Chain copolymerization coordination initiator

Some characteristics of free-radical terpolymerization of tri-butylstannyl methacrylate, styrene and maleic anhydride governed by the pentacoordination state of the tin atom are reported in Refs. 95),96). It is shown that a coordination-bound monomer has a considerable effect on chain initiation and propagation. Copolymerization mainly involves the participation of complex-bound monomers. 

The reactivity ratios for pairs of given monomers can be very different for the different types of chain-growth copolymerization free-radical, anionic, cationic, and coordination copolymerization. Although the copolymer equation is valid for each of them, the copolymer composition can depend strongly on the mode of initiation (see Figure 10.8). 

A notable effect ol rra/i.v comdination has tilso been observed for the aniitnic pttlymeriziition of methacryloni-trile (22) initiated from a living polymer ctf methyl methacrylate (21, R = Me) with an aluminum enolate reactive end (32 ), in which the chain grttwth is promoted by the trails coordination of pyridine, to afford a narrow MWD block copolymer (42)- Ott the other hand, in the absence of axially ccatrdinating pyridine under otherwise identical conditions as described, no block copolymerization of 22 from 32 takes place. 

Graft copolymers consisting of poly(n-octylallene-co-styrene) (PALST) as backbone and PCL as side chains were synthesized with the combination of coordination copolymerization of n-octylallene and styrene (catalyzed by the mixture of bis[N,N-(3,5-di-t rt-butylsalicylidene)anilinato]titanium(IV) dichloride and tri-isobutyl aluminum (Al(iBu)3)) and the ROP of s-CL (catalyzed by Sn(Oct)2). The hydroxyl functionalized copolymers, which serve as macroinitiator for ROP of CL, were prepared by the reaction of mercaptoethanol with the pendant double bond of PALST in the presence of radical initiator. The reaction is presented in Figure 9. 

Elimination of a polymerizable fragment and its incorporation in the polymeric chain (viz., in situ copolymerization with the monomer and ligand) can also lead to unit variability. In addition, radical fragments can initiate polymerization, recombine, and abstract a hydrogen atom from coordinated ligand. 

This rule is enough general to be applied to initiators resulting from ZnEt CdMe and CdEt as organometallic compounds and alcohols and 1,2 diols as chiral components. It is interesting to notice that in the copolymerization of racemic methylthiirane with achiral monomers such as ethylene sulfide or isobutylene sulfide, the choice is not modified this strongly substantiating the coordination interaction between the initiator and the monomer and the lack of existence of chain effect (39). 

At low temperatures, about -78°C, in triisobutylaluminum/ water-initiated polymerization, which is presumed to be a cationic initiation, an amorphous (elastomeric) polymer is obtained from cis-2,3-epoxybutane, and a crystalline polymer, melting point 100°C, is obtained from the trans-isomer. In a copolymerization of the two isomers, the cis-oxide enters the copolymer at about twice the rate of the trans-isomer. Further, the low-temperature, cationic poly(trans-2,3-epoxybutane) with a crystalline melting point of 100°C was found to consist of diad units with a mesodiisotactic structure, while the crystalline polymer formed by coordinate polymerization of the cis-monomer, melting point 162°C, had diad units that were racemic diisotactic. These results make apparent the importance of the monomer coordination step in polymer chain growth in coordinate polymerizations. 

Detailed mechanistic studies on C02/epoxide promoted by various A1 porphyrin initiators in the presence of a nucleophile concluded on a mono-metallic pathway with the polycarbonate chain growing on one side of the (Porph)Al backbone and with the opposite side being occupied by the Al-coordinated Lewis base cocatalyst (Scheme 10) [37]. In particular, investigations on a (TPP)A1X/DMAP catalytic systems for CO2/PO copolymerization showed that coordination of the nucleophile/... 

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