Diol prepolymer

Both TDI/MOCA and MDI/diol prepolymer systems are of importance for harder grades of printer s rollers and the wear-resisting applications such as pipes, pumps and impellers used in the mining and quarrying industries. 

An especially interesting degradation is that of polymer 2.33 (This polymer was synthesized by the route in equation 8. The isocyanate prepolymer is Hypol 2000, and the diol prepolymer is PEG-1000.) The solid polymer was readily degraded by ambient laboratory light over the course of 5 h, and as degradation occurred the solid polymer was converted back into the liquid prepolymers ... 

Prepolymers of polybutadiene diol (M. 2500), polytetramethylene oxide diol (M. 1400 and M. 2100), and prepolymer of polypropylene oxide diol (M. 1400) were used to obtain segmented elastomers SPU-1 to SPU-5. Prepolymers were prepared by reaction of appropriate diol with 2,4-toluene diisocyanate (2 moles per one mole of diol). Prepolymers of polytetramethylene oxide diol (elastomers SPU-1 and SPU-4) were cured by methylene-bis-o-chloroaniline, MOCA, or by mixture of MOCA and polytetramethylene oxide diol (SPU-2 and SPU-3). SPU-5 samples, prepared from prepolymer of polypropylene oxide diol, were cured by MOCA, and prepolymer of polybutadiene diol was cured by a mixture of MOCA and polytetramethylene oxide diol (SPU-6). Various concentrations of hard segments, Cj, in SPU were set by a ratio of mixture components and molecular weight of prepolymer (Table 10.14). Excess of NCO-groups was in the range 1.03-1.06 for SPU-1 to SPU-5 and 0.99 for SPU-6. All samples were cured at 80°C for 4 days. The... 

Figure 9J2 Elastomer stress/strain curves (6% NCO MDI/4000-MW diol prepolymers BDO cured)...

Urethane/urea chemistry has evolved and transformed to offer convenient and effective tools for the modification of biomaterials, providing them with desirable properties for biomedical applications. The efforts described above have produced an array of multifunctional urethane/urea chemistry-based biomaterials to meet the specific requirements of each application. A collection of citric acid-based PUs has been developed with tunable mechanical, degradation, photoluminescent, and biomedical properties. The CABE platform technology enables easy modulation of their unique properties by simply altering the ratios of diols, prepolymers, and other additive(s) and... 

Flexible or rigid depending mainly on branched structure of diol Prepolymer or one-shot ... 

Following this work, the y -12F-diol was used for the direct reaction with hexamethylene-1,6-diisocyanate in the presence of dibutyltin dilaurate to produce a cross-linked elastomer or a reactive prepolymer which was terminated with either isocyanate or hydroxyl groups, depending on which reactant was in excess (142,143). 

Polyurethane adhesives are known for excellent adhesion, flexibihty, toughness, high cohesive strength, and fast cure rates. Polyurethane adhesives rely on the curing of multifunctional isocyanate-terrninated prepolymers with moisture or on the reaction with the substrate, eg, wood and ceUulosic fibers. Two-component adhesives consist of an isocyanate prepolymer, which is cured with low equivalent weight diols, polyols, diamines, or polyamines. Such systems can be used neat or as solution. The two components are kept separately before apphcation. Two-component polyurethane systems are also used as hot-melt adhesives. 

Step-Growth Gopolymerization. A sample of a block copolymer prepared by condensation polymerisation is shown in equation 30 (37). In this process, a prepolymer diol (HO—Z—OH) is capped with isocyanate end groups and chain extended with a low molecular-weight diol (HO—E—OH) to give a so-called segmented block copolymer, containing polyurethane hard blocks and O—Z—O soft blocks. 

The secondary hydroxyl groups of these poly(oxypropylene) glycol diols are less reactive than the primary hydroxyl groups of the earlier polyesters. At the time of the introduction of these polyethers, the catalysts then available were insufficiently powerful for one-shot processes to be practical and so these polymers have been used primarily in prepolymer processes. 

In a second step, the prepolymer was then reacted with a low molecular weight difunctional alcohol, commonly referred to as a diol or a diamine, to connect the prepolymer oligomers into a high molecular weight polyurethane. This step was referred to as the chain extension , resulting in the use of the term chain extenders to describe the low molecular weight diols or diamines that reacted with the prepolymer oligomers. 

Polyester polyurethanes are usually based on a blend of a quasi-prepolymer (polyester/MDl) and a diol/polyester suitable for spray-up operation. An alternative is to use a solvent-containing system using blocked curatives to give an extended pot-life of 2 to 3 hours enabling them to be brush, roller or spray applied. 

Polyether polyurethanes are often based on a quasi prepolymer/diol blend reacted with a carbodiimide modified M.D.I. suitable for automatic mix-dispensers. 

For the preparation of the prepolymer, a mixture corresponding typically to mole ratios of diol unsaturated acid saturated acid of 3.3 2 1 is polymerised by stirring the ingredients together at elevated temperatures, normally 150-200 °C. The slight excess of diol is to allow for possible evaporation... 

To prepare crosslinked material, 2 eq of the diketene acetal is reacted with 1 eq of the diol and the resulting prepolymer is then reacted with a triol or a mixture of diols and triols. 

A ketene acetal-terminated prepolymer was first prepared from 2 eq of the diketene acetal 3,9-bis(ethylidene-2,4,8,10-tetraoxaspiro-[5,5]undecane) and 1 eq of the diol 3-raethyl-l,5-pentanediol and. then 30 wt% levonorgestrel, 7 wt% Mg(OH)2j and a 30 mole% excess of 1,2,6-hexanetriol mixed into the prepolymer. This mixture was then extruded into rods and cured. Erosion and drug release from these devices was studied by implanting the rod-shaped devices subcutaneously into rabbits, explanting at various time intervals, and measuring weight loss and residual drug (15). 

To obtain the polyurethanes, typically a prepolymer was first prepared by reacting the diisocyanate with various diols in dimethylformamide or dimethylacetamide in a two to one molar ratio at 100-110°C for two hours under nitrogen atmosphere. A solution of chain extenders, such as BEP, was then added to the prepolymer reaction mixture and further reacted another three hours. The polymer was isolated by quenching the reaction mixture in cold water. Fine white powder was obtained with a typical yield of around 90%. 

The above prepolymer on treatment with 2 as the chain extender in dry DMF did not proceed at ambient temperature. The mixture had to be heated to 60°C for 3 h before the reaction was complete. After curing at 60°C for 24 h, the yellow, translucent block polyurethane film (BPUR2) again showed the absence of the —NCO peak in the IR spectrum indicating that curing had been complete. The fact that a higher temperature had to be used in the case of 2 as the chain extender compared to 1 is in keeping with the lower order of reactivity of diols with diisocyanates as compared to diamines with diisocyanates. 

We can make polyurethanes via one- or two-step operations. In the single-stage process, diols and isocyanates react directly to form polymers. If we wish to make thermoplastic linear polymers, we use only diisocyanates. When thermosets are required, we use a mixture of diisocyanates and tri- or polyisocyanates residues of the latter becoming crosslinks between chains. In the first step of the two-stage process, we make oligomers known as prepolymers, which are terminated either by isocyanate or hydroxyl groups. Polymers are formed in the second step, when the isocyanate terminated prepolymers react with diol chain extenders, or the hydroxyl terminated prepolymers react with di- or polyisocyanates. 

---