A study of intramolecular reaction during linear polyurethane formation

Abstract

Eingegangen a m 6. Mai 1971) S U M M A R Y :The numbers of rings formed in the reactions of hexamethytenc diisocyanate with two polyethylene glycols have been determined as a function of dilution and ratios of reactants. I n this work the cryoscopic apparatus developed in the preceding paper has been utilised. It is found that more rings are formed (a) in dilute solutions, (b) with reactants of lower molecular weight, and (c) in reactions at equimolar concentrations. Some of the results may be interpreted approximately by means of JACOBSON and STOCKMAYER'S theory. Values of the FLORY-I~UGCINS' interaction parameter x have been determined from the cryoscopic data. They show a very marked dependence on the density of hydroxyl groups in the chain. Z U S AMM E N F A S S U N G : Die Anzahl der sich bci Reaktionen von I-iexamethylendiisocyanat rnit zwei Polyathylenglykolen bildenden Ringe wurde als Funktion der Verdiinnung und der Verhiiltnisse der Rcaktionspartncr bestimmt. Die im vorhcgehenden Bericht beschriebene Kryoskopie-Apparatur wurde bci dieser Arbeit benutzt. Es wird gefunden, daO sich mehr Ringe bilden: (a) bei verdunnten Losungen, (b) bei Reaktiouspartnern niedrigeren Molekulargewichts, (c) bei Reaktionen mit iiquimolaren Konzentrationen. Einige dieser Rcsultate konnen mit Hilfe der Theorie von J A C O~S O N und STOCKMAYER anniihernd interpretiert werden. Werte fur die hoRY-HuccINsschen Interaktionsparameter x wurden mit IIilfe der kryoskopischenDaten berechnet. Sie wcisen eine sehr deutliche Abhiingigkeit von der Dichte der Hydroxylgruppen in der Kette auf.

Polycondensation of ‘a − bn’ or ‘a2 + + bn’ Monomers ‐ A Comparison

“…Such a differentiation and characterization is useful for any kind of chemical reaction and it came into play for step-growth polymerizations when Jacobson and Stockmayer [78,79] published their studies of ring-chain equilibria and ring-formation by back-biting degradation. About thirty years ago a computer-supported speculative simulation of irreversible step-growth kinetics let Stepto et al [80,81] and Gordon and Temple [82,83] conclude that at least at low or moderate concentrations cyclization competes with each growing step. However, the lack of experimental evidence hindered a broader acceptance of this new polycondensation theory by the international community of polymer chemistry.…”

Approximate theories of gelation

“…Cex t Cex t ' N However, if this assumption is not equation [7] can be rearranged to give [12] made,…”

“…In addition, measured values of a~ are always greater (2)(3)(4)(5)(7)(8)(9)(10) than the value of 0c-1) -1 predicted by equation [1]. The measurement of pre-gel intramolecular reaction (11) as N~, the number fraction of ring structures at given extents of reaction, is difficult experimentally (11,12), but the measurement of a c is relatively simple (13), and most of the experimental data available on pre-get intramolecular reaction relate to a c.…”

The Role of Self‐Dilution in Step‐Growth Polymerizations

“…Further studies in this direction were summarized in two review articles. [9,10] Between 1970 and 1980 Stepto and coworkers, [11,12] and Gordon and coworkers [13,14] conducted speculative calculations of the kinetics of step-growth polymerizations assuming that cyclization competes with each chain-growth step. Those authors also concluded that 100% conversion should yield 100% of cyclic reaction products.…”