Phase Transition Of Copolymers Research Articles

Critical role of lattice vacancies in pressure-induced phase transitions of baroplastic diblock copolymers.

Baroplastic diblock copolymers exhibit order-disorder transitions and melt upon compression at low temperatures, in some cases even at ambient temperatures. Their unique low-temperature processability makes them promising candidates for sustainable polymeric materials. Despite their potential, however, the molecular mechanisms governing the pressure-induced phase transitions of these copolymers remain largely unexplored. This study develops a compressible self-consistent field theory for baroplastic copolymers based on a simple lattice vacancy model that explicitly incorporates voids to account for compressibility. The theory shows that the selective presence of voids in compressible domains stabilizes the ordered phase, while a reduction of voids under compression leads to the order-disorder transition. In addition, this work demonstrates for the first time the critical role of gas absorption rates in each segment in the pressure-induced order-disorder transition of baroplastic diblock copolymers. These findings have significant implications for the rational design of baroplastic polymers with tailored low-temperature processability.

Phase Transitions in Polyester-Polyether Copolymers

Using differential scanning calorimetry, phase transitions in polycarbonate-polytetramethylene oxide block copolymers were studied. It is shown that, depending on the ratio of rigid polycarbonate and flexible polytetramethylene oxide units, block copolymers can be two-phase or four-phase. It is shown that phase transitions in copolymers of a polyester-polyether depend on the ability to crystallize the components.

Amphiphilic properties of alkoxyoligoethyleneglycol methacrylates and copolymers based on them

Based on the data on the distribution of alkoxyoligo(ethyleneglycol) methacrylates in the water-hexane system, the HLB values of the macromonomers are determined. A good correlation between the temperatures of phase transitions of copolymers of alkoxyoligo(ethyleneglycol) methacrylates in aqueous solutions and calculated HLB values of the original macromonomers was shown.

Epigallocatechin Gallate-Loaded Gelatin-g-Poly(N-Isopropylacrylamide) as a New Ophthalmic Pharmaceutical Formulation for Topical Use in the Treatment of Dry Eye Syndrome

Given that biodegradable in situ gelling delivery systems may have potential applications in the design of ophthalmic pharmaceutical formulations, this study, for the first time, aims to develop gelatin-g-poly(N-isopropylacrylamide) (GN) carriers for topical epigallocatechin gallate (EGCG) administration in the treatment of dry eye disease (DED). By temperature triggered sol-gel phase transition of copolymers, EGCG-loaded GN was prepared at 32 °C and characterized by FTIR, NMR, and HPLC analyses. Results of WST-1 and live/dead assays showed that GN materials have good compatibility with corneal epithelial cells. Gradual biodegradation of delivery carriers allowed sustained release of EGCG without drug toxicity. Anti-inflammatory and antioxidant activity studies also indicated effective therapeutic drug levels at each time point within 3 days of release. In a rabbit dry eye model, corneal epithelial defects was ameliorated by treatment with single-dose administration of EGCG-containing GN. Furthermore, drug molecules released from carrier materials could prevent further tear evaporation and loss of mucin-secreting goblet cells in diseased animals. Our findings suggest that GN carrier is responsible for enhanced pharmacological efficacy of topically instilled EGCG, thereby demonstrating the benefits of using biodegradable in situ gelling delivery system to overcome the drawbacks of limited dry eye relief associated with eye drop dosage form.

Anomalous ferroelectricity in P(VDF70-TrFE30)

ABSTRACTThe ferroelectric phase transition of copolymers of vinylidene fluoride (VDF) with trifluoroethylene (TrFE) is well known and related to conformational changes in the polymer chain. Contrary to the expected paraelectric behaviour in the high temperature phase a pyroelectric investigation of the phase transition in the range from 0°C to 130°C combined with X-ray diffraction indicate the copolymer as ferroelectric when prepared and polarised in the high-temperature phase. Based on this finding the orthorhombic space-group Fmm2 is proposed for the polar high-temperature phase. Above the Curie temperature the material exhibits pyroelectricity with inverted sign, whose origin is interpreted as flexoelectricity.

Thermo-responsive triblock copolymer phase transition behaviour in imidazolium-based ionic liquids: Role of the effect of alkyl chain length of cations

Different biophysical techniques such as fluorescence spectroscopy, dynamic light scattering (DLS), viscosity (η) and Fourier transform infrared (FTIR) spectroscopy have been carried out to characterize the effect of imidazolium-based ionic liquids (ILs) on the thermo-responsive triblock copolymer, poly(ethylene glycol)-block-poly(propylene glycol)-block-poly-(ethylene glycol) (PEG-PPG-PEG). In addition, to demonstrate the distinct morphological changes of various self-assembled morphologies, we further employed field emission scanning electron microscope (FESEM). To investigate the effect of alkyl chain length of the cation, concentration of the ILs and the related Hofmeister series on the phase behaviour of PEG-PPG-PEG, we used a series of ILs possessing same Cl− anion and a set of cation [Cnmim]+ with increasing alkyl chain length of cation such as 1-ethyl-3-methylimidazolium chloride ([Emim][Cl]), 1-butyl-3-methylimidazolium chloride ([Bmim][Cl]), 1-hexyl-3-methylimidazolium chloride ([Hmim][Cl]) and 1-decyl-3-methylimidazolium chloride ([Dmim][Cl]). The critical micellization temperature (CMT) of the copolymer in the presence of well hydrated cations is directly correlated to their hydration. The overall specific ranking of ILs in decreasing the CMT of PEG-PPG-PEG in aqueous solution was [Emim][Cl]>[Bmim][Cl]>[Hmim][Cl]>[Dmim][Cl]. The trend of these ILs followed the well-known Hofmeister series of cations of ILs. The present study provides important information about the solution properties that can be helpful to tune the IL or temperature-sensitive copolymer CMT and micelle shapes which are crucial for understanding the drug delivery mechanisms.

Design of Environmentally Responsive Fluorescent Polymer Probes for Cellular Imaging.

We report the development of environmentally responsive fluorescent polymers. The reversible temperature-induced phase transition of copolymers composed of N-isopropylacrylamide and a fluorescent monomer based on the fluorescein (FL), coumarin (CO), rhodamine (RH), or dansyl (DA) skeleton was used as a molecular switch to control the fluorescence intensity. The poly(N-isopropylacrylamide) (PNIPAAm) chain showed an expanded coil conformation below the lower critical solution temperature (LCST) due to hydration, but it changed to a globular form above the LCST due to dehydration. Through the combination of a polarity-sensitive fluorophore with PNIPAAm, the synthetic fluorescent polymer displayed a response to external temperature, with the fluorescence strength dramatically changing close to the LCST. Additionally, the P(NIPAAm-co-FL) and P(NIPAAm-co-CO) polymers, containing fluorescein and coumarin groups, respectively, exhibited pH responsiveness. The environmental responsiveness of the reported polymers is derived directly from the PNIPAAm and fluorophore structures, thus allowing for the cellular uptake of the fluorescence copolymer by RAW264.7 cells to be temperature-controlled. Cellular uptake was suppressed below the LCST but enhanced above the LCST. Furthermore, the cellular uptake of both P(NIPAAm-co-CO) and P(NIPAAm-co-RH) conjugated with a fusogenic lipid, namely, l-α-phosphatidylethanolamine, dioleoyl (DOPE), was enhanced. Such lipid-conjugated fluorescence probes are expected to be useful as physiological indicators for intracellular imaging.

Thermoresponsive anionic copolymer brushes containing strong acid moieties for effective separation of basic biomolecules and proteins.

A thermoresponsive copolymer brush possessing the sulfonic acid group, poly(N-isopropylacrylamide (IPAAm)-co-2-acrylamido-2-methylpropanesulfonic acid (AMPS)-co-tert-butylacrylamide (tBAAm)), was grafted onto the surface of silica beads through surface-initiated atom transfer radical polymerization. Prepared copolymer and copolymer brushes on silica beads were characterized by observing the phase transition profile, CHNS elemental analysis, X-ray photoelectron spectroscopy, and gel permeation chromatography. The phase transition profile indicated that an appropriate AMPS composition for enabling thermally modulated property changes is 5 mol %, while excessive amounts of sulfonic acid groups prevented copolymer phase transition. Chromatographic elutions of catecholamine derivatives and basic proteins were observed, using the prepared copolymer brush-modified beads as chromatographic matrices, and the results suggest that the beads interact with these analytes through relatively strong electrostatic interactions. Thus, poly(IPAAm-co-AMPS-co-tBAAm) brush-modified beads will be useful for effective thermoresponsive chromatography matrices that separate basic biomolecules through strong electrostatic interactions.

Development of injectable, resorbable drug-releasing copolymer scaffolds for minimally invasive sustained ophthalmic therapeutics

Copolymers based on N-isopropylacrylamide (NIPAAm), acrylic acid N-hydroxysuccinimide (NAS) and varying concentrations of acrylic acid (AA) and acryloyloxy dimethyl-γ-butyrolactone (DBA) were synthesized to create thermoresponsive, resorbable copolymers for minimally invasive drug and/or cell delivery to the posterior segment of the eye to combat retinal degenerative diseases. Increasing DBA content was found to decrease both copolymer water content and lower critical solution temperature. The incorporation of NAS provided an amine-reactive site, which can be exploited for facile conjugation of bioactive agents. Proton nuclear magnetic resonance analysis revealed the onset of hydrolysis-dependent opening of the DBA lactone ring, which successfully eradicated copolymer phase transition properties and should allow the gelled polymer to re-hydrate, enter systemic circulation and be cleared from the body without the production of degradation byproducts. Hydrolytic ring opening occurs slowly, with over 85% copolymer mass remaining after 130days of incubation in 37°C phosphate buffered saline. These slow-degrading copolymers are hypothesized to be ideal delivery vehicles to provide minimally invasive, sustained, localized release of pharmaceuticals within the posterior segment of the eye to combat retinal degenerative diseases.

Dielectric Relaxation in VDF-TeFE Copolymer Near Melting Temperature

The study of dielectric response dispersion in the vicinity of melting temperature lying slightly above the ferroelectric phase transition in copolymer of vinylidene fluoride-tetrafluoroethylene P (VDF 0.88 TeFE 0.12 ) within the frequency range 25-10 6 Hz was carried out. It was found increasing of characteristic relaxation time (τ) as a temperature is approached to a point of phase equilibrium from below. The observed dependence τ (T) can be described in terms of the phenomenological theory of diffused first-order phase transition.

FTIR Microanalysis and Phase Behaviour of Ethylene/1‐Hexene Random Copolymers

AbstractEthylene/1‐hexene random copolymers with 1‐hexene content in the range of 1–5 mol‐%, synthesised in the presence of new heterogeneous catalyst systems based on bis‐carboxylato and ‐bis‐chloro‐carboxylato titanium chelate complexes, have been characterised by FTIR microspectroscopy (FTIR‐M), DSC calorimetry and X‐ray scattering. The co‐monomer content and sequence distribution in the various samples were determined by means of both FTIR‐M and 13C NMR spectroscopy. The deformation bands of methyl groups in the region of 1 400–1 330 cm−1 were used for the structural analysis of these copolymers. The effect of composition on the crystallinity and phase transitions of copolymers was analysed both in 1 500–1 300 and 760–690 cm−1 frequency ranges as a function of the annealing temperature. A neat variation of the absorbance ratio of methyl band at 1 378 cm−1 was recorded between 110 and 130 °C corresponding to the melting range of the copolymer crystals. The crystallisation behaviour of the copolymers was examined by DSC in dynamic and isothermal conditions; the isothermal kinetics were analysed according to the Avrami model. A marked decrease in the bulk crystallisation rate, accompanied by changes in the nucleation and growth of crystals, was found with an increase in the co‐monomer content. The melting behaviour of isothermally crystallised samples was also investigated and the melting temperatures of the copolymers at equilibrium conditions were related to the composition; the experimental data were consistent with the Flory exclusion model of side branches from the crystalline phase. The lowering of crystal growth rate in the copolymers has been accounted for by an increase in the free energy of formation of critical size nuclei due to the effect of the side branches.magnified image

Monte Carlo Simulation of a Model System for Ferroelectric Phase Transition in Polymers

A model for ferroelectric phase transitions in copolymers of vinylidene fluoride (VDF) and trifluoroethylene (TrFE) has been examined using Monte Carlo (MC) simulation. The model assumes simple three-states which reflect structural variation of polymers in addition to the directional degrees of freedom of dipoles attached to molecular segments. Results of the simulation qualitatively supported theoretical interpretations obtained by the Bethe approximation of the model. Furthermore, microscopic details of the phase transition were revealed. Temperature dependences of spontaneous polarization and specific heat exhibit clearly a change in a thermodynamic order of the phase transition. The phase transition is classified by a ratio n of intramolecular interaction to intermolecular interaction. The specific heat of the system becomes the maximum at the ratio n where the temperature hysteresis of the phase transition vanishes. It shows that the phase transition is changed from the first order transition to the diffuse one through the critical second order phase transition. In addition, the transformation mechanisms are predicted. The system exhibiting the first order phase transition is transformed due to nucleation and growth. The system doing the diffuse transition is transformed due to spinodal decomposition.

Effects of Polyols, Saccharides, and Glycoproteins on Thermoprecipitation of Phenylboronate-Containing Copolymers

The copolymer of 3-(acrylamido)phenylboronic acid and N-isopropylacrylamide (82:18, Mn = 47000 g/mol) was prepared by free radical polymerization. The copolymer showed typical thermoprecipitation behavior in aqueous solutions; its phase transition temperature (TP) was 26.5 +/- 0.2 degrees C in 0.1 M glycine-NaOH buffer containing 0.1 M NaCl, pH 9.2. Due to specific complex formation of the pendant boronates with sugars, TP was strongly affected by the type of sugar and its concentration at pH 9.2. Fructose, lactulose, and glucose caused the largest increase in TP (up to 4 degrees C) at 0.56 mM concentration, attributed to the high binding affinity of the sugars to borate and phenylboronate. Among the sugars typical of nonreducing ends of oligosaccharides, N-acetylneuraminic acid had the strongest effect on TP (ca. 2 degrees C at 0.56 mM concentration and pH 9.2), while the effects of other sugars are well expressed at the higher concentrations (16 and 80 mM) and decreased in the order xylose approximately galactose >or= N-acetyllactosamine >or= mannose approximately fucose >> N-acetylglucosamine. The effect exerted on the phase transition by glycoproteins was the strongest with mucin from porcine stomach and decreased in the series mucin > horseradish peroxidase > human gamma-globulin at pH 9.2. As a first approximation, the weight percentage and/or the number of oligosaccharides in glycoproteins determined the character of their interaction with the pendant phenylboronates and, therefore, the effect on the copolymer phase transition.

Copolymerization of 2-carboxyisopropylacrylamide with N-isopropylacrylamide accelerates cell detachment from grafted surfaces by reducing temperature.

Acrylic acid (AAc) has been utilized to introduce reactive carboxyl groups to a temperature-responsive polymer, poly(N-isopropylacrylamide) (PIPAAm). However, AAc introduction shifts the copolymer phase transition temperatures higher and dampens the steep homopolymer phase transition with increasing AAc content. We previously synthesized 2-carboxyisopropylacrylamide (CIPAAm) having both a similar side chain structure to IPAAm and a functional carboxylate group in order to overcome these shortcomings. In the present study, these copolymers, grafted onto cell culture plastic, were assessed for cell adhesion control using their phase transition. AAc introduction to PIPAAm-grafted surfaces resulted in excessive surface hydration and hindered cell spreading in culture at 37 degrees C. In contrast, CIPAAm-containing copolymer-grafted surfaces exhibited relatively weak hydrophobicity similar to both homopolymer PIPAAm-grafted surfaces as well as commercial ungrafted tissue culture polystyrene dish surfaces. Cells adhered and spread well on these surfaces at 37 degrees C in culture. As observed previously on PIPAAm-grafted surfaces, cells were spontaneously detached from the copolymer-grafted surfaces by reducing culture temperature. Cell detachment was accelerated on the CIPAAm copolymer-grafted surfaces compared to pure IPAAm surfaces, suggesting that hydrophilic carboxyl group microenvironment in the monomer and polymer is important to accelerate grafted surface hydration below the lower critical solution temperature, detaching cells.

Fourier transform IR spectroscopic study on phase transitions of copolymers of N-isopropylacrylamide and alkyl acrylates in water

Copolymers of N-isopropylacrylamide (IPA) and alkyl acrylates [methyl acrylate (MA), ethyl acrylate, and butyl acrylate] or vinyl acetate have been prepared and their phase transitions in water have been observed by means of IR spectroscopy. The incorporation of these alkyl acrylates into a poly(IPA) (PIPA) chain induces a decrease in the phase-transition temperatures, T p, and the magnitude increases with increasing size of the alkyl chains. The profiles of the C=O stretching absorption bands of the ester groups [ν(C=O)ester] and the IR bands due to IPA units exhibit critical changes at the T p of these copolymers. The ν(C=O)ester bands shift slightly toward higher wavenumbers (blueshift) upon phase transition, while the amide I and amide II bands of the IPA units undergo a blueshift and a redshift, respectively. Analysis of the ν(C=O)ester band of PIPA–MA by using a curve-fitting method shows that it consists of three components, at 1,703, 1,720, and 1,738 cm–1. The relative peak area of the largest component (1,720 cm–1) is almost constant, and those of the 1,703-cm–1 and 1,738-cm–1 components increase and decrease with increasing temperature during the phase transition, respectively. However, the changes are rather small, suggesting that changes in hydrogen bonding of the C=O groups of MA units upon phase transition are not significant. The ν(C=O)ester bands of other comonomers examined here also exhibit similar changes. The situation is consistent with the change in the hydration states of the amide groups of IPA units, most of which associate with water molecules through hydrogen bonds even after the phase separation.

FTIR Spectroscopic and Calorimetric Studies of the Phase Transitions of N-Isopropylacrylamide Copolymers in Water

The phase transitions of copolymers of N-isopropylacrylamide (iPA) with acrylamide (PiPA-AAm) or acrylonitrile (PiPA-AN) in water have been observed by means of Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC). The effects of both incorporation of these comonomer units and addition of salts to their aqueous solutions on the phase behaviors have been investigated. The positions of IR bands due to iPA and the comonomer units critically shift at lower critical solution temperatures (LCST) of these copolymers. The phase transition leads shifts of the amide II, C−H stretching, and C−H bending bands to lower wavenumbers and a shift of the amide I band to a higher wavenumber. The C⋮N stretching band (ν(C⋮N)) of AN units in PiPA-AN shifts to a lower wavenumber. These shifts of the IR bands indicate that corresponding chemical groups experience dehydration to some extent upon the transition. The ν(C⋮N) band is composed of two components due to the C⋮N groups that form a hy...

A simple lattice model for phase transitions in block copolymers

Phase transitions in copolymers are considered in terms of configurational probabilities. It is shown that ordering transitions in block copolymers appear as a stepped increase in the probability of a dominating configuration and a simultaneous decrease of the probabilities for other configurations.

Ordering in thin films of asymmetric diblock copolymers

The time evolution of the free surface of asymmetric diblock copolymers of polystyrene and poly(methyl methacrylate) on a strongly interacting surface was studied with atomic force microscopy. The surface morphology underwent morphological transitions to satisfy commensurability conditions. These transformations were consistent with recent self-consistent field arguments predicting the phase transitions of copolymers as a function of thickness (see M. J. Fasolka, P. Banerjee, A. M. Mayes, G. Pickett, & A. C. Balazs, Macromolecules 2000, 33, 5702).

Photo-induced phase transition of side chain liquid crystalline copolymers with photochromic group

Liquid crystalline copolymers containing 4′-cyanobiphenyl-4-oxyundecylacrylate (CBO-11-A) groups and phenylazophenyloxy-undecylacrylate (ABO-11-A) groups with various proportions were synthesized. The copolymers take a highly liquid crystalline state but the temperature range of liquid crystalline state was narrowed with increasing azobenzene content. Isothermal phase transition of copolymers was induced by the photoisomerization of the azobenzene moiety with irradiation of 365 nm light. The response time of this phase transition was measured using an excimer pulse laser (351 nm). It took from a few ms to several hundred ms at 70–80 °C to cause a phase transition in these liquid crystalline systems.

Detection of ferroelectric to paraelectric phase transition in copolymers of vinylidene fluoride by magnetic susceptibility

AbstractThe diamagnetic susceptibility of a series of random copolymers of vinylidene fluoride (VF2) with trifluoroethylene containing 60 to 100 mole‐% VF2 has been investigated, both as a function of composition and of temperature. Results show that at room temperature the molecular susceptibility of the series linearly decreases with VF2 content. Furthermore, the diamagnetic susceptibility for each composition rises gradually at the beginning of the Curie transition, reaching a plateau which characterizes the diamagnetism of the paraelectric phase. The percent increase in diamagnetism when passing from the ferroelectric to the paraelectric phase is primarily due to the changes occurring from the planar all‐trans polar conformation into the disordered molecular conformation of the high temperature phase. The reduced final increase in diamagnetism detected at the melting point suggests that conformational transformations occurring from the paraelectric phase into the molten state are small.