Dilute solutions and phase behavior of polydisperse A-b-(A-co-B) diblock copolymers

The effect of polydispersity on dilute solution properties and microphase separation of polydisperse high-molecular-weight (M_w > 10⁵ g mol⁻¹) polystyrene-block-poly(styrene-co-acrylonitrile) diblock copolymers, PS-block-P(S-co-AN), was studied in this work. For experiments, a series of diblock copolymers with variable weight fractions of acrylonitrile units (w_AN = 0.08-0.29) and length of block P(S-co-AN) was synthesized using nitroxide-mediated radical polymerization (NMP) technique, namely, by chain extension of nitroxide-terminated polystyrene (PS-TEMPO). According to light scattering and viscometry measurements in dilute tetrahydrofuran (THF) solutions the studied diblock copolymers assumed random coil conformation with the values of characteristic structure factor R_g/R_h = 1.50-1.76. It was found that polydisperse diblock copolymers being in strong segregation limit (SSL) self-assembled into microphase-separated ordered morphologies at ordinary temperature. The long periods of lamellar microdomains were larger compared to theoretical predictions for hypothetical monodisperse diblock copolymers. It was demonstrated by means of SAXS and TEM that a transition from a lamellar (LAM) to irregular face-centered-cubic (FCC) morphology occurred with increasing volume fraction of P(S-co-AN) block.     

Self-association of double-hydrophilic copolymers of acrylic acid and poly(ethylene oxide) macromonomer

Poly(ethylene oxide) (PEO) end-capped by a methacrylate unsaturation was copolymerized with acrylic acid by RAFT with dibenzyltrithiocarbonate as a chain transfer agent. Tapered triblock copolymers consisting of a poly(acrylic acid) (PAA) inner block and comb-like outer blocks of PEO macromomers were formed as result of the comonomers reactivity ratios. Composition of these copolymers and length of the PEO branches were varied. Dynamic light scattering (DLS) was used to characterize the aggregates formed in water and to investigate their response to stimuli, such as pH, temperature and ionic strength. In parallel, the morphology of the aggregates was directly observed by transmission electron microscopy (TEM). Well-defined aggregates were formed in the 5<pH<8 range, with a morphology strongly depending on the copolymer composition. At pH<5, the copolymers were poorly soluble and no well-defined structure was observed, whereas free chains were formed at pH>8 as consequence of the complete ionization of the PAA block.     

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.     

Functionalized organic nanoparticles from core-crosslinked poly(4-vinylbenzocyclobutene-b-butadiene) diblock copolymer micelles

Surface-functionalized polymeric nanoparticles were prepared by: a) self-assembly of poly(4-vinylbenzocyclobutene-b-butadiene) diblock copolymer (PVBCB-b-PB) to form spherical micelles (diameter: 15-48 nm) in decane, a selective solvent for PB, b) crosslinking of the PVBCB core through thermal dimerization at 200-240 °C, and c) cleavage of the PB corona via ozonolysis and addition of dimethyl sulfide to afford aldehyde-functionalized nanoparticles (diameter: ∼16-20 nm), along with agglomerated nanoparticles ranging from ∼30 to ∼100 nm in diameter. The characterization of the diblock copolymer precursors, the intermediate micelles and the final surface-functionalized crosslinked nanoparticles was carried out by a combination of size exclusion chromatography, static and dynamic light scattering, viscometry, thermogravimetric analysis, ¹H NMR and FTIR spectroscopy and transmission electron microscopy.     

Synthesis, characterization, and bulk crosslinking of polybutadiene-block-poly(2-vinyl pyridine)-block-poly(tert-butyl methacrylate) block terpolymers

We report on the synthesis and characterization of triblock terpolymers, polybutadiene-block-poly(2-vinyl pyridine)-block-poly(tert-butyl methacrylate) (PB-b-P2VP-b-PtBMA; BVT), via sequential living anionic polymerization in THF at low temperatures using sec-butyl lithium as initiator. In this work, 18 different BVT terpolymers were produced with volume fractions Φ_B : Φ_V : Φ_T in the range of 1 : 0.4…1.2 : 0.2…4.6. All polymers exhibit a very narrow molecular weight distribution (PDI < 1.1). They were characterized in terms of bulk morphology using small-angle X-ray scattering and transmission electron microscopy, unveiling mostly lamellar patterns or hexagonally arranged cylindrical structures. Some polymers displayed a partial gyroid structure coexisting with lamellar parts or cylinders with a non-continuous shell around the PB core and could serve as an interesting template for the facile generation of multi-compartmental self-assembled structures. In one case the middle block, P2VP, is forming a helix around the PB core. Crosslinking of the polybutadiene compartment of the bulk morphologies with an UV-photoinitiator was performed, followed by sonication-assisted dissolution of the aggregates to elucidate further use of the terpolymers for the generation of soft polymeric nanoparticles with controlled functionality. In that way, core-crosslinked cylindrical micelles could be generated and characterized.     

Aggregation behaviour of well defined amphiphilic diblock copolymers with poly(N-isopropylacrylamide) and hydrophobic blocks

Series of amphiphilic diblock copolymers with poly(N-isopropylacrylamide) as a hydrophilic block and a hydrophobic block consisting of either polystyrene or poly(tert-butyl methacrylate) were synthesised using RAFT polymerisations. Differential scanning calorimetry showed the chemically different blocks being phase separated in dry polymers. Light scattering and microcalorimetry studies were performed on aqueous solutions to investigate the phase behavior of the diblock copolymers. By carefully transferring the polymers from an organic solvent to water, either micellar particles or large aggregates were obtained depending on the relative lengths of the blocks. Large aggregates collapsed upon heating, whereas collapse occurred slowly within a broad temperature range in the case of micelle like structures. However, microcalorimetrically the collapse of the PNIPAM chains was observed to take place in all samples, suggesting that the shells of the micellar particles are crowded in a way which hinders the compression of the poly(N-isopropylacrylamide) chains.     

Preparation of diblock copolymer based on poly(4-n-butyltriphenylamine) via palladium coupling polymerization

A self-condensing monomer 4-(4′-bromophenyl)-4″-n-butyldiphenylamine (1) was synthesized, and successfully converted to poly(4-n-butyltriphenylamine) (PBTPA) by arylamination using palladium catalyst. PBTPAs can be functionalized at both terminals separately by adding an aryl bromide or arylamine derivatives as a terminator, which enabled us to prepare the diblock copolymer PBTPA-block-PEO. Polymer characterization was performed by ¹H NMR, ¹³C NMR, and DSC, which confirmed that the PEO segment was successfully introduced at the terminal of PBTPA. The surface morphology in a thin film of PBTPA-block-PEO was examined by AFM, revealing that a microphase-separated structure or cup-shaped structure with PEO sphere domains formed when the film was spin-cast from 1,1,2,2-tetrachloroethane solutions of different concentrations.     

Synthesis and micellization of thermo- and pH-responsive block copolymer of poly(N-isopropylacrylamide)-block-poly(4-vinylpyridine)

A novel double-hydrophilic block copolymer poly(N-isopropylacrylamide)-block-poly(4-vinylpyridine) (PNIPAM-b-P4VP) with low polydispersity which could respond to both temperature and pH stimuli in aqueous solution was synthesized by atom transfer radical polymerization. Micellization of the copolymer in aqueous solution was characterized by dynamic and static laser scattering, ¹H NMR and transmission electron microscopy. In aqueous solution, the copolymer existed as unimer at pH 2.8 at 25 °C. When the temperature was raised to 50 °C at pH 2.8, the copolymer associated into spherical core-shell micelles with the PNIPAM block forming the core and the P4VP block forming the shell. On the other hand, when pH was increased from 2.8 to 6.5 at 25 °C, the copolymer associated into spherical core-shell micelles with the core formed by the P4VP block and the shell formed by the PNIPAM block. The process was reversible. The critical aggregation temperature of the block copolymer is 36 °C, and the critical aggregation pH value is 4.7.     

Nanoscale localization of poly(vinylidene fluoride) in the lamellae of thin films of symmetric polystyrene-poly(methyl methacrylate) diblock copolymers

We employed thin film blends of diblock copolymers with functional homopolymers as a simple strategy to incorporate organic functional materials into nanodomains of diblock copolymers without serious synthesis. A blend pair of polystyrene-poly(methyl methacrylate) (PS-PMMA) diblock copolymers and poly(vinylidene fluoride) (PVDF) was selected as a model demonstration because PVDF is a well-known ferroelectric polymer and completely miscible with amorphous PMMA. Thin films of symmetric PS-PMMA copolymers provided the nanometer-sized PMMA lamellae, macroscopically parallel to the substrate, in which PVDF chains were dissolved. Thus, amorphous PVDF chains were effectively confined in the PMMA lamellae of thin film blends. The location of PVDF chains in the PMMA lamellae was investigated by the dependence of the lamellar period on the volume fraction of PVDF, from which we found that PVDF chains were localized in the middle of the PMMA lamellae. After the crystallization of PVDF, however, some of PVDF migrated to the surface of the film and formed small crystallites.     

Radiation degradation of statistical terpolymers of two aromatic diols with diphenyl sulphone

The variation in radiation resistance with composition of statistical terpolymers of (1) bisphenol-A and biphenol, and (2) hydroquinone and biphenol, with diphenyl sulphone was studied by electron spin resonance spectroscopy after γ irradiation at 77 K and by analysing volatile products after irradiation at 423 K. Approximately linear relationships were obtained between the radiation chemical yields for both radicals, G(R), and sulphur dioxide, G(SO₂), and the mole fraction of biphenol units in the terpolymers. Substantially higher radiation resistance was shown by biphenol units compared with either bisphenol-A or hydroquinone.     

High‐resolution carbon nuclear magnetic resonance study of styrene/α‐methylstyrene/acrylonitrile terpolymers

Terpolymers formed from styrene, α‐methylstyrene (AMS), and acrylonitrile (AN) were prepared in different proportions. According to the reaction conditions, the terpolymers presented random sequence distributions. AMS, because of steric hindrance, presented a high degree of instability, which promoted depolymerization. AN promoted a long insertion of AMS monomers, which caused an acceleration of the propagation reaction. This also caused a depolymerization process. With ¹³C‐NMR solution analysis, it was possible to detect the depolymerization process. With solid‐state NMR results, it was demonstrated that AMS constituted the highest mobility domain. Finally, the values determined for the proton spin–lattice relaxation time in the rotating frame confirmed that the prepared terpolymers were random, but a homogeneous monomer distribution sequence was also observed from this parameter. © 2003 Wley Periodicals, Inc. J Appl Polym Sci 88: 1004–1009, 2003     

Effect of interfacial tension on micellization of a polystyrene-poly(ethylene oxide) diblock copolymer in a mixed solvent system

The micellization of a polystyrene-poly(ethylene oxide) (PS-PEO) diblock copolymer in a mixed solvent of water and tetrahydrofuran (THF) was studied in terms of an aggregation number as measured by laser light scattering. The results show the aggregation number (f) of the micelle decreases monotonically as the amount of THF is increased. These experimental results are compared with a theoretical model that includes the variations in the interfacial tension. Experimentally, the interfacial tension is adjusted with the addition of relatively low levels of THF. The theory indicates that the aggregation number decreases as the interfacial tension is decreased. The theoretical prediction is in very good agreement with the experimental results. The main conclusion of this study is that the interfacial tension is the key factor in determining the aggregation number of the diblock copolymer micelle in a water-THF solvent system.     

Crystallization, melting, and morphology of a poly(ethylene oxide) diblock copolymer containing a tablet-like block of poly{2,5-bis[(4-methoxyphenyl)oxycarbonyl]styrene}

A poly(ethylene oxide) diblock copolymer containing a short block of poly{2,5-bis[(4-methoxyphenyl)oxycarbonyl]styrene} (PEO-b-PMPCS) has been successfully synthesized via atom transfer radical polymerization (ATRP) method. The number average molecular weights (M_n) of the PEO and PMPCS blocks are 5300 and 2100 g/mol, respectively. Combining the techniques of differential scanning calorimetry (DSC), optical microscopy (OM), wide angle X-ray diffraction (WAXD), and small angle X-ray scattering (SAXS), we have found that the PMPCS blocks, which are tablet-like, can significantly affect the crystallization and melting of the diblock copolymer. The sample studied can form the crystals with a monoclinic crystal structure identical to that of the homo-PEO. The melting temperature (T_m) of the diblock copolymer increases monotonically with crystallization temperature (T_c), which is remarkably similar to the behavior of long period. On the basis of Gibbs-Thomson relationship, the equilibrium T_m of the diblock copolymer is estimated to be 65.4 °C. In a wide undercooling (ΔT) range (14 °C<ΔT<30 °C), the isothermal crystallization leads to square-shaped crystals. The PEO-b-PMPCS crystallization exhibits a regime I→II transition at ΔT of 19 °C. The PEO blocks are non-integral folded (NIF) in the crystals, and the PMPCS blocks rejected to lamellar fold surfaces prevent the NIF PEO crystals from transforming to integral folded (IF) ones. Furthermore, the PMPCS tablets may adjust their neighboring positions up or down with respect to the lamellar surface normal, forming more than one PMPCS layer to accompany the increase in the PEO fold length with increasing T_c.     

Carbon nuclear magnetic resonance characterization of ethylene-propylene-1-octadecene terpolymers and comparison with ethylene-propylene-1-hexene and 1-decene terpolymers

In this paper, we report the complete ¹³C NMR characterization of a set of ethylene-propylene-1-octadecene terpolymers obtained with the metallocenic system rac-ethylene bis-indenyl zirconium dichloride, using different comonomer ratios. A detailed study of ¹³C NMR chemical shifts, triad sequence distributions, monomer average sequence lengths and reactivity ratios for these terpolymers is presented. The incorporations of 1-octadecene were superior of those obtained using 1-hexene and 1-decene in the same conditions. Catalytic activities of terpolymers of ethylene-propylene and α-olefins (α-olefins:1-hexene, 1-decene and 1-octadecene) were compared showing that they increase with the amount of propylene in the feed.     

Synthesis of block terpolymers of N-methyl methacrylamide with styrene and isoprene by living radical polymerization

The synthesis of block terpolymers of N-methyl methacrylamide (NMeMA) with styrene (St) and isoprene (Is) [poly(NMeMa-b-St-b-Is) and poly(NMeMA-b-Is-b-St)] was achieved by using heterogeneous living radical polymerization (di-t-butylperoxide–UV, benzene) and high vacuum techniques. The existence of living macroradicals was detected by electron paramagnetic resonance (EPR) spectroscopy. The terpolymers were not soluble in common organic solvents. The formation of polymeric blocks was confirmed by modulated differential scanning calorimetry (MDSC) and IR spectroscopy. © 1998 Society of Chemical Industry.     

Synthesis and characterization of nanosized poly(organophosphazenes) with methoxy-poly(ethylene glycol) and dipeptide ethyl esters as side groups

Nanosized water soluble poly(organophosphazenes) were synthesized by grafting hydrophilic methoxy poly(ethylene glycols) and hydrophobic dipeptide ethyl esters as side groups to the phosphazene backbone. Their hydrodynamic volume could be controlled in the range of 10-30 nm in diameter depending on the length of the side groups and the molecular weight of the polymers. These polymers exhibited a lower critical solution temperature in the range of 60-105 °C and hydrolytic degradability, which can afford applications to a variety of drug delivery systems. The hydrolytic properties of the present poly(organophosphazenes) have been studied at 37 °C in different pH buffer solutions by means of gel permeation chromatography. The polymers substituted with the more hydrophobic and more bulky dipeptide groups caused slower hydrolysis and the polymer hydrolysis occurred more rapidly in the acidic buffer solution than in the neutral and basic solutions.     

Facile preparation of poly(N-isopropylacrylamide)-based hydrogels via aqueous Diels-Alder click reaction

The study reports a facile method of preparing poly(N-isopropylacrylamide)- based hydrogels by means of the Diels-Alder reaction. First, polymeric dienes were synthesized by free radical copolymerization between N-isopropylacrylamide (NIPA) and furfuryl methacrylate (FM), with 2, 2′-azobisisobutyronitrile (AIBN) as an initiator, and polymeric dienophile was obtained by a coupling reaction of poly(ethylene glycol) (PEG) and N-maleoyl-l-leucine (LMI) under N, N′-dicyclohexylcarbodiimide (DCC). Afterwards, the resultant dienes and dienophiles were dissolved in water and put in a refrigerator remaining a temperature of 9 °C, gelation via Diels-Alder reaction was observed after some time. The samples obtained at different steps were characterized by FTIR, NMR, GPC, SEM, CD, etc. It was found that LCST of copolymers decreases with the increase of FM content in copolymers. And the disassembly time of the hydrogels is closely related to the temperature and the solvents used. The swelling behavior study by gravimetric measurement indicates the hydrogels possess thermosensitivity and exhibit considerable swelling in water. Due to the simplicity of synthesis and no need for initiator or catalyzer and organic solvent, the strategy described here could find a promising application in the preparation of hydrogels.     

Characterization of terpolymers containing 1,2,4‐oxadiazolic pendant groups with potential application as workover fluids

Presence of planar, bulky heterocyclic pendant groups, attached to polymer chains, alters the thermal properties and, once gelled, they modify their rheological properties as well. The authors report generation of stiff gels coming from terpolymers containing 1,2,4‐oxadiazolic pendant groups, obtained by chemical modification of commercial polyacrylonitrile. The gels formed in basic aqueous solutions were compared and the effect of substituents linked to the heterocycles on thermal stability and viscoelastic properties was also analyzed. The structural modifications were followed by FTIR. The potential use of these terpolymers as workover fluids is discussed. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis and thermoresponsive properties of four arm, amphiphilic poly(tert-butyl-glycidylether)-block-polyglycidol stars

A series of four arm stars with copolymer arms composed of poly(tert-butyl-glycidylether)-b-polyglycidol were prepared using a multi-step process based on anionic ring-opening polymerization. Control of the length of the arms and the number of functional (hydroxyl) reactive groups was achieved by anionic polymerization. Stars with molar masses up to 12200 g/mol were prepared. The amphiphilic character of the star structure was varied using different polyglycidol block lengths. The star structure and molar mass of the obtained stars were characterized by SEC-MALLS and NMR spectroscopy.The temperature behavior of an aqueous solution of the obtained polymers was also investigated. The phase transition temperature was strongly dependent on the hydrophilic-hydrophobic balance of the star structure and varied in the range of 25-59 °C. As shown by DLS and SEM, the stars formed temperature-sensitive spherical aggregates in aqueous solution. The aggregates may be used for controlled transport and release of active compounds.     

Influence of the solvent and the end groups on the morphology of cross-linked amphiphilic poly(1,2-butadiene)-b-poly(ethylene oxide) nanoparticles

The phase diagrams of nanoparticles based on self-assembled amphiphilic poly(1,2-butadiene)-b-poly(ethylene oxide) diblock copolymers (PB-b-PEO) and subsequent intra-micellar cross-linking in methanol and water show that the obtained morphology of the nanoparticles depends on: (i) the block ratio; (ii) the block length; (iii) the solvent; and (iv) the PEO-sided end group. Depending on these parameters, spherical, cylindrical and vesicle-like nanoparticles are synthesized. The PEO-sided end group is found to have an influence on the morphology of the nanoparticles and in addition, it has an impact on the characteristic dimension of the polymeric nanoparticles.