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Pure gas and hydrocarbon vapor transport properties of blends of two glassy, polyacetylene‐based polymers, poly(1‐trimethylsilyl‐1‐propyne) [PTMSP] and poly(1‐phenyl‐1‐propyne) [PPP], have been determined. Solid‐state CP/MAS NMR proton rotating frame relaxation times were determined in the pure polymers and the blends. NMR studies show that PTMSP and PPP form strongly phase‐separated blends. The permeabilities of the pure polymers and each blend were determined with hydrogen, nitrogen, oxygen, carbon dioxide, and n‐butane. PTMSP exhibits unusual gas and vapor transport properties which result from its extremely high free volume. PTMSP is more permeable to large organic vapors, such as n‐butane, than to small, permanent gases, such as hydrogen. PPP exhibits gas permeation characteristics of conventional low free volume glassy polymers; PPP is more permeable to hydrogen than to n‐butane. In PTMSP/PPP blends, both n‐butane permeability and n‐butane/hydrogen selectivity increase as the PTMSP content of the blends increases. © 1996 John Wiley & Sons, Inc.

No abstract

Ammonia/ammonium thiocyanate (NH3/NH4SCN) is an excellent swelling agent and solvent for cellulose, even at a high degree of polymerization. Because polymorphic conversion in cellulose has been a long‐standing, perplexing, troublesome problem, we have undertaken to study that mechanism. Solid state CP/MAS 13C‐NMR and X‐ray analysis proved to be very useful analytical techniques for the task. It appears that during temperature cycling, specific cellulosic inter‐ and intramolecular hydrogen‐bonds are broken as polymorphic conversion proceeds sequentially from the polymorph I to III, and finally at total solvation to amorphous. This proceeds correspondingly via transformation of the polymorph conformations of CH2OH from trans‐gauche, “tg,” to gauche‐trans, “gt,” to gauche‐gauche, “gg.” © 1994 John Wiley & Sons, Inc.

The simple, straightforward 1 H NMR spectrum of the neutron capture therapy drug, -p-boronophenylalanine (-p-BPA), in D 2 O changes to a more complex one in DMSO-d 6 in which the ratio of new species observed is highly concentration dependent. The new species detected can only be explained by an additional stereocenter being formed at the boron center by intermolecular chelation of the amino acid of another molecule of -p-BPA. This gives rise to the presence of an oligomeric species as well as another whose aromatic protons appear as a pair of sharp AB quartets centered further upfield at 6.66 and 6.84. Due to these shifts and couplings observed between the benzylic protons and the proton at the stereocenter of the amino acid, it is proposed that this species is a paracyclophane dimer of -p-BPA in which one molecule of -p-BPA chelates head-to-tail with another. This cyclophane dimer predominates in low concentrations (<50 mM) while the oligomer predominates at higher (>90 mM) concentrations. The formation of these two species is completely reversible, the addition of D 2 O completely regenerating -p-BPA. Variable temperature 1 H NMR found that the two pairs of aromatic protons of the cyclophane dimer coalesce at T c = 141 ЊC, corresponding to a ∆G ‡ = 20.6 kcal mol Ϫ1 .