Sequence Distribution of Segmented Polyurethane-Urea

Abstract

ABSTRACT:Segmented polyurethane-urea (SPU) elastomer was prepared from polytetramethyleneglycol (PTMG), 4,4'-diphenylmethane diisocyanate (MDI), and ethylenediamine (EDA). The SPU is a kind of block copolymer composed of soft and hard segments. 13 C NMR spectra of the SPU were measured and the mean sequence lengths of polyurethane block and polyurea block were estimated from the signals of aromatic carbons. The mean polyurea sequence length was shorter than the hard segment as estimated by X-ray diffraction (Kimura et al.) or by other methods (Suzuki et al.). This polymer was found to be almost a random copolymer. The reactivity of the isocyanate group in MDI decreases slightly when the other side of isocyanate has reacted. The hard segment observed by X-ray diffraction or by other methods might only be the longer fraction of polyurea sequences.KEY WORDS Polyurethane-urea / Sequence Distribution / Isocyanate / 4,4'-Diphenylmethane Diisocyanate / Reactivity Ratio/ 1 3 C NMR / Segmented polyurethane-urea (SPU) elastomer is a kind of block copolymer composed of soft and hard segments. The soft segment usually consists of aliphatic polyether or polyester urethane block and the hard segment is a polyurea block. SPU is usually prepared in two-stage reactions as shown in Figure I. A diisocyanate compound is reacted with a hydroxy terminated prepolymer (I). The amount of the isocyanate compound exceeds that of prepolymer (I) so that the unreacted isocyanate compound remains after the reaction. The resultant polymer (prepolymer (II)) is then extended with a diamine (chain extender). The mechanical properties of SPU depend on (l) the composition of soft and hard segments, (2) the length of soft and hard segments, or in other words, the molecular weight of prepolymer (I) (polyether or polyester) and the sequence length distribution, (3) anomalous linkages (branching, crosslinking), (4) molecular weight of SPU. The hydrogen-bonding in the crystal of the hard segment plays important roles in the elasticity of this polymer. 1 -3 The estimation of the lengths of soft and hard segments is essential for the investigation of SPU. Kimura et al. observed the length of hard segment directly by wide angle X-ray diffraction and by small angle X-ray scattering when the chain extender was 4,4'-diphenylmethanediamine (MDA). 4 · 5 They estimated the length of the hard segment composed of the polyurea block to be about four monomer units in the case of the molar ratio of prepolymer (1)/chain extender= 1 : 1. Suzuki et al. measured the length of the polyurea block in a similar SPU (chain extender; hydrazine) by selective degradation. 6 The length of the polyurea block agreed with the length of the hard segment estimated by Kimura et al. This suggests that the polyurea block is identical to the hard segment.The length of polyurea block depends on the reactivity ratio of isocyanate groups of diisocyanate compounds. 7 In the case of 4,4' -diphenylmethane diisocyanate (MDI), the re-1065

Carbon-13 NMR investigation of a poly(urethane-urea) system

“…These assignments are consistent with 13C solutionstate spectra. 23 The peak at 125 ppm is not yet assigned; however, if the sum intensity of these five aromatic region peaks is compared to the intensity of the soft-segment methylene peaks in fully-relaxed direct-observation spectra, the resulting ratio is comparable to the value predicted from the polymer stoichiometry.1-5 This peak at 125 ppm could arise from conformational differences that occur in the solid state. The results from the CP dipolar-dephasing experiments discussed later in this paper support this possibility.…”

Effect of Thermal History on the Rheological Behavior of Thermoplastic Polyurethanes

“…For the TPUs employed in this study, exchange reactions of ester units and urethane units might take place in the ester-based TPU (MDI/BDO/PTMA system), and exchange reactions of only urethane units might take place in the ether-based TPU (MDI/BDO/POTM system). In the past, high-resolution NMR spectroscopy was used to identify the chemical structures of various polyurethanes (PU), [46][47][48][49][50][51][52][53][54][55] indicating that 13 C NMR spectroscopy is much more useful than 1 H NMR spectroscopy in identifying the chemical structures of polyurethanes, because NH proton signals are rather sensitive to the environment (solvent, water, temperature, etc.). The assignments of 13 C NMR chemical shifts for PU are reported by several research groups, [46][47][48][49] and the assignments of 1 H NMR chemical shifts for PU are reported by Brame 54 and Okuto.…”

Synthesis and chain structure of ethylene terephthalate-?-caprolactone copolyesters

“…Degree of randomness 29 and its other similar forms, which are based on the determination of the possibility of three or more types of dyads or n-ads, have been widely used in the characterization of copolymer sequence structure, such as vinyl copolymers, 30 symmetrical copolyesters, [31][32][33] and segmented poly(urethane urea). 34,35 However, this method was unsuitable for TCL copolyesters because there is not always a common unit, OOCH 2 CH 2 OO, between ET and CL segments, and the molecular structure of the CL unit is unsymmetrical, having two different functional groups. Fortunately, another parameter, run number (R), also can be used to characterize the sequence structure of copolymers 36 ; it is the average number of sequence runs occurring in a copolymer chain per 100 monomer units.…”