Labelled initiator

For both sets of data, the radioactivity from the labeled initiator gives 96,500 cpm when converted to CO2. 

For the case of initiators that produce both primary and secondary radicals (e.g. BPO) use of a doubly labeled initiator allows the different types of end groups to be distinguished [e.g. 117 and 118 - Scheme 3.98J and the reactivities of... 

The use of l3C-labeled initiators in assessing the kinetics and efficiency of initiation2 14,32 60,84 requires that the polymer end groups, residual initiator, and various initiator-derived byproducts should each give rise to discrete signals in the NMR spectrum. So far this method has been demonstrated for homo- and copolymerizations of S and MMA prepared with AIBN-a-L C3 AIBMc-a-13C or HlKi-carbonyl- C/BVQ-rmg- C (1 1) as initiator. 

Labeled initiators have been used in evaluating the relative reactivity of a wide range of monomers towards initiating radicals.159 The method involves determination of the relative concentrations of the end groups fanned by addition to two monomers (e.g. 119 and 120) in a binary copolymer formed with use of a labeled initiator. For example, when AlBMe-a-13C is used to initiate copolymerization of MMA and VAc (Scheme 3.99),157 the simple relationship (eq. 14) gives the relative rate constants for addition to the two monomers. Copolymerizations studied in this way arc summarized in Tabic 3.13. 

JC labeled initiators 146 8 0F labeled initiators 146 8 ladder polymers... 

Cl2] = 0.0640- = 0.0176 M amount Cl2 = 2.50 Lx0.0l76 M = 0.0440 mol Cl2 Or, in the first line labeled Initial, we could have set y = number of moles of SbCl5 produced. Then our final answer would be y = 0.116 mol SbCl5. That is, we would have obtained the answer more directly. 

There are a number of Physical Methods available but of all the Physical Methods, tracer analysis using C14, H3 or S35- labelled initiators or other substances has received considerable attention. However, this method is incapable of giving results specific to the actual functional group and is highly susceptible to interference by absorbed radioactive impurities. It is moreover hazardous, expensive and needs sophisticated apparatus. 

Using labeled initiator and radiometric analysis, the number of initiator fragments from the number of end-groups, R, can be evaluated and the number of crosslinking points can be calculated. The number of unreacted double bonds can be found by the bromometric method. On the basis of such analysis, we can find the percentage of units in the multimonomer which had reacted according to template mechanism. The results of the calculations for two examined systems are presented in Tables 5.3 and 5.4... 

Much of the work with labelled initiators in radical polymerizations is quite independent of determinations of molecular weights, attention being focussed on kinetic chain lengths instead of on molecular chain lengths (10). In a sensitized polymerization, the rate of initiation is identified with the rate at which initiator fragments are incorporated in the polymer to calculate the rate of initiation, it is necessary only to determine the empirical formula shown previously for the recovered polymer and the overall rate of polymerization. No assumptions are required concerning the mechanism of termination or the frequency of transfer processes involving monomer, solvent or polymer. Errors can arise from three causes ... 

The use of labelled initiators to obtain accurate information concerning the relative reactivities of radical scavengers towards reference radicals, has been reviewed (4). Product analysis, by isotope dilution analysis, has been used in the examinations of the decompositions of certain initiators in the absence of monomers. It is possible to work with very dilute solutions and small extents of decomposition so that the conditions are similar to those prevailing when the substances are used as initiators of polymerizations. The decompositions of dibenzoyl (12) and di-anisoyl peroxides (13), for example, have been followed by determinations of the carbon dioxide evolved. 

According to this scheme, polymethyl methacrylate prepared in the absence of p benzoquinone should contain one initiator fragment per polymer molecule the addition of p benzoquinone to the polymerizing system should make this number tend towards two and at the same time the amount of combined quinone should approach one molecule per polymer molecule. Experiments with labelled initiator and labelled retarder (39) confirmed these predictions in general although not in detail. 

Grafting to rubber appears to be very strongly dependent on the nature of the initiator used for the polymerization of the monomer (767, 214). Recent experiments with wC-labeled initiators (6) demonstrate that very little graft copolymer was produced in the presence of 2,2 -azo-bis-iso-butyronitrile therefore almost all the grafting during reactions initiated... 

Allen, P. W., G. Ayrey, C. G. Moore and J. Scanlan Radiochemical studies of free-radical vinyl polymerizations. Part II. The polymerization of vinyl monomers in the presence of polyisoprenes use of C14-labeled initiators to determine the mechanism of graft-interpolymer formation. J. Polymer Sci. 36, 55 (1959). 

The course of initiation was proved by the activity of the polyester prepared by using a labelled initiator 42 54>, it also follows from the analytical determination of the epoxide by halogenide salts 59). The formation of alternating copolymer — polyester... 

Label all chemicals to be stored with date of receipt or preparation and have labels initialed by the person responsible. 

The results of incorporation experiments using tritiated thymidine lend support to the hypothesis that thymidine rhamnosyl pyrophosphate in Lactobacillus acidophilus is an intermediate on the pathway to deoxyribonucleic acid synthesis. When cells were grown in a medium containing tritiated thymidine, labeled thymidine rhamnosyl pyrophosphate constituted two-thirds of the total label in the acid-soluble fraction. When these cells were transferred to a medium containing 2-deoxyadenosine, 2-deoxy-guanosine, and 2-deoxycytidine as the nucleosides, 99 % of the label initially present was transferred to deoxyribonucleic acid after incubation for 50 minutes. Therefore, almost complete incorporation (into deoxyribonucleic acids) of the isotope from tritiated th3anidine had occurred. 

Surface Area Data. Table I summarizes the surface area data for the rocks and minerals studied. There are three groups of surface area values. Those in the column labeled initial" are those values obtained from dry-ground samples which had no contact with seawater or any other fluid. Those values in the 5th and 6th columns refer to numbers obtained from the pH 8.3-8.5, ca. 100 dissolved silica experiment... 

Abt Associates, Inc. 1999. Consumer Labelling Initiative Phase II Report, Cambridge, Massachusetts, Prepared for US EPA. 

Mazis, M. B., Morris, L. A., Swasy, J. L. (1991). An evaluation of the alcohol warning label Initial survey results. Journal of Public Policy and Marketing, 10,... 

Several methods can be used for the evaluation of the initiator efficiency. One method depends on the direct analysis of initiator fragments as end groups in the polymer formed compared to the amount of initiator consumed. The use of isotopically labeled initiators such as C-labeled benzoyl peroxide and other related peroxides, and C-labeled AIBN and S-labeled potassium persulfate provide appropriate sensitive methods for determining the number of initiator fragments trapped as end groups in the resulting polymers [10,11]. 

Next, NMR studies on end-group analysis for polymers are reviewed. The section includes the deuterated monomer method, in which a totally deuterated monomer is polymerized with an undeuterated initiator and the resultant polymer is analysed by H NMR spectroscopy to determine the initiator fragment incorporated into the polymer chain. This method, which was invented by the authors, has brought fruitful results. Other related topics of end-group analysis of vinyl polymers, including labelled initiator methods, are also reviewed. 

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