The Structure of Water in PEO‐Based Segmented Block Copolymers and its Effect on Transition Temperatures

Husken, D.; Gaymans, R.J.

doi:10.1002/macp.200700584

Cited by 13 publications

(34 citation statements)

References 47 publications

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“…At heating rates typically used in DSC scans (10 °C /min), free water shows a broad melting peak that starts at 0 °C and is centered at ~ 5 °C. At cooling rates of 10 °C/min used in this study, which are typical, the free water supercools and freezes at ~ −20 °C [11, 49]. Such sharp freezing exotherm and broad melting behavior for water was seen in all of our samples with at least ~ 1 wt % water.…”

Section: Resultsmentioning

confidence: 75%

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Microphase separation in copolymers of hydrophilic PEG blocks and hydrophobic tyrosine-derived segments using simultaneous SAXS/WAXS/DSC

Murthy

Wang

Kohn

2010

Polymer

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Hydration-and temperature-induced microphase separations were investigated by simultaneous small-and wide-angle X-ray scattering (SAXS and WAXS) and differential scanning calorimetry (DSC) in a family of copolymers in which hydrophilic poly(ethylene glycol) (PEG) blocks are inserted randomly into a hydrophobic polymer made of either desaminotyrosyl-tyrosine ethyl ester (DTE) or iodinated I 2 DTE segments. Iodination of the tyrosine rings in I 2 DTE increased the X-ray contrast between the hydrophobic and hydrophilic segments in addition to facilitating the study of the effect of iodination on microphase separation. The formation of phase-separated, hydrated PEG domains is of considerable significance as it profoundly affects the polymer properties. The copolymers of DTE (or I 2 DTE) and PEG are a useful model system and the findings presented here may be applicable to other PEG-containing random copolymers as well. In copolymers of PEG and DTE and I 2 DTE, the presence of PEG depressed the glass transition temperature (T g ) of the copolymer relative to the homopolymer, poly(DTE carbonate), and the DTE/ I 2 DTE segments hindered the crystallization of the PEG segments. In the dry state, at large PEG fractions (> 70 vol %), the PEG domains self-assembled into an ordered structure with 14-18 nm distance between the domains. These domains gave rise to a SAXS peak at all temperatures in the iodinated polymers, but only above the T g in non-iodinated polymers, due to the unexpected contrast-match between the crystalline PEG domains and the glassy DTE segments. Irrespective of whether PEG was crystalline or not, immersion of these copolymers in water resulted in the formation of hydrated PEG domains that were 10-20 nm apart. Since both water and the polymer chains must be mobile for the phase separation to occur, the PEG domains disappeared when the water froze, and reappeared as the ice began to melt. This transformation was reversible, and showed hysteresis as did the melting of ice and freezing of the water incorporated into the polymer. PEG-water complexes and PEG-water eutectics were observed in WAXS and DSC scans, respectively.

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Section: Resultsmentioning

confidence: 75%

“…The influence of PEG depends on whether the polymer is a blend [5–6], a graft [1, 7], a diblock [8–10] or a segmented block [11] copolymer. Segmented block copolymers with PEG as one the blocks have been studied in aqueous solution [12–14], gel [15], and in the solid phase [10, 16–17].…”

Section: Introductionmentioning

confidence: 99%

Microphase separation in copolymers of hydrophilic PEG blocks and hydrophobic tyrosine-derived segments using simultaneous SAXS/WAXS/DSC

Murthy

Wang

Kohn

2010

Polymer

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“…These discrete domains could be the precursors of the water channels that facilitate the erosion of the polymer. An AFM study of the morphology in a segmented block copolymer with PEG as one of the blocks in a chain of crystallizable tetra-amide segments showed that the polymer swells inhomogeneously and the surfaces have 10–50 nm high and 100 nm wide clusters [33]. In our study the PEG is incorporated into a noncrystallizable main-chain, and shows much smaller hydrated clusters.…”

Section: Resultsmentioning

confidence: 58%

Study of nanoscale structures in hydrated biomaterials using small-angle neutron scattering

Luk¹,

Murthy²,

Wang³

et al. 2012

Acta Biomaterialia

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Distribution of water in three classes of biomedically relevant and degradable polymers was investigated using small-angle neutron scattering. In semicrystalline polymers, such as poly(lactic acid) and poly(glycolic acid), water was found to diffuse preferentially into the noncrystalline regions. In amorphous polymers, such as poly(D,L-lactic acid) and poly(lactic-co-glycolic acid), the scattering after 7-days of incubation was attributed to water in microvoids that form following the hydrolytic degradation of the polymer. In amorphous copolymers containing hydrophobic segments (desaminotyrosyl-tyrosine ethyl ester) and hydrophilic blocks (poly(ethylene glycol) PEG), a sequence of distinct regimes of hydration were observed: homogeneous distribution (~ 10 Å length scales) at <13 wt% PEG (~ 1 water per EG), clusters of hydrated domains (~50 Å radius) separated at 24 wt% PEG (1 to 2 water per EG), uniformly distributed hydrated domains at 41 wt% PEG (~ 4 water per EG), and phase inversion at > 50 wt% PEG ( > 6 water per EG ). Increasing PEG content increased the number of these domains with only a small decrease in distance between the domains. These discrete domains appeared to coalesce to form submicron droplets at ~60 °C, above the melting temperature of crystalline PEG. Significance of such observations on the evolution of μm size channels that form during hydrolytic erosion is discussed.

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“…This scattering arises from the fluctuations in the distribution of water at 10 –100 nm length scale. These fluctuations could be in the form of clusters, domains or networks of water shown schematically in the inset to the figure [36–37]. The q -range of these plots suggests that the length scale of these structures is 10–100 nm.…”

Section: Resultsmentioning

confidence: 99%

Multiscale analysis of water uptake and erosion in biodegradable polyarylates

Valenzuela

Zhang

Flach

et al. 2012

Polymer Degradation and Stability

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The role of hydration in degradation and erosion of materials, especially biomaterials used in scaffolds and implants, was investigated by studying the distribution of water at length scales from 0.1 nm to 0.1 mm using Raman spectroscopy, small-angle neutron scattering (SANS), Raman confocal imaging, and scanning electron microscopy (SEM). The measurements were demonstrated using L-tyrosine derived polyarylates. Bound- and free- water were characterized using their respective signatures in the Raman spectra. In the presence of deuterium oxide (D2O), H-D exchange occurred at the amide carbonyl but was not detected at the ester carbonyl. Water appeared to be present in the polymer even in regions where there was little evidence for N-H to N-D exchange. SANS showed that water is not uniformly dispersed in the polymer matrix. The distribution of water can be described as mass fractals in polymers with low water content (~5 wt%), and surface fractals in polymers with larger water content (15 to 60 wt%). These fluctuations in the density of water distribution are presumed to be the precursors of the ~ 20 μm water pockets seen by Raman confocal imaging, and also give rise to 10–50 μm porous network seen in SEM. The surfaces of these polymers appeared to resist erosion while the core of the films continued to erode to form a porous structure. This could be due to differences in either the density of the polymer or the solvent environment in the bulk vs. the surface, or a combination of these two factors. There was no correlation between the rate of degradation and the amount of water uptake in these polymers, and this suggests that it is the bound-water and not the total amount of water that contributes to hydrolytic degradation.

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The Structure of Water in PEO‐Based Segmented Block Copolymers and its Effect on Transition Temperatures

Cited by 13 publications

References 47 publications

Microphase separation in copolymers of hydrophilic PEG blocks and hydrophobic tyrosine-derived segments using simultaneous SAXS/WAXS/DSC

Microphase separation in copolymers of hydrophilic PEG blocks and hydrophobic tyrosine-derived segments using simultaneous SAXS/WAXS/DSC

Study of nanoscale structures in hydrated biomaterials using small-angle neutron scattering

Multiscale analysis of water uptake and erosion in biodegradable polyarylates

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