PDMAEMA Block Length Research Articles

Carbon dioxide-switched removal of nitrate ions from water by cellulose nanocrystal-grafted and free multi-responsive block copolymers

Temperature- and carbon dioxide (CO2)-responsive block copolymers of dimethylaminoethyl methacrylate (DMAEMA) and N-isopropylacrylamide (NIPAAm) (PDMAEMA-b-PNIPAAm) with different block lengths were synthesized by atom transfer radical polymerization (ATRP). In addition, cellulose nanocrystals (CNCs) were grafted with PDMAEMA-b-PNIPAAm chains through surface initiated-ATRP. After studying self-assembly and responsivity of the free PDMAEMA-b-PNIPAAm to different stimuli, the free and CNC-grafted PDMAEMA-b-PNIPAAm chains were finally used as CO2-switched absorbents of nitrate ions from aqueous solutions. Temperature responsivity investigations showed different critical solution temperatures (CST) for the copolymers depending on the length of blocks. CO2-responsivity of the copolymers is accompanied by reduction of pH upon the purging CO2 and protonation of the tertiary amine groups of PDMAEMA block as CO2-responsive functionalities. Micellar and vesicular morphologies were estimated for the free copolymers with different ratios of hydrophilic/hydrophobic blocks. CO2-switched removal of nitrate ions was carried out at temperature below and above the CST of the copolymers (40 and 60 °C, respectively). The free copolymers with higher length of PDMAEMA block shows the highest absorption capacity of nitrate ions (490 mg/g) through the electrostatic interactions in the presence of CO2 at temperatures below the CST. N2-switched ion desorption, temperature responsivity, and filtration ability of the CNC-grafted copolymers provide the easy regeneration process.

Modification of cellulose nanocrystal with dual temperature- and CO2-responsive block copolymers for ion adsorption applications

Cellulose nanocrystal (CNC)-grafted smart polymers have potential applications as adsorbents by providing simple regeneration process. In this study, carbon dioxide (CO2)- and temperature-responsive free block copolymers of N-isopropylacrylamide and (2-dimethylaminoethyl) methacrylate with different block lengths were synthesized using reversible addition-fragmentation chain transfer (RAFT) polymerization. In addition, CNC was modified with the similar block copolymers by surface-initiated RAFT method. The synthesized block copolymers were used in nitrate ion removal from aqueous solutions. The synthesis process was confirmed by Fourier-transform infrared spectroscopy, proton nuclear magnetic resonance (1H NMR) analysis, thermal gravimetric analysis, scanning electron microscopy, and transmission electron microscopy. Stimuli-responsivity of the free polymers was studied by pH measurement, turbidity investigation, and dynamic light scattering analysis. CO2-responsivity of the block copolymers in aqueous solution was confirmed by reduction of pH in the presence of CO2 by protonation of the PDMAEMA blocks. The copolymers with higher length of PDMAEMA showed highly intense CO2-responsivity. Deprotonation of the PDMAEMA units by purging N2 represents reversible responsivity of the copolymers. Turbidity analysis showed different critical solution temperatures (CST) for the block copolymers with various block lengths. Two different micellar and vesicular morphologies were observed for the self-assembled copolymers at temperatures above and below CST of the copolymers, which is related to the hydrophobic/hydrophilic block ratio. CO2-switched nitrate ion adsorption from aqueous solution at two temperatures (37 and 60 °C) was studied by UV–vis spectroscopy using the synthesized products as adsorbent. Adsorption of nitrate ions from aqueous solutions was increased by protonation of the PDMAEMA segments upon CO2 purging. Presence of CNC, morphology of the self-assembled copolymers, temperature, and time of CO2 purging affect the nitrite ion adsorption capacity. The maximum adsorption capacity (420 mg/g) is related to the sample with vesicular assemblies in aqueous solution and higher PDMAEMA block length at temperatures below CST of the block copolymer. N2 purging resulted in deprotonation of the PDMAEMA blocks and regeneration of the samples. Finally, the CNC substrate can be used in regeneration of the samples with simple filtration process in addition to the stimuli-regeneration process.

Two-Way CO2-Responsive Polymer Particles with Controllable Amphiphilic Properties.

Multiple stimuli-responsive amphiphilic block copolymers of poly(methacrylic acid) (PMAA) and poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) were used as emulsifiers to prepare two-way CO2 stimuli-responsive poly(methyl methacrylate) (PMMA) latex particles via aqueous emulsion polymerization. The polymerization at pH 2 and 50 °C produced mainly PDMAEMA-surfaced PMMA latex particles, whereas the polymerization at pH 12 and 50 °C produced mainly PMAA-surfaced particles. Both types of latex particles appeared to precipitate at higher pH values from the emulsifier of a longer PDMAEMA block length. The direction from precipitation to dispersion for PDMAEMA-surfaced particles or from dispersion to precipitation for PMAA-surfaced particles in response to CO2 bubbling of the pH 12 dispersion of particles depended on the PDMAEMA block length. Together, this study reveals that—by tuning the PDMAEMA block length in PMAA-b-PDMAEMA used as an emulsifier and polymerization at pH 2 or 12—PMMA latex particles can exhibit two-way CO2 responsiveness between dispersion and precipitation. Thus, due to their simple preparation and unique dual pH and CO2 responsiveness, these newly developed PMAA-b-PDMAEMA emulsifiers provide a highly efficient approach for the development of smart PMMA latex nanoparticles with desirable multifunctional properties.

Poly[2,7-(9,9-dihexylfluorene)]-block-poly[2-(dimethylamino)ethylmethacrylate] as resilient cathode interlayers in polymer solar cells: the effect of block ratios

A series of alcohol-soluble diblock copolymers PF15-b-PDMAEMA975 are applied as cathode interlayers in the PSCs based on PTB7-Th:PC71BM. Herein, the PF units are fixed at 15, and the PDMAEMA units vary as 60, 150 and 975. The device results show that varying the length of PDMAEMA block has a little effect on the performance of the devices, and all the devices show comparable and even higher performances in comparison to the devices based on the well-known PFN-Br. Control experiment indicates that the PF unit is necessary for the high performances. The improvement of the performance should be attributed to the reduction of work function and balance of charge carrier mobilities upon addition of the cathode interlayers. We believe that this type of copolymers should be resilient to the block ratios, and may be developed to a potential cathode interfacial material in highly efficient organic solar cells.

Multistimuli-Responsive Emulsifiers Based on Two-Way Amphiphilic Diblock Polymers.

Diblock copolymers of poly(tert-butyl methacrylate) (PtBuMA) and poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) of four different block lengths were prepared by sequential two-step reversible addition–fragmentation chain transfer radical polymerization, followed by hydrolysis of the PtBuMA blocks to obtain poly(methacrylic acid)-b-PDMAEMA (PMAA-b-PDMAEMA). The effect of the PDMAEMA block length on the multistimuli-responsive amphiphilic features of both types of diblock copolymers was investigated as CO2-switchable emulsifiers for emulsification/demulsification of n-octane (an oil) in water in response to CO2/N2 bubbling. The amphiphilicity of PtBuMA-b-PDMAEMA was switched on, and the amphiphilicity of PMAA-b-PDMAEMA was switched off by CO2 bubbling at pH 12 and 25 °C to achieve emulsification/demulsification. A longer PDMAEMA block length in PMAA-b-PDMAEMA conferred more sensitive CO2-responsive amphiphilicity but reduced the extent of recovery of emulsification ability on N2 bubbling. This newly developed diblock copolymer system could potentially serve as a “multifunctional surfactant” for CO2-switchable emulsification/demulsification of oil-in-water and water-in-oil mixtures.

Influence of pH-Responsive Monomer Content on the Behavior of Di-Block Copolymers in Solution and as Stabilizers of Pickering Latex Particle Emulsifiers

In this study, diblock copolymers poly(methyl methacrylate)—block—poly (2-dimethylaminoethyl methacrylate) (pMMA-b-pDMAEMA) are investigated for the steric stabilization of latex particles and the subsequent use of these latex particles as Pickering emulsifiers. Solution properties of the diblock copolymers highlight that the pDMAEMA block length influences the critical micelle concentration (CMC) and micelle hydrodynamic diameter in response to changes in pH and the pKa. The block length can also be used as a way to control the particle size of sterically stabilized polystyrene latex particles prepared via emulsion polymerization. The suspension properties of these latex particles are also presented. Emulsion studies using these latex particles as emulsifiers show that both continuous phase pH and electrolyte concentration affect emulsion stability to coalescence. At high pH, stable emulsions are formed due to the affinity of the particles to the interface. At low pH, protonation of the amine groups reduces the affinity and thus droplet coalescence is observed. Increasing the electrolyte concentration improves emulsion stability, but causes an increase in droplet size due to adsorption of flocculated/aggregated particles. Finally, it is shown that these latex particles can be used in conjunction with membrane emulsification techniques to produce emulsions with low polydispersity.

Self-Assembly of Amphiphilic Triblock Terpolymers Mediated by Multifunctional Organic Acids: Vesicles, Toroids, and (Undulated) Ribbons

The self-assembly of block copolymers in the presence of additives represents an elegant strategy to adjust micellar morphologies in solution and to design complex structures that are not accessible otherwise. Herein, we use linear ABC triblock terpolymers comprising a polyamine block: polybutadiene-block-poly(tert-butyl methacrylate)-block-poly(2-(dimethylamino)ethyl methacrylate) (PB-b-PtBMA-b-PDMAEMA) terpolymers coassembled with organic di- or triacids in mixtures of THF and water. The interactions between the organic multiacids and the hydrophilic PDMAEMA block can be adjusted via the chain architecture, amount, and functionality of added acid, the solvent quality, and the PDMAEMA block length. Consequently, these parameters allow a certain level of control over the resulting micellar morphology. Characterization by (cryogenic) transmission electron microscopy and atomic force microscopy revealed the formation of spherical, disk-shaped, and toroidal structures, alongside ribbons featuring enlarged end-caps. In the latter case, changing the solvent composition or the amount/type of organic diacid induced the formation of undulated ribbons and, eventually, partition into spherical particles.

Effect of hydrophilic chain length on the aqueous solution behavior of block amphiphilic copolymers PMMA‐b‐PDMAEMA

AbstractA series of amphiphilic block copolymers, polymethyl methacrylate (PMMA)‐b‐poly[2‐(dimethylamino)ethyl methacrylate] (PDMAEMA), were synthesized by atom transfer radical polymerization (ATRP) method. Surface tension, dynamic light scattering (DLS), transmission electron microscope (TEM), and atomic force microscopy (AFM) studies were performed to investigate the aqueous micellar behavior of these block amphiphiles. At a fixed degree of polymerization (DP) of PMMA block (DP = 55), the PDMAEMA block length was found to have a significant influence on the critical micelle concentration (cmc) values and hydrodynamic size of aggregates. An increase in the DP of PDMAEMA from 11 to 337, resulted in a decrease in the cmc from 1.44 × 10−5 to 5.81 × 10−7 M (a factor of almost 24.8), and a decrease in the Z (2Rh) from 85.5 to 15.5 nm (pH = 4), respectively. TEM and AFM results indicated that by changing the soluble block lengths, spherical, short rod, crew‐cut, vesicles or large aggregates can be observed in the solution. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Thermal and pH‐sensitive gold nanoparticles from H‐shaped block copolymers of (PNIPAM/PDMAEMA)‐b‐PEG‐b‐(PNIPAM/PDMAEMA)

AbstractWell‐defined H‐shaped pentablock copolymers composed of poly(N‐isopropylacrylamide) (PNIPAM), poly(N,N‐dimethylaminoethylacrylamide) (PDMAEMA), and poly(ethylene glycol) (PEG) with the chain architecture of (A/B)‐b‐C‐b‐(A/B) were synthesized by the combination of single‐electron‐transfer living radical polymerization, atom‐transfer radical polymerization, and click chemistry. Single‐electron‐transfer living radical polymerization of NIPAM using α,ω azide‐capped PEG macroinitiator resulted in PNIPAM‐b‐PEG‐b‐PNIPAM with azide groups at the block joints. Atom‐transfer radical polymerization of DMAEMA initiated by propargyl 2‐chloropropionate gave out α‐capped alkyne‐PDMAEMA. The H‐shaped copolymers were finally obtained by the click reaction between PNIPAM‐b‐PEG‐b‐PNIPAM and alkyne‐PDMAEMA. These copolymers were used to prepare stable colloidal gold nanoparticles (GNPs) in aqueous solution without any external reducing agent. The formation of GNPs was affected by the length of PDMAEMA block, the feed ratio of the copolymer to HAuCl4, and the pH value. The surface plasmon absorbance of these obtained GNPs also exhibited pH and thermal dependence because of the existence of PNIAPM and PDAMEMA blocks. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010

Effect of Block Length on Solvent Response of Block Copolymer Brushes: Combinatorial Study with Block Copolymer Brush Gradients

Block copolymer (BC) brush gradient libraries were examined as high-throughput platforms to study the effect of relative block lengths on the response to solvents. BC brushes of poly(n-butyl methacrylate) (PBMA) and poly(2-(N,N‘-dimethylamino)ethyl methacrylate) (PDMAEMA) were synthesized via surface-initiated atom transfer radical polymerization (ATRP). The gradient libraries had uniform bottom PBMA blocks and molecular mass gradient top PDMAEMA blocks. The rearrangement of the BC brushes upon exposure to water and hexane was assessed by water contact angle (θw) measurements. θw mapping of each gradient library illustrated how the top PDMAEMA block length influenced the response of BC brushes to solvents. Comparison among libraries with different bottom PBMA thicknesses revealed how the bottom block length affected the solvent response of BC brushes. Our results indicate that the solvent response behavior of the BC brushes is greatly influenced by their relative block lengths. While surface response properties can be suppressed by a long top block, they can be enhanced by the extension of the bottom block. In addition, our work suggests that BC brushes could be fabricated to provide tunable surfaces with gradient responsive properties.

Amphiphilic diblock, triblock, and star block copolymers by living radical polymerization: Synthesis and aggregation behavior

AbstractCopper(I)‐mediated living radical polymerization was used to synthesize amphiphilic block copolymers of poly(n‐butyl methacrylate) [P(n‐BMA)] and poly[(2‐dimethylamino)ethyl methacrylate] (PDMAEMA). Functionalized bromo P(n‐BMA) macroinitiators were prepared from monofunctional, difunctional, and trifunctional initiators: 2‐bromo‐2‐methylpropionic acid 4‐methoxyphenyl ester, 1,4‐(2′‐bromo‐2′‐methyl‐propionate)benzene, and 1,3,5‐(2′‐bromo‐2′‐methylpropionato)benzene. The living nature of the polymerizations involved was investigated in each case, leading to narrow‐polydispersity polymers for which the number‐average molecular weight increased fairly linearly with time with good first‐order kinetics in the monomer. These macroinitiators were subsequently used for the polymerization of (2‐dimethylamino)ethyl methacrylate to obtain well‐defined [P(n‐BMA)x‐b‐PDMAEMAy]z diblock (15,900; polydispersity index = 1.60), triblock (23,200; polydispersity index = 1.24), and star block copolymers (50,700; polydispersity index = 1.46). Amphiphilic block copolymers contained between 60 and 80 mol % hydrophilic PDMAEMA blocks to solubilize them in water. The polymers were quaternized with methyl iodide to render them even more hydrophilic. The aggregation behavior of these copolymers was investigated with fluorescence spectroscopy and dynamic light scattering. For blocks of similar comonomer compositions, the apparent critical aggregation concentration (cac = 3.22–7.13 × 10−3 g L−1) and the aggregate size (ca. 65 nm) were both dependent on the copolymer architecture. However, for the same copolymer structure, increasing the hydrophilic PDMAEMA block length had little effect on the cac but resulted in a change in the aggregate size. © 2002 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 439–450, 2002; DOI 10.1002/pola.10122