Polyurethane (PU) foams are the most widely used polymer foams [1][2][3][4][5] with a production of millions of tons every year. [4] Ranging from flexible to rigid and from open to closed-cell foams, PU foams span a particularly wide range of uses from seating applications to thermal and acoustic insulation. The PU industry now masters very well the PU chemistry, providing explicit and fine control over the involved reactions and the final polymer properties. However, two important challenges remain in the optimization of the foaming processes: 1) explicit control over pore sizes, pore size distribution, and pore arrangement. 2) explicit control over the degree of the pore connectivity (open vs. closed cells);This missing control results from a threefold complexity:1) complexity of the commonly employed foaming techniques (chemical or physical blowing) which provide large bubble size distributions; 2) complex polyurethane (PU) chemistry with a number of side reaction, especially in the presence of water; 3) complex interplay between the chemistry and the physics of the liquid foam before and during solidification.Moreover, these three aspects are strongly coupled. [2,3,6] Decades of experience provide now reasonable control of these processes within certain parameter ranges which allow the adaptation of different foam types to applications. [1][2][3] In parallel, 3D-imaging and computational techniques evolve rapidly to characterize the structural parameters of PU foams and to predict their properties. [1] However, an experimental technique which provides explicit and fine-control over foam morphology, density, pore connectivity, and polymer properties is still to be found. [1,7] Goal of this work is therefore to propose a simple approach to the generation of PU foams, which keeps the complexity of the involved chemical reactions at a minimum and which allows the generation of foams composed of equal-volume pores with well-controlled spatial organization ( Figure 1). For this purpose, we reduce the PU chemistry to its most basic ingredients: one polyol, one isocyanate, one catalyst and one foam stabilizer. These are physically foamed by a well-controlled bubbling process, in which an inert gas is injected bubble by bubble into the PU mixture in the liquid state. All processing parameters are optimized in such a way that a sufficiently stable liquid foam is obtained at the outset in which the bubbles have time to find their equilibrium positions. As such, we can directly build on an available vast experience concerning the control and description of structural properties of liquid foams in equilibrium. [8][9][10][11] Once the desired foam properties are obtained, the liquid foam is solidified in situ in such a way that the foam structure remains unchanged. In this process, fine-tuning of the system parameters also provides explicit control over the rupture of the thin films separating neighboring bubbles and therefore over the final poreconnectivity of the foams.For the implementation of this approach, we use mill...

Copolymers from methacrylic acid (1) and trimethylsilyl methacrylate (2) have been synthesized by free radical copolymerisation and by controlled desilylation of poly(trimethylsilyl methacrylate) (3). The reactivity ratios were r1 = 2.75, r2 = 0.004. Differential scanning calorimetry showed a linear correlation between the peak temperature of the endotherm for the formation of cyclic anhydrides and the content of methacrylic acid in the copolymer. Obviously, the acid catalyses this reaction. The copolymers as well as poly(trimethylsilyl methacrylate) have a ceiling temperature. Sequence distributions were calculated and used to predict glass transition temperatures for comparison to the experimental results. The microstructure of the copolymers obtained by the different synthetic routes is different as shown from Tg and from their solubility. Those from desilylation are random with “reactivity ratios” of 1, those from copolymerisation seem to have longer sequences of methacrylic acid leading to formation of intermolecular aggregates. Dependence of DSC peak temperature of anhydride formation on methacrylic acid content.magnified imageDependence of DSC peak temperature of anhydride formation on methacrylic acid content.

Free radical copolymerisation of tert‐butyl methacrylate (1) with trimethylsilyl methacrylate (2) and methacrylic acid (3) has been investigated. Reactivity ratios for methacrylic acid and tert‐butyl methacrylate indicate an azeotropic copolymerisation (r1 = 0.476 ± 0.103; r3 = 0.300 ± 0.032), whereas the two esters show preferential incorporation of 2 (r1 = 0.170 ± 0.050; r2 = 1.170 ± 0.124). Thermal cis‐elimination of isobutylene from the tert‐butyl ester and subsequent formation of six‐membered cyclic anhydride moieties has been studied. For poly(methacrylic acid‐co‐tert‐butyl methacrylate) thermogravimetry could be used to determine copolymer composition. Solvolytic desilylation of the trimethylsilyl ester groups has been investigated as an alternative route to poly(methacrylic acid‐co‐tert‐butyl methacrylate). The tert‐butyl ester is not affected under the conditions of desilylation. Sequence distribution of both copolymers has been calculated using the method introduced by Bruns and Motoc.