The initially formed carbanion from dimethylsilacyclobutane and potassium tert-butoxide was trapped in as high as 88% yield in the presence of 1,1-diphenylethylene as evidenced by quenching with methyl iodide. The initiator efficiency of 76% was obtained by using a combination of potassium tert-butoxide, dimethylsilacyclobutane, and 1,1-diphenylethylene carbanion pump system as an initiator in the polymerization of methyl methacrylate.
Since the concept was established by Szwarc in 1956, 1 living anionic polymerization has been utilized to synthesize unique polymers, such as A-B-A triblock copolymers and star-shaped polymers. However, anionic multiblock polymerization has some limitation in selection of monomers, because of the difference in the reactivity of the propagating anionic species.2 For instance, block polymerization from poly(styrene) to ethylene oxide is possible, but impossible vice versa because the propagating oxyanion (O-anion) cannot initiate the polymerization of styrene to form carbanion (C-anion).Since silacyclobutanes give polymers by thermal, 3 transition metal-catalyzed,4 and anionic 5 polymerization due to their high ring-opening reactivity resulting from the large distortional energies (24.5 kcal mol-1 ), 6 it was anticipated that O-anion might open silacyclobutane ring to form C-anion. We actually showed the ring opening reaction of 1-trialkylsiloxysilacyclobutanes by lithium alkoxide.7 Similar ring opening of benzosilacyclobutanes by alcohols was also reported.8 This ring opening could be a method to convert less reactive propagating O-anion into more reactive C-anion. This function is significant from the viewpoint of the unrestricted design of multi-block copolymers from various combination of ring-opening and vinyl monomers. A similar idea using 1,1,2,2-tetramethyl-or 1-phenyl-1,2,2-trimethyl-l,2-disilacyclopentane was reported by Teyssie et al. to polymerize vinyl monomers by potassium silanolate and poly(ethylene oxide) potassium salt.
9In this communication, we report our preliminary results of the anionic polymerization of styrene with potassium t-butoxide in the presence of a silacyclobutane derivative (SB).1,1-Dimethylsilacyclobutane (DMSB), 10 1-methyl-1-phenylsilacyclobutane (MPSB) 11 and 1,1-diphenylsilacyclobutane (DPSB) 12 • 13 were synthesized according to the literature and purified by distillation over calcium hydride. Styrene (St) and potassium t-butoxide (BuOK) were purified in a common way. Tetrahydrofuran (THF) was dried over sodium and vacuum-transferred. Polymerization was initiated by injection of a silacyclobutane to the mixture of St and BuOK in THF under argon atmosphere and terminated by addition of triphenylchlorosilane (TPCS).When DMSB (2.5 mmol) was injected into a THF (40 mL) solution of Bu OK (2.5 mmol) and St (75 mmol), reddish color of poly (St) * on the combination of Shodex KF-8031 (exclusion limit: Mn = 7 X 10 4 , poly(styrene)) and KF-804 (exclusion limit: Mn = 4 X 105, poly(styrene)) columns (linear calibration down to Mn = 100, poly-(styrene)) using THF as an eluent.
Unreinforced- and glass fiber-reinforced-polyamide 6,6 specimens were subjected to dry, 50% RH, and wet conditions. FLD study showed that more fiber degradation occurred during processing of the composites with higher fiber loading. TGA results revealed that about 2% and 5% levels of moisture have been absorbed by the specimens subjected to 50% RH and wet conditions, respectively. From DSC results, with moisture uptake, there were no significance changes in the melting temperature, crystallization temperature, and enthalpy of crystalline; however, degree of crystallinity and enthalpy of melting decreased. Tensile strength, tensile modulus, flexural strength, and flexural modulus decreased with moisture uptake, while tensile strain and flexural displacement increased. DMA study showed that tan delta at room temperature and tan delta maxima increased with moisture absorption, while temperatures at maximum tan delta in α- and β-transition regions decreased.
Injection-molded short-and long-glass fiber/polyamide 6,6 composites were subjected to tensile tests. To measure the effectiveness of the fibers in reinforcing the composites, a computational approach was employed to compute the fibermatrix ISS, orientation factor, reinforcement efficiency, tensile-, and fiber length-related properties. Although the LFCs showed great improvement in fiber characteristics compared to the SFCs, enhancement in tensile properties was small, which is believed to be due to the larger fiber diameter. Kelly-Tyson model provides good approximation for the computation of ISS and tensile-related properties.
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