Poly(dimethylsiloxane)‐poly(ethylene oxide)‐heparin block copolymers III: Surface and bulk compositional differences

Abstract

Previously observed bioactivity of poly(dimethylsiloxane)-poly(ethylene oxide)-heparin (PDMS-PEO-Hep) triblock copolymers has prompted studies of the surface and bulk character of this copolymer using angular-dependent electron spectroscopy for chemical analysis (ADESCA), static secondary mass spectroscopy (SIMS), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). Because the low-energy PDMS phase dominates surfaces of this copolymer when solvent cast under air or vacuum conditions, attempts were made to explain surface restructuring and rearrangements induced in hydrated or aqueous environments that permit surface accessibility and bioactivity of heparin moieties. Based on comparisons with PDMS, PEO, and heparin homopolymers, PEO/heparin blends, and an unheparinized PDMS-PEO diblock copolymer, PDMS-PEO-heparin demonstrates both phase-mixed and phase-separated regions in DSC analysis. During annealing cycles above the Tg values of the copolymer constituents, phase-mixed regions become increasingly phase separated and PEO enriched. TGA analysis confirmed the presence block copolymer constituents and presented evidence of intermolecular segmental interactions, hence phase-mixing in the copolymers. ADESCA analysis indicates that the outer 5 A of both the PDMS-PEO and PDMS-PEO-Hep copolymers is essentially pure PDMS. However, significant amounts of PEO are detected 5 to 20 A below the surface. Static SIMS also detects the presence of PDMS at the surfaces of the PDMS-PEO and PDMS-PEO-Hep copolymers. Compositional models based on ADESCA, SIMS, and DSC data are presented for desiccated and hydrated copolymer surfaces.

Highly Permeable Oligo(ethylene oxide)‐co‐poly(dimethylsiloxane) Membranes for Carbon Dioxide Separation

“…It is observed that over 95% of NB‐oligo(EO) is decomposed at 450 °C, while it is only ≈5% for PDMS moiety. Based on previous studies, PDMS is typically stable until around 430 °C, while PEO is likely to be completely decomposed at this temperature . Thus, in this study, the oligo(EO) compositions are estimated from the weight percentage at the 450 °C (see the vertical dashed line in Figure ), which corresponds to the onset of PDMS decomposition.…”

On the Composition of the Top Layer of Microphase Separated Thin PS-PEO Films

“…This confirms previous studies that found that the surface of a PS-PEO film is hydrophobic when exposed to air, but upon exposure to water, the surface of turns rapidly hydrophilic. 27,57 This behavior indicates that the PS block is present at the air/film interface, but upon exposure to water the chains of PS block move away from the water/film interface and are replaced by the more hydrophilic chains of the PEO block.…”

“…This question is important from a fundamental scientific point of view, but it is also significant for applications, because copolymers containing PEO are often being used as biocompatible coatings, and the ability of its films to repel proteins depends crucially on the composition of the top surface. 27,28 Few publications have investigated specifically this aspect. 12,[29][30][31] It is well-known that a PEO layer is in contact with the supporting silicon substrate, given its higher polarity respect to PS.…”

Heparin-containing block copolymers

“…With this technique it is possible to resolve structural components, such as different domains in polymeric materials [10]. The application of XPS can provide detailed information about the topography and composition in the top layer of a few nm of the surface [8,[11][12][13][14].…”