The comonomer inducing selective β‐methyl elimination chain transfer: A new approach for end‐functionalizations of syndiotactic polypropylene‐based copolymers

The end‐functionalization of syndiotactic polypropylene‐based copolymers can be accomplished by conducting propylene polymerization in the presence of norbornene using Me₂C(Cp)(Flu)ZrCl₂/MAO as the catalyst. The detailed structural analyses clearly reveal the occurrence of the β‐methyl elimination chain transfer reaction that leads to the generation of the ethenyl group end‐capped syndiotactic polypropylene‐based propylene–norbornene copolymer. Subsequently, the ethenyl group end‐capped copolymer can be used for the preparation of other end‐functionalized syndiotactic polypropylene‐based copolymers by conducting organic functional group transformation reactions. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2167–2176, 2008     

End‐functionalization of isotactic polypropylene via consecutive chain transfer reaction to norbornadiene and hydrogen

Structurally well‐defined end functionalized isotactic polypropylene (iPP) is prepared by conducting a selective chain transfer reaction during the isospecific polymerization of propylene in the presence of norbornadiene (NBD) and hydrogen using rac‐Me₂Si(2‐Me‐4‐Ph‐Ind)₂ ZrCl₂/MAO as the catalyst. The production of NBD‐capped iPP involves a unique consecutive chain transfer reaction, first to NBD and then to hydrogen, for situating the incorporated NBD at the iPP chain end. The NBD end group of NBD‐capped iPP can be converted into other reactive functional group through functional group transformation reactions. The resulting functional group end‐capped iPP can be used for the construction of stereoregular block copolymers (e.g., iPP‐b‐PMMA and iPP‐b‐PS) through postpolymeriztion reactions. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Ethylene–propylene copolymerization behavior of ansa‐dimethylsilylene(fluorenyl)(amido)dimethyltitanium complex: Application to ethylene–propylene–diene or ethylene–propylene–norbornene terpolymers

Copolymerization behavior of ethylene (E) and propylene (P) using ansa‐dimethylsilylene(fluorenyl)(amido)dimethyltitanium complex was investigated. P was more reactive than E regardless of the chain‐end monomer unit, which was very unusual in the coordination polymerization system. The terpolymerizations of E, P and norbornene (NB) or 5‐ethylidene‐2‐norbornene (5E2N) were also performed. The each content in the E/P/NB terpolymer was independently controlled by the initial concentration of NB and E/P feed ratio. Glass transition temperature (T_g) of the terpolymer was raised in proportion to the NB content and close to that of the corresponding NB/E random copolymer with the same NB content. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 685–691     

Homo‐ and copolymerization of ethylene and norbornene with bis(β‐diketiminato) titanium complexes activated with methylaluminoxane

Homo‐ and copolymerization of ethylene and norbornene were investigated with bis(β‐diketiminato) titanium complexes [ArNC(CR₃)CHC(CR₃)NAr]₂TiCl₂ (R = F, Ar = 2,6‐diisopropylphenyl 2a; R = F, Ar = 2,6‐dimethylphenyl 2b ; R = H, Ar = 2,6‐diisopropylphenyl 2c ; R = H, Ar = 2,6‐dimethylphenyl 2d) in the presence of methylaluminoxane (MAO). The influence of steric and electric effects of complexes on catalytic activity was evaluated. With MAO as cocatalyst, complexes 2a–d are moderately active catalysts for ethylene polymerization producing high‐molecular weight polyethylenes bearing linear structures, but low active catalysts for norbornene polymerization. Moreover, 2a – d are also active ethylene–norbornene (E–N) copolymerization catalysts. The incorporation of norbornene in the E–N copolymer could be controlled by varying the charged norbornene. ¹³C NMR analyses showed the microstructures of the E–N copolymers were predominantly alternated and isolated norbornene units in copolymer, dyad, and triad sequences of norbornene were detected in the E–N copolymers with high incorporated content of norbornene. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 93–101, 2008     

Facile postpolymerization end‐modification of RAFT polymers

One‐pot methods for the end‐group postpolymerization modification of reversible addition fragmentation chain transfer (RAFT) derived polymers were investigated. Dithioester‐terminated polymers were transformed into ω‐functionalized polymers through conjugate addition of a variety of acrylates with an intermediate thiol. These methods provide a versatile means of introducing a variety of functionalities onto the polymer terminus, while simultaneously removing the residual dithiobenzoate group. A series of functionalized polymethylmethacrylate‐b‐polystyrene (PMMA‐b‐PS) polymers were synthesized utilizing the developed methods to probe the effect of charged end groups on diblock copolymer phase separation in thin films. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 346–356, 2009     

Linear pentablock quintopolymers (l‐SIDMV) with five incompatible blocks: Polystyrene,polyisoprene‐1,4, poly(dimethylsiloxane), poly(tert‐butyl methacrylate), and poly(2‐vinylpyridine)

Three linear pentablock quintopolymers (l‐SIDMV), where S is polystyrene (PS), I polyisoprene‐1,4 (PI), D poly(dimethylsiloxane) (PDMS), M poly(tert‐butyl methacrylate) (PtBuM), and V poly(2‐vinylpyridine) (P2VP), were synthesized by anionic polymerization high vacuum techniques. The approach involves the following: (a) The synthesis of living triblock terpolymer PS‐b‐PI‐b‐PDMSLi and diblock copolymer P2VP‐b‐PtBuMK by sequential polymerizations of the corresponding monomers with sec‐BuLi and benzyl potassium, respectively; and (b) The selective linking of the living triblock terpolymer with the chlorosilane group of 2‐(chloromethylphenyl)ethyldimethylchlorosilane (CMPDMS), followed by linking of the living block copolymer with the remaining chloromethyl group of CMPDMS. Molecular characterization carried out by size exclusion chromatography, membrane osmometry, solution (in CDCl₃ or d₈‐toluene) and solid‐state ¹H‐NMR spectroscopy indicated a high degree of molecular and compositional homogeneity. Differential scanning calorimetry results on the precursors and final polymers were discussed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3938–3946, 2008     

Radiation‐induced fabrication of polymer nanoporous materials from microphase‐separated structure of diblock copolymers as a template

Polymer nanoporous materials with periodic cylindrical holes were fabricated from microphase‐separated structure of diblock copolymers consisting of a radiation‐crosslinking polymer and a radiation‐degrading polymer through simultaneous crosslinking and degradation by γ‐irradiation. A polybutadiene‐block‐poly(methyl methacrylate) (PB‐b‐PMMA) diblock copolymer film that self‐assembles into hexagonally packed poly(methyl methacrylate) cylinders in polybutadiene matrix was irradiated with γ‐rays. Solubility test, IR spectroscopy, and TEM and SEM observations for this copolymer film in comparison with a polystyrene‐block‐poly(methyl methacrylate) diblock copolymer film revealed that poly(methyl methacrylate) domains were removed by γ‐irradiation and succeeding solvent washing to form cylindrical holes within polybutadiene matrix, which was rigidified by radiation crosslinking. Thus, it was demonstrated that nanoporous materials can be prepared by γ‐irradiation, maintaining the original structure of PB‐b‐PMMA diblock copolymer film. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5916–5922, 2007     

Synthesis,characterization, and self‐assembly of ion‐bonded A2B rod‐coil copolymer with oligo(para‐phenyleneethynylene) as rod segment

Supramolecular A₂B rod‐coil copolymer, composed of two polystyrene (PSt) arms and one oligo(para‐phenyleneethynylene) (OPE) arm linked via ionic bond, has been designed and successfully synthesized. First, a trifunctional initiator, methyl 1,3‐bis(bromomethyl)benzonate, was prepared and used to initiate the polymerization of styrene under atom transfer radical polymerization (ATRP) condition to provide polystyrene (PSt) carrying monoester group at the middle of polymer chain. Then, the ester group was transferred into tertiary amino group to give amino‐functionalized PSt, (PSt)₂? N(CH₃)₂. Subsequently, the ion‐bonded rod‐coil copolymer, (PSt)₂? OPE, was obtained by the reaction of (PSt)₂? N(CH₃)₂ with carboxy‐terminated OPE (OPE? COOH). The resulting copolymer was characterized by nuclear magnetic resonance (NMR), Fourier transformer infrared (FTIR), and gel permeation chromatography (GPC) techniques. Vesicles and spherical micelles were generated from this supramolecular rod‐coil copolymer through the manipulation of the initial polymer concentration in toluene. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7667–7676, 2008     

Influence of the stirring speed and CaCl2 concentration on the nano‐object morphologies obtained via RAFT‐mediated aqueous emulsion polymerization in the presence of a water‐soluble macroRAFT agent

Aqueous emulsion polymerizations of styrene were performed in the presence of a macromolecular reversible addition‐fragmentation chain transfer (RAFT) agent (macroRAFT) composed of acrylic acid (AA) and poly(ethylene oxide) methyl ether acrylate (PEOA), end‐capped by a reactive dodecyl trithiocarbonate group (P(AA‐co‐PEOA)‐TTC). The influence of the stirring speed or the presence of different amounts of a divalent salt, CaCl₂, were investigated in this polymerization‐induced self‐assembly process, in which spherical and nonspherical nano‐objects were formed upon the synthesis of amphiphilic diblock copolymers in situ. It appeared that the addition of CaCl₂ led to the controlled formation of different nano‐objects such as spheres, fibers or vesicles, whereas an appropriate stirring speed was required for the formation of nanofibers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Light‐driven and aggregation‐induced emission from side‐chain azoindazole polymers

The well‐defined azoindazole‐containing homopolymer, poly(6‐{6‐[(4‐dimethylamino) phenylazo]‐indazole}‐hexyl methacrylate) (PDHMA), and amphiphilic diblock copolymer, poly({6‐[6‐(4‐dimethylamino)phenylazo]‐indazole}‐hexyl methacrylate)‐b‐poly(2‐(dimethylamino)ethylmethacrylate) (PDHMA_m‐b‐PDMAEMA_n), were successfully prepared via reversible addition‐fragmentation chain transfer polymerization technique. The homopolymer and amphiphilic diblock copolymer in CH₂Cl₂ exhibited intense fluorescence emission accompanied by trans–cis photoisomerization of azoindazole group under UV irradiation. The experiment results indicated that the intense fluorescence emission may be attributed to an inhibition of photoinduced electron transfer of the cis form of azoindazole. On the other hand, the intense fluorescence emission of amphiphilic diblock copolymers in water‐tetrahydrofuran mixture was observed, which increased with the volume ratio of water in the mixed solvent. The self‐aggregation behaviors of three amphiphilic diblock copolymers were examined by transmission electron microscopy, laser light scattering, and UV–vis spectra. The restriction of intramolecular rotation of the azoindazole groups in aggregates was considered as the main cause of aggregation‐induced fluorescence emission. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Block and star block copolymers by mechanism transformation 9: Preparation and characterization of poly(methyl methacrylate)/poly(1,3‐dioxepane)/polystyrene ABC miktoarm star copolymers by combination of reversible addition–fragmentation chain‐transfer polymerization and cationic ring‐opening polymerization

The miktoarm ABC star copolymer with three different branches, polystyrene (PS), poly(1,3‐dioxepane) (PDOP), and poly(methyl methacrylate) (PMMA), was successfully prepared. PS with two transfer groups, hydroxyl and dithiobenzoate groups [PS‐HECA‐SC(S)Ph], was synthesized by the reaction of a dithiobenzoate group at the end of PS with hydroxyethylene cinnamate (HECA) in tetrahydrofuran solution. Then, the cationic ring‐opening polymerization of 1,3‐dioxepane was initiated by triflic acid in the presence of PS‐HECA‐SC(S)Ph and diblock copolymer, PS‐PDOP, was formed. Finally, the diblock copolymer with the dithiobenzoate group situated between the two blocks was used in the reversible addition–fragmentation transfer (RAFT) process of methyl methacrylate (MMA). The miktoarm ABC star copolymer S(PS)(PDOP)(PMMA) was characterized by ¹H NMR spectroscopy and gel permeation chromatography. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1243–1250, 2003     

High‐Density Liquid‐Crystalline Polymer Brushes Formed by Surface Segregation and Self‐Assembly

High‐density polymer brushes on substrates exhibit unique properties and functions stemming from the extended conformations due to the surface constraint. To date, such chain organizations have been mostly attained by synthetic strategies of surface‐initiated living polymerization. We show herein a new method to prepare a high‐density polymer brush architecture using surface segregation and self‐assembly of diblock copolymers containing a side‐chain liquid‐crystalline polymer (SCLCP). The surface segregation is attained from a film of an amorphous base polymer (polystyrene, PS) containing a minor amount of a SCLCP‐PS diblock copolymer upon annealing above the glass‐transition temperature. The polystyrene portion of the diblock copolymer can work as a laterally mobile anchor for the favorable self‐assembly on the polystyrene base film.     

Radical‐cured block copolymer‐modified thermosets

Poly(ethylene‐alt‐propylene)‐b‐poly(ethylene oxide) (PEP‐PEO) diblock copolymers were synthesized and added at 4 wt % to 2,2‐bis[4‐(2‐hydroxy‐3‐methacryloxypropoxy)phenyl]propane (BisGMA), a monomer that cures using free radical chemistry. In separate experiments, poly(ethylene glycol) dimethacrylate (PEGDMA) was combined as a secondary monomer with BisGMA and the monomers were loaded with 4 wt % PEP‐PEO. The diblock copolymers self‐assembled into well‐dispersed spherical micelles with PEP cores and PEO coronas. No appreciable change in the final extent of cure of the thermosets was caused by the addition of diblock copolymer, except in the case of BisGMA, where the addition of the block copolymer increased extent of cure by 12%. Furthermore, the extent of cure was increased by 29% and 37% with the addition of 25 and 50 wt % PEGDMA, respectively. Elastic modulus and fracture resistance were also determined, and the values indicate that the addition of block copolymers does not significantly toughen the thermoset materials. This finding is surprising when compared with the large increase in fracture resistance seen in block copolymer‐modified epoxies, and an explanation is proposed. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Control of pore size and pore uniformity in films based on self‐assembling block copolymers

Blends of self‐assembling polystyrene‐block‐poly(4‐vinyl pyridine) (PS‐b‐P4VP) diblock‐copolymers and poly(4‐vinyl pyridine) (P4VP) homopolymers were used to fabricate isoporous and nanoporous films. Block copolymers (BCP) self‐assembled into a structure where the minority component forms very uniform cylinders, while homopolymers, resided in the core of the cylinders. Selective removal of the homopolymers by ethanol immersion led to the formation of well‐ordered pores. In films without added homopolymer, just immersion in ethanol and subsequent swelling of the P4VP blocks was found to be sufficient to create pores. Pore sizes were tuned between 10 and 50 nm by simply varying the homopolymer content and the molecular weight of the block‐copolymer. Uniformity was lost when the average pore size exceeded 30 nm because of macrophase separation. However, preparation of films from low M_W diblock copolymers showed that it is possible to have excellent pore size control and a high porosity, while retaining a low pore size distribution. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1568–1579     

Synthesis and micellization of PSt‐PNIPAM‐PDMAEMA hetero‐arm star polymer with double thermo‐responsibility

A hetero‐arm star polymer, polystyrene‐poly(N‐isopropylacrylamide)‐ poly(2‐(dimethylamino)ethylmethacrylate) (PSt‐PNIPAM‐PDMAEMA), was synthesized by “clicking” the alkyne group at the junction of PSt‐b‐PNIPAM diblock copolymer onto the azide end‐group of PDMAEMA homopolymer via 1,3‐dipolar cycloaddition. The resultant polymer was characterized by gel permeation chromatography, proton nuclear magnetic resonance spectroscopy and Fourier transform infrared spectroscopy. PSt‐PNIPAM‐PDMAEMA micelles with PSt block as core and PNIPAM and PDMAEMA blocks as shell were formed when adding the copolymer solution in THF into 10 folds of water. Lower critical solution temperature (LCST) of PNIPAM and PDMAEMA homopolymer is 32 °C for PNIPAM and 40 to 50 °C for PDMAEMA, respectively. Upon continuous heating through their LCSTs, PSt‐PNIPAM‐PDMAEMA core‐shell micelles exhibited two‐stage thermally induced collapse. The first‐stage collapse, from 20 to 34 °C, is ascribed to the shrinkage of PNIPAM chains; and the second‐stage collapse, from 38 to 50 °C, is due to the shrinkage of PDMAEMA chains. Dynamic light scattering was used to confirm the double phase transitions. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 786–796, 2009     

Polymerization‐induced self‐assembly of block copolymer through dispersion RAFT polymerization in ionic liquid

Polymerization‐induced self‐assembly of block copolymer through dispersion RAFT polymerization has been demonstrated to be a valid method to prepare block copolymer nano‐objects. However, volatile solvents are generally involved in this preparation. Herein, the in situ synthesis of block copolymer nano‐objects of poly(ethylene glycol)‐block‐polystyrene (PEG‐b‐PS) in the ionic liquid of 1‐butyl‐3‐methylimidazolium hexafluorophosphate ([BMIN][PF₆]) through the macro‐RAFT agent mediated dispersion polymerization is investigated. It is found that the dispersion RAFT polymerization of styrene in the ionic liquid of [BMIN][PF₆] runs faster than that in the alcoholic solvent, and the dispersion RAFT polymerization in the ionic liquid affords good control over the molecular weight and the molecular weight distribution of the PEG‐b‐PS diblock copolymer. The morphology of the in situ synthesized PEG‐b‐PS diblock copolymer nano‐objects, e.g., nanospheres and vesicles, in the ionic liquid is dependent on the polymerization degree of the solvophobic block and the concentration of the fed monomer, which is somewhat similar to those in alcoholic solvent. It is anticipated that the dispersion RAFT polymerization in ionic liquid broads a new way to prepare block copolymer nano‐objects. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1517–1525     

Synthesis,characterization, and property of amphiphilic fluorinated abc‐type triblock copolymers

Novel amphiphilic fluorinated ABC‐type triblock copolymers composed of hydrophilic poly(ethylene oxide) monomethyl ether (MeOPEO), hydrophobic polystyrene (PSt), and hydrophobic/lipophobic poly(perfluorohexylethyl acrylate) (PFHEA) were synthesized by atom transfer radical polymerization (ATRP) using N,N,N′,N″,N″‐pentamethyldiethylenetriamine (PMDETA)/CuBr as a catalyst system. The bromide‐terminated diblock copolymers poly(ethylene oxide)‐block‐polystyrene (MeOPEO‐b‐PSt‐Br) were prepared by the ATRP of styrene initiated with the macroinitiator MeOPEO‐Br, which was obtained by the esterification of poly(ethylene oxide) monomethyl ether (MeOPEO) with 2‐bromoisobutyryl bromide. A fluorinated block of poly(perfluorohexylethyl acrylate) (PFHEA) was then introduced into the diblock copolymer by a second ATRP process to synthesize a novel ABC‐type triblock copolymer, poly(ethylene oxide)‐block‐polystyrene‐block‐poly(perfluorohexylethyl acrylate) (MeOPEO‐b‐PSt‐b‐PFHEA). These block copolymers were characterized by means of proton nuclear magnetic resonance (¹H NMR) and gel permeation chromatography (GPC). Water contact angle measurements revealed that the polymeric coating of the triblock copolymer (MeOPEO‐b‐PSt‐b‐PFHEA) shows more hydrophobic than that of the corresponding diblock copolymer (MeOPEO‐b‐PSt). Bovine serum albumin (BSA) was used as a model protein to evaluate the protein adsorption property and the triblock copolymer coating posseses excellent protein‐resistant character prior to the corresponding diblock copolymer and polydimethylsiloxane. These amphiphilic fluoropolymers can expect to have potential applications for antifouling coatings and antifouling membranes. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

NIR light and enzyme dual stimuli‐responsive amphiphilic diblock copolymer assemblies

Using atom transfer radical polymerization (ATRP) and macromolecular azo coupling reaction, both o‐nitrobenzyl (ONB) group and azobenzene group were efficiently incorporated into the center of the amphiphilic diblock copolymer chain. The prepared diblock copolymer was well characterized by UV–vis, ¹H NMR, and GPC methods. Self‐assembly of the amphiphilic copolymer in selected solvents can result in uniform self‐assembly aggregates. In the presence of external stimuli [upconversion nanoparticles (UCNPs)/NIR light or enzyme], the amphiphilic diblock copolymer chain could be broken by the cleavage of ONB or azobenzene group, which would lead to the disruption of the self‐assembly aggregates. This photo‐ and enzyme‐triggered disruption process was proved by using transmission electron microscopy (TEM) and GPC method. Fluorescence emission spectra measurements indicated that the release of Nile red, a hydrophobic dye, encapsulated by the self‐assembly aggregates, could be successfully realized under the NIR light and enzyme stimuli. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2450–2457     

Synthesis and characterization of PEE‐PEO diblock copolymers with complementary end‐groups for hydrogen‐bond heteroassociation

Poly(ethylethylene‐b‐ethylene oxide) (PEE‐PEO) diblock copolymers with pyridine‐benzoic acid end‐groups for heterodimeric hydrogen bonding were designed as a possible means to noncentrosymmetric organizations by spontaneous self‐assembly. These end‐functionalized polymers were synthesized by anionic living polymerization with protected initiator and terminating reagents. A series of polymeric intermediates with different end‐groups was characterized by proton nuclear magnetic resonance, matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry, and gel permeation chromatography. Preliminary studies of solid‐state organization by differential scanning calorimetry and small‐angle X‐ray scattering provided evidence for a long‐range order that was sensitive to chain length, copolymer composition, and end‐group structure. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 207–219, 2000     

Effect of binary block‐selective solvents on self‐assembly of ABA triblock copolymer in dilute solution

We have studied the self‐assembly of the ABA triblock copolymer (P4VP‐b‐PS‐b‐P4VP) in dilute solution by using binary block‐selective solvents, that is, water and methanol. The triblock copolymer was first dissolved in dioxane to form a homogeneous solution. Subsequently, a given volume of selective solvent was added slowly to the solution to induce self‐assembly of the copolymer. It was found that the copolymer (P4VP₄₃‐b‐PS₃₆₆‐b‐P4VP₄₃) tended to form spherical aggregate or bilayer structure when we used methanol or water as the single selective solvent, respectively. However, the aggregates with various nanostructures were obtained by using mixtures of water and methanol as the block‐selective solvents. The aggregate structure changed from sphere to rod, vesicle, and then to bilayer by changing water content in the block‐selective solvent from 0 to 100%. Moreover, it was found that the vesicle size could be well controlled by changing the copolymer content in the solution. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1536–1545, 2008