Synthesis,characterisation and solution thermal behaviour of a family of poly (N-isopropyl acrylamide-co-N-hydroxymethyl acrylamide) copolymers

Thermo-responsive copolymers of poly (N-isopropyl acrylamide-co-N-hydroxymethyl acrylamide)p(NIPAAm-co-HMAAm) with a range of content of hydroxy groups have been synthesised by free radical polymerisation. The polymers were characterised by NMR, FTIR and GPC. A detailed study of the solution thermal properties showed that polymers with up to about 50 wt.% hydroxy monomer show lower critical solution temperature (LCST) properties in water. Polymers with higher hydroxy monomer content are fully soluble at all temperatures up to 100 °C. The effect of pH, salts and solvent additives on the solution thermal behaviour of the copolymers was investigated, showing that “salting-out” salts lowered the LCST and “salting-in” salts caused an initial increase in LCST at low concentrations, but reduced LCST at higher concentrations, in line with the Hoffmeister series. The LCST of any copolymer composition from this family in pure water can be predicted from the empirical equation; LCST = 0.015x² + 0.25x + 31.76, where x is the fraction of the hydroxy monomer. Due to differences in polarity and the length of the carbon chain, methanol and ethanol altered LCST of p(NIPAAm) and its hydroxyl copolymers in different manners, showing a transition from cononsolvency to cosolvency as the hydroxyl content of the copolymer increased. A more complex polyhydroxy compound, sucrose, had very little effect on LCST for either p(NIPAAm) or its hydroxyl copolymers.     

Synthesis,characterization and thermal properties of homo and copolymers of 3,5-dimethoxyphenyl methacrylate with glycidyl methacrylate: Determination of monomer reactivity ratios

The new methacrylic monomer, 3,5-dimethoxyphenyl methacrylate (DMOPM) was synthesized by reacting 3,5-dimethoxyphenol dissolved in ethyl methyl ketone (EMK) with methacryloyl chloride in presence of triethylamine as a catalyst. The homopolymer and copolymers of DMOPM with glycidyl methacrylate (GMA) were synthesized by free radical polymerization in EMK solution at 70 ± 1 °C using benzoyl peroxide as a free radical initiator. The copolymerization behaviour was studied in a wide composition interval with the mole fractions of DMOPM ranging from 0.15 to 0.9 in the feed. The homopolymer and the copolymers were characterized by FT-IR, ¹H NMR and ¹³C NMR spectroscopic techniques. The solubility was tested in various polar and non-polar solvents. The molecular weight and polydispersity indices of the polymers were determined using gel permeation chromatography. The glass transition temperature of the copolymers increases with increase in DMOPM content. The thermogravimetric analysis of the polymers showed that the thermal stability of the copolymer increases with DMOPM content. The copolymer composition was determined using ¹H NMR spectra. The monomer reactivity ratios were determined by the application of conventional linearization methods such as Fineman–Ross (r₁ = 0.520, r₂ = 2.521), Kelen–Tudos (r₁ = 0.629, r₂ = 2.554) and extended Kelen–Tudos methods (r₁ = 0.600, r₂ = 2.502).     

Kinetic study of atom transfer radical homo- and copolymerization of styrene and methyl methacrylate initiated with trichloromethyl-terminated poly(vinyl acetate) macroinitiator

Atom transfer radical bulk copolymerization of styrene (St) and methyl methacrylate (MMA) was performed in the presence of CuCl/PMDETA as a catalyst system and trichloromethyl-terminated poly(vinyl acetate) telomer as a macroinitiator at 90 °C. The overall monomer conversion was followed gravimetrically and the cumulative average copolymer composition at moderate to high conversion was determined by ¹H NMR spectroscopy. Reactivity ratios of St and MMA were calculated by the extended Kelen–Tudos (KT) and Mao–Huglin (MH) methods to be r_St = 0.605 ± 0.058, r_MMA = 0.429 ± 0.042 and r_St = 0.602 ± 0.043, r_MMA = 0.430 ± 0.032, respectively, which are in good agreement with those reported for the conventional free-radical copolymerization of St and MMA. The 95% joint confidence limit was used to evaluate accuracy of the estimated reactivity ratios. Results showed that in the controlled/living radical polymerization systems such as ATRP, more reliable reactivity ratios are obtained when copolymer composition at moderate to high conversion is used. Good agreement between the theoretical and experimental composition drifts in the comonomer mixture and copolymer as a function of the overall monomer conversion was observed, indicating the accuracy of reactivity ratios calculated by copolymer composition at the moderate to high conversion. Instantaneous copolymer composition curve and number-average sequence length of comonomers in the copolymer indicated that the copolymerization system tends to produce a random copolymer.     

Copolymers of 4(5)-vinylimidazole and ethyleneglycol methacrylate phosphate: Synthesis and proton conductivity properties

A series of copolymers were produced by conventional free-radical polymerization of ethyleneglycol methacrylate phosphate (EGMAP) and 4(5)-vinylimidazole (4-VIm) at several feed compositions using DMF as solvent. The copolymers were characterized by ¹H NMR and FT-IR. Copolymer compositions were obtained by elemental analysis. Reactivity ratios of the monomers are equal to: r₁ = 0.12 ± 0.03 and r₂ = 0.19 ± 0.05 for 4-VIm–EGMAP system that exhibited an alternating behavior. Thermal properties of the dry copolymers were investigated via thermogravimetry analysis (TG) and differential scanning calorimetry (DSC). The ion exchange capacity (IEC) and anhydrous proton conductivities of the samples were measured and analyzed according to copolymer composition.     

Synthesis and characterization of poly(N-propargylurea)s with helical conformation,optical activity and fluorescence properties

This article presents novel N-propargylurea-based copolymers that contain both carbazole and urea moieties in their side chains. The homopolymer of monomer 1 with a carbazole group exhibited interesting fluorescence properties, while the homopolymer of monomer 2 with a chiral center formed helical structures. The copolymerizations of monomers 1 and 2 provided optically active helical copolymers, which had fluorescence properties, even for the copolymer that contained as low as 20 mol% of monomer unit 1. Fluorescent and optically active composite films were further prepared based on the copolymers and with poly(vinyl butyl) as the supporting material. This study contributes to the intriguing research field of optically active helical polymers and their practical applications.     

Sustained release of ibuprofen from polymeric micelles with a high loading capacity of ibuprofen in media simulating gastrointestinal tract fluids

Amphiphilic diblock copolymers with poly(ethylene glycol) as the hydrophilic block and a random copolymer of n-butyl methacrylate or styrene and (N,N-diethylamino)ethyl methacrylate as the hydrophobic block were prepared by atom transfer radical polymerization (ATRP). Ibuprofen, a model drug that contains a carboxylic group and hydrophobic moiety, was loaded into micelles formed from the amphiphilic diblock copolymers by a combination of ionic interaction and hydrophobic effect. The loading capacity of ibuprofen in the micelles reached 60%. Loaded ibuprofen was released in a sustained fashion into media simulating gastric fluid (pH 1.6, 2 h), small intestinal fluid (pH 7.4, 4 h), and colon fluid (pH 6.7, 18 h). Simulating the case of oral administration at 2 doses per day, loaded ibuprofen was released almost linearly against time after the second dose in media simulating human gastrointestinal tract fluids.     

The preparation of copolymerized fluorescent microspheres of styrene using detergent-free emulsion polymerization

The polymerisable fluorescent monomer, 4-ethoxyl-N-allyl-1,8-naphthalimide, was synthesized from 4-bromo-1,8-naphthalic anhydride and characterized using FT-IR spectra, ¹H NMR and fluorescence spectra. A copolymer of styrene and 4-ethoxyl-N-allyl-1,8-naphthalimide was prepared by detergent-free emulsion polymerization and characterized using fluorescence spectra, SEM and fluorescence microscopy. The fluorescence spectrum of the copolymer displayed excitation at 365 nm and emission at 435 nm in acetone. SEM revealed that the copolymers were microspheres, with smooth surfaces and displayed intense blue fluorescence.     

Synthesis and swelling properties of poly[acrylamide-co-(crotonic acid)] superabsorbents

Superabsorbent polymers of acrylamide (AAm)/crotonic acid (CA) were synthesized by foamed polymerization in an aqueous solution of AAm with CA as a comonomer, initiated by an initiator couple of ammonium persulfate and N,N,N′N′-tetramethylethylenediamine. A crosslinking agent N,N′-methylenebisacrylamide, a foaming agent sodium bicarbonate, and a foam stabilizer, a triblock copolymer of polyoxyethylene/polyoxypropylene/polyoxyethylene, were used in the polymerization. The influences of the relative contents of CA, crosslinking agent, and initiator, on the swelling properties of the superabsorbent polymer systems were examined. The superabsorbent polymer synthesized with an AAm/CA ratio of 98:2 by mole, 0.5 wt.% of N,N′-methylenebisacrylamide and 1 wt.% of ammonium persulfate at 250 rpm and 50 °C for 30 min of polymerization time produced the highest water absorption of 211 ± 9 times its dried weight and could absorb water up to 162 ± 4 g g⁻¹ of the dry copolymer within 10 min. The electrochemical reaction for acrylamide–crotonic acid polymerization was investigated by cyclic voltammetry. The anodic current indicated that acrylamide acting as an electron donor whereas crotonic acid performed as an electron receiver, then providing the cathodic current. The diffusion of water into the superabsorbent polymer was non-Fickian (case II and anomalous). Acrylamide–crotonic acid superabsorbents containing various crosslinker concentrations had a water swelling in the range of 79–289 g g⁻¹. The diffusion coefficients varied between 6.9 × 10⁻⁹ and 5.1 × 10⁻⁸ cm² s⁻¹. Adsorption of the basic dye by the superabsorbent was a monolayer evaluated by the Langmuir isotherm. The superabsorbents can thus be used to adsorb cationic dyes in textile industry.     

Helical poly(N-propargylamide)s with functional catechol groups: Synthesis and adsorption of metal ions in aqueous solution

A novel type of helical N-propargylamide (PA) copolymer was synthesized by catalytic polymerization of monomer 1 (M1), which provided pendent functional catechol groups, and monomer 2 (M2), which endowed the expected copolymer backbones with helical structures. With [(nbd)Rh⁺B^?(C₆H₅)₄ (nbd = 2,5-norbornadiene)] as catalyst, PA copolymers could be obtained with moderate molecular weights (3800–14,000) in high yields (?96%). The functional catechol groups enhanced the hydrophilicity of the hydrophobic mono-substituted polyacetylenes and aided the helical PA copolymers in showing a considerable adsorbance toward metal ions [Fe(III), Cr(III), Ni(II), Zn(II), Cu(II) and Cu(I)] in aqueous solution. The prepared copolymer in which M1/M2 was 0.1/0.9 [mol/mol, poly(1_0.1-co-2_0.9)] showed the highest adsorption capacity among the examined helical copolymers. In particular, for Fe(III), the maximum adsorption capacity was 186 mg g^?1.     

Synthesis and study of copolymer of vinylferrocene,acrylamide and 2-(diethylamino)ethyl methacrylate as a polymeric mediator for electrochemical biosensors

Copolymer of vinylferrocene, acrylamide and 2-(diethylamino)ethyl methacrylate was synthesized by free-radical polymerization. Proton nuclear magnetic resonance and inductively coupled plasma-optical emission spectroscopy confirmed successful incorporation of ferrocene moieties in the copolymer. The effect of monomer feed ratio on copolymer molecular weight was studied and it was found that the increase in 2-(diethylamino)ethyl methacrylate fraction in the monomer feed facilitated incorporation of vinylferrocene and led to decrease in copolymer molecular weight. The synthetic process was scaled up in a pilot plant and an ultrafiltration method was developed to reduce residual levels of each monomer below 0.1% w/w. The copolymer displayed reversible redox electrochemical characteristics of the ferrocene moieties and mediation of glucose oxidation with enzyme flavin adenine dinucleotide-glucose dehydrogenase in phosphate buffered saline. A diffusion coefficient of 3.36 × 10^?7 cm²/s for the dissolved polymeric mediator was estimated from Randles–Sevcik analysis. The copolymer and the enzyme were mixed with water-based carbon ink and then screen-printed to form working electrodes. These biosensors established equilibrium current responses in less than 3 min following step changes of glucose concentration within the clinically relevant range of 8–735 mg/dL when exposed to a continuous flow of blood at 15 μL/min. The calibration plot of three biosensors aligned closely to a quadratic regression line (R square 0.9909) suggesting reasonable sensor measurement reproducibility and low levels of ferrocene leaching out of the polymeric mediator during the 7.5 h test period. A Michaelis constant for the sensor was estimated at 655 mg/dL.     

Synthesis and photoresponsive behavior of the high-Tg azobenzene polymers via RAFT polymerization

Well-defined photo-responsive alternating copolymers, poly(4-(N-maleimido)azobenzene-alt-styrene)s (PMSts), were successfully synthesized via reversible addition–fragmentation chain transfer (RAFT) polymerization. A divinyl monomer was used in this polymerization to prepare high molecular weight azobenzene polymers. These polymers had good solubility in most organic solvents, formed films well, and had high glass transition temperatures (T_g = 174–250 °C) and were heat resistant (T_d > 320 °C). The photo-induced trans–cis isomerization of the copolymers was examined in chloroform solution. Surface-relief-gratings (SRGs) formed on the polymer films were also investigated using illumination from a linearly polarized Kr⁺ laser beam.     

Synthesis and characterization of a new alternating copolymer containing quaterphenyl and fluorenyl groups

An alternating copolymer was synthesized by Suzuki reaction from 4,4′-dibromo-p-quaterphenyl (PPP oligomer) and 9,9-dioctylfluorene-2,7-diboronic acid in good yield (84%). The copolymer is partially crystalline, readily soluble in organic solvents, presents high fluorescence quantum yield (85.6%) and high thermal stability. The copolymer absorption as well as the emission spectra are red shifted compared to those of monomers. Ultrafast time-resolved fluorescence experiments on the copolymer were carried out and confirmed the results obtained from stationary experiments. The copolymer fluorescence decay is found to be bi-exponential with fluorescence lifetimes of 297 ± 6 ps and 942 ± 5 ps.     

Azlactone functionalization of magnetic nanoparticles using ATRP and their bioconjugation

Surface modification of magnetite nanoparticle (MNP) with poly(poly(ethylene glycol) methyl ether methacrylate-stat-2-vinyl-4,4-dimethylazlactone) copolymers (Poly(PEGMA-stat-VDM)) via atom transfer radical polymerization (ATRP) and its application to anchor thymine peptide nucleic acid (PNA) monomer are reported. ATRP of PEGMA and VDM was first performed in a solution system to optimize the reaction condition and the optimal condition was then applied in the surface-initiated ATRP of MNP. Fourier transform infrared spectroscopy (FTIR) indicated the presence of the copolymer in the MNP complexes. After immobilization of thymine PNA monomer, thermogravimetric analysis (TGA) results indicated that there were 4 wt% of the PNA monomer in the complex (1.2 μmol/g complex). The existence of the PNA monomer in the complex was also confirmed via FTIR and vibrating sample magnetometry (VSM). The MNP complex with active surface might be efficiently used as magnetically guidable nanosolid support for PNA oligomers and other molecules containing affinity functional groups.     

Studies on graft copolymerization of chitosan with acrylonitrile by the redox system

Graft copolymers of chitosan with acrylonitrile (AN) were prepared by free radical polymerization using initiator pair of ammonium persulfate and sodium thiosulfate as redox system firstly. Graft copolymerization was confirmed by FTIR spectra, X-ray diffraction and ¹H NMR spectra measurements. The mechanism of graft copolymerization and factors affected graft reaction were explored in details, and the optimum reaction conditions were obtained at [AN] 0.9 mol/L, [CS] 13.3 g/L, [Initiator] 0.006 mol/L, 62 ± 1 °C and 2 h. Then the solubility of chitosan-g-PAN was investigated by using several solvents. The concentrated nitric acid solution and NaSCN solution are good solvents for the graft product. It's confirmed that composites of graft copolymer and PAN had a good film-forming property, and it is suggested that the graft copolymer is promising for fabrication of acrylic fibers as a kind of functional additive.     

Preparation and self-assembly of a dual-functional copolymer for cancer therapy

The pH-responsive amphiphilic copolymer poly(SDMA-co-OEGMA) (PSO) was prepared from the pH-sensitive hydrophobic monomer 2-styryl-1,3-dioxan-5-yl methacrylate (SDMA) and the hydrophilic monomer oligo(ethylene glycol) methyl ether methacrylate (OEGMA) by radical polymerization. Polymeric aggregates with about 130 nm diameter were obtained by the self-assembly of PSO in neutral aqueous solution. The critical aggregation concentration of the copolymer was determined to be 6.5 mg/L (1.2 × 10^?7 M). Cinnamic aldehyde (CA) small molecules are broken away from PSO side chains after the hydrolysis of acid-labile cyclic acetal in cultured A375 human melanoma cells and further suppress the proliferation of this kind of tumor cells. Furthermore, the PSO aggregate was demonstrated to be a drug carrier for encapsulating Nile Red as model drug in in vitro testing. Based on the pH-responsive characteristic, the Nile Red molecules loaded in self-assembly process could be released from the aggregate inside cultured B16 mouse melanoma cells.     

A new simple procedure to calculate monomer reactivity ratios by using on-line 1H NMR kinetic experiments: Copolymerization system with greater difference between the monomer reactivity ratios

Free radical copolymerization reaction of vinyl acetate (VA) and methyl acrylate (MA) in solution of benzene-d₆ using benzoyl peroxide (BPO) as the initiator was studied with on-line ¹H NMR kinetic experiments at 60 °C. It was observed that composition drifts in the comonomer mixture with reaction progress is significant. Hence, the monomer reactivity ratios of VA/MA system could be calculated by the data collected only from one sample via on-line following the comonomer mixture and copolymer compositions at different reaction time intervals up to medium overall monomer conversions. The results were in good agreement with the literature data reported for this system. The good fitting between theoretical and experimental changes in the comonomer mixture compositions as a function of reaction progress was observed, indicating the accuracy of the monomer reactivity ratios calculated by the new procedure presented here.     

Freezing as a path to build macroporous structures: Superfast responsive polyacrylamide hydrogels

Macroporous polyacrylamide (PAAm) hydrogels were prepared from acrylamide monomer and N,N′-methylene(bis)acrylamide (BAAm) crosslinker in frozen aqueous solutions. It was found that the swelling properties and the elastic behavior of the hydrogels drastically change at a gel preparation temperature of −6 °C. The hydrogels prepared below −6 °C exhibit a heterogeneous morphology consisting of pores of sizes 10–70 μm, while those formed at higher temperatures have a non-porous structure. PAAm networks with largest pores were obtained at −18 °C. The pore size of the networks increased while the thickness of the pore walls decreased by decreasing the monomer concentration. The hydrogels formed below −6 °C exhibit superfast swelling and deswelling properties as well as reversible swelling–deswelling cycles in water and in acetone, respectively.     

Abundant graft chains do not influence coil-to-helix but α-to-β transition of polylysine backbone,resulting in thermoreversible β-to-α transition

We have demonstrated that cationic comb-type copolymers (PLL-g-Dex) consisting of a cationic polylysine backbone and abundant grafts of water-soluble polymers stabilize DNA hybrids. Furthermore, the copolymers were found to accelerate the strand exchange reaction between a double-stranded DNA and its complementary single-stranded DNA. In this study, we investigated pH-induced coil-to-helix and temperature-induced α-to-β transition of PLL-g-Dex to evaluate the effect of the graft chains on conformation of the polylysine backbone. The coil-to-helix transition was hardly influenced by the grafted dextran. The copolymer having 24 mol% (93 wt%) dextran still underwent coil-to-helix transition. No change in transition pH with dextran grafting density of the copolymer was observed. In contrast to the coil-to-helix transition, the dextran grafts impacted the temperature-induced α-to-β transition. The graft chains even at 1 mol% (38 wt%) affected α-to-β transition of the PLL backbone. The transition temperature increased from 45°C to 77 °C by 11 mol% (88 wt%) dextran grafting, resulted in stabilization of helical structure at the higher temperature. Furthermore, thermoreversible β-to-α transition of the copolymer was observed for the copolymer with a particular grafting degree. The grafted dextran seemingly modified inter-strands or inter-segments interactions of the polylysine backbones which are required for β-sheet assembling.     

Radical copolymerization of N-vinylcarbazole and p-bromostyrene: determination of monomer reactivity ratios by SEC-multidetection

N-Vinylcarbazole (A)/p-bromostyrene (B) copolymers were prepared by radical copolymerization. Size exclusion chromatography (SEC) equipped with a refractometer and UV-vis spectrophotometer was found to be a very convenient technique to follow copolymerizations and to determine monomer conversions, copolymer composition, average molecular weights, polydispersity indexes versus time. The monomer reactivity ratios r_A (N-vinylcarbazole) and r_B (p-bromostyrene) were determined by using the Finemann-Ross (FR), the inverted Finemann-Ross (IFR), the Kelen-Tüdos (KT), and the fitting curve graphical methods. The four methods were in good agreement and led to very different values for r_A (0.55) and r_B (12.3) which induces a preference for the incorporation of B in the copolymer structure. Eventually, with these results the influence of initial feed on the microstructure of the copolymer has been predicted.     

Synthesis and investigation of monomodal hydroxy-functionalized PEG methacrylate based copolymers with high polymerization degrees. Modification by “grafting from”

The synthesis of monomodal copolymers with poly(ethylene glycol) (PEG) side chains from commercial poly(ethylene glycol) methacrylates (PEGMA) by atom transfer radical polymerization (ATRP) is verified. Two hydroxy-functionalized PEGMA macromonomers (520 g/mol and 360 g/mol) were copolymerized with methyl methacrylate (MMA) using various initial feed (1.5/98.5–50/50 mol.%). The copolymers P(MMA-co-PEGMA) with high degree of polymerization, e.g. 100–275 of repeating units in the backbone including 7–56 PEG side chains, were obtained. The relative reactivity ratios of PEGMA and MMA determined by the Jaacks method indicated slightly faster incorporation of macromonomer into polymeric chain than MMA (r_MMA = 0.79; r_PEGMA = 1.27). The polymers containing at least 17 mol.% of PEGMA units were water-soluble and exhibited clouding point at temperature in a broad range of 39–70 °C. The temperature-sensitive effect makes these polymers as a potential carriers in drug delivery systems. In the case of copolymers insoluble in water, a three-step procedure, including esterification to ATRP multifunctional macroinitiators, ATRP of tert-butyl methacrylate (tBMA) by grafting from, deprotection of carboxylic groups by removing tert-butyl groups, was applied to extend PEG grafts and expand the content of hydrophilic fraction (32–94 mol.%), what efficiently developed polymer solubility in polar solvents giving possibility for the future biomedical applications.