Segmented polyurethanes polymerization

Ishihara K, Tanaka S, Furukawa N, Kurita K, and Nakabayashi N. Improved blood compatibility of segmented polyurethanes by polymeric additives having phospholipid polar groups. I. Molecular design of polymeric additives and their functions. J Biomed Mater Res, 1996, 32(3), 391-399. 

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. 

Stepwise addition polymerization is used in the preparation of segmented polyurethanes (compare Sect. 4.2.1), e.g., poly(ester ether) urethanes which also find application in thermoplastic elastomers. Here, both blocks are preformed separately and are linked together by reaction with isocyanates ... 

Lee and Matsuda modified a segmented polyurethane film with a dithio-carbamate moiety and then initiated the polymerization of (ethylene glycol) methacrylate and N,N-dimethylacrylamide [35]. The resulting films were hy-drophihc and were shown to inhibit adhesion of platelets. Such films could be useful as anti-coagulant substrates for devices implanted in vivo. 

The polyurethane samples were kindly supplied by F. E. Critchfield of Union Carbide Corporation. The samples were made by a one-step batch process with curing at 145°C for 16 hr. Details of the polyurethane polymerization are described elsewhere (9). The hard segment consists of 4,4 -diphenylmethane diisocyanate (MDI) and 1,4-butanediol (BDO) (MDI/BDO)i, and the soft segment consists of MDI and polycaprolac-tone diol (PCP) with Mn — 2000 (PCP/MDI),. 

Figure 8. Effect of soft segment content on point of phase separation during polyurethane polymerization as indicated by discontinuity in DSC reaction profile. Dotted line shows theoretical prediction assuming separation at constant number-average sequence length (1.3) of hard segments ("see text).

Reaction polymerization reactions of isocyanates with suitable monomers can he performed in an extruder or in a RIM machine. In the latter reaction thermosets (cross-hnked polymers) are produced. In an extruder usually linear polymers are manufactured. For example from methylene di-p-phenylene isocyanate (MDI), with some macroglycols and 1,4-hutanediol as extenders, segmented polyurethane elastomers are produced in an extruder (6). However, linear condensation polymers are also produced in a vented extruder. For example from MDI, with macrodicarboxylic acids and dicarboxyhc acids as extenders thermoplastic block copolyamide elastomers are produced. The by-product of the condensation reaction, carbon dioxide, is removed in the vented extruder. The polycondensation process can also be performed in solution. For example, MDI can be added to a solution of dicarboxyhc acids in tetramethylene sulfone, with simultaneous removal of the carbon dioxide. Tetramethylene sulfone is the solvent of choice for solution polymerization of isocyanates (7). In addition to dicarboxyhc acids trimellitic acid anhydride and benzophenonetetracarboxylic acid dianhydride (BTDA) are utilized as monomers for condensation polymers. With these monomers poly(amide imides) and poly(imides) are produced. The diisocyanate-derived commercial polycondensation products are listed in Table 1. 

Abouzahr S, Wilkes GL. Structure property smdies of polyester-and polyether-based MDI-BD segmented polyurethanes effect of one-vs two-stage polymerization conditions. J Appl Polym Sci 1984 29(9) 2695-711. 

Chang A, et al. Morphological study of the structure developed during the polymerization of a series of segmented polyurethanes. Polymer 1982 23(7) 1060-8. 

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