AB-type Block Copolymers Research Articles

Water-soluble polyion complex associates of DNA and poly(ethylene glycol)-poly(L-lysine) block copolymer.

Complex formation of poly(ethylene glycol)-poly(L-lysine) (PEG-PLL) AB type block copolymer with salmon testes DNA or Col E1 plasmid DNA in aqueous milieu was studied. The PLL segment of PEG-PLL interacts with nucleic acid through an electrostatic force to form a water-soluble complex associate with a diameter of ca. 50 nm. PEG segments surrounding the core of the polyion complex prevented the complex from precipitation even under stoichiometric conditions, at which the unit ratio of L-lysine in PEG-PLL and phosphate in the DNA is equal. The profile of the thermal melting curve revealed a higher stabilization of DNA structure in PEG-PLL/DNA complexes compared to that in the complex made from DNA and PLL homopolymer with the same molecular weight as the PLL segment in PEG-PLL. This stabilizing effect on the DNA structure may be due to the compartmentalization of DNA into the microenvironment of PEG with low permittivity. The reversible nature of the PEG-PLL/DNA complex was further verified through the addition of polyanion [poly-(L-aspartic acid)]: Poly(L-aspartic acid) replaced DNA in the complex with PEG-PLL, resulting in the release of free DNA in the medium. Furthermore, the PEG-PLL/DNA complex showed high resistance against DNase I attack, suggesting DNA protection through the segregation into the core of the associate having PEG palisade.

Synthesis of block copolymers by radical polymerization of end-functional polystyrene

End-functional polystyrenes with an N,N-diethyldithiocarbamyl group were prepared by the photopolymerization of styrene with novel diethyldithiocarbamate derivatives as photoiniferters. Under ultraviolet light, the end-functional polymers could initiate a second monomer to polymerize and form block copolymers, such as polystyrene-b-poly(methyl methacrylate), polystyrene-b-poly(vinyl acetate), and polystyrene-b-poly(n-butyl acrylate). According to end group analysis and electron spin resonance (ESR) spectroscopy, AB-type block copolymers were produced. The glass transition temperature and thermal stability of the block copolymers were investigated by means of thermal analysis. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1169–1174, 1997

Synthesis of Block Copolymers by Photocopolymerization of Vinyl Monomers with Diethyldithiocarbamyl End-Functional Polystyrene

End-functional polystyrenes with the N,N-diethyldithiocarbamyl group were prepared by the photopolymerizations of styrene using alkyl diethyldithiocarbamylacetates as photoiniferters. Under UV light the end-functional polymers could initiate vinyl monomer to polymerize and form block copolymers, such as polystyrene-block-poly(methyl meth-acrylate), polystyrene-block-poly(vinyl acetate), and polystyrene-block-poly(n-butyl acrylate). According to end group analysis and EPR spectroscopy, AB-type block copolymers were produced. The glass transition temperatures and thermal stabilities of the block copolymers were investigated by means of thermal analysis.

The effects of transesterification on structure development in PC-PBT blends

A series of polycarbonate-poly(butylene terephthalate) (PC-PBT) blends has been formed via reactive melt-blending in a torque rheometer. The degree of transesterification between the two homopolymers was controlled by the incorporation of an alkyl titanium catalyst. Resultant materials were characterised using DSC, DMA, FTIR and SEM. As the degree of transesterification increased composition of the blends became increasingly complex, comprising mixtures of the homopolymers and various AB-type block copolymers of PC-PBT, with concomitant changes in their thermal behaviour. A corresponding transformation in materials morphology was observed: the relatively coarse structure characteristic of essentially two-phase blends, developed into a more refined structure exhibited by blends containing significant volumes of interphase material. This morphological change was due to the formation of increasing concentrations of random block copolyesters.

Synthesis of block copolymer containing dextran and polyamide sequences

AbstractA novel AB‐type block copolymer composed of dextran and polyamide sequences was prepared through the following two approaches. One is a coupling reaction of a terminal functional group introduced in the dextran chain with that in the polyamide chain, such as the reaction of an amine group with an acyllactam group or that of a lactone group with an amine group at the corresponding chain ends. The other is an anionic polymerization of a bicyclic lactam activated with a trimethylsilylated dextran derivative having an acyllactam end group. The latter procedure was found to be more effective for the preparation of the block copolymer having a high molecular weight polyamide sequence.

An Acyllactam-Type Growable End Group Formed in the Anionic Polymerization of a Bicyclic Oxalactam. The Isolation of the Polyamide and Its Use as an Activator in the Polymerization of 2-Pyrrolidone

A bicyclic oxalactam, 8-oxa-6-azabicyclo[3.2.1]octan-7-one was anionically polymerized in dimethyl sulfoxide at room temperature and the resulting hydrophilic polyamide having an acyllactam-type growable chain end was isolated from the polymerization system. The reactive end group was found to be easily converted to other functional groups by the hydrolysis or aminolysis with suppressing the simultaneous decomposition of the polyamide chain. The terminal acyllactam group in the polyamide, which was used as an activator in the anionic polymerization of 2-pyrrolidone, was quantitatively consumed and all of the macromolecular activator could be incorporated into the resulting copolymer. The thermal behavior and crystallization of the AB-type block copolymer composed of the hydrophilic polyamide and nylon-4 segments were influenced by the characteristics of the hydrophilic polyamide segment.

Synthesis and characterization of polystyrene–poly(ethylene oxide)–heparin block copolymers

AbstractA procedure for the preparation of new block copolymers composed of a hydrophobic block of polystyrene, a hydrophilic spacer‐block of poly(ethylene oxide) and a bioactive block of heparin was investigated. Polystyrene with one amino group per chain was synthesized by free radical oligomerization of styrene in dimethylformamide, using 2‐aminoethanethiol as a chain transfer agent. This amino group was used in the coupling reaction with amino‐telechelic poly(ethylene oxide) to produce an AB type diblock copolymer with one amino group per polystyrene (PSt)–poly(ethylene oxide) (PEO) chain. The amino‐semitelechelic oligo‐styrene was converted into the isocyanate‐semitelechelic oligo‐styrene using toluene 2,4‐diisocyanate and subsequent coupling with H2N–PEO–NH2 afforded AB type block copolymers with terminal amino groups. The coupling of PSt–PEO–NH2 with heparin was performed in a DMF–H2O mixture, first by activating the heparin carboxylic groups with EDC at pH 5.1–5.2 and subsequently reacting the activated carboxylic groups with the amino groups of the PSt–PEO–NH2 at pH 7.5. Depending on the molecular weights of the diblock copolymer used 25–29% w/w heparin was incorporated. These polymers will be further evaluated for their blood‐compatibility.

Vinyl Polymerization. 431. Vinyl Polymerizations Initiated by Block and Random Poly(Styrene-co-Sodium Methacrylate)

Abstract The polymerization of some kinds of vinyl monomer was found to occur without an ordinary initiator in aqueous solutions of AB-type block or random copolymers of sodium methacrylate with styrene as a so-called “uncatalyzed polymerization.” Although the spin trapping technique showed that the initiation mechanism by the block copolymer was the same as that by the random copolymer, the initiating ability of the block copolymer was lower than that of the random copolymer. Such results are attributable to the difference in the incorporating ability of monomer into the micelles formed by the block copolymer and into the hydrophobic areas formed by the random copolymer.

Oligomers Derived from 2-Oxazolines

Abstract This paper describes the synthesis and properties of oligomer chains derived from 2-oxazolines. First, poly(styrene-g-N-acetyl-ethylenimine) was prepared, and its hydrolysis gave poly(styrene-g-ethylenimine) which showed good chelating properties. Secondly, ABA type triblock copolymers were prepared in which an N-acylethylenimine chain is used as A block and ethylene oxide chain is employed as B block. These triblock copolymers showed good compatibility with Nylon 6, which were shown to posecess effective anti-electrostatic properties for Nylon 6. Thirdly, AB type block copolymers from 2-oxazolines have been prepared by using living polymerization technique. These block copolymers are soluble in water and showed good surfactant nature as reflected by surface tension (γ), when A block is consisted from N-acetyl- or N-propionylethylenimine chain (hydro-philic) and B block is made of N-tridecanoyl or N-aroylethylenimine chain (lipophilic). Finally, graft copolymers of cellulose diacetate having N-ac...

Synthesis of the AB type block copolymers (polyvinyltrimethylsilane-polydimethylsiloxane)

Novel AB type block copolymers (polyvinyltrimethylsilane-polydimethylsiloxane) containing different amounts of the constituent blocks have been synthesizeed by anionic sequential polymerization of vinyltrimethylsilane and hexamethylcyclotrisiloxane. A method for the preparation of block copolymers that are compositionally homogeneous and free of homopolymers has been developed.

Morphology of ethylene-propylene copolymers

A separated phase has been observed in ethylene-propylene block copolymers. However, the morphology of this separated phase, identified by Differential Interference Contrast Microscopy (d.i.c.), depends on the method of manufacture and it has been suggested that the difference in morphology arises from the formation of an amount of true AB-type block copolymer manufactured in the gas-phase process. This component is not thought to be present in copolymers so far examined, produced by means of the diluent process.

Rheological properties of concentrated solutions of styrene-lsoprene block copolymers

Abstract It is well known that block copolymers cast from solution form morphological structures such as microdomains and micelles. In a previous study we measured the flow properties of concentrated solutions of AB type block copolymers in good solvents and found that there exists a similar structure formed by polymer chains even in solution. In the present study, rheological properties of concentrated solutions of AB type copolymers in various solvents have been measured. The relationship between the rheological behavior and the structure formed in the solution and breakdown and re-formation of structure by shear were discussed in terms of the solvent power and the composition of the copolymers.

Features of the rheological behaviour of solutions of AB-type block copolymers of styrene and butadiene

Relations between viscosity and the rate of shear and elastic modulus G′ and between the dynamic viscosity ν′ and frequency have been investigated for solutions of diblock copolymers of styrene and butadiene in decalin and tetralin at 25° in the concentration interval from 0·05 to 50 g/dl. The observed effects of pseudoplasticity and anomalous frequency dependences of G′ are explained from the standpoint of formation of a macronetwork consisting of segregated domains of PS, the latter network being unstable with respect to the action of the velocity gradient field. In tetralin (a “good” solvent for both copolymer blocks) the effect is associated with thermodynamic incompatibility of the blocks. In decalin (φ-solvent for PS) at room temperature the effect is intensified on account of selective action of the solvent.