Phase behavior of poly(2-propyl-2-oxazoline)s

Poly(2-oxazoline)s consist of a -(CH2-CH2-N)- main chain and an N-acyl substituent. They were reported for the first time in 1966/67. They have been investigated in the bulk, in solutions and in dispersions. The recent interest lies primarily in their chemical versatility and their potential for nanomedical applications. Tailoring materials for such specific applications requires a sound knowledge of their phase behaviors, which depends on intensive parameters. Amongst others, composition and temperature are of particular interest. The phase behaviors of poly(2-propyl-2-oxazoline)s (PPOxs) will be the main focus of this thesis. PPOx homopolymers are investigated as well as block copolymers (BCPs) and blends of poly(2-isopropyl-2-oxazoline) (PiPOx) and poly(lactide) (PLA). The first part describes the synthesis of the polymers. The PPOxs are prepared by cationic ring opening polymerization. They are linear, narrowly dispersed, and bear at the termini one methyl- and one azide-group. Semi-crystalline as well as amorphous PLA is synthesized by ring opening polymerization of L-lactide and DL-lactide, respectively. The linear PLAs are terminated with one propargyl- and one hydroxyl-group. Coupling of the azido- and alkyne-functional homopolymers gives a library of 18 PiPOx-b-PLA BCPs. This approach allows to compare the phase behaviors of the BCPs with those of the individual components. The next part is dedicated to a study of the solution properties of three PPOx homopolymers, namely poly(2-n-propyl-2-oxazoline) (PnPOx), poly(2-cyclopropyl-2-oxazoline) (PcyPOx) and PiPOx in water, in methanol and in water/methanol mixtures. Nuclear magnetic resonance (NMR) spectroscopy of the three polymers reveals significant differences in the side-group’s rotational freedom. Unexpectedly, these differences are reflected in the calorimetric assessment of the coil-to-globule phase transition. The phase diagrams in respect to the water/methanol composition are constructed based on transmittance measurements. Methanol is a good solvent up to its boiling point for the three PPOxs. The solubility of PnPOx in water decreases when up to 40 vol% methanol is added. This behavior termed “cononsolvency” was first reported for ternary polymer/water/methanol mixtures of poly(N-isopropyl acrylamide), a structural isomer of PnPOx and PiPOx. PiPOx and PcyPOx do not exhibit cononsolvency in the investigated ternary system. The PPOxs’ solution behaviors depend on the rotational freedom of the side-groups. In the third part, the bulk phase behavior of PiPOx, its blends with PLA, and PiPOx-b-PLA BCPs is studied. The PiPOx volume fractions in the BCPs varies from 14 to 82 %. PiPOx and PLA are miscible based on the single glass transition criterion and small angle x-ray scattering at a temperature above the melting points of the two polymers. Infrared spectroscopy indicates an attractive dipole-dipole interaction between the carbonyl moieties of the PiPOx amide and the carbonyl of the PLA ester. PiPOx and the stereo-regular PLLA are semi-crystalline. The influence of the miscibility on the crystallization is investigated by polarized optical microscopy, differential scanning calorimetry and wide-angle x-ray scattering. It is found that the presence of PLA increases the crystallization rate of PiPOx. In contrast, PLLA remains amorphous in most of the BCPs. The last part focuses on aqueous dispersions of the self-assembled PiPOx-b-PLA BCPs. The dispersions were prepared by adding a solution of a BCP in THF to water, a non-solvent of PLA but a solvent of PiPOx at low temperature. Contrary to expectation PiPOx resides in the particle interior, together with PLA. It does not form a shell of hydrated chains around the PLA core. This conclusion was attained on the basis of NMR spectroscopy and evaluation of the thermo-responsive properties of the BCP particle dispersions in water. At room temperature the particles are colloidally stable for 20 days at least. The particle morphology is investigated by cryogenic transmission electron microscopy, light scattering and small angle neutron scattering. The particles are spherical and permeated with water over the wide PiPOx volume fraction. Short segments of PiPOx reside on the particle/water interface and stabilize the dispersion. The thermo-responsive properties of the dispersions depend on the configuration and length of these segments. Attractive interactions between soluble and insoluble block are an important factor for the self-assembly of amphiphilic BCPs.Materiaalin ominaisuudet riippuvat olosuhteista ja usein olosuhteista joissa ne on työstetty. Normaalissa ilmanpaineessa vesi on kiinteä aine kun lämpötila on alle 0 °C, neste lämpötilavälillä 0 – 100 °C ja kaasu, kun lämpötila ylittää 100 °C. Rautaa ja sen seoksia lämpökäsitellään monin eri tavoin, ja kaikki johtavat erilaisiin mekaanisiin ja kemiallisiin ominaisuuksiin. Materiaalin eri fysikaalisia tiloja eri olosuhteissa kustsutaan materiaalin faasikäyttäytymiseksi. Tieto siirtymistä yhdestä tilasta toiseen on oleellisen tärkeää materiaalin sovellusten kannalta. Polymeeritieteessä materiaalien faasikäyttäytyminen on tärkeää. Useat polymeerit siirtyvät järjestymättömästä rakenteesta korkeasti järjestyneeseen kiteiseen muotoon kiteytymislämpötilassa, prosessi on analoginen veden jäätymisen kanssa. Kiteytyminen on kriittinen tuotteen mekaanisten ja optisten ominaisuuksien kannalta ja vaikuttaa tuotannon nopeuteen. Kysymys, sekoittuvatko polymeerit A ja B toisiinsa vai erottuvatko ne toisistaan, on sekin faasikäyttäytymiseen liittyvä ilmiö. Usein eri polymeereja on yhdistettävä, jotta saadaan sovelluksen vaatimia ominaisuuksia. Tärkeä kysymys on myös polymeerien liukoisuus nesteisiin. Sadetakin kuitujen ei pidä liueta veteen, mutta astianpesukoneen pesuainetabletin pinnoitteen on liuettava. Jotkut polymeeriliuokset ovat herkkiä lämpötilan muutokselle. Liukoinen polymeeri muuttuu liukenemattomaksi kriittisessä lämpötilassa lämpötilaa nostettaessa tai laskettaessa. Kriittinen lämpötila riippuu polymeerikonsentraatiosta ja muiden yhdisteiden läsnäolosta. Tällaiset polymeeriliuokset ovat kiinnostavia sellaisten sovellusten kannalta, joissa tarvitaan suuria ominaisuuksien muutoksia kapealla lämpötilavälillä. Kolloidiset dispersiot ovat esimerkki heterogeenisistä kaksifaasisysteemeistä. Kolloidinen dispersio koostuu jatkuvasta nestefaasista johon on dispergoitu partikkeleita joiden koko on luokkaa 1-1000 nm. Kolloidisysteemejä esiintyy luonnossa ja niitä valmistetaan synteettisesti. Esimerkkejä ovat maito ja lateksimaalit. Molemmissa yksi dispergoituneen faasin aineosa on polymeeri. Kolloidi on stabiili silloin kun riittävän korkea kynnys estää partikkelien aggregoitumisen. Tämä taas riippuu useista tekijöistä kuten lämpötilasta ja muista kolloidiin liuenneista aineista. Tässä työssä on tutkittu erilaisia poly(2-propyyli-2-oksatsoliinien) (PPOx) faasikäyttäytymiseen liittyviä ilmiöitä. Nämä polymeerit kiinnostavat tutkijoita niiden kemiallisen moninaisuuden vuoksi ja koska niitä voidaan käyttää biolääketieteellisissä sovelluksissa

Inversion of crystallization rates in miscible block copolymers of poly(lactide)-block-poly(2-sopropyl-2-oxazoline)

Miscible block copolymers (BCPs) are rarely studied. When one or both components of such BCPs are semi-crystalline polymers, strong effects on the crystallization behavior can be expected. We present a study of 18 miscible BCPs comprised of poly(lactide) (PLLA, semi-crystalline and PDLLA, amorphous) and poly(2-isopropyl-2-oxazoline) (PiPOx, semi-crystalline) with PiPOx volume fractions of 0.14 <phi(PiPOx) <0.82. All BCPs exhibit a single glass transition and form a homogeneous melt. Mixing has a plasticizing effect on PiPOx and increases its crystallization rates (DSC). In contrast, the crystallization rates of PLLA are dramatically reduced, or in most cases entirely prevented. During isothermal crystallization at 130 degrees C, the crystallization rates of the BCPs were inverted in comparison with those of the parent homopolymers. Crystallization drives the BCPs to phase separate and the formed crystalline structure is that of the parent homopolymers. The fast crystallization of PiPOx confines the observed superstructure. The BCPs were studied on multiple length scales - from the atomic level (WAXS, IR spectroscopy) to the meso level (AFM, SAXS) and the macroscopic superstructure (polarized optical microscopy). A mechanism of the structure evolution is presented.Peer reviewe

Poly(2-isopropyl-2-oxazoline)-b-poly(lactide) (PiPOx-b-PLA) Nanoparticles in Water : Interblock van der Waals Attraction Opposes Amphiphilic Phase Separation

Poly(2-isopropyl-2-oxazoline)-b-poly(lactide) (PiPOx-b-PLA) diblock copolymers comprise two miscible blocks: the hydrophilic and thermosensitive PiPOx and the hydrophobic PLA, a biocompatible and biodegradable polyester. They self-assemble in water, forming stable dispersions of nanoparticles with hydrodynamic radii (R-h) ranging from similar to 18 to 60 nm, depending on their molar mass, the relative size of the two blocks, and the configuration of the lactide unit. Evidence from H-1 nuclear magnetic resonance spectroscopy, light scattering, small-angle neutron scattering, and cryo-transmission electron microscopy indicates that the nanoparticles do not adopt the typical core-shell morphology. Aqueous nanoparticle dispersions heated from 20 to 80 degrees C were monitored by turbidimetry and microcalorimetry. Nanoparticles of copolymers containing a poly(DL-lactide) block coagulated irreversibly upon heating to 50 degrees C, forming particles' of various shapes (R-h similar to 200-500 nm). Dispersions of PiPOx-b-poly(L-lactide) coagulated to a lesser extent or remained stable upon heating. From the entire experimental evidence, we conclude that PiPOx-b-PLA nanoparticles consist of a core of PLA/PiPOx chains associated via dipole-dipole interactions of the PLA and PiPOx carbonyl groups. The core is surrounded by tethered PiPOx loops and tails responsible for the colloidal stability of the nanoparticles in water. While the core of all nanoparticles studied contains associated PiPOx and PLA blocks, fine details of the nanoparticles morphology vary predictably with the size and composition of the copolymers, yielding particles of distinctive thermosensitivity in aqueous dispersions.Peer reviewe

Poly(N,N-dimethylaminoethyl methacrylate) for removing chromium (VI) through polymer-enhanced ultrafiltration technique

This work is focused on the removal of Cr(VI) ions from aqueous solution using polymer-enhanced ultrafiltration (PEUF) techniques with water-soluble poly(N,N-dimethylaminoethyl methacrylate), PDMAEMA, used as sorbent. The polymer was prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization at different reaction times, characterized by size exclusion chromatography (SEC) and proton nuclear magnetic resonance (1H NMR). The sorption of Cr(VI) was studied by PEUF as a function of pH, the polymer:Cr(VI) molar ratio, and the presence of interfering ions. The PEUF-enrichment mode was used to saturate the polymer and further determine the release of Cr(VI) and regeneration of the polymer using sorption-desorption process. The RAFT polymerization showed a yield in the range 46% to 79% (determined by 1H NMR) for polymers with molecular weight (Mn) between 28 and 195 kg mol−1. The polydispersity estimated by SEC was between 1.1 and 1.8. The capacity of PDMAEMA as sorbent of Cr(VI), by the PEUF technique showed an efficient removal of Cr(VI) (100%, 25 mg L−1 in the feed) at pH 4 using polymer:Cr molar ratio of 40:1. The presence of interfering ions does not significantly decrease the retention capacity of PDMAEMA. Finally the results indicated that PDMAEMA can release Cr(VI) and be regenerated.Peer reviewe

Poly(2-propyl-2-oxazoline)s in Aqueous Methanol : To Dissolve or not to Dissolve

At room temperature, poly(N-isopropylacrylamide) (PNIPAM) is soluble in water and methanol, but it is not soluble in certain water/methanol mixtures. This phenomenon, known as cononsolvency, has been explored in great detail experimentally and theoretically in an attempt to understand the complex interactions occurring in the ternary PNIPAM/water/co-nonsolvent system. Yet little is known about the effects of the polymer structure on cononsolvency. To address this point, we investigated the temperature-dependent solution properties in water, methanol, and mixtures of the two solvents of poly(2-cyclopropyl-2-oxazoline) (PcyPOx) and two structural isomers of PNIPAM (M-n similar to 11 kg/mol): poly(2-isopropyl-2-oxazoline) (PiPOx) and poly(2-n-propyl-2-oxazoline) (PnPOx). The phase diagram of the ternary water/methanol/poly(2-propyl-2-oxazolines) (PPOx) systems, constructed based on cloud point (T-CP) measurements, revealed that PnPOx exhibits cononsolvency in water/methanol mixtures. In contrast, methanol acts as a cosolvent for PiPOx and PcyPOx in water. The enthalpy, Delta H, and temperature, T-max, of the coil-to-globule transition of the three polymers in various water/methanol mixtures were measured by high-sensitivity differential scanning calorimetry. T-max follows the same trends as T-CP, confirming the cononsolvency of PnPOx and the cosolvency of PiPOx and PcyPOx. Delta H decreases linearly as a function of the methanol content for all PPOx systems. Ancillary high-resolution H-1 NMR spectroscopy studies of PPOx solutions in D2O and methanol-d(4), coupled with DOSY and NOESY experiments revealed that the n-propyl group of PnPOx rotates freely in D2O, whereas the rotation of the isopropyl and cyclopropyl groups of PiPOx and PcyPOx, respectively, is limited due to steric restriction. This factor appears to play an important role in the case of the PPOxs/water/methanol ternary system.Peer reviewe

Poly(2-propyl-2-oxazoline)s in Aqueous Methanol : To Dissolve or not to Dissolve

At room temperature, poly(N-isopropylacrylamide) (PNIPAM) is soluble in water and methanol, but it is not soluble in certain water/methanol mixtures. This phenomenon, known as cononsolvency, has been explored in great detail experimentally and theoretically in an attempt to understand the complex interactions occurring in the ternary PNIPAM/water/co-nonsolvent system. Yet little is known about the effects of the polymer structure on cononsolvency. To address this point, we investigated the temperature-dependent solution properties in water, methanol, and mixtures of the two solvents of poly(2-cyclopropyl-2-oxazoline) (PcyPOx) and two structural isomers of PNIPAM (M-n similar to 11 kg/mol): poly(2-isopropyl-2-oxazoline) (PiPOx) and poly(2-n-propyl-2-oxazoline) (PnPOx). The phase diagram of the ternary water/methanol/poly(2-propyl-2-oxazolines) (PPOx) systems, constructed based on cloud point (T-CP) measurements, revealed that PnPOx exhibits cononsolvency in water/methanol mixtures. In contrast, methanol acts as a cosolvent for PiPOx and PcyPOx in water. The enthalpy, Delta H, and temperature, T-max, of the coil-to-globule transition of the three polymers in various water/methanol mixtures were measured by high-sensitivity differential scanning calorimetry. T-max follows the same trends as T-CP, confirming the cononsolvency of PnPOx and the cosolvency of PiPOx and PcyPOx. Delta H decreases linearly as a function of the methanol content for all PPOx systems. Ancillary high-resolution H-1 NMR spectroscopy studies of PPOx solutions in D2O and methanol-d(4), coupled with DOSY and NOESY experiments revealed that the n-propyl group of PnPOx rotates freely in D2O, whereas the rotation of the isopropyl and cyclopropyl groups of PiPOx and PcyPOx, respectively, is limited due to steric restriction. This factor appears to play an important role in the case of the PPOxs/water/methanol ternary system.Peer reviewe