# Tuning of Morphology and Surface Properties of Porous Silicones by Chemical Modification
## 3 Results and Discussion  
The emulsion stabilizer was an in-house prepared telechelic siloxane oligomer with aminopyridyl end groups (Scheme 1, n = 15, HLB 4.4), which is soluble in toluene. The medium internal phase emulsion (f = 0.5) of water in toluene was stable from one day to another, when partial demulsification was observed and re-emulsification was very easily performed with an ultrasonic cleaning bath. The stability of the emulsion at 50 \({}^{\circ}\)C was also very good within the timeframe of the reaction, since its appearance remained unchanged (Figure S1). The surface tension of the emulsion was 25.27 \(\pm\) 0.07 mN/m at room temperature and 24.43 \(\pm\) 0.1 mN/m at 50 \({}^{\circ}\)C (by the Wilhelmy plate method). The dehydrocoupling reaction of PMHS was used to generate pores in combination with the emulsion template method. This reaction, occurring very fast in the presence of Karstedt catalyst at room temperature in bulk, is accompanied by the evolution of hydrogen gas, due to atmospheric moisture. The first step is the partial hydrolysis of Si-H groups in the precursor PHMS [17], followed by the condensation of Si-H and Si-OH groups. In our case, PMHS was formulated as emulsion, and important volume expansion due to the evolution of hydrogen was instantaneously observed once the Pt catalyst was added. The tight cross-linking by Si-O-Si bridges (Scheme 1A) generated a rigid, rather frail foam, in which unreacted Si-H and Si-OH groups were still present, due to the high reaction rate leading to a high cross-linking density and thus rapidly reduced mobility. These reminiscent functional groups can be observed in the FT-IR spectrum (Figure S2), at 3440 cm\({}^{-1}\) (OH), 2174 cm\({}^{-1}\) (Si-H), shifted from 2170 cm\({}^{-1}\) in PMHS, and around 910 cm\({}^{-1}\) (Si(H)CH\({}_{3}\)). The wide polysiloxane (Si-O-Si) band is located at 1030-1140 cm\({}^{-1}\) in PMHS and DH100. Other bands at 1410 cm\({}^{-1}\) (asymmetric deformation vibration of the CH\({}_{3}\) group), 1261 cm\({}^{-1}\) (symmetric deformation vibration of the CH\({}_{3}\) group), 845, and 781 cm\({}^{-1}\) (methyl rocking vibration and Si-C stretching vibration) are characteristic of siloxane compounds [30]. The same reaction was used for preparing several porous silicones (Table 1), varying the amount of Si-H groups, either by using a poly(dimethyl-methylhydrogen)siloxane with 30% Si-H groups (DH30) or by combining PHMS with a copolymer with 10% (DH70) or 30% Si-H groups (DH44). In this way, polydimethylsiloxane (PDMS) chains were introduced, which are known as hydrophobic and ensure a more elastic framework, which is useful for certain applications. The presence of PDMS segments was seen in FT-IR by a narrower polysiloxane band, with peaks at 1024 and 1094 cm\({}^{-1}\), a stronger band at 2968 cm\({}^{-1}\) (CH\({}_{3}\) asymmetric stretching vibration), and shifted Si-C stretching vibration bands, the strongest one at 800 cm\({}^{-1}\) (Figure S2). In Table 2, the theoretical cross-linking degree (CLD) is the proportion of Si-H groups in the reaction mixture. However, since the dehydrocoupling reaction cannot be total, the CLD was calculated from the FT-IR spectrum, by the ratio between the absorption of Si-H and Si-CH\({}_{3}\) groups, reported to the same ratio of intensities in PMHS, which was practically 1. So, the calculated CLD in DH100 was 77%. Small Si-H signals were observed in the copolymers, too, and the CLD was calculated for DH30, takingas a reference the CoSiH30 precursor. For the remaining DH materials, the CLD cannot be calculated in the same manner, since in these cases the proportion of CH\({}_{3}\) groups is not constant. PHMS was chemically modified with hexene (DHH) or with allyltrimethylsilane (DHS), both hydrosilylation reactions occurring in the presence of Karstedt catalyst, simultaneously with the dehydrocoupling reaction. The long hexyl and the trimethylsilyl groups were intended to increase the hydrophobic character of the porous materials.