SYNTHESIS OF HETEROARM STAR POLYMERS COMPRISING POLY(4-METHYLPHENYL VINYL SULFOXIDE) SEGMENT BY LIVING ANIONIC POLYMERIZATION

A series of 3-arm ABC and AA＇B and 4-arm ABCD, AA＇BC and AA＇A＂B heteroarm star polymers comprising one poly（4-methylphenyl vinyl sulfoxide） segment and other segments such as polystyrene, poly（a-methylstyrene）, poly（4-methoxystyrene） and poly（4-trimethylsilylstyrene） were synthesized by living anionic polymerization based on diphenylethylene （DPE） chemistry. The DPE-functionalized polymers were synthesized by iterative methodology, and the objective star polymers were prepared by two distinct methodologies based on anionic polymerization using DPE-functionalized polymers. The first methodology involves an addition reaction of living anionic polymer with excess DPE-functionalized polymer and a subsequent living anionic polymerization of 4-methylphenyl vinyl sulfoxide （MePVSO） initiated from the in situ formed polymer anion with two or three polymer segments. The second methodology comprises an addition reaction of DPE-functionalized polymer with excess sec-BuLi and a following anionic polymerization of MePVSO initiated from the in situ formed polymer anion and 3-methyl-1,1-diphenylpentyl anion as well. Both approaches could afford the target heteroarm star polymers with predetermined molecular weight, narrow molecular weight distribution （Mw/Mn 〈 1.03） and desired composition, evidenced by SEC, 1H-NMR and SLS analyses. These polymers can be used as model polymers to investigate structure-property relationships in heteroarm star polymers.

Role of Hydrodynamic Interactions in the Deformation of Star Polymers in Poiseuille Flow

Stretching polymer in fluid flow is a vital process for studying and utilizing the physical properties of these molecules,such as DNA linearization in nanofluidic channels.We studied the role of hydrodynamic interactions(His)in stretching a free star polymer in Poiseuille flow through a tube using mesoscale hydrodynamic simulations.As increasing the flow strength,star polymers migrate toward the centerline of tube due to His,whereas toward the tube wall in the absence of His.By analyzing the end monomer distribution and the perturbed flow around the star polymer,we found that the polymer acts like a shield against the flow,leading to additional hydrodynamic drag forces that compress the arm chains in the front of the star center toward the tube axis and lift the arm chai ns at the back toward the tube wall.The balanced hydrodynamic forces freeze the polymer into a trumpet structure,where the arm chains maintain a steady strongly stretched state at high flow strength.In contrast,the polymer displays remarkably large conformational change when switching off His.Our simulation results explained the coupling between His and the structure of star polymers in Poiseuille flow.

PREPARATION OF STAR NETWORK PEG-BASED GEL POLYMER ELECTROLYTES FOR ELECTROCHROMIC DEVICES

An amorphous,colorless,and highly transparent star network polymer with a pentaerythritol core linking four PEG-block polymeric arms was synthesized from the poly(ethylene glycol)(PEG),pentaerythritol,and dichloromethane by Williamson reaction.FTIR and ~1H-NMR measurement demonstrated that the polymer repeating units were C[CH_2-OCH_2O-(CH_2CH_2O)_m-CH_2O-(CH_2CH_2O)_n-CH_2O]_4.The polymer host held well mechanical properties for pentaerythritol cross-linking.The gel polymer electrolytes based on Lithium pe...

Synthesis and Characterization of Lactone Functional Macromonomers by End Group Deactivation and Their Use in Miktoarm Star Polymer

Newly designed miktoarm star-shaped copolymers made of poly[(benzyl methacrylate(BMA)-co-(ε-caprolacton)(CL)] and poly[(BMA-b-MMA-b-BMA)-co-ε-caprolacton)(CL)] were synthesized by combining ring-opening polymerization (ROP) of ε-caprolactone (CL) and poly(BMA) five membered lacton fuctionalized prepared via atom transfer radical polymerization (ATRP) of BMA, and ε-CL and P(BMA-b-MMA-b-BMA) dual functionalized diblock copolymer, in the presence of tin(II) bis(2-ethylhexanoate) (Sn(Oct)2). Although lactone ended poly(benzyl methacrylate) with ε-caprolactone monomer gave ring open polymerization by Sn(Oct)2, the macromonomer itself did not give any poly- merization The macromonomers, and the miktoarm star-shaped copolymers were analyzed by FT-IR and 1H-NMR spectroscopies and GPC (gel permeation chromatograph), Differential scanning calorimetry (DSC-50) and termo- gravimetric analysis (TGA-50). These copolymers exhibited the expected structure. The crystallization of star-shaped copolymers was studied by DSC. The results show that when the content of the BMA block increased, the Tm of the star-shaped block copolymer increased.

Precision Synthesis of End-Functionalized Star Poly(vinyl alcohol)s by RAFT Polymerization and Post-polymerization Modification

Poly(vinyl alcohol)(PVA)has been widely used in industrial and consumer products.In this study,we aimed to address this challenge by synthesizing well-defined multiarm poly(vinyl acetate)(PVAc)through the use of nonhydrolyzable vinyl ethertype multifunctional RAFT agents.The control over molecular weights was achieved by the RAFT process to afford polymers with dominant head-to-head linkages at the terminal.Especially,quantitative end-functionalization of the synthesized PVAc was performed using Michael thiol−ene or disulfide exchange reactions.Consequently,saponification of the PVAc enabled the synthesis of end-functionalized multiarm PVA in an efficient manner.This straightforward approach afforded well-defined functional PVAs,which enable further chemical modification,thus widening the utility of PVA in a range of applications,such as precisely controlled network synthesis and bioconjugation.

Synthesis of methyl methacrylate star-branched polymer with divinylbenzene as a linking agent via controlled/living photopolymerization

HTEMPO-functionalized central cores were formed with divinylbenzene in ＇＇core first＇＇ method,and the four or five arms star polymers were built via controlled/living free radical photopolymerization.The four arms star polymers were also prepared with controlled/living free radical photopolymerization in ＇＇arm first＇＇ method.The resulting polymers had been confirmed by GPC and 1 H NMR.It showed that the star polymers had low polydispersities and molecular weight（M n） with the 85,000-560,000 g/mol range.

Synthesis and Rheological Investigation of Model Symmetric 3-Arm Star Polyethylene

A variety of linear and 3-arm star polyethylene （PE） model polymers covering a wide range of molecular weight are synthesized by the living polymerization of butadiene and the subsequent hydrogenation. Several rheological parameters of these model linear and 3-arm star PE samples are analyzed for detecting the long chain branching （LCB） structure. It is found that the analyses based on zero shear viscosity, vGP plot and flow activation energy are very sensitive to the 3-arm star PEs. The information on the presence of LCB can be obtained with these methods even for low molecular weight samples, which can not be determined by GPC-MALLS. However the information about the LCB structure can not be obtained by the rheological methods alone.

Multiarm Star Poly(ε-caprolactone) with Hyperbranched Polyamidoamine as Core Capable of Selective Accommodating Cationic or Anionic Guests

Hyperbranched polyamidoamines （HPAs） were directly employed as macroinitiators to initiate the Sn（Oct）2 catalyzed ring-opening polymerization of ε-caprolactone （CL）, resulting in multiarm star copolymers with poly（6- caprolactone） （PCL） as shells and HPA as core （HPA-b-PCL）. From 1H-NMR characterization it was deduced that both the primary amines and the secondary amide groups of HPAs could initiate the CL polymerization, and the initiation efficiency increased when more CL monomers were fed. The average arm-numbers of the obtained stars were in the range of 115-353. Differential scanning calorimetry measurements demonstrated that the melting and crystallization temperatures, fusion and crystallization enthalpy and the degree of crystallinity of the star polymers increased as the PCL arm length increased. HPA- b-PCL stars could be used as nanocarriers to efficiently accommodate anionic dyes at acidic condition, while load cationic dyes at basic condition. Compared with the dye-loading behavior of multiarrn star PCL with the neutral hyperbranched polyglycerol as core, it was deduced that HPA-b-PCL nanocarriers accommodated anionic dyes using the HPA core, while loaded cationic dyes using both the HPA core and the PCL shell. Dynamic light scattering analyses also supported such deduction. Furthermore, HPA-b-PCL nanocarriers could selectively load the anionic Eosin Y or the cationic methylene blue from their mixture at pH = 6 or 9, respectively, realizing their separation.

Synthesis of Star Polymeric Ionic Liquids and Use as the Stabilizers for High Internal Phase Emulsions

A series of well-defined core cross-linked star （CCS） polymeric ionic liquids （PILs） were synthesized via a three- step approach. First, the styrenic imidazole-based CCS polymer （S-PVBnIm） was prepared by the RAFT-mediated heterogeneous polymerization in a water/ethanol solution, followed by the quaternization of S-PVBnIm with bromoalkanes and anion exchange. The CCS polymers were characterized by gel permeation chromatography （GPC）, nuclear magnetic resonance （NMR） spectroscopy, Fourier transform infrared spectroscopy （FTIR）, thermal gravimetric analysis （TGA）, and differential scanning calorimetry （DSC）. The obtained CCS polymers were used as the effective emulsifiers for oil-in-water high internal phase emulsions （HIPEs）. Multiple oils with different polarity including n-dodecane, undecanol, toluene and octanol were emulsified using 0.5 wt% S-PVBnIm aqueous solution under the acidic condition to form HIPEs with long-term stabilities. The excellent emulsification properties of CCS PILs were demonstrated by HIPE formation for a variety of oils. The properties of HIPEs in terms of emulsion type and oil droplet size were characterized by the confocal laser scanning microscopy （CLSM）. The intriguing capability of CCS PILs to stabilize HIPEs of various oils holds great potentials for the practical applications.

SYSTHESIS OF DOUBLE-HYDROPHILIC CORE-SHELL TYPE MULTIARM STAR COPOLYMER POLYETHYLENIMINE-block-POLY(2-HYDROXYETHYL METHACRYLATE)

Multiarm star block copolymers hyperbranched polyethylenimine-b-poly（2-hydroxyethyl methacrylate） （HPEI-b- PHEMA） with average 28 PHEMA arms have been prepared by atom transfer radical polymerization （ATRP） of HEMA in a mixed solvent of methanol and water using a core-first strategy. The hyperbranched macroinitiator employed was prepared on the basis of well-defined hyperbranched polyethylenimine with Mw/Mn of 1.04 by amidation with 2-bromo-isobutyryl bromide. The polymerization condition was optimized to prepare star copolymers with narrow dispersity, and the variables included the volume ratio of methanol to water, the molar ratio of initiating site to CuC1 and the molar ratio of [CuCl]：[CuBr2]. Under the optimized polymerization condition, the lowest Mw/Mn value of the obtained star copolymers was around 1.3. Kinetic analysis showed that an induction period existed in the polymerization of HEMA. After this induction period, a linear dependence of ln（[M]0/[M]t） on time was observed. The obtained HPEI-b-PHEMA could adsorb hydrophilic molecules. The comparison with the star copolymer with hydrophobic core and hydrophilic PHEMA shell verified that both the hydrophilic core and shell could host the hydrophilic guests, but the amidated HPEI core was more effective than the PHEMA shell.

Molecular Dynamics Study of Star Polymer Melts under Start-up Shear

It has been established that star polymers with a large number of arms display both the conventional chain relaxation and a slower interchain relaxation due to the formation of hard cores,which is called the local structural relaxation.Here,we demonstrate that this unique relaxation property of multi-arm stars leads to unusual rheological behaviors.We study the response of star polymer melts with various arm numbers to start-up shear flow via nonequilibrium molecular dynamics simulation.Our simulation results indicate that the stress-strain response of multi-arm star polymer melts differs from that of star polymers with a small number of arms in both quantitative and qualitative manners.While the multi-arm star polymer melts exhibit an overshoot peak in the stress-strain curve both at relatively small and sufficiently large shear rates,two overshoot peaks appear when the flow strength is comparable to the relaxation time of the star polymers.This double stress overshoot is absent in linear polymers and star polymers with a small number of arms and is evidently related to the presence of the local structural relaxation in star polymers with a large number of arms.We present a detailed analysis of the conformational and dynamical properties of star polymer melts under start-up shear to gain a molecular understanding of their stress response.

A STEERED MOLECULAR DYNAMICS SIMULATION ON THE ELASTIC BEHAVIOR OF ADSORBED STAR POLYMER CHAINS

Elastic behavior of 4-branched star polymer chain with different chain length N adsorbed on attractive surface is investigated using steered molecular dynamics （SMD） simulation method based on the united-atom （UA） model for branched alkanes. The simulation is realized by pulling up the chain via a linear spring with a constant velocity v = 0.005 nm/ps. At the beginning, the chain lies extensionally on adsorbed surface and suffers continuous deformations during the tensile process. Statistical parameters as mean-square radii of gyration 〈S2〉xy, 〈S2〉z, shape factor 〈δ〉, describing the conformational changes, sectional density 〈den〉 which gives the states of the chain, and average surface attractive energy 〈Ua〉, average total energy 〈U〉, average force 〈f〉 probed by the spring, which characterize the thermodynamic properties, are calculated in the stimulant process. Remarkably, distinguishing from the case in linear chains that there only exists one long plateau in the curve of 〈f 〉, the force plateau in our study for star chains is multiple, denoting different steps of desorption, and this agrees well with the experimental results in essence. We find during the tensile process, there are three characteristic distances Zc, Zt and Z0 from the attractive surface, and these values vary with N. When Z = Zc, the chain is stripped from the surface, but due to the form of wall-monomer interaction, the surface retains weak influence on the chain till Z = Zc. From Z = Zt, parameters 〈Ua〉, 〈U〉 and 〈f〉 respectively reach a stable value, while the shape and the size of the chain still need adjustments after Zt till Zo to reach their equilibrium states. Specifically, for short chain of N = 41, Zt and Z0 are incorporated. These results may help us to deepen the knowledge about the elastic behavior of adsorbed star polymer chains.

Preparation of a Star Network PEG-based Gel Polymer Electrolyte and Its Application to Electrochromic Devices

A star network polymer with a pentaerythritol core linking four PEG-block polymeric arms was synthesized, and its corresponding gel polymer electrolyte based on lithium perchlorate and plasticizers EC/PC with the character being colorless and highly transparent has been also prepared. The polymer host was characterized and confirmed to be of a star network and an amorphous structure by FTIR, ^1H NMR and XRD studies. The polymer host hold good mechanical properties for pentaerythritol cross-linking. Maximum ionic conductivity of the prepared polymer electrolyte has reached 8.83 × 10 ^-4 S·cm^-1 at room temperature. Thermogravimetry （TG） of the polymer electrolyte showed that the thermal stability was up to at least 150 ℃. The gel polymer electrolyte was further evaluated in electrochromic devices fabricated by transparent PET-ITO and electrochromically active viologen derivative films, and its excellent performance promised the usage of the gel polymer electrolyte as ionic conductor material in electrochrornic devices.

Synthesis and Self-assembly of a Triarm Star-shaped Rod-Rod Block Copolymer

We designed and synthesized a triarm star-shaped rod-rod block copolymer（BCP）,（poly{2,5-bis[（4-methoxyphenyl）-oxycarbonyl]styrene}-block-poly（γ-benzyl-L-glutamate））3,（PMPCS-b-PBLG）3. The triarm core with three PMPCS-N3 segments was prepared by copper-mediated atom transfer radical polymerization of 2,5-bis[（4-methoxyphenyl）-oxycarbonyl]styrene initiated by a trifunctional initiator and a subsequent azide reaction. And the PBLG block with alkyne functionality was synthesized through ring-opening polymerization of γ-benzyl-L-glutamate N-carboxyanhydride initiated by propargylamine. Finally, Huisgen＇s 1,3-dipolar cycloaddition was employed to combine the triarm（PMPCS-N3）3 and PBLG segments. The chemical structure of the BCP was confirmed by 1H-NMR spectroscopy, Fourier-transform infrared spectroscopy, and gel permeation chromatographic analysis. Results from differential scanning calorimetry, polarized light microscopy, one-dimensional and two-dimensional wide-angle X-ray diffraction, and transmission electron microscopy techniques demonstrate that the triarm star-shaped rod-rod BCP self-assembles into a hexagon-in-lamella morphology, with the PMPCS block in the columnar nematic phase and the PBLG block in the hexagonal columnar arrangement packed in bilayers due to the rigid nature of the two blocks and the covalent connections in the star-shaped BCP.

Positioning a fluorescent probe at the core of a glassy star polymer for detection of local dynamics

Accessing local dynamics within a single macromolecule is the key to understand the physical origin of the viscoelasticity and especially the glass transition. In order to extract specific information on the dynamics of the branch point of a star polymer around its glass transition temperature, four-arm star poly （n-butyl methacrylate） with a fluorescent core was synthesized using perylene diimide as initiator and polymerization conducted via atom transfer radical polymerization. The process is found to be effective in positioning the fluorophore at the branch point with the fluorophore intact, which allows the successful application of single molecule fluorescence defocus imaging in examining the local site- sensitive dynamics. The power spectra of rotation trajectories, the population of rotating fluorophores as well as the distribution of angular displacement were used to revel the difference in local dynamics between branch point and the arm＇s end. It is discovered that the local dynamics at the core of the star polymer is much less activated than that at the arm＇s end. The results demonstrate the strong effect dues to the topological constrain at the branch point and the more free space at the arm＇s end.

Synthesis and MALDI-TOF Characterization of β-CD Core ATRP Initiators and RAFT Chain Transfers with Different Degrees of Substitution

In this paper, three different kinds of β-CD derivatives were synthesized as atom transfer radical polymerization（ATRP） initiator or reversible addition-fragmentation chain transfer polymerization（RAFT） chain transfers. The degree of substitution for each derivative was carefully characterized through 1H-NMR, 13C-NMR spectroscopy and matrix-assisted laser desorption/ionization time of flight mass spectrometry（MALDI-TOF-MS）. The factors influencing the degree of substitution were discussed. Moreover, the comparison between ATRP and RAFT was shown in the polymerization of Nisopropyl acrylamide（NIPAM）.

Synthesis of mid-dicarboxy polystyrene by ATRP and formation of ionic-bonded supramolecules

Dimethyl 4,6-bis(bromomethyl)isophthalate was synthesized by bromomethylation,oxidation,esterification and bromination of 1,3-dimethylbenzene.This was used to initiate the atom transfer radical polymerization of styrene successfully.Results showed that the process had some of the good characteristics of controlled/living free radical poly-merization.The molecular weight of the obtained polymer increased linearly with monomer conversion,its molecular weight distribution was very narrow,and a linear relationship between ln([M]0/[M])and polymerization time was found.A well-defined novel structural polystyrene containing two ester groups in the mid-main chain was prepared with con-trolled molecular weight and narrow polydispersity.The structure of the polymer was confirmed by 1H-NMR spectra.After being hydrolyzed,dicarboxy polystyrene was obtained and used to form ionic-bonded supramolecules with 1-dodecanamine as a model of the star-shaped supramolecules.The supramolecules formed were characterized by Fourier transform infrared(FTIR)spectrum.