Isocyanate–catalyst and hydroxyl–catalyst complex formation

Reegen, S. L.; Frisch, K. C.

doi:10.1002/pol.1970.150081014

Cited by 41 publications

(20 citation statements)

References 9 publications

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“…It is commonly accepted that urethane formation results from the activation of one or both reactants (isocyanate and hydrogen‐containing compound) by a species that contains the metal center. Of two possible reaction paths, one is a Lewis acid mechanism in which the isocyanate is firstly activated by coordination to the metal via oxygen or nitrogen atom44, 45 followed by the nucleophilic attack of the hydroxyl group from the alcohol;46 the other is the prior activation of the alcohol by the metal catalyst, followed by the complexation to the isocyanate 47…”

Section: Resultsmentioning

confidence: 99%

Synthesis, characterization and thermal dissociation of 2‐butoxyethanol‐blocked diisocyanates and their use in the synthesis of isocyanate‐terminated prepolymers

Ahmad

Zaidi

Hussain

et al. 2007

Polymer International

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A series of blocked diisocyanates has been synthesized from toluene diisocyante (TDI), isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), 4,4′‐diphenylmethane diisocyanate (MDI) and 2‐butoxyethanol. The synthesis of blocked diisocyanate adducts was confirmed by Fourier transform infrared, 1H NMR, electron impact mass spectrometry and nitrogen analysis. Differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA) and carbon dioxide evolution were used to determine the minimum de‐blocking temperatures. De‐blocking temperatures determined by these three techniques were found to be in the order DSC > TGA > CO2 evolution. The effect of different metal catalysts on thermal de‐blocking reaction of the blocked diisocyanates was studied, using the carbon dioxide evolution method. It was found that iron(III) oxide has the maximum catalytic activity on de‐blocking. The solubility of the blocked diisocyanate adducts was determined in different solvents. The study revealed that at 30 °C blocked IPDI and HDI adducts show better solubility than adducts based on TDI and MDI. Isocyanate‐terminated prepolymers of blocked diisocyanates and hydroxyl‐terminated polybutadiene (HTPB) were prepared. The storage stability and gelation times of the prepolymers were studied. Results showed that all the diisocyanate‐HTPB compositions are stable at 50 °C for more than three months. However, aliphatic diisocyanate‐HTPB compositions require greater gelation time than aromatic diisocyanate‐HTPB compositions at their respective de‐blocking temperatures. Copyright © 2007 Society of Chemical Industry

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Section: Resultsmentioning

confidence: 99%

Synthesis, characterization and thermal dissociation of 2‐butoxyethanol‐blocked diisocyanates and their use in the synthesis of isocyanate‐terminated prepolymers

Ahmad

Zaidi

Hussain

et al. 2007

Polymer International

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“…For four series of reactions with different reagent concentrations, we have log R 04 ϭ log k ϩ nЈ log͓NCO͔ 04 ϩ hЈ log͓OH͔ 04 ϩ d log͓DBTDL͔ 04 (19) log R 05 ϭ log k ϩ nЈ log͓NCO͔ 05 ϩ hЈ log͓OH͔ 05 ϩ d log͓DBTDL͔ 05 (20) log R 06 ϭ log k ϩ nЈ log͓NCO͔ 06 ϩ hЈ log͓OH͔ 06 ϩ d log͓DBTDL͔ 06 (21) log R 07 ϭ log k ϩ nЈ log͓NCO͔ 07 ϩ hЈ log͓OH͔ 07 ϩ d log͓DBTDL͔ 07 (22) In this experiment, four series of reaction conditions, as shown in (k ϭ 1, 2) are known, after determining the initial reaction rates R 01 , R 02 , and R 03 , and R 04 , reaction orders h', n', and d can be computed. Following the same method as that developed for the study of a noncatalyzed system, the NCO concentration changes as a function of reaction time for each reaction system was measured, and [NCO] as a function of time (Figure 4) was determined.…”

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confidence: 99%

Kinetics and mechanisms of catalyzed and noncatalyzed reactions of OH and NCO in acrylic polyol–1,6‐hexamethylene diisocyanate (HDI) polyurethanes. VI

Han

Urban

2002

J of Applied Polymer Sci

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Fourier transform infrared spectroscopy was used to study the kinetics of noncatalyzed and catalyzed polyurethanes. These studies show that for noncatalyzed acrylic polyol-hexamethylene diisocyanate (HDI) trimer reactions, the reactions between OH and NCO of HDI exhibit second-order kinetics, with first-order kinetics with respect to NCO and OH. On the other hand, when dibutyltin dilaurate (DBTDL) is used as a catalyst in acrylic polyol-HDI trimer reactions, the reaction rate is first order with respect to NCO and 0.5 order in OH and DBTDL concentrations. A mechanism for the catalyzed acrylic polyol-HDI trimer crosslinking reactions is proposed and it appears that an equilibrium involving associations between OH and DBTDL exists, resulting in the formation of an active anion, which interacts with NCO to generate polyurethanes. To further verify this mechanism, the influence of acidity on the reaction rate constant was investigated. When the acidity of the system is increased, retardation of urethane formation occurs.

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“…It was later found that metals can complex with isocyanate,27, 29–33 with alcohol,27, 32, 34–39 and with both isocyanate and alcohol 27, 28, 31. For example, Reegen and Frisch,32 who were studying isocyanate–DBTDL and 1‐methoxy‐2‐propanol–DBTDL complex formation in benzene solutions, concluded that DBTDL could complex with both isocyanate and alcohol, the fraction of the catalyst involved in the isocyanate complexes being significantly larger (40–50% of the DBTDL molecules being tied up in those complexes) than in complexes with alcohol (13–21% of the DBTDL molecules). They postulated the structure of the binary tin complex with 1‐methoxy‐2‐propanol, isocyanate, and bridge‐type ternary complexes of various structures.…”

Section: Resultsmentioning

confidence: 99%

Brachytherapy in total coronary occlusions: Quidquid agis, prudenter agas, et respice finem

Hehrlein¹

2003

Cathet Cardio Intervent

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In the study by Jain et al. presented in this issue, vascular brachytherapy was performed, applying a betaradiation source (BetaCath TM) to reduce restenosis rates after PTCA of chronic total occlusions (CTOs). The outcome of radiotherapy after percutaneous revascularization of 82 CTOs were analyzed from the RENO registry database, which contains 1,098 consecutive patients undergoing brachytherapy. The results were comparable with those known for brachytherapy of nonocclusive in-stent restenosis with respect to prevention of new restenosis. Why is this finding remarkable?It has become general knowledge that treating chronic coronary occlusions by conventional PTCA is a "different animal" compared with PTCA of plain coronary artery stenosis [1]. Many studies have shown that restenosis rates are extremely high in patients with CTO, even when stenting is performed [2]. Some institutions leave treatment of symptomatic CTOs primarily to the cardiac surgeon. Revascularization of CTO is favorable over medical treatment at least when treated surgically [3]. Therefore, it is important to realize from the report by Jain et al. that restenosis rates of PTCA in CTO have been reduced dramatically using vascular brachytherapy. However, there is the problem of thrombotic vessel occlusion increasing MACE rates, which needs to be understood and acted on. Brachytherapy was plagued from the beginning with the occurrence of late and "late late" thrombosis [4]. Yet only half of all patients of the RENO registry were kept on the combined antiplatelet therapy of aspirin and clopidogrel for a period of 6 months. In addition, new stents were implanted, which tended to reocclude the coronary arteries. What are the lessons we learn from this report? In the words of Gesta Romanorum: "Quidquid agis, prudenter agas, et respice finem." Whatever you do, do it thoughtfully, and kept in mind the goal.Brachytherapy of chronic coronary occlusions requires special attention to the increased risk of thrombotic vessel occlusion. Potential means for reducing the risks of MACE are as follows: apply aspirin and clopidogrel for a minimum period of 12 months (perhaps as lifelong addition of clopidogrel to aspirin medication); use a minimum of new stents to reduce foreign-body activation of platelets; study an increased loading and maintenance dose of clopidogrel in a randomized fashion in the setting of CTO; and, most importantly, remember that CTO patents only benefit from revascularization if viable myocardium is present [5].Mixed results were obtained by other investigators in two recent studies applying brachytherapy in CTO. One group reported similar efficacy and complication rates with intracoronary brachytherapy of occluded in-stent restenosis using a gamma-emitter (Ir-192) compared with irradiation for nonocclusive in-stent restenosis [6]. The other group, however, clearly pointed out that radiotherapy of total occlusions from in-stent restenosis causes increased MACE rates compared with brachytherapy of plain in-stent restenosis [7]. In summary, m...

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Isocyanate–catalyst and hydroxyl–catalyst complex formation

Cited by 41 publications

References 9 publications

Synthesis, characterization and thermal dissociation of 2‐butoxyethanol‐blocked diisocyanates and their use in the synthesis of isocyanate‐terminated prepolymers

Synthesis, characterization and thermal dissociation of 2‐butoxyethanol‐blocked diisocyanates and their use in the synthesis of isocyanate‐terminated prepolymers

Kinetics and mechanisms of catalyzed and noncatalyzed reactions of OH and NCO in acrylic polyol–1,6‐hexamethylene diisocyanate (HDI) polyurethanes. VI

Brachytherapy in total coronary occlusions: Quidquid agis, prudenter agas, et respice finem

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