Solution properties of styrene-p-chlorostyrene diblock copolymers—I. Conformational behaviour in dilute solutions

The conformational behaviour of styrene-p-chlorostyrene diblock copolymers in dilute solutions was studied and compared with that of the corresponding triblock copolymers. Eight styrene-p-chlorostyrene diblock copolymers, of almost equimolar composition but with different molecular weights, were prepared using an anionic polymerization technique. The intrinsic viscosities of the copolymers were measured in non-selective solvents, such as toluene and 2-butanone, and in a selective solvent, cumene. The osmotic second virial coefficients of the diblock copolymers were measured in toluene. The data were analysed on the basis of two parameter theories. The unperturbed dimensions for the diblock copolymers can be expressed as a composition average of those for the parent homopolymers and the long-range interaction parameters of the diblock copolymers in toluene, 2-butanone and cumene are smaller than those of the triblock copolymers of the same composition. It means that the diblock copolymer chains in these 3 solvents had a more compact conformation than the triblock copolymers of the same composition and molecular weight.     

Solution properties of styrene-p-chlorostyrene diblock copolymers—II. Light scattering studies in a selective solvent

Conformational behaviour of styrene-p-chlorostyrene diblock copolymers in cumene (a good solvent for polystyrene but a θ solvent for poly-p-chlorostyrene) was studied over the temperature range 15–60° by light scattering, osmotic pressure and intrinsic viscosity measurements. Two samples of copolymer (AB-4 and AB-2) were used. The composition of the samples was c. 50 mol% of styrene and the number-average molecular weights were 27.7 × 10⁴ for the AB-4 and 19.5 × 10⁴ for the AB-2. It was found that below 40° the number-average molecular weight of the AB-4 sample seemed to increase gradually with decreasing temperature and around 40°, marked decreases in the osmotic second virial coefficient and intrinsic viscosity were observed. The Zimm plot for the AB-2 sample was fairly normal at 40°. It seems that the temperature where an anomaly becomes evident in Zimm plots is dependent on the molecular weight of the sample. The experimental results for the diblock copolymers could be understood from the view that intermolecular association took place to some extent in the solutions on lowering the temperature giving rise to multi-molecular micelles.     

Conformational behavior of styrene–p-chlorostyrene triblock copolymers in dilute solutions. I. Composition dependence of conformational behavior

Dilute solution properties of (styrene-p-chlorostyrene) triblock copolymers in various solvents were studied over a wide range of molecular weight and composition. Viscosity and osmotic pressure results indicate that the conformational behavior of the B_mA_nB_m and A_mB_nA_m copolymers (A = styrene; B = p-chlorostyrene; m and n denote the number of units) are similar in nonselective solvents such as toluene and 2-butanone, but different in selective solvents such as carbon tetrachloride and cumene. Short-range and long-range interaction parameters of the block copolymers were determined by applying the Stockmayer–Fixman method to viscosity data and also by application of the equation relating the osmotic virial coefficient and the excluded volume. The results show that the unperturbed dimensions of the block copolymers vary linearly with composition, and long-range interaction parameters in nonselective solvents can be expressed by those of the parent homopolymers, the chemical composition, and values of the interaction parameter β_AB between styrene and p-chlorostyrene monomeric units.     

The synthesis and solution behaviors of novel amphiphilic block copolymers based on d-galactopyranose and 2-(dimethylamino)ethyl methacrylate

A series of novel stimuli-responsive AB, ABA, and BAB type block copolymers based on 6-O-methacryloyl-1,2:3,4-di-O-isopropylidene-d-galactopyranose (MAIpGP:A block) and 2-(N,N-dimethylamino)ethyl methacrylate (DMAEMA: B block) were synthesized via ATRP techniques using ethyl 2-bromoisobutyrate (EBiB) as monofunctional ATRP initiator in the case of diblock copolymer and diethyl meso-2,5-dibromoadipate (DEDBA) as bifunctional ATRP initiator in the case of triblock copolymers. The PMAIpGP blocks of the AB, ABA, and BAB type linear block copolymers were converted to water soluble PMAGP blocks via deprotection process under mild acidic conditions. Both proton NMR and DLS studies demonstrated that block copolymers were temperature-sensitive, whereby the lower critical solution temperature (LCST) of polymers varied with the polymerization degrees of comonomers in the block copolymers. LCST was determined to be between ∼35 °C and 55 °C depending on the type and the comonomer compositions of the block copolymers. It was observed that an increase on the percentage of hydrophilic PMAGP block in block copolymer caused an increase on the LCST value as expected.     

Formation of block copolymer micelles in solutions of a linear homopolymer in a good solvent

The existence of micelles of polystyrene-block-poly(ethylene/propene) in solutions of polystyrene in toluene was investigated. Toluene is a good solvent of both copolymer blocks whereas polystyrene and poly(ethylene/propene) are immiscible polymers. The presence of homopolystyrene at high enough concentration can induce the micellization of polystyrene-block-poly(ethylene/propene) in solution of a good solvent such as toluene. The thermodynamics of this new micelle system at a given polystyrene concentration was studied. Light scattering measurements were carried out in order to determine the critical micelle temperature (CMT) of different micellar solutions. Standard Gibbs energy, enthalpy and entropy of micellization were estimated from CMT and concentration data. The numerical values found were less negative than those found for micelle systems consisting in a block copolymer dissolved in a single selective solvent.     

A method for studying micellar aggregates in block and graft copolymers

A method has been developed for studying the presence of micellar aggregates in block and graft copolymers. Specimens for examination in the electron microscope were prepared using a freeze-etching/replication technique. Four well-characterized copolymers were studied: a polystyrene-polyisoprene two-block copolymer, a (polystyrene-polyisoprene-)₄Si star-block copolymer, and two polystyrene-g-polyisoprene graft copolymers. Technical white oil, which is a very poor solvent for polystyrene, was taken as the solvent for the copolymers. For the purpose of comparison, a study was also made of specimens prepared from polystyrene homopolymer dissolved in a 1:1 mixture by vol of technical white oil and toluene.     

Infrared spectra of polymer solutions. I. Conformational stability of isotactic polymer chains in solution

The infrared spectra of isotactic polystyrene, polypropylene, and poly-p-chlorostyrene were measured in dilute solutions or gels at various temperatures ranging from room temperature to ?100°C. For isotactic polystyrene and polypropylene, all the absorption bands characteristic of the helical conformation of the molecules increase in intensity with decreasing temperature, and show intensities at low temperature as strong as in the highly crystallized samples. This suggests that the molecules can assume very regular conformations even in solution. Similar temperature dependence of the spectra was observed for a homogeneous gel of isotactic poly-p-chlorostyrene, which is believed to be noncrystalline. These experimental facts lead to the conclusion that the stability of the TG type helical conformation of these isotactic polymers may be ascribed to the intramolecular forces within a molecule. The fact that these spectral changes are reversible has permitted a thermodynamic treatment of the conformational regularity in solution on the basis of the infrared data. The temperature dependence of the absorption intensities has been interpreted quantitatively by a simple statistical mechanical model, and the enthaply and the entropy differences between the helical and the random states of the monomeric residue in the molecular chain have been estimated.     

Magnetic circular dichroism studies of polystyrene solutions

The magnetic circular dichroism (MCD) spectra of “atactic” and isotactic polystyrene solutions have been found to be sensitive to configurational and conformational differences. The ratio of B terms for “atactic” polystyrene (predominantly syndiotactic) to that of cumene was found to pass through a minimum as the coil expanded in various solvents. The ratio of dipole strengths D also passed through a minimum. For isotactic polystyrene and cumene the ratio of B terms increased with increasing coil size in the range of solvents utilized. The ratio of B terms of isotactic polystyrene over atactic polystyrene was found to go through a maximum as the coil expanded whereas the ratio of dipole strengths was found to continuously decrease. These results have been interpreted on the basis of the change in short range and long range orientation and interaction distances between chromophores during coil expansion. It is concluded that the microscopic conformation of isotactic and atactic polystyrene are very different in very good solvents. The B/D ratio for cumene was found generally to decrease with increasing solvent power.     

Multiblock copolymers of styrene and isoprene. II. Microstructure and dilute solution properties

Dilute solution properties of linear (SI)₃ six-block copolymers of styrene and isoprene are compared to those of random, two-block, and three-block copolymers of the same system. All the copolymers were prepared with sec-butyllithium in benzene. The microstructure of the polyisoprene blocks is close to that of homopolyisoprene prepared under the same conditions. In contrast, the random copolymer shows a larger amount of trans-1,4 isoprene units. The intrinsic viscosities of the copolymers in methylisobutyl ketone, a poor solvent for both polystyrene and polyisoprene, and in toluene, a good solvent for both homopolymers, are examined on the basis of the Fox–Flory relation for homopolymers. All the copolymers behave similarly in each solvent. In methylisobutyl ketone, the viscosity results indicate a random coil conformation with a small expansion owing to the extra repulsive interactions between the dissimilar units. In all cases, the heterocontact repulsive interactions are small and can be characterized by an interaction parameter χ_ab close to 0.025. In toluene, the perturbation caused by the heterocontacts becomes negligible and the expansion factor α_η can be predicted from a weighted average of those of the parent homopolymers of the same molecular weight as the copolymer.     

Miscibility and phase behavior in atactic polystyrene and poly(o-chlorostyrene-co-p-chlorostyrene) blends: Effect of polystyrene molecular weight and copolymer composition

Miscibility in blends of random copolymers of o-chlorostyrene and p-chlorostyrene [P(oClSy-co-pClS_1-y)] with 8 atactic polystyrene (aPS) fractions has been studied at temperatures ranging from 150°C to 300°C. Miscibility windows whose size depends on the molecular weight of the PS and on the copolymer composition, y, were observed for each blend. From these data, the temperature dependence of the three segmental interaction parameters required to describe this system were obtained.     

含聚氧乙烯链段的两亲嵌段共聚物及接枝共聚物的分子设计,合成及性能

论述了由聚烯链段与聚苯乙烯或聚（甲基）丙烯酸酯链段组成的各种嵌段或接枝共聚物（包括二嵌段、两种三嵌段、星型嵌段、多嵌段、二种规整接枝共聚物等）的分子设计及合成,并总结了其两亲性质、络合碱金属离子性及微观相分离等特性。     

Aggregative behavior of AB and ABC block copolymers in the solid phase and in a nonselective solvent

Effects of the amount of chemically dissimilar blocks (two or three) and their polarity on the aggregative behavior of АВ and АВС linear block copolymers of various compositions that are based on polystyrene, poly(n-butyl acrylate), and either poly(acrylic acid) or poly(tert-butyl acrylate) in bulk and in the nonselective solvent DMF are studied via differential scanning calorimetry and dynamic light scattering. АВ block copolymers composed of two chemically dissimilar blocks in the diluted solution in DMF are fully dispersed into macromolecular coils. However, the simultaneous incorporation of three incompatible blocks of different polarities (polystyrene, poly(acrylic acid), and poly(n-butyl acrylate)) into the copolymer is accompanied by a well-defined segregation of blocks in the nonselective solvent, regardless of the composition of the block copolymer and the length and sequence of blocks. This phenomenon makes itself evident as the formation of intermacromolecular aggregates in diluted solutions with a mean hydrodynamic radius of 60–120 nm that are stable in the range 10–60°C. A decrease in the level of the thermodynamic incompatibility of blocks (replacement of a poly(acrylic acid) polar block with a less polar poly(tert-butyl acrylate) block) or the selective improvement of solvent quality with respect to the polar block (the addition of LiBr to DMF) suppresses the segregation of blocks and may lead to the formation of a molecularly dispersed solution of the block copolymer.     

嵌段序列对聚合物囊泡形成过程影响的Monte Carlo模拟

采用Monte Carlo模拟方法研究了具有相同链长和组分比的不同嵌段序列的AB两嵌段共聚物与ABA三嵌段共聚物在选择性溶剂中形成囊泡的动力学过程. 模拟结果表明, AB两嵌段共聚物囊泡的形成与ABA三嵌段共聚物囊泡的形成的动力学过程不同. 在慢速退火条件下, ABA三嵌段共聚物囊泡是通过亲水链段向胶束的表面和中心扩散而形成的, 而AB两嵌段共聚物囊泡则由片层弯曲闭合而形成. 相对而言, 退火速度对AB两嵌段共聚物囊泡形成的动力学过程没有显著影响, 其改变仅影响亲水链段与疏水链段发生相分离的难易程度. 当退火速度较快时, 亲水链段和疏水链段发生相分离的速度较快且相分离发生在囊泡形成之前; 而当退火速度较慢时亲水链段和疏水链段之间的相分离在囊泡形成之后仍在进行.     

Preparation of polymeric vesicles through ultrasonic treatment of poly(styrene‐block‐2‐vinylpyridine) micelles under alkaline conditions

An approach for the preparation of block copolymer vesicles through ultrasonic treatment of polystyrene‐block‐poly(2‐vinyl pyridine) (PS‐b‐P2VP) micelles under alkaline conditions is reported. PS‐b‐P2VP block copolymers in toluene, a selective solvent for PS, form spherical micelles. If a small amount of NaOH solution is added to the micelles solution during ultrasonic treatment, organic‐inorganic Janus‐like particles composed of the PS‐b‐P2VP block copolymers and NaOH are generated. After removal of NaOH, block copolymer vesicles are obtained. A possible mechanism for the morphological transition from spherical micelles to vesicles or Janus‐like particles is discussed. If the block copolymer micelles contain inorganic precursors, such as FeCl₃, hybrid vesicles are formed, which may be useful as biological and chemical sensors or nanostructured templates. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 953–959     

Polypeptide hybrid copolymers as selective micellar nanocarriers in nonaqueous media

The self-assembly of polystyrene-block-poly(l-lysine) (PS-PLLys·HCl) copolymers with different block lengths has been studied in toluene. The obtained spherical micelles exhibit size variations upon addition of acids or bases, as indicated by light and neutron scattering studies. It is shown that pyridine induces a shrinking of the polystyrene chains in the corona region of the micelles, decreasing the aggregate solvent interface. The addition of benzoic acid, on the other hand, leads to a swelling of the copolymer micelles proportional to the molar fraction of polypeptide. This behavior suggests a selective permeability of the PS-PLLys micelles and the possibility to encapsulate organic compounds in toluene depending on their chemical nature.     

Cohesive energy densities of polymers from turbidimetric titrations

Turbidimetric titrations have been made on polystyrene and poly-o-chlorostyrene in a series of solvents to deduce the solubility parameters of polymers from the Flory-Huggins interaction parameter χ. The assigned solubility parameter for polystyrene agrees well with the reported values obtained from swelling measurements. Brief discussion of the exceptional behavior in the solvent powers of paraffins is given.     

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.     

分子水平研究不同嵌段结构苯乙烯/丁二烯共聚物的表面结构

利用具有准单分子层灵敏度的和频振动光谱(SFG)、原子力显微镜(AFM)和接触角(CA)测定技术研究链结构和溶剂对苯乙烯(S)/丁二烯(B)嵌段共聚物表面准分子层化学结构形成的影响.结果表明,两嵌段共聚物SB比三嵌段共聚物SBS更有利于聚丁二烯(PB)组分在膜表面富集.利用PB的选择性溶剂环己烷做溶剂时,SB膜表面层完全由纯的PB组分组成,而SBS表面则是聚苯乙烯(PS)与PB二组分共存.利用PS的选择性溶剂甲苯做溶剂时,SB与SBS表面都是PS与PB二组分共存,其中SBS表面PS组分的含量更高.原因是由于溶剂影响嵌段共聚物分子在溶液中的构象从而影响溶剂挥发后聚合物表面结构的形成.     

Study of molecular motion of block copolymers in solution by high-resolution proton magnetic resonance

Molecular motions of hydrophobic–hydrophilic water-soluble block copolymers in solution were investigated by high-resolution proton magnetic resonance (NMR). Samples studied include block copolymers of polystyrene–poly(ethylene oxide), polybutadiene–poly(ethylene oxide), and poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide). NMR measurements were carried out varying molecular weight, temperature, and solvent composition. For AB copolymers of polystyrene and poly(ethylene oxide), two peaks caused by the phenyl protons of low-molecular-weight (M?_n = 3,300) copolymer were clearly resolved in D₂O at 100°C, but the phenyl proton peaks of high-molecular-weight (M?_n = 13,500 and 36,000) copolymers were too broad to observe in the same solvent, even at 100°C. It is concluded that polystyrene blocks are more mobile in low-molecular-weight copolymer in water than in high-molecular-weight copolymer in the same solvent because the molecular weight of the polystyrene block of the low-molecular-weight copolymer is itself small. In the mixed solvent D₂O and deuterated tetrahydrofuran (THF-d₈), two peaks caused by the phenyl protons of the high-molecular-weight (M?_n = 36,000) copolymer were clearly resolved at 67°C. It is thought that the molecular motions of the polystyrene blocks are activated by the interaction between these blocks and THF in the mixed solvent.     

Synthesis of sterically stabilized polystyrene latex particles using cationic block copolymers and macromonomers and their application as stimulus-responsive particulate emulsifiers for oil-in-water emulsions

2-(Dimethylamino)ethyl methacrylate (DMA) was block copolymerized with methyl methacrylate (MMA) using group transfer polymerization to give four AB diblock, ABA triblock, and BAB triblock copolymers of low polydispersity (Mw/Mn < 1.20). In addition, a near-monodisperse styrene-functionalized DMA-based macromonomer was synthesized via oxyanionic polymerization using a potassium 4-vinylbenzyl alcoholate initiator. These five well-defined, tertiary amine methacrylate-based copolymers were evaluated as steric stabilizers for the synthesis of polystyrene latexes via emulsion and dispersion polymerization. The most efficient steric stabilizers proved to be the DMA-MMA diblock copolymer and the DMA-based macromonomer. The polystyrene latexes were characterized in terms of their particle size and morphology, stabilizer content, surface charge, and surface activity using dynamic light scattering, scanning electron microscopy, 1H NMR spectroscopy, aqueous electrophoresis measurements, and surface tensiometry, respectively. The pH-dependent surface activity exhibited by selected latexes suggests potential applications as stimulus-responsive particulate emulsifiers for oil-in-water emulsions.