Jan Kurjata

Synthesis of a paraffin phase change material microencapsulated in a siloxane polymer

The coemulsification method suitable for the formulation of microcapsules of n-eicosane coated with a polysiloxane is developed. This method allows to synthesize core–shell microcapsules of paraffin which have the shape of spheres or distorted spheres and are designed for the use as phase change materials. The microcapsules are formed in aqueous phase by the precipitation of n-eicosane together with modified polyhydromethylsiloxane from a common solvent which is miscible with aqueous media. The polysiloxane is modified by the attachment of silylvinyl and alkoxy functions before coemulsification with the paraffin. It also contains the Pt(0) Karstedt catalyst. The microcapsules formed by coemulsification are stabilized by the in situ cross-linking of the polysiloxane shell. The shell is additionally modified by the in situ generation of silanol groups which provide colloidal stabilization of microspheres in aqueous phase. Microcapsules were studied by DSC, SEM, optical polarized microscope, and by thermooptical analysis (TOA).

Organic polysilanes interrupted by heteroatoms

Abstract This review article covers the synthesis and properties of organic polysilanes having SiSi sequences interrupted by heteroatoms. Thus, as a rule, silicon based polymers which have ∼SiSiX∼ fragments in the skeleton are regarded, where X are atoms of Groups VIA, VA, IVA (excluding carbon), IIIA, as well as atoms of metals. X may be also a characteristic group of atoms, such as silole or metallocene. Particular attention is paid to polysilanes interrupted by oxygen in a regular way, as these polymers can be considered as silicon analogues of polyethers. Since their structure is a hybrid of those of polysilane and polysiloxane, the knowledge of the behavior of these polymers permits a deeper understanding of the chemistry of polysiloxanes and polysilanes. This is the reason why oxygen interrupted polysilanes have been studied more extensively than the polysilanes interrupted by other heteroatoms. Methods of the synthesis of these polymers, including mechanism and equilibria of the ring-opening polymerization of (SiMe 2 O) 2 , are discussed. Some attention is also devoted to thermal properties and morphology. The article is concluded by a section in which prospective practical uses of polysilanes interrupted by heteroatoms are discussed.

Thermal decomposition of poly(tetramethyloxydisilaethylene)

Thermal decomposition of poly[oxybis(dimethylsilylene)] having chains terminated with trimethylsiloxy groups was studied by thermogravimetry, pyrolysis-mass spectrometry, and infrared spectroscopy. The polymer is thermally less stable than poly(dimethylsiloxane). Depolymerization occurs at temperatures of 250–350°C, although this process also takes place at lower temperatures. The depolymerization produces cyclic oligomers of general formula [(Me2Si)2O]n, with predominant formation of the oligomern=2. The depolymerization is accompanied by processes which are referred to as restructurization because they change the structure of the polymer backbone. Decomposition may lead also to the formation of branching points. The shape of the thermograms taken under isothermal conditions is in agreement with an unzipping mechanism for depolymerization involving random initiation. Excluding the short initial period of the process, the unzipping is terminated at a restructurization point. A low activation energy points to initiation induced by electron transfer, presumably involving traces of contaminant. At higher temperatures, 350–600°C, loss of organic parts of the polymer takes place along with further restructurization. At higher temperatures the polymer was also found to undergo easily oxygenation of its backbone with atmospheric oxygen, which leads to the formation of siloxane groups.

Synthesis of the first POSS cage–anthracycline conjugates via amide bonds

Silsesquioxane derivatives widely used as polymer modifiers and catalytic supports have many interesting features making them potential nanocarriers in biomedicine. Two alternative synthetic routes were described, leading to the conjugates of functional POSS structures: octa(3-chloroammoniumpropyl)silsesquioxane and octa(carboxydecylthioethyl)silsesquioxane with anticancer drugs – anthracyclines.

Tertiary trisilyloxonium ion in cationic ring-opening polymerisation of a model cyclic siloxane, octamethyl-1,4-dioxatetrasilacyclohexane

Abstract The formation of the cyclic trisilyloxonium ion is observed by the 29 Si-NMR spectroscopy as a result of hydride transfer reaction between triethylsilane and Ph 3 C + B(C 6 F 5 ) 4 − in the presence of octamethyl-1,4-dioxatetrasilacyclohexane, 2 D 2 . This ion is transformed by the reaction with another 2 D 2 molecule into the cyclic trisilyloxonium ion at the polymer chain end. The mechanism of polymerisation of 2 D 2 is discussed in relation with the mechanism of polymerisation of cyclic siloxanes.

Star-Shaped and Linear POSS-Polylactide Hybrid Copolymers

Novel octakis-2[(6-hydroxyhexyl)thio]ethyl-octasilsesquioxane (POSS-S-OH) as well as heptaisobutyl-2[(6-hydroxyhexyl)thio]ethyl-octasilsesquioxane (iBu-POSS-S-OH) were synthesized. POSS structures, bearing both types of groups i.e., 2[(6-hydroxyhexyl)thio]ethyl and the vinyl ones, pendant from the octahedral cage are also described. The synthetic pathway involved thiol-ene click reaction of 6-mercapto-1-hexanol (MCH) to octavinyloctasilsesquioxane (POSS-Vi), and heptaisobutylvinyloctasilsesquioxane (iBu-POSS-Vi), in the presence of 2,2′-azobisisobutyronitrile. The functionalized silsesquioxane cages of regular octahedral structure were used further as initiators for ring opening polymerization of l,l-dilactide, catalyzed by tin (II) 2-ethylhexanoate. The polymerization afforded biodegradable hybrid star shape and linear systems with an octasilsesquioxane cage as a core, bearing polylactide arm(s).

Organosilicon Fragrance Carriers

Five different organosilicon carriers, with various molecular architectures - [(poly-(dimethylsiloxane-co- methylsiloxane) (containing 61 % of [–SiMeHO-] monomeric units) (P), silicone resin (Q), tetramethyldisiloxane (M) tetramethylcyclotetrasiloxane (D) and tris (dimethylsilyl)methane [HC(SiMe2H)3, (T)] were covalently bonded with model fragrant systems, including 1- and 2-phenylethyl alcohol, acetophenone, 2-phenylpropionic aldehyde, geraniol, 2-phenyl-1-propyl alcohol, 2-octanone and octyl aldehyde in order to obtain novel controlled fragrance release systems. Hydrolytic release of the fragrances was studied under base (NaOH) and acid (HCl) catalysis. It has been shown that polymer carriers allow for a controlled slow release of the relevant fragrant ingredients from the conjugates, whereas the low molecular weight systems (M, D and T) more easily cleave off fragrant moieties.

Synthetic routes to nanomaterials containing anthracyclines: noncovalent systems

Chemotherapy still constitutes a basic treatment for various types of cancer. Anthracyclines are effective antineoplastic drugs that are widely used in clinical practice. Unfortunately, they are characterized by high systemic toxicity and lack of tumour selectivity. A promising way to enhance treatment effectiveness and reduce toxicity is the synthesis of systems containing anthracyclines either in the form of complexes for the encapsulation of active drugs or their covalent conjugates with inert carriers. In this respect nanotechnology offers an extensive spectrum of possible solutions. In this review, we discuss recent advances in the development of anthracycline prodrugs based on nanocarriers such as copolymers, lipids, DNA, and inorganic systems. The review focuses on the chemical architecture of the noncovalent nanocarrier-drug systems.

Liquid Crystal Mono- and Nano-Layers Covalently Bonded to Silicon and Silica Surface for Alignment of LC Layers

We synthesized two types of liquid crystalline nano-layers covalently bonded to Si and Si/SiO2 wafers. Monolayers of terminal and lateral low molecular weight mesogens exhibit spontaneous homeotropic orientation, while planar orientation is obtained by means of rubbing process. On the other hand a novel polymer liquid crystal nano-layer, obtained via atom transfer radical polymerization (ATRP) of acrylate monomer from Si/SiO2 surface, exhibits planar orientation of liquid crystalline side chain moieties. Structure of such novel composites was confirmed by optical studies as well as spectroscopic methods, including ellipsometry. The goal was to obtain low molecular weight liquid crystals alignment just from the mentioned above, modified surfaces.