A catalyst- and additive-free synthesis of alkoxyhydrosiloxanes from silanols and alkoxyhydrosilanes.

A convenient method for the selective synthesis of alkoxyhydrosiloxanes that bear SiH and SiOR2 groups on the same silicon atom, R13Si-O-SiR32-n(OR2)nH (n = 0, 1, or 2), via a simple catalyst- and additive-free dealcoholization reaction between silanols and alkoxyhydrosilanes has been developed. These alkoxyhydrosiloxanes can be easily converted into Si(OR2)3-containing siloxanes by zinc catalyzed alkoxylation and alkoxy-containing silphenylene polymers by platinum catalyzed hydrosilylation.

Organocatalytic controlled/living ring-opening polymerization of cyclotrisiloxanes initiated by water with strong organic base catalysts.

Organocatalytic controlled/living ring-opening polymerization of cyclotrisiloxanes, such as hexamethylcyclotrisiloxane, 1,3,5-trimethyl-1,3,5-triphenylcyclotrisiloxane, 1,3,5-trimethyl-1,3,5-trivinylcyclotrisiloxane, and 1,3,5-trimethyl-1,3,5-tris(3,3,3-trifluoropropyl)cyclotrisiloxane, using water as an initiator and strong organic bases, such as amidines, guanidines, phosphazene bases, and proazaphosphatrane, as catalysts produced a variety of polysiloxanes with controlled number-average molecular weights (M n = 2.64-102.3 kg mol-1), narrow polydispersity (D = 1.03-1.16), and well-defined symmetric structures. Controlled syntheses of statistical copolymers and triblock copolymers were achieved by copolymerizations of two cyclotrisiloxanes. Various terminal functionalities were successfully introduced by the end-capping reaction of propagating polysiloxanes using functional chlorosilanes. Kinetic investigations demonstrated that the polymerization proceeded through the initiator/chain-end activation mechanism, namely activations of water in the initiation reaction and of terminal silanols in propagating polysiloxanes in the propagation reaction. Catalytic activities of strong organic bases were revealed to depend on their Brønsted basicity and efficiency of the proton transfer in the initiation and propagation reactions. Guanidines possessing an R-N[double bond, length as m-dash]C(N)-NH-R' unit, in particular 1,3-trimethylene-2-propylguanidine, showed excellent performance as a catalyst. In this system, even non-dehydrated solvents are usable for the polymerization.

A photolithographic approach to spatially resolved cross-linked nanolayers.

The preparation of cross-linked nanosheets with 1-2 nm thickness and predefined shape was achieved by lithographic immobilization of trimethacryloyl thioalkanoates onto the surface of Si wafers, which were functionalized with 2-(phenacylthio)acetamido groups via a photoinduced reaction. Subsequent cross-linking via free radical polymerization as well as a phototriggered Diels-Alder reaction under mild conditions on the surface led to the desired nanosheets. Electrospray ionization mass spectrometry (ESI-MS), X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), as well as infrared reflection-absorption spectroscopy (IRRAS) confirmed the success of individual surface-modification and cross-linking reactions. The thickness and lateral size of the cross-linked structures were determined by atomic force microscopy (AFM) for samples prepared on Si wafers functionalized with a self-assembled monolayer of 1H,1H,2H,2H-perfluorodecyl groups bearing circular pores obtained via a polymer blend lithographic approach, which led to the cross-linking reactions occurring in circular nanoareas (diameter of 50-640 nm) yielding an average thickness of 1.2 nm (radical cross-linking), 1.8 nm (radical cross-linking in the presence of 2,2,2-trifluoroethyl methacrylate as a comonomer), and 1.1 nm (photochemical cross-linking) of the nanosheets.

B(C6F5)3-Catalyzed Group Transfer Polymerization of n-Butyl Acrylate with Hydrosilane through In Situ Formation of Initiator by 1,4-Hydrosilylation of n-Butyl Acrylate.

The group transfer polymerization (GTP) of n-butyl acrylate (nBA) using hydrosilane (R3SiH) and tris(pentafluorophenyl)borane (B(C6F5)3) has been studied, which did not need to use the initiator of a silyl ketene acetal (SKA) as the starting polymerization component. B(C6F5)3 catalyzed the in situ 1,4-hydrosilylation of nBA by R3SiH to generate the corresponding SKA prior to the polymerization of nBA, which was confirmed by the 1H NMR measurement of the model reaction. The formed SKA performed as the initiator for the B(C6F5)3-catalyzed GTP of nBA leading to well-defined polymers with targeted molar masses and low dispersities.

Thermoresponsive vesicular morphologies obtained by self-assemblies of hybrid oligosaccharide-block-poly(N-isopropylacrylamide) copolymer systems.

This work discusses the self-assembly properties of thermoresponsive hybrid oligosaccharide-block-poly(N-isopropylacrylamide) copolymer systems: maltoheptaose-block-poly(N-isopropylacrylamide) (Mal(7)-b-PNIPAM(n)) copolymers. Those systems at different molar masses and volume fractions were synthesized using Cu(I)-catalyzed 1,3-dipolar azide/alkyne cycloaddition, so-called "click" chemistry, between an alkynyl-functionalized maltoheptaose (1) and poly(N-isopropylacrylamide) having a terminal azido group (N(3)-PNIPAM(n)) prepared by atom transfer radical polymerization (ATRP). While the cloud point (T(cp)) of the N(3)-PNIPAM(n) ranged from 36.4 to 51.5 degrees C depending on the degree of polymerization, those obtained of the diblock copolymers ranged from 39.4 to 73.9 degrees C. The self-assembly of such systems is favored due to the hydrophobicity of the PNIPAM in water above the T(cp). While the N(3)-PNIPAM(n) present polydisperse globular shape with a mean diameter of 500 nm, well-defined vesicular morphologies with an approximate diameter of 300 nm are obtained in diblock copolymer systems. These results were obtained and confirmed using static and dynamic light scattering as well as imaging techniques such as transmission electron microscope experiments.