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.     

Über die verträglichkeit von copolymeren mit den entsprechenden homopolymeren

Two polymers being generally incompatible, it was interesting to examine if compatibility of two homopolymers can be realized by addition of a corresponding: graft, block, or random copolymer. Our study was limited to two systems of atactic polymers: polystyrene-polymethacrylate and polystyrene-1,4 cis polyisopren, mainly because no crystallisation is observed in this case at common temperatures. For mixtures of copolymers and homopolymers in the solid state, it is possible by examination of films, obtained by solution evaporation, to determine the limits of the compatibility region and the most important corresponding parameters, that is composition of the mixture, molecular weight, and structure of the copolymer. Ternary diagrams, for mixtures of two homopolymers and a copolymer, show that only block copolymers are able to achieve better compatibility, especially if their composition is near 50:50 and if molecular weight of the homopolymers is lower than those of block copolymers. Graft and random copolymers however have practically less or no effect on compatibility. Further for the system polystyrene–polyisopren and the corresponding block-copolymer, the relation between compatibility and shock resistance has been shown.     

Preparation and crystalline structure of random copolymers of glycine and β-alanine

Copolymers of glycine and β-alanine within a range of amount-of-substance compositions from 3:1 to 1:9 were prepared by polycondensation of mixtures of the respective pentachlorophenyl ester hydrobromides. Number-average molecular weights between 2 500 and 9 000 were obtained, the lower values corresponding to those copolymers with a higher content in glycine. Sequence distributions were evaluated by means of 50,3 MHz ¹³C NMR spectroscopy and the crystalline structure was examined by wide-angle X-ray diffraction. Random copolymers having similar contents in glycine and β-alanine were found to crystallize in a bidimensional hexagonal lattice (a = 4,79 Å) with chains packed in a similar manner as they do in the crystalline structure of polyglycine II. On the contrary, a heterogeneous product consisting of homopolymer and random copolymer fractions results from mixtures which are enriched in one of the two amino acids. The random copolymer poly(glycine-ran-β-alanine) adopts a packing scheme similar to that found for the helical form of the alternating copolymer nylon 2/3. Chains are hexagonally arranged and interlinked by a three-dimensional network of hydrogen bonds as described for the well known model of polyglycine II, although in the present case no order along the chain axis should be expected.     

High-pressure free-radical copolymerization of ethene and butyl acrylate

The free-radical copolymerization of ethene and butyl acrylate was studied between 130 and 225°C at pressures from 1 500 to 2 500 bar. The reactions which were induced either thermally or laser-photochemically were run in two types of continuously operated devices. Reactivity ratio data referring to ethene-rich monomer mixtures are presented. These data allow to estimate the copolymer composition in ethene/butyl acrylate copolymerizations carried out in a wide range of temperatures and pressures.     

Polymer diffusion in mixtures of polystyrene and polymethylstyrene studied by forced rayleigh scattering and photon correlation spectroscopy

Tracer diffusion coefficients D^* of both components were measured in mixtures of polystyrene (PS) and polymethylstyrene (PMS), a random copolymer from 60 wt.-% of m-methylstyrene and 40 wt.-% of p-methylstyrene. The results are interpreted in terms of the free-volume theory which yields master curves even for “asymmetric” mixtures of oligomer and polymer chains, if D^* is drawn versus the distance from the glass transition temperature, T–T_g. Whereas D^* was measured by the forced Rayleigh scattering technique, we also studied photon correlation spectroscopy in these mixtures and observed “slow modes” with decay constants that correspond to diffusion coefficients 2–3 decades smaller than the interdiffusion coefficient.     

Single crystals of syndiotactic poly[propene-co-(1-octene)] and syndiotactic polypropene crystallized in bulk

Single crystals grown in bulk samples of a syndiotactic random copolymer of propene and 1-octene with 4 wt.-% 1-octene are compared with single crystals of syndiotactic polypropene homopolymer. The random copolymer during isothermal crystallization at low supercoolings forms rectangular single crystals similar to syndiotactic polypropene. The single crystals of the random copolymer do not exhibit transverse cracks in contrast to neat syndiotactic polypropene. Both polymers have nearly the same linear thermal expansion coefficients along their crystallographic a- and b-axis, calculated from temperature-dependent wide-angle X-ray scattering (WAXS) measurements. Therefore, the absence of transverse cracks in single crystals of the random copolymer can only be explained by the relatively high disorder of the crystallite surface caused by the exclusion of 1-octene segments which leads to a more isotropic thermal expansion coefficient in this region.     

Cyclo-copolymerization of 1,6-diene with monoolefin, 2. The copolymer composition equation and the relative rates of addition in the cyclo-copolymerization of diallyl ether with maleic anhydride and fumaronitrile

A copolymer composition equation is derived for the cyclo-copolymerization of a 1,6-diene with a monoolefin that do not homopolymerize. The theory is applied to the free radical copolymerization of diallyl ether (DAE) with maleic anhydride (MA) and to that of DAE with fumaronitrile (FN). Both systems fall in the special case where there are no unreacted C?C bonds left in the copolymer. The copolymer compositions are between 1:1 and 1:2 (=[diene]:[monoolefin]) over a wide range of monomer feed composition. The reactivity ratios obtained from the equation indicate that for the DAE/MA system, the intramolecular cyclization of the uncyclized DAE radical is 2,9 times more effective than the addition of MA monomer to the uncyclized DAE radical, and that for the system of DAE/FN, the intramolecular cyclization of DAE radical is 6,7 times more effective than the addition of FN monomer.     

Application of Nitroxide‐Terminated Polymers Prepared by Sonochemical Degradation in the Synthesis of Block Copolymers

Summary: The ultrasonic irradiation of a polymer solution results in the breakage of macromolecular C? C bonds. In the presence of radical scavengers the formed macroradicals are prevented from termination reactions as combination or disproportionation. Using nitroxides as trapping agents the polymer is transformed into a macroinitiator, which can be used in controlled free‐radical polymerization to synthesize block copolymers. In this work several polymers were exposed to sonochemical degradation and terminated with various nitroxides, e.g. OH‐TEMPO and TIPNO. In a second reaction step the prepared polymer‐nitroxide‐adducts were applied as macroinitiators in controlled free‐radical polymerizations with styrene. The obtained products were mixtures of block copolymer and the corresponding homopolymers. The visco‐elastic properties were investigated by rheological analysis. A special separation technique with selective solvents was applied to determine the content of block copolymer.

Synthesis of block copolymers with sonochemically prepared macroinitiators.     

Universal Bioinert Control of Polystyrene Interfaces via Hydrophobic‐Driven Self‐Assembled Surface PEGylation with a Well‐Defined Block Sequence

This work proposes a new molecular insight of interfacial design in the control of antifouling performance for the versatile biofoulants, including proteins, blood cells, tissue cells, and bacteria. A self‐assembled bioinert interface with universal fouling resistance to general biofoulants via hydrophobic‐driven surface PEGylation is presented. The study systematically discriminates the optimum PEGylated block polymer configuration and hydrophobic/hydrophilic segmental ratio enabling to optimize the surface coverage by the bioinert moieties, thus ensuring the best resistance to biofouling. For similar copolymer molecular weights and similar polystyrene (PS)/poly(ethylene glycol) methacrylate (PEGMA), the coating density obtainable is the highest if a random copolymer is used, while it is the lowest with a triblock copolymer. That measured with a diblock copolymer lies in between. Random copolymers offer more numerous anchoring possibilities than diblock copolymers, while they are importantly fewer if triblock copolymers are used. For similar total number of hydrophilic blocks, the diblock copolymer is more efficient to resist larger cells (leukocytes, fibroblasts) while the triblock is better to promote mitigate biofouling by smaller molecules or cells (proteins, platelets, red blood cells). The length of the hydrophilic PEGylated block seems to dominate fouling resistance of large biofoulants.     

Sequential reordering in condensation copolymers, 2. Melting- and crystallization-induced sequential reordering in miscible poly(butylene terephthalate)/polyarylate blends

A 50/50 (weight ratio (38/62 mole ratio referred to repeating units)) blend of poly(butylene terephthalate) (PBT) and polyarylate (PAr), was studied by means of thermal, solubility, X-ray and nuclear magnetic resonance techniques after annealing procedures that enable transesterification. Prolonged thermal treatment at 290°C gives rise to a copolymer that no longer reveals melting or crystallization. In accordance with previous reports, this effect is attributed to the formation of a random copolymer. Additional annealing of such samples at the relatively low temperature of 140°C results in the reappearance of melting endotherms in the differential scanning calorimetry curves. This effect is explained by crystallization-induced sequential reordering from random to block copolymer by means of transreactions. In that way a PBT/PAr blend was shown to be another polymer system, along with poly(ethylene terephthalate) (PET)/polycarbonate (PC) and PET/PAr blends, in which the entire cycle is realized, from two homopolymers via a block- and random copolymer to a block copolymer. The unusually low temperature at which the crystallization-induced sequential reordering to block polymers takes place is explained by the miscibility of PBT and PAr which enables transreactions to take place in the bulk.     

Sequential reordering in condensation copolymers, 4. Crystallization-induced sequential reordering in poly(ethylene terephthalate)/polycarbonate copolymers as revealed by the behavior of the amorphous phases

An equimolar blend of poly(ethylene terephthalate) (PET) 3

1 Systematic IUPAC name: poly(oxyethyleneoxyterephthaloyl).

and bisphenol-A-polycarbonate (PC) 4

2 Systematic structure-based IUPAC nomenclature: poly(oxycarbonyloxy-1,4-phenylene-1-methylethylidene-1,4-phenylene).

is studied by dynamic-mechanical thermal analysis (DMTA) and X-ray scattering after thermal treatment that enables transesterification. As demonstrated by wide-angle X-ray scattering (WAXS) measurements, prolonged thermal treatment at 280°C gives rise to a copolymer that no longer reveals melting or crystallization. In accordance with previous reports, this effect is attributed to the formation of a random copolymer. Additional annealing of such samples below the melting temperature of PET results in restoration of the crystallization ability. This effect is explained by crystallization-induced sequential reordering from random to block copolymer by means of transreactions which closes the cycle of transformations from two homopolymers via block- and random copolymer back to a block copolymer. The behavior of the amorphous phases is studied by means of DMTA demonstrating that their glass transition temperatures T_g's vary in accordance with the crystallinity changes. The random copolymer is characterized by a more or less homogeneous amorphous phase. In contrast to this, the mechanical mixture and the two block copolymers (the initial and that with the restored blocky structure) show DMTA peaks of two amorphous phases, clearly separated and with distinct individual T_g's. Viscosity measurements also demonstrate that the random copolymer significantly differs in its viscosity as compared to all other samples. These results represent a further evidence for the effect of block restoration via crystallization-induced sequential reordering.     

Polymer conformation and NMR chemical shifts, 7. Conformational analysis of random copolymers

A method is developed for the conformational analysis of copolymers with randomly distributed stereo- and comonomer-sequences. The conformational probabilities of dyad sequences constituting a random copolymer chain are calculated as a function of the copolymer composition which is derived from the monomer reactivity ratios and the comonomer feed ratio. The applicability of this method is verified in the conformational analyses of poly(methyl acrylate-co-styrene) and poly(methyl methacrylate-co-styrene). The calculation indicates that the conformational stabilities of dyad sequences are scarcely dependent on the copolymer composition in the former copolymer, whereas they are susceptible to the composition in the latter copolymer. This conformational behavior apparently reflects the geometrical difference between the copolymers: the former is composed of two mono-substituted monomers and the latter of sterically nonequivalent monomers, viz. mono- and di-substituted vinyl compounds. The composition-dependences of ¹³C NMR chemical shifts of these copolymers are interpreted, based on the conformational calculation by this method.     

Compatibilizing Effect of Transesterification Copolymers on Bisphenol‐A Polycarbonate/Poly(ethylene terephthalate) Blends

After considerably long time of transesterification reactions between poly(ethylene terephthalate) (PET) and bisphenol‐A polycarbonate (PC) in the molten state, random copolymers, referred to be TCET's, can be obtained, which have fairly good compatibilizing effect on the immiscible PC/PET blend. The compatibilizing effect of these transesterification random copolymers is proved to be closely related to their compatibility with PET and PC. Being completely compatible both with PET and PC, the TCET50 copolymer with 50 wt.‐% ethylene terephthalate content is an efficient compatibilizer, it can greatly improve the compatibility between PET and PC. With increasing content of the TCET50 copolymer in the PC/PET/TCET50 ternary blend, the two glass transition temperatures, which belong to the PET‐rich and PC‐rich phase respectively, approach each other gradually. When the content of the TCET50 copolymer in the blend reaches 60 wt.‐%, only one glass transition temperature can be detected by differential scanning calorimetry (DSC). The TCET30 and TCET70 copolymer, which have 30 and 70 wt.‐% ethylene terephthalate content respectively, are less efficient in compatibilizing the PC/PET blend, since the TCET30 copolymer and PET, as well as the TCET70 copolymer and PC, are compatible to a certain degree instead of being completely compatible.     

Copolymerization of vinyl and cyclic monomers in the solid state

A study has been made of the polymeric product obtained by exposure to γ-rays of carefully dried eutectic mixtures of styrene and β-propiolactone which were sealed in vacuum and maintained at a few degrees below the melting point. No copolymer was formed, only a mixture of homopolymers. However, evidence was obtained which supports an earlier claim that a copolymer is formed by γ-irradiation of a solid mixture of acrylonitrile and β-propiolac tone.     

Polymer-solvent interactions in mixed solvents, 2. Isotactic,syndiotactic and atactic poly(methacrylic acid-co-benzyl methacrylate) in water/2-chloroethanol mixtures

The viscosimetric behaviour and the preferential solvation of syndiotactic, isotactic and atactic copolymers of methacrylic acid and benzyl methacrylate are studied in water/2-chloroethanol mixtures. The experimental results show that the presence of benzyl groups stabilizes the compact structure. In the case of the syndiotactic samples, the extent of the preferential hydration domain, which is related to the existence of the compact structure, is dependent on the composition of the copolymer. Experimental results also suggest that the presence of the benzyl groups destabilizes the inverse compact structure existing in 2-chloroethanol-rich mixtures.     

Polymer recycling in aqueous two-phase extractions using thermoseparating ethylene oxide--propylene oxide copolymers

This is a study on the recovery and recycling of copolymer in aqueous two-phase systems containing random copolymers of ethylene oxide (EO) and propylene oxide (PO). The random copolymers separate from water solution when heated above the lower critical solution temperature (LCST). The primary phase systems were composed of EOPO copolymer and hydroxypropyl or hydroxyethyl starch. After phase separation the upper EOPO phase was removed and subjected to temperature induced phase separation. Copolymers with different EO/PO compositions have been investigated, EO50P050 [50% EO and 50% PO (w/w)], EO30PO70 and EO20P080. The temperature required for thermoseparation decreases when the PO content of the copolymer is increased. The effect on the recovery of copolymer after addition of salts, a second polymer or protein was investigated. The added components increased the recovery of copolymer after thermoseparation, e.g., increased the amount copolymer separated from the water phase after thermoseparation. Recycling of copolymer and measurements of polymer concentrations in the primary top and bottom phases after repeated recycling steps was performed. The fluctuation in polymer concentration of the phases was very small after recycling up to four times. Partitioning of the proteins BSA and lysozyme was studied in primary phase systems after recycling of copolymer. The partition coefficients of total protein and lysozyme was not significantly changed during recycling of copolymer. More than 90% of the copolymer could be recovered in the thermoseparation step by optimising the temperature and time for thermoseparation. In repeated phase partitionings in EOPO-starch systems the EO50PO50 copolymer could be recovered to 77% including losses in primary system and thermoseparation, which is equivalent to a total copolymer reuse of 4.3 times.     

Lipase‐Catalyzed Ring‐Opening Polymerization of Lactones in the Presence of Aliphatic Polyesters to Ester Copolymers

Ring‐opening polymerization of macrolides in the presence of aliphatic polyesters has been performed using Pseudomonas lipase as catalyst to produce ester copolymers with molecular weights of several thousands. The polymerization behavior was monitored by SEC and NMR. ¹³C NMR analysis showed that the resulting polymer was not a mixture of the starting polyester and the polymer from the macrolide, but a random copolymer consisting of both units. These data indicate that the lipase catalyzed the polymerization of the macrolide as well as the intermolecular transesterification of the starting and resulting polymers. The random copolymer was found to be highly crystalline by DSC and WAXD measurement. The present specific catalysis of the lipase was applied to the synthesis of ester copolymers by transesterification between two different polyesters.     

Spontaneous Self‐Assembly and Micellization of Random Copolymers in Organic Solvents

Spontaneous self‐assembly of random and statistical copolymers in solution, especially in organic solvents, is unusual due to the structural irregularity of the copolymer chain and close proximity of short incompatible segments. This study describes the first observation of supramolecular structures such as micelles and vesicles formed by a random copolymer in organic solvents. Upon dissolution in methanol or tetrahydrofuran, the random copolymer poly(trifluoroethyl methacrylate‐random‐methacrylic acid) forms small spherical micelles, worm‐like assemblies, and large vesicles spontaneously. Self‐assembly is driven by the high incompatibility between the fluorinated and acidic repeat units. Micelle size can also be altered by the addition of metal ions, which interact with the carboxylic acid groups of methacrylic acid through complexation or Coulombic forces. These findings demonstrate an easy, single‐step approach to creating nanoscale structures with tunable size and morphologies in organic solvents from easily synthesized random copolymers, with potential applications in coatings, selective membranes, catalysis, and drug delivery.     

Miscibility and morphology of AB/C-type blends composed of block copolymer and homopolymer or random coploymer, 2. Blends with random copolymer effect

This work is an extension of the concept of miscibility window in homopolymer/random copolymer blends to blends containing block copolymers. The miscibility and morphology of THF-cast blends composed of the block copolymer polyisoprene-block-poly(methyl methacrylate) (Pl-b-PMMA) and the random copolymer poly(styrene-ran-acrylonitrile) (SAN) (22 wt.-% AN) has been studied by transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). Most blends show miscibility between PMMA blocks and SAN, presenting a homogeneous microdomain structure. Coupling of macrophase separation occurs only when the ratio of molecular weights of SAN to the PMMA bock is very large and SAN becomes the dominant component. The excellent miscibility in the block copolymer/random copolymer blends can be understood by considering that the monomer unit composition of SAN is within the miscibility window in PMMA/SAN blends. The main driving force for the miscibility is repulsion between S and AN units rather than hydrogen bonding between SAN and PMMA, since a proton-acceptor type solvent does not show any effect on the miscibility in the blends. Apparent broadening of the glass transition of the ‘hard phase’ is observed and explained with the aid of the segment density gradient model.