UV-initiated polymerization

The fact that the polyreaction of diacetylenes is topochemically controlled is especially well documented by the polymerization behavior of the sulfolipid (22)23 . (22) forms two condensed phases when spread on an acidic subphase at elevated temperatures (Fig. 10). UV initiated polymerization can only be carried out at low surface pressures in the first condensed phase, where the molecules are less densely packed. Apparently, in the second phase at surface pressures from 20 to 50 mN/m the packing of the diyne groups is either too tight to permit a topochemical polymerization or a vertical shift of the molecules at the gas/water interface causes a transition from head packing to chain packing (Fig. 10), thus preventing the formation of polymer. 

Fig. 6.21. Electrochromatographic separation of benzene derivatives on monolithic capillary column prepared by UV initiated polymerization. Conditions capillary column, 100 pm i.d. x 25 cm active length stationary phase poly(butyl methacrylate-co-ethylene dimethaciylate) with 0.3 wt. % 2-acrylamido-2-methyl-l-propanesulfonic acid pore size, 296 nm mobile phase, 75 25 vol./vol mixture of acetonitrile and 5 mmol/L phosphate buffer pH 7 UV detection at 215 nm 25 kV pressure in vials, 0.2 MPa injection, 5 kV for 3 s. Peaks thiourea (1), benzyl alcohol (2), benzaldehyde (3), benzene (4), toluene (5), ethylbenzene (6), propylbenzene (7), butylbenzene (8), and amylbenzene (9).

Photoinitiated polymerization of the same mixtures at 20°C generally yields monoliths with larger pores compared to those initiated thermally. Thus, reduced contents of dodecanol in the polymerization mixture has to be used for UV initiated polymerizations in order to obtain pore sizes comparable to those of their thermally polymerized analogs. For example, a polymerization mixture containing only 30% dodecanol can be used to produce a 2-hydroxyethyl methacrylate monolith with 1,000 nm pores by UV polymerization at 20°C. These shifts can readily be explained by the effect of the polymerization temperature, since the creation of larger pores is favored at lower temperatures [59],... 

Fig. 6.30. Column efficiencies for (S) enantiomer determined from DNZ-(R,S)-Leu separations on quinidine-functionalized monoliths as a function of pore diameter. (Reprinted with permission from [60]. Copyright 2000 American Chemical Society). Conditions polymerization mixture, chiral monomer 8 wt%, 2-hydroxyethyl methacrylate 16 wt%, ethylene dimethacrylate 16 wt%, porogenic solvent 60 wt% (consisting of 1-dodecanol and cyclohexanol in different proportions), UV initiated polymerization for 16 h at room temperature ( ) and thermally initiated polymerization for 20 h at 60°C ( ), capillary columns 335 mm (250 mm active length) x 0.1 mm i.d., mobile phase 0.4 mol/L acetic acid and 4 mmol/L triethylamine in 80 20 acetonitrile-methanol, separation temperature 50°C, voltage -25 kV.

Absorption, evaporation, polycondensation, UV-initiated polymerization, molecular resonance heating (microwave)... 

Absorption, evaporation, air oxidation polymerization, UV initiated polymerization Physical barrier spray powder, emulsion coating... 

Evaporation, UV initiated polymerization Evaporation, UV initiated polymerization Evaporation... 

Figure 29 Separation of the nonsteroidal anti-inflammatory drugs ibuprofen (peak 1), naproxen (2), ketoprofen (3), and suprofen (4) in anion-exchange CEC mode using a strong anion-exchange monolithic column. Conditions on-column alkylated monolith prepared from mixtures consisting of 8% 2-dimethylaminoethyl methacrylate, 24% 2-hydroxyethyl methacrylate, 8% ethylene dimethacrylate, 20% cyclohexanol, 40% 1-dodecanol UV-initiated polymerization at room temperature for 16 h cfpmode= 1423 nm. Column dimensions inner diameter 0.1 mm, total length 335 mm, effective length 250 mm. Mobile phase 0.4 mol/L acetic acid and 4 mmol/L triethylamine in acetonitrile/methanol (60/40), voltage -25 kV, injection -5 kV for 5 s, temperature 50°C, UV detection at 250 nm. (Reprinted from Ref. 127, with permission.)...

The development of polymerizable microemulsions consisting of only three basic components (except a water component) for producing transparent solid polymers with nanostructure is a recent achievement [87]. For example. Fig. 5 shows the SEM micrograph of the fractured polymer prepared by the UV-initiated polymerization of a bicontinuous microemulsion consisting of 35 wt% water, 35 wt% AUDMAA and 30 wt% MMA. This micrograph reveals randomly distributed bicontinuous nanostructures of water channels and polymer domains. The widths of the bicontinuous nanostructures were about 40-60 nm. The sizes of the nanostructures can be readily reduced by adding 2-hydro-... 

The chain reaction process can be used as a diagnostic aid to determine whether free radicals are generated from a drug when irradiated. Acrylamide is an acrylic monomer, which is widely used in gel electrophoresis, as a polymer formed in situ by peroxide or UV-initiated polymerization. This monomer is a water soluble solid, more easily handled than most other vinyl monomers, and the progress of its polymerization can be readily followed by measuring its contraction in volume utilizing dilatometry, or its increase in viscosity in a viscometer. Details of this experimental technique can be found in Moore and Burt (18). 

It has been found [105,106] in particular that the reaction product [poly (BMEGMA-co-MMA)] derived from glycidyl methacrylate/methyl methacrylate copolymers [poly(GMA-co-MMA)] and a-(2-carboxyethyl)benzoin methyl ether (CEBME) (Scheme 26), although less efficient than CEBME alone in the UV initiated polymerization of styrene, exhibits a markedly enhanced photocrosslinking activity. 

Copolymers of MBA with styrene [poly(MBA-co-St)] containing variable amounts of MBA co-units, have also been applied [107] to the UV initiated polymerization of MMA in benzene solution. 

Indeed, photophysical studies by laser flash photolysis combined with the determination of MMA polymerization rate (Rp) in toluene solution, have allowed evaluation of the triplet state lifetime of the above systems, as well as their relative quantum yields of initiation ( j) and a-cleavage ( ). As reported in Table 22, 3, values for poly(MBA) and poly(MBVE) are appreciably lower than those for MBI and MBEE, respectively. On this basis, the polymeric photoinitiators would be expected to display lower activity than the models in the polymerization of acrylic monomers. On the contrary, poly(MBA) and poly(MBVE), together with the related copolymers, show higher values of Rp and hence i, in the UV initiated polymerization of MMA in toluene solution. These findings, therefore, confirm the previously obtained results in film matrix, where a HDDA/BA equimolar mixture was used as curing formulation (Table 21). 

All the MBA/A(,iV-dialkylamino acrylate copolymers behave similarly to poly(MBA-co-MtA)s (Tables 21 and 25), thus suggesting that the replacement of MtA by A,A(-dialkylamino acrylate co-units does not markedly affect the photoinitiation activity of the system. Accordingly, BMI/A,A(-dialkylamino isobutyrates mixtures exhibit substantially the same activity as MBI alone [118]. Similar results have previously been obtained for 2,2-dimethoxy-2-phenyl acetophenone (DMPA), when additioned with diethylmethylamine, in the UV initiated polymerization of -butyl methacrylate [113]. However, a remarkable shortening of the induction period (to) of UV curing is observed for all the polymeric photoinitiators in the presence of tertiary amines as compared with the low-molecular-weight MBl/A,A(-diatkylamino isobutyrates systems, the maximum effect resulting in the case of MBA/A(,iV-dialkylamino acrylate copolymers (Table 25). 

Indeed, photopolymerization of acrylamide in aqueous solution on cell-GEHMP gives cellulose with the surface covered by a poly acrylamide) gel. Similarly, UV initiated polymerization of 2-hydroxyethyl acrylate, 2-(dimethylamino) ethyl methacrylate and A -vinylpyrrolidone carried out with the above functionalized Si(>2 results in the formation of a surfece polymer coating. 

Figure 13.24 Separation of racemic DNZ-leucine on polymeric monolithic material. Conditions polymerization mixture, chiral monomer 76 8wt%, 2-hydroxyethyl methacrylate 24wt% ethylene dimethacrylate 8wt%, 1-dodecanol 45 wt%, and cyclohexanol 15wt% UV-initiated polymerization for 16 h at room temperature ...

Meier et al. [101] employed a different approach in which a BLM is formed from a mixture of nonpolymerizable lipids and water-insoluble, nonlipid monomers (styrene and divinylbenzene). After UV-initiated polymerization to produce a two-dimensional, cross-linked network in the membrane, its stability was enhanced as... 

BMA and EGDMA monomers and UV-initiated polymerization to generate a cross-linked poly(methacrylate) network in the POPC bilayer. The substrate, ampicillin, diffused into liposomes through the OmpF channels and was converted to ampi-cillinoic acid. Thus a polymer-stabilized, vesicle-sized bioreactor with selective permeability was created, allowing for retention of the enzyme and ingress/egress of substrate and product. 

Composite materials based on monomer-polymeric systems have been obtained by UV-initiated polymerization method. The flow characteristics of these compositions and their effect on further polymerization have been studied. The polymerization of monomers in the presence of dissolved polymers and properties of the materials have been investigated. 

Breslow and Kutner12 studied the polymerization of sodium ethylenesulfonate in aqueous solution using the persulfate-bisulfite redox couple as initiator at 5°C. UV-initiated polymerization at 30 °C was equally effective. 

The UV-initiated polymerization of vinyl acetate, sensitized with various quantities of AIBN at — 19°C, gives polymeric products which, upon saponification and reacetylation, produce polymers with substantially the same molecular weight as that initially observed. These observations contribute to the postulate that at low temperatures, polymerizations proceed essentially with the formation of branched chains [26]. 

The UV-initiated polymerization of allyl methacrylate is carried out in a 500-ml Pyrex or Vycor Erlenmeyer flask with a side arm. The front of the flask is painted black except for an area of 4 x 11 cm which assures that a constant area is exposed to the radiation source. The back and bottom of the flask is covered with aluminum foil. The side arm is used for withdrawing samples periodically. The charged flask is kept in a stirred, water thermostat controlled to 1°C. Preparations are run under a slight positive pressure of purified nitrogen. 

The flow control elements or valves developed in Sandia were plugs of nonporous monolithic polymer prepared from fluorinated acrylates via UV-initiated polymerization directly in one of the channels. The reason for using the fluorinated monomers is to manage the surface energy, decrease their friction in channel, enable actuation at a low pressure, as well as to avoid both swelling and shrinking in solvents typically used in reversed-phase separations such as water and acetonitrile. The friction could be further decreased by modification of the valve channel with fluorinated alkylsilane. However, the latter may be counterproductive in systems used for the separation of proteins and peptides because they tend to adsorb on highly hydrophobic surfaces. 

Figure 3 UV-initiated polymerization of epoxies. Copyright 2003 by Taylor Francis Group, LLC...

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