Manfred Arnold

Synthesis and characterization of LC side chain AB blockcopolymers

SummaryThe synthesis of liquid crystalline side chain A-B blockcopolymers, prepared by living anionic polymerization in combination with a polymeranalogous reaction is reported. Thereby the A-block was formed from a non mesogenic monomer (styrene, butadiene and n-butylmethacrylate) and the B-block from a monomer with a lateral active group (2-(trimethylsiloxy)-ethylmethacrylate), used for introduction of the side chain mesogens (cholesterylformyl- and 2-(4-[5-hexylpyrimidin-2-yl]-benzoyloxy)-groups). The obtained copolymers show mostly phase separation phenomenons. In dependence of the content of LC side groups a mesomorphic behaviour was observed.

On the interaction of the morphological structure and the LC behaviour of LC side chain block copolymers

The interaction between morphological structure and phase behaviour of a LC side group block copolymer has been investigated using DSC, TEM and small angle X-ray diffraction. All samples of Polystyrene-block-2-(3-cholesteryloxycarbonyloxy)ethyl methacrylate (PS-b-PChEMA) show a phase separation between the two blocks. It was found that in the case of those samples where the liquid crystalline sub-phase is not continuous (spheres), only a nematic phase is seen, whereas in all samples in which there is a continuous liquid crystalline sub-phase, the smectic A phase of the homopolymer is formed. On the other hand, the block copolymer seems to stabilize the LC phase; no dependency of the clearing temperatures on the molecular weight of the LC blocks has been observed.

Synthesis and characterization of branched polypropenes obtained by metallocene catalysis

The homopolymerization of propene, 4-methyl-1-pentene, 1-octene and the copolymerization of propene with 4-methyl-1-pentene and 1-octene, respectively, was carried out with the isospecific metallocene catalyst system rac-[(dimethylsilylene)bis(2-methylbenzo(e)indenyl)]zirconium dichloride/methylaluminoxane at 30°C in toluene. By variation of the monomer ratio, it is possible to produce copolymers in the entire composition range. The activity, the amount of comonomer insertion, and the molecular masses obtained in the propene/1-octene copolymerization are significantly higher compared to the respective values of the system propene/4-methyl-1-pentene. It is possible to synthesize polymers with glass transition temperatures ranging from −65 up to 26°C. Whereas the incorporation of more than 20 mol-% 1-octene leads to amorphous polymers, the propene/4-methyl-1-pentene copolymers with less than 15 and more than 60 mol-% 4-methyl-1-pentene are semicrystalline. All melting points vary in the range from 50 to 225°C. Wide angle X-ray scattering measurements indicate an increase of the γ-modification compared to the γ-modification with increasing comonomer content and crystallization temperature. Typical supermolecular morphologies different from spherulites and known for the γ-phase of the isotactic polypropene homopolymer are observed for the copolymers by polarized light microscopy.

Poly-α-olefins from polypropene to poly-1-eicosene made with metallocene catalysts

ABSTRACT Linear α-olefins from propene to 1-eicosene have been polymerized using a zirconocene catalyst and a hafnocene catalyst. The resulting isotactic polymers were characterized by NMR, GPC and DSC analysis. Compared to the zirconocene products the molecular weights of the poly-α-olefins made with the hafnocene catalyst were higher. The molecular weight distribution was found to be narrow as expected for metallocene polymers. DSC measurements showed that side chain crystallization occurs for the polymers from poly-1-decene to poly-1-eicosene.

Basis of Solid-Phase Grafting of Polypropylene

Abstract The chemical modification of polymers opens new dimensions for the development and design of materials based on plastics. The chemical modification of polymers by reactions is performed by reactions in a melt, in a solution, or in a solid phase. The modification of polymers in solid phases (powder or granular material directly from the polymerization) has great advantages compared with reactions in solution or melt. The advantages are lower costs and, most important, greater creative variability. A special advantage of solid-phase modification of polypropylene (PP) is the fact that the degradation reaction is reduced.

Liquid crystalline side-group block copolymers with triblock structure : Investigations on the influence of the block arrangement on the morphology and the LC-phase behavior

Liquid crystalline triblock copolymers with LC inner block and amorphous outer blocks have been synthesized by living anionic polymerization and investigated using DSC, TEM, and small-angle x-ray diffraction. All samples of poly[styrene-block-2-(3-cholesteryloxycarbonyloxy) ethyl methacrylate-block-styrene] (PS-b-PChEMA-b-PS) show liquid crystalline behavior and phase separation between the blocks. Compared to triblock copolymers with PS inner block (PChEMA-b-PS-b-PChEMA) and diblock copolymers (PS-b-PChEMA) the LC block copolymers with PS outer blocks have the same properties. The LC behavior and the morphology do not depend on the block arrangement ; they are only influenced by the volume fractions of the blocks. Those samples in which the liquid crystalline subphase is not continuous (spheres) only a nematic phase was found, whereas in all samples with a continuous liquid crystalline subphase, the smectic A phase of the homopolymer was observed.

Modified polypropylenes by copolymerization with nonconjugated dienes and additional chemical reactions

Modified polypropylenes were synthesized by copolymerization of propene with several nonconjugated dienes using a constrained geometry catalyst in combination with methylaluminoxane. The incorporation of the dienes yields in polymer structures containing both cyclic units and linear branches, respectively. By variation of the polymerization conditions the cyclization tendency can be reduced. The resulting propene/diene copolymers are equipped with higher amounts of pendant double bonds which can be used for following chemical reactions. As an example, the epoxidation of the free double bonds was carried out using several epoxidation reagents. In a further modification step, the ring opening of the epoxy groups is presented demonstrating the simplicity of the chemical modification possibilities of such polypropylene materials.

MODIFIED POLYPROPENES VIA METALLOCENE CATALYSIS

The copolymerization of propene with 1-olefins and other comonomers via metallocene catalysis is an important key to polymeric materials with a great variety of properties. The random incorporation of different side chains into the polypropene backbone gives access to a broad spectrum of properties of the polypropene materials ranging from thermoplastics across thermoplastic elastomers to olefin rubber which can be tailored using metallocene catalysts. With a lot of different 1-olefins it is possible to synthesize both copolymers of every desired composition as well as poly-1-olefins. Molecular, thermal, and mechanical properties of propene copolymers are determined by type and amount of the comonomer. The use of metallocene catalysis for the copolymerization of propene and cyclic olefins allows the incorporation of the cyclic olefin without ring opening reactions. This provides the way to a synthesis of copolymers with varying content of the cyclic olefin and interesting material properties. Polypropene graft copolymers used as single materials or acting as compatibilizer in polyolefin blends are very attractive polymeric products. Furthermore, via metallocene catalysis it is possible to synthesize polypropene-graft-polystyrene or polypropene-graft-polyisobutene. The method of synthesis as well as certain applications of such materials will be the main focus of this report.

Synthesis, dynamic‐mechanical and morphological behavior of styrene/butyl methacrylate diblock copolymers

In order to investigate the structure-property relationship of styrene/butyl methacrylate (PS/PBMA) diblock copolymers, two ranges of polymers with Mn ≈ 100 000 and Mn > 200 000, respectively, with polydispersity indexes Mw/Mn < 1.15 are synthesized with varying ratios of the block lengths. The molecular weights of these polymers are determined by size exclusion chromatography (SEC). Thermal behavior and morphology are characterized by dynamic-mechanical analysis (DMA) and transmission electron microscopy, respectively. Whereas for unsymmetrical diblock copolymers with an overall molecular weight of Mn ≈ 100 000 only one broadened glass transition due to their disordered state is found, nearly symmetrical diblock copolymers show a partial miscibility which can be ascribed to the proximity of the order-disorder transition and the annealing temperature of the samples. In the case of unsymmetrical high molecular weight diblock copolymers a partial miscibility is observed as well. The high molecular weight diblock copolymers with Mn > 200 000 at all compositions show microphase-separated structures in contrast to the diblock copolymers with an overall molecular weight of Mn ≈ 100 000. Compared with styrene/isoprene diblock copolymers a relatively wide range for lamellar structures is found.

Thermoanalytische messungen an ausgewählten polymeren

The possibility to interpret data obtained by thermoanalysis is increased considerably by combing thermoanalytical method with other chemical and physical ones. This is shown by testing polydimethacrylates and butadiene-ethene-copolymers.ZusammenfassungDie Aussagefähigkeit thermoanalytischer Messungen steigt beträchtlich, wenn diese mit anderen chemischen und physikalischen Methoden kombiniert werden. Dies wird durch Untersuchungen an Polydimethacrylaten und Butadien-Ethen-Coplymeren gezeigt.