We report on the physical characterization of a dioctyl‐substituted polyfluorene, both in solution and in the solid state. We focus on studies of chain geometry both by molecular modeling and by gel permeation chromatography coupled with light scattering. We determine experimentally a Kuhn segment length, lk = 17.1 ± 2.1 nm and a characteristic ratio C∞ = 21.5 %plusmn; 4.3 indicative of a stiff polymer chain. The effects on absorption and emission spectra of intermolecular interactions that lead to gelation or precipitation from solution are reported. We discuss these results in the context of the strong current interest in the nature of aggregation phenomena and their role in controlling the emissive properties of conjugated polymers. We further show that a markedly enhanced dichroism can be achieved through suitable control of the polymer microstructure.

The microstructure of segmented block copoly(ether esters) composed of poly(tetramethylene oxide) (PTMO) “soft” blocks and poly(butylene terephthalate) (PBT) “hard” blocks was investigated. A variety of analytical techniques, including 13C solid-state NMR, infrared spectroscopy, dynamical mechanical analysis, dielectric spectroscopy, differential scanning calorimetry, and transmission electron microscopy, were applied. The samples vary in the amount (35−60 wt %) and block length (1000−2000 g/mol) of the soft component. It is generally assumed in the literature that copoly(ether esters) have a two-phase structure consisting of a crystalline PBT phase surrounded by an amorphous phase which is a homogeneous mixture of PTMO soft segments and amorphous PBT segments. Our experimental results reveal that the amorphous phase is not a homogeneous mixture of “hard” and “soft” segments but consists of a highly mobile “PTMO-rich phase” and a less mobile “PBT/PTMO mixed phase”. The extent of microphase separation in the amorphous phase appeared to be strongly dependent on the block length and composition. Those samples that revealed a strong microphase separation showed strain-induced crystallization of the soft segments upon mechanical deformation.

AFM nanoindentations show a dependence of penetration, i.e., the relative motion between the sample and the tip (indenter), on material elastic properties when using the same load. This relationship becomes visible by using of samples being homogeneous down to the scale of nanoindentation. They were prepared from materials covering a broad range of mechanical behavior: from rubbery networks to glassy and semicrystalline polymers. The elastic modulus can be obtained applying Sneddon's elastic contact mechanics approach. To do this, some calibrations and instrumental features have to be measured accurately. All the polymers tested show that the contact between the tip and the sample is dominated by elastic behavior with negligible plastic deformation. In contrast to a standard metallic material like lead, the penetration dependence on load follows an exponent of 1.5, consistent with elastic contact mechanics. This can be justified on the basis of the large elastic range polymers exhibit, on the constraints due to the geometry of the deformation during indentation and to the critical yielding volume needed in order to induce plasticity. For the polymers studied, this volume is chosen in such a way that a significant material volume is irreversibly deformed. Elastic moduli taken from AFM force curves show a very good agreement with bulk values obtained by macroscopic tensile testing, on all the polymers tested. This result confirms that AFM nanoindentations in polymers take place mostly in the elastic range and opens the possibility to characterize the mechanical behavior of polymers on an unparalleled small scale compared to commercial DSI (depth sensing instruments), which use a much blunter indenter.

The relation between rheology and the time dependent morphology of a phase-separating binary blend of polystyrene and poly(vinyl methyl ether) was investigated by heating a sample from the single-phase (at 90°C) into the two-phase regime (at 124°C, 16 K above the LCST) and maintaining its temperature there while measuring the evolution of the dynamic moduli G′ and G′′. Morphological changes occurred slowly so that there was sufficient time to cycle the dynamic mechanical measurements repeatedly over five decades in frequency. The morphology was observed on length scales from 1 mm down to 1 nm by conventional optical microscopy combined with digital image analysis, Hoffman modulation microscopy, TEM, and WISE NMR with spin diffusion. NMR shows that major compositional changes occur mostly in the first 20 min and then the composition remains constant at about 60:40 PS/PVME for the PS-rich matrix and 5:95 PS/PVME for the PVME-rich microdomains. The PVME-rich microdomains are separated by thin layers of the PS-rich phase which forms the matrix. On a larger scale, shape and geometry change during the entire experiment (42 h). The linear domain growth appears to be consistent with the theories of Siggia and Doi-Ohta. The initial increase of the dynamic moduli is attributed to the formation of highly interconnected PVME-rich and PS-rich phases during spinodal decomposition. The subsequent decrease of the values of the dynamic moduli is considered to be the result of the loss of the interconnectivity between the two phases due to the breakup of the PS-rich phase network and the coalescence of the PVME-rich domains.