AB Block Research Articles

Liquid‐Crystalline side‐chain AB block copolymers by direct anionic polymerization of a mesogenic methacrylate

AbstractAB block copolymers with a liquid‐crystalline and an amorphous block are synthesized by anionic copolymerization of 4‐[4‐(4‐methoxyphenylazo)phenoxy]butyl methacrylate (1) with either styrene or methyl methacrylate (MMA). The polymerization of 1 proceeds from polystyrenelithium capped with 1,1‐diphenylethylene to produce polystyrene‐block‐poly(1), while poly(1)‐block‐PMMA is prepared by addition of MMA to the “living” poly(1) anion. A large variety of block copolymers is obtained with narrow molecular weight distribution and definite composition. The mesophase behaviour of these samples is analyzed with respect to the chain length of the liquid‐crystalline block. Electron microscopy of a high‐molecular‐weight polystyrene‐block‐poly(1) provides direct evidence for a microphase‐separated structure composed of spherical polystyrene domains embedded in a liquid‐crystalline matrix. For the corresponding poly(1)‐block‐PMMA, however, electron microscopy indicates no structure, although dynamic mechanical analysis proves microphase separation.

Synthesis and characterization of poly (2‐vinylpridine)‐b‐poly (t‐butyl methacrylate)

AbstractThe synthesis of well defined and monodisperse (Mw/Mn ≤ 1.2) narrow molecular weight distribution poly (2‐vinylpyridine)‐poly (t‐butyl methacrylate) (P2VP‐PTBMA) AB block copolymers is carried out by initiation of 2‐vinylpyridine polymerization by 1,1‐diphenylhexyllithium in THF at‐78°C, followed by addition of TBMA and termination at −78°C using MeOH. The formation of the BAB block copolymer is carried out in a similar fashion except that 1,4‐dilithio‐1,1,4,4‐tetraphenylbutane is used as initiator. The corresponding synthesis of P2VP‐PMMA block copolymers is carried in a similar manner, except that 1‐2 equivalents of TBMA is used to end‐functionalize the living P2VP before the addition of MMA. Without the addition of TBMA, trimodal molecular weight distributions in P2VP‐b‐PMMA are obtained. All the block copolymers are characterized by Size Exclusion Chromatography (SEC), Nuclear Magnetic Resonance (NMR), and Differential Scanning Calorimetry (DSC). © 1994 John Wiley & Sons, Inc.

Star‐shaped polymers by living cationic polymerization, 6. Amphiphilic star‐shaped block copolymers of vinyl ethers with carboxyl groups: synthesis and host‐guest interaction

AbstractAmphiphilic star‐shaped polymers (5 and 6) of vinyl ethers (VEs), the arms of which consist of apoly(carboxylic acid)/poly(alkyl VE) AB block copolymer, were prepared on the basis of living cationic polymerization. Thus, a sequential living polymerization of a VE with a pendant malonate group [CH2  CHOCH2CH2CH(COOCH2CH3)2] and and isobutyl VE with HI/ZnI2 at −15°C in toluene led to a living block copolymer (3a), which was subsequently allowed to react with a small amount of a bifunctional vinyl ether [1; CH2  CHOCH2CH2OC6H4C(CH3)2‐C6H4OCH2CH2OCH  CH2] to give a star‐shaped block copolymer (4a). Alkaline hydrolysis of the ester functions of 4a, followed by neutralization, gave the amphiphilic star copolymer (5a, diacid form; \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm \{ H\rlap{--} [CH}_2 {\rm CH(OCH}_2 {\rm CH}_2 {\rm X)\rlap{---} ]}_m {\rm \rlap{--} [CH}_2 {\rm CH(O}i{\rm Bu)\rlap{--} ]}_n \} _f - {\rm (core)}, $\end{document} X = CH(COOH)2) with hydrophilic poly(carboxylic acid) segments in the outer region, and subsequent decarboxylation led to the monoacid form 6a (X = CH2COOH). Amphiphilic star copolymers (5b and 6b; \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm \{ H\rlap{--} [CH}_2 {\rm CH(O}i{\rm Bu)\rlap{---} ]}_m {\rm \rlap{--} [CH}_2 {\rm CH(OCH}_2 {\rm CH}_2 {\rm X)\rlap{--} ]}_{n'} \} _f - {\rm (core)}, $\end{document} 5b: X = CH(COOH)2, 6b: X = CH2COOH) with an opposite segment sequence(inner polyacid chains) were also prepared. The star copolymer 5b (m′ = 30, n′ = 10) was insoluble in methanol, in which the polymer 5a (m = 10, n = 30) with the opposite segment sequence was soluble, and both 5a and 5b as well as both 6a and 6b differed in solubility from the corresponding linear polymer. The amphiphilic polymers 5 and 6 were also found to interact selectively with guests with polar functional groups such as benzoic acid and benzylamine.

Branched polymers by cationic ring‐opening polymerization

AbstractTwo methods for the synthesis of branched (co)polymers by cationic ring‐opening polymerization are presented. The first method is based on the spontaneous intermolecular termination that is observed in the polymerization of the four‐membered cyclic sulfides (thietanes). The branching points in these polymers are sulfonium ions. This method has been extended to polyether ‐ polysulfide block copolymers obtained by sequential polymerization of THF and a thietane. In the thus obtained AB block polymers, the branching points are concentrated in the sulfide segments only. By similar techniques, ABA types of block copolymer networks have been obtained making use of bifunctional initiators.The second method consists of copolymerizing a cyclic acetal such as 1,3‐dioxolane (DXL), with a “monofer”, which is a monomer that contains also a chain‐transfer function. As monofers for the DXL polymerization glycidol and glycerol formal were used. The end products are polyacetal‐polyols which contain a hydroxyl group at each of the chain ends. Reaction of these polyols with di‐isocyanates leads to the corresponding polyacetal polyurethanes.

Multifunctional coupling agents for living cationic polymerization. I. Sodiomalonate anions for vinyl ethers

AbstractA series of multifunctional malonate anions, [Na⊕⊖C(COOEt)2CH2]mC6H6−m(I; m = 2–4), were examined as polymer coupling agents for the living cationic polymerization of vinyl ethers initiated with the hydrogen iodide/zinc iodide (HI/ZnI2) initiating system. The bifunctional anion (2;I, m = 2), 1,4‐[Na⊕⊖C(COOEt)2CH2]2C6H4, terminated living polymers of isobutyl vinyl ether (IBVE) (DPn = 10) almost quantitatively in toluene at −15°C to give coupled living polymers with doubled molecular weights in 96% yield; the dianion 2 was dissolved in tetrahydrofuran containing 18‐crown‐6 for maintaining the solution homogeneous. The yield of the coupled polymers was increased with shorter living chains or in less polar solvents. Also by coupling via 2, ABA block copolymers were obtained from living AB block polymers of IBVE and an ester‐functionalized vinyl ether (CH2CHOCH2CH2OCOCH3). Coupling of living poly(IBVE) with the trifunctional anion (3; I, m = 3) led to tri‐armed polymers in 56% yield, whereas with the tetrafunctional version (4; I, m = 4), only three out of the four anions reacted to give another tri‐armed polymer in 85% yield. © 1993 John Wiley & Sons, Inc.

Micelles based on AB block copolymers of poly(ethylene oxide) and poly(.beta.-benzyl L-aspartate)

Micelles based on AB block copolymers of poly(ethylene oxide) and poly(.beta.-benzyl L-aspartate)

Phase Separation of AB Block Copolymer and Blend——A MONTE CARLO STUDY

Bond fluctuation model and vacancy diffusion algorithm have been used to simulate the phase separation 0ξ AB block copolymer and blend in a highly concentrated system.The results are as follows:(i)The mixing is nonrandom even in athermal condition where the microscopic interaction energy between A and B monomers e*=0,so that the assump. tion of random mixing in the mean-field theory is just a rough approximation.(ii)The Flory-Huggins(FH)parameter, X ,is just a phenomenological parameter.Therefore,the X value of the block copolymer is higher than that of the corresponding blend although the reduced microscopic molecular interaction energies e * are the same.(iii)In the case of the same A,B composition and the same molecular weight of corresponding blocks,the phase separation of AB blend is easier than that of AB block copolymer.Their critical values of the X are: Xc blend=0.1, Xc block=0.41 for the case of chain lengths L A=10, L B=11.

Synthesis of side chain liquid crystal polymers by living ring-opening metathesis polymerization. 4. Synthesis of AB block copolymers containing amorphous and side chain liquid crystal blocks

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSynthesis of side chain liquid crystal polymers by living ring-opening metathesis polymerization. 4. Synthesis of AB block copolymers containing amorphous and side chain liquid crystal blocksZen Komiya and Richard R. SchrockCite this: Macromolecules 1993, 26, 6, 1387–1392Publication Date (Print):March 1, 1993Publication History Published online1 May 2002Published inissue 1 March 1993https://doi.org/10.1021/ma00058a030RIGHTS & PERMISSIONSArticle Views338Altmetric-Citations61LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (2 MB) Get e-Alerts Get e-Alerts

Biodistribution of micelle-forming polymer-drug conjugates.

Polymeric micelles have potential utility as drug carriers. To this end, polymeric micelles based on AB block copolymers of polyethylene oxide (PEO) and poly(aspartic acid) [p(Asp)] with covalently bound Adriamycin (ADR) were prepared. The micelle forming polymer-drug conjugates [PEO-p(Asp(ADR)] were radiolabeled and their biodistribution was investigated after intravenous injection in mice. Long circulation times in blood for some compositions of PEO-p[Asp(ADR)] conjugates were evident, which are usually atypical of colloidal drug carriers. This was attributed to the low interaction of the PEO corona region of the micelles with biocomponents (e.g., proteins, cells). Low uptake of the PEO-p(Asp(ADR)] conjugates in the liver and spleen was determined. The biodistribution of the PEO-p[Asp(ADR)] conjugates was apparently dependent on micelle stability; stable micelles could maintain circulation in blood, while unstable micelles readily formed free polymer chains which rapidly underwent renal excretion. Long circulation times in blood of PEO-p(Asp(ADR)] conjugates are thought to be prerequisite for enhanced uptake at target sites (e.g., tumors).

Effect of looping on the microstructure of linear multiblock copolymers

The effect of looping on the free energy and microstructure of linear multiblock copolymer(AB) n is investigated. Looping statistics are generated as a function of the number of AB block pairs n and are incorporated directly as conformational constraints into a confined single chain formalism. Predictions for the free-energy, along with microstructural dimensions such as the periodicity, are provided as functions of n and the number of looping events per molecule

Synthesis of AB(BA), ABA and BAB block copolymers of tert‐butyl methacrylate (A) and ethylene oxide (B)

AbstractWell‐defined AB(BA), ABA, and BAB block copolymers of tert‐butyl methacrylate (tBMA) (A) and ethylene oxide (EO) (B) have been prepared by sequential living anionic polymerization of the two comonomers, irrespective of their addition order. Diphenyl methyl potassium and naphthalene potassium have been successfully used as mono‐ and difunctional initiators, respectively. In all cases, molecular weight and composition of the block copolymers can be predicted on the basis of the monomer over initiator molar ratio, and the molecular weight distribution is relatively narrow. Size exclusion chromatography, selective extractions of homopolymers, and 1H‐ and 13C‐NMR spectroscopy support that block copolymerization proceeds without homopolymer formation nor side reactions, e.g., transesterification reactions. The PtBMA blocks have been quantitatively hydrolyzed into polyacid ones with formation of polyacid‐b‐polyether block copolymers as supported by titration, 1H‐NMR, and IR analysis. © 1992 John Wiley & Sons, Inc.

Molecular Engineering of Liquid Crystal Polymers by Living Polymerization. XXIII. Synthesis and Characterization of AB Block Copolymers Based on ω-[(4-Cyano-4′ -Biphenyl)-oxy]alkyl Vinyl Ether, 1H, 1H, 2H, 2H-Perfluorodecyl Vinyl Ether, and 2-(4-Blphenyloxy)ethyl Vinyl Ether with 1H, 1H, 2H, 2H-Perfluorodecyl Vinyl Ether

Abstract This paper describes the synthesis and characterization of AB block copolymers based on ω-[(4-cyano-4′-biphenyl)oxy]alkyl vinyl ether (6-n), with alkyl being ethyl (6-2), propyl (6-3), nonyl (6-9), and undecanyl (6-11), with 1H, 1H, 2H, 2H-perfluorodecyl vinyl ether (CF8), poly[(-6-n)-b-CF8]X/Y (where X/Y refers to the weight ratio of the two segments), and of 2-(4-biphenyloxy)ethyl vinyl ether (BEVE) with 1H,-1H, 2H, 2H-perfluorodecyl vinyl ether, poly[BEVE-b-CF8]X/Y. They were prepared by living cationic polymerization and exhibit a narrow molecular weight distribution. All block copolymers display a micro-phase-separated morphology when the A segment is in the liquid crystalline phase. Block copolymers based on 6-2, 6-3, and BEVE with CF8 also exhibit a microphase-separated morphology in the melt phase of A and B blocks.

Morphological studies of linear (AB)n multiblock copolymers and their blends

Block copolymers are composed of sequences of dissimilar chemical moieties covalently bonded together. If the block lengths of each component are sufficiently long and the blocks are thermodynamically incompatible, these materials are capable of undergoing microphase separation, a weak first-order phase transition which results in the formation of an ordered microstructural network. Most efforts designed to elucidate the phase and configurational behavior in these copolymers have focused on the simple AB and ABA designs. Few studies have thus far targeted the perfectly-alternating multiblock (AB)n architecture. In this work, two series of neat (AB)n copolymers have been synthesized from styrene and isoprene monomers at a composition of 50 wt% polystyrene (PS). In Set I, the total molecular weight is held constant while the number of AB block pairs (n) is increased from one to four (which results in shorter blocks). Set II consists of materials in which the block lengths are held constant and n is varied again from one to four (which results in longer chains). Transmission electron microscopy (TEM) has been employed here to investigate the morphologies and phase behavior of these materials and their blends.

Catalytic hydrogenation of diene polymers: Part II. Kinetic analysis and mechanistic studies on the hydrogenation of styrene—butadiene copolymers in the presence of RhCl(PPh 3) 3

Homogeneous catalytic hydrogenation of unsaturated polymers is a useful method of altering the chemical and physical properties of the parent polymer. Presented here is a detailed kinetic study of the hydrogenation of styrene—butadiene copolymers (AB and ABA block) using Wilkinson's catalyst, RhCl(PPh 3) 3. The effects of polymer, hydrogen, catalyst and added PPh 3 concentration, as well as temperature, on the rate of hydrogenation were examined. From this information a rate law has been developed for which the associated rate and equilibrium constants were estimated. These rate constants are compared with those previously obtained for other polybutadiene systems. The reaction kinetics provide a further understanding of the RhCl(PPh 3) 3 catalysed mechanism of hydrogenation of polymers. The steric effect of the aromatic ring in the styrene—butadiene copolymer chain and the compatibility of the polymer with the solvent are important factors governing the rate of hydrogenation. Quantitative hydrogenation was confirmed by IR spectroscopy and 1H NMR. Gel permeation chromatography suggests no significant change in the chain length of the polymer upon hydrogenation.

Conformation and dynamics of colloidal aggregates in detergent and copolymer systems

The conformation and dynamics of colloidal aggregates, from small detergent molecules to copolymers in solution may be investigated by combining laser light scattering and (synchrotron) small angle X-ray scattering with measurements of rheological properties of the supramolecules. The inter- and intramolecular interactions may be complex in nature involving, in addition to hydrophobic-hydrophilic interactions, solvent-non-solvent considerations and metal coordination type complexation. Nevertheless, scattering techniques can provide useful information on the size, size distribution and conformation of the aggregates. Studies of microstructures of the colloidal aggregates at dilute concentrations become feasible with intense synchrotron X-rays. Recent investigations of detergent molecules, such as cobalt monooleate in apolar organic solvents, of polymer colloids, such as polystyrene/polyisoprene AB block copolymers, and block copoly(oxyethylene/oxypropylene/oxyethylene) in organic solvents are presented.

Block copolymers of p-tert-butoxystyrene with isobutyl vinyl ether or styrene derivatives via sequential living cationic polymerization: synthesis of amphiphilic macromolecules with a poly(p-vinylphenol) segment

Block copolymers of p-tert-butoxystyrene (tBOS) with isobutyl vinyl ether (IBVE), p-methoxystyrene (pMOS), and p-methylstyrene (pMS) were synthesized by sequential living cationic polymerizations with the hydrogen iodide/zinc halide initiating systems in toluene. These tBOS-based AB block copolymers possessed controlled molecular weights and narrow molecular weight distributions. The poly-(tBOS) segments in the block copolymers could be converted into poly(p-vinylphenol) segments by acidolysis. The deprotected block polymers were insoluble in benzene and dichloromethane

Lithium and potassium alcoholates of poly(ethylene glycol)s as initiators for the anionic polymerization of 2,2-dimethyltrimethylene carbonate. Synthesis of AB and ABA block copolymers

Alkali metal salts of poly(ethylene glycol)s (PEG) and poly(ethylene glycol) monomethylethers (PEGMe) may be used as initiators for the anionic ring-opening polymerization of 2,2-dimethyltrimethylene carbonate (DTC). The potassium salts of PEG and PEGMe are highly cryptated and lead under the reaction conditions to low block copolymer yields and relatively high yields of cyclic DTC oligomers. The lithium salts, however, lead to high yields of block copolymers of the AB and ABA types, depending on the initiator used—PEGMe or PEG. The properties of the copolymers are strongly dependent on the molar ratio of the repeating units. In ABA triblock copolymers having large B blocks, two melting transitions corresponding to each block are observed, especially upon the second heating. The thermal properties as compared to the homopolycarbonate are not influenced by small PEG blocks; therefore, the dilithium salt of PEG 200 can be considered to be a good bifunctional initiator for the polymerization of DTC. PEG-PDTC block copolymers with equal size of the PDTC block show no difference in the GPC elution volume with THF as solvent when the PEG block increases in size.

Block Copolymer Thermodynamics: Theory and Experiment

Block copolymers are macromolecules composed of sequences, or blocks, of chemically distinct repeat units. The development of this field originated with the discovery of termination-free anionic polymerization, which made possible the sequential addition of monomers to various carbanion-ter­ minated (living) linear polymer chains. Polymerization of just two dis­ tinct monomer types (e.g. styrene and isoprene) leads to a class of materials referred to as AB block copolymers. Within this class, a variety of molec­ ular architectures is possible. For example, the simplest combination, obtained by the two-step anionic polymerization of A and B monomers, is an (A-B) dioblock copolymer. A three-step reaction provides for the preparation of (ABA) or (BAB) triblock copolymer. Alternatively, living diblock copolymers can be reacted with an n-functional coupling agent to produce (A-B)n star-block copolymers, where n = 2 constitutes a triblock copolymer. Several representative (A-B)n block copolymer architectures

Synchrotron SAXS measurements on solutions of poly(styrene-isoprene) AB block copolymer in aniline

Synchrotron small angle X-ray scattering (SAXS) has been performed on solutions of a poly (styrene-isoprene) AB block (PS/PIP) copolymer in aniline. The copolymer forms aggregates in this particular solvent. Earlier investigations could not determine whether the aggregates were micelle-like or vesicle-like. In order to distinguish between these two possibilities, the form factor has to be known over a wide range of the scattering vector ( q) to within a satisfactory precision. Due to the high intensity of synchrotron radiation, it was possible to obtain SAXS results with a sufficient precision, which allowed the conclusion that the aggregates were vesicle-like when the PS block was sufficiently short. The effect of polydispersity on the form factor is also discussed.

Synthesis of block copolymers of p-methoxystyrene and vinyl ethers by the hydrogen iodide/zinc iodide initiating system

Amphiphilic or polar-nonpolar AB block copolymers of p-methoxystyrene (pMOS) and vinyl ethers (VE; methyl or isobutyl) were synthesized by the sequential living cationic polymerization initiated with the hydrogen iodide/zinc iodide (HI/ZnI2) system in toluene at -15 and +25 °C. pMOS-VE block copolymers of narrow molecular weight distributions (\(\overline M _w /\overline M _n \) = 1.05−1.25; \(\overline {\text{M}} _n \) = 6000−16000) were obtained in nearly quantitative blocking efficiency, when methyl or isobutyl VE was polymerized first by HI/ZnI2, followed by addition of pMOS to the resulting living polymer solutions; an additional amount of ZnI2 was required to accelerate the second-phase living polymerization of the less reactive styrenic monomer. Similar block polymerizations in an opposite monomer-addition sequence (from pMOS to VE), in contrast, resulted in mixtures of the desired block polymer and homopolymer of pMOS.