Intrachain Repulsion Research Articles

Blends containing tetramethyl bisphenol-A polycarbonate: 1. Styrenic polymers

The phase behaviour of blends of tetramethyl bisphenol-A polycarbonate, MPC, with styrene copolymers and substituted styrene homopolymers was examined using d.s.c. and optical indications of phase separation on heating, i.e. lower critical solution temperature, LCST, behaviour. MPC was found to be miscible with styrene/acrylonitrile copolymers, SAN, having an AN content smaller than 13%, with a styrene/maleic anhydride copolymer, SMA, having an MA content equal to 8% and with oligomeric styrene/allyl alcohol copolymers, SAA, having an AA content less than 19.1%. MPC was also found to be miscible with an oligomeric poly(α-methyl styrene), PαMS, and a copolymer of α-methyl styrene/acrylonitrile, PαMSAN. Some of the mixtures showed LCST behaviour and based on this and excess volume measurements, to the extent possible, qualitative conclusions were made concerning the relative strength of the interactions among the various blend pairs. It appears that small amounts of AN or MA in the copolymers apparently increases the strength of interactions relative to those observed in polystyrene blends with MPC, whereas the inclusion of a methyl group in the styrenic repeat unit has the opposite effect. The phase behaviour of MPC with styrene based copolymers appears to be influenced by intrachain repulsion between styrene and comonomer units. MPC was found to undergo thermal and solvent induced crystallization when blends were cast from tetrahydrofuran and toluene solutions, but no crystallinity was observed when methylene chloride was used as the solvent.

Interaction between styrene–ethylene oxide block copolymers and sodium lauryl sulfate in aqueous solution

AbstractInteractions of water‐soluble AB block copolymers of polystyrene and poly(ethylene oxide) with sodium lauryl sulfate (SLS) in aqueous solution were investigated by high‐resolution proton magnetic resonance (NMR). The viscosity in aqueous SLS solution was also measured. From the NMR results in D2O, it appears that molecular motions of the polystyrene blocks of the copolymer in aqueous solution are activated by interaction between the polystyrene blocks and the added SLS. From solution viscosity, on the other hand, it is apparent that a complex is formed between the copolymer and SLS and that it exhibits typical polyelectrolyte properties. The polyelectrolyte character is attributable largely to intrachain repulsions between like charges of the SLS anions adsorbed on the poly(ethylene oxide) blocks of the copolymers since the polystyrene blocks are insoluble in water and the styrene content is less than 10%.

Sedimentation and optical rotation behavior of bovine plasma albumin at low pH in the presence of various anions. Effect of charge on molecular expansion

In order to clarify the role of net molecular charge in the expansion of plasma albumin at low pH, sedimentation and optical rotation measurements were carried out in the presence of anions differing widely in their extent of binding to BPA. Thus it was possible to vary the net charge on the protein molecule independent of the extent of binding of protons. It was demonstrated as a first approximation that the extent of expansion, as determined from both sedimentation and rotation measurements, is a function of the net charge on the molecule. Quantitatively, however, specific rotation and molecular size do not always change in a parallel manner, nor are they affected in the same way by changes in ionic strength. Changes in specific rotation may be attributed to partial breakdown of the secondary (possibly helical) structure as a result of intrachain charge repulsion, while interchain repulsion (changes in tertiary structure) are held responsible for a large part of the change observed in viscosity and sedimentation constant. Conversion of the native albumin molecule to “expandable” form appeared to be accompanied by a moderate increase in molecular radius in the presence of chloride ion. On the other hand, this isomerization can occur without increase in radius in the presence of thiocyanate ion. No significant change in optical rotation accompanies formation of the “expandable” molecule.