X-ray diffraction studies of ABA propylene–ethylene block copolymers

ABA triblock copolymers of propylene and ethylene, where the central block is a random copolymer of ethylene and propylene and the A blocks are either isotactic polypropylene or polyethylene, are described. Structural changes induced by stretching at room and elevated temperatures are reported. WAXS was used to monitor these changes. The results indicate theat block copolymers were synthesized and that different combinations of mechanical properties may be obtained by varying the type and length of the A blocks and adjusting the monomer ratio in the random B block.     

Synthesis and self-association in aqueous media of poly(ethylene oxide)/poly(ethyl glycidyl carbamate) amphiphilic block copolymers

New temperature sensitive AB, ABA, and BAB amphiphilic block copolymers consisting of hydrophilic poly(ethylene oxide) and hydrophobic poly(ethyl glycidyl carbamate) blocks were synthesized by anionic polymerization followed by chemical modification reactions. The self-association of the block copolymers in aqueous media was studied by UV-vis spectroscopy and dynamic and static light scattering. The obtained block copolymers spontaneously form micelles in aqueous media. The critical micellization concentration varied from 0.5 to 4 g/L depending on the copolymer architecture and composition. The influence of the temperature upon the self-association of the block copolymers was investigated. The increase of temperature did not affect the value of the critical micellization concentration, but led to the formation of better defined micelles with narrow size distribution.     

Physical properties of isobutylene based block copolymers

Physical, mechanical and thermal properties of a new class of isobutylene based model block copolymers are studied and contrasted with those of traditional thermoplastic elastomers based on polydienes and saturated polydienes (polyolefins) such as Kraton (or Vector) and Kraton G block copolymers. Melt state rheological and dynamic mechanical measurements confirm that thermodynamic interactions between polystyrene (S) and polyisobutylene (iB) or poly‐p‐tert‐butylstyrene (tbS) and iB are comparable to, if not larger than, those between S and polybutadiene (B) or S and ethylene/butene‐1 copolymer (EB). Physical properties for the S‐iB‐S and tbS‐iB‐tbS block copolymers, particularly the injection‐moldability and cut‐growth characteristics, are found to be considerably different from those found for the S‐B‐S and S‐EB‐S systems. We attribute this behavior to the longer entanglement chain length of iB compared with those for B and EB.     

New self-assembling biocompatible-biodegradable amphiphilic block copolymers

New biodegradable-biocompatible amphiphilic block copolymers were prepared in good yields by SnOct₂ catalyzed ring opening polymerization of ε-caprolactone initiated by monomethoxy-terminated poly(ethylene glycol) (MPEG). Coupling of the AB copolymers with hexamethylene diisocyanate afforded ABA (formally ABBA) block copolymers. Both AB and ABA copolymers were thoroughly characterized by IR and NMR spectroscopy, size exclusion chromatography, TGA and DSC thermal analysis. In particular, DSC measurements evidenced that the copolymer hydrophilic-lipophilic balance appreciably affected the state of adsorbed water. Polarized optical microscopy of bulk materials and pyrene fluorescence emission of polymer water solutions highlighted the copolymer tendency to phase separation and self-organization, respectively. Most of the prepared materials formed micelles in water and the copolymer structure appreciably affected their critical micellar concentration. In vitro cytocompatibility tests confirmed the low toxicity of the prepared polymeric materials which enhances their potential for biomedical applications.     

Rheological,mechanical and thermal properties of propylene‐ethylene block copolymer/polyalphaolefins blends

The rheological, thermal, and mechanical properties of propylene–ethylene block copolymer (PPB) blends with predominantly atactic molecular structure of low molecular weight polypropylene and propylene copolymers with either ethylene or 1‐butene (APAO) have been studied. It has been found that blend properties depend on comonomer type, content, and molecular weight of APAO as well as blend composition. APAO having ethylene comonomer showed better miscibility with PPB than the other ones, and high comonomer content of APAOs gave dramatic increase in impact strength over 30 wt%. It has been concluded that APAO can be used as an effective modifier of PPB. POLYM. ENG. SCI., 47:1905–1911, 2007. © 2007 Society of Plastics Engineers     

Novel non-ionic block copolymers tailored for interactions with phospholipids

The bulk of literature on phospholipid membrane interactions with non-ionic amphiphilic block copolymers deals with ABA triblock copolymers of poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide). This is partially the result of their commercial availability. In recent years novel block copolymers have been synthesized and their interactions with phospholipids structured as Langmuir monolayers, liposomes, bilayer lipid membranes, tethered bilayers, and living cells have been studied. This review describes some new block copolymers with potential to interact with phospholipids. There is a tremendous progress in synthesis of amphiphilic block copolymers triggered by new controlled polymerization techniques as atom transfer radical polymerization or nitroxide mediated polymerization and by the possibility to ‘click’ preformed blocks together using quantitative reactions of functional endgroups. A special focus is given to novel water soluble amphiphilic triblock copolymers of poly(glycerol monomethacrylate)-b-poly(propylene oxide)-b-poly(glycerol monomethacrylate) and their interactions with phosphatidylcholine lipids. Also block copolymers containing hydrophobic blocks with perfluoroalkyl groups are discussed since they are special in a sense that their fluorophilic blocks are neither hydrophilic nor oleophilic as this is the case for conventional amphiphilic block copolymers. Experimental methods to study block copolymer–phospholipid interactions are summarized and selected results based on special experimental techniques such as isothermal titration calorimetry, infrared reflection absorption spectroscopy and ion conductance are presented. This work is intended to convey a better quantitative understanding of amphiphilic block copolymers used for in vitro and in vivo experiments in medicine and pharmacy.     

The measurement of compositional heterogeneity in a propylene–ethylene block copolymer

¹³C nuclear magnetic resonance (n.m.r.) and Fourier transform infra-red (FTi.r.) spectroscopies, as well as wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (d.s.c.) and temperature rising elution fractionation (TREF), have been combined to measure the composional heterogeneity of a commercial propylene–ethylene block copolymer. It has been shown that the copolymer contains molecular species with a wide variation in composition, and the copolymer products range from amorphous ethylene–propylene rubbers (EPR) to crystallisable propylene–ethylene statistical copolymers, polyethylene and polypropylene homopolymers as well as blocks of various lengths. The so-called block copolymer was composed of about 15% amorphous EPR, 5% random copolymer, 28% block copolymers with long propylene and long ethylene sequences, and 52% homopolypropylene. The crystallisation and melting behaviour of these fractions have been investigated.     

聚酯酰亚胺聚醚嵌段共聚物的合成与性能研究

采用均苯四酸酐与氨基乙酸合成了酰亚胺二元酸单体,此单体与乙二醇、聚乙二醇熔融缩聚合成3 种不同软／硬段比例分别为7／3,6／4,5／5的耐高温聚酯酰亚胺聚醚嵌段共聚物。通过红外光谱与氢谱确定 了酰亚胺二元酸单体的化学结构,DSC测定其熔点为358℃;利用显微熔点仪、乌式粘度计测定了共聚物的 熔点和特性粘数,3种共聚物熔点分别为232,248,260℃,软／硬段比例为7／3的共聚物的特性粘数为1.12 dL／g。将共聚物熔融纺丝,可纺性较好,纤维在120℃较160℃热定型效果好。     

苯乙烯类嵌段共聚物黏弹行为研究进展

综述了国内外苯乙烯类嵌段共聚物黏弹行为研究进展。着重从苯乙烯类嵌段共聚物溶液和熔体的黏弹行为两方面介绍苯乙烯类嵌段共聚物所表现出的特殊流变特性,以及流变特性与形态结构之间的关联。并基于已有的研究现状提出了苯乙烯类嵌段共聚物黏弹行为研究的前沿与重点。     

Synthesis, characterization and properties of chitosan modified with poly(ethylene glycol)-polydimethylsiloxane amphiphilic block copolymers

Synthesis of poly(ethylene glycol)-polydimethylsiloxane amphiphilic block copolymers is discussed herein. Siloxane prepolymer was first prepared via acid-catalyzed ring-opening polymerization of octamethylcyclotetrasiloxane (D₄) to form polydimethylsiloxane (PDMS) prepolymers. It was subsequently functionalized with hydroxy functional groups at both terminals. The hydroxy-terminated PDMS can readily react with acid-terminated poly(ethylene glycol) (PEG diacid) to give PEG-PDMS block copolymers without using any solvent. The PEG diacid was prepared from hydroxy-terminated PEG through the ring-opening reaction of succinic anhydride. Their chemical structures and molecular weights were characterized using ¹H NMR, FTIR and GPC, and thermal properties were determined by DSC. The PEG-PDMS copolymer was incorporated into chitosan in order that PDMS provided surface modification and PEG provided good water swelling properties to chitosan. Critical surface energy and swelling behavior of the modified chitosan as a function of the copolymer compositions and contents were investigated.     

Polyurethane tri‐block copolymers—Synthesis,mechanical, elastic,and rheological properties

A series of polyurethane tri‐block copolymers were synthesized by reacting a 4,4′‐methylenebis(phenyl isocyanate) (MDI)‐endcapped poly(tetramethylene oxide) (PTMO, M_n = 2,000 g/mol) with a monoamine‐diamide (6T6m) hard segment (HS). The concentration of the HS in the copolymer was varied between 9 and 33 wt % by changing the length of the soft mid‐block segment. The structure of the copolymers was analyzed by nuclear magnetic resonance, the amide crystallinity was investigated by Fourier transform infra‐red and the thermal properties were studied by differential scanning calorimetry. The mechanical and elastic properties of the tri‐block copolymer were subsequently explored by dynamic mechanical analysis, compression set and tensile experiments, and the melt rheological behavior was studied by a parallel plate method. The amide end groups displayed a high crystallinity and the modulus of the tri‐block copolymers was relatively high. The fracture strain increased strongly with the molecular weight and the copolymers demonstrated a ductile fracture behavior for molecular weights above 6000 g/mol. Good compression set values were obtained for the tri‐block copolymers despite their low molecular weight. In the molten state, the tri‐block polymers displayed a gelling effect at low frequencies, which was believed to be a result of a clustering of the end‐segments. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Rheological and mechanical properties of PEO/block copolymer blends

Small quantities of block copolymers from two families, styrene‐butadiene‐methylmethacrylate (SBM) and methylmethacrylate‐butylacrylate‐methylmethacrylate (MAM) have been added to a polyethylene oxide (PEO) in order to improve its processability, namely increasing its elastic modulus without increasing too much its shear viscosity. The copolymers contain one block of polymethylmethacrylate (PMMA) that is compatible with PEO; the other blocks create nano phases, dispersed in the PEO matrix. Considerable efforts were devoted to finding the best blending method, either melt processing or solution casting. PEO is very sensitive to shear, and was found to degrade both in the bulk and in solution. Degradation, which cannot be avoided, was quantified through intrinsic viscosity measurements. The rheological characterization of blends containing 1, 2, and 5 wt% block copolymer was carried out. The elastic modulus was found to increase more than the complex viscosity. Blends obtained by solution casting technique gave better results. The elongational viscosity obtained for one blend containing 5 wt% of SBM showed a slight increase with respect to the pure PEO. Mechanical properties were then investigated, through tensile tests and dynamic mechanical analysis in flexion and in torsion; the copolymer generally enhanced the mechanical properties. POLYM. ENG. SCI., 45:1385–1394, 2005. © 2005 Society of Plastics Engineers     

Melt rheological and thermodynamic properties of polyethylene homopolymers and poly(ethylene/α-olefin) copolymers with respect to molecular composition and structure

Various types of polyethylene homopolymers and copolymers, including linear high-density polyethylene (HDPE), branched low-density polyethylene (BLDPE), poly(ethylene vinyl acetate) copolymer (EVA), heterogeneous linear poly(ethylene/α-olefin) copolymer (het-LEAO) or commonly known as linear low-density polyethylene, homogeneous linear poly(ethylene/α-olefin) copolymer (hom-LEAO), and homogeneous branched poly(ethylene/α-olefin) copolymer (hom-BEAO), were evaluated for their melt rheological and thermodynamic properties with emphasis on their molecular structure. Short-chain branching (SCB) mainly controls the density, but it has little effect on the melt rheological properties. Long-chain branching (LCB) has little effect on the density and thermodynamic properties, but it has drastic effects on the melt rheological properties. LCB increases the pseudo-plasticity and the flow activation energy for both the polyethylene homopolymer and copolymer. Compared at a same melt index and a similar density, hom-LEAO has the highest viscosity in processing among all polymers due to its linear molecular structure and very narrow molecular weight distribution. Small amounts of LCB in hom-BEAO very effectively reduce the average viscosity and also improve the flow stability. Both hom-LEAO and hom-BEAO, unlike het-LEAO, have thermodynamic properties similar to BLDPE. © 1996 John Wiley & Sons, Inc.     

Biodegradable elastomers based on ABA triblocks: influence of end‐block crystallinity on elastomeric character

ABA triblock copolymers, based on biodegradable monomers, namely ε‐caprolactone (CL) and L ‐lactide (LLA), were synthesized and studied. The end‐blocks were mostly poly(L ‐lactide) while the middle segments were a random copolymer of PCL and PLLA. Synthesis of these copolymers was performed by varying the end‐block segment length while retaining a fixed middle‐block segment length and vice versa. Nuclear magnetic resonance studies confirmed the designed structure of the copolymers and their thermal properties were studied with differential scanning calorimetry. Mechanical and thermomechanical properties were determined with an Instron tester and by dynamic mechanical analysis, respectively. The elastomeric character of the copolymers was verified by cyclic test as well as by creep and recovery measurements. Changes made to the middle‐ and end‐block segment lengths had a significant influence on the mechanical properties of the copolymers, especially their extendibility and recoverability. An increase in the crystallinity of the end‐blocks in the copolymers caused a drop in their elastomeric character. In cyclic testing, under conditions of 50% and 150% strain, copolymers with low end‐block crystallinity could recover more than 85% whereas copolymers with high crystallinity showed reduced recovery values as low as 60%. Copyright © 2011 Society of Chemical Industry     

Polymerization of α, α-disubstituted-β-propiolactones and lactams. 9. ABA block copolymers of α-methyl-α-butyl-β-propiolactone and pivalolactone

ABA block copolymers were prepared by the anionic polymerization of α-methyl-α-butyl-β-propiolactone, MBPL (B block), and pivalolactone, PL (A blocks). The MBPL block had a very low decree of crystallinity and a glass temperature of ? 13°C, so phase separation with extensive crystallization of the PL blocks gave thermoplastic elastomers when the MBPL block constituted the principal and continuous phase. The observed crystallinity and melting point of 40–45°C in the MBPL homopolymer have not been previously reported. Measurements were obtained by electron microscopy of the initial size distribution of the PL domains as a function of copolymer composition and degree of polymerization, and on the effect of annealing on this parameter. Tensile strengths and elongations at break were both less than those previously observed for equivalent ABA block copolymers of PL and α-methyl-α-propyl-β-propiolactone.     

Effect of molecular structure of styrene–butadiene block copolymers on morphology,rheological properties,and impact strength of polystyrene/polyethylene blends

The effect of molecular structure of six model styrene–butadiene (SB) block copolymers with various number of blocks and two lengths of styrene blocks on morphology, rheological properties, and impact strength of polystyrene (PS)/high‐density polyethylene (PE) blends was studied. It was found that location of SB copolymers in the blends is determined by the length of styrene blocks. The length of styrene blocks has similar effects on impact strength and linear viscoelastic properties of the blends. On the other hand, the correlation was not found between the effects of a number of blocks on impact strength and linear viscoelastic properties of the blends. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2303–2309, 2003     

Effect of the molecular structure of ethene–propene and styrene–butadiene copolymers on their compatibilization efficiency in low‐density polyethylene/polystyrene blends

The effect of the molecular structure of styrene–butadiene (SB) block copolymers and ethene–propene (EPM) random copolymers on the morphology and tensile impact strength of low‐density polyethylene (LDPE)/polystyrene (PS) (75/25) blends has been studied. The molecular characteristics of SB block copolymers markedly influence their distribution in LDPE/PS blends. In all cases, an SB copolymer is present not only at the interface but also in the bulk phases; this depends on its molecular structure. In blends compatibilized with diblock copolymers, compartmentalized PS particles can also be observed. The highest toughness values have been achieved for blends compatibilized with triblock SB copolymers. A study of the compatibilization efficiency of SB copolymers with the same number of blocks has shown that copolymers with shorter PS blocks are more efficient. A comparison of the obtained results with previous results indicates that the compatibilization efficiency of a copolymer strongly depends both on the blend composition and on the properties of the components. The compatibilization efficiency of an EPM/SB mixture is markedly affected by the rheological properties of the copolymers. The addition of an EPM/SB mixture containing EPM with a higher viscosity leads to a higher improvement or at least the same improvement in the tensile impact strength of a compatibilized blend as the same amount of neat SB. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

The melt rheological behavior of AB,ABA, BAB,and (AB)n block copolymers with monodisperse aramide segments

The melt rheological behavior of segmented block copolymers with high melting diamide (A) hard segments (HS) and polyether (B) soft segments was studied. The block copolymers can be classified as B (monoblock), AB (diblock), ABA (triblock, diamide end segment), BAB (triblock, diamide mid‐segment) and ? (AB)_n? (multiblock) block copolymers. Varied were the number of HS in the chain, the HS concentration, the position of the HS (in the chain or at the end of the chain) and the molecular weight of the copolymers. The melt rheological behavior of the copolymers was studied with a plate–plate method. The materials B (monoblock), BAB (triblock, diamide mid‐segment), and ? (AB)_n? (multiblock) block copolymers had a rheological behavior of a linear polymer and the complex viscosity increased with molecular weight. Surprisingly, the diblock copolymers AB and the triblock copolymers ABA at low frequencies and near the melting temperature of the copolymers had the behavior of a gelled melt. The diamide segments at the chain end seemed to form aggregates, whereas the diamide mid‐segments did not. Also, time‐dependent rheology of diblock copolymer confirmed the network structure built up in the melt. The block copolymers with H‐bonding diamide end segments had a thixotropic behavior. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Properties of Block Copolymers of Poly(Butylene Terephthalate) and Polyoxytetramethylene Glycol

Synthesis of polyester thermoelastoplasts, block copolymers of polyoxytetramethylene glycol and poly(butylene terephthalate) of the polyblock type, was developed and implemented in pilot industrial conditions. POTM blocks act as flexible molecular decouplings that give the copolymer elasticity, while PBT blocks form physical linkages and are responsible for the mechanical strength and hardness of the material. The composition of the reaction systems, process stage sequence, and synthesis parameters are optimized for block copolymers with a concentration of the flexible POTM block of 65-10 wt. % and a molecular weight of 1000. The structure is investigated, and the physicochemical and mechanical properties of the material obtained are determined. It was found that the concentration of flexible blocks has a determining effect on the physicochemical structure and properties of the block copolymers. For a 40% concentration of the flexible block, the character of the concentration curves of the physicomechanical indexes changes significantly due to phase-structural transformations in the block copolymers.     

Emulsifying properties,of block copolymers. Oil-water emulsions and microemulsions

The emulsifying effect of poly(styrene-b-ethylene oxide) block copolymers (Cop PS-PEO) has been studied for the toluene-water system as a function of the molecular characteristics of the copolymer (composition, molecular weight, and structure). To demonstrate the surfactive properties of Cop PS-PEO, we determined the interfacial tension γ_i for the toluene-water system in the presence of these block copolymers. For oil/water (O/W) and water/oil (W/O) emulsions, prepared in the presence of Cop PS-PEO, we determined the phase inversion point, the particle size of the dispersed phase, the stability and the viscosity as a function of the PEO content, the molecular weight, and the structure of the block copolymers. It appeared that the best results for the emulsification are obtained with Cop PS-PEO having molecular weights less than 100, 000. Stable O/W emulsions of small particle size are preferentially prepared with di- or triblock copolymers having a PEO content of 60-80 percent. In contrast, stable W/O emulsions are obtained with diblock copolymers having a PS content of 60-80 percent. The difference in behavior between diand triblock copolymers also showed the importance of the chain conformation at the toluene-water interface. As an extension, we have shown that microemulsions can be obtained with such polymeric surfactants. Isopropanol and butylamine appeared to be efficient cosurfactants for the system water/toluene/Cop PS-PEO.