Synthesis and aqueous solution properties of functionalized and thermoresponsive poly(D,L-lactide)/polyether block copolymers

Tri- and pentablock amphiphilic copolymers containing hydrophobic poly(D,L-lactide) block(s) and hydrophilic polyethers were synthesized in order to obtain new precursor architectures suitable for drug delivery systems. Polyglycidol-6-poly(ethylene oxide)-b-poly(D,L-lactide) possess high hydroxyl functionality provided by the linear polyglycidol block. Thus very stable hydroxyl functionalized micelles in aqueous media were obtained. On the other hand poly(D,L-lactide)-b-poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide)-b-poly(D,L-lactide) form temperature sensitive aggregates. The copolymers obtained were analyzed by SEC and NMR, and their aqueous solution properties were followed by cloud point measurements and determination of critical micellization temperature. TEM was used for particles visualization.     

Triphilic pentablock copolymers with perfluoroalkyl segment in central position

Adding perfluoroalkyl (PF) segments to amphiphilic copolymers yields triphilic copolymers with new application profiles. Usually, PF segments are attached as terminal blocks via Cu(I) catalyzed azide-alkyne cycloaddition (CuAAC). The purpose of the current study is to design new triphilic architectures with a PF segment in central position. The PF segment bearing bifunctional atom transfer radical polymerization (ATRP) initiator is employed for the fabrication of triphilic poly(propylene oxide)-b-poly(glycerol monomethacrylate)-b-PF-b-poly(glycerol monomethacrylate)-b-poly(propylene oxide) PPO-b-PGMA-b-PF-b-PGMA-b-PPO pentablock copolymers by a combined ATRP and CuAAC reaction approach. Differential scanning calorimetry indicates the PF-initiator to undergo a solid–solid phase transition at 63°C before the final crystal melting at 95°C. This is further corroborated by polarized optical microscopy and X-ray diffraction studies. The PF-initiator could successfully polymerize solketal methacrylate (SMA) under typical ATRP conditions producing well-defined Br-PSMA-b-PF-b-PSMA-Br triblock copolymers that are then converted into PPO-b-PSMA-b-PF-b-PSMA-b-PPO pentablock copolymer via CuAAC reaction. Subsequently, acid hydrolysis of the PSMA blocks afforded water soluble well-defined triphilic pentablock copolymers PPO-b-PGMA-b-PF-b-PGMA-b-PPO with fluorophilic central segment, hydrophilic middle blocks, and lipophilic outer blocks. The triphilic block copolymers could self-assemble, depending upon the preparatory protocol, into spherical and filament-like phase-separated nanostructures as revealed by transmission electron microscopy.     

Synthesis and characterization of ABA‐type amphiphilic tri‐block copolymers through anionic polymerization using end functionalized poly(ethylene oxide) oligomers

ABA‐type amphiphilic tri‐block copolymers were successfully synthesized from poly(ethylene oxide) derivatives through anionic polymerization. When poly(styrene) anions were reacted with telechelic bromine‐terminated poly(ethylene oxide) ( 1 ) in 2:1 mole ratio, poly(styrene)‐b‐poly(ethylene oxide)‐b‐poly(styrene) tri‐block copolymers were formed. Similarly, stable telechelic carbanion‐terminated poly(ethylene oxide), prepared from 1,1‐diphenylethylene‐terminated poly (ethylene oxide) ( 2 ) and sec‐BuLi, was also used to polymerize styrene and methyl methacrylate separately, as a result, poly (styrene)‐b‐poly(ethylene oxide)‐b‐poly(styrene) and poly (methyl methacrylate)‐b‐poly(ethylene oxide)‐b‐poly(methyl methacrylate) tri‐block copolymers were formed respectively. All these tri‐block copolymers and poly(ethylene oxide) derivatives, 1 and 2 , were characterized by spectroscopic, calorimetric, and chromatographic techniques. Theoretical molecular weights of the tri‐block copolymers were found to be similar to the experimental molecular weights, and narrow polydispersity index was observed for all the tri‐block copolymers. Differential scanning calorimetric studies confirmed the presence of glass transition temperatures of poly(ethylene oxide), poly(styrene), and poly(methyl methacrylate) blocks in the tri‐block copolymers. Poly(styrene)‐b‐poly(ethylene oxide)‐b‐poly(styrene) tri‐block copolymers, prepared from polystyryl anion and 1 , were successfully used to prepare micelles, and according to the transmission electron microscopy and dynamic light scattering results, the micelles were spherical in shape with mean average diameter of 106 ± 5 nm. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Hydrogen bond mediated self-assembly of two diblock copolymers

Two chemically dissimilar diblock copolymers, polybutadiene-b-poly(acrylic acid), PBd-b-PAA (M_w = 5.8–4 kg mol⁻¹) and poly(styrene)-b-poly(ethylene oxide), PS-b-PEO (M_w = 9–5 kg mol⁻¹) were blended in an effort to achieve morphologies typical of triblock copolymers. Blend compatibility was achieved by the hydrogen bond driven association of the PAA block of one diblock with the PEO block of the other. Small angle X-ray scattering was used to determine the morphologies of the compositions, which were further investigated using transmission electron microscopy and selective staining techniques. The crystallinity of the PEO block was determined by differential scanning calorimetry. The hydrogen bond interactions between PEO and PAA yielded a complex triblock lamellar morphology of the form PS-b-(PEO/PAA)-b-PBd-b-(PEO/PAA). This morphology was stable when crystallization of PEO was suppressed by sufficient interaction with PAA.     

Syntheses of amphiphilic biodegradable copolymers of poly(ethyl ethylene phosphate) and poly(3-hydroxybutyrate) for drug delivery

Biodegradable and amphiphilic triblock copolymers poly(ethyl ethylene phosphate)-poly(3-hydroxy-butyrate)-poly(ethyl ethylene phosphate) (PEEP-b-PHB-b-PEEP) have been successfully synthesized through ring-opening polymerization. The structures are confirmed by gel permeation chromatography and NMR analyses. Crystallization investigated by X-ray diffraction reveals that the block copolymer with higher content of poly(ethyl ethylene phosphate) (PEEP) is more amorphous, showing decreased crystallizability. The obtained copolymers self-assemble into biodegradable nanoparticles with a core-shell micellar structure in aqueous solution, verified by the probe-based fluorescence measurements and transmission electronic microscopy (TEM) observation. The hydrophobic poly(3-hydroxybutyrate) (PHB) block serves as the core of the micelles and the micelles are stabilized by the hydrophilic PEEP block. The size and size distribution are related to the compositions of the copolymers. Paclitaxel (PTX) has been encapsulated into the micelles as a model drug and a sustained drug release from the micelles is observed. MTT assay also demonstrates that the block copolymers are biocompatible, rendering these copolymers attractive for drug delivery. Supported by the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No.20060358036)     

Cytotoxicity of nonionic amphiphilic copolymers

The purpose of this study is to ascertain the relationship between the structure of an amphiphilic nonionic polymer and its toxicity for cells (cytotoxicity) growing in a culture. To this end, 16 polymers of different architectures and chemical structures are tested, namely, linear triblock copolymers of poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (Pluronics); diblock copolymers of propylene oxide, ethylene oxide, and hyperbranched polyglycerol; alternating and diblock copolymers of ethylene oxide and dimethylsiloxane; and two surfactants containing linear (Brij-35) or branched (Triton X-100) aliphatic chains. Polymer-cell interaction is assayed in a culture medium in the absence of serum. Effective concentrations of the polymers causing 50% cell death, EC₅₀, vary within three orders of magnitude. Toxic concentrations of the alternating copolymer, Triton X-100, and Brij-35 are lower than their CMC values. In contrast, all block copolymers, regardless of their chemical structures, become toxic at concentrations above the CMC; that is, they acquire cytotoxicity only in the micellar form. The EC₅₀ values of the copolymers depend on their hydrophilic-liphophilic balance (HLB) through the following empirical formula: EC₅₀ × 10⁶ = 8.71 × HLB^2.1. This relationship makes it possible to predict the cytotoxic concentration region of a block copolymer of a known structure.     

Poly(2-[dimethylamino]ethyl methacrylate)-b-poly(hydroxypropyl methacrylate)/DNA polyplexes in aqueous solutions

This study involves the investigation of the complexation ability of poly(2-[dimethylamino]ethyl methacrylate)-b-poly(hydroxypropyl methacrylate) (PDMAEMA-b-PHPMA) amphiphilic pH and thermoresponsive block copolymers, and their quaternized counterparts QPDMAEMA-b-PHPMA, toward short DNA in aqueous solutions. The PDMAEMA-b-PHPMA amphiphilic block copolymers present various self-assembly characteristics when inserted into aqueous media, depending on the composition, the solubilization protocol, the acidity and the temperature of the aqueous media. Copolymer aggregates-DNA interactions and nanostructure formation after complexation are investigated by dynamic light scattering and intensity measurements in aqueous solutions in a fixed temperature range, utilizing two different solubilization protocols for the copolymers. Ethidium bromide assays by fluorescence spectroscopy and ζ-potential measurements were also utilized to investigate the structure and properties of the DNA/copolymer polyplexes. The interpretation of such physicochemical characterization provides extra comprehension of the novel (Q)PDMAEMA-b-PHPMA copolymers self-assembly characteristics and assesses their ability for DNA complexation, stabilization, and delivery.     

Synthesis,Characterization and Aqueous Solution Behavior of a pH-responsive Double Hydrophilic Block Copolymer

The pH-responsive double hydrophilic block copolymer poly(ethylene glycol)-b-poly(methacylic acid-co-4-vinyl benzylamine hydrochloride salt) (PEG-b-PMAA/PVBAHS) was synthesized. A series of PEG-b-PMAA/PVBAHS with different molecule weights and compositions were characterized by IR, ¹H-NMR, elemental analysis and TGA. With different MAA/VBAHS ratio, the PEG-b-PMAA/PVBAHS copolymers had the different isoelectric point (IEP). Supermolecular structures of the block copolymers could be formed by the interionic interactions at different solution pH. Experiment results showed that the structures of the pH-responsive copolymers in aqueous solution could be changed at different pH environments. The aggregation of this double hydrophilic block copolymer in aqueous solution was determined by both of solution pH and copolymer composition.     

Poly(2-(dimethylamino)ethyl methacrylate)-b-poly(hydroxypropyl methacrylate) copolymers/bovine serum albumin complexes in aqueous solutions

Complexation ability of poly(2-(dimethylamino)ethyl methacrylate)-b-poly(hydroxy propyl methacrylate) (PDMAEMA-b-PHPMA) amphiphilic doubly thermo-responsive block copolymers, and their quaternized counterparts QPDMAEMA-b-PHPMA, toward bovine serum albumin (BSA) is studied in aqueous solutions. The PDMAEMA-b-PHPMA amphiphilic block copolymers self-assemble in nanostructured aggregates with PDMAEMA coronas having different inner structure and micro-polarity depending on the solubilization protocol utilized when inserted in aqueous media. By incorporating different BSA concentrations, we investigate the copolymer–protein interactions by light scattering measurements in aqueous solutions in a broad temperature range, utilizing different solubilization protocols for the copolymers. Fluorescence spectroscopy and ζ-potential measurements were also utilized to investigate the structure and properties of the copolymer/protein complexes formed in each case. Such knowledge may lead to a better understanding of the inner structure and micro polarity of the nanostructured aggregates formed by the novel (Q)PDMAEMA-b-PHPMA copolymers, along with their potential abilities in nanocarrier formation, protein complexation, stabilization, and delivery.     

Hierarchical mesostructures of biodegradable triblock copolymers via evaporation-induced self-assembly directed by alkali metal ions

Hierarchical mesostructures of poly(ε-caprolactone)-b-poly(ethylene oxide)-b-poly(ε-caprolactone) (PCL-PEO-PCL) triblock copolymers have been grown from evaporation-induced self-assembly directed by alkali metal ions. The self-assembly process began with a dilute homogeneous solution of the triblock copolymers in a mixture of tetrahydrofuran (THF) and water. THF preferentially evaporated under reduced pressure and induced the formation of amphiphilic polymer micelles. The spherical polymer micelles formed both in deionized water and NaOH aqueous solution. However, different mesostructures were discovered during the film depositing process for scanning electron microscopy observation. The polymer micelles were observed for the deposition sample in deionized water while sisal-like hierarchical mesostructures resulted from the film deposition of polymer micelles in NaOH aqueous solution. The sisal-like mesostructures and their formation process were observed through scanning electron microscopy, transmission electron microscopy, fluorescent microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. Detailed study revealed that during evaporation-induced self-assembly of PCL-PEO-PCL amphiphilic triblock copolymer directed by alkali metal ions, the sodium ions and polymer micelles increasingly concentrated in NaOH aqueous solution and the solvent quality for the diblock progressively decreased, which resulted in the stronger coordination between alkali metal ions and PEO ligands in the block copolymer and PEO segment crystallization.     

Effect of stereocomplex formation between enantiomeric poly(l,l-lactide) and poly(d,d-lactide) blocks on self-organization of amphiphilic poly(lactide)-block-poly(ethylene oxide) copolymers in dilute aqueous solution

The effect of crystallization of a hydrophobic poly(lactide) block on the self-organization of biocompatible and biodegradable amphiphilic poly(lactide)-block-poly(ethylene oxide) (PLA-b-PEO) copolymers in a dilute aqueous solution has been investigated. It was demonstrated that the co-crystallization of poly(L,L-lactide) [P(L,L)LA] and poly(d,d-lactide) [P(d,d)LA] chains under equimolar mixing of P(L,L)LA₄₆-b-PEO₁₁₃ and P(d,d)LA₅₆-b-PEO₁₁₃ copolymers resulted in the formation of stable and spontaneously water-redispersible stereocomplex micelles with semicrystalline P(L,L)LA/P(d,d)LA cores. It was shown that the P(L,L)LA₄₆ / P(d,d)LA₅₆-b-PEO₁₁₃ stereo-complex micelles produced by dialysis can be potential vehicles for the anticancer agent oxaliplatin     

Novel synthesis of biodegradable poly(lactide-co-ethylene glycol) block copolymers

Biodegradable and amphiphilic diblock copolymers [polylactide-block-poly(ethylene glycol)] and triblock copolymers [polylactide-block-poly(ethylene glycol)-block-polylactide] were synthesized by the anionic ring-opening polymerization of lactides in the presence of poly(ethylene glycol) methyl ether or poly(ethylene glycol) and potassium hexamethyldisilazide as a catalyst. The polymerization in toluene at room temperature was very fast, yielding copolymers of controlled molecular weights and tailored molecular architectures. The chemical structure of the copolymers was investigated with ¹H and ¹³C NMR. The formation of block copolymers was confirmed by ¹³C NMR and differential scanning calorimetry investigations. The monomodal profile of the molecular weight distribution by gel permeation chromatography provided further evidence of block copolymer formation as well as the absence of cyclic species. Additional confirmation of the block copolymers was obtained by the substitution of 2-butanol for poly(ethylene glycol); butyl groups were clearly identified by ¹H NMR as polymer chain end groups. The effects of the copolymer composition and lactide stereochemistry on the copolymer properties were examined. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2235–2245, 2007     

Thermal and self-nucleation behavior of molecular complexes formed by p-nitrophenol and the poly(ethylene oxide) end block within an ABC triblock copolymer

We have been able to prepare a molecular complex between the poly(ethylene oxide) block of a poly(ethylene)-b-poly(ethylene-alt-propylene)-b-poly(ethylene oxide) triblock copolymer and p-nitrophenol (PNP). The composition of the copolymer employed was: 24% PE, 57% PEP and 19% PEO in weight percent. The pure copolymer exhibited a non-conventional thermal behavior since the PEO block displayed a fractionated crystallization process during cooling. The PEO block/PNP complex did not show any apparent crystallization during cooling, instead cold crystallization during heating was observed and an approximately 30°C increase in melting point as compared to the neat PEO block within the copolymer. This caused an overlap in the melting regions of the PE block and the PEO block/PNP complex. The self-nucleation of the PE-b-PEP-b-PEO/PNP complex is very different from that of the neat triblock copolymer. An increased capacity for self-nucleation of the PEO block was produced by the complexation with PNP and therefore the three self-nucleation domains were clearly encountered for both the PE block and for the PEO block/PNP complex. Self-nucleation was able to show that the two crystallizable blocks can be self-nucleated and annealed in an independent way, thereby ascertaining the presence of separate crystalline regions in the triblock copolymer. Through the use of PNP, both the crystallinity and the melting point of the PE-b-PEP-b-PEO block copolymer employed here can be substantially increased. Similar results were obtained by complexation of the same ABC triblock copolymer with resorcinol.     

New Segmented Copolymers by Combination of Atom Transfer Radical Polymerization and Ring Opening Polymerization

Atom transfer radical polymerization (ATRP) and ring opening polymerization (ROP) were combined to synthesize various polymers with various structures and composition. Poly(ε-caprolactone)-b-poly(n-octadecyl methacrylate), PCL-PODMA, was prepared using both sequential and simultaneous polymerization methods. Kinetic studies on the simultaneous process were performed to adjust the rate of both polymerizations. The influence of tin(II) 2-ethylhexanoate on ATRP was investigated, which led to development of new initiation methods for ATRP, i.e., activators (re)generated by electron transfer (AGET and ARGET). Additionally, block copolymers with two crystalizable blocks, poly(ε-caprolactone)-b-poly(n-butyl acrylate)-b-poly(n-octadecyl methacrylate), PCL-PBA-PODMA, block copolymers for potential surfactant applications poly(ε-caprolactone)-b-poly(n-octadecyl methacrylate-co-dimethylaminoethyl methacrylate), PCL-P(ODMA-co-DMAEMA), and a macromolecular brush, poly(hydroxyethyl methacrylate)-graft-poly(ε-caprolactone), PHEMA-graft-PCL, were prepared using combination of ATRP and ROP.     

Low temperature ATRP of POSS-MA and its amphiphilic pentablock copolymers

A low temperature ATRP of methacryloisobutyl POSS (POSS-MA) is carried out, using poly(propylene glycol) (PPG)-based macroinitiator, in toluene with CuCl/PMDETA as the catalyst system, generating well-defined P(POSS-MA)-b-PPG-b-P(POSS-MA) triblock copolymer with Р~ 1.1. The semilogarithmic kinetic plot reveals first-order kinetics and the dispersity is observed to decrease as the reaction progresses—an indication of the controlled behavior of the polymerization. To assess the chain-end fidelity of the produced block copolymer, chain extension is carried out with oligo(ethylene glycol methacrylate) (OEGMA) that afforded water-soluble P(OEGMA)-b-P(POSSMA)-b-PPG-b-P(POSSMA)-b-P(OEGMA) pentablock copolymers. The SEC profiles suggest a quantitative initiation by the macroinitiator. By varying the monomer to initiator molar ratio, block copolymers with various P(OEGMA) chain lengths, ranging from 19 to 58 units on each side have been achieved with relative lower dispersity (Р< 1.4). Kinetic analysis of the ATRP of OEGMA, with P(POSSMA)-b-PPG-b-P(POSSMA) as the macroinitiator, suggests first-order kinetics and controlled nature of the polymerization. The PPG and P(OEGMA) segments impart a thermosensitive character to the obtained water-soluble amphiphilic hybrid block copolymers; hence they display temperature-dependent self-assembly behavior in aqueous medium.     

Synthesis of Amphiphilic ABCBA-Type Pentablock Copolymer from Consecutive ATRPs and Self-Assembly in Aqueous Solution

Summary: A novel amphiphilic ABCBA-type pentablock copolymer with properties that are sensitive to temperature and pH, poly(2-dimethylaminoethyl methacrylate)-block-poly(2,2,2-trifluoroethyl methacrylate)-block-poly(ε-caprolactone)-block-poly(2,2,2- trifluoroethyl methacrylate)-block-poly(2-dimethylaminoethyl methacrylate) (PDMAEMA- b-PTFEMA-b-PCL-b-PTFEMA-b-PDMAEMA), was synthesized via consecutive atom transfer radical polymerizations (ATRPs). The copolymers obtained were characterized by gel permeation chromatography (GPC) and ¹H nuclear magnetic resonance (NMR) spectroscopy, respectively. The aggregation behaviors of the pentablock copolymers in aqueous solution with different pH (pH = 4.0, 7.0 and 8.5) were studied. Transmission electron microscopic images revealed that spherical micelles from self-assembly of the pentablock copolymer were prevalent in all cases. The mean diameters of these micelles increased from 34, 46, to 119 nm when the pH of the aqueous solution decreased from 8.5, 7.0, to 4.0, respectively.     

Synthesis and characterization of aba-type block copolymer of poly(ϵ-caproplactone) with poly(ethylene glycol), by mean of activation end groups

Poly(?-caprolactone)-b-poly(ethylene glycol)-b-poly(?-caprolactone) (PCL-b-PEG-b-PCL) triblock copolymer were synthesized by mean anionic activation of the hydroxyl end groups of poly(ethylene glycol) in presence of diphenylmethylsodium. Copolymers were characterized by SEC, FT-IR and ¹H-NMR spectroscopy, TGA and DSC. Size exclusion chromatographic analysis of obtained copolymers indicated incorporation of CL monomer into PEG without formation of PCL homopolymer. Characterization by FT-IR and ¹H NMR spectroscopy of the resulting polymeric products, with respect to their structure, end-groups and composition, showed that they are best described as ester-ether-ester triblock copolymers, whose compositions can be adjusted changing the feeding molar ratio of PEG to CL. The thermal stability of triblock copolymers was less that PEG precursor, but higher that PCL homopolymer. Analysis by mean DSC showed that all copolymers were semi-crystalline and their thermal behavior depending on their composition.     

Effect of surface charge of polymeric micelles on in vitro cellular uptake

This work focuses on the interaction between polymeric micelles with different charged surfaces and cancer cells in order to study the influence of surface charge on the in vitro cellular uptake efficiency. The amphiphilic diblock copolymers poly(ε-caprolactone)-b-poly(ethylene oxide) (PCL-b-PEO) with different functional groups at the end of hydrophilic block were synthesized. The functional groups endue the micelles with different charges on the surfaces. The cellular uptake of micelles to T-24 cells (human bladder tumor cells), HepG2 cells (human liver hepatocellular carcinoma cell line) and Hela cells (human epithelial cervical cancer cells) was studied by means of flow cytometer and confocal laser scanning microscopy. The results indicate that the surface charges showed great influence on zeta potential of micelles at different pH values. The in vitro cellular uptake efficiency of micelles with different charged surfaces demonstrated different cellular uptake patterns to three kinds of cancer cells.     

Model block–graft copolymer via anionic living polymerization: Preparation and characterization of polystyrene-block-[poly(p-hydroxystyrene)-graft-poly(ethylene oxide)]-block-polystyrene

A model graft copolymer in which position of graft points was set to the center of a backbone molecule was prepared via anionic living polymerization. Polystyrene-block-poly(p-tert-butoxystyrene)-block-polystyrene (PSt-b-PBSt-b-PSt) was prepared by three-stage sequential addition. The tert-butyl group was removed from PBSt by hydrogen bromide to yield PSt-b-PHSt-b-PSt, having a poly(p-hydroxystyrene) (PHSt) block. The hydroxyl group of PHSt was reacted with dimeric potassium dianions of 1, 1-diphenylethylene (DPE-K) or cumyl potassium (cumyl K) to yield the corresponding macromolecular initiators of PSt-b-PHSt⁻K⁺-b-PSt containing the potassium alkoxide ion of PHSt. The newly formed alkoxide groups and remaining initiators of DPE-K or cumyl K are capable of initiating the additionally introduced ethylene oxide (EO). Thus, two block–graft copolymers of polystyrene-block-[poly(p-hydroxystyrene)-graft-poly(ethylene oxide)]-block-polystyrene (PSt-b-(PHSt-g-PEO)-b-PSt) were prepared by a “grafting from” process (backbone initiation). A PSt-b-PHSt-b-PSt backbone (M_n = 1.7₅ × 10⁵ by osmometry and M_w/M_n = 1.0₈ by GPC), and two PSt-b-(PHSt-g-PEO)-b-PSt block–graft copolymers (M_n = 2.4₅ × 10⁵ by osmometry and M_w/M_n < 1.1₀ by GPC) had narrow molecular weight distributions. A relationship between nonquantitative metallation and spacing of the graft points on a backbone molecule was discussed in detail. Two benzene-cast films formed clear microphase-separated structures of lamellar structure. The dependence of composition on the morphology of the block–graft copolymers was found to differ from that of common block copolymers. A degree of crystallinity of PEO segment and lamellar thickness of PEO phase serving as graft molecule were also found to differ from those of homo PEO and/or PEO segment in common block copolymer. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 3021–3034, 1998     

Block copolymers with liquid crystalline segments

This paper describes the synthesis and characterization of polystyrene-block-poly(2,2'-dimethyl-4,4'-biphenylene phenylterephthalate)-block-polystyrene and of poly(ethylene glycol)-black-poly(2,2'-dimethyl-4,4'-biphenylene phenylterephthalate)-block-poly (ethylene glycol) block copolymers. The ABA-triblock copolymers were synthesized by condensation reaction of telechelic poly(2,2'-dimethyl-4,4'-biphenylene phenylterephthalate) with ω-hydroxy polystyrene and ω-hydroxy poly(ethylene glycol) methyl ether of different molecular weights prepared by anionic polymerization. Some aspects of the liquid crystalline behavior and the phase transitions with respect to the block copolymer composition will be discussed.