Functionalised initiator

A comparison of Eqs. (12) and (13) with Eqs. (18) and (19) respectively, shows that for type 2 polymerisations is equal to co,. for type 1 polymerisations multiplied by the factor (1 + Z )/(l + Z). Since (1 + Z ) < (1 + Z) for Z > 0.0, it is obvious that to, for type 2 polymerisations will always be smaller than for type 1 polymerisations i.e. the use of a functionalised initiator with a monomer whose dominant radical-radical termination mode is combination will always result in a lower yield of polymer possessing the required functionality. 

Now (1 -H 2Z -I- Z ) is always <(2 + 3Z + Z ) for Z 0, Therefore to, for type 3 polymerisations will always be smaller than to, for type 4 polymerisations, i.e. the use of a functionalised initiator with type monomers is desirable since it reduces the amount of unwanted polymer formed during a matched chain transfer free radical polymerisation. For type monomers (see Sect. 3.2) the opposite effect is predicted i.e. the use of a functionalised initiator actually increases ft),. 

Monomer Type %Xon monomer (w/w) DP m, with — — without a functionalised initiator ... 

Not all bimolecular radical-radical termination reactions lead to polymer molecules with unwanted functionality. Thus, the weight fraction of polymer molecules produced by bimolecular termination reactions and which posses unwanted functionality (cOt) is dependent upon the dominant bimolecular termination mode of the monomer and the particular combination of initiator and transfer agent used for the polymerisation. The use of a functionalised initiator in conjunction with a functionalised transfer agent causes a decrease in oo, for type monomers and an increase in co, for type monomers. 

The potential of Fischer carbene complexes in the construction of complex structures from simple starting materials is nicely reflected in the next example. Thus, the reaction of alkenylcarbene complexes of chromium and tungsten with cyclopentanone and cyclohexanone enamines allows the di-astereo- and enantioselective synthesis of functionalised bicyclo[3.2.1]octane and bicyclo[3.3.1]nonane derivatives [12] (Scheme 44). The mechanism of this transformation is initiated by a 1,4-addition of the C -enamine to the alkenylcarbene complex. Further 1,2-addition of the of the newly formed enamine to the carbene carbon leads to a metalate intermediate which can... 

As already shown, it is technically possible to incorporate additive functional groups within the structure of a polymer itself, thus dispensing with easily extractable small-molecular additives. However, the various attempts of incorporation of additive functionalities into the polymer chain, by copolymerisation or free radical initiated grafting, have not yet led to widespread practical use, mainly for economical reasons. Many macromolecular stabiliser-functionalised systems and reactive stabiliser-functionalised monomers have been described (cf. ref. [576]). Examples are bound-in chromophores, e.g. the benzotriazole moiety incorporated into polymers [577,578], but also copolymerisation with special monomers containing an inhibitor structural unit, leading to the incorporation of the antioxidant into the polymer chain. Copolymers of styrene and benzophenone-type UV stabilisers have been described [579]. Chemical combination of an antioxidant with the polymer leads to a high degree of resistance to (oil) extraction. 

Suitably functionalised crown-ethers and cryptands have been synthesi -ed and reacted with chloromethyl polystyrene. Initially... 

Wang identified a series of Michael/Michael and Michael/aldol sequences catalysed by diarylprolinol ethers that led directly to densely functionalised five-mem-bered rings [172-174]. For example, highly diastereoselective and enantioselective double Michael addition reactions were achieved by treatment of a,p-unsaturated aldehydes with triester 113 catalysed by 30 (Scheme 45). Initial conjugate addition... 

PolyHIPE has found a successful application in the field of solid phase peptide synthesis (SPPS), where the highly porous microstructure acts as a support material for a polyamide gel [134]. The polystyrene matrix is functionalised to give vinyl groups on its internal surfaces, and is then impregnated with a DMF solution of N, JV -dimethylacrylamide, acryloylsarcosine methyl ester, crosslinker and initiator. Polymerisation grafts the soft gel onto the rigid support, giving a novel composite material (Fig. 16). 

Initial work involved the functionalisation of C as a TBDPS ether (as in 59a) However, this proved to be incompatible with our overall approach. An alternative, and somewhat more direct strategy involved the incorporation of a halogen at C from the outset. This was expected to be entirely compatible with subsequent steps, conveniently undergoing transformation into the corresponding triphenylphosphonium salt at a later stage. Initially, the bromide 59b was chosen and indeed was found to be admirably compatible with the ensuing chemistry. However, during... 

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