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Anionic polymerization of MMA in THF was studied by a capillary flow method with the dianion of a-methylstyrene tetramer and sodium naphthalene as initiators. From the analysis of the methanol formed, it was found that both the initiation and propagation reactions proceed without side reaction at -78°C. However, at ca. -65°C, a certain amount of initiator is consumed by carbonyl attack in the initiation step though no side reaction is observed in the propagation step. At room temperature, the carbonyl attack is found in both steps and the polymerization stops at a certain degree of polymerization. The apparent propagation rate constants were determined at -78°C and ca. -65°C. They increase with rising temperature and become too high to be determined at room temperature. The dependence of the rate constants on the propagating anion concentr~tion revealed that the contribution of free ion to the propagation is relatively small and' that the propagation rate constant of ion pair is about 1 x 102 / mol-1 sec-1 at these low temperatures. These data are compared with the rates of homopolymerization of styrene and the reactivities of the propagating species of the two monomers are discussed. KEY WORDS Anionic Polymerization / Polar Solvent / Methyl Methacrylate / Initiation / Propagation / Rate Constant / Ion Pair / Carbonyl AttackAnionic polymerization of MMA is strongly affected by both solvents and gegen ions. Hitherto, -most of its kinetic studies have been made in nonpolar solvents with Lfi-as a gegen ion. i-s The mechanism of anionic polymerization of MMA in these systems is very complex and the molecular weight distribution of the polymer obtained is usually very broad. 2 -4 • One of the main reasons for this peculiar behavior of the polymerization is the strong coordination of Li+ with the carbomethoxy group. This coordination seems to be related to the formation of isotactic PMMA in nonpolar solvents. The peculiarity of the polymerization is partially retained in a mixed solvent such as toluene-THF when gegen ion is Li+. 7 On the other hand, Allen, et al.,8 have shown that, in a similar toluene-THF mixture, anionic polymerization of MMA with Na+ as a gegen ion is relatively simple as far as the kinetics is concerned. of MMA in pure THF has not yet been reported. But PMMA prepared anionically in THF at low temperature with Na+ as a gegen ion is reported to have a very narrow molecular weight distribution and little isotactic structure. 9 -u Hence, it· is expected that the anionic polymerization of MMA under these conditions will be relatively simple and nearly the same in nature as the anionic polymerization of styrene in THF except for possible side reactions such as chain transfer or termination due to the presence of the carbomethoxy group. Methanol formation by carbonyl attack has often been reported for the nonpolar solvent-Li+ systems. 3 , 5 , 7 Consequently whether the same reaction is observed or not for THF-Na+ system must be established before determination of propagation rate constants.A kinetic stu...

SynopsisA new method is proposed to improve the cut growth resistance of polyether-based polyurethane elastomers, i.e., polyethers used in this method are characterized by a double-humped distribution of molecular weight (DHDM), prepared by blending low-molecular-weight components and highmolecular-weight ones. The measurements of stress-strain curves, viscoelastic properties, and DSC thermograms of polyurethane elastomers before and after fatigue tests indicate that the destruction of the super molecular structure because of fatigue is smaller in the elastomer by our method, while in the conventional elastomer it is greatly destructed to change into fibrous structure. Further, the broad line NMR measurements show that the molecular motion of DHDM-type elastomers is more active, which is considered to contribute to the improved cut growth resistance of the elastomers. INTRODUCTIONFor practical importance, few articles dealing with flex crack resistance of polyurethane elastomers have been published. Several ways have been known to improve the flex crack resistance of polyurethane elastomers:(1) decreasing modulus by reducing the content of hard segments or compounding plasticizers;(2) decreasing chemical crosslink density by adjusting the molar ratio of active hydrogens to isocyanate groups to a value larger than 1.0 (ref. 1); and (3) decreasing the molecular weight of the polyurethane elastomer.2 McGillvary combined (1) and (2) to achieve so excellent a flex crack resistance as to be durable for tire t e s t i n g~.~ However, for tire application, not only crack initiation but also cut growth resistance is important. In this case, tear resistance might be considered to be one of the most important factors as well. Several attempt^"^ have been made to increase the tear resistance of segmental block polyurethane elastomers:(4) using chain extenders and diisocyanate compounds of bulky and symmetrical molecular structure, as shown by Buist and Gudgeon4;(5) employing a polymer glycol that is polar and that easily crystallizes by elongation, for instance, poly(ethy1ene adipate)glycol5; (6) increasing the length of hard segments by keeping their fraction constant6; and (7) modifying the polyurethane by the interpenetrating polymer network (IPN) r n e t h~d .~ In this article we would like to disclose that segmental polyurethane elastomers prepared from specially designed polyethers with double-humped distribution of molecular weight (DHDM) should be improved in cut growth resistance without any significant disadvantage to other mechanical properties of conventional polyurethane elastomers. This conclusion is derived through discussion of cut growth resistance, tensile properties, viscoelastic properties, heat of fusion, and half-width of broad line NMR comparing DHDM types of polyurethanes with conventional ones. EXPERIMENTAL MaterialsAll the poly(oxytetramethy1ene)glycols (PTMGs) employed were from Dainihon Ink Co., Ltd.; their molecular weights are listed in Table 11. PTMG6000, PTMG10000, and PTMG20000 were prepared ...

SynopsisCarboxylic acids with weak acidities showed large catalytic activity. For instance, for chlorinesubstituted acetic acid the activity increased with decreasing chlorine content. For benzoic acid derivatives, electron acceptor substituents, such as NOa, C1, and OH, lowered the catalytic activity, while electron donor substituents such as alkyl and alkoxy groups increased it. Detailed study on the cure rate of polyureaurethane, with 2-methyl benzoic acid as a catalyst, showed that pot life (PL) and the minimum demolding time (DT) had a correlation with the catalyst amount [X] represented by the following equation:where A and R are constants. Further, use of appropriate amounts of the catalyst enhanced tensile strength at break for polyureaurethane.

Synopsis2-Methyl benzoic acid as a new catalyst for urea formation reaction has a significant effect on the molecular structure of polyureaurethane. For instance, it increased molecular weight of polyureaurethane, hut decreased chemical crosslink density. The minimum demolding time (DT) of polyureaurethane as an index of catalytic activity was also discussed based on the mechanical properties. DT is defined as the torque time for a mixture of curative and prepolymer to reach 90% of its nearly final value. A marked increase in extension ratio a t break ( E B ) before DT was partially attributed to intermolecular entanglements which arose a t molecular weights higher than 4500 [rheological critical molecular weight of poly(oxytetramethylene)glycol]. Primary aliphatic amines in amide solvents selectively cleaved hiuret or allophanate bonds of polyureaurethane. This helped to determine molecular weight of crosslinked polyureaurethane.