“…Low-molecular-weight samples of PIB ( M n 960−3400) were therefore obtained in CH 2 Cl 2 at −50 °C by initiation with Cp*TiMe 2 (μ-Me)B(C 6 F 5 ) 3 followed by immediate termination with methanol. We show in Figure the structural features anticipated for PIB formed via carbocationic processes and the approximate 1 H and 13 C chemical shifts reported previously in the literature, , and in Table the chemical shifts and assignments of all resonances observed here. 2 …”
Section: Resultssupporting
confidence: 67%
“…A 13 C{ 1 H} spectrum of low-molecular-weight polymer exhibited the anticipated strong main chain butyl resonances at δ 31.46, 38.2, and 59.66 and also resonances corresponding to the tert -butyl groups at δ 32.58 (br, tert- butyl Me group) and the “tail” olefinic end group at δ 114.5 and 143.0 (CH 2 and quaternary C in PIB−(CH 3 ) C CH 2 ). The resonances at δ 25.94 and 29.5 were assigned to methyl groups next to the “tail” end group in PIBC( C H 3 ) 2 CH 2 C( C H 3 )CH 2 , while resonances at δ 58.8, 58.3 (CH 2 ) and δ 57.04, 53.75 (CH 2 ) are attributed to secondary carbon atoms situated one and two isobutyl units distance from the “head” and “tail” end groups, respectively . A quaternary 13 C resonance at δ 36.3 is attributable to carbon atoms vicinal to the olefin end group while resonances at δ 37.8−37.92 are attributable to carbon atoms situated in the proximity of both types of end groups 8b…”
Section: Resultsmentioning
confidence: 97%
“…NMR Spectra of the PIB Obtained with Cp*TiMe 2 ( μ -Me)B(C 6 F 5 ) 3 . Polyisobutylene (PIB) is generally formed as a head-to-tail polymer (CH 2 CMe 2 ) n and ignoring end groups, 1 H NMR spectra exhibit two resonances, at δ ∼1.1 (s, 6H, Me) and ∼1.4 (s, 2H, CH 2 ), while 13 C{ 1 H} NMR spectra exhibit three resonances, at δ ∼31 (Me), ∼38 ( tert -C), and ∼60 (CH 2 ), depending on the solvent . As indicated in the Experimental Section, the samples of PIB obtained were readily characterized by these criteria.…”
Section: Resultsmentioning
confidence: 99%
“…All the polymers formed were characterized using gel permeation chromatography, the GPC chromatograms being obtained at room temperature in THF and calibrated using polystyrene standards. The polymers were also characterized by 1 H NMR and 13 C{ 1 H} NMR spectroscopy …”
Isobutylene polymerization is initiated by Cp*TiMe2(μ-Me)B(C6F5)3, formed by combining
Cp*TiMe3 and B(C6F5)3 in a 1:1 ratio. The polymerization process exhibits the signature of a carbocationic
mechanism, as molecular weights generally increase with decreasing temperature, polydispersities are
∼2, and polymers contain vinylidene end groups. Initiation probably occurs via η-coordination of a
molecule of monomer to the cationic species [Cp*TiMe2]+, while propagation and chain transfer proceed
as with conventional Lewis acid initiators. Although addition of the proton trap 2,6-di-tert-butylpyridine
does have an adverse effect on polymerization, this is not because traces of possible protic initiators are
being scavenged but rather because the 2,6-di-tert-butylpyridine coordinates to the titanium cation and
inhibits activation of monomer. Further evidence that [Cp*TiMe2]+ behaves as a carbocationic initiator
is that the system induces dimerization of 1,1-diphenylethylene to 1,3,3-triphenyl-3-methylindan and
also the formation of isobutylene−isoprene copolymers (butyl rubber) in which the isoprene is incorporated
via trans-1,4-addition, again typical of conventional initiators. This initiator system is the first
metallocene-based carbocationic initiator system to be discovered, and it also appears to be one of the
more active.
“…Low-molecular-weight samples of PIB ( M n 960−3400) were therefore obtained in CH 2 Cl 2 at −50 °C by initiation with Cp*TiMe 2 (μ-Me)B(C 6 F 5 ) 3 followed by immediate termination with methanol. We show in Figure the structural features anticipated for PIB formed via carbocationic processes and the approximate 1 H and 13 C chemical shifts reported previously in the literature, , and in Table the chemical shifts and assignments of all resonances observed here. 2 …”
Section: Resultssupporting
confidence: 67%
“…A 13 C{ 1 H} spectrum of low-molecular-weight polymer exhibited the anticipated strong main chain butyl resonances at δ 31.46, 38.2, and 59.66 and also resonances corresponding to the tert -butyl groups at δ 32.58 (br, tert- butyl Me group) and the “tail” olefinic end group at δ 114.5 and 143.0 (CH 2 and quaternary C in PIB−(CH 3 ) C CH 2 ). The resonances at δ 25.94 and 29.5 were assigned to methyl groups next to the “tail” end group in PIBC( C H 3 ) 2 CH 2 C( C H 3 )CH 2 , while resonances at δ 58.8, 58.3 (CH 2 ) and δ 57.04, 53.75 (CH 2 ) are attributed to secondary carbon atoms situated one and two isobutyl units distance from the “head” and “tail” end groups, respectively . A quaternary 13 C resonance at δ 36.3 is attributable to carbon atoms vicinal to the olefin end group while resonances at δ 37.8−37.92 are attributable to carbon atoms situated in the proximity of both types of end groups 8b…”
Section: Resultsmentioning
confidence: 97%
“…NMR Spectra of the PIB Obtained with Cp*TiMe 2 ( μ -Me)B(C 6 F 5 ) 3 . Polyisobutylene (PIB) is generally formed as a head-to-tail polymer (CH 2 CMe 2 ) n and ignoring end groups, 1 H NMR spectra exhibit two resonances, at δ ∼1.1 (s, 6H, Me) and ∼1.4 (s, 2H, CH 2 ), while 13 C{ 1 H} NMR spectra exhibit three resonances, at δ ∼31 (Me), ∼38 ( tert -C), and ∼60 (CH 2 ), depending on the solvent . As indicated in the Experimental Section, the samples of PIB obtained were readily characterized by these criteria.…”
Section: Resultsmentioning
confidence: 99%
“…All the polymers formed were characterized using gel permeation chromatography, the GPC chromatograms being obtained at room temperature in THF and calibrated using polystyrene standards. The polymers were also characterized by 1 H NMR and 13 C{ 1 H} NMR spectroscopy …”
Isobutylene polymerization is initiated by Cp*TiMe2(μ-Me)B(C6F5)3, formed by combining
Cp*TiMe3 and B(C6F5)3 in a 1:1 ratio. The polymerization process exhibits the signature of a carbocationic
mechanism, as molecular weights generally increase with decreasing temperature, polydispersities are
∼2, and polymers contain vinylidene end groups. Initiation probably occurs via η-coordination of a
molecule of monomer to the cationic species [Cp*TiMe2]+, while propagation and chain transfer proceed
as with conventional Lewis acid initiators. Although addition of the proton trap 2,6-di-tert-butylpyridine
does have an adverse effect on polymerization, this is not because traces of possible protic initiators are
being scavenged but rather because the 2,6-di-tert-butylpyridine coordinates to the titanium cation and
inhibits activation of monomer. Further evidence that [Cp*TiMe2]+ behaves as a carbocationic initiator
is that the system induces dimerization of 1,1-diphenylethylene to 1,3,3-triphenyl-3-methylindan and
also the formation of isobutylene−isoprene copolymers (butyl rubber) in which the isoprene is incorporated
via trans-1,4-addition, again typical of conventional initiators. This initiator system is the first
metallocene-based carbocationic initiator system to be discovered, and it also appears to be one of the
more active.
“…The initiator residue (CH 3 ) 3 CCH 2 C(CH 3 ) 2 and the CH 2 C(CH 3 ) 2 CH 2 C(CH 3 ) 2 Cl tail group in PIB prepared with TMPCl/TiCl 4 have been identified 28, 29. PNBD obtained by the TMPCl/TiCl 4 system shows the three terminal methyl carbons of the head group (M1) at δ = 32.5, the methylene carbon (Me) at δ = 55.1, and the two adjacent methyl carbons (M2) that produce multiple signals at δ ∼ 29.5 ppm.…”
The rotablator burr rarely becomes trapped within calcified lesions. Manual traction can be ineffective and dangerous. We report a case that illustrates a novel technique involving use of a percutaneous snare in conjunction with partial disassembly of the rotablator device to remove a trapped burr without need for open surgical intervention.
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