Trifunctional catalyst system

Star-shaped polymers have been of interest since the development of CRP methods. Matyjaszewski et al. showed that ATRP can be used to prepare star polymers [114], when a hexafunctional initiator was used for the ATRP of St using the CuCl/bpy catalyst system, resulting in a 6-arm star with a narrow molecular weight distribution. Hawker et al. reported the synthesis of star polymers using TEMPO-mediated polymerizations. They demonstrated that star polymers of pSt could be prepared using a trifunctional unimolecular TEMPO initiator [294]. Since then, many reports on star polymers with various types of copolymer arms have been reported. 

Sawamoto et al. investigated the use of di- and trifunctional chloracetate initiators to carry out ATRP of MMA using the RuCl2(PPh3)3/Al(OiPr)3 catalyst system, then extended this to prepare calix [n arene-based multifunctional cores [346,347]. These cores were synthesized through the reaction of dichloroacetyl chloride and the corresponding calix [n] arene (Scheme 56) [346]. 

Kennedy et al. used living cationic polymerization from a tricumyl initiator to prepare an allyl-terminated 3-arm star of pIB, followed by hydroboration/oxida-tion to generate hydroxy chain ends which were esterified with 2-bromoisobutyryl bromide to generate the ATRP trifunctional macroinitiator (Scheme 58) [354]. They subsequently carried out ATRP of MMA in toluene using the Cu(I)/N-( -pentyl)2-pyridylmethanimine catalyst system with the addition of Cu° powder [242] to maintain a sufficient concentration of active Cu(I) [354]. Macroinitiators of Mn=9200 and 15,000 were prepared and both had narrow molecular weight distributions (Mw/Mn=1.15 and 1.09, respectively). The formation of block copoly-... 

Another advance in this field is the catalytic enantioselective a-fiuorination of acid chlorides (eq 28). Here, NFSi is an effective electrophilic fiuorination reagent in the presence of a trifunctional catalytic system. This is a practical method that produces a-fluorocarboxylic acid derivatives. A third catalyst, a Lewis acidic lithium salt, could be introduced to amplify yields of aliphatic products, primarily through activation of the NFSi. 

Catalysts obtained from metal alkyl and a bi- or trifunctional protic compound, e.g. in systems such as AlEt3—H20 [17], ZnEt2—H20 [16] and ZnEt2—Ar(OH)3 [31], which are characterised by the appearance of associated multinuclear species with condensed metal atoms ( Mt—O—Mt—O ), also form epoxide polymers with a very high molecular weight and broad molecular weight distribution therefore, in this case also, only a small fraction of the metal species in the catalyst is effective for the polymerisation. 

A second example of latent biphasic catalysis used the polymer-bound trifunctional base catalyst 129 as a dimethylaminopyridine analog in acylation of 2,6-dialkylphenols by (Boc)20 in a 1 1 heptane-ethanol solvent mixture. After acylation of the phenol was complete, the addition of 10 vol% H2O perturbed the system. The yields of product carbonate from Eq. 66 were 35,66,89,99%, 99, and 99% through the first six cycles. 

We have examined some of these materials in the prior section, but here we will focus on additional examples. Organotin catalysts for use in polyurethane systems have been produced using reactions of R2Sn and R2SnCl2 in the presence of polyfunctional molecules such as in structure 33. These products are presumably crosslinked because of the trifunctional nature of the nonorganotin reactant. The products are used in cationic electrodepositable polyurethane compounds. 

---