S. Höring

Synthesis and characterization of poly(ethylene oxide) and poly(perfluorohexylethyl methacrylate) containing triblock copolymers

A new series of poly(perfluorohexylethylmethacrylate)-block-poly(ethylene oxide)-block-poly(perfluorohexylethyl methacrylate), PFMA-b-PEO-b-PFMA triblock copolymers has been synthesized by atom transfer radical polymerization using bifunctional PEO macroinitiators. The molecular structure of the block copolymers was confirmed by 1 H NMR spectroscopy and SEC. X-ray scattering studies have been carried out to investigate their bulk properties. SAXS has shown cubic arrangement of spheres (bcc), hexagonally packed cylinders (hpc) and lamellar microdomain formation in the melt of triblock copolymers investigated, depending on composition. Crystallization was, however, found to destroy the ordered melt morphology and imposes a lamellar crystalline structure. WAXS, DSC and polarized light microscopy measurements confirmed the crystallization of PEO segments in block copolymers. Long PFMA blocks were found to have significant effect on PEO crystallization.

The anionic block copolymerization of ethylene oxide with tert-butyl methacrylate. Diblock and multiblock copolymers

Abstract Diblock copolymers were synthesized by anionic polymerization in the order tert-butyl methacrylate-ethylene oxide and ethylene oxide-tert-butyl methacrylate using a monofunctional initiator in tetrahydrofuran. By repeated alternate addition of these monomers, we produced block copolymers with a larger number of sequences. The resulting block copolymers were analysed by size exclusion chromatography, osmometry and extraction. The morphology and properties of the polymers were investigated using transmission electron microscopy and measurements of the interfacial activity.

Crystallization of Frustrated Alkyl Groups in Polymeric Systems Containing Octadecylmethacrylate

This chapter deals with the crystallization behavior of long frustrated alkyl groups as part of side chain polymers. Results from crystallization experiments on poly(n-octadecylmethacrylate) [PODMA] homopolymers with different molecular weight and on microphase-separated poly(styrene−block−octadecylmethacrylate) block copolymers [P(S−b−ODMA] by calorimetry and scattering techniques are presented. A phenomenological picture describing the different stages of the side chain crystallization in PODMA is given. The influence of additional constraints in P(S−b−ODMA) block copolymers containing PODMA lamellae or cylinders in a glassy environment is studied. It is shown that these block copolymers are systems with a hierarchy of length scales in the nanometer range. The crystallization behavior in PODMA lamellae is basically bulk-like while strong confinement effects are indicated in case of PODMA cylinders with a diameter <20 nm by increasing crystallization times and broader transformation intervals in isothermal crystallization curves. These effects can be explained by changes concerning nucleation mechanism and crystal growth. The reduced degree of crystallinity in small cylinders is discussed based on hypothetical pictures for the internal structure of the PODMA domains.

Synthesis of ethylene oxide/methyl methacrylate diblock copolymers by group transfer polymerization of methyl methacrylate with poly(ethylene oxide) macroinitiators

Ethylene oxide/methyl methacrylate diblock copolymers were prepared by group transfer polymerization (GTP) of methyl methacrylate (MMA) with poly(ethylene oxide) macroinitiators (1). The macroinitiator containing silyl ketene acetal end-groups was synthesized by hydrosilation of poly(ethylene glycol) monomethacrylate which was previously prepared by esterification of poly(ethylene glycol) monomethyl ether (PEO-OH). All synthesized macroinitiators initiated the GTP of MMA in tetrahydrofuran with tetrabutylammonium cyanide or tris(dimethyiamino)sulfonium difluoride as catalysts. The polymerization proceeds rapidly at room temperature to quantitative yield. The block copolymers are contaminated with small fractions of PEO homopolymer as a result of uncomplete macroinitiator synthesis. Unreacted PEO-OH, which is present in very small amounts, reduces the concentration of active centers. Therefore, the degree of polymerization is not in good agreement with the theoretical value calculated for a living polymerization taking the monomer to macroinitiator ratio. However, after extraction of the PEO homopolymer, the block copolymers show a narrow molecular weight distribution. Induction periods in time-conversion curves obtained with 1 as initiator vanished nearly, when the reaction was started with the addition product of 1 and MMA. This is an indication, that in the system under investigation a slow initiation step between 1 and the first MMA unit precedes the propagation reaction. Tacticity measurements yield about 56% syndiotactic, 40% heterotactic and 4% isotactic triads for PMMA in the block copolymers.

Struik law for enthalpy retardation at the glass transition in poly(n-alkylmethacrylates) measured by DSC aging experiments

Results of calorimetric (DSC) experiments on a series of poly (n-alkylmethcrylates), from methyl to pentyl, after different aging timeste at different aging temperaturesTe are presented. The aging behavior is quite different from that in other polymers, for example PS. For all poly(n-alkylmethacrylates) investigated the aging peak temperatureTmax is shifted parallel to the aging temperatureTe in a large temperature interval below the glass temperature. The results are discussed with respect to shear and entropy response in the αβ splitting region.