Abstract
Polystyrene (PS) microspheres were functionalized with poly(styrene-b-tert-butyl acrylate) (P(S-b-tBA)) by adsorption from supercritical mixture of CO2 and hexane. Supercritical deposition formed a shell-core structure that contained a shell of poly(tert-butyl acrylate) (PtBA) blocks and a core of the PS blocks entangling with the PS microspheres. The thickness of the PtBA layer and thereby the areal density of tert-butyl ester groups increased with the deposition pressure until plateau values attained at 20 MPa and higher. The tert-butyl ester groups were hydrolyzed to carboxyl groups for conjugation with tert-butylamine molecules via amide bonds that were further chlorinated into biocidal N-halamine moieties. The functionalization layer and its bonded N-halamine moieties were stable in flowing water and the chlorine could be regenerated upon eventual loss. This functionalization concept is applicable to polymers of any external and internal surfaces to achieve diverse surface properties by varying block copolymer and conjugated moieties.
Highlights
Most polymers, despite desirable bulk properties such as stability and mechanical strength, may have restricted applications due to the lack of satisfying surface properties including adhesion, wettability and antibacterial activity
P(S-b-tBA) was chosen to modify PS microspheres for several reasons: after deposition, the poly(tert-butyl acrylate) (PtBA) block is thermodynamically driven to air-polymer interface via preferential surface segregation because of its lower surface tension,while the PS block interpenetrates with the PS microspheres due to its higher surface tension and identical chemistry with substrate
P(S-b-tBA) acts as surfactant and orders at the modified surfaces; PtBA is expected to be slightly soluble in scCO2[24, 25] that makes P(S-b-tBA) soluble in scCO2 with a small amount of organic cosolvent; and it initially offers a tert-butyl ester groups covered hydrophobic surface to satisfy the need of a release surface, but can generate a hydrophilic one by photolytic or acid catalyzed hydrolysis of the tert-butyl ester groups to carboxyl groups[26]
Summary
Despite desirable bulk properties such as stability and mechanical strength, may have restricted applications due to the lack of satisfying surface properties including adhesion, wettability and antibacterial activity. The introduced functional groups can endorse desirable surface properties by either themselves or their bonded chemical moieties through subsequent surface reactions such as polymerization, grafting and conjugation[3−5]. High energy irradiations and chemical reactions generate functional groups on surfaces through oxidation reaction[6, 7]. These methods are brute forces in nature and do not provide precise control of variables such as the type of the functional groups produced or depth of the surface functionalization. The surfaces they produce can be thermodynamically unstable and subject to reorganization effects[1]. Chemical reactions are restricted due to the lack of available reactions, and lead to polymer decomposition and cause environmental pollution sometimes[8]
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