Nanophase separation on length scales of 1-5 nanometres has been reported previously for small-molecule liquids, metallic glasses and also for several semicrystalline, liquid-crystalline and amorphous polymers. Here we show that nanophase separation of incompatible main and side-chain parts is a general phenomenon in amorphous side-chain polymers with long alkyl groups. We conclude from X-ray scattering and relaxation spectroscopy data for higher poly(n-alkyl acrylates) (PnAA) and poly(n-alkyl methacrylates) (PnAMA) that alkyl groups of different monomeric units aggregate in the melt and form self-assembled alkyl nanodomains with a typical size of 0.5-2 nm. A comparison with data for other polymer series having alkyl groups reveals that important structural and dynamic aspects are main-chain independent. A polyethylene-like glass transition within the alkyl nanodomains is observed and discussed in the context of a hindered glass transition in self-assembled confinements. This is an interesting link between central questions in glass-transition research and structural aspects in nanophase-separated materials.

The development of the dynamic glass transition in poly(n-alkyl methacrylate)s is investigated with broad-band dielectric spectroscopy in the frequency range from 10-4 to 109 Hz. The experimental data were analyzed by adjustment with one or a sum of two Havriliak Negami functions. Upon decreasing the temperature, the high-temperature relaxation (a) changes into the local β relaxation (Johari Goldstein mode), and the cooperative α relaxation sets in close to this aβ transition. For poly(n-butyl methacrylate) a separate onset (zero intensity) of the α process and a parallel course of both traces in the Arrhenius diagram were observed. The activation energy of the β process does not change in spite of the parallel development of the α process. On the other hand, for poly(ethyl methacrylate) the α onset is close to a bend in the local process, i.e., the activation energy of the latter changes after the α onset. In both materials the intensity of the α process linearly increases with falling temperatures but with different intensity. Several scenarios for the αβ-splitting region are suggested.

No abstract

We show that nanoconfinement is a handle to rationally produce and stabilize otherwise metastable or transient polymorphs of pharmaceuticals, as required for controllable and efficient drug delivery. The systematic investigation of crystallization under confinement unveils thermodynamic properties of metastable polymorphs not accessible otherwise and may enhance the understanding of the crystallization behavior of pharmaceuticals in general. As an example in this case, we studied acetaminophen confined to inexpensive and biocompatible nanoporous host systems. Calorimetric and X-ray scattering data clearly evidence that either the stable polymorph form I or the metastable polymorph form III can be stabilized in high yields. Thermodynamic parameters for form III of acetaminophen are reported, and strategies to manipulate the crystalline state in pores by thermal treatments are presented.

Shear data in the temperature range from −145 °C to the flow zone are presented for the poly(n-alkyl methacrylate)s from methyl (C = 1) to lauryl (C = 12). Three qualitatively different glass transitions are observed in the shear curves at 10 rad/s:  (i) the conventional α process in the C < 5 members, (ii) the high temperature a process in the C > 5 members, and (iii) an additional polyethylene-like glass transition, αPE, in the C ≥ 3 members. All three processes depend systematically on side chain length. Two alternative empirical pictures for the coexistence of two glass transitions are discussed:  (a) a static nanophase separation between main chains and side chains and (b) a dynamic heterogeneity with two different time and length scales.