DBTDL as catalyst

Secondly, the reaction was inhibited by both strong and weak acids. Strong acids, such as HBF4, completely stopped the reaction. Weaker acids, snch as acetic acid, had a much less pronounced and concentration-dependent effect. It has been snggested that the concept of the ionic mechanism mnst be viewed with some degree of caution, since the reaction proceeded faster in non-polar solvents, snch as cyclohexane, compared with a dipolar aprotic solvent, snch as dimethylformamide, whereas one wonld expect that the polarity of the solvent wonld significantly stabilize the ionic catalyst intermediates. However, Urban et al. have demonstrated that an ionic mechanism is likely operative in the reaction of hexamethylene diisocyanate with an acrylic polyol, nsing DBTDL as catalyst. 

The effect of type of catalyst on the reactivity of phenol and benzyl alcohol with phenyl isocyanate can be seen in Table III. In the case of tertiary amine (DMCHA), there is a relatively small difference in the reactivity of both the phenol and benzyl alcohol with phenyl isocyanate. Using DBTDL as catalyst, benzyl alcohol was found to be 26 times more reactive than phenol in the reaction with phenyl isocyanate. 

With respect to IPDI, it should be noted that with DBTDL as catalyst the secondary isocyanate is approximately 10-20 times more reactive than the primary isocyanate. With a tertiary amine as catalyst, however, the primary isocyanate is about five times more reactive than the secondary isocyanate. 

Figure 12 shows the preparation scheme of polycaprolactone derivatives (CAPCL s) based on cellulose acetate (CA). As shown in the scheme, CAPCL s were synthesized from cellulose acetate by reaction with e-caprolactone by using dibutyltin dilaurate (DBTDL) as catalyst. 

Triethylenediamine (DABCO) and dibutyltin dilaurate (DBTDL) have been used as catalysts with concentrations of 0.25 and 0.06Z (w/w) on binder, respectively. 

Spindler and Frechet used 3,5-bis((benzoxy-carbonyl)imino)benzyl alcohol which decomposed thermally in THF solution containing DBTDL as a catalyst [97]. The resulting polymer was found to be insoluble unless an end-capping alcohol was added from the beginning. The end-capping groups determined the properties of the polymers such as glass transition temperature, thermal stability, and solubility. 

As an example, the temperature rise for the formation of a polyurethane by reaction of a polymethylenpolyphenyl isocyanate (average functionality = 2.7), with a polyfunctional polyol based on sorbitol, using dibutyltin dilaurate (DBTDL) as a catalyst, is shown in Fig. 5.19 for two different catalyst concentrations (Marciano et al., 1982). 

Table 6.2.8 Potlife of high solids polyester/HDI trimer with DBTDL as a catalyst and 2,4-pentanedione as a stabilizer ...

Phenol blocked isocyanates also have been used to prepare hyperbranched polyurethanes by a step-growth polycondensation mechanism, using DBTDL as a catalyst. 4... 

Materials. The polyurethane precursor materials were Adiprene L-lOO (Uniroyal, Inc.), a poly(oxytetramethylene glycol) capped with toluene diisocyanate, eq. mol. wt. 1030 1,4-butanediol (BD) and 1,1,1-trimethylolpropane (TMP) and, as catalyst, dibutyltin dilaurate (DBTDL). Acrylic precursors included n-butyl methacrylate (BMA), washed with 10% aq. NaOH to remove inhibitor tetramethylene glycol dimethacrylate (TMGDM) crosslinker and benzoin sec-butyl ether (BBE) as a photosensitizer. These materials were dried appropriately but not otherwise purified. 

DBTDL, based on the total sample weight, and 0.1 A BBE, based on the weight of the BNA, were used as catalysts. 

With DBTDL as a catalyst, the replacement of a non-activated alcohol (1 or 2-butanol) by an activated one (A, B, or C) has a depressive kinetic effect. Surprisingly, the same behavior is not observed when 1-butanol is substituted by 6-dimethylaminoethanol. This apparent contradiction can be explained by the coordination of the amine instead of the isocyanate. Two arguments can be forwarded that are in favor of this hypothesis. 

The first polyurethane obtained by FP has been derived by the reaction between 1,6-hexamethylene diisocyanate (HDI) and ethylene glycol (EG) in the presence of dibutyltin dilaurate (DBTDL) as a catalyst, and pyrocatechol as an additive necessary for ensuring a sufficiently long pot-life (25). Indeed, if this latter compound is not present, instantaneous SP occurs. Furthermore, fingering was avoided by adding 3 wt.-% fumed silica (Cabosil ) to the above components dissolved in 18 wt.-% dimethylsulfoxide (DMSO). 

Samples FI-3 have been synthesized by using different amounts of DBTDL. As already mentioned, the larger the catalyst content is, the higher Tmax Is. Besides, it is noteworthy that intrinsic viscosity increases as well. Namely, FP3 sample is characterized by [r ] = 0.76 dl/g, that is the larger value found in this work (19). 

The gels are produced from a mixture of TMOS, water, and solvent (Table 1) without catalyst and with dibutyl tin dilaurate (DBTDL), W-methylimidazole (NMIM), or HCl as catalyst. 

Mesua ferrea L. seed oil-based polyurethane (PU) resins, poly(urethane ester) (PUE) and poly(urethane amide) (PUA) with varying NCO/OH ratios have been prepared using the one shot process in the presence of DBTDL as a catalyst. Monoglyceride of the oil is used for poly(urethane... 

The analogous thiopolyurethanes with the side tolylmethylthiomethyl or naphthylmethylthiomethyl chains (306) were obtained from 2-(p-tolylmethylthiomethyl)-l,4-butanediol (TB) or 2-(l-naphthylmethylthiomethyl)-1,4-butanediol and HDI or Izocyn T-80 [TDI-80, the mixture of 2,4-TDI (80 wt%) and 2,6-TDI (20 wt%)] by solution (benzene) polymerization in the presence of di-n-butyltin dilaurate (DBTDL) [77-58-7] as catalyst. The polymer based on TB and HDI (ijred = 117 dL/g) was a high elasticity thermoplastic elastomer with tensile strength of 2.2 MPa and elongation at break of 780%. 

The previuosly described 4 Cla pseudo[2]rotaxane (Fig. 30.3) was the ideal candidate to attempt the synthesis of a calix-threaded [2]catenane by a [1 +1] cyclocondensation clipping with the appropriate diisocyanate derivative 26 (Scheme 30.13). Therefore, pseudo[2]rotaxane 4 cla, previously formed in dry CHCI3 (starting from a 6 x 10 M initial concentration of each precursor), and diisocyanate 3b (6 x 10 M in dry CHCI3) were added, at a rate of 0.6 mL/min from two distinct dropping reservoirs, to 2.0 mL of dry CHCI3 under stirring in the presence of dibutyltin dilaurate (DBTDL) as the catalyst. Under these conditions... 

Figures 20.13 and 20.14 describe the effect of dibutyltin dilaurate (DBTDL) on the tensile strength and tensile modulus for the 25/75 LCP/PEN blend fibers at draw ratios of 10 and 20 [13]. As expected, the addition of DBTDL slightly enhances the mechanical properties of the blends up to ca. 500 ppm of DBTDL. The optimum quantity of DBTDL seems to be about 500 ppm at a draw ratio of 20. However, the mechanical properties deteriorate when the concentration of catalyst exceeds this optimum level. From the previous relationships between the rheological properties and the mechanical properties, it can be discerned that the interfacial adhesion and the compatibility between the two phases, PEN and LCP, were enhanced. Hence, DBTDL can be used as a catalyst to achieve reactive compatibility in this blend system. This suggests the possibility of improving the interfacial adhesion between the immiscible polymer blends containing the LCP by reactive extrusion processing with a very short residence time.

Figure 2. Dynamic mechanical properties for the M-B-23/25-48 series as a function of catalyst concentration. %DBTDL x 1000 , 05 , 30 , 75.

It was also demonstrated that reaction of 6 with ethanol leads cleanly to methyl M-phenylcarbamate and tribntyltin ethoxide (Fignre 6.2.6). There is no report of any cross-over products. Others have argued that mixed carboxylate/alkoxides such as 7 are the active species, but it was admitted that the carboxylate had a higher affinity for tin than alkoxide and thus formation of the critical first catalytic intermediate in the process is not favorable. Indeed, NMR was used to measure an equilibrium constant of 8.3 x 10 for exchange of 2-propanol into di-n-butyltin dilaurate (DBTDL) (Ki of Figure 6.2.7). But at the extremely high hydroxyl/catalyst ratios observed in real systems, this can result in a significant conversion of the catalyst to the first intermediate proposed in the insertion mechanism. 

Wicks has reviewed the various reaction mechanisms with blocked isocyanates. There are two general mechanisms (addition-elimination and elimination-addition) by which the blocked isocyanate reacts with a hydroxyl compound (Figure 6.2.11, A and B). It is possible that a particular type of blocked isocyanate can function by either mechanism, depending on such factors as the type of blocking group, type of hydroxyl compound, temperature, and the polarity of the solvent. Tin catalysts such as DBTDL are often included in such formulations, but higher concentrations are required than in reactions with isocyanates and the role of the catalyst is not always well defined. 

DBTDL was used as a catalyst in the frontal polymerization of 1,6-hexanediisocyanate with ethylene glycol. In frontal polymerization the polymerization is locally initiated and the exotherm of the reaction propagates the polymerization throughout the system. Pyrocatechol was used to avoid spontaneous polymerization. Pyrocatechol chelates tin and depresses the catalytic activity at room temperature without affecting catalysis at the higher temperature. To achieve a uniform advancing reactive front, and to avoid fingering, the viscosity of the blend was increased with colloidal silica. 

Di-n-butyltin catalysts are being used in the preparation of polyurethane foams. Most polyurethane foams utilize aromatic isocyanates such as toluene diisocyanate (TDI) or diphenylmethane diisocyanate (MDI) as the isocyanate, and a polyester or polyether polyols as the coreactant. Tertiary amine catalysts are used to accelerate the reaction with water and formation of the carbon dioxide blowing agent. To achieve a controlled rate of reaction with the polyol, an organotin catalyst can be used. Polyurethane foams are not only applied in place, but are also cast in a factory as slabstocks. These foam slabs are then cut for use in car seats, mattresses, or home furnishings. DBTDL is an excellent catalyst in high resiliency slabstock foams. DBTDL shows an excellent reaction profile for this application replacement for DBTDL in such an end-use is difficult and requires a substantial reformulation of the foam. 

---