Stimulus-responsive, surface confined poly(N-isopropylacrylamide) (pNIPAAM) brush nanopatterns were prepared on gold-coated silicon substrates in a "grafting-from" approach that combines "nanoshaving", a scanning probe lithography method, with surface-initiated polymerization using atom transfer radical polymerization (ATRP). The reversible, stimulus-responsive conformational height change of these nanopatterned polymer brushes was demonstrated by inverse transition cycling in water, and water−methanol mixtures (1:1, v:v). Our findings are consistent with the behavior of laterally confined and covalently attached polymer chains, where chain mobility is restricted largely to the out-of-plane direction. Our nanofabrication approach is generic and can likely be extended to a wide range of vinyl monomers.

In this paper we report the surface-initiated polymerization of poly(N-isopropylacrylamide) (pNIPAAM), a stimulus-responsive polymer, from monolayers of ω-mercaptoundecyl bromoisobutyrate on gold-coated surfaces. pNIPAAM was polymerized in aqueous solution at a low methanol concentration at room temperature to maintain the growing pNIPAAM chains in a hydrophilic and an extended conformational state. Under these conditions thick polymer brush layers (up to 500 nm in the swollen state) are produced after 1 h of polymerization. We present a new and simple strategy to fabricate stimulus-responsive, surface-confined pNIPAAM brush nanopatterns prepared in a “grafting-from” approach that combines “nanoshaving”, a scanning probe lithography method, with surface-initiated polymerization. The reversible, stimulus-responsive conformational height change of bulk and nanopatterned polymer brushes was demonstrated by repeated cycling in water and water/methanol mixtures (1:1, v/v). Our findings are consistent with the behavior of laterally confined and covalently attached polymer chains, where chain mobility is restricted largely to the out-of-plane direction. The present work is significant because the triggered control of interfacial properties on the nanometer scale holds significant promise for actuation in bio-nanotechnology applications where polymeric actuators may manipulate the transport, separation, and detection of biomolecules.

A number of bridged cyclic phosphine oxides, both saturated and unsaturated, have been reduced with silicon-based reagents. Evidence was obtained that pentacoordinate intermediates can have special importance in such reductions, since the contracted angle in the cycle is more compatible with the 90' angle offered by apical-equatorial bonding in the trigonal bipyramid. Thus, while HSiC13 and C6H5SiH3 reduce noncyclic oxides with stereochemical retention, phosphines with either retained or inverted configuration can result from angle-contracted, cyclic oxides, and in the 7-phosphanorbornene system (but not in higher homologues) the P(II1) intermediate can undergo retrocycloaddition, causing loss of the phosphorus bridge. However, when the pyridine complex of HSiC1, is used, these complications are avoided, apparently because of a change in mechanism. The bridged phosphines have been characterized by "C NMR spectroscopy, which is especially useful in revealing stereochemical features and modifications in the hybridization at phosphorus. Angle contraction in the ring diverts s-character into the exocyclic bond, causing extremely large lJpc values. Syn,anti isomers then appear to have different hybridization as judged by variations in their lJPc values. 31P NMR chemical shifts occur far downfield in 7-phosphanorbornenes, apparently as a result of U--T hyperconjugation; the anti isomer experiences a second effect, tentatively attributed to repulsion of the lone pair by interaction with the r-electrons, which superimposes shielding on 31P and causes their shifts to be significantly upfield of the syn isomers. The downfield shifting is weaker in 8-phosphabicyclo[3.2.l]octenes and absent in the [4.2.1] homologue. Saturated strained phosphines have shifts in the range of acyclic compounds. In two diphosphines, P-P coupling is present and its magnitude shown to be controlled by the orientation of the lone pair on phosphorus.The placement of phosphorus in heterocyclic frameworks can cause some important modifications in the properties associated with the particular phosphorus functionality.2 This is especially true when the creation of the cyclic structure requires strong contraction of the bond angles around the phosphorus atom, as in bridged ring systems. In working with tertiary phosphines and phosphine oxides containing this structural feature, we have encountered unique features in their reaction chemistry and NMR spectral properties. In this paper attention is focused on the stereochemical aspects of the highly important deoxygenation of phosphine oxides by silicon hydride^,^ which is generally the principal method by which phosphines with bridged rings are approached. While not a systematic study, our research has gathered enough information to show that serious departures from the mechanistic and stereochemical pathways established for simpler compounds can occur when phenylsilane and trichlorosilane are used as the reducing agents. Two configurations are usually possible for phosphines in bridged structures, and it ...

Nanopatterned polymer structures are fabricated on SiO2 by combining AFM anodization nanolithography (see upper figure) with surface‐initiated ring‐opening metathesis polymerization (ROMP, lower figure). This process offers a powerful set of tools for the fabrication of highly functional polymer brushes. The simplicity and speed of anodization lithography promises its massively parallel implementation using anodization stamps. The fabrication approach is universal and can easily be adapted to other surface initiated polymerizations.