components in aliquots taken from the reactor at various times. It was found that four-arm star is formed within 30 min after the addition of the chlorosilane linking agent. There is a linear relationship between the logarithm of molecular weight of the star samples and logarithm of time of the reaction after the formation of the four-arm star. © 1997 John Wiley & Sons, Inc.

This paper reports on the synthesis and morphological characterization of graft block copolymers in which a single polystyrene (PS) arm was grafted at an asymmetric position along a polyisoprene (PI) backbone. These materials represent a model series of asymmetric simple graft (ASG) block copolymer structures. The synthesis of these materials was carried out with methods developed for three-arm "miktoarm" star copolymers using anionic polymerization high-vacuum techniques with cholorosilane linking agents. The three arms were two polyisoprene blocks with different degrees of polymerization and one deuterated polystyrene block, which formed an asymmetric simple graft structure (ASG). Molecular characterization was performed using size exclusion chromatography (SEC) with refractive index and UV detection, membrane osmometry, and low-angle laser light scattering. These techniques confirmed that the materials exhibited narrow molecular weight distributions and low compositional heterogeneity. The morphologies formed by these samples were characterized using transmission electron microscopy (TEM) and small-angle neutron scattering (SANS). The ASG structures were compared with structures formed by linear diblock copolymers and other samples having miktoarm structures, like I2S (symmetric simple graft with PI backbone and one PS branch grafted from the middle) and I3S (three equal PI arms and one PS arm). Comparisons of the morphologies formed and their dimensions indicated that the chain stretching and lateral crowding due to the miktoarm architecture was partially alleviated by the different lengths of PI blocks in ASG.

The micellization behaviors of graft copolymers consisting of polystyrene, PSt, backbones and poly(tert-butyl methacrylate), PtBuMA, or poly(methacrylic acid), PMAA, branches were studied in dilute solutions by low angle laser light scattering, LALLS, viscometry, and dynamic light scattering, DLS. tert-Amyl alcohol, a selective solvent for the PtBuMA branches, and tetrahydrofuran, THF, a selective solvent for the PSt backbones, were used to promote the formation of micelles from the PSt-g-PtBuMA and PSt-g-PMAA graft copolymers, respectively. Low aggregation numbers were obtained in all cases due to the specific architectural characteristics of the samples. Aggregation numbers were dependent on the type of the component (backbone or branches) that was insoluble in the selective solvent. The formation of micelles from the PSt-g-PtBuMA graft copolymers in tert-amyl alcohol is evidenced by the appearance of large and rather loose aggregates at a certain concentration range. This kind of behavior was not observed for the micelles formed from the graft copolymers with PMAA branches in THF. Stable and compact structures were obtained in this case, with their hydrodynamic behavior resembling that of hard spheres.

The composition and concentration dependencies of the self-diffusion coefficients for a series of miktoarm star block copolymers of the A2B type in solutions in a common good solvent have been investigated by pulsed-field-gradient nuclear magnetic resonance; the graft copolymers are composed of A = polyisoprene and B = polystyrene, where the B block was attached either in the middle of the A block (τ = 0.5) or at a position with τ = 0.25. The dependence of the diffusion coefficients on concentration, in both A2B graft copolymers and AB diblock copolymers, can be collapsed onto a master curve with a proposed scaling procedure which takes into account the difference in the entanglement characteristics of the parent homopolymers and the different radii of gyration of stars vs linear polymers. The exponential slowing down of the diffusivities expected for star molecules was not observed due to the only moderately high molecular weights and concentrations.

The morphologies formed by block copolymers with a double-graft, H or S2IS2 architecture were investigated using transmission electron microscopy (TEM) and small angle neutron scattering (SANS). Here S and I represent blocks of polystyrene and polyisoprene, respectively. These materials were synthesized using anionic polymerization and chlorosilane linking, and they were characterized using size exclusion chromatography, membrane osmometry, and low-angle laser light scattering This characterization work confirmed the desired molecular architectures and narrow molecular weight distributions. The results of morphological characterization indicate that one can understand complex grafting architectures by decomposing them into fundamental building blocks which are taken as the component single graft structures out of which the larger structure is constructed We propose rules for dividing structures into these components, which we call constituting block copolymers. The morphological behavior of the more complex architecture is approximately equivalent to that of the constituting block copolymer structure. Through the use of the constituting block copolymers we map the experimentally determined morphological behavior of the H architecture onto the morphology diagram calculated by Milner for miktoarm stars [Macromolecules 27, 2333 (1994)]. Mapping the H architecture onto the morphology diagram in this way produces general agreement between experimental results and the model. However, it is found that in the case of the H architecture, as well as in previously published results for I2S and I3S miktoarm star materials, that the morphology diagram slightly overestimates the amount of shift in the order-order transition lines produced by asymmetry in molecular architecture. This overestimation in the theory is attribute to a junction point localization effect which was neglected in Milner's calculation. © 1997 American Institute of Physics.

The dilute solution properties of model graft copolymers of the H, S2IS2, and π type, (S,I)I-(I,S), have been studied in common good (THF) and selective (n-decane and ethyl acetate) solvents. The molecules have two trifunctional branch points and are composed of polyisoprene (PI) bridges and polystyrene (PS) or polyisoprene branches. Three different methods were employed, low-angle laser light scattering, dynamic light scattering, and viscometry, in order to extract information about the aggregation number, the size, and the shape of the micelles formed in selective solvents for the PI backbones (n-decane) and for the PS branches (ethyl acetate). Both graft copolymers form multimolecular micelles in n-decane. Their hydrodynamic behavior resembles that of hard spheres. In the case of the H copolymer in ethyl acetate, large, loosely bound aggregates are formed above the cmc which are transformed to more compact micelles at higher concentrations. For the π copolymer, regions of existence of unimolecular and compact multimolecular micelles were observed, together with a sharp and relatively high critical micelle concentration. The behavior is in agreement with the closed association model. In both cases, the aggregation numbers were lower than the ones observed for diblock and triblock copolymers in similar solvents. The influence of macromolecular architecture on the micellization behavior of these model compounds is discussed in view of the additional constraints and parameters imposed by the macromolecular topology.

Results are presented from static low-angle and dynamic light scattering as well as viscometry experiments for ω-functionalized diblock copolymers of styrene and isoprene in n-decane, a nonpolar selective solvent for the polyisoprene block. The copolymers have dimethylamino and sulfobetaine zwitterionic groups at the end of the polystyrene block. The amine-capped copolymers show moderate aggregation in n-decane- Aggregation numbers for the zwitterionic copolymers are larger relative to the amine precursors. There is an enhancement in the degree of association arising from the presence of the highly polar group at the end of the insoluble block. Some differences in the size, shape, and hydrodynamic and thermal behavior of the micelles formed by the different species, reflecting the nature of the end group, are identified by comparing the results from the various techniques used.

A new equilibrium morphology consisting of randomly oriented wormlike micelles dispersed in a continuous matrix is observed in a neat, strongly segregated I2S simple graft block copolymer. The equilibrium nature of the worm phase is determined via a set of selective solvent casting and prolonged annealing experiments. Transmission electron microscopy (TEM) experiments on quenched samples allow a unique opportunity to directly observe the transition of a kinetically trapped, nonequilibrium folded-layer morphology, formed by casting the sample with a solvent selective for polyisoprene (PI), into the equilibrium, randomly oriented worm phase through an intermediate folded-lace morphology. The folded-lace intermediate is similar to the "mesh" structure previously observed by Hashimoto et al. in starblock/ homopolymer blends.1 The simple graft block copolymer, formed by grafting a single polystyrene (PS) chain onto the center of a polyisoprene backbone, introduces a 2:1 PI/PS arm number asymmetry in the microphase separated state. The 0.81 volume fraction of the PS graft is theoretically predicted2 to be the first volume fraction of graft large enough to force the two PI arms per molecule to the concave side of the PI/PS interface in the microphase separated state. This unique volume fraction, coupled with the novel graft architecture, seems to frustrate the system from choosing a lattice during the microphase separation process.

The influence of the end groups on the glass transition temperature, Tg, of the polyisoprene block of styrene-isoprene diblocks was studied by differential scanning calorimetry. The end-functionalized styrene-isoprene diblock samples used have dimethylamino and sulfobetaine groups attached on the polyisoprene chain end. An increase in the low temperature (polyisoprene-type) Tg value was observed for the lower molecular weight zwitterion capped polymers. This effect is attributed to restricted segmental mobility of the polyisoprene chains found in the proximity of the ionic aggregates. Copyright © 1996 Elsevier Science Ltd.

Well-defined graft copolymers with polyisoprene backbones and polystyrene branches, having trifunctional branch points, of the type S2IS2 (H-shaped) and (SI)I(SI) (π-shaped) were synthesized by anionic polymerization high-vacuum techniques. The synthetic strategy involves the preparation of the outer parts of the molecules, carrying one reactive Si-Cl bond, followed by coupling with difunctional living poly(isoprenyllithium) chains. In this way, the number and placement of the branches can be precisely controlled. Molecular characterization of the fractionated samples by size exclusion chromatography with UV and RI detection, membrane osmometry, low-angle laser light scattering, and 1H-NMR spectroscopy confirmed that the materials exhibit narrow molecular weight distributions and low compositional heterogeneity. The strongly microphase-separated morphologies of these two samples were characterized using TEM and SAXS. The π architecture with a PS volume fraction of 0.21 was found to form body-centered cubic spheres, while the H architecture with a PI volume fraction of 0.64 was found to form a lamellar morphology. The observed morphology for these architectures was rationalized by formally dividing the π and H architectures into component simple (single) graft block copolymers which were mapped onto Milner's morphology diagram for simple graft copolymers.