Condensation photopolymerization

Condensed monolayer films of pure 6 polymerized rapidly, as did mixed 6/DSPE films of up to 75% DSPE, provided the monolayers were in the condensed state [33], In the liquid-expanded state, polymerization did not occur. In the condensed state, lateral diffusion of individual lipids within the monolayer is severely restricted compared to the liquid-like state. This precludes initiation of polymerization by diffusive encounter between excited-state and ground-state diacetylene lipids. In order for polymerization to occur in the condensed state, the film must be separated into domains consisting of either pure 6 or pure DSPE. A demonstration that the rates of photopolymerization for pure 6 and mixed 6/DSPE monolayers are equal would be a more stringent test for separate domains of the lipids, but no kinetic data have been reported for this system. 

Since cholesterol is an important component of many biological membranes mixtures of polymerizable lipids with this sterol are of great interest. In mixed monolayers of natural lipids with cholesterol a pronounced condensation effect , i.e. a reduction of the mean area per molecule of phospholipid is observed68. This influence of cholesterol on diacetylenic lecithin (18, n = 12), however, is not very significant (Fig. 32). Photopolymerization indicates phase separation in this system. Apparently due to the large hydrophobic interactions between the long hydrocarbon chains of... 

This paper presents studies of solid state polymerization aimed towards formulating a dynamic model of reactivity in the condensed phase. Phonon spectroscopy is successfully used to elucidate the mechanism of lattice control of the reaction. Novel concepts of phonon-assisted thermal and photochemical reactions are introduced, supported by experimental data. Non-linear laser spectroscopy is used to find the importance of biexcitonic processes in photopolymerization. Also, spectroscopic studies of reactions in Langmuir-Blodgett films and at gas-solid interface which produce ordered polymers are presented. 

Hybrid Sol-Gel Photopolymerization Photosensitive organic-inorganic sol-gel glasses are interesting alternative materials that combine the properties of glasses and polymers [316]. A typical hybrid sol-gel material consists (10.88) in an acrylated silane derivative (which in a first step, leads to a glass-like material via hydrolysis and condensation) and a photoinitiator that allows the free radical photopolymerization of the acrylate. The requirements for the choice of the photoinitiator in such a matrix are crucial solubility, thermal stability, PH compatibility, polarity, and so on. 

In principle macroscopic surfaces of different chemical nature should )3e accessible to coreactive initiator coupling and siibsequent photopolymerization. The capacity of a macroscopic surface like glass, metal, ceramics or plastics for initiator coupling might tse very low compared to porous silica gel. Nevertheless few initiation centers could lead to a high degree of polymerization especially if the monomer is applied as condensed phase. 

The efficiency of various substituted benzophenones for initiating the photopolymerization of multifunctional monomers in condensed phase was evaluated by IR spectroscopy from conversion versus exposure time kinetic curves. The best results were obtained with diphenoxy- benzophenone (DPB) associated to an hydrogen donor, like methyl- diethanolamine, for a one to one mixture of hexanetfrol-diacrylate (HDDA) and of a polyurethane-diacrylate (Actilane 20 fix)m SNPE). Figure 1 shows some typical polymraization profiles obtained for a 30 im thick film exposed, in the presence of air, to the UV radiation of a medium pressure mercury lamp at a light intensity of 1.5 X lO einsteins l cm-2. 

Gratings could not be formed with MM-TMS. Dramatic enhancing in the diffraction efficiency to about 86% (induction period of 144 s) was observed in the case of MM-TMOS, even with only 10 wt% TMPTA. Figure 4.13 shows the realtime diffraction efficiency of holographic gratings formed with various < >-metha-cryloxyalkyltrialkoxysilanes capable of radical photopolymerization and hydrolysis condensation. 

Photopolymerization of bisimides by a photocycloaddition mechanism has also been extensively studied [271,272]. The reaction is a real stepwise condensation process since every chain propagation step involves the absorption of a photon [273,274]. 

---