Phase Transition Behavior Of Poly Research Articles

Regulatory effects of cyclodextrins on light-responsive phase transition behaviors of poly(N-isopropylacrylamide-co-N-(4-phenylazophenyl)methylacrylamide)

The physicochemical properties of light-responsive polymers have attracted widespread attention due to their ability to be precisely and conveniently modulated by light without additives or contact. Here, we report a thermo/light dual-responsive polymer, PNMA, synthesized through the free radical copolymerization of azobenzene derivative (mAzo) and N-isopropylacrylamide (NIPAM) monomers. By switching between 365 nm UV light and 450 nm visible light, the E/Z photoisomerization of the light-responsive mAzo can be reversibly controlled, and thereby adjusting the conformational changes of the PNMA polymer chain. Significantly, the stretching and contraction conformations of PNMA polymer chains can be manipulated by incorporating different types of cyclodextrins. A comprehensive comparative study was conducted to determine the light-controlled binding and dissociation processes between the azobenzene units and CDs (α-CD, β-CD and γ-CD), the influences of CDs on the photoisomerization kinetics and complexation constants of azobenzene with CDs, as well as the effect of CDs on the light-responsive phase transition behaviors of PNMA. Our results highlight the superior advantage of α-CD in constructing light-responsive systems with significant changes in hydrophilicity. Notably, by tuning the concentration of α-CD and the proportion of mAzo in PNMA, the range of light-induced thermosensitive response is significantly expanded. This study is the first to present a comparative study on the effects of three CDs on the thermo/light dual-responsive properties of polymer systems based on PNIPAM and azobenzene, providing new ideas for CD selection in the design and construction of advanced light-responsive materials based on light-responsive guest-host dissociation or hydrophilic changes of azobenzene/CD complexes.

Phase Transition Behaviors of Poly(N-isopropylacrylamide) Nanogels with Different Compositions Induced by (−)-Epigallocatechin-3-gallate and Ethyl Gallate

Phase transition behaviors of poly(N-isopropylacrylamide) nanogels with different compositions induced by (−)-epigallocatechin-3-gallate (EGCG) and ethyl gallate (EG) has been investigated systematically. Monodisperse poly(N-isopropylacrylamide-co-N-hydroxymethyl acrylamide) (P(NIPAM-co-NMAM)) and poly(N-isopropylacrylamide-co-2-hydroxyethyl methacrylate) (P(NIPAM-co-HEMA)) nanogels with different feeding monomer ratios were prepared by emulsion polymerization. P(NIPAM-co-NMAM) nanogels exhibit rapid isothermal phase transition behavior in EGCG solutions with low concentration (10−3 mol/L) in less than 10 minutes. The thermosensitive phase transition behaviors of nanogels are affected not only by the copolymerized monomers but also by the concentrations of EGCG and EG in aqueous solutions. Nanogels remain in a shrunken state and do not exhibit thermosensitive phase transition behaviors in EGCG solutions (≥5 mmol/L), whereas they display thermo-responsive phase transition behaviors in EG solutions. The volume phase transition temperature (VPTT) shifts to lower temperatures with increasing EG concentration. The diameters of P(NIPAM-co-NMAM) nanogels decrease with increasing EG concentration at temperatures between 29 and 33 °C. In contrast, the diameters of P(NIPAM-co-HEMA) nanogels increase with increasing EGCG concentration at temperatures between 37 and 45 °C. The results demonstrate the potential of nanogels for simple detection of EG and EGCG concentrations in aqueous solutions over a wide temperature range, and EGCG can serve as a signal for the burst-release of drugs from the P(NIPAM-co-NMAM)-based carriers at physiological temperature.

Influence of poly(methyl methacrylate) on the structure and phase transition behavior of poly(vinylidene fluoride)

The structure and organization of poly(vinylidene fluoride) (PVDF) spherulites in blends with poly(methyl methacrylate) of high (PMMA-H) and low (PMMA-L) molecular weights, respectively, have been studied in details. It is confirmed that the addition of PMMA-H and PMMA-L have different influence on the morphologies of PVDF spherulites in several aspects, such as the spacing of ring-band α-PVDF spherulites, the kinetics of both α-PVDF crystallization and α−γ′ solid phase transition, as well as the formation of Wagon-Wheel spherulites. First, incorporation of PMMA-L enlarges the band spacing, which is associated to the increased chain mobility of crystallizable PVDF that helps to release the surface stresses of lamellae. In contrast, the low mobility of PMMA-H chains enhances the congestion at fold surfaces, which results in a vigorous twisting and thus the formation of tightened ring-band α-PVDF structure. Second, the PMMA-H reduces the crystallization rate of PVDF more severely than the PMMA-L, resulting in an extremely slow growth rate of α-PVDF spherulites in PVDF/PMMA-H sample at 160 °C, only about one-twenty-third compared to the neat PVDF. Third, the remarkably reduced α-PVDF spherulite growth rate and enhanced α−γ′ transition rate at 160 °C lead to the formation of Wagon-Wheel PVDF spherulites with inner γ′-PVDF crystals and outer γ crystals. It originates from the synchronization of slow α-PVDF growth and accelerated α−γ′ transition rate through homoepitaxy. That is, when the α−γ′ transition with exceeded rate reaches the growth front of the original α-PVDF spherulite, the transformed γ′-PVDF crystals trigger the growth of γ-PVDF crystals directly from melt with non-band feature. These results help to unravel the formation mechanism of Wagon-Wheel PVDF spherulites to be the competition of α-γ′ crystal transformation and α-spherulite radial growth rates.

Effect of Tacticity Sequence of the Poly(N-isopropylacrylamide) Oligomer on Phase Transition Behavior in Aqueous Solution.

The tacticity of poly(N-isopropylacrylamide) (PNIPAM) has a strong impact on the lower critical solution temperature (LCST) in aqueous solution. The sequence of meso diads (m) and racemo diads (r) further contributes to such an effect. In this work, the phase transition behaviors of poly(N-isopropylacrylamide) pentamers with four kinds of sequences, i.e., rrmm, rmmr, mrrm, and rmrm, in water were studied applying replica exchange molecular dynamics with a modified OPLS/AA force field. The difference in local component concentration in the system was used as an order parameter to quantitatively describe the phase separation extent. It was found that the phase separation degree of rrmm and rmmr is higher than that of mrrm and rmrm at the same temperature. The LCSTs of rrmm and rmmr are lower than those of mrrm and rmrm. The radial distribution function and hydrogen bond analysis revealed that the average values of hydrogen bonds between pentamers for rrmm and rmmr are greater than those of mrrm and rmrm, whereas the average values of hydrogen bonds between pentamers and water for rrmm and rmmr are less than those of mrrm and rmrm. It was demonstrated that the isotactic triad (mm) plays an important role in the thermosensitive behaviors of the PNIPAM pentamer. The increase of isotactic triad (mm) content in the PNIPAM chain promotes the formation of intermolecular hydrogen bonds between amide and amide and leads to a higher aggregation of the pentamer with the sequence of rrmm or rmmr. Finally, the effect of the isotactic triad was qualitatively explained with the mean-field theory.

Phototunable Cloud Point Temperatures Stemming from Cyclic Topology: Synthesis and Thermal Phase Transition Behavior of Cyclic Poly(N-acryloylsarcosine methyl ester).

Cyclic polymers possess distinct properties compared with their linear counterparts, such as smaller hydrodynamic volume, lower viscosity, and higher glass-transition temperature, etc. To explore the impact of the cyclic topology on the thermo-induced phase transition behavior of poly(N-acryloylsarcosine methyl ester) (PNASME), the anthracene-terminated telechelic PNASMEs are synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization of monomer NASME using a bifunctional chain transfer agent (CTA) with two anthryl groups. Subsequently, cyclic PNASMEs are prepared via UV-induced cyclization under 365nm UV. There are considerable increases (up to 50°C) for the cloud point temperatures (Tcp s) of cyclic PNASMEs compared with the linear counterparts. In view of the increment, the Tcp of PNASME is tuned by varying the cyclic/linear ratio (the molar ratio between cyclic PNASME and linear PNASME in the product) with different irradiation time.

Phase transition behavior of Poly(vinylidene fluoride) in a blend with Poly(butylene adipate) at high temperature

Blends of poly(vinylidene fluoride)/poly(1,4-butylene adipate) (PVDF/PBA) with a mass ratio of 80/20 were prepared and then isothermally crystallized at high temperature. It appears that the presence of PBA can promote the α-to-γ′ phase transition of PVDF in the blends. The phase transition of PVDF in the blends can take place after shorter time and at relatively lower temperature than that in the neat PVDF. The α-to-γ′ transition prefers to start from the central part of the original α-spherulites and propagate along radial direction. Moreover, the morphology changes on lamellae scale after α-to-γ′ transition, i.e., the band structure of some α-spherulites disappears and much more lamellae become cross-linked. This is in contradictory to the proposed solid-to-solid transition mechanism in the literature.

Thermal phase transition of poly(N-vinyl caprolactam)-based copolymers: the distribution of hydrophilic units within polymeric chains

Here, cloud temperature and aggregation behaviors of poly(N-vinyl caprolactam)-based polymer were investigated with the addition of hydrophilic units. Copolymers composed of N-vinyl caprolactam and polyethyleneglycol methylacrylate (POEGMA) were firstly synthesized through a reversible addition fragmentation chain transfer technology with benzylsulfanylthiocarbonylsulfanyl propionic acid (BPA) as chain transfer agent and 4,4′-azobis(4-cyanovaleric acid) as initiator. The cloud points measurements indicated that comparing with pure poly(N-vinyl caprolactam), little amount of POEGMA would dramatically decrease copolymers’ cloud temperature while further addition of POEGMA would inversely increase the cloud temperature. The contribution of POEGMA within polymeric chains was modulated by adding POEGMA after 30 min of initiating polymerization. Both the DLS and TEM measurements showed that micelles instead of random structures were formed through a self-assembling process above the cloud temperature. These results emphasized the importance of the contribution of hydrophilic units in predicting the thermal phase transition behavior of poly(N-vinyl caprolactam)-based materials.

Observing Phase Transition of a Temperature-Responsive Polymer Using Electrochemical Collisions on an Ultramicroelectrode.

Herein, a study on a new lower critical solution temperature (LCST) polymer in an organic solvent by an electrochemical technique has been reported. The phase-transition behavior of poly(arylene ether sulfone) (PAES) was examined on 1,2-dimethoxyethane (DME). At a temperature above the LCST point, polymer molecules aggregated to create polymer droplets. These droplets subsequently collided with an ultramicroelectrode (UME), resulting in a new form of staircase current decrease. The experimental collision frequency and collision signal were analyzed in relation to the concentration of the polymer. In addition, the degree of polymer aggregation associated with temperature change was also observed.

The dependence of the β-to-α phase transition behavior of poly(1,4-butylene adipate) on phase separated morphology in its blends with poly(vinylidene fluoride).

Synchrotron wide-angle X-ray diffraction was used to monitor the melting and β-to-α transition behavior of β-poly(1,4-butylene adipate) (β-PBA) and its blends with poly(vinylidene fluoride) (PVDF). Two kinds of typical phase separated morphologies are prepared: interfabrillar (70/30 PBA/PVDF) and interlamellar (50/50 PBA/PVDF) morphologies. After melt recrystallization at 10 °C, β-PBA crystals are obtained. The thermal expansion, phase transition and melting behavior of β crystals highly depend on the phase separated morphology. The β crystals show the highest melting temperature and β-to-α phase transition temperature in 70% PBA, which is caused by the thick lamellae of PBA and/or the lower surface energy of chain folding, while the β crystals show the lowest melting temperature and β-to-α phase transition temperature in 50% PBA, which is caused by the thinner lamellae of PBA. An unexpectedly high melting temperature of α crystals transited from β crystals observed in 50% PBA due to the lamellar thickening occuring in the heating process. The different phase separated morphologies lead to different lamellae thicknesses and surface energies of chain folding which consequently alter the stability of the crystals. The phase transition and melting behavior of β-PBA in PBA/PVDF is also compared with its blends with poly(vinyl phenol) (PVPh). Completely different factors influence the phase transition behavior of β crystals in these two systems.

The role of unique spatial structure in the volume phase transition behavior of poly(N-isopropylacrylamide)-based interpenetrating polymer network microgels including a thermosensitive poly(ionic liquid).

Well-defined poly(N-isopropylacrylamide)/poly(tributylhexylphosphonium 3-sulfopropylmethacrylate) (PNIPAM/P[P4,4,4,6][MC3S]) interpenetrating polymer network (IPN) microgels were synthesized by two-step precipitation polymerization, and the thermally induced phase transition mechanism of IPN microgels was investigated using dynamic light scattering (DLS), temperature-dependent IR spectroscopy together with the perturbation correlation moving window (PCMW) technique and two dimensional correlation spectroscopy (2Dcos). For comparison, PNIPAM/P[P4,4,4,6][MC3S] polymer mixture was also studied to reveal the influence of the complex spatial network of IPN on the thermoresponsive behavior. Due to the strong hydrophilic feature of P[P4,4,4,6][MC3S] and the special IPN structure, PNIPAM and P[P4,4,4,6][MC3S] moieties exhibited different phase transition tendencies during heating. In detail, the dehydration behavior of the PNIPAM part seemed gradual and continuous, whereas that of ester C[double bond, length as m-dash]O in the P[P4,4,4,6][MC3S] part became sharp. The two components dehydrated independently and successively in the polymer mixture without any mutual interaction. The collapse of the P[P4,4,4,6][MC3S] network at the second transition stage increased the amount of intramolecular hydrogen bonding (amide C[double bond, length as m-dash]OD-N) in the PNIPAM moiety. Additionally, the electrostatic interaction in the P[P4,4,4,6][MC3S] network played a non-ignorable role in enhancing the swelling property of PNIPAM/P[P4,4,4,6][MC3S] IPN microgels.

Crystal structures and phase transition behavior of Poly(nonamethylene terephthalamide) and its model compounds

The crystal structure and phase transition behavior of poly(nonamethylene terephthalamide) (PA9T, -[CO-C6H4-CONH-(CH2)9-NH]n-) and its related model compounds (ATm,C6H5-CONH-(CH2)m-NHCO-C6H5 (m = 7–12)) have been investigated by carrying out the temperature dependent measurements of wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS) and infrared spectra along with the DSC measurement. The crystal structure of PA9T at room temperature was determined by analyzing the X-ray diffraction diagram measured for the uniaxially-oriented sample. The nonamethylene segmental part takes the zigzag conformation, which was supported by the quantitative analysis of the methylene progression bands observed in the infrared spectra. The temperature dependence of WAXD, SAXS and infrared spectra of PA9T revealed the existence of the 2-staged order-to-disorder phase transitions: at room temperature this polymer exists as phase I, the crystal structure of which was analyzed as mentioned above. In the relatively low and wide temperature region (190–270 °C for the unoriented sample), phase I transforms to phase II, in which the methylene conformation is disordered, the aromatic amide part is slightly rotated and the intermolecular hydrogen bonds become weaker but the hydrogen bonds are still kept alive. In the temperature region immediately below the melting point (270–310 °C for the unoriented sample), the phase II is melted once and recrystallizes into phase III, where the intermolecular hydrogen bonds are mostly broken in addition to the further disordering of the methylene segments and aromatic amide groups. The thus-occurring violent thermal motions cause a remarkable increase of the long period in this transition region. The molecular chains are still highly oriented and so the phase III may be assumed to be in a kind of liquid crystalline state. The crystal structural changes detected in these phase transitions of PA9T were confirmed by the analysis of the X-ray diffraction and IR spectral data collected for the low molecular-weight model compounds.

The structure and volume phase transition behavior of poly(N-vinylcaprolactam)-based hybrid microgels containing carbon nanodots.

In this paper, we investigated the internal structure and the volume phase transition (VPT) behavior of poly(N-vinylcaprolactam-co-vinylimidazole)/polymerizable carbon nanodot (P(VCL-co-VIM)/PCND) microgels with different amounts of PCNDs. Our study shows that compared to the pure P(VCL-co-VIM) microgel, the hybrid microgels undergo a two-step VPT as the temperature increases and a core-shell(-corona) structure of the hybrid microgels is formed by copolymerization with PCNDs. A change in the amount of PCNDs has effects on both of the volume phase transition temperature and internal structure of microgels. Moreover, based on FT-IR in combination with perturbation correlation moving window (PCMW) and two-dimensional correlation spectral (2Dcos) analyses, the difference in VPT behavior between the shell and the core (corona) structure of the hybrid microgels at the molecular level is elucidated. The core/shell of the hybrid microgels fixed with hydrophilic PCNDs has a higher transition temperature during heating and a more compact structure due to the additional crosslinkers PCNDs.

Micro-dynamics mechanism of the phase transition behavior of poly(N-isopropylacrylamide-co-2-hydroxyethyl methacrylate) hydrogels revealed by two-dimensional correlation spectroscopy

The micro-dynamics mechanism of the volume phase transition of PNIPAM-co-HEMA hydrogels was established using temperature-dependent FTIR spectroscopy, PCMW2D, and 2DCOS analysis.

The effect of counter cation species on the formation of various crystal forms and their phase transition behavior of poly(vinyl alcohol)-iodine complex

Poly(vinyl alcohol) [PVA, -(CH2CH(OH))n-] forms the crystalline complexes I and II with iodine ions (I3−) when PVA is immersed in the KI/I2 aqueous solutions of 0.1–0.5 and 1–3 mol/l concentration, respectively. On the basis of the X-ray diffraction and the ultraviolet-visible, IR and Raman spectral data, we have found that the immersion of PVA films into the iodine aqueous solutions containing the different type of counter ions (K+, Na+, Li+, H+, or Cs+) creates the various types of the crystal modification. When PVA sample was immersed in the solution of relatively low concentration, all the types of counter ion gave the complex I structure. When the concentration of the solution was increased to 1–3 mol/l, the sample immersed for several hours showed the formation of the complex II. In the case of H+ ion, the longer immersion was found to give a new crystal form or complex III with the different packing mode of PVA and I3− ions as determined by the X-ray structure analysis. In the cases of Na+ and Li+ ions, the complex II was disordered by the longer immersion in such a highly-concentrated solution. As clarified by the infrared spectral data, the hydrogen bonds of O–H ⋯ I type are formed in the iodine complex, the strength of which was found also to be different depending on the type of counter ion species. In this way, the present paper has revealed the important role of the counter cations on the formation and stability of the PVA-iodine complexes for the first time.

The phase transition behavior of poly(butylene adipate) in the nanoporous anodic alumina oxide

PBA nanotubes with different diameters have been prepared.

Conformational Identification and Phase Transition Behavior of Poly(trimethylene 2,6-naphthalate) α-Form Modification

Poly(trimethylene 2,6-naphthalate) (PTN) is one of the 1,3-propanediol (PDO)-based aromatic polyesters which has potential applications for special barrier films and packaging due to its excellent oxygen and carbon dioxide gas barrier property. In this work, we investigated the chain conformation and phase transition behavior of poly(trimethylene 2,6-naphthalene) (PTN) α-form crystal with synchrotron wide- and small-angle X-ray scattering (WAXS and SAXS), attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, and differential scanning calorimetry (DSC) methods. ATR-FTIR results showed that the infrared bands at 1327 and 987 cm–1 were sensitive to PTN α-form crystalline phase and were assigned to trans conformers of trimethylene group, whereas the infrared bands at 1357 and 1372 cm–1 were sensitive to PTN β-form crystalline phase and were assigned to gauche conformers of the trimethylene group. The results showed that the conformation of trimethylene glycol residue in PTN α-form cr...

Effect of arm number of poly(acrylic acid) on cloud point temperature of poly(2-ethyl-2-oxazoline)

The phase transition behavior of poly(2-ethyl-2-oxazoline) (PEtOx) under complexation with star-shaped poly(acrylic acid) (PAA) having various arm numbers (two, three, four, and six) has been studied by turbidity and laser light scattering measurements. The change in cloud point temperature (T cp) of PEtOx was monitored as a function of pH, ionic strength, and arm number of the star polyelectrolyte. The shift in T cp to a lower value than that of pure PEtOx was more pronounced at pH 4.2 (pH pKa ), when the acid moieties are partially ionized. Dynamic light scattering showed that these complexes may have micellar core-shell type structure with a mean hydrodynamic radius (R h) ranging from 12 nm to ∼200 nm depending upon the temperature. Significant shift in T cp was observed for six-arm star poly(acrylic acid) complexes at both pH values. This change in the T cp is accredited to the differences in the driving forces of phase transition, including hydrogen bonding between carboxylic acid groups of PAA and the carbonyl moiety of PEtOx as well as the hydrophobic interactions.

The unusual volume phase transition behavior of the poly(N-isopropylacrylamide)–poly(2-hydroxyethyl methacrylate) interpenetrating polymer network microgel: different roles in different stages

Dynamic thermal phase transition behavior of a well-defined poly(N-isopropylacrylamide)–poly(2-hydroxyethyl methacrylate) (PNIPAM–PHEMA) interpenetrating polymer network (IPN) microgel in D2O synthesized by two-step precipitation polymerization was studied by means of IR spectroscopy in combination with the perturbation correlation moving window (PCMW) technique and two-dimensional correlation spectroscopy (2Dcos) analysis. Due to the hydrophobic and non-thermo-responsive properties of PHEMA and the special IPN structure, the IPN microgel exhibited an unusual thermally induced collapse process. The introduction of PHEMA would lower the volume phase transition temperature (VPTT) and the volume phase transition degree. 2Dcos was finally employed to discern the sequence order of all the group motion during heating and cooling processes. PHEMA plays different roles in different stages during the volume phase transition. Additionally, as PHEMA exhibits only a slight response to temperature, it would provide the PNIPAM–PHEMA IPN microgel with good reversibility.

On the thermodynamic phase behavior of poly(N-vinylcaprolactam) solution in the presence of different ionic liquids

The influence of different Ionic Liquids (ILs) on the phase transition behavior of poly(N-vinylcaprolactam) (PVCL) solution is investigated by differential scanning calorimetry (DSC) and turbidity measurements, in combination with FT-IR spectroscopy. The DSC and turbidity results reveal that hydrophilic ILs at a concentration of 0.25 mol L−1 only slightly change the transition temperature. The LCST experiences an increase while the phase separation behavior disappears gradually as the concentration of 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]) increases from 0 to 1.0 mol L−1. In contrast, the addition of hydrophobic ILs, especially 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([EMIM][NTf2]), even at a low concentration, greatly raises the LCST, indicating the possibility of hydrogen bonding between [EMIM][NTf2] and PVCL. Finally, temperature-dependent FTIR spectra are employed to elucidate the dynamic mechanism of the different influences on the phase transition of PVCL. The hydrophilic ILs can change the state of the PVCL chains indirectly by varying their interaction with water molecules. For comparison, the formation of hydrogen bonds between the unsaturated C–H of [EMIM][NTf2] and the CO of PVCL results in a higher temperature and more energy to complete the phase transition. However, with the continual increasing of the concentration, extra [EMIM][NTf2] can not be well dispersed in water due to its hydrophobicity, so the LCST undergoes a decrease and finally reaches an equilibrium. Additionally, hydrophilic ILs tend to distribute in the solution, while hydrophobic ILs, especially [EMIM][NTf2], are prone to be wrapped in polymer chains of the aggregates after phase separation. Furthermore, both types of IL experience the process of hydrogen bond disruption and chain aggregation.

Synthesis and unusual volume phase transition behavior of poly(N-isopropylacrylamide)–poly(2-hydroxyethyl methacrylate) interpenetrating polymer network microgel

The poly(N-isopropylacrylamide)–poly(2-hydroxyethyl methacrylate) (PNIPAM–PHEMA) interpenetrating polymer network (IPN) microgel was synthesized for the first time. FT-IR, AFM and DLS were used to help propose the mechanism of formation of the IPN microgel. Due to the hydrogen bonds between the NIPAM and HEMA monomers, polymerization of HEMA takes place earlier inside the PNIPAM microgel than on the outside. We also focus our research on the volume phase transition temperature (VPTT) of the IPN microgels obtained at different reaction times during polymerization. Due to the incorporation of the PHEMA chains, the VPTT of the IPN microgel exhibits a decreasing trend with increasing reaction time, which is unusual for an IPN microgel.