DMPA

Figure Bl.16.15. TREPR spectmm after laser flash photolysis of 0.005 M DMPA (5) in toluene, (a) 0.7 ps, 203 K, RE power 10 mW O, lines CH (8), spacing 22.8 G , benzoyl (6), remaining lines due to (7). (b) 2.54 ps, 298 K, RE power 2 mW to avoid nutations, lines of 7 only. Reprinted from [42].

Contradictory evidence regarding the reaction to fonn 8 and 9 from 7 led the researchers to use TREPR to investigate the photochemistry of DMPA. Figure B1.16.15A shows the TREPR spectrum ofthis system at 0.7 ps after the laser flash. Radicals 6, 7 and 8 are all present. At 2.54 ps, only 7 can be seen, as shown in figure B1.16.15B. All radicals in this system exliibit an emissive triplet mechanism. After completing a laser flash intensity sPidy, the researchers concluded that production of 8 from 7 occurs upon absorption of a second photon and not tiiemially as some had previously believed. 

Dimethyl ester-diol polyesterifications, 84 Dimethyl formamide (DMF), 79, 295 Dimethyl isophthalate (DMI), 106 Dimethylol propionic acid (DMPA), 238 Dimethyl sulfoxide (DMSO), 83, 185,... 

The recoveries of clomeprop and its metabolite DMPA in soil after extraction with acetonitrile-water (4 1, v/v) by HPLC/UV (234 nm) are >90% The recoveries of propanil and its metabolite, 3,4-dichloroaniline, in soil are 95 and 76%, respectively, by Soxhlet extraction and LC/PAD determination. Diflufenican is added to soil in the range 0.002-0.008 mg kg to validate the method developed by Conte et al. The average recovery from the soil by this method is 92 5%. 

The nomenclature for associating individual fatty acid groups with particular phosphodig-lyceride derivatives is straightforward. For instance, a phosphatidic acid (PA) derivative which contains two myristic acid chains is commonly called dimyristoyl phosphatidic acid (DMPA). Likewise, a PC derivative containing two palmitate chains is called dipalmitoyl phosphatidyl choline (DPPC). Other phosphodiglyceride derivatives are similarly named. 

Trimethylolpropane triacrylate (TrMPTrA, mw 296.3, Polysciences Inc., Warrington, PA) was mixed with 1 wt% 2,2-dimethoxy-2-phenyl-acetophenone (DMPA, mw 256.3, Aldrich Chemical Co., Milwaukee, WI) as a photoinitiator. For... 

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. 

The monomers studied, 2-hydroxyethyl methacrylate (HEMA) and diethylene glycol dimethacrylate (DEGDMA), were obtained from Aldrich (Milwaukee, WI) and Polysciences, Inc. (Warrington, PA), respectively, and were used after dehibition to remove the hydroquinone inhibitor. 2,2-Dimethoxy-2-phenyl acetophenone (DMPA), the conventional initiator used in this study, was obtained from Ciba-Geigy (Hawthorne, NY) and the tetraethylthiuram disufide (TED) was obtained from Aldrich. 

The rate behavior is modeled using kinetic expressions based on elementary reactions of the species involved. Generation of radicals can occur through five different initiation mechanisms. First, species such as DMPA or TED can generate either two carbon radicals or two DTC radicals. If XDT-like initiators are considered, one carbon radical and one DTC radical are generated upon photolysis, and a similar reaction for reinitiation of DTC-terminated polymer chains exists. Lastly, initiation of polymer chains by DTC radicals should be included for completeness. These reactions can be summarized as ... 

Rc and Rs represent the carbon radicals and DTC radicals, respectively. Icc, ICs and ISs possible initiator species (DMPA, XDT and TED, respectively), M represents the monomer, P the polymer and Rs-P the telechelic... 

When the polymerization is initiated by a conventional initiator such as DMPA, HEMA and DEGDMA display rate curves as shown in Figures 1 and 2. In these... 

Figure 1. Experimental and simulated normalized rates of polymerization for HEMA initiated by DMPA.

Figure 3. Experimentally determined kinetic constants for propagation and termination in DMPA-initiated HEMA polymerization.

Figure 5. Normalized rates of polymerization for DEGDMA initiated by DMPA in the presence of increasing amounts of TED.

Figure 5 shows similar experimental rate data for the DEGDMA/DMPA/TED polymerization. As seen in the case of HEMA, TED addition decreases both the initial rate and the maximum rate of polymerization of DEGDMA. As described earlier, polymerization of DEGDMA results in a highly crosslinked polymer. The autoacceleration effect is characterisitc of highly crosslinked systems as the diffusional limitations reduce the carbon-carbon radical termination kinetic constant... 

Figure 6. Estimated carbon radical concnetrations as a function of conversion for DMPA-initiated HEMA polymerization with and without TED present.

In this paper, the kinetics and polymerization behavior of HEMA and DEGDMA initiated by a combination of DMPA (a conventional initiator) and TED (which produces DTC radicals) have been experimentally studied. Further, a free volume based kinetic model that incorporates diffusion limitations to propagation, termination by carbon-carbon radical combination and termination by carbon-DTC radical reaction has been developed to describe the polymerization behavior in these systems. In the model, all kinetic parameters except those for the carbon-DTC radical termination were experimentally determined. The agreement between the experiment and the model is very good. 

From these experimental and modeling studies, the mechanism of the living free radical polymerizations initiated by a combination of TED and DMPA have been elucidated. The TED produces DTC radicals that preferentially cross-terminate with the propagating carbon radicals. By this cross-termination reaction, the carbon radical concentration is kept low (as was shown in figure 6) and the rate of polymerization is decreased, as is the autoacceleration effect. This suppression of the autoacceleration peak in HEM A polymerizations and, interestingly, in DEGDMA polymerization has been observed to increase as the TED concentrations are increased. This behavior has been predicted successfully by the model as well. 

Fig. 10 Influence of the photoinitiator (1 wt %) on the temperature profile in UV curing of a PUA film. DMPA dimethoxyphenylacetophenone HPK hydroxy-phenylketone.

CHCs, even those with less than 35 meg estrogen, can cause small increases in blood pressure (6 to 8 mm Hg) in both normotensive and hypertensive women. In women with hypertension, OCs have been associated with an increased risk of MI and stroke. Use of CHCs is acceptable in women younger than 35 years with well-controlled and monitored hypertension. Hypertensive women with end-organ disease or who smoke should not use CHCs. Progestin-only pills and depot medroxyprogesterone acetate (DMPA) are choices for women with hypertension. 

Women with migraine headaches, history of thromboembolic disease, heart disease, cerebrovascular disease, SLE with vascular disease, and hypertriglyceridemia are good candidates for progestin-only methods (e.g., minip-ills, DMPA, and the levonorgestrel intrauterine system). Women older than 35 years who are smokers or are obese, or who have hypertension or vascular disease, should use progesterone-only methods. 

DMPA 150 mg administered by deep intramuscular injection in the gluteal or deltoid muscle within 5 days of the onset of menstrual bleeding inhibits ovulation for more than 3 months, and the dose should be repeated every 12 weeks to ensure continuous contraception. A new formulation contains 104 mg of DMPA (Depo-SubQ Provera 104), which is injected subcutaneously into the thigh or abdomen. The manufacturer recommends excluding pregnancy in women more than 1 week late for repeat injection of the intramuscular formulation or 2 weeks late for repeat injection of the subcutaneous formulation. 

DMPA can be given immediately postpartum in women who are not breast-feeding, but in women who are breast-feeding, it should not be given until 6 weeks postpartum. 

Women using DMPA have a lower incidence of Candida vulvovaginitis, ectopic pregnancy, pelvic inflammatory disease, and endometrial and ovarian cancer compared to women using no contraception. The median time to conception from the first omitted dose is 10 months. 

The most frequent adverse effect of DMPA is menstrual irregularities, which decrease after the first year. Breast tenderness, weight gain, and depression occur less frequently. 

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