Exploration of Doubly Thermal Phase Transition Process of PDEGA-b-PDMA-b-PVCL in Water

Understanding Polyproline's Unusual Thermoresponsive Properties Using a Polyproline-Based Double Hydrophilic Block Copolymer

Polyproline is a unique thermoresponsive polymer characterized by large thermal and conformational hysteresis. This article employs polyproline-based double hydrophilic block copolymers (PNIPAMn-b-PLPm) to gain insight into polyproline's thermoresponsive mechanism. The amine-terminated poly(N-isopropylacrylamide) (NH2-PNIPAMm) was used as the macroinitiator for ring-opening polymerization of proline-NCA monomers, resulting in various block copolymers (PNIPAMn-b-PLPm) with varying PLP block lengths. Block copolymers' thermal phase transitions were compared with their homopolymer counterparts using turbidimetry, variable-temperature NMR, dynamic light scattering, and circular dichroism spectroscopy. These experiments revealed that regardless of their compositions, all block copolymers exhibited a two-stage collapse (TCP(PLP) > TCP(PNIPAM)) during the heating cycle. In contrast, only one clearing temperature (TCL) was observed during cooling. The observed clearing temperature is closely correlated to the clearing temperature of PNIPAM blocks, suggesting the role of water-soluble PNIPAM blocks in resolving the PLP blocks. Moreover, thermal and conformational hysteresis related to the polyproline block is significantly suppressed in the presence of a PNIPAM block. Linking PNIPAM blocks has two significant effects on PLP segments' thermoresponsive behavior. For example, during the heating cycle, the precollapsed PNIPAM chains (as TCP(PNIPAM) < TCP(PLP)) prevent orderly aggregation within the PLP block. Meanwhile, during the cooling cycle below the clearing temperature of the PNIPAM block, the PNIPAM chains impart water solubility (as TCL(PNIPAM) > TCL(PLP)) to the collapsed PLP chains. Overall, the PNIPAM block imparts water solubility and perturbs PLP chains to form the native aggregate structure, suppressing the hysteresis effect. Accordingly, the large thermal and conformational hysteresis associated with native PLP chains appears to result from a noninterfering aggregation above the critical temperature.

Thermoresponsive oligo(ethylene glycol) methyl ether methacrylate based copolymers: composition and comonomer effect

Thermoresponsive polymers based on oligo(ethylene glycol) (OEG) methyl ether methacrylate monomers from unimers to micelles to precipitation.

Latest Advances on the Synthesis of Linear ABC-Type Triblock Terpolymers and Star-Shaped Polymers by RAFT Polymerization

This review article aims to cover the most recent advances regarding the synthesis of linear ABC-type triblock terpolymers and star-shaped polymers by RAFT polymerization, as well as their self-assembly properties in aqueous solutions. RAFT polymerization has received extensive attention, as it is a versatile technique, compatible with a great variety of functional monomers and reaction conditions, while providing exceptional and precise control over the final structure, with well-defined side-groups and post-polymerization engineering potential. Linear triblock terpolymers synthesis can lead to very interesting novel ideas, since there are countless combinations of stimuli/non-stimuli and hydrophilic/hydrophobic monomers that someone can use. One of their most interesting features is their ubiquitous ability to self-assemble in different nanostructures depending on their degree of polymerization (DP), block composition, solubilization protocol, internal and external stimuli. On the other hand, star-shaped polymers exhibit a more stable nanostructure, with a distinct crosslinked core and arm blocks that can also incorporate stimuli-responsive blocks for "smart" applications.

Thermoresponsive Nanogels Based on Different Polymeric Moieties for Biomedical Applications

Nanogels, or nanostructured hydrogels, are one of the most interesting materials in biomedical engineering. Nanogels are widely used in medical applications, such as in cancer therapy, targeted delivery of proteins, genes and DNAs, and scaffolds in tissue regeneration. One salient feature of nanogels is their tunable responsiveness to external stimuli. In this review, thermosensitive nanogels are discussed, with a focus on moieties in their chemical structure which are responsible for thermosensitivity. These thermosensitive moieties can be classified into four groups, namely, polymers bearing amide groups, ether groups, vinyl ether groups and hydrophilic polymers bearing hydrophobic groups. These novel thermoresponsive nanogels provide effective drug delivery systems and tissue regeneration constructs for treating patients in many clinical applications, such as targeted, sustained and controlled release.

Effects of Chemical Modifications on the Thermoresponsive Behavior of a PDMAEA-b-PNIPAM-b-POEGA Triblock Terpolymer

In this work, the synthesis, selective chemical modifications, and self-assembly behavior in aqueous media of a novel poly(2-(dimethylamino)ethyl acrylate)₂₀-b-poly(N-isopropylacrylamide)₁₁-b-poly(oligo ethylene glycol methyl ether acrylate)₁₈ (PDMAEA₂₀-b-PNIPAM₁₁-b-POEGA₁₈) dual-responsive (pH and temperature) and triply hydrophilic amino-based triblock terpolymer are reported. The amine functional triblock terpolymer was synthesized by sequential reversible addition fragmentation chain transfer polymerization (RAFT) polymerization and molecularly characterized by size exclusion chromatography (SEC) and ¹H-NMR spectroscopy that evidenced the success of the three-step polymerization scheme. The tertiary amine pendant groups of the PDMAEA block were chemically modified in order to produce the Q₁PDMAEA₂₀-b-PNIPAM₁₁-b-POEGA₁₈ as well as the Q₆PDMAEA₂₀-b-PNIPAM₁₁-b-POEGA₁₈ quaternized triblock terpolymers (Q₁ and Q₆ prefixes show the number of carbon atoms (C1 and C6) attached on the PDMAEA groups) using methyl iodide (CH₃I) and 1-iodohexane (C₆H₁₃I) as the quaternizing agents and the SPDMAEA₂₀-b-PNIPAM₁₁-b-POEGA₁₈ sulfobetainized triblock terpolymer using 1,3 propanesultone (C₃H₆O₃S) as the sulfobetainization agent. The self-assembly properties of the triblock terpolymers in aqueous solutions upon varying temperature and solution pH were studied by light scattering and fluorescence spectroscopy experiments. The novel triblock terpolymers self-assemble into nanosized aggregates upon solution temperature rise above the nominal lower critical solution temperature (LCST) of the temperature-responsive PNIPAM block. The remarkable stimuli-responsive self-assembly behavior of the novel triblock terpolymers in aqueous media make them interesting candidates for biomedical applications in the fields of drug and gene delivery.

Insulin-induced conformational transition of fluorescent copolymers: a perspective of self-assembly between protein and micellar solutions of smart copolymers

Synthesizing and understanding phase transition behavior of novel block copolymers is very crucial for fabricating next generation of smart materials with foreseeable applications. In this regard, we synthesized three random (r) copolymers of poly(N-vinyl-caprolactam) (PVCL) and poly(2-dimethyl amino ethyl methacrylate) (PDMAEMA) with varying percentages of each block and characterized them using nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) patterns, time-resolved fluorescence spectroscopy, and atomic force microscopy (AFM). Synthesized copolymers i.e. PVCL₃₀-PDMAEMA₇₀, PVCL₅₀-PDMAEMA₅₀ and PVCL₇₀-PDMAEMA₃₀ have fluorescence properties, which were confirmed by time-resolved fluorescence spectra and emission spectra, and emission bands were observed at ∼310, ∼435 and ∼424 nm, respectively. The fluorescence lifetime for PVCL₅₀-PDMAEMA₅₀ is larger than those of the other two copolymers suggesting a slow decay of the excited state. The copolymers have spherical geometry as micelles, which were confirmed by TEM. We observed patterned arrangement of micelles and the arranged micelles appear to be pentagon in shape, creating space in between the arranged micelles; however, for PVCL₅₀-PDMAEMA₅₀, the arranged micelles do not form any particular shape. The thermal phase transition of PVCL-r-PDMAEMA in aqueous solution was studied by differential scanning calorimetry and thermal fluorescence spectroscopy. In order to design a biomimetic polymer for bio-specific applications and to understand novel concepts towards polymer-protein interactions, we studied the effect of insulin on lower critical solution temperature (LCST) of PVCL-r-PDMAEMA using multiple sophisticated techniques. The LCST is finely tuned by incorporation of two blocks with various block compositions and the value falls within the range of human body temperature, making PVCL₅₀-PDMAEMA₅₀ a highly compatible material for bio-medical and bio-material applications. Insulin forms a self-assembly with the monomers of PVCL-r-PDMAEMA, which leads to enhancing the micellar aggregates and the eventual decrease in the LCST of the diblock copolymer aqueous solution. The present study provides new insights into insulin-copolymer interactions and can be used for self-assembling nanocarriers and designing protein resistance surfaces.

Effect of chain architecture on the swelling and thermal response of star-shaped thermo-responsive (poly(methoxy diethylene glycol acrylate)-block-polystyrene)3 block copolymer films

The effect of chain architecture on the swelling and thermal response of thin films obtained from an amphiphilic three-arm star-shaped thermo-responsive block copolymer poly(methoxy diethylene glycol acrylate)-block-polystyrene ((PMDEGA-b-PS)₃) is investigated by in situ neutron reflectivity (NR) measurements. The PMDEGA and PS blocks are micro-phase separated with randomly distributed PS nanodomains. The (PMDEGA-b-PS)₃ films show a transition temperature (TT) at 33 °C in white light interferometry. The swelling capability of the (PMDEGA-b-PS)₃ films in a D₂O vapor atmosphere is better than that of films from linear PS-b-PMDEGA-b-PS triblock copolymers, which can be attributed to the hydrophilic end groups and limited size of the PS blocks in (PMDEGA-b-PS)₃. However, the swelling kinetics of the as-prepared (PMDEGA-b-PS)₃ films and the response of the swollen film to a temperature change above the TT are significantly slower than that in the PS-b-PMDEGA-b-PS films, which may be related to the conformation restriction by the star-shape. Unlike in the PS-b-PMDEGA-b-PS films, the amount of residual D₂O in the collapsed (PMDEGA-b-PS)₃ films depends on the final temperature. It decreases from (9.7 ± 0.3)% to (7.0 ± 0.3)% or (6.0 ± 0.3)% when the final temperatures are set to 35 °C, 45 °C and 50 °C, respectively. This temperature-dependent reduction of embedded D₂O originates from the hindrance of chain conformation from the star-shaped chain architecture.

Least Squares Moving-Window Spectral Analysis

Least squares regression is proposed as a moving-windows method for analysis of a series of spectra acquired as a function of external perturbation. The least squares moving-window (LSMW) method can be considered an extended form of the Savitzky-Golay differentiation for nonuniform perturbation spacing. LSMW is characterized in terms of moving-window size, perturbation spacing type, and intensity noise. Simulation results from LSMW are compared with results from other numerical differentiation methods, such as single-interval differentiation, autocorrelation moving-window, and perturbation correlation moving-window methods. It is demonstrated that this simple LSMW method can be useful for quantitative analysis of nonuniformly spaced spectral data with high frequency noise.

Analytical and Numerical Characterization of Autocorrelation and Perturbation-Correlation Moving-Window Methods

Moving-window (MW) approaches to two-dimensional correlation spectroscopy (2D-COS) make it possible to characterize spectral changes occurring in a narrow range of perturbation variable (e.g., time, temperature, and concentration). Despite the wide range of application, the physical meanings of MW correlation intensities have been only qualitatively associated with the direction and curvature of spectral intensity change with regard to a perturbation variable. Here are full and simplified analytical expressions of autocorrelation moving-window (ACMW) and synchronous and asynchronous perturbation-correlation moving-window ( s-PCMW and as-PCMW) intensities. When the window is set sufficiently narrower than the bandwidth of spectral change, the square root of ACMW intensity and s-PCMW intensity becomes proportional to the first order derivative, and as-PCMW intensity becomes proportional to the negative of the second order derivative. This paper demonstrates that both ACMW and PCMW profiles can be significantly altered by non-uniform perturbation spacing. It is also found that intensity noise can cause ACMW to display a false offset drift. This analytical and numerical characterization of the two MW correlation intensities elucidates their physical meanings and ascertains the analysis conditions for reliable interpretation.

PDMAEMA-b-PLMA-b-POEGMA triblock terpolymers via RAFT polymerization and their self-assembly in aqueous solutions

Novel PDMAEMA-b-PLMA-b-POEGMA triblock terpolymers were synthesized by RAFT polymerization. Triblock polyelectrolytes were obtained by quaternization. PDMAEMA-b-PLMA-b-POEGMA and QPDMAEMA-b-PLMA-b-POEGMA terpolymers self-assemble into spherical micelles with a mixed corona in aqueous media.

A new thermoresponsive polymer of poly(N-acryloylsarcosine methyl ester) with a tunable LCST

A thermoresponsive polymer of the tertiary amide-based polyacrylamide, PNASME, was synthesized and its tunable thermoresponse was investigated.