Donor-Acceptor Complexes in Copolymerization. IX. Kinetic Features of Copolymerization of Styrene and Methyl Methacrylate… Al(C2H5))1.5Cl1.5

The kinetic features of the copolymerization of styrene and methyl methacrylate in the presence of ethylaluminum sesquichloride in toluene do not unequivocally distinguish between first- and second-order reactions. The reaction does not attain steady-state conditions. The course of the reaction is apparently influenced by many factors including the dissociation of the polymerizable complex into unreactive monomeric species and physical phenomena such as diffusion and dilution effects as well as matrix formation. The use of azobisisobutyronitrile as an initiator indicates apparent bimolecu-lar termination but the kinetic curves show deviation from linearity.     

Inexpensive,efficient optical fiber end-face mirror

The rapid fabrication of inexpensive, efficient optical fiber end-face mirrors by dipping the fiber into a small-volume drop of a molten, low-melting-point metal alloy is described. The technique uses a small (a couple hundred micrometers thick, about 1 mm wide) drop of molten metal to achieve reliable, repeatable adhesion of the metal to the fiber that is not possible with larger volumes. The resulting mirrors have an average reflectance of 65–75% for wavelengths in the telecommunications range of 1300–1600 nm. The efficient and robust nature of the resulting mirrors is demonstrated with a novel end-of-fiber mirrored long-period fiber grating.     

Proposed Participation of Excited Monomer in the Free Radical-Catalyzed High Pressure,High Temperature Polymerization of Ethylene

The radiation-induced copolymerization of ethyl vinyl ether with dibutyl maleate was investigated over a wide range of comonomer compositions, dose rates, and in the temperature range from ?25 to 75° C. Both the rates of copolymerization and the molecular weights of the resulting copolymers were found to depend strongly on the initial comonomer composition, both reaching a maximum value at an equimolar comonomer composition. A copolymer was obtained in which the co-monomers alternate with regularity along the polymer chain over the entire range of comonomer compositions investigated. The monomer reactivity ratios were determined and found to be practically zero. The apparent activation energy was found to change at 35° C, the boiling point of the ethyl vinyl ether, from a value of 10.48 kJ/mole to a value of 18.86 kJ/mole above this temperature. This phase change also resulted in a marked decrease in the molecular weights of the copolymers formed above 35° C. The dose-rate dependence of the rate of copolymerization was found to be 0.70 over the dose-rate range     

Donor-Acceptor Complexes in Copolymerization. XXVI. Effect of Solvent,Temperature, and Complexing Agent on the Polymerization of Comonomer Charge Transfer Complexes

The copolymerization of styrene with methyl methacrylate (S/MMA = 4/1) or acrylonitrile (S/AN = 1/1) in the presence of ethylaluminum sesquichloride (EASC) yields 1/1 copolymer in toluene or chlorobenzene. In chloroform the S-MMA-EASC polymerization yields 60/40 copolymer while the S-AN-EASC polymerization yields 1/1 copolymer. In the presence of EASC, styrene-α-chloroacrylonitrile yields 1/1 copolymer (DMF or DMSO), S-AN yields 1/1 copolymer (DMSO) or radical copolymer (DMF), S-MMA yields radical copolymer (DMF or DMSO), α-methylstyrene-AN yields radical copolymer (DMSO) or traces of copolymer (DMF), and α-MS-methacrylo-nitrile yields traces of copolymer (DMSO) or no copolymer (DMF). When zinc chloride is used as complexing agent in DMF or DMSO, none of the monomer pairs undergoes polymerization. However, radical catalyzed polymerization of isoprene-AN-ZnCl₂ in DMF yields 1/1 alternating copolymer. The copolymerization of S/MMA in the presence of EASC yields 1/1 alternating copolymer up to 100°C, while the copolymerization of S/AN deviates from 1/1 alternating copolymer above 50°C. The copolymerization of S/MMA deviates from 1/1 copolymer at MMA/EASC mole ratios above 20 while the copolymerization of S/AN deviates from 1/1 copolymer at MMA/EASC ratios above 50.     

Donor-Acceptor Complexes in Copolymerization. XLIV. Copolymerization of Styrene and α-Methylstyrene with Acrylic and α-Substituted Acrylic Esters in the Presence of Aluminum Compounds

Abstract

The copolymerization of styrene (S) with methyl acrylate (MA) and with methyl methacrylate (MMA) in the presence of AlEt₃ yields equimolar, alternating copolymers while no polymer is formed in α-methylstyrene (MS)-MA and MS-MMA systems. In the presence of AlEt_1.5Cl_l,5 (EASC), S-MA and S-MMA yield alternating copolymers, S-methyl a-chloroacrylate (MCA), MS-MA and MS-MMA yield a mixture of alternating and cationic polymers, and MS-MCA yields cationic polymer only. In the presence of A1C1₃, S-MA and MS-MA yield a mixture of alternating and cationic polymers and S-MMA and MS-MMA yield cationic polymer only. The cotacticity distributions of the alternating S-MA and S-MMA copolymers prepared in the presence of AlEt₃, EASC, and A1C1, are the same; the coisotactic, co-heterotactic, and cosyndiotactic fractions being approximately in the ratio 1:2:1. The cosyndiotactic fractions of the alter-nating copolymers prepared in the presence of EASC are in the order MS-MMA > MS-MA > S-MCA > S-MMA=S-MA.     

X-ray fluorescence in some rare earth and high Z elements excited by 661.6 keV γ-rays

The K-shell X-ray fluorescence cross sections are determined experimentally for 10 elements such as Pb, Hg, Ir, W, Lu, Tm, Dy, Tb, Gd and Nd at excitation energy of 661.6 keV associated with γ-rays of ¹³⁷Cs radioisotope. The technique employed involves the measurement of total intensity of fluorescent K X-rays that follow the photoeffect absorption of a known flux of γ-rays using a well type Nal(Tl) detector. The obtained results are compared with the available theoretical values and other measured values.     

Donor–acceptor complexes in copolymerization. XLIII. Cyclization of alternating and random styrene–(meth)acrylic ester copolymers

Equimolar alternating copolymers of styrene and methyl methacrylate (prepared with Et_1.5AlCl_1.5, SnCl₄, and ZnCl₂) as well as equimolar random copolymer were treated with polyphosphoric acid at 135°C. The extent of cyclization of the alternating copolymers was about 40%, independent of the cotacticity of the copolymer, and there was little or no crosslinking. The random copolymer underwent only 10% cyclization and considerable crosslinking. The extent of cyclization of the alternating copolymer of styrene and methyl acrylate (prepared with Et_1.5AlCl_1.5) was the same as that of the random copolymer and was lower than that of the corresponding methyl methacrylate copolymer. Both alternating and random copolymers underwent extensive crosslinking.     

Architectural issues related to the optical implementation of an EGS network based on embedded control

Free-space optical implementations of switching networks have been proposed to circumvent many of the system-level problems that may be encountered in systems that require many high-density, high-bandwidth connections. The details of a new class of switching network (the EGS network), that is well-suited to free-space implementations, is described. The common control injection problem that plagues most free-space photonic networks, i.e. how can control information from an electronic source be injected into the network for applications that require relatively high network reconfiguration rates, is examined. A new technique for control injection, called embedded control, which permits network operation even with relatively high network reconfiguration rates is also proposed.     

A theory of the stress-induced crystallization of crosslinked polymeric networks

A non-Gaussian theory of the stress-induced crystallization of polymeric networks is presented. It is predicted that for uniaxial extension of crosslinked polyethylene, a perfectly oriented, extended-chain crystal is formed initially, changing to one-fold crystal oriented perpendicular to the stretch direction at low extension and to a two-fold crystal having nearly perfect orientation at high extension. The stress is predicted to decay initially and then to rise as the network chains switch from an extended- to a folded-chain morphology, the rise being delayed and finally suppressed by additional crosslinking. The final, equilibrium birefringence is calculated and found to be negative at low extension and positive at high extension. The initial rate of crystallization is calculated using irreversible thermodynamics and is found to increase with extension and decrease with increasing crosslinking and temperature. All of the theoretical predictions are in qualitative agreement with experiment.