Two step prepolymer synthesis

PUc2 A two-step prepolymer synthesis where two moles of DBDI was first... 

Two step prepolymer synthesis where DBDI is first reacted, followed by the addition of MDI. 

The synthesis of the PUc2 polymers involved a two step prepolymer synthesis where the first introduced diisocyanate was DBDI, followed by the distribution of MDI in the prepolymer. The synthesis of PUc3 polymers was achieved similarly, except that the first introduced diisocyanate was MDI, followed by the distribution of DBDI in the prepolymer. 

PUci Single step prepolymer synthesis which used a melt mixture of the two... 

Fig. 4.2 Stress-strain curves during loading at nominal strain-rate 0.0042 s for PUs with PEA as a soft phase. Material C was achieved by using a single step prepolymer synthesis using a melt mixture of the two isocyanates (MDl+DBDl) [280]...

The two copolyurethane elastomers of type C (PU18 (I = 110) and 19 (I = 110) in Table 4.15), containing mixtures of the diisocyanates MDI and DBDI randomly distributed, were synthesized by using a one step prepolymer synthesis where a melt mixture of DBDI and MDI was used in equal molar proportions, which was then introduced into the anhydrous macrodiol [60, 61]. 

Figure 6.3 Two-step polyurethane synthesis. First step prepolymer synthesis from a diisocyanate and a macrodiol. Second step chain extension.

The classical synthetic pathway to prepare polyimides consists of a two-step scheme in which the first step involves polymerization of a soluble and thus processable poly(amic acid) intermediate, followed by a second dehydration step of this prepolymer to yield the final polyimide. This preparative pathway is representative of most of the early aromatic polyimide work and remains the most practical and widely utilized method of polyimide preparation to date. As illustrated in Scheme 4, this approach is based on the reaction of a suitable diamine with a dianhydride in a polar, aprotic solvent such as dimethyl sulfoxide (DMSO), dimethylacetamide (DMAc), dimethylformamide (DMF), or AT-methylpyrrolidone (NMP), generally at ambient temperature, to yield a poly(amic acid). The poly(amic acid) is then cyclized either thermally or chemically in a subsequent step to produce the desired polyimide. This second step will be discussed in more detail in the imidization characteristics section. More specifically, step 1 in the classical two-step synthesis of polyimides... 

Considerable research effort has been devoted in recent years to the use of chloral derivatives for the synthesis of linear heterocyclic polymers. Of these, the most common are aromatic polyimides [1-12], Many of these polymers have been synthesised from compounds like 4,4 -diaminobenzophenone, and other diamines, which, as demonstrated in the previous chapter, can be obtained from chloral. Polyimides prepared from these diamines were largely synthesised by the conventional two-step procedure [11, 12] involving mild reaction of the diamines with the bis(phthalic)anhydrides, isolation of poly(o-carboxy)amide (PCA) prepolymers, and then processing into products followed by thermal or chemical imidisation [13—16] (Scheme 3.1). Some properties of polyimides prepared from 4,4 -diaminobenzophenone are provided in Table 3.1. 

Separately, Gu et al. [46] reported the use of lipases to facilitate the synthesis of a family of polyaminoamides. The polyaminoamides were made by a two-step reaction, where the first step was Michael addition of 1 mole of a polyamine and 2 moles of an acrylic compound to form an amine-containing diester, and the second step was the polymerization of additional polyamine with the resulting diester prepolymer at 70-140 °C or in the presence of an enzyme at 60-80 °C. 

Segmented polyurethanes were synthesized from the a, to diol polyethers listed in Table I and the diisocyanates IV, V, and VI by the two-step process shown in Figure 1 or the three-step process in Figure 2. In all cases, chain extension of isocyanate-terminated prepolymers was accomplished with ethylenediamine. The synthesis took place in a 2 1 (v/v) mixture of dimethyl sulfoxide and 4-methyl-2-pentanone at 60°C. 

Both processes may be carried out in one or two reaction steps, the so-called one-shot process and prepolymer method , respectively (Vermette et al., 2001). In two-step synthesis (Fig. 6.3), an isocyanate end-capped prepolymer is first synthesised through the reaction between a polyol and a diisocyanate then, adding a chain extender that reacts with the residual isocyanate functionality, the chain is extended producing a multi-block copolymer (Lamba et al., 1998 Vermette et al., 2001 ... 

Polyanhydrides have been synthesized by various techniques such as melt polycondensation, ring-opening polymerization, interfacial polycondensation, dehydrochlorination, and dehydrative coupling (13,14). The most widely used technique for polyanhydride synthesis is melt polycondensation, which occurs in two steps. In the first step, dicarboxylic acid monomers react with excess acetic anhydride to form acetyl-terminated anhydride prepolymers (1) with a degree of polymerization (DP) ranging from 1 to 20 (eq. 1). 

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