Peter Friedel

Synthesis and Phase Separation Behaviour of High Performance Multiblock Copolymers

The phase separation behaviour of block copolymers of the type (A–B) n (segmented block copolymers, multiblock copolymers) containing segments with different degrees of flexibility was investigated using a stepwise variation of the incorporated blocks A and B. Amorphous/rigid blocks (polysulfone segments) were systematically combined with amorphous/flexible blocks (poly(tetramethylene glycol), semiflexible/nematic blocks (different kinds of aromatic polyesters and poly(ester imides) as well as semicrystalline fluorinated polyester blocks). All multiblock copolymers were synthesized using a conventional transesterification polycondensation in the melt and the polycondensation results are discussed. The phase separation in the synthesized block copolymers was investigated both experimentally and theoretically. Flory–Huggins interaction parameters of the block copolymers were calculated and used together with mean field calculations in order to understand the phase separation behaviour of all block copolymers correlated to their chemical structure. On the other hand, the onset of phase separation in a series of block copolymers with a systematic variation of block molecular weights was examined experimentally, mainly by DSC and SAXS. Finally, the question is discussed whether or not the degree of phase separation in the investigated systems determines the properties of the polymers or not. This is for example outlined for the mechanical properties and, in particular, the surface properties of fluorinated block copolymers.

Modelling of the phase separation behaviour of semiflexible diblock copolymers

For a realistic theoretical description of the structure factor and the phase behaviour of melts of block copolymers, the partial stiffness of the chains has to be taken into account, particularly for diblocks consisting of blocks of very different chain stiffness. In this paper, a simple theoretical description for the structure factor of semiflexible microdisperse diblock copolymers is presented. It is derived by introducing the persistence length in addition to the monomer length and is based on the random phase approximation (RPA) in combination with a cumulant expansion for the semiflexible form factor. The persistence lengths of the two blocks are in general different and arbitrary, encompassing all experimentally important cases of Gaussian-Gaussian, semiflexible-semiflexible, rod-rod, Gaussian-semiflexible, Gaussian-rod and semiflexible-rod diblocks. It is shown that the formalism is capable of predicting reasonable structure factors and spinodals for semiflexible diblock copolymers. In particular, the experimentally observed unsymmetry of the spinodals for copolymers with blocks of different stiffness is reflected in the theory, as presented in this investigation.

Self-assembly and viscoelastic properties of semifluorinated polyesters

The structure and dynamics of polyesters composed from a rigid aromatic backbone and oxyalkylperfluoroalkyl side chains have been studied using differential scanning calorimetry, small- and wide-angle X-ray scattering, pressure-volume-temperature measurements and rheology. The system was found to undergo three phase transitions. Starting from lower temperatures they reflect the melting of the fluorinated side chains, the unfreezing of the backbone mobility and the melting of the smectic layered structure. In addition, rheology has shown that these compounds are thermorheologically complex at all temperatures investigated and exhibit non-Newtonian low-frequency response.

W.a.x.s. and force field constrained RIETVELD modelling of meta-linked fully aromatic copolyesters: 1. Poly(p-phenylene isophthalate)

Abstract Fully aromatic copolyester with regular chain structure containing kinked monomer units were investigated by powder diffraction experiments combined with structure modelling. Temperature dependent X-ray measurements show the existence of low and high temperature solid state modifications of poly( p -phenylene isophthalate), (IPA-HQ) n . From the X-ray scattering data, d -spacings were determined taking some experimental corrections into account. Lattice parameters as well as atom coordinates of lt -(IPA-HQ) n were calculated and optimised by means of modelling procedures based on force field constrained RIETVELD algorithms. From this, a monoclinic unit cell of lt -(IPA-HQ) n with a = 0.775 nm, b = 0.567 nm, c = 2.410 nm, β = 91.8° was found considering the chemical structure as well as interactions between the particles. The (IPA-HQ) n polyester is a typical representative of this kind of polymer with kinked monomeric, and hence is useful for further structural investigations.

Structure investigations of regular main chain copolyesters

Aromatic copolyesters with regular chain structure were investigated in order to correlate their primary chemical structure, some molecular characteristics (inherent viscosity, molecular weight) and crystallographic data as well as melting behaviour. A series of copolyesters were synthesized by polycondensation of complex aromatic dicarboxylic acid chlorides with variable diols. By means of wide angle X-ray diffraction it was found that the kind of diol component strongly influences the phase structure as well as the crystallinity of the polymers. A monoclinic symmetry was supposed for some of the high crystalline samples. Molecular modelling, including ab initio calculations and computing of the solid state, was carried out for two representatives of p-linked fully aromatic copolyesters. A good agreement of experimental and calculated scattering data was obtained by using the space group P1.

Dendronized Hyperbranched Macromolecules: Soft Matter with a Novel Type of Segmental Distribution.

Dendronization of a hyperbranched polyester with different generation dendrons leads to pseudo-dendritic structures. The hyperbranched core is modified by the divergent coupling of protected monomer units to the functional groups. Compared to dendrimers, the synthetic effort is significantly less, but the properties are very close to those of high-generation dendrimers. The number of functional groups, molar mass, and rheology behavior even in the early generation (G1-G4) pseudo-dendrimers strongly resembles the behavior of dendrimers in higher generations (G5-G8). Comparison of the segmental and internal structure with perfect dendrimers is performed using SANS, dynamic light scattering and viscosity analysis, microscopy and molecular dynamics simulation. The interpretation of the results reveals unique structural characteristics arising from lower segmental density of the core, which turns into a soft nano-sphere with a smooth surface even in the first generation.

Synthesis of PEEK/PSU Multiblock Copolymers

The goal of the work presented here was to synthesize multiblock copolymers based on transesterification polycondensation of end group functionalized PEEK with PSU oligomers in the melt. In the synthesis of PEEK oligomers by nucleophilic aromatic substitution cyclization occured observed by decreasing amount of end groups. The phase behavior of the multiblock copolymers was examined by differential scanning calorimetry and transmission electron microscopy and a phase diagram was constructed. The experimental results were compared with spinodals calculated by Mean Field Modelling. It could be shown that the very similar structure of the blocks and the insufficient high block molecular weights were responsible for the observed non-phase separated morphologies. The thermal properties of the multiblock copolymers can be controlled by the segment length of the PSU oligomers. The glass transition temperature is increased provided that the segment length of PSU oligomers is lower than 8000 g mol−1

Temperature dependant structural changes in thin films of random semifluorinated PMMA copolymers

Semifluorinated (SF) side chain polymers show phase separation between polymer backbone and SF side chains. Due to strong interaction between SF segments the side chains determine the structure behaviour strongly, often resulting in layered structures in which backbones and layers of SF side chains alternate. The interest in this work was directed to find out the dependence of these structures on concentration of SF side chains. Thin films of random copolymers consisting of methylmethacrylate (MMA) and semifluorinated side chain methacrylate (SFMA) segments and with different fluorine content in the perfluoroalkyl side chains (abbreviated as H10F10 and H2F8) were prepared by spin-coating. Phase separation and structure changes were initiated by external subsequent annealing. Corresponding bulk material served as basic information. Generation of ordered structures and variation of film parameters were observed using different X-ray scattering methods (XRR, GIWAXS, and GISAXS). The phase behaviour in bulk is governed by the SF side chain amount and their specific fluorine content which control the self-organization tendency of SF side chains. Additionally, the confinement in thin films generates an orientation of side chains normally to film surface. Key words: T-dependant X-ray scattering, GISAXS, phase separation, thin films, random copolymers, semifluorinated polymers a) Author to whom correspondence should be addressed. Electronic mail: djeh@ipfdd.de

Thin-film morphologies of block copolymers with nanoparticles

Diblock copolymers (BCPs) show phase separation on mesoscopic length scales and form ordered morphologies in both bulk and thin films, the latter resulting in nanostructured surfaces. Morphologies in thin films are strongly influenced by film parameters, the ratio of film thickness and bulk domain spacing. Laterally structured polymer surfaces may serve as templates for controlled assembly of nanoparticles (NPs). We investigated the BCP of poly( n -pentyl methacrylate) and poly(methyl methacrylate) which show bulk morphologies of stacked lamellae or hexagonally packed cylinders. Thin films were investigated by atomic force microscopy and grazing-incidence small-angle X-ray scattering. For film thicknesses f well below d bulk , standing cylinder morphologies were observed in appropriate molar ratios, while film thicknesses around and larger than d bulk resulted in cylinders arranged parallel to surface. To alter and/or improve the morphology also in presence of different NPs (e.g., silica, gold), solvent vapour annealing (SVA) was applied. The BCP morphology usually remains unchanged but periodicities change depending on type and amount of incorporated NPs. It was found that silica clusters enlarge lateral distances of cylinders, whereas Au NPs reduce it. The effect of SVA is weak. The quality of morphology is slightly improved by SVA and lateral distances remain constant or are slightly reduced.

Wide angle X-ray diffraction and force field constrained Rietveld modelling of m-linked fully aromatic copolyesters. 2. Poly(p-phenylene terephthalate-co-p-phenylene isophthalate)

Abstract Fully aromatic copolyesters with regular chain structure containing kinked monomer units were investigated by powder diffraction experiments combined with structure modelling. The proposed series of copolyester structures including isophthalic acid was continued with (TPA–HQ–IPA–HQ) n (containing 104 atoms as repeating unit). The monoclinic unit cell has a=0.781 nm , b=0.557 nm , c=5.03 nm and β =89.2° as atom coordinates. The symmetry of the unit cell was determined by means of a force field constrained Rietveld refinement algorithm including nonbonding interactions (Lennard-Jones potentials) and chain continuation enforcement (penalty functions) in the force field. A reliability factor R Rietveld of 9.5% was calculated.