Macrodiol

The melt temperature of a polyurethane is important for processibiUty. Melting should occur well below the decomposition temperature. Below the glass-transition temperature the molecular motion is frozen, and the material is only able to undergo small-scale elastic deformations. For amorphous polyurethane elastomers, the T of the soft segment is ca —50 to —60 " C, whereas for the amorphous hard segment, T is in the 20—100°C range. The T and T of the mote common macrodiols used in the manufacture of TPU are Hsted in Table 2. 

The choice of macrodiol influences the low temperature performance, whereas the modulus, ie, hardness, stiffness, and load-beating properties, increases with increasing hard-segment content. 

Martin D.J., Warren L.A.P., Gunatillake P.A., McCarthy S.J., Meijs G.F., and Schindhelm, K. Polydimethylsiloxane/polyether-mixed macrodiol-based polyurethane elastomer. Biomaterials, 21, 1021, 2000. 

These structures are well defined by conducting the polymerization in the presence of appropriate mono- and difunctional reagents. They are of considerable interest for the preparation of segmented block copolymers.24,25 For instance, the fluorinated macrodiols 21 have already been used to prepare an interesting new series of partially fluorinated segmented polyurethanes,26 and we are investigating other novel polymers that can be prepared from these intermediates. 

The one-prepolymer method involves one of the above prepolymers with two small reactants. The macrodiol is reacted with a diol and diisocyanate... 

The block lengths and the final polymer molecular weight are again determined by the details of the prepolymer synthesis and its subsequent polymerization. An often-used variation of the one-prepolymer method is to react the macrodiol with excess diisocyanate to form an isocyanate-terminated prepolymer. The latter is then chain-extended (i.e., increased in molecular weight) by reaction with a diol. The one- and two-prepolymer methods can in principle yield exactly the same final block copolymer. However, the dispersity of the polyurethane block length (m is an average value as are n and p) is usually narrower when the two-prepolymer method is used. 

The prepolymers described above are one type of telechelic polymer. A telechelic polymer is one containing one or more functional end groups that have the capacity for selective reaction to form bonds with another molecule. The functionality of a telechelic polymer or prepolymer is equal to the number of such end groups. The macrodiol and macrodiisocyanate telechelic prepolymers have functionalities of 2. Many other telechelic prepolymers were discussed in Sec. 2-12. (The term functional polymer has also been used to describe a polymer with one or more functional end groups.)... 

To obtain elastomers, one or two diols can be reacted with the isocyanate. When two diols are used, the first one is a macrodiol with a molar mass in the range 500-10000 g mol-1, and the second one is a short diol, typically 1,4-butanediol. The PU may be prepared by either the one-shot process (three components reacting together), or the prepolymer approach a prepolymer is prepared first (Eq. 2.36) and then reacted with the short diol (chain extender) ... 

When a macrodiol is reacted with a diisocyanate and a monoalcohol is employed instead of a chain extender, oligomers are formed ... 

In this case of three-monomer polyurethane synthesis, there is no thermodynamic driving force for phase separation. The formation of clusters is fully controlled by the initial composition of the system, the reactivity of functional groups, and the network formation history (one or two stages, macrodiol or triol reacted with diisocyanate first, etc.). 

The presence of hard clusters affects mechanical properties. The major problem is the way to define elastically active network chains (EANC) and crosslinks (Chapter 3, Fig. 3.3). It has been demonstrated that hard clusters must be considered as multifunctional crosslinks (fc = 6 in Fig. 7.6a) while macrodiol chains behave as EANC. 

In the case of Fig. 7.6a the cluster formation and the size distribution can be influenced not only by chemical reactions but also by partial miscibility of the substructures during reaction. Polyurethane networks prepared from polyolefin instead of polyester or polyether as macrodiol, can serve as an example. In this particular case an agglomeration of hard domains takes place in the pregel stage, produced by a thermodynamic driving force. 

The sol-gel chemistry has also been used to prepare inorganic inhomogeneities in an organic matrix. Silane end-capped macrodiols can be used. Hydrolysis and condensation of alkoxy silane groups lead to inorganic hard clusters (Fig. 7.6b). Intramolecular reactions and the miscibility of the soft-segment chains with the relatively polar crosslinks determine the size distribution of the clusters (nanofillers). 

Figure 7.7 SAXS profiles for two hydroxyl-terminated oligomers crosslinked by alkoxysilane sol-gel chemistry. First, 1 mole of macrodiol, SS (hydrogenated polybutadiene, HPBD or polycaprolactone, PCL, Mn= 2 kg mol-1), was reacted at 80°C with 2 mole of dicyclohexylmethane diisocyanate, H12 MDI. After complete reaction, the prepolymer was dissolved in tetrahydro-furan and the y-aminosilane, yAPS was added dropwise at room temperature. After 1 h of reaction, the solvent was removed under pressure. The final network was obtained in the absence of a solvent by hydrolysis and condensation of the ethoxysilane groups by the addition of 0.1 mol% TFA, trifluor-oacetic acid. After stirring at room temperature, the mixture was cast into a mold and cured for 24 h at 100°C under pressure, and then postcured at 150°C for 12 h. (Cuney et al., 1997 - Copyright 2001, Reprinted by permission of John Wiley Sons, Inc.)...

Synthesis of macrodiols after selective reduction of acid terminal groups in hydroxyl groups... 

The processes described in Table 2 present a peculiar interest in the working out of new materials as polyurethanes. These last polymers are very often based on macro diols coming from polyethers or polyesters, a-co functional polyolefins being relatively uncommon. Hence, Rhein and Ingham [139] prepared macrodiols by ozonization of polyisobutylene in CC14 at... 

Poly 1-4 isoprene Inert solvent -70 °C to 30 °C Reduction with LiAlH4 a, -Macrodiols [129, 130]... 

Acrylonitrile-butadiene Tetrahydrofuran 15 °C Reduction with Na borohydrides a, -Macrodiols [132-133]... 

Polyisobutylene Cyclohexane Reduction with H2/Ni Raney a, U-Macrodiols [134]... 

Figure 9. Plot of heat of fusion vs. weight fraction of hard segment for each random copolymer, assuming k > 1 or k > 6, where k is the number of diisocyanate (hard-segment) units betwen two consecutive macrodiol (soft-segment) units. (Peebles (30) calculation of hard, block-length distribution in segmented polyurethane block copolymer is applied.)...

ESTRA-1,3,5(10)-TRIENE-3,17-P-DIOL 17-P-ESTRA-1,3,5(10)-TRIENE-3,17-DIOL 1,3,5-ESTRATRIENE-3,17-P-DIOL ESTROVITE FEMESTRAL FEMOGEN GYNERGON GYNESTREL GYNOESTRYL LAMDIOL MACRODIOL MACROL MICRODIOL... 

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