The Homopolymerization of Monoisocyanates

Shashoua, Victor E.; Sweeny, W.; Tietz, Raymond F.

doi:10.1021/ja01489a026

Cited by 267 publications

(135 citation statements)

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“…12, No. 9,1980 population of active species as the relatively slow initiation process proceeds, and analysed by the plot of Figure 3(b) to yield the ratio of initiation to propagation rate constants, kJ kP r::; 5 x 10-5 at -80°C. It may seem surprising that such a low ratio is still compatible with near quantitative consumption of initiator (I) (shown by the observed near-ideal degree of polymerization P" […”

Section: Polymerizations Initiated By Phosphinesmentioning

confidence: 99%

“…However the earlier-proposed termination reaction in pyridine-initiated polymerizations, namely loss of pyridine to yield either oligomeric rings or chain extended polymers 1 must still be regarded as a possibility at high temperatures, by analogy with the production of cyclic dimers and trimers in the pyridine-initiated polymerization of isocyanates. 9 …”

Section: Mechanismsmentioning

confidence: 99%

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Kinetics and Mechanisms of Zwitterionic Polymerizations of Alkyl Cyanoacrylates

Pepper

1980

Polym J

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ABSTRACT:The paper reviews work in the author's laboratory on the polymerization of alkyl cyanoacrylates, chiefly the butyl ester, in THF, by organic bases, phosphines and amines. It presents evidence that the bases initiate by addition, thus forming zwitterionic propagating species. Polymerizations initiated by Ph3P are confirmed as "living polymerizations," but with relatively slow initiation (e.g., k;/k", x 10-5 at -80°C). Acid-inhibition studies of amine-initiated reactions show that rates of initiation are complex and have negative temperature dependence. This makes unnecessary an earlier postulate that these polymerizations involved a combinationtermination process. A "slow-initiated, non-terminated'' kinetic scheme quantitatively describes polymerizations by pyridine, 4-vinylpyridine, 2,6-lutidine, and benzyldimethylamine, yielding kP values ((2-8) x 10 5 I mol-1 s -I at 20°C) consistent among themselves and with that from the Ph 3 Pinitiated kinetics.KEY WORDSCyanoacrylates I Zwitterions I Phosphines I Tertiary Amines I Slow-Initiated-Non-Terminated Kinetics I When these polymerizations were first reviewed in 1977, 1 the major unsettled questions were seen to be: 1) What is the electrochemical nature of the growing species when the polymerizations are initiated by covalent bases, amines or phosphines? Are they simple anions (with ammonium or phosphonium counter cations), as would follow if initiation somehow (not obviously) involved proton abstraction? Or are they, as expected, genuine zwitterions, formed by addition of the bases to the monomer?2) What explains the striking difference between the overall kinetics of polymerizations initiated by phosphines (which appeared to be near-ideal "living polymerizations," i.e., terminationless) and by amines, which showed a negative temperature coefficient of overall rate, at that time interpreted by the postulate of a highly temperature dependent (combination) termination process.As will be described below, evidence for zwitterion formation has now been provided by spectroscopic demonstration of the presence of phosphonium, pyridinium and carbanion groups in the polymer 2 and by the demonstration that graft copolymers are formed, when polymerization is by poly(vinylpyridine? or poly(styryldiphenylphosphine).4The different overall kinetics of phosphine-and amine-initiated polymerizations can now be reconciled by the conclusion that in neither case is there any intrinsic terminatipn process, and that the differences arise from different complexities in the processes which generate the active species. This conclusion follows from the discovery that, under appropriate conditions in the presence of added strong acids, amine-initiated polymerizations showed clear-cut inhibition periods, from which the rates of chain-initiation could be deduced. These are found to have a negative temperature coefficient capable of explaining that of the overall rates, i.e., permit evaluation of the concentration of active species, and hence of propagation rate constants, virtually iden...

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Section: Polymerizations Initiated By Phosphinesmentioning

confidence: 99%

Section: Mechanismsmentioning

confidence: 99%

Kinetics and Mechanisms of Zwitterionic Polymerizations of Alkyl Cyanoacrylates

Pepper

1980

Polym J

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“…The chemical and thermal instabilities of polyisocyanates have been pointed out since the discovery of these polymers by Shashoua et al 10 When polyisocyanates stand at room temperature in N,N-dimethylformamide containing sodium cyanide, the polymer undergoes depolymerization to give cyclic trimers. 10 The unfavorable stabilities of polyisocyanates restrict their utilization, in spite their interesting characteristics.…”

mentioning

confidence: 99%

“…10 The unfavorable stabilities of polyisocyanates restrict their utilization, in spite their interesting characteristics. One mechanism 11 proposed for the depolymerization of the PHIC is the back-biting reaction, shown in Scheme 1.…”

mentioning

confidence: 99%

Preparation of α-, ω-End-Functionalized Poly(n-hexyl isocyanate) Heterotelechelics

Lien

Kikuchi

Narumi

et al. 2008

Polym J

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“…of impairing the structure by removing constitutional hydroxyls and this especially may take place when the dehydration occurs under vacuum. Con-303 versely, if the mineral has not been properly dehydrated, the presence of water will cause hydrolysis of the isocyanate with urea formation (Cram and Hammond, 1964), and possibly a polycondensation of the organic compound (Shaskova et al, 1960).…”

Section: --Oh + O~-c--n--r ~ O----nh--r Y-and Omentioning

confidence: 99%

The Surface Reactivity of Vermiculite Towards Hexamethylene Diisocyanate (HMDI)

Siffert¹

1976

Clays and clay miner.

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Abstract--The reaction of hexamethylene diisocyanate with the surface of heat-activatecl vermlcunte parallels the reactions with the oxides SiO2, A1203, MgO considered individually, which a number of authors have already described. The fixation ratio is about 5 molecules per 100 A 2 area. Nearly one half of the grafted molecules retain a "free" isocyanate function, which is requisite for a subsequent polyaddition of the processed mineral. The interaction with vermiculite occurs according to three principal processes; (i) formation of a surface urethane, (ii) formation of a surface carbamate, (iii) fixation by hydrogen bonds.

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The Homopolymerization of Monoisocyanates

Cited by 267 publications

References 0 publications

Kinetics and Mechanisms of Zwitterionic Polymerizations of Alkyl Cyanoacrylates

Kinetics and Mechanisms of Zwitterionic Polymerizations of Alkyl Cyanoacrylates

Preparation of α-, ω-End-Functionalized Poly(n-hexyl isocyanate) Heterotelechelics

The Surface Reactivity of Vermiculite Towards Hexamethylene Diisocyanate (HMDI)

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