Spatial open-network formed by mixed triblock copolymers as a new medium for double-stranded DNA separation by capillary electrophoresis

A mixture of two polyoxybutylene-polyoxyethylene-polyoxybutylene (BEB) triblock copolymers (B6E46B6 and B10E271B10, respectively) was used as a new separation medium for separating double-stranded DNA (dsDNA) fragments by capillary electrophoresis (CE). The two block copolymer mixtures were designed to form mixed flower-like micelles in dilute solution and a homogeneous gel-like open-network with hydrophobic clusters as cross-linking points at higher polymer concentrations. Being a polyoxyalkylene block copolymer gel, the separation medium has some special advantages, including the temperature-dependent sol-gel transition that makes sample injection easy, and the self-coating of the inner capillary wall that makes experimental procedures simple and reproducible. Furthermore, it can shorten the elution time and further improve the separation resolution, especially for small dsDNA fragments, when compared with EPE-type separation media, e.g., F127 (E99P69E99, with P being polyoxypropylene) block copolymer gels formed by the closed packing of spherical micelles. Single base pair resolution can be achieved by using the new separation medium for dsDNA fragments up to over 100 base pairs.     

Mixed triblock copolymers used as DNA separation medium in capillary electrophoresis

A polymer solution, formed by mixing two polyoxybutylene-polyoxyethylene-polyoxybutylene (BEB) triblock copolymers (B10E270B10 and B6E46B6), was tested as a new separation medium for double-stranded DNA separation in capillary electrophoresis. The mixture of B10E270B10 and B6E46B6 has a viscosity-adjustable property and a dynamic coating ability, which makes the medium very easy to handle. The performance of the mixture on the DNA separation is greatly affected by the mass ratio of the two constituents. There is a minimum amount of concentration for B10E270B10, below which the medium will lose its performance. The addition of B6E46B6 increases both the selectivity and the separation efficiency. The optimal concentration, with 3% (w/v) B10E270B10 and 5% (w/v) B6E46B6, is determined with the consideration of both speed and resolution. A resolution of 1.3 was achieved on the separation of 123/124 base pairs in the pBR322/HaeIII digest within 20 min by using a 10 cm column of 75 microm I.D., demonstrating the potential use of mixtures of amphiphilic block copolymers as an effective DNA separation medium.     

Synthesis of urea‐containing ABA triblock copolymers: Influence of pendant hydrogen bonding on morphology and thermomechanical properties

Reversible addition‐fragmentation chain transfer (RAFT) polymerization produced novel ABA triblock copolymers with associative urea sites within pendant groups in the external hard blocks. The ABA triblock copolymers served as models to study the influence of pendant hydrogen bonding on polymer physical properties and morphology. The triblock copolymers consisted of a soft central block of poly(di(ethylene glycol) methyl ether methacrylate) (polyDEGMEMA, 58 kg/mol) and hard copolymer external blocks of poly(2‐(3‐hexylureido)ethyl methacrylate‐co‐2‐(3‐phenylureido)ethyl methacrylate) (polyUrMA, 18‐116 kg/mol). Copolymerization of 2‐(3‐hexylureido)ethyl methacrylate (HUrMA) and 2‐(3‐phenylureido)ethyl methacrylate (PhUrMA) imparted tunable hard block T_g's from 69 to 134 °C. Tunable hard block T_g's afforded versatile thermomechanical properties for diverse applications. Dynamic mechanical analysis (DMA) of the triblock copolymers exhibited high modulus plateau regions (∼100 MPa) over a wide temperature range (−10 to 90 °C), which was indicative of microphase separation. Atomic force microscopy (AFM) confirmed surface microphase separation with various morphologies. Variable temperature FTIR (VT‐FTIR) revealed the presence of both monodentate and bidentate hydrogen bonding, and pendant hydrogen bonding remained as an ordered structure to higher than expected temperatures. This study presents a fundamental understanding of the influence of hydrogen bonding on polymer physical properties and reveals the response of pendant urea hydrogen bonding as a function of temperature as compared to main chain polyureas. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1844–1852     

Synthesis and characterization of biodegradable triblock copolymers based on bacterial poly[(R)‐3‐hydroxybutyrate] by atom transfer radical polymerization

Biodegradable poly(tert‐butyl acrylate)–poly[(R)‐3‐hydroxybutyrate]–poly (tert‐butyl acrylate) triblock copolymers based on bacterial poly[(R)‐3‐hydroxybutyrate] (PHB) were synthesized by atom transfer radical polymerization. The chain architectures of the triblock copolymers were confirmed by ¹H NMR and ¹³C NMR spectra. Gel permeation chromatography analysis was used to estimate the molecular weight characteristics and lengths of the PHB and poly(tert‐butyl acrylate) blocks of the copolymers. The thermal properties of the copolymers were studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). TGA showed that the triblock copolymers underwent stepwise thermal degradation and had better thermal stability than their respective homopolymers, whereas DSC analyses showed that a microphase‐separation structure was formed only in the triblock copolymers with the longer PHB block. As a similar result, from wide‐angle X‐ray diffraction experimentation, the crystalline phase of PHB could not be seen evidently in the triblock copolymers with the shorter PHB block. The enzymatic hydrolysis of the copolymer films was carried at 37 °C and pH 7.4 in a potassium phosphate buffer with an extracellular PHB depolymerase from Penicillum sp. The biodegradability of the triblock copolymers increased with an increase in the PHB block content. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4857–4869, 2005     

Phase‐transition characteristics of amphiphilic poly(2‐ethyl‐2‐oxazoline)/poly(ε‐caprolactone) block copolymers in aqueous solutions

Amphiphilic diblock and triblock copolymers of various block compositions based on hydrophilic poly(2‐ethyl‐2‐oxazoline) (PEtOz) and hydrophobic poly(ε‐caprolactone) were synthesized. The micelle formation of these block copolymers in aqueous media was confirmed by a fluorescence technique and dynamic light scattering. The critical micelle concentrations ranged from 35.5 to 4.6 mg/L for diblock copolymers and 4.7 to 9.0 mg/L for triblock copolymers, depending on the block composition. The phase‐transition behaviors of the block copolymers in concentrated aqueous solutions were investigated. When the temperature was increased, aqueous solutions of diblock and triblock copolymers exhibited gel–sol transition and precipitation, both of which were thermally reversible. The gel–sol transition‐ and precipitation temperatures were manipulated by adjustment of the block composition. As the hydrophobic portion of block copolymers became higher, a larger gel region was generated. In the presence of sodium chloride, the phase transitions were shifted to a lower temperature level. Sodium thiocyanate displaced the gel region and precipitation temperatures to a higher temperature level. The low molecular weight saccharides, such as glucose and maltose, contributed to the shift of phase‐transition temperatures to a lower temperature level, where glucose was more effective than maltose in lowering the gel–sol transition temperatures. The malonic acid that formed hydrogen bonds with the PEtOz shell of micelles was effective in lowering phase‐transition temperatures to 1.0M, above which concentration the block copolymer solutions formed complex precipitates. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2400–2408, 2000     

Clouding Behavior of Ethylene Oxide‐Propylene Oxide Block Copolymer P85: The Effect of Additives

The characteristic feature of nonionic poly(ethylene oxide)‐poly(propylene oxide)‐poly(ethylene oxide) (PEO‐PPO‐PEO) triblock copolymers is that at higher temperatures they undergo clouding and liquid‐liquid phase separation. The clouding temperature of such block copolymers can be profoundly altered in the presence of various additives. In this work the effect of various additives on the clouding phenomenon of triblock copolymer P85[(EO)₂₆(PO)₃₉(EO)₂₆] is discussed.     

Structural Transitions in Triblock Copolymers Based on Poly(ethylene oxide) and Polyacrylamide under the Temperature Influence

Thermal transitions in the bulk structure of triblock copolymers (PAA-b-PEO-b-PAA) based on polyacrylamide and poly(ethylene oxide) with varying molecular weight (length) of PEO block comparing with the structures of individual polymers and polymer mixtures were investigated. A lot of effects, such as the melting temperature depression, decreasing of the crystallinity degree of PEO and also appearance of the microphase separation in amorphous regions of the polymer mixtures and the triblock copolymers were found. Such investigations pointed to a strong intramolecular interaction of the polymer blocks in the triblock copolymers that is confirmed by the results of IR spectroscopy. It was shown that PEO and PAA blocks formed the system of H-bonds with participant of trans-multimers of amide groups.     

Nanocrystallization-locked Network of Poly(styrene-b-isobutylene-b-styrene)-g-Polytetrahydrofuran Block Graft Copolymer

Poly(styrene-b-isobutylene-b-styrene) triblock copolymer(SIBS), a kind of thermoplastic elastomer with biocompatibility and biostability containing fully saturated soft segments, could be synthesized via living cationic copolymerization. A novel poly[(styrene-comethylstyrene)-b-isobutylene-b-(styrene-co-methylstyrene)]-g-polytetrahydrofuran(M-SIBS-g-PTHF) block graft copolymer was prepared to increase the polarity and service temperature of SIBS by grafting polar PTHF segments onto SIBS. A series of the above block graft copolymers with average grafting numbers from 2 to 6 and molecular weights of PTHF branches ranging from 200 g·mol~(-1) to 4200 g·mol~(-1) were successfully synthesized via living cationic ring-opening polymerization of tetrahydrofuran(THF) coinitiated by AgClO_4. The introduction of PTHF branches led to an obvious microphase separation due to thermodynamic incompatibility among the three kinds of segments of polyisobutylene(PIB),polystyrene(PS) and PTHF. Moreover, the microphase separation promotes the rearrangement of PTHF branches to form the nanocrystallizationlocked physically cross-linked network after storage at room temperature for 2 months, leading to insolubility of the copolymers even in good solvents. The melting temperature and enthalpy of PTHF nanocrystallization locked in hard domains of M-SIBS-g_5-PTHF~(-1).1 k block graft copolymer increased remarkably up to 153 °C and 117.0 J·g~(-1) by 23 °C and 11.6 J·g~(-1) respectively after storage for long time. Storage modulus(G')is higher than loss modulus(G') of M-SIBS-g-PTHF block graft copolymer at temperatures ranging from 100 °C to 180 °C, which is much higher than those of the SIBS triblock copolymer. To the best of our knowledge, this is the first example of high performance M-SIBS-g-PTHF block graft copolymers containing segments of PIB, PS and PTHF with nanocrystallization-locked architecture.     

聚(L-谷氨酸γ-苄酯)-聚四氢呋喃-聚(L-谷氨酸γ-苄酯)三嵌段共聚物的合成与表征

聚氨基酸是一类低毒性、生物相容性良好、易被机体吸收和代谢的可降解合成高分子材料，在药物控释载体、组织工程支架、生物材料表面改性方面得到了广泛应用．但其降解周期及降解速度通常难以控制，应用受到一定限制．通过共聚方法将生物相容和亲水性良好的聚乙二醇（PEG）引入聚氨基酸链段中形成两亲性嵌段共聚物旧，研究其自组装行为，及作为基因转染和药物控释载体等已成为高分子科学领域新的研究热点．     

Thermoresponsive hydrogels from symmetrical triblock copolymers poly(styrene-block-(methoxy diethylene glycol acrylate)-block-styrene)

A series of symmetrical, thermo-responsive triblock copolymers was prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization, and studied in aqueous solution with respect to their ability to form hydrogels. Triblock copolymers were composed of two identical, permanently hydrophobic outer blocks, made of low molar mass polystyrene, and of a hydrophilic inner block of variable length, consisting of poly(methoxy diethylene glycol acrylate) PMDEGA. The polymers exhibited a LCST-type phase transition in the range of 20-40 °C, which markedly depended on molar mass and concentration. Accordingly, the triblock copolymers behaved as amphiphiles at low temperatures, but became water-insoluble at high temperatures. The temperature dependent self-assembly of the amphiphilic block copolymers in aqueous solution was studied by turbidimetry and rheology at concentrations up to 30 wt %, to elucidate the impact of the inner thermoresponsive block on the gel properties. Additionally, small-angle X-ray scattering (SAXS) was performed to access the structural changes in the gel with temperature. For all polymers a gel phase was obtained at low temperatures, which underwent a gel-sol transition at intermediate temperatures, well below the cloud point where phase separation occurred. With increasing length of the PMDEGA inner block, the gel-sol transition shifts to markedly lower concentrations, as well as to higher transition temperatures. For the longest PMDEGA block studied (DP(n) about 450), gels had already formed at 3.5 wt % at low temperatures. The gel-sol transition of the hydrogels and the LCST-type phase transition of the hydrophilic inner block were found to be independent of each other.     

Liquid crystalline side-group block copolymers with triblock structure: Investigations on the influence of the block arrangement on the morphology and the LC-phase behavior

Liquid crystalline triblock copolymers with LC inner block and amorphous outer blocks have been synthesized by “living” anionic polymerization and investigated using DSC, TEM, and small-angle x-ray diffraction. All samples of poly[styrene-block-2-(3-cholesteryloxycarbonyloxy) ethyl methacrylate-block-styrene] (PS-b-PChEMA-b-PS) show liquid crystalline behavior and phase separation between the blocks. Compared to triblock copolymers with PS inner block (PChEMA-b-PS-b-PChEMA) and diblock copolymers (PS-b-PChEMA) the LC block copolymers with PS outer blocks have the same properties. The LC behavior and the morphology do not depend on the block arrangement; they are only influenced by the volume fractions of the blocks. Those samples in which the liquid crystalline subphase is not continuous (spheres) only a nematic phase was found, whereas in all samples with a continuous liquid crystalline subphase, the smectic A phase of the homopolymer was observed. © 1996 John Wiley & Sons, Inc.     

Nanostructured organic–inorganic hybrid films prepared by the sol–gel method from self‐assemblies of PS‐b‐paptes‐b‐PS triblock copolymers

ABA‐based triblock copolymers of styrene as block ends and gelable 3‐acryloxypropyltriethoxysilane (APTES) as the middle block were successfully prepared through nitroxide‐mediated polymerization (NMP). The copolymers were bulk self‐assembled into films and the degree of phase separation between the two blocks was evaluated by differential scanning calorimetry (DSC). Their morphology was examined through small angle X‐ray scattering (SAXS) and transmission electron microscopy (TEM), whereas the mechanical properties of the corresponding cross‐linked self‐assembled nanostructures were characterized by dynamic mechanical analysis (DMA). Acidic treatment of the triblock copolymers favored the hydrolysis and condensation reactions of the APTES‐rich nanophase, and induced a mechanical reinforcement evidenced by the increase of storage modulus values and the shift of the glass transition temperature to higher temperatures due to confinement effects. In addition, the lamellar structure of the hybrid films was retained after the removal of the organic part by calcination. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Morphology study of a series of azobenzene-containing side-on liquid crystalline triblock copolymers

A series of azobenzene containing side-on liquid crystalline ABA triblock copolymers were investigated.This triblock series possesses the same central liquid crystal block B and various lengths of the amorphous block A.Transmission electron microscopy(TEM),small angle X-rays and neutron scattering(SAXS and SANS) were used to study their morphologies.After annealing the samples over weeks at a temperature within the nematic temperature range of block B, different morphologies(disordered,lamellar,perforated layer and hexagonal cylinder) were observed by TEM.The alignment behavior of these azo triblock copolymers in the magnetic field for artificial muscle application,as well as the phase period and the order-disorder transition(ODT) were studied in situ by SANS.     

Glass transition temperature of low molecular weight styrene–isoprene block copolymers

Different series of poly(styrene–isoprene) diblock and poly(styrene–isoprene–styrene) triblock copolymers were prepared. In each series, the low molecular weight polystyrene block was kept constant, and the molecular weight of the polyisoprene block varied. The glass transition behavior of these polymers was studied and their glass transition temperatures compared with those of the random copolymers of styrene and isoprene. It is concluded that some low molecular weight styrene-isoprene block copolymers form a single phase. Krause's thermodynamic treatment of phase separation in block copolymers was applied to the data. One arrives at a polystyrene–polyisoprene interaction parameter χ1,2 ≈ 0.1. The experimental and theoretical limitations of this result are discussed.     

温敏性PCL-PEG-PCL水凝胶的合成、表征及蛋白药物释放

考察了温敏性PCL-PEG-PCL水凝胶中聚乙二醇(PEG)及聚己内酯(PCL)不同嵌段组成对其溶胶-凝胶相转变温度以及亲水性药物(牛血清白蛋白, BSA)释放速率的影响. 采用开环聚合法, 以辛酸亚锡为催化剂、PEG1500/PEG1000为引发剂, 与己内酯单体发生开环共聚, 合成了一系列具有不同PEG和PCL嵌段长度的PCL-PEG-PCL型三嵌段共聚物. 通过核磁共振氢谱及凝胶渗透色谱对其组成、结构及分子量进行了表征. 共聚物的溶胶-凝胶相变温度由翻转试管法测定. 利用透射电镜、核磁共振氢谱及荧光探针技术证实了该材料在水溶液中胶束的形成. 以BSA为模型蛋白药物, 制备载药水凝胶, 利用microBCA法测定药物在释放介质中的浓度, 研究其体外释放行为. 实验结果表明, 共聚物的溶胶-凝胶相变温度与PCL及PEG嵌段长度紧密相关, 即在给定共聚物浓度情况下, 固定PEG嵌段长度而增加PCL嵌段长度, 会导致相变温度降低; 而固定PCL嵌段长度而增加PEG嵌段长度, 其相变温度相应升高. 水凝胶中蛋白药物的释放速率与疏水的PCL嵌段长度无关, 而与亲水的PEG嵌段长度密切相关, 即PEG嵌段越长, 蛋白药物释放越快.     

Synthesis and characterization of ABA triblock copolymers containing poly(2,6-dimethyl-1,4-phenylene oxide) as A blocks and tetramethyl bisphenol-A polysulfone as B blocks

α, β-Bis(hydroxyphenol) tetramethyl bisphenol-A polysulfone (PSUT) was synthesized by two different methods, one using a strong base, the other using a weak base. The bifunctional polysulfone containing tetramethyl bisphenol-A chain ends was exploited as a model telechelic that can be used for the preparation of ABA triblock copolymers containing poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) as A segments and PSUT as B segments. PSUT and PPO were incorporated into triblock copolymers by an oxidative coupling copolymerization of PSUT with 2,6-dimethylphenol or by the redistribution of PPO in the presence of PSUT. The mechanism of block copolymerization is discussed. DSC studies indicate that short immiscible PPO and PSUT segments incorporated into a triblock copolymer do not exhibit phase separation. Polymer blends of the PPO–PSUT–PPO triblock copolymers with PPO homopolymer were analyzed by DSC. Both miscible and phase-separated blends can be prepared depending on the molecular weight of both PPO homopolymer and of the PPO segment present in the triblock copolymer. Polymer blends of the PPO–PSUT–PPO triblock copolymer with PSUT were miscible at all compositions.     

Preparation and properties of phenylene oxide–aryl ether sulphone block copolymers and their blends

We have prepared triblock copolymers of poly(phenylene oxide) (PPO) and polysulphone (PSF) of the form PPO–PSF–PPO in order to assess their intrinsic mechanical properties and their potential as interfacial compatibilizers in polystyrene/PSF blends. For sufficiently long polysulphone block lengths, we observed microphase separation both in the triblock copolymers and in their blends with polystyrene. The triblock polymers, nevertheless, showed very similar microdeformation behavior to the PPO homopolymer, suggesting the phase separation to play a minor role. On the other hand, the compatibility of the poly(phenylene oxide) blocks and polystyrene ensured a high degree of interphase adhesion in blends containing both polystyrene and free PSF, even for relatively high homopolymer molecular weights. © 1996 John Wiley & Sons, Inc.     

Temperature-induced self-assembly of triple-responsive triblock copolymers in aqueous solutions

A series of triple-thermoresponsive triblock copolymers from poly(N-n-propylacrylamide) (PNPAM, A), poly(methoxydiethylene glycol acrylate) (PMDEGA, B), and poly(N-ethylacrylamide) (PNEAM, C) was synthesized by sequential reversible addition-fragmentation chain transfer polymerizations. Polymers of differing block sequences, ABC, BAC, and ACB, with increasing phase transition temperatures in the order A < B < C were prepared. Their aggregation behavior in dilute aqueous solution was investigated using dynamic light scattering, turbidimetry, and NMR spectroscopy. The self-organization of such polymers was found to dependent strongly on the block sequence. While polymers with a terminal low-LCST (lower critical solution temperature) block undergo aggregation above the first phase transition temperature at 20-25 °C, triblock copolymers with the low-LCST block in the middle show aggregation only above the second phase transition. The collapse of the middle block is not sufficient to induce aggregation but produces instead stable, unimolecular micelles with a collapsed middle block, as supported by NMR and fluorescence probe data. Continued heating of all copolymers led to two additional thermal transitions at 40-55 and 70-80 °C, which could be correlated to the phase transitions of the B and C blocks, respectively. All polymers show a high tendency for cluster formation, once aggregation is induced. The carrier abilities of the triple responsive triblock copolymers for hydrophobic agents were probed with the solvatochromic fluorescence dye Nile Red. With passing through the first thermal transition, the block copolymers are capable of solubilizing Nile Red. In the case of block copolymers with sequences ABC or ACB, which bear the low-LCST block at one terminus, notable amounts of dye are solubilized already at this stage. In contrast, the hydrophobic probe is much less efficiently incorporated by the BAC triblock copolymer, which forms unimolecular micelles. Only after the collapse of the B block, when reaching the second phase transition at about 45 °C, does aggregation occur and solubilization becomes efficient. In the case of ABC and ACB polymers, the hydrophobic probe seems to partition between the originally collapsed A chains and the additional hydrophobic chains formed after the collapse of the less hydrophobic B block.     

Stereocomplexation and Mechanical Properties of Polylactide-b-poly(propylene glycol)-b-polylactide Blend Films: Effects of Polylactide Block Length and Blend Ratio

In the present work, poly(propylene glycol)(PPG) was block copolymerized to form polylactide-poly(propylene glycol)-polylactide(PL-PPG-PL) triblock copolymers for preparing flexible stereocomplex PL(sc PL) blend films. The sc PL blend films were prepared by solution blending of poly(L-lactide)-PPG-poly(L-lactide)(PLL-PPG-PLL) and poly(D-lactide)-PPG-poly(D-lactide)(PDL-PPG-PDL) triblock copolymers before film casting. The influences of PL end-block lengths(2×10~4 and 4×10~4 g/mol) and blend ratios(75/25, 50/50 and 25/75 W/W) on the stereocomplexation and mechanical properties of the blend films were evaluated. From DSC and WAXD results, the 50/50 blend films had complete stereocomplexation. Phase separation between the sc PL and PPG phases was not observed from their SEM images. The tensile stress and elongation at break increased with the sterecomplex crystallinities and PL end-block lengths. The PPG middle-blocks enhanced elongation at break of the sc PL films. The results showed that the PL-PPG-PL triblock structures did not affect stereocomplexation of the PLL/PDL block blending. In conclusion, the phase compatibility and flexibility of the sc PL films were improved by PPG block copolymerization.     

Synthesis of macrocyclic polystyrene-polydimethylsiloxane block copolymers

A series of macrocyclic polystyrene (PS)-polydimethylsiloxane (PDMS) block copolymers and similar block copolymers was synthesized by sequential polymerization of styrene and hexamethyl cyclotrisiloxane (D₃) initiated by a difunctional anionic initiator in THF at −78° followed by coupling with Cl₂SiMe₂ in very dilute (10⁻⁵ – 10⁻⁶ M) solutions. Total molecular weights ranged from about 2–85 × 10³. The formation of monodisperse macrocyclic block copolymers was indicated by the lower (15–30%) hydrodynamic volume of the rings compared to that of the linear block copolymers. Carbon-13 and ²⁹Si NMR likewise supported the absence of linear polymer in the macrocyclic block copolymer. The behavior of second virial coefficient A₂ of the rings and the linears versus temperature was examined by static light scattering in cyclohexane. Below 20° the A₂ for the linear polymer goes negative while that for the cycle remains positive. Dynamic light scattering (DLS) as a function of temperature also reflects that the cyclic polymers remain well solvated even down to 12°C. The DLS autocorrelation functions for the linear triblock however demonstrate the onset of aggregation and phase separation as the temperature is reduced below 20°C.