Isopropyl end-groups

Lieber and Brintzinger reported a detailed study using mixtures of precatalysts with different stereospecificities [25], Isospecific precatalyst 10 undergoes facile chain transfer to TMA, as revealed by an increase in isopropyl end groups and a sharp reduction in molecular weight in the presence of TMA (there was no exchange with TiBA). An aspecific precatalyst 7 was affected similarly by TMA... 

Hydrolytic workup of the polymer cleaves the aluminium-polymer bond to yield an isopropyl end group. 

The catalytic system 11/MAO shows lower activity in propylene polymerization as compared to polymerization of ethylene, with a similar trend in the relationship between the polypropylene yield and Al Zr ratio (compare entries 1,2 7, and 8). The proton and carbon spectroscopic analysis of the polypropylene obtained revealed only vinyl/isopropyl end groups. The fact that... 

Park and Skene [65] found that the effectiveness of the initiator end groups for causing dehydrochlorination was in the ratio lauroyl peroxide-isopropyl peroxidi-carbonate-benzoyl peroxide-azoisobutyronitrile = 9.7 5.8 4.4 1.6. These values were obtained at 220°C, and the degradation rates were taken as the mean value for 0-20% dehydrochlorination. 

The relative importance of the various pathways depends on the alkyl groups (R). The rate constants for scission of groups (R ) from /-aikoxy radicals (RR C-O) increase in the order isopropylalkyl radical is less important when R is methyl than when R is a higher alkyl group, if the pathway to alkylperoxy radicals is dominant, the resultant polymer is likely to have a proportion of peroxy end groups.200 211... 

In the case of allyl peroxides (12 X= CH2, A=CH2, BO),1 1 1 intramolecular homolytic substitution on the 0-0 bond gives an epoxy end group as shown in Scheme 6.18 (1,3-Sn/ mechanism). The peroxides 52-59 are thermally stable under the conditions used to determine their chain transfer activity (Table 6.10). The transfer constants are more than two orders of magnitude higher than those for dialkyi peroxides such as di-f-butyl peroxide (Q=0.00023-0.0013) or di-isopropyl peroxide (C =0.0003) which are believed to give chain transfer by direct attack on the 0-0 bond.49 This is circumstantial evidence in favor of the addition-fragmentation mechanism. 

In experiment Rll the reaction mixture was treated with 14C-labelled 2-propanol, and the resulting polymer contained negligible activity. It follows that the reaction of the end-groups with the alcohol does not produce a detectable concentration of isopropyl ether end-groups. When the alcohol was added to the reaction mixture, the conductivity fell to zero within half a minute, which indicated a rapid removal of ions from the organic phase. 

Polymerization of propylene with complex 5 (Table 4) at atmospheric pressure produces an atactic polypropylene having the same features regarding the temperature and Al Zr ratio as for ethylene. The H and 13C-NMR spectroscopic analysis of polypropylene reveals only vinyl/isopropyl, but no vinylidene/n-propyl, end groups, similar to the polymers obtained with zirconocenes [67,68]. Polymers with these end groups may be formed from at least three different mechanisms. The first involves an allylic C-H activation of propylene, the second, a /1-methyl elimination, and the third, a /1-hydrogen elimination from a polymer chain in which the monomer inserts in a 2,1 fashion [69]. Since in the... 

Parker [4] end-group functionalized poly(1,3-butadiene) polymers with isopropyl hydroxyl-amines to improve the affinity and interaction with carbon black and silica fillers to extend tire lifetime. 

In agreement with this mechanism terminal groupings (methyl from polyethylene and isopropyl from polypropene) increase in concentration. When deuterium is used the end groups are CH2D [34] and with tritium two atoms per molecule have been found one from initiation by the metal hydride bond and the other on chain transfer [82]. 

Figure 3-6. The configuration of heptamers of propylene, each having one isopropyl and one isobutyl end group. The molecule has two equal end groups with respect to configurational analysis (structural analysis), but not with respect to the polymerization (process analysis). The configuration is given in the Fischer projection (see below). The arrows point to pseudoasym-metric carbon atoms. R and S are used in the sense as defined by organic chemistry configurational analysis.

The thiocarbonylthio and trithiocarbonate end groups which result from RAFT polymerization can also be converted to hydrogen-terminated polymer in the presence of a free-radical reducing agent, composed of a free-radical source and a hydrogen atom donor. Examples of free-radical reducing agents include tributylstannane, tris(trimethylsilyl)silane, hypophosphite salts, and isopropyl alcohol. ... 

HU2 Huber, S., Hutter, N., and Jordan, R., Effect of end group polarity upon the lower critical solution temperature of poly(2-isopropyl-2-oxazoline). Colloid Polym. Sci., 286, 1653,2008.1... 

Similar architectures have also been developed by Schubert and coauthors. Their stimuli-responsive systems relied on metal-ligand interactions between a divalent metal such as Fe " " or Zn + with the 2,2 6, 2"-terpyridine (tpy) moiety, attached as an end-group to a poly(A-isopropyl-acrylamide) backbone (13, Figure 22). 

The first step of the coordination-insertion mechanism (I) consists of the coordination of the monomer to the Lewis-acidic metal center (Fig. 3.7). The monomer subsequently inserts into one of the aluminum-alkoxide bonds via nucleophilic addition of the alkoxy group on the carbonyl carbon (11) followed by ring opening via acyl-oxygen cleavage (1) hydrolysis of the active metal-alkoxide bond leads to the formation of a hydroxyl end group, while the second chain end is capped with an isopropyl ester, as indicated by NMR characterization of the resulting polymers [48]. 

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