Synthesis of densely grafted comblike copolymers

Densely grafted copolymers were synthesized using the “grafting from” approach via the combination of reversible addition‐fragment chain transfer polymerization (RAFT) and atom transfer radical polymerization (ATRP). First, a novel functional monomer, 2,3‐di(2‐bromoisobutyryloxy)ethyl acrylate (DBPPA), with two initiating groups for ATRP was synthesized. It was then polymerized via RAFT polymerization to give macroinitiators for ATRP with controlled molecular weights and narrow molecular weight distributions. Last, ATRP of styrene was carried out using poly(DBPPA)s as macroinitiators to prepare comblike poly(DBPPA)‐graft‐polystyrenes carrying double branches in each repeating unit of backbone via “grafting from” approach. Furthermore, poly(DBPPA)‐graft‐[polystyrene‐block‐poly(t‐BA)]s and their hydrolyzed products poly(DBPPA)‐graft‐[polystyrene‐block‐poly(acrylic acid)]s were also successfully prepared. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 362–372, 2008     

Morphology and physical properties of triblock copolymers with crystalline end blocks

The morphology of crystalline end-block copolymers of poly(thiacyclobutane-b-isoprene-b-thiacyclobutane) (TCB–I–TCB) was studied by optical microscopy, electron microscopy, and small-angle x-ray scattering (SAXS). A spherulitic texture was observed for both the TCB homopolymer and the TCB–I–TCB block copolymers. Well-defined phases arranged in an ordered structure exist when the films are cast above the melting temperature of the crystalline end blocks. The dimensions and the arrangements of the domains have been derived from both SAXS and electron microscope measurements. The deformation mechanism of the 41% end-block copolymer sample was also examined by a combination of SAXS and stress–strain studies. It was found that the interdomain spacing increased along the stretching direction as the extension ratio was increased. The morphology changes from hexagonally packed cylinders to rowtype cylinders upon the application of stress.     

Synthesis of well-defined ABC triblock copolymers with polypeptide segments by ATRP and click reactions

Well-defined ABC block copolymers consisting of poly(ethylene oxide) monomethylene ether (MPEO) as A block, poly(styrene) (PS) as B block and poly(γ-benzyl-l-glutamate) (PBLG) as C block were synthesized by the combination of atom transfer radical polymerization (ATRP) and click reactions. The bromine-terminated diblock copolymer poly(ethylene oxide) monomethylene ether-block-poly(styrene) (MPEO-PS-Br) was prepared by ATRP of styrene initiated with macro-initiator MPEO-Br, which was prepared from the esterification of MPEO and 2-bromoisobutyryl bromide, and converted into the azido-terminated diblock copolymer MPEO-PS-N₃ by simple nucleophilic substitutions in DMF in the presence of sodium azide. Propargyl-terminated PBLGs were synthesized by ring-opening polymerization of γ-benzyl-l-glutamate-N-carboxyanhydride in DMF at room temperature using propargyl amine as an initiator. ABC triblock copolymers MPEO-PS-PBLG with a wide range of number-average molecular weights from 1.55 to 3.75 × 10⁴ and a narrow polydispersity from 1.07 to 1.10 were synthesized via the click reaction of MPEO-PS-N₃ and the propargyl-terminated PBLG in the presence of CuBr and 1,1,4,7,7-pentamethyldiethylenetriamine (PMDETA) catalyst system. The structures of these ABC block copolymers and corresponding precursors were characterized by NMR, IR and GPC. The results showed that click reaction was efficient. Therefore, a facile approach was offered to synthesize ABC triblock copolymers composed of crystallizable polymer MPEO, conventional vinylic polymer PS and rod-like α-helix polypeptide PBLG.     

Synthesis of graft copolymers with polyisobutylene branch chains

<正>The copolymerization of 4-vinylbenzyl chloride(VBC) and vinyl acetate(VAC) was carried out in toluene at 75℃via radical polymerization using 2,2'-azo-bis-(isobutyronitrile)(AIBN) as an initiator.The random copolymers of poly(4-vinylbenzyl chloride-co-vinyl acetate)(P(VBC-co-VAC)) with number average molecular weight(M_n) from 2000 to 6900,relatively narrow molecular weight distribution(MWD,M_w/M_n ca.2.0) and with different copolymer composition of 4-vinylbenzyl chloride(VBC) from 17 mol%to 62 mol%could be obtained.The P(VBC-co-VAC) copolymers with an average number of 7 to 13 initiating sites of benzyl chloride per macromolecule could be used for the cationic polymerization of isobutylene(IB).The cationic polymerizations of IB were further conducted by using P(VBC-co-VAC) copolymers as macroinitiators in conjunction with TiCl_4 at -40℃in CH_2Cl_2.The effects of VBC/TiCl_4(molar ratio) on monomer conversion,M_n and MWD of the resultant copolymers were investigated under 3 sets of conditions.It is found that P(VBC-co-VAC)-g-PIB copolymers with relatively narrow MWD(M_w/M_n ca.2.0) and with terminal tert-chlorine functional groups in branched PIB chains could be successfully synthesized when VBC/TiCl_4(molar ratio) was set in the range from 0.10 to 1.12.The unimodal GPC curve of the P(VBC-co-VAC)-g-PIB copolymers by RI detector was almost in harmony with the GPC curve by UV detector.The TEM image of the P(VBC-co-VAC)-g-PIB copolymer stained by RuO indicated that the copolymer formed a two-phase morphology with P(VBC-co-VAC)-rich domains of 20-100 nm in size tethered by PIB branch segments.     

Molecular and morphological characterization of midblock‐sulfonated styrenic triblock copolymers

Midblock‐sulfonated triblock copolymers afford a desirable opportunity to generate network‐forming amphiphilic materials that are suitable for use in a wide range of emerging technologies as fuel‐cell, water‐desalination, ion‐exchange, photovoltaic, or electroactive membranes. Employing a previously reported synthetic strategy wherein poly(p‐tert‐butylstyrene) remains unreactive, we have selectively sulfonated the styrenic midblock of a poly(p‐tert‐butylstyrene‐b‐styrene‐b‐p‐tert‐butylstyrene) (TST) triblock copolymer to different extents. Comparison of the resulting sulfonated copolymers with results from our prior study provides favorable quantitative agreement and suggests that a shortened reaction time is advantageous. An ongoing challenge regarding the morphological development of charged block copolymers is the competition between microphase separation of the incompatible blocks and physical cross‐linking of ionic clusters, with the latter often hindering the former. Here, we expose the sulfonated TST copolymers to solvent‐vapor annealing to promote nanostructural refinement. The effect of such annealing on morphological characteristics, as well as on molecular free volume, is explored. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 490–497     

Synthesis of 1-chloro-1-phenylethyl-telechelic polyisobutylene,a new potential macroinitiator by living cationic polymerization

1-Chloro-1-phenylethyl-telechelic polyisobutylene (PIB) was synthesized by living carbocationic polymerization (LCCP). LCCP of isobutylene was induced by a difunctional initiator in conjunction with TiCl₄ as coinitiator in the presence of N,N-dimethylacetamide in CH₂Cl₂/hexane (40:60 v/v) solvent mixture at −78°C. After complete isobutylene conversion a small amount of styrene was added leading to a rapid crossover reaction and thus to the attachment of short outer polystyrene (PSt) blocks to the PIB segment. Quenching the living polymerization of styrene yielded 1-chloro-1-phenylethyl terminal groups. The resulting telechelic polymer (Cl-PSt-PIB-PSt-Cl) is a potential new macroinitiator for atom transfer radical polymerization of a variety of vinyl monomers.     

Synthesis of PDMAEMA-PCL-PDMAEMA triblock copolymers

The synthesis of ABA triblock copolymers of the type PDMAEMA-PCL-PDMAEMA was achieved by atom transfer radical polymerization (ATRP) of DMAEMA using difunctional polycaprolactone (PCL) as macroinitiator. First, ring-opening polymerization (ROP) of ε-caprolactone (ε-CL) was carried out in the presence of 1,2-diaminoethane/tin (II) octanoate. Dihydroxy PCL thus obtained was end-functionalized in a quantitative manner using 2-bromoisobutyryl bromide. The resulting Br-PCL-Br was used as macroinitiator in the ATRP of DMAEMA leading to triblock copolymers with PCL as the central block and PDMAEMA sequences of different lengths. NMR and SEC analyses confirmed the formation of ABA triblocks.     

Synthesis and characterization of a new fluorinated macroinitiator and its diblock copolymer by AGET ATRP

A new fluorinated macroinitiator of poly 2,2,3,4,4,4-hexafluorobutyl methacrylate-Br (PHFMA-Br) was prepared via activator generated by electron transfer atom transfer radical polymerization (AGET ATRP), and then a series of fluorinated block copolymers with different fluorine content were successfully synthesized from the macroinitiator by the second step AGET ATRP. GPC, FTIR and ¹H NMR data obtained verified the synthesis. Contact angle measurement indicated that proper fluorine content could decrease the surface energy and increase the contact angle of the copolymer films. XPS characterization showed that the large difference in surface energy between the block and random copolymer film resulted from the difference of the fluorine content on the surface, although the fluorine content of the two copolymers in bulk was similar. The self-assembly behavior of the fluorinated block copolymer in selective solvents was evaluated by the TEM study, and the stable micelles with a core-shell structure were observed when the copolymer content was about 1 wt%.     

Diblock and triblock copolymers of styrene and acetoxymethylstyrene by one‐pot ATRP

We describe the synthesis of diblock and triblock copolymers by sequential atom transfer radical polymerization of styrene and acetoxymethylstyrene. Contrary to the usual block copolymerization involving isolation of the macroinitiator, a convenient one‐pot procedure is developed. This is possible because of the preferential polymerization of acetoxymethylstyrene, even in the presence of residual styrene, as inferred from characterization of the intermediate polystyrenes and the block copolymers by size exclusion chromatography, ¹H NMR, Fourier transform infrared spectroscopy, differential scanning calorimetry, and GPEC techniques. The latent acetoxy functionalities in these block copolymers are shown to be easily unmasked to ? OH and ? Br functionalities, with the potential for block ionomers and dense graft architectures. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 575–583, 2005     

Enhancement of mechanical properties of triblock copolymers by random copolymer middle blocks

Symmetric styrene-b-styrene-co-butadiene-b-styrene (S-SB-S) tri-block copolymers with varying middle and outer block composition have been studied. We report our findings based on a systematic variation of the effective interaction parameter (χ) by adjusting the composition of the random copolymer in the middle block and of the outer blocks (in terms of PS-chain length) which allows us to explore the χ-parameter space with regard to molecular architecture more thoroughly than in SBS triblock copolymers. A variation in the S/B middle block composition or in the PS outer block content leads to a change in phase behaviour and morphology simultaneously accompanied by significant changes in mechanical properties, varying from elastomeric to thermoplastic property profile. Despite high PS contents of 55-75 wt.% these S-SB-S triblock copolymers reveal high strain at break values between 650% and 350% which is in striking contrast to the conventional SBS triblock copolymers where only about 10% strain at break have been reported to be achieved with similar PS-content (∼75 wt.%).     

Thermoresponsive star triblock copolymers by combination of ROP and ATRP: From micelles to hydrogels

Novel biocompatible, biodegradable, four‐arm star, triblock copolymers containing a hydrophobic poly(ε‐caprolactone) (PCL) segment, a hydrophilic poly(oligo(ethylene oxide)475 methacrylate) (POEOMA475) segment and a thermoresponsive poly(di(ethylene oxide) methyl ether methacrylate) (PMEO₂MA) segment were synthesized by a combination of controlled ring‐opening polymerization (ROP) and atom transfer radical polymerization (ATRP). First, a four‐arm PCL macroinitiator [(PCL‐Br)₄] for ATRP was synthesized by the ROP of ε‐caprolactone (CL) catalyzed by stannous octoate in the presence of pentaerythritol as the tetrafunctional initiator followed by esterification with 2‐bromoisobutyryl bromide. Then, sequential ATRP of oligo(ethylene oxide) methacrylate (OEOMA475, M_n = 475) and di(ethylene oxide) methyl ether methacrylate) (MEO₂MA) were carried out using the (PCL‐Br)₄ tetrafunctional macroinitiator, in different sequence, resulting in preparation of (PCL‐b‐POEOMA475‐b‐PMEO₂MA)₄ and (PCL‐b‐PMEO₂MA‐b‐POEOMA475)₄ star triblock copolymers. These amphiphilic copolymers can self‐assemble into spherical micelles in aqueous solution at room temperature. The thermal responses of the polymeric micelles were investigated by dynamic light scattering and ultraviolet spectrometer. The properties of the two series of copolymers are quite different and depend on the sequence distribution of each block along the arms of the star. The (PCL‐b‐POEOMA475‐b‐PMEO₂MA)₄ star copolymer, with the thermoresponsive PMEO₂MA segment on the periphery, can undergo reversible sol‐gel transitions between room temperature (22 °C) and human body temperature (37 °C). © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis and characterization of thermoplastic elastomers with polyisobutylene and polyalloocimene blocks

This article presents the synthesis and characterization of diblock, triblock, and tetrablock copolymers of alloocimene (Allo), a terpene from renewable resources, and isobutylene (IB) using the recently reported two‐phase living carbocationic system. The addition of a second Allo increment to diblocks of Allo and IB yielded triblock and tetrablock structures. The block copolymers showed thermoplastic elastomeric (TPE) properties. It is demonstrated that the unusual behavior of diblocks exhibiting TPE properties is due to the strain‐induced crystallization of the polyisobutylene block. The polyalloocimene blocks can be cured, making this material a potential replacement of halobutyl rubber without halogen content. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1567–1574     

Synthesis and characterization of conjugated triblock copolymers

A series of conjugated triblock copolymers containing hole-transporting polycarbazole segments, electron-transporting polyoxadiazole segments, and blue-light-emitting polyfluorene segments were prepared with a two-step palladium-catalyzed Suzuki polycondensation (SPC). First dibromo-terminated polymer precursors (polyfluorenes and polyoxadiazoles) were synthesized as the central buildingblocks. Then, the dibromo-terminated polymer precursors were further polymerized with AB-type monomers [2-bromo-7-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9-octylcarbazole, 3-bromo-6-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9-octylcarbazole, and 2-bromo-7-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9,9-dioctylfluorene] to achieve the target triblock copolymers under SPC conditions. The formation of the triblock copolymers was confirmed by gel permeation chromatography and NMR spectroscopy. The triblock copolymers exhibited good thermal stability. An investigation of the photophysical properties indicated that efficient, photoinduced through-bond energy transfer occurred in such triblock copolymer systems. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2410–2424, 2007     

One‐step synthesis of hyperbranched polyethylene macroinitiator and its block copolymers with methyl methacrylate or styrene via ATRP

Block copolymers of hyperbranched polyethylene (PE) and linear polystyrene (PS) or poly(methyl methacrylate) (PMMA) were synthesized via atom transfer radical polymerization (ATRP) with hyperbranched PE macroinitiators. The PE macroinitiators were synthesized through a “living” polymerization of ethylene catalyzed with a Pd‐diimine catalyst and end‐capped with 4‐chloromethyl styrene as a chain quenching agent in one step. The macroinitiator and block copolymer samples were characterized by gel permeation chromatography, ¹H and ¹³C NMR, and differential scanning calorimetry. The hyperbranched PE chains had narrow molecular weight distribution and contained a single terminal benzyl chloride per chain. Both hyperbranched PE and linear PS or PMMA blocks had well‐controlled molecular weights. Slow initiation was observed in ATRP because of steric effect of hyperbranched structures, resulting in slightly broad polydispersity index in the block copolymers. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3024–3032, 2010     

Synthesis of polyacrylonitrile-block-polydimethylsiloxane-block-polyacrylonitrile triblock copolymers via RAFT polymerization

A new A-B-A type of block copolymers,polyacrylonitrile-block-polydimethylsiloxane-block-polyacrylonitrile(PAN-b-PDMSb-PAN),which comprises two polymer blocks of different polarities and compatibilities,were synthesized for the first time via reversible addition-fragmentation chain transfer polymerization.Reaction kinetics was investigated.PAN-b-PDMS-b-PAN films were prepared by spin-coating on glass chips.Significant order on the film surface morphologies was observed.     

Synthesis of triblock copolymers from glycolysed poly(ethylene terephthalate) by living radical polymerization

Valorization of poly(ethylene terephthalate) (PET) waste has been achieved using glycolysis. The resulting diols were employed for the synthesis of triblock copolymers by atom transfer radical polymerization using copper (I) bromide and (1,1,4,7,10,10)‐hexamethyltriethylenetetramine as catalyst system. Macroinitiator was obtained after depolymerization of PET waste followed by functionalization of the obtained glycolysate with 2‐bromoisobutyrate bromide. Polymerization of styrene (S) and glycidyl methacrylate (GMA) has been achieved leading to PS‐b‐PETG‐b‐PS and (PS‐stat‐PGMA)‐b‐PETG‐b‐(PS‐stat‐PGMA) triblock copolymers. Best results were obtained at 100 °C. At this temperature, termination reaction were negligible and the measured number‐average molar mass of the product increased linearly with monomer conversion in agreement with the theoretical M_n with low polydispersity products achieved. Polymers were also characterized by ¹H NMR. This work presents a original valorization of PET waste as (PS‐stat‐PGMA)‐b‐PETG‐b‐(PS‐stat‐PGMA) copolymer could be used as heat curable coatings. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 433–443, 2008     

Synthesis and characterization of H-type amphiphilic liquid crystalline block copolymers by ATRP

H-type amphiphilic liquid crystalline block copolymers containing azobenzene were synthesized by atom transfer radical polymerization （ATRP）. Macroinitiators prepared by the esterification between poly（ethylene oxide） （PEG） and 2,2-dichloroacetyl chloride were utilized to initiate the polymerization of 6-[4-（4-ethoxyphenylazo）phenoxy]hexyl rnethacrylate （M6C）. The resulting macroinitiators and block copolymers were characterized by ^1H NMR, gel permeation chromatography （GPC）. Polarizing optical microscopy （POM） and differential scanning calorimetry （DSC） preliminarily revealed the liquid crystalline property of these block copolymers. This series of liquid crystalline block copolymers are promising in some areas, such as optical data storage, optical switch, and molecular devices.     

Vesicles with asymmetric membranes from amphiphilic ABC triblock copolymers

A new amphiphilic ABC triblock copolymer (poly(ethylene oxide)-poly(dimethyl siloxane)-poly(methyl oxazoline)) has been synthesized and demonstrated to form vesicular structures with asymmetric membranes in aqueous media.