Solution properties of ultrahigh molecular weight polymers, 1. Methyl methacrylate-styrene 50:50 random copolymers

The paper is concerned with light scattering studies on solutions of ultrahigh molecular weight random copolymers of methyl methacrylate and styrene (50:50 mol/mol). The dependence of the radius of gyration and of the second virial coefficient on the weight-average molecular weight of the copolymers was established. The value of the steric factor of the copolymer compared to those of the corresponding homopolymers confirms the random character of the copolymer chain. The interpenetration function Ψ(Z), calculated on the basis of different theoretical approximations, is discussed for the expansion factor α_s³ > 7.     

Preparation of ABCBA-type block copolymers by use of macro-initiators containing peroxy and azo groups

Some new macroinitiators ( 5 ) containing azo and peroxy groups were synthesized by transformation of esters of poly(ethylene glycol) ( 1 ) (PEG) of different molecular weight with hydroxyl end groups and an azo group in the middle into the corresponding polymers with tert-butylperoxycarbonyl end groups by reaction with terephthaloyl chloride and subsequently with tert-butyl hydroporoxide. Decomposition in the presence of styrene at 60°C or with 3,6,9-triazaun-decane-1,11-diamine in presence of methyl methacrylate gave the corresponding ABA block copolymer 6 and the ABBA block copolymer 7 , respectively. Both block copolymers were used as polymeric initiators. The ABCBA block copolymer 8 was synthesized from 6 and methyl methacrylate or from 7 and styrene by thermally induced polymerization at 80°C. The resulting block copolymers were separated from the homopolymers by selective solvent extraction and characterized by spectroscopic and fractional precipitation methods.     

The uptake of N-(2-hydroxypropyl)-methacrylamide based homo, random and block copolymers by human multi-drug resistant breast adenocarcinoma cells

A series of well-defined, fluorescently labelled homopolymers, random and block copolymers based on N-(2-hydroxypropyl)-methacrylamide were prepared by reversible addition–fragmentation chain transfer polymerization (RAFT polymerization). The polydispersity indexes for all polymers were in the range of 1.2–1.3 and the number average of the molar mass (M_n) for each polymer was set to be in the range of 15–30 kDa. The cellular uptake of these polymers was investigated in the human multi-drug resistant breast adenocarcinoma cell line MCF7/ADR. The uptake greatly depended on the polymer molecular mass and structure. Specifically, smaller polymers (approx. 15 kDa) were taken up by the cells at much lower concentrations than larger polymers (approx. 30 kDa). Furthermore, for polymers of the same molar mass, the random copolymers were more easily internalized in cells than block copolymers or homopolymers. This is attributed to the fact that random copolymers form micelle-like aggregates by intra- and interchain interactions, which are smaller and less stable than the block copolymer structures in which the hydrophobic domain is buried and thus prevented from unspecific interaction with the cell membrane. Our findings underline the need for highly defined polymeric carriers and excipients for future applications in the field of nanomedicine.     

Second virial coefficient of three-block copolymers

The two leading terms in the perturbation series expansion of the second virial coefficient A₂ have been derived for a three-block copolymer. The theoretical dependences of second virial coefficients on composition of a two-block copolymers AB, b three-block copolymers ABA and c mixtures of two homopolymers A and B have been compared at low values of the excluded volume parameters z_A, z_B and z_AB. It follows from these calculations that with increasing thermodynamic quality of the solvent (with respect to both homopolymers) the effect of repulsive interaction between unlike segments of types A and B on the second virial coefficient of the copolymer decreases. The applicability of perturbation series to block copolymers is discussed.     

Gemische von polymeren durch cofällung,III. Mitt. Untersuchung der binären polymersysteme: Polyacrylnitril/acetylcellulose,polyvinylacetat/acetylcellulose und polyvinylacetat/polyacrylnitril

The variation of the activation energy of the thermal degradation of polymer mixtures with their composition leads to valuable indices concerning the compatibility or incompatibility of the homopolymers. By this method it is possible to accentuate small deviations of the activation energy from the additivity and to delimit the interval of maximum compatibility. Also it is possible to predict if the formed pseudosolutions will be more or less thermostable than the corresponding homopolymers. During the mixing of pseudocompatible polymers generally two opposite tendencies can be observed: (a) an increase of activation energy by the formation of associates and therefore an increase of thermostability, and (b) a decrease of activation energy by the formation of solid solutions with eutecticum, which are less thermostable than the initial homopolymers. Thus, the cellulose acetate/polyacrylonitrile coprecipitation polymers show negative deviations of the activation energy, with a minimum of ΔE = ?14,8 kcal/mole for the eutecticum. This coprecipitation polymer decomposes 25°C lower than the corresponding homopolymers. The polyacrylonitrile/poly(vinyl acetate) coprecipitation polymer on the other hand shows positive deviations of the activation energy with a maximum of ΔE = 12,3 kcal/mole for the 1:1 mixture. The corresponding initial decomposition temperature rises about 15°C. The activation energy of the cellulose acetate/poly(vinyl acetate) mixtures obeys the additivity; these polymers are not compatible.     

Modulation of marrow stromal cell function using poly(D,L-lactic acid)-block-poly(ethylene glycol)-monomethyl ether surfaces.

The adhesion of marrow stromal osteoblasts and the adsorption of fetal bovine serum (FBS) proteins to end-capped poly(D,L-lactic acid) 50:50 (PLA50) of molecular weight 17,000 (PLA5017), non-end-capped PLA50 of molecular weight 11,000 (PLA5011h), and a diblock copolymer made of poly(ethylene glycol)-monomethyl ether of molecular weight 5,000 and PLA50 of molecular weight 20,000 (Me. PEG5-PLA20) were investigated. Cell attachment and proliferation on both PLA50 polymers were equally good. The block copolymer did not allow the proliferation of cells. However, the attached cells were highly differentiated and metabolically active in contrast to the cells on PLA50. Moreover, surface analysis studies using electron spectroscopy revealed that FBS proteins adsorbed well from aqueous solutions to the PLA50 surfaces while they adsorbed substantially less to the block copolymer. These results suggest that Me.PEG-PLA block copolymers may be used to regulate protein adsorption and, therefore, cell adhesion by varying the block composition of the copolymer.     

Segregation of diblock copolymers to the interface between weakly incompatible polymers

The interface between thin films of polystyrene (PS) and polyparamethylstyrene (PpMS) was investigated in the presence of the diblock copolymer P(S-b-pMS). The use of neutron reflectivity and ¹⁵N nuclear reaction analysis in combination with suitable deuteration of the components provides information on the interface width and the distribution of the diblock copolymer at the interface. By variation of the molecular weight of the homopolymers, compatibility can be changed from compatible to incompatible. Depending on molecular weight the diblock copolymers segregate to the interface between the incompatible phases, while in weakly incompatible systems (χN = 3) copolymers are dissolved to a considerable amount in the homopolymer phases. At large copolymer concentration even full compatibility of components can be achieved, which is in good agreement with mean field predictions.     

Block copolymers of poly(ether-ether-sulfones) with liquid-crystalline/non-liquid-crystalline polyesters

The synthesis of telechellcs of poly(ether-ether-sulfones) (PEES) is controlled by high-resolution gel-permeation chromatography to optimize for low content of side products. Under optimum conditions the bifunctional polymer-homologous series is formed to 99,9%. These telechrcs were used to synthesize block copolymers with aromatic polyesters. The polyesters (PE) contain phenylhdroquinone and terephthalic acid (semicrystalline liquid-crystalline (LC) polyester), phenylterephthalic acid (amorphous LC polyester) or isophthalic acid (amorphous non-LC polyester). Block copolymers with amorphous polyesters show one glass transition temperature depending on the composition but blends of corresponding homopolymers are biphase. Block copolymers with semicrystalline LC polyesters are phase-separated. Incorporation of semicrystalline LC polyester segments into PEES increases their solvent resistance. The storage modulus of the block copolymer with 50 wt.-% of the semicrystalline polyester shows the same temperature dependence as PEES. Homogeneous block copolymers show anisotropy only if the weight fraction of polyester is larger than 0,5 whereas phase-separated systems show anisotropy at smaller fractions of polyester.     

Synthesis and properties of liquid-crystalline AB-block copolymers poly[6-(4′-methoxy-4-biphenylyloxy)hexyl methacrylate]-block-polystyrene

Liquid-crystalline AB-block copolymers poly[6-(4′-methoxy-4-biphenylyoxy)hexyl methacrylate]-block-polystyrene were synthesized by direct coupling of the homopolymers with functional end groups. Like the liquid-crystalline homopolymer with mesogenic units in the side chain, all block copolymers show a nematic mesophase. The transition temperatures are hardly affected by the composition and molecular weight of the block copolymers.     

Synthesis and characterization of injectable,water-soluble copolymers of tertiary amine methacrylates and poly(ethylene glycol) containing methacrylates

Several homopolymers and copolymers of 2-(diethylamino)ethyl methacrylate (DEAEM) and poly(ethylene glycol) methyl ether methacrylate (PEGMEM) were synthesized using anionic polymerization initiated by potassium t-butoxide. The polymers were characterized by average molecular weight, polydispersity and monomeric unit composition. A very narrow molecular weight distribution was achieved with a well-controlled composition. The glass transition temperatures and compositions of the copolymers followed a Gordon-Taylor relationship. The water solubility and biocompatibility of the copolymers was compared to their parent homopolymers to determine if the addition of a poly(ethylene glycol) group was sufficient to solubilize the polymers in aqueous buffer solutions and to increase the biocompatibility of the polymers. These water-soluble, injectable cationic copolymers have potential applications in gene delivery as well as other biomaterial applications.     

Role of High‐Molecular‐Weight Homopolymers on Block Copolymer Self‐Assembly: From Morphology Modifier to Template

For block copolymer (BCP)/homopolymer self‐assembly systems, the molecular weight of homopolymers is usually lower than that of BCPs. Herein, the cooperative self‐assembly of polystyrene‐b‐poly(ethylene glycol) (PS‐b‐PEG) BCPs with high‐molecular‐weight polystyrene (PS) homopolymers is reported. The molecular weight of PS homopolymers is 3–63 times that of the PS blocks. Typically, a spherical micelle–vesicle–large sphere morphology transition is observed by increasing the weight fraction of PS homopolymers in the polymer mixtures (f _HP). Dynamic process studies reveal that with adding water to the solution of polymer mixtures in organic solvent, the homopolymers first collapse into globules, and their size increases with f _HP and the molecular weight. Then these PS globules cooperatively self‐assemble with the PS‐b‐PEG BCPs. Depending on their size, these PS globules play different roles in the self‐assembly process. Small PS globules act as morphology modifiers inducing the micelle–vesicle transition, while large PS globules serve as self‐assembly templates for PS‐b‐PEG resulting in large spheres.     

Die chemische heterogenität von copolymerisaten. 4. Experimentelle untersuchungen zur verträglichkeit

Two chemically homogeneous methyl methacrylate/butyl acrylate copolymers form optically homogeneous (i.e. clear) mixtures in bulk only if the difference in their methyl methacrylate content does not exceed 10–20 mole-%. As torsional vibration experiments show, the mechanical homogeneity limit occurs at the same difference in the methyl methacrylate content. In inhomogeneous systems of two homogeneous copolymers these are found two corresponding damping maxima. Electron micrographs show the presence of structures of the order of magnitude of 30 Å even in some optically or mechanically homogeneous systems. The phase size increase suddenly near the turbidity limit. In mixtures of three components, the copolymer with a composition which lies in the middle does not aid compatibility. In copolymers with broad continuous chemical distributions microphases are formed from mutually compatible macromolecules. Optical and mechanical homogeneity or inhomogeneity is then a question of the size of the individual microphases. Suppression of transfer reactions in the polymer leads to an increase in the size of the microphases, while the size decreases when these reactions are encouraged. In agreement with this, graft copolymerization has a homogenizing effect. Preliminary experiments on copolymers of other monomers indicate that these observations are generally valid.     

Antithrombogenicity and oxygen permeability of block and graft copolymers of polydimethylsiloxane and poly(alpha-amino acid)

A-B-A-type block copolymers consisting of poly(alpha-amino acid) as A component and polydimethylsiloxane as B component and graft copolymers consisting of polydimethylsiloxane as trunk polymer and poly(alpha-amino acid) as branch polymer were synthesized. gamma-Benzyl-L- or DL-glutamate, epsilon-benzyloxycarbonyl L-lysine, and sarcosine were used as alpha-amino acid. Different microphase-separated structures were found on the film surface according to the copolymer composition and the casting conditions. In vitro antithrombogenicity test showed higher antithrombogenicity of block or graft copolymers than homopolymers. The best antithrombogenicity was independent of the kind of alpha-amino acid and the degree of polymerization of copolymers. The best ratio was 65-75% in block copolymer and 40-50% in the case of graft copolymer. The oxygen permeability of block and graft copolymer film was intermediate between those of homopolymers and varied with changing the composition of the copolymer. These experiments showed that the microphase-separated structure on the film surface was most important both for the antithrombogenicity and oxygen permeability of these copolymer films.     

Zur ermittlung der struktur und unverträglichkeit von pfropfcopolymeren durch messungen der lichtstreuung und phasentrennung in lösung

From theoretical considerations it is concluded that molecular weights and radii of gyration of the grafted chains in graft copolymers as well as the incompatibility of the grafted chains with the backbone polymer can be determined by light-scattering measurements in solution if the solvent used for these measurements is isorefractive with respect to the backbone polymer and if the weight fraction of the grafted chains is known. The new method for determining the incompatibility from anomalous Zimm-Diagrams is illustrated for mixtures of polystyrene and a chemically homogeneous ethylene/vinyl acetate random copolymer and is applied to fractions of the corresponding graft copolymers. The results of the light scattering measurements are compared with phase separation data from turbidimetric measurements.     

Synthesis and characterization of non‐covalent liquid crystalline diblock copolymers

Poly(dimethylaminoethylmethacrylate)‐b‐poly(sodium methacrylate) diblocks, (polyDMAEMA‐b‐polyMA), were synthesized as precursors of liquid crystalline (LC) copolymers. These LC copolymers were prepared by proton‐transfer between a carboxylic acid‐containing mesogen (A) and the dimethylamino substituent of the polyDMAEMA block and by electrostatic interactions between the polyMA subunits and an ammonium‐containing mesogen (B). When mesogen A is complexed with DMAEMA units, a dramatic enhancement of the mesophase stability is noted. The mesogenic properties of these LC copolymers were compared to those ones of the parent LC homopolymers, in relation to the copolymer composition. The supramolecular organization of the LC diblock copolymers was studied by small‐angle X‐ray scattering (SAXS), and smectic mesophases were observed in some LC (co)polymers. For samples containing a major LC block, a smectic mesophase coexists with microphases formed by the second amorphous block. Different organizations, including a body‐centered lattice of spheres and a hexagonal array of cylinders, were observed, depending on the investigated copolymers and their composition. When the LC block is the minor component, it forms microdomains too small for a liquid crystalline order to emerge. Moreover, no supramolecular organization of these dispersed microdomains was detected by SAXS. A homogeneous smectic mesophase was observed when the two blocks are bearing liquid crystalline moieties.     

Block copolymers with controlled interphase width. Effects of interphase and composition on domain dimensions

Ultrathin osmium tetroxid stained sections of solution cast block copolymer films were studied by electron microscopy. Two morphological systems were prepared from diblock copolymers containing 80 wt.-% styrene and 20 wt.-% isoprene: Systems with asymmetric lamellar morphology cast from cyclohexane, a preferential solvent for PI; and spherical morphology of rubber spheres in a continuous PS matrix, cast from tetrachloromethane, a non-selective solvent. For the two morphologies the variation of domain dimensions was studied in dependence of molecular weight in the range from 70 000 to 600 000 g/mol. Two types of block copolymers were investigated: Unmodified block copolymers and block copolymers containing 10 wt.-% of a random interblock between the pure polystyrene and polyisoprene blocks. For both kinds of morphologies the domain dimensions of the unmodified systems vary with M_n^2/3 as predicted by Helfand's theory. In the modified block copolymers a much weaker increase with M_n is found for both morphological systems. The results can be understood in terms of equilibrium domain dimensions controlled by an interfacial tension depending on both composition and sequence structure of the block copolymers.     

Synthèse et caractérisation de copolymères séquencés polystyrène/polydiméthylsiloxane et polyisoprène/polydiméthylsiloxane

Polystyrene/polydimethylsiloxane and polyisoprene/polydimethylsiloxane block copolymers were synthesized by anionic polymerization in cyclohexane (styrene and isoprene) and in a cyclohexane-diglyme mixture (hexamethylcyclotrisiloxane) with the use of sec-butyllithium as initiator. Polymers have been fractionated from benzene solution by progressive addition of methanol. Gel permeation chromatography (GPC), light scattering, osmometry, and elementary analysis were used to characterize the fractions. Copolymers, thus prepared, are free of homopolymers and the polydispersity of molecular weight and composition of the fractions is very low.     

Synthesis,Characterization, and Thermal Properties of Block Copolymers Containing Poly(styrene‐co‐4‐vinylpyridine) and Poly(styrene‐co‐butyl acrylate) by Controlled Radical Polymerization

Radical polymerization of styrene and mixtures of styrene and 4‐vinylpyridine was performed in the presence of 2,2,6,6‐tetramethylpiperidine‐N‐oxyl (TEMPO) producing polymers with controlled molecular weights and molecular weight distributions. The living nature of these polymers was confirmed by using them as macroinitiators in the block copolymerization of styrene and butyl acrylate. The thermal properties of the synthesized statistical diblock copolymers measured by differential scanning calorimetry indicated that a phase‐separated morphology was exhibited in most of the block copolymers. The results were confirmed by transmission electron microscopy (TEM) and small angle X‐ray scattering (SAXS) showing microphase‐separated morphology as is known for homo A‐B diblock polymers.

SAXS of a block copolymer synthesized from S/V 70:30 macroinitiators (03) with one detected T_g.     

Nitroxide-controlled free radical polymerization of a sugar-carrying acryloyl monomer

Controlled free radical polymerization of a sugar-carrying acrylate, 3-O-acryloyl-1,2 : 5,6-di-O-isopropylidene-α-D -glucofuranoside (AIpGlc), was achieved in p-xylene at 100°C by using a di-tert-butyl nitroxide (DBN)-based alkoxyamine as an initiator and dicumyl peroxide (DCP) as an accelerator. The polymerization gave low-polydispersity (1.2 < M_w/M_n < 1.6) polymers with predicted molecular weights. The same approach with a DBN-capped polystyrene (PS-DBN) as an initiator afforded block copolymers of the type PS-b-PAIpGlc. The acidolysis of the homopolymers and block copolymers gave well-defined glucose-carrying polymers PAGlc and PS-b-PAGlc, respectively. These amphiphilic PS-b-PAGlc block copolymers were observed to exhibit microdomain surface morphologies that differ for different copolymer compositions. This success opens up a new, simple route to the synthesis of well-defined sugar-carrying polymers of various architectures.     

Calculation of domain sizes in block copolymers with broad interphase

The domain dimensions of poly(styrene-b-isoprene) diblock copolymers with polyisoprene spheres in a continuous polystyrene matrix, in which the interphase is broadened by a random poly(isoprene-co-styrene) copolymer block, are significantly smaller than in unmodified block copolymers. The depression of domain sizes and the reduced exponent of the molecular weight dependence in these systems are calculated on the basis of Helfand's theory in which the surface and the conformational entropy were appropriately modified. The domain dimensions of unmodified block copolymers, for which hitherto larger than experimental radii were predicted by the original theory, are also in good agreement if calculated by the proposed phenomenological approach.