Light scattering determination of weight-average molecular mass M w of a copolymer has historically required that measurements be made in at least three separate solvents of different index of refraction. Recently, however, it was demonstrated that, in principle, the evolution of M w of a copolymer can be followed during copolymerization reactions using automatic continuous online monitoring of polymerization reactions (ACOMP). The continuous measurement of M w by ACOMP is made possible by the fact that ACOMP provides the comonomer concentrations and absolute light scattering intensity at each instant of time during conversion and, hence, also yields the evolution of the average and instantaneous composition distribution. In this work, a workable and practical formalism for determination of M w during reactions, using a single solvent, is developed for the case of N comonomers. The traditional method quickly becomes intractable since the number of solvents required grows as N(N + 1)/2, and the number of auxiliary measurements of differential index of refraction of polymers in the solvents is N(N + 1) 2 /2. The formalism is applied to experimental cases involving copolymerization of styrene and methyl methacrylate, and M w and apparent mass M ap are compared. Results are correlated with traditional multisolvent determinations on endproducts and gel permeation chromatography approaches.

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We report progress on an experiment to measure the neutron lifetime using magnetically trapped neutrons. Neutrons are loaded into a 1.1 T deep superconducting Ioffe-type trap by scattering 0.89 nm neutrons in isotopically pure superfluid 4He. Neutron decays are detected in real time using the scintillation light produced in the helium by the beta-decay electrons. The measured trap lifetime at a helium temperature of 300 mK and with no ameliorative magnetic ramping is substantially shorter than the free neutron lifetime. This is attributed to the presence of neutrons with energies higher than the magnetic potential of the trap. Magnetic field ramping is implemented to eliminate these neutrons, resulting in an 833−63+74s trap lifetime, consistent with the currently accepted value of the free neutron lifetime.

The kinetics; evolution of molar mass; solution conductivity, sigma; intrinsic viscosity; and average composition drift; and distribution were determined by monitoring the synthesis of copolymeric polycations of acrylamide (Am) and [2-(acryloyloxy)ethyl]-trimethylammonium chloride (Q9). The quantitative relationship between diminishing sigma and charged co-monomers incorporation was monitored for the first time and provided novel data on counterion condensation, which occurs gradually over a broad composition regime. This new capability allows predictions concerning the relationship between copolymer composition and linear charge density, xi, to be tested and models of trivariate mass, composition, and xi distributions to be built. This approach, hence, brings together the previously disparate fields of synthetic chemistry of copolymers and physical chemical properties of polyelectrolytes. Monitoring was achieved with a new implementation of the ACOMP (automatic continuous online monitoring of polymerization reactions) platform. Reactivity ratios determined by ACOMP were rQ9 = 0.47 and rAm = 1.10. Opposite trends in composition drift and final molar mass were found; low starting percentage of Q9 led to low composition drift and high molar mass, whereas the opposite was found at high starting percentage of Q9. Complementary end-product analysis by multidetector gel permeation chromatography supported the ACOMP results. End-product polyelectrolyte properties were characterized by automatic continuous mixing, revealing that combined electrostatic persistence length and excluded volume effects led to the expected large changes in polyelectrolyte conformation and interactions. These results set the groundwork for semibatch control of molar mass, composition, and xi, and eventually for monitoring and control for inverse emulsion-based reactions of this type.