Synthesis Of Triblock Copolymers By Radical Trap Assisted-Atom Transfer Radical Coupling

Monobrominated diblock copolymers composed of poly(styrene) (PSt), poly(methylacrylate) (PMA), or poly(methyl methacrylate) (PMMA) were synthesized by consecutive atom transfer radical polymerizations (ATRP). The brominated diblocks were utilized in atom transfer radical coupling (ATRC) and radical trap-assisted ATRC (RTA-ATRC) reactions to form ABA type triblock copolymers. Once PMMA-PStBr and PSt-PMABrBr were produced by ATRP, the synthes of PSt-PMA-PSt and PMMA-PSt- PMMA by ATRC and also by RTA-ATRC were attempted. The coupling methods were compared and it was found that RTA-ATRC succeeded in synthesizing PSt-PMA-PSt where ATRC could not, and that RTA-ATRC improved coupling over ATRC for PMMAPSt- PMMA. Incorporation of the radical trap 2-methyl-2-nitrosopropane (MNP) midchain allowed for simple thermal cleavage of the triblock to confirm the RTA-ATRC pathway occurred in preference over the head to head radical coupling pathway of ATRC. Triblocks made by ATRC did not cleave under our conditions, as no MNP was present and thus no labile C-O bond was incorporated. The RTA-ATRC pathway allowed for lower catalyst amounts (2 molar equivalents of copper(I)bromide and 2 molar equivalents of copper metal) and a high degree of coupling at lower temperatures (40°C). The RTA-ATRC improved upon ATRC because of its ability to generate a persistent radical and proceed by first order kinetics with respect to the chain end radical.

Dimerization of Poly(methyl methacrylate) Chains Using Radical Trap-Assisted Atom Transfer Radical Coupling

End-brominated poly(methyl methacrylate) (PMMABr) was prepared by atom transfer radical polymerization (ATRP) and employed in a series of atom transfer radical coupling (ATRC) and radical trap-assisted ATRC (RTA-ATRG) reactions. When coupling reactions were performed in the absence of a nitroso radical trap-traditional ATRC condition-very little coupling of the PMMA chains was observed, consistent with disproportionation as the major termination pathway for two PMMA chain-end radicals in our reactions. When 2-methyl-2-nitrosopropane (MNP) was used as the radical trap, coupling of the PMMA chains in this attempted RTA-ATRC reaction was again unsuccessful, owing to capping of the PMMA chains with a bulky nitroxide and preventing further coupling. Analogous reactions performed using nitrosobenzene (NBz) as the radical trap showed significant dimerization, as observed by gel permeation chromatography (GPC) by a shift in the apparent molecular weight compared to the PMMABr precursors. The extent of coupling was found to depend on the concentrion of NBz compared to the PMMABr chain ends, as well as the temperature and time of the coupling reaction. To a lesser extent, the concentrations of copper(I) bromide (CuBr), nitrogen ligand (N,N,N',N',N"-pentamethyldiethylenetriamine = PMDETA), and elemental copper (Cu) were also found to play a role in the success of the RTA-ATRC reaction. The highest levels of dimerization were observed when the coupling reaction was carried out at 80 degrees C for 0.5h, with ratio of 1:4:2.5:8:1 equiv of NBz: CuBr:Cu:PMDETA:PMMABr.

Democratic Transition and Political Patronage

Mr. Korosenyi begins by analysing the particular relationship holding between politics and administration in different countries. Within Europe three major patterns have emerged in the 20th century. Firstly there is the politically neutral British Civil Service, secondly the German and French state bureaucracies, which traditionally are supposed to embody the "common good", and thirdly there is the patronage system of the so-called consociate democracies, e.g. Austria. In general Mr. Korosenyi believes that, though politics do not penetrate into the Hungarian administration to the extent they do in Belgium and Austria, nevertheless, there is a stronger fusion than there is in the traditional British pattern. He is particularly interested in this relationship with regard to its effect on democratic institution building and the stabilisation of the new regime in Hungary, now the old "nomenklatura" system has been abolished. The structure of the Hungarian government was a result of the constitutional amendments of 1989 and 1990. Analysing this period, it becomes clear that for all the political actors who initiated and supported the democratic transition to democracy, the underlying assumption was a radical depoliticisation of the administration in order to maintain its stability. The political leadership of the executive is a cabinet government. The government is structured along ministries, each headed by a politician, i.e. the minister, who is a member of the cabinet. The minister's political secretary is not a cabinet member, but he or she is a politician, usually a member of the parliament. The head of the administration of the ministry is the administrative state secretary, who is a civil servant. He or she usually has four deputies, also civil servants. Naturally it is assumed that there should be a clear separation between politicians and civil servants. However in practice, the borders can be blurred, giving rise to a hybrid known as the "political civil servant". Mr. Korosenyi analyses the different faces of these hybrids. They are civil servants for the following reasons. They need special educational qualifications, working experience, a civil service exam etc., they are not allowed to do anything which is incompatible with their impartial role, and they cannot occupy political office nor may they appear in the name of any political party. On the other hand, the accepted political dimension to their function is revealed by the following facts. The state secretary (a civil servant) may participate in cabinet meetings instead of the minister. The state secretary is employed by the minister. A state secretary or any of their deputies can be dismissed at any time by the minister or the prime minister. In practice then, ministers appoint to these senior administrative positions civil servants whose personal and political loyaties are strong. To the second level of political patronage in ministries belong the ministerial cabinet, press office and public relation office. The ministerial cabinet includes the private advisors and members of the personal staff of the minister. The press office and the PR office, if they exist, are not adjusted to the administrative hierarchy of the ministry, but under the direct control of the minister. In the beginning of the 1990s, such offices were exceptions; in the second half of the 90s they are accepted and to be found in most ministries. Mr. Korosenyi's work, a 92-page manuscript of a book in Hungarian, marks the first piece of literature within the field of political science which analyses the structure of the Hungarian government in the 1990s and the relationship between the political leadership and the public administration.