*2.3. Membranes*

The utilization of polydimethylsiloxanes and silicon-rich homopolymers such as poly(trimethylsilylpropyne) [136] and poly(vinyltrimethylsilane) [137] for gas separation membranes has been established. The removal of volatile organic compounds from aqueous mixtures has been more effectively addressed by hybrid polymer systems in which there is formation of siloxane microphases in continuous organic phases. Reports on graft polymer and interpenetrating polymer networks were able to demonstrate selective pervaporation and removal of organics from aqueous streams [138,139]. The control of selectivity and permeation rates has been accomplished with copolymers derived from methacrylate functional macromers copolymerized with a variety of other methacrylate monomers. Uragami demonstrated that macromers with molecular weights of ~4000 Daltons formed copolymers with methyl methacrylate which, depending on comonomer content, allowed selective permeation of water or ethanol from ethanol–water solutions by varying comonomer contents [140]. In a series of reports, Urgami extended these systems to styrene copolymers and the incorporation of ionic liquids, enabling the selective pervaporation of volatile organics, including toluene and chlorinated organics, from aqueous streams [141–143].

#### *2.4. Surface Properties/Modification*

2.4.1. Dyes, Micelles and Particles for Advanced Printing, Reprographics, and Lithography

Methacrylate functional macromers have been used in both organic dye [89] and pigment-based printing applications [98,99,144]. While these technologies are quite different, the role of the silicone macromer has common features in each. In ink-jet applications, a bulk solvent-based polymerization with dye is accomplished, after which micelles are formed via the addition of water and simultaneous evaporation of solvent. In pigmentbased applications, the polymer forms an encapsulant or binder. In both cases, the silicone macromer appears to serve as a hydrophobic outer surface of the micelle or pigment, thereby helping to control particle charging and, secondarily, contributing to the spread and adhesion of the micelles or particles on the substrate. Polymersomes with controlled architecture in both their overall dimensions and membrane thickness have been prepared from diblock polymers of cabinol-termined siloxane macromers and methyloxazolidine [82].

Interestingly, while the ability of styrene-PDMS deblock polymers generated via living AROP to form micelles was recognized during early development efforts [145], no recent commercial applications have been reported.

Colored fluids for electrowetting and electrofluidic applications have also been generated from highly polar dyes by reaction with aminopropyl-terminated siloxane macromers [80]. For example, the yellow dye 2-(4-carboxyphenylazo)acetoacetanalide reacted with a 1000 Mn amino-terminated macromer to form the product 4-(E)-(2,4-dioxopentan-3-yl)diazenyl-N-polydimethylsiloxane-benzamide, which was soluble in non-polar fluids including silicones. Radiation-curable films for adhesive and lithographic applications, in which aminopropyl-terminated siloxane macromers are acrylated, were reported by Leir [146]. Carbinol-terminated siloxane macromers were converted to phosphate-terminated macromers by Tao and then reacted with the surfaces of CdSe quantum dots before incorporation into bulk silicones to form electroluminescent transparent films, as shown in Figure 6 [85].

**Figure 6.** Electroluminescent transparent quantum dot composites (Tao) [85]. Left: depiction of macromers (blue) modifying a CdSe QD (red) in a silicone matrix; Right: specimen of composite. (Reprinted with permission from Ref. [85] Copyright 2013 the Royal Society of Chemistry).

#### 2.4.2. Coatings Additives—Leveling Agents, Clean Surfaces and Release

Siloxane macromer block polymers are offered commercially as leveling agents to reduce waviness and orange peel in organic coatings. The effect occurs at low concentrations and is based on activity at the liquid–gas interface, in which these polymers are oriented due to limited incompatibility with the actual binder component of the coating system [147,148]. Their versatile chemistry and modular molecular structure make it possible to adjust the properties of these macromers for specific applications. For example, further improvements in levelling have been reported when a fluorinated oxetane is reacted with unsaturated termination in macromers [149].

High silicone content macromers can impart anti-graffiti properties to coated surfaces, though this often requires concentrations higher than those used in levelling applications. Macromers with a lower silicone content can reduce surface tension and improve substrate wetting without impairing recoatability. In the case of automotive coatings, other benefits include retaining the bonding characteristics of films and adhesives, while anti-blocking properties can also be achieved in decorative coatings [150,151].

One of the earliest applications of styryl and methacrylate functional macromers was for controlling release in adhesive tapes [54]. The investigators showed a correlation between molecular weight and release characteristics—e.g., in butyl methacrylate, acrylic acid, and macromer terpolymers—with macromers of low molecular weight proving ineffective but macromers with molecular weights ≥2000 providing control. The same general chemistry has been utilized more recently in dirt resistant coatings [93]. Release coatings, including ice-phobic coatings, have been generated from carbinol-terminated siloxane macromers by reaction with isocyanate and epoxy functional prepolymers to form amphiphilic, self-stratified thin films [152]. A reduction of marine biofouling was observed when aminopropyl-terminated macromers were incorporated into isophorone diiosocyanate-derived urethanes, with low molecular weight macromers (1000 Daltons) providing more favorable results than high molecular weight macromers [81]. Methacrylateterminated siloxane macromers with embedded hydrophilicity have also been used in this application [108]. Ultraphobic coatings—i.e., coatings exhibiting both superhydrophobic

and oleophobic behavior—in which combinations of epoxy functional siloxane telechelics and macromers are reacted with linear and/or branched polyethylenimine (PEI), have been reported by Soane and Ready [94,107]. Hydride-terminated macromers have been used to modify vinyl POSS structures in slippage coatings for ice-phobic applications [91]
