Modification of ATRP Surface-Initiated Poly(hydroxyethyl methacrylate) Films with Hydrocarbon Side Chains

Abstract

Poly(2-hydroxyethyl methacrylate) (PHEMA) films were grown onto gold via water-accelerated, surfaceinitiated atom transfer radical polymerization (ATRP), and the resulting side chains were modified by reaction with alkanoyl chlorides (C m H 2m+1 COCl; m ) 1, 7, 11, 13, 15, and 17) to incorporate hydrocarbon side groups within the film. We have previously demonstrated the ability to react ∼70-80% of PHEMA hydroxyl side chains with fluorocarbon acid chlorides to prepare partially fluorinated films. Here we convert the side chains to hydrocarbon esters with diminishing conversion (80 to 40%) as m is increased and compare the resulting films with fluorocarbon-modified PHEMA. Based on IR spectra and wetting data, hydrocarbon side chains structure the film to a greater extent as m is increased. A critical chain length (m ) 15) was required to orient chains normal to the interface at the outer film surface and impart the wetting properties of a dense methyl surface. The resistances of the films against the transport of redox probes were greatly enhanced with increasing conversion of hydroxyl groups within the film and were modestly affected by film structuring to create a densely packed methyl surface. For example, capping the hydroxyl groups of PHEMA by reaction with acetyl chloride resulted in an unstructured film with >90% conversion that increased film resistance by almost four orders of magnitude over the base PHEMA film without a significant volumetric enhancement of the side chains. Also, the decreasing conversion as m is increased from 7 to 17 resulted in a decreasing film resistance even though the longer chains structured the film and surface to a greater extent. These results illustrate the important effect on barrier properties of unreacted hydroxyl groups, which possibly associate to create water and ion-diffusing pathways within the film. The barrier properties of these hydrocarbon-modified PHEMA films are comparable to those of fluorocarbon-modified PHEMA when both conversion and the molecular weight of the modifying group are similar.

Physicochemical Properties of Surface‐Initiated Polymer Films in the Modification and Processing of Materials

“…[64] Low-energy surfaces are commonly generated by preparing thin films in which relatively non-polar groups such as ±CF 3 or ±CH 3 dominate the surface composition. We have recently used surface-initiated ATRP to grow poly(hydroxyethyl methacrylate) (PHEMA) films on gold that were subsequently modified by acylation with acid chlorides (RCOCl) of hydrocarbon (R = C p H 2p+1 ) [71] or fluorocarbon (R = C m F 2m+1 ; R = C 6 F 5 ) [69,70] composition to produce ester-linked side groups (Scheme 1). The wettability of these films, also shown in Scheme 1 via advancing contact angles of water and hexadecane, depended on the composition and chain length of the side group.…”

“…The low critical surface tension and high hexadecane contact angle for this film are consistent with a normal orientation of the fluorocarbon chains at the outer surface, such that the terminal CF 3 group dominates surface properties. [69] With hydrocarbon modification of PHEMA, [71] the advancing hexadecane contact angle increases with chain length and approaches the value for a densely packed methyl-terminated SAM (~50). [76] The critical surface tension of these fluorocarbon-and hydrocarbon-modified films can be tuned from 9±27 mN m ±1 , depending on the selection of R. These results demonstrate the importance of molecular engineering of polymer films to tailor surface composition, and show that surface-initiated polymer films can present densely packed surfaces that approach the wettability behavior of monolayer films.…”

Formation of surface-grafted polymeric amphiphilic coatings comprising ethylene glycol and fluorinated groups and their response to protein adsorption

“…[21][22][23][24][25] Three different acylchlorides were employed ͑all obtained from Sigma-Aldrich͒: heptafluorobutyryl chloride ͑C 3 F 7 COCl, F3͒, pentadecafluoro-octanoyl chloride ͑C 7 F 15 COCl, F7͒, and pentafluorobenzoyl chloride ͑C 6 F 5 COCl, PFA͒. Substrates with PHEMA brushes were exposed to 80 mM solutions of a given acylchloride with 100 mM pyridine in dichloromethane for 24 h at room temperature to modify PHEMA films with fluorinated side chains ͑see Fig.…”

Poly(glycidyl methacrylates)-Grafted Zinc Oxide Nanowire by Surface-Initiated Atom Transfer Radical Polymerization

“…One of the most successful processes is ATRP [16][17][18], which offers efficient, well-controlled grafting and narrow molecular weight distributions of the polymers grown from the surfaces. The radical reactions involved in the ATRP process enable a wide range of monomers to be used, leading to polymer-modified surfaces with new functionality [16].…”

“…The radical reactions involved in the ATRP process enable a wide range of monomers to be used, leading to polymer-modified surfaces with new functionality [16]. This, together with the halogen end-groups, can significantly enhance the physicochemical compatibility of the resulting composites, making the design and preparation of novel materials with DOI:10.3786/nml.v2i4.p285-289…”