Phase behavior of linear polystyrene-block-poly(2-vinylpyridine)-block-poly(tert-butyl methacrylate) triblock terpolymers

Using sequential living anionic polymerization we synthesized well-defined linear ABC triblock terpolymers from polystyrene (PS), poly(2-vinylpyridine) (P2VP), and poly(tert-butyl methacrylate) (PtBMA). The length of the PtBMA block was systematically increased at constant block length ratios of the PS and P2VP blocks. The microdomain structures were characterized by transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS). With increasing PtBMA block size we observe a systematic change in the bulk structure of the block copolymers.     

Solvent induced morphologies of poly(methyl methacrylate-b-ethylene oxide-b-methyl methacrylate) triblock copolymers synthesized by atom transfer radical polymerization

Poly(methyl methacrylate-b-ethylene oxide-b-methyl methacrylate) (PMMA-PEO-PMMA) triblock copolymers were synthesized using atom transfer radical polymerization (ATRP) and halogen exchange ATRP. PEO-based macroinitiators with molecular weight from M_n = 2000 to 35,800 g/mol were used to initiate the polymerization of MMA to obtain copolymers with molecular weight up to M_n = 82,000 g/mol and polydispersity index (PDI) less than 1.2. The macroinitiators and copolymers were characterized by gel permeation chromatography (GPC) and nuclear magnetic resonance (NMR) spectroscopy. The melting temperature and glass transition temperature of the copolymers were measured by differential scanning calorimetry (DSC). Crystallinities of the PEO blocks were determined from the WAXS patterns of both homopolymers and block copolymers, which revealed the fragmentation of PEO blocks due to the folding of the PMMA chains. Interestingly, the fragmentation was less pronounced when cast on surfaces compared to that in bulk, as measured by GISAXS. Solvent casting was used to control the morphology of the copolymers, permitting the formation of various states including amorphous, induced micellar with a PMMA core and flower-like PEO arms, and a cross-linked gel. Atomic force microscopy (AFM) was used to visualize the different copolymer morphologies, showing micellar and amorphous states.     

Syntheses of well-defined poly(siloxane)-b-poly(styrene) and poly(norbornene)-b-poly(styrene) block copolymers using functional alkoxyamines

Functional alkoxyamines, 1-[4-(4-lithiobutoxy)phenyl]-1-(2,2,6,6-tetramethylpiperidinyl-N-oxyl)ethane (2) and 1-[4-(2-vinyloxyethoxy)phenyl]-1-(2,2,6,6-tetramethylpiperidinyl-N-oxyl)ethane (3) were prepared, and well-defined poly(hexamethylcyclotrisiloxane)-b-poly(styrene)[poly(D₃)-b-poly(St)] and poly(norbornene)-b-poly(St) [poly(NBE)-b-poly(St)] were prepared using the alkoxyamines. The first step was preparation of poly(D₃) and poly(NBE) macroinitiators, which were obtained by the ring-opening anionic polymerization of D₃ using 2 as an initiator and the ring-opening metathesis polymerization of NBE using 3 as a chain transfer. The radical polymerization of St by the poly(D₃) and poly(NBE) macroinitiators proceeded in the ‘living’ fashion to give well-defined poly(D₃)-b-poly(St) and poly(NBE)-b-poly(St) block copolymers.     

Nanoscale structure of SAN-PEO-SAN triblock copolymers synthesized by atom transfer radical polymerization

Low molecular weight triblock copolymers (TBCs) with poly(styrene-co-acrylonitrile) (SAN) end-blocks and poly(ethylene oxide) (PEO), poly(propylene oxide) (PPO) or polycaprolactone (PCL) mid-blocks were synthesized using atom transfer radical polymerization (ATRP). The influence of molecular weight, composition (mid-block mole fraction), and interaction parameter on the crystallinity and on the formation of an ordered nanoscale phase-separated structure was investigated using thermal analysis, X-ray scattering, and electron microscopy. The TBCs with PEO mole fractions of over 0.5 exhibited PEO crystallinities of around 40% (compared to 72% for the PEO homopolymer) and lamellar nanoscale periodicities of around 176 Å (compared to 143 Å for the PEO homopolymer). The TBCs with PEO, PCL or PPO mole fractions of less than 0.5 exhibited relatively low crystallinities and did not exhibit ordered structures. These results emphasize the importance of the mid-block mole fraction in determining the ability to form an ordered nanoscale structure through mid-block crystallization. The ordered structure disappeared on heating the TBCs above the mid-block melting point, but below the SAN glass transition temperature. The crystallinity was reduced significantly in TBCs that were annealed or cast from a solvent.     

Synthesis of poly(ethylene oxide)-block-poly(methyl methacrylate)-block-polystyrene triblock copolymers by two-step atom transfer radical polymerization

The synthesis of ABC triblock copolymer poly(ethylene oxide)-block-poly(methyl methacrylate)-block-polystyrene (PEO-b-PMMA-b-PS) via atom transfer radical polymerization (ATRP) is reported. First, a PEO-Br macroinitiator was synthesized by esterification of PEO with 2-bromoisobutyryl bromide, which was subsequently used in the preparation of halo-terminated poly(ethylene oxide)-block-poly(methyl methacrylate) (PEO-b-PMMA) diblock copolymers under ATRP conditions. Then PEO-b-PMMA-b-PS triblock copolymer was synthesized by ATRP of styrene using PEO-b-PMMA as a macroinitiator. The structures and molecular characteristics of the PEO-b-PMMA-b-PS triblock copolymers were studied by FT-IR, GPC and ¹H NMR.     

Functionalization of amphiphilic coil-rod-coil triblock copolymer poly(2-vinylpyridine)-b-poly(n-hexyl isocyanate)-b-poly(2-vinylpyridine) with florescence moiety and C60

We recently achieved quantitative synthesis of an amphiphilic coil-rod-coil triblock copolymer, poly(2-vinylpyridine)-b-poly(n-hexyl isocyanate)-b-poly(2-vinylpyridine), by coupling in situ living diblock copolymer poly(2-vinylpyridine)-b-poly(n-hexyl isocyanate) (P2VP-b-PHIC) using malonyl chloride in the presence of pyridine. This led to the introduction of an active methylene group that is a site for further functionalization in the rod block. The Michael addition reaction of the triblock copolymer with 7-(4-trifluoromethyl) coumarin acrylamide led to copolymer bearing a fluorescent pendent in the rod block. The fluorescent labeled copolymers were isolated in ∼94% yields. Similarly C₆₀ pendent was introduced to the rod block by the Bingel reaction. The yields of C₆₀ functionalized copolymers were ∼54%. The precursor and functionalized amphiphilic coil-rod-coil copolymer show diverse morphologies, such as micelles and vesicles by simply changing the solvent. For the C₆₀ functionalized block copolymer, structural constraints in micelles and vesicles prevented C₆₀ pendents to aggregate.     

One-pot synthesis of poly(methacrylic acid)-b-poly(2,2,2-trifluoroethyl methacrylate) diblock copolymers via RAFT polymerization

In this work, the reversible addition-fragmentation chain transfer (RAFT) polymerization was utilized to synthesize the amphiphilic diblock copolymers of poly(methacrylic acid)-b-poly(2,2,2-trifluoroethyl methacrylate) (PMAA-b-PTFEMA) via one-pot two-step reaction protocol. The controlled radical polymerization of MAA monomer was first carried out in pure water by using 4-cyanopentanoic acid dithiobenzoate (CADB) as chain transfer agent. Subsequently, the as-synthesized PMAA homopolymers with dithiobenzoate end-groups were employed as macro-CTA and chain-extended in situ with the hydrophobic TFEMA monomer. The reactions were carried out in 1,4-dioxane/water medium. Both the polymerization of PMAA and PTFEMA blocks showed the well controllability on the molecular weighs and distributions. It was found that the amphiphilic diblock copolymers formed the stable spherical particles via the polymerization-induced self-assembly. Meanwhile, the effect of various parameters, such as the concentration ratio of TFEMA monomer over PMAA macro-CTA, the solvent condition (different ratio of 1,4-dixane/water), and the pH, on the RAFT polymerization of TFEMA monomer were investigated in detail. Their kinetic results suggested that the propagation of TFEMA monomer on the macro-CTA was performed at the particle/water interfaces. The concentration of chain transfer agents at the interfaces determined the polymerization rate. Finally, the stability of the fluorinated polymer dispersions was also evaluated in this work.     

Poly[(2-ethylhexyl acrylate)-ran-(tert-butyl acrylate)]-block-poly(2-cinnamoyloxyethyl acrylate) synthesis and properties

Poly[(2-ethylhexyl acrylate)-ran-(tert-butyl acrylate)]-block-poly(2-cinnamoyloxyethyl acrylate) or P(EXA-r-tBA)-PCEA was synthesized by atom transfer radical polymerization. Reactivity ratios of EXA and tBA for copolymerization were determined. The specific refractive index increments of six diblocks were measured as a function of their composition. The diblocks were thermally stable and formed micelles in an automobile engine oil. Such micelles may be useful as an anti-friction additive in lubricating oils.     

Synthesis of ABA triblock copolymer of poly(potassium acrylate-styrene-potassium acrylate) by atom transfer radical polymerization and the self-assembly in selective solvents

A series of well-defined ABA triblock copolymers of poly(methyl acrylate)-polystyrene-poly(methyl acrylate) (PMA-b-PS-b-PMA) with different molecular weights were synthesized using Cl-PS-Cl as macroinitiator, CuCl/N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA) as catalyst system via atom transfer radical polymerization (ATRP). Amphiphilic triblock copolymer poly(potassium acrylate)-polystyrene-poly(potassium acrylate) (PKAA-b-PS-b-PKAA) was obtained by hydrolyzing PMA-b-PS-b-PMA. The self-assembly behavior of the triblock copolymers in organic solutions, which is a good solvent for the PS block and in aqueous solutions, which is a good solvent for the PKAA blocks was studied by high performance particle sizer (HPPS). The results showed that the Z-average size of the micelles obviously increases with increase in molecular weight of triblock copolymers, and the micelles in organic solutions are relatively more stable than in aqueous solutions. The effect of the length of PS block on the Z-average size of the micelles is more obvious in organic solution than in aqueous solution. The morphology of triblock copolymers PKAA-b-PS-b-PKAA in aqueous solution, which is a nearly ‘pearl-necklace’-like shape, was examined by transmission electron microscopy (TEM) at room temperature.     

Synthesis and morphological studies of polyisoprene-block-polystyrene-block-poly(vinyl methyl ether) triblock terpolymer

The triblock terpolymer (PI-b-PS-b-PVME) consisting of polyisoprene (PI), polystyrene (PS) and poly(vinyl methyl ether) (PVME) was synthesized by coupling reaction between living PI-b-PS anion and end-chlorinated PVME prepared via living cationic polymerization. This polymer is an amphiphilic block polymer and unique in a sense that it exhibits complex phase behavior because PS and PVME have a lower critical solution temperature (LCST)-type phase diagram while PI and PS (or PVME) have an UCST-type phase diagram. This unique architecture would result in a step-wise microphase separation to form a three-phase microdomain structure. It was observed by transmission electron microscopy with ultrathin sections that the toluene-cast film of PI-b-PS-b-PVME has a two-phase lamellar structure consisting of PI microdomains and mixed PS/PVME microdomains. Applying a drop of water onto the ultrathin sections induced further microphase separation between PS and PVME within the lamellar microdomains resulting in the three-phase structure. Water is a selective solvent for PVME and might have lowered the order-disorder temperature between PS and PVME. This step-wise microphase separation may be a new technique to control microphase-separated structures in triblock terpolymers.     

Internal plasticization of poly(vinyl chloride) by grafting acrylate copolymers via copper-mediated atom transfer radical polymerization

Internal plasticization of poly(vinyl chloride) (PVC) was achieved in one-step using copper-mediated atom transfer radical polymerization to graft different ratios of random n-butyl acrylate and 2–2-(2-ethoxyethoxy)ethyl acrylate copolymers from defect sites on the PVC chain. Five graft polymers were made with different ratios of poly(butyl acrylate) (PBA) and poly(2–2-(2-ethoxyethoxy)ethyl acrylate) (P2EEA); the glass transition temperatures (T_g) of functionalized PVC polymers range from − 25 to − 50°C. Single T_g values were observed for all polymers, indicating good compatibility between PVC and grafted chains, with no evidence of microphase separation. Plasticization efficiency is higher for polyether P2EEA moieties compared with PBA components. The resultant PVC graft copolymers are thermally more stable compared to unmodified PVC. Increasing the reaction scale from 2 to 14 g produces consistent and reproducible results, suggesting this method could be applicable on an industrial scale.     

Analysis of poly(ethylene oxide)-b-poly(propylene oxide) block copolymers by MALDI-TOF mass spectrometry using collision induced dissociation

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) was used to analyse the block length of commercially available block copolymers of poly(ethylene oxide) and poly(propylene oxide) (PEO-b-PPO) based on the fragmentation behaviour in collision induced dissociation (CID) experiments.MALDI-CID-TOF² analysis is a complex procedure depending on a number of different experimental parameters. Therefore, a step-by-step procedure was used starting with PEG and PPG standards, PEG-PPG blends and endgroup-functionalized PPGs, to understand the fragmentation behaviour of the different species. These results showed that characteristic fragment patterns of the homopolymers and PEG-PPG mixtures can be obtained that facilitate the interpretation of the fragment spectra of PEO-b-PPO di- and triblock copolymers. It was found that di- and triblock copolymers can be differentiated by their fragment spectra. In addition, the sequence of monomer units in the diblock copolymers could be determined.     

Synthesis and phase separation during film formation of novel methyl methacrylate/n-butyl acrylate/methacrylic acid (MMA/BA/MAA) hybrid urethane/acrylate colloidal dispersions

Hybrid acrylic/urethane colloidal dispersions were prepared by incorporation of a novel multifunctional urethane castor vinyl ether (UCVE) macromonomer derived from castor oil in acrylic latexes. Single-stage and two-stage semi-continuous emulsion polymerization processes were utilized to control placement of UCVE in colloidal dispersions with core/shell and spherical particle morphologies. While the single-stage process resulted in optically clear and chemically homogeneous films, the two-stage process led to heterogeneous film formation. Internal reflection infrared imaging (IRIRI) spectroscopic analysis of the film-air (F-A) interfaces revealed phase-separated urethane- and urea-rich domains ranging in size from approximately 4-40 μm. Based on these measurements, a model of film formation is proposed which incorporates the effect of exceedingly high shear conditions to achieve fine dispersions of UCVE. These experiments indicate that features of the single-stage process facilitate uniform dispersion of UCVE and efficient grafting between UCVE and the acrylic polymer matrix resulting in intimately mixed networks and homogeneous films.     

Synthesis of defined polyhedral oligosilsesquioxane‐containing diblock and triblock methacrylate copolymers by atom transfer radical polymerization

Defined diblock and triblock copolymers composed of methyl methacrylate‐co‐glycidyl methacrylate block and 3‐{3,5,7,9,11,13,15‐hepta(2‐methylpropyl)‐pentacyclo[9.5.1.1^3,9.1^5,15.1^7,13]‐octasiloxan‐1‐yl}propyl methacrylate block(s), i.e., P(MMA‐co‐GMA)‐b‐PiBuPOSSMA and PiBuPOSSMA‐b‐P(MMA‐co‐GMA)‐b‐PiBuPOSSMA, were synthesized by atom transfer radical polymerization (ATRP). First, monofunctional and bifunctional P(MMA‐co‐GMA) copolymers were synthesized by ATRP. Subsequently, these copolymers were successfully used as macroinitiators for ATRP of POSS‐containing methacrylate monomer. The process showed high initiation efficiency of macroinitiators and led to products with low dispersity. The synthesized block copolymers were characterized by size exclusion chromatography, ¹H‐NMR spectroscopy and their glass transition temperatures were determined by differential scanning calorimetry. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Methacrylate/acrylate ABA triblock copolymers by atom transfer radical polymerization; their properties and application as a mediator for organically dispersible gold nanoparticles

This investigation reports the preparation of a series of well-defined Poly(methyl methacrylate)-b-poly(hexyl acrylate)-b-poly (methyl methacrylate) (PMMA-b-PHA-b-PMMA) triblock copolymers by Atom Transfer Radical Polymerization (ATRP). Their morphology, dynamic mechanical and tensile properties are thoroughly investigated. Phase separation is observed for all the above-mentioned triblock copolymers, which contain PMMA outer blocks in the molecular weight (M_n) range of 10,000-80,000 and PHA inner blocks with M_n in the range 20,000-40,000. The dynamic mechanical measurements essentially reveal two glass transitions and an intermediate flat rubbery plateau in between. Tensile studies indicate that as the PMMA content increases, there is an increase in tensile strength and decrease in elongation at break, which is the case for most of the thermoplastic elastomers (TPE). Eventually, the as prepared block copolymers (with PMMA content 50-80%) offer to be an effective stabilizer for preparing gold nanoparticle aggregates, the shape and size of which can be modulated by tuning the block copolymer composition. The formation of nanoparticle aggregates and their possible non-covalent interaction with the base polymer has been substantiated by UV-vis analysis, transmission electron microscopy, energy-dispersive X-ray spectroscopy, dynamic light scattering and Fourier transform infrared spectroscopy.     

Well-defined diblock copolymers of poly(tert-butyldimethylsilyl methacrylate) and poly(dimethylsiloxane) synthesized by RAFT polymerization

We report the application of reversible addition-fragmentation chain transfer (RAFT) polymerization using poly(dimethylsiloxane) (PDMS) chain transfer agents toward the synthesis of a variety of diblock copolymers containing tert-butyldimethylsilyl methacrylic (MASi) monomer units. The methodology relies on the synthesis of PDMS monofunctional chain transfer agents easily available in one synthetic step from commercially available hydroxylated PDMSs. The RAFT process enables access to polymer chains with narrow molar mass distributions and high conversions. Data from differential scanning calorimetric measurements revealed that the diblock copolymers exhibited two glass transition temperatures, corresponding to the PDMS- and PMASi-enriched phases, respectively. Copolymerizations of MASi and butyl methacrylate (BMA) within the second block led to immiscible phases with lower glass transition temperatures than PDMS-block-PMASi copolymers.     

Synthesis and characterisation of hydroxyl end-capped telechelic polymers with poly(methyl methacrylate)-block-poly(n-butyl acrylate) backbones via atom transfer radical polymerisation

Hydroxyl end-capped telechelic polymers with poly(methyl methacrylate)-block-poly(n-butyl acrylate) (PMMA-b-PBA) backbones have been prepared via atom transfer radical polymerisation (ATRP) together with a nucleophilic substitution reaction. A hydroxyl-functionalised PMMA macroinitiator (HO-PMMA-Br) was prepared via ATRP at the optimised reaction temperature (60 °C) using 2-hydroxyethyl 2-bromoisobutyrate as the initiator. The high functionality of the bromo end group in the macroinitiator was confirmed by both ¹H NMR technique and a chain-extension reaction. Electrospray ionisation mass spectrometer proved to be a valuable tool for characterising PMMAs with a bromo end group (PMMA-Br), which provided signals corresponding to the intact polymers although multiply charged polymer chains were observed. The well-defined block copolymers HO-PMMA-b-PBA-Br were obtained by the ATRP of n-butyl acrylate using HO-PMMA-Br as a macroinitiator in a one-pot reaction at 100 °C. The kinetics as well as the dependence of the M_n,SEC and PDIs of the obtained block copolymers on the conversions of n-butyl acrylate in the chain-extension reaction suggested negligible radical termination during the reaction, demonstrating that the well-defined HO-PMMA-b-PBA-Br with a high functionality of bromo end group were obtained. The nucleophilic substitution reaction of a monohydroxyl-functionalised block copolymer HO-PMMA-b-PBA-Br with 5-amino-1-pentanol in dimethyl sulfoxide at room temperature was verified with ¹H and ¹³C NMR techniques, which resulted in a series of telechelic polymers HO-PMMA-b-PBA-OH with a functionality of hydroxyl groups up to 1.7 according to the gradient polymer elution chromatography.     

Frustrated structures of polycaprolactam and poly(p-benzamide) in their rod-coil-rod triblock copolymers

A series of rod-coil-rod triblock copolymers were synthesized by two-step polycondensation with polycaprolactam (PA6) as the flexible block and poly(p-benzamide) (PBA) as the rod. Proton nuclear magnetic resonance (¹H NMR), UV-vis spectrophotometry and differential scanning calorimetric (DSC) were first performed to determine the fundamental molecular structure and thermal property of each polymer. Through wide angle X-ray scattering (WAXS), and Fourier transformation infrared spectroscopy (FT-IR) measurements, frustrated structures of both components were studied. For PA6, a quasi-γ mesomorphic order was found in the transition-region nearby the PBA domain which is more favored with the increase of the PBA content owing to stretching from the PBA rod block and different cross-section areas of the rod and coil chains. On the other hand, the mesomorphic order of PA6 segments imposes stretching and constraint on the PBA blocks, which leads to a reduction of order of PBA block when the volume fraction of rod reaches approximately 45%. α crystals of PA6 can form only in the triblock copolymer with low volume fraction of PBA, which exhibit the Brill transition feature during the heating process though this transition ends prematurely as the melting of crystals.     

Synthesis and characterization of poly(dimethylamino ethyl methacrylate)–poly(ethylene oxide)–poly(dimethylamino ethyl methacrylate) triblock copolymers

Novel, monodispersed, and well‐defined ABA triblock copolymers [poly(dimethylamino ethyl methacrylate)–poly(ethylene oxide)–poly(dimethylamino ethyl methacrylate)] were synthesized by oxyanionic polymerization with potassium tert‐butanoxide as the initiator. Gel permeation chromatography and ¹H‐NMR analysis showed that the obtained products were the desired copolymers with molecular weights close to calculated values. Because the poly(dimethylamino ethyl methacrylate) block was pH‐ and temperature‐sensitive, the aqueous solution behavior of the polymers was investigated with ¹H‐NMR and dynamic light scattering techniques at different pH values and at different temperatures. The micelle morphology was determined with transmission electron microscopy. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis of amphiphilic triblock copolymer of polystyrene and poly(4-vinylbenzyl glucoside) via TEMPO-mediated living radical polymerization

4-Vinylbenzyl glucoside peracetate 1 was polymerized with α,α′-bis(2′,2′,6′,6′-tetramethyl-1′-piperidinyloxy)-1,4-diethylbenzene 2 in chlorobenzene using (1S)-(+)-10-camphorsulfonic acid anhydrous (CSA) as an accelerator ([1]=0.4 M,[1]/[2]/[CSA]=75/1/1.3) at 125 °C for 5 h. The polymerization afforded poly(4-vinylbenzyl glucoside peracetate) having TEMPO moieties on both sides of the chain ends, 3, with a molecular weight (M_w,SLS) of 8500, a polydispersity index (M_w/M_n) of 1.09, and an average degree of polymerization of the 1 unit (x) of 17. Styrene (St) was polymerized with 3 in chlorobenzene at 125 °C (St/chlorobenzene=1/2, w/w). The polymerization successfully afforded polystyrene-poly(4-vinyl glucoside peracetate)-polystyrene, 4, when the polymerization time was below about 2 h. Polymer 4 with the M_w,SLS of 12,500, 17,900, and 29,400, the compositions (y-x-y) of 20-17-20, 45-17-45, and 100-17-100, and the M_w/M_n of 1.12, 1.14 and 1.17 were modified by deacetylation using sodium methoxide in dry-THF into polystyrene-poly(4-vinyl glucoside peracetate)-polystyrene, 5. The solubility of polymer 5 was examined using a good solvent for polystyrene such as toluene and for the saccharide such as H₂O.