ABSTRACT:An attempt was made for quantitative synthesis of segmented poly(urethane-urea)s (PUUs), not via solution state, but directly from an isocyanate-terminated prepolymer prepared from an excess molar concentration of 4,4'-methylenediphenyldiisocyanate with poly(tetramethyleneoxide) (M.=2010) and reaction products from acetone and ethylenediamine (EDA) consisting of N-isopropylideneethylenediamine (I), N,N'-diisopropylideneethylenediamine (2), 2,2-dimethylimidazolidine (3) as main product, water, and the unreacted raw materials. With increasing the masking ratio of acetone to EDA, the concentrations of the ketimine groups and water increase while those of the imidazolidine and EDA generally decrease, the molar fraction of the by-product from the reaction of an isocyanate group with water was increased mainly because of the catalytic effect of the ketimine groups. Acetic acid played the significant roll to eliminate the side reaction by accelerating disappearance rate of (I) ((2)) and the quantitative yield of PUU was attained at 40°C when the acid concentration and the masking ratio were 3.50 x 10-3 mo! kg-1 and 1.4, respectively.KEY WORDS Poly(urethane-urea)s / Bulk Polymerization / Quantitative Yield/ Isocyanate-Terminated Prepolymer / Masked Diamines /Water/ Acid/ Segmented poly(urethane-urea)s (PUUs) compose of a class of elastomers exhibiting superior extensibility, toughness and durability over segmented poly(urethane)s and are extensively used in the fields from textile fibers to medical prosthesis.

ABSTRACT:An attempt was made to clarify the mechanism of the reactions of acetone with propylenediamine (PDA) or ethylenediamine (EDA) for direct synthesis of poly(urethane-urea) (DSPUU reaction) by using the reaction products (masked diamines) and an isocyanate-terminated prepolymer. In the masking reaction of acetone with PDA at 40°C, 1-(N-isopropylidene )propanediamine (1), 2-(N-isopropylidene )propanediamine (l '), 2,2-dimethyl-4-methylimidazolidine (3) as main product, N,N' -diisopropylidenepropylenediamine (2) were formed in this order due to the dominant rate (k 30 = 3.0kgmol-1 min -1 ) of the water-catalyzed reaction to form (3) in addition to the slow rate (k20 = 3.2 x 10-3 kgmol-1 min-1 ) of (2). The concentration of (l ') remained lower than (1) because of the steric hindrance of the methyl group of the former. The formation reactions of (1) and (2) were more acid-catalyzed than the reverse reactions, leading to shorter equilibrated time and larger molar fractions of these compounds. The reaction profiles for acetone-EDA were analogous except for lower molar fraction of 2,2-dimethylimidazolidine (6) and larger N,N'-diisopropylideneethylenediamine. The rates of demasking reactions which are of importance in DSPUU reactions using masked ED As were as follows; (i) the water-and acid-catalyzed ring opening reaction rate of (6), k _ 30 and k_ 3 = 1.43 and 0.26 kg mo!-1 min -, and (ii) the acid-catalyzed hydrolysis reaction rates of the ketimine groups, k_ 1 = 5.09 and k_ 2 =3.13kg 2 mo1-2 min-1 , respectively.

An attempt was made to clarify the mechanism of a chain-extending reaction of NCO-terminated prepolymers in the synthesis of segmented poly(urethane–urea) using blocked ethylenediamine (EDA) with acetone (ACE). For this purpose, an ACE/EDA mixture was allowed to react with phenyl isocyanate (PhNCO) as a model of the prepolymer. The reaction of PhNCO with the ACE/EDA mixture, which was proved to contain ketimine and imidazolidine compounds by NMR measurements, gave 1,1′-ethylenebis[3-phenylurea] (M-Ur-1) as the main product; at the same time 1,3-diphenylurea (1,3-DPU) was assumed to be formed as a side-reaction product between PhNCO and H2O, inevitably existing in the mixture as the result of condensation. From a considerable increase in the yield of M-Ur-1 upon the addition of an excess amount of H2O to the reaction system, H2O was elucidated to participate in the acceleration of the main reaction, giving M-Ur-1 as well as in the side reaction, yielding 1,3-DPU. The excess H2O added to the system might preferentially facilitate the former reaction, rather than the latter.

SynopsisCopolymers of 3,4-dihydro-2II-pyran-2-carboxyaldehyde (acrolein dimer ) with phenyl isocyanate were obtained under several conditions. Infrared and NMR analyses showed that the isocyanate always reacted with acrolein dimer forming urethane linkages, not block units of isocyanate. An alternating copolymer was obtained from the copolymerization in the presence of anionic catalysts such as butyllithium at room temperatiire, irrespective of the monomer ratios employed. The isocyanate content in the copolymer prepared with an Al(C2Hj),Cl catalyst was increased by elevating polymerization temperature. The copolymerizability of aldehydes with the isocyanate depends upon the polarity of aldehyde grorip.

ABSTRACT:Detailed structures of methacrolein dimer (MAD) were analyzed by nuclear magnetic resonance (NMR) and theoretical calculations. Two dimensional 1 H and 13 C NMR peaks were assigned. Relative stability of conformations and interconversion barrier height were studied by semi-empirical MNDO and ab initio OFT calculations. Barrier height between pseudoaxial and pseudoequatorial half-chair conformers was 5.8 kcal mol-1 . Separations of chemical shifts of two protons bonded to the same methylene carbons became larger as measurement temperature decreased, due to reduced mobility of the ring framework.KEY WORDS [IliA]As MAD became available from several sources at present, polymerization mechanism and conditions of such a unique polymer were studied again in this paper.MAD has an asymmetric carbon in the ring to which the aldehyde group is bonded. Therefore, MAD has two stereo isomers (enantiomers S and R) and each isomer takes several conformations arising from ring puckering deformation and rotation of the aldehyde group around the C*-CHO axis.' To whom correspondence should be addressed.As a result of torsional constraint imposed by the double bond in the ring framework, conformational variation in the 3,4-dihydropyran ring is rather limited compared to the oxycyclohexane ring such as pyranose. MAD is also important in oligo saccharides synthesis, 3 • 4 but information about the structures and reactivities is surprisingly scarce. In early works, Bushweller and O'Neil assumed the predominant existence of a halfchair conformer for 3,4-dihydropyran based on nuclear magnetic resonance (NMR) spectra 5 In another NMR measurement, Eliel et a/. 6 • 7 reported analysis of MAD structures by use of 13 C and 1 H NMR, but did not give detailed assignments of CH 2 and CH 3 .3,4-Dihydropyran has been analyzed theoretically only by the force field approach but there is no study on MAD. Force field studies are appropriate for hydrocarbons such as cyclohexane and cyclohexene, but simple force field potential does not well account for oxygen lone pair and double bond n-electron effects. Highly accurate ab initio calculation is indispensable for determination of the conformer geometries and precise prediction of the barrier height. This paper focuses on conformational preference and interconversion of MAD molecule after successful assignment of 1 H and 13 C NMR peaks of MAD. Various conformers of MAD and the interconversion barrier height were determined by electronic structure calculations. NMR and computational results herein set foundations for the reactivity of MAD in cationic polymerization and are discussed in our sequel papers. EXPERIMENTAL Preparation of Methacrolein DimerMAD was prepared by thermal dimerization of dry methacrolein in the presence of hydroquinone (I% by weight in methacrolein) at 160°C for 3 h under nitrogen 891