Photopolymerization HEMA

Entrapment of GOx in photopolymerized HEMA although limited at present by the pattern resolution, is another approach to the spatially control deposition of enzymatic layers. When performed at the on wafer level it allows strongly adhering membranes, displaying large glucose responses with linear ranges up to 12 mM to be obtained. 

A variety of photo-initiators and water-soluble diluents were used to study the photopolymerization of 2-hydroxyethyl methacrylate (HEMA). The rate of polymerization can be correlated to the structures as well as the concentration of initiators and diluents. It was found that, in terms of rate of polymerization,... 

Figure 1. A typical exothermic profile of photopolymerization of HEMA.

Table 2 summarizes the peak times for the photopolymerization of HEMA. Among initiators with structures known, the ranking of more active initiators, in terms of decreasing polymerization rate was ... 

In this work, the kinetics of these reactions are closely examined by monitoring photopolymerizations initiated by a two-component system consisting of a conventional photoinitiator, such as 2,2-dimethoxy-2-phenyl acetophenone (DMPA) and TED. By examining the polymerization kinetics in detail, further understanding of the complex initiation and termination reactions can be achieved. The monomers discussed in this manuscript are 2-hydroxyethyl methacrylate (HEMA), which forms a linear polymer upon polymerization, and diethylene glycol dimethacrylate (DEGDMA), which forms a crosslinked network upon polymerization. 

Di-block copolymers may also be formed by using dithiocarbamate free radicals. Indeed, copoljoners containing poly(styrene) and poly(hydroxyethyl methacrylate) blocks have been obtained by a two-step procedure [145]. Firstly, styrene is photopolymerized in the presence of benzyl A,A-diethyldithiocarbamate (BDC) by a living radical mechanism [146]. In fact, as the benzyl and thiyl radicals, formed by the photoliagmentation of BDC, participate mainly in the initiation and termination reactions respectively, polystyrene with a dithiocarbamate end group is thus obtained. The successive UV irradiation of this polymer, in the presence of hydroxyethyl methacrylate (HEMA), gives rise to the di-block copolymer, according to Scheme 42. 

Figure 3 (a) Typical plot showing the conversion during photopolymerization. In this plot, t shows induction time, / p is the rate of polymerization, and RC refers to unreacted components, (b) Typical FTIR spectra for HEMA monomer showing the spectrum before and after UV exposure. A and B refer to the area under each curve with subletters a and b indicating after and before UV, respectively. 

Figures Illustration of common shear rheology measurements for photopolymerization reactions, (a) Evolution of dynamic viscosity with exposure time for HEMA, HEMA MMA, and MMA monomers photo-polymerized with Darocur 1173. The gel point is defined as the time at which viscosity goes to infinity, (b) Typical profile for modulus change in photopolymerizable gels. G and G" denoting shear (storage) and loss (viscous) moduli. Gel point is defined as when G -G".

PA-1 was shown to be able to interact with HAP. The photopolymerization behavior of PA-1 was also investigated. Unfortunately, it was shown that PA-1 was not able to homopolymerize. Moreover, the addition of 10 wt% of PA-1 to Bis-GMA resulted in a drop of both the conversion and the rate of polymerization. The same drawback was observed when PA-2 was copolymerized with HEMA, in the presence of water. 

Under the assumption of bimolecular termination, the reaction diffusion parameter R (equation (4.2)) was determined for the bulk photopolymerization of multifunctional (meth)acrylates [I, 3, 6, 17, 481. It was found that for methacrylates at the plateau level, R was in the order of 2 1 moP [6] and for acrylates R was 3-5 1 moP [I7J. In general, reduction of network cross-linking density by co-polymerization with a difunctional reactive diluent (2-hydroxyethyl methacrylate (HEMA), octyl methacrylate) [3] increased the values of R due to increased mobility of the polymerization system until a plateau is reached. The addition of an inert diluent (polyethylene glycol 400 (PEG 400) [3, 6] or hydrogenated monomers [25. 53]) to a flexible monomer of low viscosity did not change R,... 

These semi-IPNs were synthesized [169] by the sequential method the PU network was synthesized (Sect. 2.3) and then swollen with 2-hydroxyethyl methacrylate (HEMA) monomer followed by its photopolymerization. The PHEMA content in these semi-IPNs varied from 10 to 57 wt%. 

S. Eu, K.S. Anseth, Photopolymerization of multilaminated poly(HEMA) hydrogels for controlled release. Journal of Controlled Release, 57, 291-300, 1999. 

Guo, X., Wang, Y, Spencer, R, Ye, Q., Yao, X. Effects of water content and initiator composition on photopolymerization of a model BisGMA/HEMA resin. Dent. Mater. 24, 824-831 (2008)... 

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