Initiators / modifiers Photoinitiators

Benzophenone (BP) is a photoinitiator that can be employed in a number of ways for the preparation of patterned graft polymers. BP can be directly used as an initiator for radical polymerization, either via immobilization of BP on the surface or by adding BP to the monomer solution (Figures 3.9A and 3.9B). Another possibility is to synthesize initiators modified with BP, which can then be immobilized on surfaces using UV light (Figure 3.9C). Yet another alternative is to add BP to the initiator solution for BP-mediated attachment of the initiator to the surface (Figure 3.9D). 

Liska reported preparation of water-soluble photoinitiators that contain carbohydrate residues as well as copolymerizable derivatives of the carbohydrate residues. These materials consist of alkylphenones, benzophenones and thioxanthones. To these compounds were attached carbohydrates like glucose, cellobiose, and 1-amino-1-deoxy-D-glucitol. In addition selected initiators were reacted with methacryloyl chloride to form polymerizable photoinitiators. The glucose modified photoinitiators were claimed to yield the best results with respect to compatibility with resins, reactivity and gel content. ... 

The most important practical application of the organometallic complex photoinitiators is the possibility of using these types of initiators in modifying the pre-existing polymer chain, e.g., block, graft, and crosslinked copolymers preparation. 

Surface-initiated polymerization (SIP) has been carried out with a variety of initiators and Fig. 2 describes some of the most common photoinitiators [9-14]. For SIP applications, these initiators are typically modified and... 

Recently, Dyer used the same strategy to perform a photoinitiated synthesis of a mixed brush by using an AIBN-type initiator boimd to gold [57]. Specifically, they used initiator (24) to modify gold substrates with a binary brush composed of PS and PMMA. As Fig. 11 describes, mixed brushes will respond to the polarity of the solvent. For example, immersion into a non-selective solvent like THF brings both components to the air/hquid interface since PS and PMMA are both soluble in THF. However, immersion into a polar solvent, such as isobutanol, will selectively bring PMMA to the air/hquid interface, while the nonpolar PS collapses into the interior of the film. In contrast, immersion into cyclohexane brings PS to the air/hquid interface and PMMA is driven to the interior. The cycle is completely reversible after immersion into a nonselective solvent like THF. 

Photopolymerization, that is, a polymerization process initiated by photochemical production of the reactive species initiators (Section 6.8.1), is largely used in industry. Polymers can be synthesized by photoinitiation, but can also be modified by photochemical cross-linking (photochemical hardening or UV curing photoimaging photolithography see Special Topic 6.27). 

Hilal et al. [25] studied the surface structure of molecularly imprinted poly(ether sulfone) membranes (called MIP membranes) by AFM and quantified the pore size and the surface roughness. They modified PES microfiltration membranes with a normal pore diameter of 0.22 j,m and a thickness of 150 (Am (Millipore). First, the membranes were coated with photoinitiator by soaking them in a 0.25 M solution of benzoin ethyl ether (BEE) in methanol and then immersing them in a mixture of 80 mM trimethyl propane trimethacrylate (TRIM), 40 mM 2-hydroxyethyl methacrylate (HEMA), and 2 mM adenosine 3 ,5 -cyclic monophosphate (cAMP) in an ethanol-water mixture (70 30 vol.%). Thereafter, the membranes were exposed to a B-100 lamp of relative radiation intensity 21.7 mW cm at 355 nm. Membranes with different modifications were obtained using various UV exposure times. The residual nongrafted polymer, monomer, initiator, and the template were extracted with methanol. After drying, the degree of modification (DM) was calculated from the... 

This modifieation does extend the sensitivity to longer wave length ultraviolet light. The eompounds were reported to display exeellent thermal lateney in the presence of various monomer systems and high effieieney as photoinitiators for cationic polymerization. Furthermore, their initiation efficiency was reported to be on par with current commercial triaryl sulfonium salts. 

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