Luminescence studies of hydrophobically modified, water-soluble polymers. I. Fluorescence anisotropy and spectroscopic investigations of the conformational behaviour of copolymers of acrylic acid and styrene or methyl methacrylate

Abstract

Fluorescence spectroscopy and anisotropy measurements have been used to study a series of styrene -acrylic acid, STY-AA, and methyl methacrylate -acrylic acid, MMA-AA, copolymers in dilute methanolic and aqueous solutions. Copolymerization of either STY or MMA with AA has little effect upon the rate of intramolecular segmental motion in methanol solutions. In aqueous media, intramolecular hydrophobic aggregation occurs and restricts the macromolecular dynamics to an extent dependent upon pH, nature of the comonomer, and copolymer composition. The hydrophobic domains formed in these copolymer systems can solubilize organic guests. In this respect, STY is a more powerful modifier of AA-based polymer behaviours than is MMA. In general, the hydrophobic modification increases the solubilization power of the resultant polymer. Furthermore, the copolymers retain their solubilization capacities to higher values of pH the more hydrophobic the comonomer and the greater its content in the copolymer. The interiors of the hydrophobic aggregates reduce the mobilities of occluded guests: the microviscosities of the domain interiors depend upon the nature of the hydrophobe, pH, and copolymer composition.

Fluorescence studies of pyrene-labelled, pH-responsive diblock copolymer micelles in aqueous solution

“…This is contrary to expectation: previous fluorescence measurements using a methyl orange probe confirmed [54] that the homopolymer, PDMA, changes from an extended structure at low pH to a compact coil at high pH [55,56]. From our experience of the conformational behaviour of smart polymers using a pyrene probe [8,15,49,50], and with reference to the literature [1,4,6], it was expected that the fluorescence lifetime of the label should increase assuming that the DMA component induces a chain collapse in the block copolymer. (Under these circumstances the fluorophore would experience a more hydrophobic environment).…”

“…This form of data treatment has proven particularly informative in our previous studies of the conformational behaviour of stimulus-responsive polymers [8,10,15,49,50]. The ht f i values obtained for py-DEA 30 eDMA 130 from this form of analysis for all pH values are listed in Table 1.…”

“…Indeed, t f data, coupled with information derived from the analysis of vibrational fine structure of the fluorescence emission, have been used to investigate the conformational behaviour of pH-responsive, water-soluble polymers [1,3,4,6,10,15,49,50]. Previous work on PDEA-b-PDMA block copolymer micelles has utilised the sensitivity of pyrene (present as a probe) to its environment: the hydrophobicity of the micellar core increased on adjusting the pH from 7 to 9 [38].…”

Luminescence techniques and characterization of the morphology of polymer latices

“…See, for example, Refs. [5] and [26] and references therein.) The time-resolved fluorescence behavior of the various labels of the PBMA latices is somewhat similar to that which each label would exhibit in the hypercoiled acidic form of PMAA in aqueous media.…”

Measuring poly(acrylamide) flocculants in fresh water using inter-polymer complex formation

“…This results in a dramatic increase in the correlation time (τ c ) of the fluorophore. Usually the correlation time of the PAA probe in acidic media will be 6 nanoseconds 24 . However in the presence of polyacrylamide the correlation time was documented to rise as high as 180 nanoseconds because of the severe restriction on rotation due to formation of an IPC.…”