Synthesis of polystyrene-styrene/butadiene diblock copolymers via reversible addition-fragmentation chain transfer miniemulsion polymerization

Polystyrene-styrene/butadiene diblock copolymers were synthesized via reversible addition-fragmentation chain transfer （RAFT） miniemulsion polymerization.During the polymerization process,the molecular weight distribution was narrow and the numerical molecular weight of the copolymers increased with increasing conversion of monomers,which was close to the theoretical.FT-IR and ^1H NMR results indicated that the microstructure of the polymer was mainly 1,4-trans-butadiene with small amount of 1,2-units,and composition in the copolymers was obtained.

"LIVING" FREE RADICAL SYNTHESIS OF NOVEL RODCOIL DIBLOCK COPOLYMERS WITH POLYSTYRENE AND MESOGEN-JACKETED LIQUID CRYSTAL POLYMER SEGMENTS

The synthesis of rod-coil diblock copolymers was achieved for the first time by TEMPO-mediated 'living' free radical polymerization of styrene and 2,5-bis [(4-methoxyphenyl)oxycarbonyl] styrene(MPCS). The block architecture of the two diblock copolymers thus prepared, MPCS-b-St(5400/2400) and MPCS-b-St(10800/8700), was confirmed by GPC, DSC studies and the formation of multimolecular micelles. (Author abstract) 10 Refs.

Self-assembly of lamella-forming diblock copolymers confined in nanochannels: Effect of confinement geometry

The self-assembly of symmetric diblock copolymers confined in the channels of variously shaped cross sections （regu- lar triangles, squares, and ellipses） is investigated using a simulated annealing technique. In the bulk, the studied symmetric diblock copolymers form a lamellar structure with period LL. The geometry and surface property of the confining channels have a large effect on the self-assembled structures and the orientation of the lamellar structures. Stacked perpendicular lamellae with period LL are observed for neutral surfaces regardless of the channel shape and size, but each lamella is in the shape of the corresponding channel＇s cross section. In the case of triangle-shaped cross sections, stacked parallel lamel- lae are the majority morphologies for weakly selective surfaces, while morphologies including a triangular-prism-shaped B-cylinder and multiple tridentate lamellae are obtained for strongly selective surfaces. In the cases of square-shaped and ellipse-shaped cross sections, concentric lamellae are the signature morphology for strongly selective surfaces, whereas for weakly selective surfaces, stacked parallel lamellae, and several types of folding lamellae are obtained in the case of square-shaped cross sections, and stacked parallel lamellae are the majority morphologies in the case of ellipse-shaped cross sections when the length of the minor axis is commensurate with the bulk lamellar period. The mean-square end- to-end distance, the average contact number between different species and the surface concentration of the A-monomers are computed to elucidate the mechanisms of the formation of the different morphologies. It is found that the resulting morphology is a consequence of competition among the chain stretching, interfacial energy, and surface energy. Our results suggest that the self-assembled morphology and the orientation of lamellae can be manipulated by the shape, the size, and the surface property of the confining channels.

Phase behaviors in a binary mixture of diblock copolymers confined between two parallel walls

The phase behaviors in a binary mixture of diblock copolymers confined between two parallel walls are investigated by using a cell dynamics simulation of the time-dependent Ginzburg-Landau theory.The morphological dependence of the wall-block interaction and the distance between walls（confinement degree） has been systematically studied,and the effect of repulsive interactions between different monomers is also discussed.It is interesting that multiple novel morphological transitions are observed by changing these factors,and various multilayered sandwich structures are formed in the mixture.Furthermore,the parametric dependence and physical reasons for the microdomain growth and orientational order transitions are discussed.From the simulation,we find that much richer morphologies can form in a binary mixture of diblock copolymers than those in a pure diblock copolymer.Our results provide an insight into the phase behaviors under parallel wall confinement and may provide guidance for experimentalists.This model system can also give a simple way to realize orientational order transition in soft materials through confinement.

Cylindrical-confinement-induced phase behaviours of diblock copolymer melts

The phase behaviours of diblock copolymers under cylindrical confinement are studied in two-dimensional space by using the self-consistent field theory. Several phase parameters are adjusted to investigate the cylindrical-confinement-induced phase behaviours of diblock copolymers. A series of lamella-cylinder mixture phases, such as the mixture of broken-lamellae and cylinders and the mixture of square-lamellae and cylinders, are observed by varying the phase parameters, in which the behaviours of these mixture phases are discussed in the corresponding phase diagrams. Furthermore, the free energies of these mixture phases are investigated to illustrate their evolution processes. Our results are compared with the available observations from the experiments and simulations respectively, and they are in good agreement and provide an insight into the phase behaviours under cylindrical confinement.

Adsorption of Diblock Copolymers from Non-selective Solvent: Comparison Between Scheutjens-Fleer Theory and Monte Carlo Simulation

Systematic comparison between computer simulation results and those predicted by Scheutjens-Fleer (SF) self-consistent-field theory is presented for the adsorption of diblock copolymers from a non-selective solvent on attractive surface. It is shown that although SF is a mean-field theory, it can qualitatively describe the adsorption phenomena of diblock copolymers. However, systematic discrepancy between the theory and simulation still exists. The approximations inherited in the mean-field theory such as random mixing inside a layer and the allowance of direct back folding may be responsible to those deviations.

EFFECT OF AMPHIPHILIC POLY (STYRENE-B-ETHYLENE OXIDE) DIBLOCK COPOLYMER INTERCALATED LAYERED SILICATE AS FILLER ON ACRYLONITRILE-BUTADIENE-STYRENE RESIN

The diblock copolymers intercalated layered silicate was prepared via a melt dispersion technique. Then the effect of intercalated hybrid as filler on acrylonitrile- butadiene-styrene resin was characterized by X-ray diffraction, transmission electron microscopy, stress-strain measurements in elongation.

MECHANISM-TRANSFORMATION SYNTHESIS AND CHARACTERIZATION OF POLY(STYRENE-b-2-ETHYL-2-OXAZOLINE) DIBLOCK COPOLYMER

By mechanism-transformation (anionic --> cationic) poly(styrene-6-2-ethyl-2-oxazoline) diblock copolymer, PS-b-PEOx, was synthesized in two steps. The first step is the polymerization of styrene block capped with ethylene oxide and its tosylation; the second step is the cationic ring-opening polymerization of 2-ethyl-2-oxazoline. The products were thoroughly characterized by various methods, such as H-1-NMR, IR, DMA, TEM and SAXS. The results show that the copolymer obtained possesses high molecular weight and narrow molecular weight distribution.

Surface-field-induced effects on morphologies of lamella-forming diblock copolymers in nanorod arrays

The surface-induced effect on the morphologies of lamella-forming diblock copolymers in nanorod arrays is studied by using the self-consistent field theory. In the simulation study, a rich variety of novel morphologies are observed by variations in the strength of the surface field for the diblock copolymers. Different surface-field-induced effects are examined for the diblock copolymers in the arrays with distinct preferential surfaces. It is observed that the majority-block preferential surfaces have more obvious induced effects than those of minority-block preferential surfaces. The strong surface fields exhibit different behaviours from those observed in the weak surface fields, by which the morphologies possess cylindrical symmetries. Results from this research deepen the knowledge of surface-induced effects in a confinement system, which may aid the fabrication of polymer-based na^omaterials.

THE EFFECTS OF PATTERNED SURFACES ON THE PHASE SEPARATION FOR DIBLOCK COPOLYMERS

The phase behaviors of symmetric diblock copolymer thin films confined between two hard, parallel and diversified patterned surfaces are investigated by three-dimensional dissipative particle dynamics (DPD) simulations. The induction of diversified patterned surfaces on phase separation of symmetric diblock copolymer films in snapshots, density profiles and concentration diagrams of the simulated systems are presented. The phase separations can be controlled by the patterned surfaces. In the meantime, the mean-square end-to-end distance of the confined polymer chains < R(2)> is also discussed. Surface-induced phase separation for diblock copolymers can help us to create novel and controlled nanostructured materials.

Temperature dependence of microscopic properties in diblock copolymer films:A dissipative particle dynamics simulation

Temperature dependence of microscopic properties in diblock copolymer films has been investigated by dissipative particle dynamics simulations. Results show the relation between mean-square bond length （MSBL） and system temperature can be described as a quadratic curve. The root-mean-square radius of gyration （RMSGR） and end-end distance （RMSED） increase gradually as the temperature rises and composition fraction changes from 0.1 to 0.5, in which the effect of the former is primary. Especially, the relation between RMSGR and temperature is nearly linear in the confinement-introduced direction. Density distribution of each component in the films can be controlled and adjusted effectively by its interaction with other components and boundaries. Moreover, the changes of system temperature and composition fraction can both affect the density distributions to a certain extent.

Thermodynamically consistent model for diblock copolymer melts coupled with an electric field

We present a thermodynamically consistent model for diblock copolymer melts coupled with an electric field derived using the Onsager linear response theory.We compare the model with the thermodynamically inconsistent one previously used for the coupled system to highlight their differences in describing transient dynamics.

Biodegradable Blend Nanoparticles of Amphiphilic Diblock Copolymers Prepared by Nano-Precipitation Method

Nanoparticles of biodegradable methoxy poly(ethylene glycol)-b-polyester amphiphilic diblock copolymers have widely investigated for use as controlled release drug delivery carriers. In this work, blend nanoparticles of methoxy poly(ethylene glycol)-b-poly(D,L-lactide) (MPEG-b-PDLL) and methoxy poly(ethylene glycol)-b-poly(ε-caprolactone) (MPEG- b-PCL) were prepared by nano-precipitation method without any surfactants. 1H-NMR spectra showed significant difference in integral peak areas, suggesting the nanoparticles with different MPEG-b-PDLL/MPEG-b-PCL blend ratios can be prepared. Transmission electron microscope revealed the blend nanoparticles had nearly spherical in shape with smooth surface. Average size of the blend nanoparticles obtained from light-scattering analysis slightly decreased with increase in blend ratio of MPEG-b-PCL. The MPEG-b-PDLL and MPEG-b-PCL were amorphous and semi-crystalline, respectively. Thermal transition properties of the blend nanoparticles were studied with differential scanning calorimetry (DSC). The DSC results showed that glass transition temperatures of the blend nanoparticles decreased and heats of melting steadily increased, while the melting temperature did not change as the MPEG-b-PCL blend ratio increased. This indicates the miscibility of MPEG-b-PDLL and MPEG-b-PCL in the amorphous phase of the blend nanoparticles. Thermogravimetric analysis showed that the blend nanoparticles clearly exhibited two thermal decomposition steps due to MPEG-b-PDLL decomposition followed with MPEG-b-PCL. The blend nanoparticles had two temperatures of maximum decomposition rate (Td, max) accorded to each blend component. The Td, max of MPEG-b- PDLL phase significantly decreased, while Td, max of MPEG-b-PCL phase did not change as the MPEG-b-PCL blend ratio increased. These results suggested that the desired thermal properties of blend nanoparticles can be tailored by varying the blend ratio.

Synthesis of P4VP-b-PBLG Diblock Copolymers and Their Self-Assembly Behavior

Well-defined P4VP-b-PBLG diblock polymer composed of poly (4-vinylpyridine) (P4VP) and poly (γ-benzyl-L-glutamate) (PBLG) was synthesized by click reaction with alkyne- and azide-functionalized homopolymers. Besides, P4VP blocks were synthesized by copper-mediated atom transfer radical polymerization (ATRP) with a chlorine-containing alkyne bifunctional initiator, and the azido-terminated PBLG homopolymers were synthesized by ring-opening polymerization (ROP) of γ-benzyl-L-glutamate with an amine-containing azide initiator. In addition, the synthesized P4VP-b-PBLG with different block ratios has been characterized by proton nuclear magnetic resonance (1H NMR), Gel permeation chromatograph (GPC) and fourier transform infrated spectroscopy (FT-IR). Then, the self-assembly behaviors of P4VP-b-PBLG have been studied by changing parameters like dripping speed and block ratio. The morphologies of self-assembly of spherical, disk-like and ellipsoid-like shape particles have been observed and analyzed by scanning electron microscopy (SEM). These results have provided guidelines for the design of macromolecular self-assembly.

Preparation and Characterization of Nimodipine-loaded Methoxy Poly(ethylene glycol)-poly(lactic acid) Diblock Copolymer Nanoparticles

Amphiphilic diblock copolymers, methoxy poly(ethylene glycol)-poly(lactic acid) (MePEG-PLA), were synthesized from monomers of DL-lactide and methoxy poly(ethylene glycol) by a ring opening bulk polymerization in the presence of stannous octoate. Their chemical structure and physical properties were investigated using FTIR, NMR, GPC, and fluorescence spectroscopy. To estimate the feasibility as colloidal drug carrier, nimodipine (ND) was loaded into MePEG-PLA block copolymer nanoparticles by phase-separation/dialysis method. The mean diameter and drug loading efficiency of ND-loaded MePEG-PLA copolymer nanoparticles depended on PLA/MePEG block composition of the copolymer and drug/polymer feed ratio in preparation. NMR study confirmed that nimodipine was entrapped into the hydrophobic inner core of MePEG-PLA copolymer nanoparticles and hydrophilic PEG chains were located on the surface of the drug-loaded polymer nanoparticles. In vitro release experiments exhibited the sustained release behavior of nimodipine from MePEG-PLA copolymer nanoparticles, without any burst effect.

Morphological stability of worm-like vesicles consisting of amphiphilic diblock copolymer against external stress

The morphological stability of vesicles consisting of an amphiphilic poly(methacrylic acid)- block-poly(methyl methacrylate-random-methacrylic acid) diblock copolymer, PMAA-b-P(MMA-r-MAA), was investigated against the external stresses of pH, salt concentration and polyamine. The worm-like vesicles underwent a partial fusion at pH 12, however, they retained the worm-like shape at pH 13 due to electrostatic repulsion. On the other hand, the spherical vesicles were completely fused at pH 12, transformed into a sheet and did not retain their shape under the higher basic condition. Similarly, the worm-like vesicles retained their morphology in 0.1 mol% solutions of sodium chloride and sodium dodecyl sulfate, while the spherical vesicles caused division and fusion even at much lower concentrations. Poly(2-dimethylaminoethyl methacrylate)(PDMAEMA) transformed the worm-like vesicle into a cleavable sheet, while it changed the spherical vesicles into a sheet without a specific form. It was found that this transformation based on the acid-base interaction between the carboxylic acid of the MAA block and the amine of the PDMAEMA was dependent on the molecular weight of the PDMAEMA. The short PDMAEMA retarded the fusion of the vesicles.

SYNTHESIS AND CHARACTERIZATION OF POLY(STYRENE - ETHYLENE OXIDE) DIBLOCK COPOLYMERS

Well - defined diblock copolymers Of styrene (St ) and ethylene oxide (EO )have been prepared by sequential living anionic polymerization of the twocomonomers in THF. Diphenyl methyl potassium has been used as initiator. Theblock copolymers were characterized in detail by methods Of size exclusion chromatography (SEC ) , 1H - Nab, FT - IR, dynamic mechanical analysis(Daal ) and WAXD.

Synthesis of Polynorbornene-Poly(ethylene-co-propylene)Diblock Copolymer

Transformation of living ring-opening metathesis polymerization into coordination polymerization by converting the titanacyclobutane group attached to a polynorbornene chain into titanocene alkoxide has been used for the synthesis of polynorbornene-poly(ethylene-co-propylene) block copolymer. Preliminary characterizations of the copolymerization products by solvent extraction and C-13 NMR spectrum are reported.

Microphase Separation of Semiflexible Ring Diblock Copolymers

Aiming at the difficult problem of solving the conformation statistics of complex polymers, this study presents a novel and concise conformation statistics theoretical approach based on Monte Carlo and Neural Network method. This method offers a new research idea for investigating the conformation statistics of complex polymers, characterized by its simplicity and practicality. It can be applied to more complex topological structure, more higher degree of freedom polymer systems with higher dimensions, theory research on dynamic self-consistent field theory and polymer field theory, as well as the analysis of scattering experimental data. The conformation statistics of complex polymers determine the structure and response properties of the system. Using the new method proposed in this study, taking the semiflexible ring diblock copolymer as an example, Monte Carlo simulation is used to sample this ring conformation to construct the dataset of polymer. The structure factor describing conformation statistics are expressed as continuous functions of structure parameters by neural network supervised learning. This is the innovation of this work. As an application, the structure factors represented by neural networks were introduced into the random phase approximation theory to study the microphase separation of semiflexible ring diblock copolymers. The influence of the ring's topological properties on the phase transition behavior was pointed out.

Particle Distribution Informed by Chain Rigidity in Diblock Copolymer Melts: The Effect of Entropy

We study the effect of chain rigidity on tailoring the nanoparticle locations for neutral and selective particles embedded in the lamellar morphology formed by semiflexible diblock copolymer chains using self-consistent field calculations. The nanoparticles are modeled through a cavity function, and the semiflexible chains are represented by the continuous Kratsky-Porod chain model. In general situation, the nanoparticles prefer to stay at the interface in order to reduce the interface areas and thus the system free energy. However, the particle distribution at the domain center is subtle, and the underlying physics is intrinsically different depending on the polymer flexibility. In the case of flexible chains, the entropy just contributes a constant shift to the free energy when the nanoparticles move around the domain center indicating that the local metastable state if appears at the domain center is wholly attributed to the local minimum in the enthalpy. If the polymers are rigid, the variation of the particle distribution at the domain center has a close relation with the polymer rigidity and nanoparticle size. In the case of strongly rigid polymers with small nanoparticles, a nearly uniform particle distribution at the domain center is observed, while in other cases, a local enhancement of particle distribution there is found. In contrast to the case of flexible chains, further analysis reveals the crucial role of entropy in controlling the shape of particle distributions at the phase domain. Specifically, the local metastable state appears in the domain center is determined by the large entropy there which arises from the weak coupling of bond orientations that allows the polymer chains to be relatively relaxed. When the particle becomes selective, its distribution in the phase domain exhibits a shift almost uniformly rather than changes its profile, and the underlying physics still holds. In all, our study establishes a strong coupling between the chain rigidity and effect of entropy.