Polyurethanes molecular weight characterization

As the reaction proceeds beyond the gel point, the molecular weight of EANCs decreases and the fraction of material in the EANCs increases. The fraction of material in dangling chains passes through a maximum but their molecular weight decreases. Figure 5.5 characterizes the behavior of simple polyurethane systems. 

Urethanes Precursors. Polyurethanes can be produced by the reaction of oligomeric diols with diisocyanates. The properties of the polyurethanes are intimately related to the chemicals contained in the starting materials. Specifically, the molecular weight distribution of the diols and the functionality of the isocyanates affect the properties. We have found SFC useful for characterizing the building blocks of polyurethanes, namely diols and isocyanates. 

SYNTHESIS OF METAL INCORPORATED LOW MOLECULAR WEIGHT POLYURETHANES FROM NOVEL AROMATIC DIOLS, THEIR CHARACTERIZATION AND BACTERICIDAL PROPERTIES... 

In contrast to solvent-based systems, the PUR dispersions (Section 5.4) are characterized by their incombustibility and thus by considerably smoother processing. They are high molecular weight hydroxyl polyurethanes disperged in water. Apart from the physically setting one-component systems, two-component systems are also applied, with component B containing special polyisocyanates that react with the -O-H-groups of the hydroxyl polyurethane in aqueous solution. 

J/n < 6,000). Often, no analytical data or structural characterization was provided. Room-temperature interfacial polycondensation methods were also investigated as a convenient alternative to classical polycondensations. Such methods were first reported for the preparation of polyamides and polyesters from the reaction of l,l -ferrocenyldi-carbonyl chloride with several diamines and diols. The synthesis of polyurethanes using this technique was also reported and involved the condensation of l,T-ferrocenedimethanol and l,T-bis(dihydroxyethyl)ferrocene with diisocyanates. Once again, however, these polymers possessed low molecular weights.The early research in these areas has been summarized and critically reviewed and will not be discussed further here. ... 

In the 1980s, the successful synthesis of elastomeric polyamides 120 of high molecular weight (d/n =10,000-18,000) was reported from the polycondensation of l,l -bis(/ -aminoethyl)ferrocene with diacid chlorides (Scheme 13). Also, polyureas 121 were prepared from the same ferrocene monomer and diisocyanates, and polyesters and polyurethanes were prepared from l,l -bis(/ -hydroxyethyl)ferrocene. However, the latter materials had much lower molecular weights and were characterized only by scanning electron microscopy. X-ray, and IR analyses. The introduction of ferrocenes in which the functional groups are separated from the cyclopentadienyl ring by at least two methylene units was crucial in order to reduce steric effects and to avoid the instability found previously in polymers of a-functionalized ferrocene due to the a-ferrocenyl carbonium ion stability. 

Ferrocene-containing polymers with long spacers have been prepared as new NLO materials for SHG applications (e.g., frequency doubling).The use of ferrocene derivatives in this area is attractive as a result of their demonstrated large hyperpolarizability values combined with their thermal and photochemical stability. These factors make polyferrocenes desirable candidates for use as processable NLO materials. The polyurethane co-polymer 123 was synthesized using a functional ferrocene monomer (Equation (45)) and was well characterized the molecular weight was estimated by GPC to be = 7,600. The two possible orientations of the ferrocene NLO chromophore monomer unit that correspond to opposite dipole orientations were both present in the main chain. 

In 2001, an efficient step-growth polycondensation approach, reminiscent of that used to prepare metal-metal-bonded polymers 217 and 218, was successfully developed to yield polyurethanes 225 with Mo2lt2 clusters in the backbone. " Well-characterized polymers with molecular weights of up to 136,000 (PDI = 3.1), which correspond to a number average of around 30 clusters per polymer chain, were obtained by means of this method. It involved treatment of a diol of the Mo2lt2 cluster with the diisocyanate OCN-R-NGO (R = aliphatic or aromatic spacer) in the presence of a tin catalyst. The unusual optical properties of organometallic clusters will drive applications-oriented work on these materials. " ... 

Essential details of four graft copolymer samples (25a-25d) thus obtained are given in Table 11. The samples have been briefly examined by sedimentation equilibrium analysis. The molecular weights (M ) obtained by this method are consistent with, but lower than, the expected values recorded in Table 11. Another series of amphiphilic graft copolymers with a double comb structure has also been synthesized (26, in Fig. 19) [47]. Similarly, type 27 graft copolymers have been prepared by the reaction of the activated copolymer with hydroxy-terminated polyurethanes, but these have not so far been characterized. 

As a conclusion, it should be emphasized that by FP polyurethanes characterized by [ti] (i.e. molecular weight) higher than diose prepared by the classical batch procedure are obtainable. Moreover, the reaction takes much shorter times and does not require external heating except for the ignition. 

---