The preparation and properties of BAB block copolymers based on polyethylene sulphide and polyisoprene

Block copolymers of ethylene sulphide (B) and isoprene (A) have been prepared by anionic synthesis using alkali metal complexes of naphthalene as initiator. Two series of block copolymers have been synthesized, one (based on sodium naphthalenide as initiator) having high molecular weights and the other (based on lithium naphthalenide) having low molecular weights.Physical properties of the block copolymers as a function of composition, molecular weight and polyisoprene microstructure have been studied. Polymers containing high molecular weight polyethylene sulphide sequences were difficult to process without degradation. By lowering the molecular weight of the polyethylene sulphide segment, block copolymers of improved processibility were obtained.The centre block polyisoprene microstructure has been varied from 100% 1,2/3,4 configuration to 80% 1,4 configuration by preparing a “seed” polymer in tetrahydrofuran followed by solvent removal and replacement by hexane. Changes in microstructure affect low temperature flexibility, resilience and tensile strength of the block copolymer.The BAB block copolymers are biphasic and exhibit elastomeric properties with improved network stability compared with polystyrene-polybutadiene-polystyrene ABA block copolymers.     

Surface properties of styrene–ethylene oxide block copolymers

Hydrophobic–hydrophilic block copolymers were prepared by “living” anionic polymerization. They consist of polystyrene and poly(ethylene oxide) blocks, and are soluble in water. Their interfacial properties were investigated, employing aqueous solutions. The block copolymers lowered the surface tension of water in analogy with the low molecular weight surfactants such as sodium lauryl sulfate and heptaethylene oxide n-dodecyl ether. Their aqueous solutions exhibited solubilization properties differing from those of polyethylene glycol. Therefore, it is thought that the polystyrene blocks produce solubilization phenomena. In samples of the same styrene content, the precipitation temperature of a high molecular weight copolymer in water was lower than that of a low molecular weight copolymer at the same concentration in the same solvent. The surface tension and precipitation temperature of aqueous solutions seem to be influenced by molecular weight and composition.     

Crystalline-crystalline block copolymers of regioregular poly(3-hexylthiophene) and polyethylene by ring-opening metathesis polymerization

Block copolymers of regioregular poly(3-hexylthiophene) (P3HT) and polyethylene (PE) were synthesized through the chain transfer of olefin-terminated P3HT in the presence of cyclooctene via ring-opening metathesis polymerization (ROMP). Subsequent hydrogenation of the poly(cyclooctene) block yielded high molecular weight, crystalline-crystalline P3HT-PE block copolymers, which are thermally stable and resistant to solvents under ambient conditions. These copolymers were characterized by 1H NMR, DSC, and WAXS and represent the first materials of a class of crystalline-crystalline semiconducting-insulating block copolymers.     

Preparation of polyethylene block copolymers by a combination of postmetallocene catalysis of ethylene polymerization and atom transfer radical polymerization

The synthesis of block copolymers consisting of a polyethylene segment and either a poly(meth)acrylate or polystyrene segment was accomplished through the combination of postmetallocene-mediated ethylene polymerization and subsequent atom transfer radical polymerization. A vinyl-terminated polyethylene (number-average molecular weight = 1800, weight-average molecular weight/number-average molecular weight =1.70) was synthesized by the polymerization of ethylene with a phenoxyimine zirconium complex as a catalyst activated with methylalumoxane (MAO). This polyethylene was efficiently converted into an atom transfer radical polymerization macroinitiator by the addition of α-bromoisobutyric acid to the vinyl chain end, and the polyethylene macroinitiator was used for the atom transfer radical polymerization of n-butyl acrylate, methyl methacrylate, or styrene; this resulted in defined polyethylene-b-poly(n-butyl acrylate), polyethylene-b-poly(methyl methacrylate), and polyethylene-b-polystyrene block copolymers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 496–504, 2004     

Synthesis of Polyacrylamide Flocculants with Polyethylene Glycol Segments by Photopolymerization

Abstract

Macro photoinitiators possessing polyethylene glycol(PEG) segments were used for radical polymerization of acrylamide(AAm) to yield high molecular weight block copolymers (PAAm-b-PEG-b-PAAm) composed of PEG and polyacrylamide(PAAm) as the inner segment and outer segment respectively. The block copolymers were used as flocculates to clear a saturated borax solution prepared from tincal concentrate and showed good flocculating properties.     

聚己内酯,聚乙二醇及其嵌段物的结晶行为

聚己内酯，聚乙二醇及其嵌段物的结晶行为高家武，段跃新，王身国，邱波（北京航空航天大学材料科学与工程系北京１０００８３）（中国科学院化学研究所北京）关键词聚己内酯，聚乙二醇，嵌段共聚物，结晶度，结晶动力学聚己内酯（ＰＣＬ）作为生物降解材料，无毒、无副作...     

基于聚乙烯的无规和嵌段接枝共聚物的制备

采用乙烯配位聚合和巯基-烯点击化学相结合的方法制备了羟基封端的线性聚乙烯,末端羟基含量接近100%;利用酰氯与羟基的高效反应,将羟基封端的聚乙烯转化为降冰片烯封端的聚乙烯大单体(PE-NB).使用Grubbs II代催化剂,将大分子单体与降冰片烯(NB)单体进行开环易位共聚,通过调整单体的投料比和加料方式制备了分子量和组成可控的聚降冰片烯-g-聚乙烯(PNB-g-PE)接枝共聚物.其中,无规共聚时,大单体的转化率接近100%,所得无规接枝共聚物的重均分子量为1.79×10~4~3.14×10~4,分子量分布指数为2.09~2.60,聚乙烯链段的质量分数为4.6%~16.8%;而嵌段共聚时,由于空间位阻原因,大单体的转化率约为80%.热分析研究发现,由于空间位阻,接枝共聚物的结晶度较聚乙烯前驱体略有下降,且接枝度越大,结晶能力下降得越多.     

“Super microcapsules” (SMC). I. Preparation and characterization of star polymethylene oxide (PEO)?polylactide (PLA) copolymers

A new model of molecular scale microcapsule named “super microcapsule” (SMC) obtained from a star copolymer consisting of hydrophilic and hydrophobic blocks was presented. As a first stage, 3 and 4-arm star polyethylene oxide-polylactide copolymers (s-PEO-PLA) were synthesized by the use of triethanolamine and pentaerythritol and initiating agent, respectively. The block length of PLA and PEO for the copolymers can be controlled by feed and reaction conditions. The molecular weight distributions found to be in the range of 1.3–1.7. The DTA data indicated that the phase separation behavior of s-PEO? PLA copolymers is different from that of linear PEO? PLA copolymers with comparable block length. As a evidence of SMC, the shell-core structure of s-PEO? PLA copolymers in solid state was observed by TEM. The SMC dimensions were estimated to be about 400–1000 Å     

Evaluation of methoxy polyethylene glycol‐polylactide diblock copolymers as additive in hypromellose film coating

This paper deals with a new application of diblock methoxy polyethylene glycol‐polylactide block copolymers, a class of synthetic biomaterials largely studied in the pharmaceutical and biomedical fields owing to their favorable properties such as biocompatibility, biodegradability, low immunogenicity, and good mechanical properties. In this work, these materials were evaluated as additives for gastro‐soluble pharmaceutical coating aimed to reduce film stiffness and water permeability. Two copolymers with different polylactide chain lengths were synthesized and characterized in term of molecular weight and solid‐state properties. A series of free films with different hypromellose/copolymers ratio were prepared and characterized in terms of appearance, components miscibility, plasticity, and water vapor permeability. The obtained results demonstrate that copolymers effectively influence hypromellose film properties according to their concentration and molecular weight. Specifically, the addition of the copolymer with a molecular weight of 6.5 kDa in a ratio hypromellose:polymer 5:1, allowed to obtain films with good appearance, improved plasticization, and water permeability properties. For higher molecular weight, copolymer or different ratios was not possible to observe the improvement of all the properties at the same time. The results also make possible to define the critical features to improve in order to use block copolymers as additive in hypromellose film coating. The availability of new water‐soluble additives able to work as plasticizer and moisture sealer in polymeric films represents an important progress not only in the field of pharmaceutical coating but also in that of food coatings, as for example in the formulation of edible films. Copyright © 2013 John Wiley & Sons, Ltd.     

Block copolymers of ethylene. I. Butadiene

Block copolymers of ethylene and butadiene have been prepared to study their properties. The method of preparation of polybutadiene, polyethylene, and block copolymers of ethylene and butadiene with n-butyl lithium-tetramethyl ethylene diamine complex is outlined. Kinetic studies have been reported elsewhere and these are assessed to determine that suitability of the system to produce monodispersed “living” chains so that simple correlations between physical properties and molecular weight can be made. The properties were somewhat restricted by the 1,2-microstructure of the butadiene block.     

Interaction forces between polyethylene oxide-polypropylene oxide ABA copolymers adsorbed to hydrophobic surfaces

Block and graft copolymers are frequently used as stabilizing agents in colloidal dispersions. One common material is the range of polymers known as "Pluronics," which is a BASF trade name for ABA block copolymers composed of a propylene oxide anchoring block (B block) and two ethylene oxide buoy or stabilizing blocks (A block); the equivalent ICI (Uneqima) trade name is Synperonic. In the work presented here the interactions between adsorbed layers of these materials immersed in 10(-2) M sodium sulfate solutions are presented. The block copolymers investigated had an approximately fixed molecular weight of around 3250 Da for the anchoring B block, whilst the molecular weight of the stabilizing polyethylene oxide chains varies around 800-6500 Da. Hydrophobic glass surfaces were used as the test substrate. It was found that in the absence of polymer a long ranged attractive interaction is observed, typical for the interaction between hydrophobic surfaces in aqueous media, but that in the presence of the polymers a repulsion was observed. The repulsion became longer ranged as the molecular weight of the ethylene oxide chain increased. On separation of the surfaces, the interaction was slightly longer ranged, suggesting that the two polymer layers intertwine and stretch each other on separation. This effect was more noticeable for the higher molecular weight polymers. The compression data were well described using a scaling analysis for the interaction between polymer brushes.     

The crystallization characteristics of ethylene block copolymers

Block copolymers of ethylene and butadiene with short ethylene sequences and degrees of polymerization up to 250 have been studied calorimetrically to determine their structure in the melt and also on crystallization. Crystallization rate characteristics and the thermodynamic parameters of the melting of block copolymers were studied. Block copolymers with ethylene sequences with degrees of polymerization below 20–30 were amorphous. Those with ethylene sequences of 35–45 units crystallized with extended chain crystals; above 45 units the polyethylene blocks crystallized with chain folding. There was a corresponding reduction in the melting point of the crystals and in the surface free energy of the crystals. The extent of crystallinity that developed within the copolymers was dependent on crystallization temperature and independent of time. This behavior was unlike that exhibited by polyethylene samples of similar molecular weight and was considered due to the effect of phase separation of the two blocks in the melt and nucleation control of the crystallization of the isolated domains. Analogous behavior was observed with polyethylene for polymer blends with polystyrene.     

Morphologies and domain sizes of microphase-separated structures of block and graft copolymers of different types

Well-defined block and graft copolymers of different types with different compositions and molecular weights, such as styrene(S)-2-vinylpyridine(P) diblock copolymers, SP star-shaped block copolymers, PSP triblock copolymers, styrene(S)-isoprene(I) multiblock copolymers of the (SI)_n type, ISP triblock copolymers, SPP graft copolymers and their deuterated samples were prepared. Variations of the morphologies with compositions, molecular weight dependences of the lamellar domain sizes and conformations and distributions of block chains in the lamellar domains were studied in the strong segregation limit. Besides typical morphologies such as spherical, cylindrical and lamellar structures, ordered bi- and tri-continuous structures were found between cylindrical and lamellar structures for SP diblock copolymers, PSP and ISP triblock copolymers, respectively. The composition ranges of morphologies are different for the block and graft copolymers of different types. The molecular weight dependences of lamellar domain sizes are about the same, but their magnitudes are not always the same for the block and graft copolymers of different types. These results are well explained by the theories of Helfand-Wasserman and Semenov. Block chains in lamellae are extended along the direction perpendicular to lamellae, but they are contracted along the parallel direction. The former result is well explained by the theories, but the latter is not. Chains adjacent to the junction points between different block chains are localized near the domain interface, but chains at the free-ends of block chains are widely distributed in the domain with the maximum at the center of domain.     

聚对苯二甲酸乙二醇酯/聚乙二醇醚插层嵌段共聚物的结晶性能

合成了不同用量、不同分子量的聚乙二醇醚(PEG)或聚丁二醇醚(PTMC)与聚对苯二甲酸乙二醇酯(PET)/蒙脱土(MMT)的嵌段共聚物。研究了MMT在共聚物中的分散状态及PEG或PTMG对PET/MMT插层聚合物结晶性能的影响。结果表明,MMT在共聚物中以纳米尺寸分散;加入PEG或PTMG增强了聚酯链段的柔顺性,使共聚物熔体降温过程的结晶温度提高,冷结晶温度降低,即插层嵌段共聚物的结晶速率提高;在合成的共聚物中,分子量为2000,用量为DMT的6%的PEG对插层共聚物结晶速率的促进作用最大     

Morphology and domain size of a model graft copolymer

We prepared well-defined styrene (S)-2-vinyl-pyridine (P) graft copolymers of the ABB type or SPP graft copolymers, in which as block chain is grafted at the center of a block chain, as a model graft copolymer by anionic polymerization and coupling reaction. The composition dependence of morphology of SPP graft copolymers is qualitatively the same as that of SP diblock copolymers, but the composition range of each structure is shifted to the higher volume fraction of S block chain. The molecular weight dependence of lamellar domain size of SPP graft copolymers is almost the same as that of SP diblock copolymers, but the magnitudes are smaller. These experimental results are well explained by the difference in chain architectures.     

Structure and properties of sequentially polymerized propylene-b-[ethylene-co-propylene]-b-propylene copolymers

The structure and properties of presumed block copolymers of polypropylene (PP) with ethylene-propylene random copolymers (EPR), i.e., PP-EPR and PP-EPR-PP, have been investigated by viscometry, transmission electron microscopy, dynamic mechanical analysis, differential scanning calorimetry, gel permeation chromatography, wide-angle x-ray diffraction, and other techniques testing various mechanical properties. PP-EPR and PP-EPR-PP were synthesized using δ-TiCl₃-Et₂-AlCl as a catalyst system. The results indicate that the intrinisic viscosity of these polymers increases with each block-building step, whereas the intrinsic viscosity of those prepared by chain transfer reaction (strong chain-transfer reagent hydrogen was introduced between block-building steps during polymerization) hardly changes with the reaction time. Compared with PP/EPR blends, PP-EPR-PP block copolymers have lower PP and polyethylene crystallinity, and lower melting and crystallization temperatures of crystalline EPR. Two relaxation peaks of PP and EPR appear in the dynamic spectra of blends. They merge into a very broad relaxation peak with block sequence products of the same composition, indicating good compatibility between PP and EPR in the presence of block copolymers. Varying the PP and EPR content affects the crystallinity, density, and morphological structure of the products, which in turn affects the tensile strength and elongation at break. Because of their superior mechanical properties, sequential polymerization products containing PP-EPR and PP-EPR-PP block copolymers may have potential as compatibilizing agents for isotactic polypropylene and polyethylene blends or as potential heat-resistant thermoplastic elastomers.     

Effect of structure of PEO-PPO-PEO copolymers on reverse micelle formation induced by compressed CO2

The micellization of PEO-PPO-PEO block copolymers in p-xylene has been studied in the presence of CO2. With the application of CO2, some copolymers with suitable molecular weights and EO ratios can form reverse micelles with critical micellization pressure up to 5.8 MPa. For the copolymers with the same length of PO block, higher EO ratios facilitate reverse micelle formation. For the copolymers with the same composition, higher molecular weight is favorable to form reverse micelles. With the suitable composition and molecular weight, the critical micelle pressure (CMP) of copolymers decreases with the increase in the lengths of PEO and PPO blocks due to the hydrophilic and folding effects, respectively. Both the EO ratios and the molecular weights are important for the formation of reverse micelle. The reverse micelle solution can solubilize water with W0 (molar ratio of water to EO segment) up to 3.3.     

Environment-responsive polymers for coating of pharmaceutical nanocarriers

Polyethylene glycol derivatives, such as block copolymers of polyethylene glycol and diacyllipids (for example, phosphatidylethanolamine) are widely used for surface modification of various pharmaceutical carriers in order to impart them longevity in the body. To make polyethylene glycol detachable from the surface of pharmaceutical carrier and facilitate the interaction of the carrier with target cells when in pathological zone, we have prepared a set of polyethylene glycol-phosphatidylethanolamine block copolymers with the pH sensitive hydrazone bond between polyethylene glycol and phosphatidylethanolamine, which destabilizes at lowered pH values typical for tumors and inflammation zones. We have demonstrated that the stability of the hydrazone bond at normal physiological pH (7.4) as well as the rate of its hydrolysis at pH 6 and below strongly depend on the type of substitutions at this bond. Using aliphatic and aromatic aldehydes and ketones, polyethylene glycol-phosphatidylethanolamine block copolymers were prepared with different stabilities and degradation rates, which can be useful in constructing stimuli-sensitive pharmaceutical carriers. The text was sabmitted by the authors in English. This work was supported by the NIH grants RO1 HL55519 and RO1 CA121838 to V.P. Torchilin.     

One-Step Synthesis of Triblock Copolymers via Simultaneous Reversible-Addition Fragmentation Chain Transfer (RAFT) and Ring-Opening Polymerization Using a Novel Difunctional Macro-RAFT Agent Based on Polyethylene Glycol

One-step synthesis of the triblock copolymers was carried out by reversible addition–fragmentation chain transfer (RAFT) polymerization of methyl methacrylate (MMA) and ring-opening polymerization (ROP) of β-butyrolactone (BL) or ?-caprolactone (CL) using a novel difunctional macro-RAFT agent. For this purpose, primarily PEG-Br (polyethylene glycol bromine) was obtained by using 3-bromopropanoyl chloride and PEGs (polyethylene glycols) with different molecular weights. Then, macro-RAFT agent was synthesized by the reaction of potassium ethyl xanthogenate and PEG-Br. By using macro-RAFT agent, poly(MMA-b-EG-b-BL), and poly(MMA-b-EG-b-CL) triblock copolymers were synthesized by changing some polymerization conditions such as monomer/initiator concentration, polymerization time. The effect of the reaction conditions on the polydispersity and molecular weights were also investigated. The block lengths of the triblock copolymers were calculated by using ¹H-nuclear magnetic resonance (¹H-NMR) spectra. It was observed that the block length could be altered by varying the monomer and initiator concentrations. The characterization of the products were achieved using ¹H-NMR, Fourier-transform infrared spectroscopy (FTIR), gel-permeation chromatography (GPC), thermogravimetric analysis (TGA), and fractional precipitation (γ) techniques.     

ABA triblock copolymers with a ring‐opening metathesis polymerization/macromolecular chain‐transfer agent approach

Block copolymers containing polystyrene and polycyclooctene were synthesized with a ring‐opening metathesis polymerization/chain‐transfer approach. Polystyrene, containing appropriately placed olefins, was prepared by anionic polymerization and served as a macromolecular chain‐transfer agent for the ring‐opening metathesis polymerization of cyclooctene. These unsaturated polymers were subsequently converted to the corresponding saturated triblock copolymers with a simple heterogeneous catalytic hydrogenation step. The molecular and morphological characterization of the block copolymers was consistent with the absence of significant branching in the central polycyclooctene and polyethylene blocks [high melting temperatures (114–127 °C) and levels of crystallinity (17–42%)]. A dramatic improvement in both the long‐range order and the mechanical properties of a microphase‐separated, symmetric polystyrene–polycyclooctene–polystyrene block copolymer sample was observed after fractionation. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 361–373, 2007