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The present study describes the temporaryevolution of size andmorphology of thermosensitive and biocompatible microgel particlesbased on ethylene glycol (EG). P-MeO2MA-co-OEGMA particles were synthesized by precipitation polymerization.The growth of the microgel particles was analyzed at different reactiontimes using dynamic light scattering (DLS) and small-angle neutronscattering (SANS). The scattering data show the increase of particlesize and swelling capability during the polymerization process. After60 min further continuation of the polymerization reaction causesno further change of neither external nor internal particle properties.SANS measurements reveal the formation of a dense core, mainly consistingof cross-linker at an early polymerization state. This is followedby the growth of a loosely packed polymer shell. Nanodomains, observedduring the volume phase transition (VPT), as well as a second correlation-lengthof the network fluctuations arise with progressing polymerizationreaction related to the buildup of the shell. [ABSTRACT FROM AUTHOR]

Syndiotactic polystyrene (sPS) occupies a peculiar position among crystalline polymers: it forms co-crystals with many different kinds of chemical compounds, where the molecules are confined as guests in the regularly arranged cavities surrounded by the side phenyl groups. The guest molecules can be replaced smoothly by exposure to a vapour or a liquid of another compound, keeping the framework of the host polymer crystallites. It has been confirmed that the guestexchange procedure is an effective way to incorporate a variety of chemical species into the crystalline region of syndiotactic polystyrene. In order to elucidate its characteristics, the guest-exchange process in co-crystals of syndiotactic polystyrene has been studied by in situ time-resolved small-angle neutron scattering measurements, exploiting the scattering length difference between fully protonated and deuterated isotopologues of guest compounds and employing fully deuterated syndiotactic polystyrene as the host matrix to avoid strong incoherent scattering. In this study, the guest-exchange process induced by exposure to the gas of small guest molecules was followed by monitoring of the reflections from crystalline lamellae. The lamellar reflections showed significant variations in intensity during the guest exchange, from which the diffusion coefficients of the guest molecules in the crystalline region could be evaluated. [ABSTRACT FROM AUTHOR]

The amphiphilic copolymers of the Pluronic family are known to be excellent dispersants for single-walled carbon nanotubes (SWCNT) in water, especially F108 and F127, which have rather long end-blocks of poly(ethylene oxide) (PEO). In this study, the structure of the CNT/polymer hybrid formed in water is evaluated by measurements of small-angle neutron scattering (SANS) with contrast variation, as supported by cryo-transmission electron microscopy (cryo-TEM) imaging. The homogeneous, stable, inklike dispersions exhibited very small isolated bundles of carbon nanotubes in cryo-TEM images. SANS experiments were conducted at different D2O/H2O content of the dispersing solvent. The data for both systems showed surprisingly minimal intensity values at 70% D2O solvent composition, which is much higher than the expected value of 17% D2O that is based on the scattering length density (SLD) of PEO. At this near match point, the data exhibited a q−1power law relation of intensity to the scattering vector (q), indicating rodlike entities. Two models are evaluated, as extensions to Pederson’s block copolymer micelles models. One is loosely adsorbed polymer chains on a rodlike CNT bundle. In the other, the hydrophobic block is considered to form a continuous hydrated shell on the CNT surface, whereas the hydrophilic blocks emanate into the solvent. Both models were found to fit the experimental data reasonably well. The model fit required special considerations of the tight association of water molecules around PEO chains and slight isotopic selectivity. [ABSTRACT FROM AUTHOR]

Complexes formed between cyclodextrins(CDs) and polymers - pseudopolyrotaxanes(PPRs) - are the starting point of a multitude of supramolecular structures,which are proposed for a wide range of biomedical and technologicalapplications. In this work, we investigate the complexation of a rangeof cyclodextrins with Tetronic T1307, a four-arm block copolymer ofpoly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) witha pH-responsive central ethylene diamine spacer, and its impact onmicellization and the sol–gel transition. At low concentrations,small-angle neutron scattering (SANS) combined with dynamic lightscattering (DLS) measurements show the presence of spherical micelleswith a highly hydrated shell and a dehydrated core. Increasing thetemperature leads to more compact micelles and larger aggregationnumbers, whereas acidic conditions induce a shrinking of the micelles,with fewer unimers per micelle and a more hydrated corona. At highconcentrations, T1307 undergoes a sol–gel transition, whichis suppressed at pH below the pKa,1(4.6).SANS data analysis reveals that the gels result from a random packingof the micelles, which have an increasing aggregation number and increasinglydehydrated shell and hydrated core with the temperature. Native CDs(α, β, γ-CD) can complex T1307, resulting in theprecipitation of a PPR. Instead, modified CDs compete with micellizationto an extent that is critically dependent on the nature of the substitution. 1H and ROESY NMR combined with SANS demonstrate that dimethylatedβ-CD can thread onto the polymer, preferentially binding tothe PO units, thus hindering self-aggregation by solubilizing thehydrophobic block. The various CDs are able to modulate the onsetof gelation and the extent of the gel phase, and the effect correlateswith the ability of the CDs to disrupt the micelles, with the exceptionof a sulfated sodium salt of β-CD, which, while not affectingthe CMT, is able to fully suppress the gel phase. [ABSTRACT FROM AUTHOR]

Inclusion complexes between cyclodextrinsand polymersso-calledpseudopolyrotaxanes (PPR)are at the origin of fascinatingsupramolecular structures, which are finding increasing uses in biomedicaland technological fields. Here we explore the impact of both nativeand a range of modified cyclodextrins (CD) on the self-assembly ofX-shaped poly(ethylene oxide)–poly(propylene oxide) block copolymers,so-called Tetronics or poloxamines, by focusing on Tetronic 904 (T904, Mw6700). The effects are markedly dependenton the type and arrangement of the substituents on the macrocycle.While native CDs drive the formation of a solid PPR, most substitutedCDs induce micellar breakup, with dimethylated β-CD (DIMEB)having the strongest impact and randomly substituted CDs a much weakerdisruptive effect. Using native α-CD as a “moleculartrap”, we perform competitive binding experimentswheretwo types of CDs thread together onto the polymer chainstoestablish that DIMEB indeed has the highest propensity to form aninclusion complex with the polymer, while hydroxypropylated CDs donot thread. 1D 1H NMR and ROESY experiments confirm theformation of a soluble PPR with DIMEB in which the CD binds preferentiallyto the PO units, thus providing the drive for the observed demicellization.A combination of dynamic light scattering (DLS) and small-angle neutronscattering (SANS) is used to extract detailed structural parameterson the micelles. A binding model is proposed, which exploits the chemicalshifts of selected protons from the CD in conjunction with the Hillequation, to prove that the formation of the PPR is a negatively cooperativeprocess, in which threaded DIMEBs hamper the entrance of subsequentmacrocycles. [ABSTRACT FROM AUTHOR]

By the use of small angle neutron scattering, the chain conformation in a polymer nanocomposite was studied as a function of the nanoparticle fraction for two different molecular weights. A repulsive system was realized in mixing poly(ethylene−propylene) and hydrophobically modified silica. All nanocomposite SANS data exhibit a pronounced scattering peak at intermediate momentum transfers, which is closely connected with the particle structure. Even under contrast matching conditions, the hydrophobic surface layer of the nanoparticles was found to contribute significantly to the scattering signal. In particular, in the short chain matrix the peak origin is exclusively related to direct particle scattering. In the long chain matrix, an additional peak contribution is present. Possible origins include void correlation scattering or polymer correlation scattering. We show unambiguously that the conformation of short chains with a molecular weight of 3000 g/mol is not visibly disturbed by the presence of the nanoparticles. In contrast to that a polymer matrix with 50 000 g/mol chains is affected by the particle presence. The chain radius of gyration Rgdecreases. [ABSTRACT FROM AUTHOR]

The structure of poly(vinyl alcohol) (PVA) hydrogels formed as a result of freeze/thaw treatments of aqueous solutions of the polymer (11 wt % PVA) in the freshly prepared state is analyzed through the combined use of small (SANS) and ultrasmall (USANS) angle neutron scattering techniques. The structure of these hydrogels may be described in terms of polymer rich regions, with dimensions of the order of 1−2 m, dispersed in a water rich phase, forming two bicontinuous phases. The PVA chains in the polymer rich phase form a network where the cross-linking points are mainly crystalline aggregates of PVA having average dimensions of ∼45 Å. The structural organization of freeze/thaw PVA hydrogel membranes does not change either after rehydration of dried gels or in the presence of a tensile force. Finally, addition of surfactant micelles inside the gel provides a formulation with both hydrophobic and hydrophilic regions, which demonstrates the potential of the system for drug delivery. Both SANS and EPR measurements show that sodium decylsulfate (C10OS) micelles do not significantly interact with the PVA gel. Variation of the gel structure by the number of freeze/thaw cycles should modulate the rate of release of an active constituent, for example, in a dermal patch. [ABSTRACT FROM AUTHOR]