Novel thermoresponsive and pH-responsive aggregates from self-assembly of triblock copolymer PSMA-b-PNIPAAm-b-PSMA

A series of novel triblock copolymers of poly(stearyl methacrylate)-b-poly(N-isopropylacrylamide)-b-poly(stearyl methacrylate) (PSMA-b-PNIPAAm-b-PSMA) with different molecular weights was synthesized through carboxyl-terminated trithiocarbonates as a highly efficient RAFT agent via reversible addition-fragmentation chain transfer (RAFT) polymerization. The resultant polymers were characterized by 1H NMR, FT-IR spectroscopy, and GPC. By varying the organic solvent used in the self-assembly procedure and adjusting the copolymer composition, multiple morphologies ranging from vesicles and core-shell spherical aggregates with different dimensions to pearl-necklace-like aggregates were obtained. The aggregates showed thermoresponsive and pH-responsive properties through the lower critical solution temperature (LCST) of PNIPAAm and the two carboxyl end groups of the copolymer.     

Synthesis of amphiphilic diblock copolymers poly[2-(<Emphasis Type="Italic">N</Emphasis>, <Emphasis Type="Italic">N</Emphasis>-dimethylamino)ethyl methacrylate]-<Emphasis Type="Italic">b</Emphasis>-poly(stearyl methacrylate) and their self-assembly in mixed solvent

Amphiphilic diblock copolymers consisting of 2-(N, N-dimethylamino)ethyl methacrylate (DMAEMA, abbreviated as DMA) and stearyl methacrylate (SMA) with different degrees of polymerization and compositions were prepared by reversible addition–fragmentation chain transfer (RAFT) copolymerization. The composition and chemical structures of (co)polymers were confirmed by the measurements of ¹H NMR spectroscopy and gel permeation chromatography (GPC). The self-aggregating structures of amphiphilic diblock copolymers with the concentration of 0.1~0.3 wt.% in THF/water mixed solvent was investigated by transmission electron microscopy (TEM) and dynamic light scattering (DLS). It was found that both the morphologies and aggregating particle size resulted from the amphiphilic diblock copolymers depended on the variation of pH values, the lengths of the hydrophobic PSMA chains, and the weight ratio of THF/water mixed solvent.     

Phase diagrams,mechanisms and unique characteristics of alternating-structured polymer self-assembly via simulations

Alternating-structured polymers(ASPs), like alternating copolymers, regular multiblock copolymers and polycondensates, are very important polymer structures with broad applications in photoelectric materials. However, their self-assembly behaviors,especially the self-assembly of alternating copolymers, have not been clearly studied up to now. Meanwhile, the unique characteristics therein have not been systematically disclosed yet by both experiments and theories. Herein, we have performed a systematic simulation study on the self-assembly of ASPs with two coil alternating segments in solution through dissipative particle dynamics(DPD) simulations. Several morphological phase diagrams were constructed as functions of different impact parameters. Diverse self-assemblies were observed, including spherical micelles, micelle networks, worm-like micelles, disklike micelles, multimicelle aggregates, bicontinuous micelles, vesicles, nanotubes and channelized micelles. Furthermore, a morphological evolutionary roadmap for all these self-assemblies was constructed, along with which the detailed molecular packing models and self-assembly mechanisms for each aggregate were disclosed. The ASPs were found to adopt a folded-chain mechanism in the self-assemblies. Finally, the unique characteristics for the self-assembly of alternating copolymers were revealed especially, including(1) ultra-fine and uniform feature sizes of the aggregates;(2) independence of self-assembled structures from molecular weight and molecular weight distribution;(3) ultra-small unimolecular aggregates. We believe the current work is beneficial for understanding the self-assembly of alternating structured polymers in solution and can serve as a guide for the further experiments.     

Thiol-terminated hydroxy-functional polymer as a transtab toward polymer latex particles

Hydroxy-functional macrodisulfides have been synthesized by atom transfer radical polymerization of 2-hydroxyethyl methacrylate or 2-hydroxypropyl methacrylate in 2-propanol. Mean degrees of polymerization of the polymer chains beside the disulfide were fixed at 30, 60, and 90; since ATRP has reasonably good living character, the molecular weight distribution is relatively narrow. Furthermore, the macrodisulfides were reduced to synthesize corresponding thiol-terminated polymers with relatively narrow molecular weight distributions. ¹H nuclear magnetic resonance and gel permeation chromatography were used to characterize the macrodisulfides and thiol-terminated polymers in terms of their chemical structure, molecular weight, and polydispersity, respectively. Dispersion polymerizations of styrene using the thiol-terminated hydroxy-functional polymers as a transtab (chain transfer agent + colloidal stabilizer) in ethanol resulted in colloidally stable submicrometer-sized polystyrene latex particles. Scanning electron microscopy, Fourier transform infrared spectroscopy, and elemental microanalysis were used to characterize the particles in terms of their morphologies, particle sizes and their distributions, and chemical compositions.     

Synthesis and self-assembly of comb-like amphiphilic copolymer poly(maleic anhydride-<Emphasis Type="Italic">alt</Emphasis>-stearyl methacrylate)-<Emphasis Type="Italic">b</Emphasis>-poly(stearyl methacrylate)

Comb-like amphiphilic block copolymers of maleic anhydride (MA) and stearyl methacrylate (SMA) were prepared through the reversible-addition-fragmentation-transfer polymerization. The resultant copolymers were characterized by gel permeation chromatograph and ¹H NMR. The aggregation behaviors of P(MA-alt-SMA)-b-PSMA were investigated in tetrahydrofuran/water. It is of great interest that the aggregates with different morphologies and dimensions could be obtained by adjusting the polymer concentration, water content, and pH. The dimension and structure of these aggregates were investigated by transmission electron microscopy and dynamic light scattering. The effect of the copolymer–solvent interaction on these aggregations was discussed.     

Near‐monodisperse α‐hydroxy and α,ω‐dihydroxy amine‐based polymers: Synthesis and characterization

α‐Hydroxy and α,ω‐dihydroxy polymers of 2‐(dimethylamino)ethyl methacrylate (DMAEMA) of various molecular weights were synthesized by group transfer polymerization (GTP) in tetrahydrofuran (THF), using 1‐methoxy‐1‐(trimethylsiloxy)‐2‐methyl propene (MTS) as the initiator and tetrabutylammonium bibenzoate (TBABB) as the catalyst. The hydroxyl groups were introduced by adding one 2‐(trimethylsiloxy) ethyl methacrylate (TMSEMA) unit at one or at both ends of the polymer chain. The ends were converted to 2‐hydroxyethyl methacrylate (HEMA) units after the polymerization by acid‐catalyzed hydrolysis. Gel permeation chromatography (GPC) in THF and proton nuclear magnetic resonance (¹H‐NMR) spectroscopy in CDCl₃ were used to determine the molecular weight and composition of the polymers. These mono‐ and difunctional methacrylate polymers can be covalently linked at the hydroxy termini to form star polymers and model networks, respectively. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1597–1607, 1999     

Polymeric Nitrofuran Derivatives. I. Radical-Initiated Homo- and Copolymerization of 5-Nitrofurfuryl Methacrylate

The radical homopolymerization of 5-nitrofurfuryl methacrylate (NFMA) and the copolymerization of NFMA with methyl methacrylate and various vinyl monomers, respectively, have been studied in dimethylformamide at 65°C. NFMA and poly(NFMA) have been characterized by ¹H-NMR, IR, and UV spectroscopy. The influence of polymerization conditions on monomer conversion and on the molecular weight of the polymers obtained has been investigated. The thermal behavior of the polymers obtained has been studied by TGA and DSC analysis.     

Peroxide crosslinking of poly(n-alkyl methacrylates)

The action of dicumyl peroxide on poly(n-butyl methacrylate) and poly(n-nonyl methacrylate) produces degradation and crosslinking reactions in both polymers. Crosslinking and degradation of poly(n-alkyl methacrylates) are influenced also by the initial molecular weight of the polymer as well as by the type of alkyl group. The ratio of degradation to crosslinking p/q determined on the basis of the equation of Charlesby and Pinner, S + S^0.5 = (p/q) + (1/qP_n) is for poly(n-butyl methacrylate) of viscosity molecular weight 0.923 × 10⁶ and 2.16 × 10⁶ of 0.78 and 0.60, respectively; for poly(n-nonyl methacrylate) of weight average molecular weight 3.83 × 10⁵, p/q is 0.16. Crosslinking efficiencies (moles of crosslinks per mole of decomposed dicumyl peroxide) of the above polymers are relatively very low: 0.014, 0.005, and 0.039, respectively. The critical concentration of dicumyl peroxide necessary for the formation of gel, provided it undergoes complete decomposition, is for the above polymers 1.82, 1.65, and 0.98 wt.-%, respectively. Under the critical concentration of dicumyl peroxide the limiting viscosity number of poly(n-butyl methacrylate) increases with increasing concentration of dicumyl peroxide. An initial decrease of the value of the limiting viscosity number, which is characteristic for polymers undergoing simultaneous degradation and crosslinking, was not observed.     

Atom transfer radical polymerization synthesis and photoresponsive solution behavior of spiropyran end‐functionalized polymers as simplistic molecular probes

Poly(methyl methacrylate)s (PMMAs) of two different molecular weights having a single photochromic benzospiropyran (BSP) end‐group were synthesized by atom transfer radical polymerization (ATRP). Polymer characterization by ¹H NMR and matrix‐assisted laser desorption/ionitiation time of flight‐mass spectroscopy confirms that using an ATRP initiator equipped with BSP, a near quantitative functionalization of the PMMA with the BSP was achieved. Both polymers exhibit photochroism characterized by the UV‐induced transition from BSP to benzomerocyanine (BMC) in acetonitrile. However, a strong molecular weight dependence of the thermal relaxation kinetic of the BMC was found with a significantly faster temperature‐dependent transition for the higher molecular weight polymer. Thermodynamic analysis of the process revealed a higher gain in the entropy of activation ΔS^± for the transition process in the higher molecular weight polymer. This suggests an energetically unfavorable nonpolar environment of the BMC group in the higher molecular weight polymers, although a higher solvation of the BMC in the lower molecular weight polymer contributes to its stabilization. The ability of the BMC polymer end‐groups to organize was shown in metal ion‐binding experiments forming bivalently linked complexes with Co ions. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis and Characterization of Novel Methacrylates Derived from Morpholine and Pyrrolidine: The Determination of Kinetic Parameters with Thermogravimetric Analysis

Abstract

The synthesis of two new methacrylate esters containing morpholine and pyrrolidine group are described. The monomers produced from the reaction of corresponding morpholino chloroacetamide and pyrrolidino chloroacetamide with sodium methacrylate were polymerized in DMSO solution at 65°C using AIBN as an initiator. The monomers and their polymers were characterized by Fourier transform infrared (FTIR), ¹H‐ and ¹³C‐NMR spectroscopy. The glass transition temperature of the polymers were investigated by DSC and thermal decomposition activation energies were calculated by the Ozawa method using the SETARAM Labsys thermogravimetric analysis (TGA) thermobalance, respectively. By using gel permeation chromatography, weight average (M¯_w) and number average (M¯_n) molecular weights and polidispersity indices of the polymers were determined.     

Thermal Decomposition and Glass Transition Temperature of Poly(phenyl Methacrylate) and Poly(cyclohexyl Methacrylate)

The thermal decomposition and the glass transition temperature T_g of poly(phenyl methacrylate) (PPhMA) and poly(cyclohexyl methacrylate) (PcHU) were studied with a differential scanning calorimeter (DSC). The undecomposed and decomposed polymers were analyzed by gel permeation chromatography (GPC) for molecular weight distributions and by DSC for changes in the thermal properties, e.g., T_g. For all values of weight-loss α, the thermal stability of the polymers follows the order: Poly-(methyl methacrylate) (PMMA) = PcHMA > poly(ethyl methacrylate) (PEMA) > PPhMA > poly(n-butyl methacrylate) (PnBuMA) > poly(isobutyl methacrylate) (PiBuMA). In the depolymerization reactions that occur during the isothermal decomposition of PPhMA, there is no specific preference for longer or shorter chains although a minor fraction of the volatilized fraction with an [Mbar]_w 10^?5 of 2.5 and an [Mbar] _n |MX 10.^?5 of 1.5 does undergo chain recombination yielding high molecular weight products with an M_w × 10^?6 of 1.35 and an M_n × 10^?6 of 1.0 to 1.23. In the case of PcHMA, depolymerizations did show a preference for longer chains. No chain recombination, however, was found to take place. Activation energy of decomposition for substituted poly-methacrylates follows the order: PnBuMA = PiBuMA >; PEMA >; PcHMA >; PMMA >; PPhMA. T_{g e} values of PPhMA samples varied from 362 K for undecomposed polymers to 396 K for a polymer treated at 300° C. The literature value of 383 K does fall within this range. In the case of PcHMA, an average T_ge of 356 f 6.0 ± is not far removed from the reported value of 359 K.     

A detailed surface analytical study of degradation processes in (meth)acrylic polymers

The present study investigates the degradation behavior of various high‐molecular‐weight acrylic polymers (50,000 < M_n/g mol^?1 < 100,000), namely poly(methyl methacrylate) (PMMA), poly(n‐butyl methacrylate) (PBMA), poly(n‐butyl acrylate) (PBA), and poly(lauryl methacrylate) (PLMA), under extreme environmental conditions. These polymers were synthesized via various polymerization techniques to create different end‐groups. The polymers chosen are readily applicable in the formulation of surface coatings and were degraded under conditions which replicate the harsh Australian climate, where surface coatings may reach temperatures of up to 95 °C and are exposed to broad‐spectrum UV radiation of up to 1 kW m^?2. The degradation behavior of the polymeric materials on their surface was followed via ATR‐IR spectroscopy, high resolution FTIR microscopy, and X‐ray photoelectron spectroscopy. The extent of the observed thermal and photo‐oxidation is directly related to the length of the ester side group, with the degradation susceptibility decreasing in the order of PLMA > PBMA/PBA > PMMA, with PMMA still stable even after 5 months exposure to the harshest condition used (UV light at 95 °C). The general degradation mechanism involves the loss of the ester side groups to form methacrylic acid followed by cross‐linking. The effect of the variable end groups was found to be minimal. The results from this study are in good agreement with previous studies of low‐molecular‐weight model polymers under identical conditions. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Atom transfer radical polymerization of 1-phenoxycarbonyl ethyl methacrylate monomer

Atom transfer radical polymerization conditions with copper(I) bromide/2,2^′-bipyridine (Cu/2,2^′-bpy) as the catalyst system were employed for the homopolymerization and random copolymerization of 1-phenoxycarbonyl ethyl methacrylate (PCMA) with methyl methacrylate (MMA). Temperature studies indicated that the polymerizations occurred smoothly in bulk at 110 °C. Poly(PCMA)(polydispersity index=1.27) homopolymer was characterized and then used as macroinitiator for increasing its molecular weight. The homopolymerization of PCMA was also carried out under free radical conditions using 2,2^′-azobisisobutyronitrile as an initiator.The monomer and polymers were characterized by FT-IR and ¹H and ¹³C-NMR techniques. The glass transition temperatures, the solubility parameters and average-molecular weights of the polymers were determined. Thermal stabilities of the polymers were given as compared with each other by using TGA curves. Thermal degradation products of poly(PCMA)s obtained by ATRP and free radical polymerization were compared with each other by using ¹H-NMR technique.     

Study of radiation-induced polymerization of vinyl monomers adsorbed on inorganic substances. V. Effects of p-benzoquinone and dose rate on methyl methacrylate–silica gel system

In order to elucidate the mechanism of radiation-induced polymerization of methyl methacrylate adsorbed on silica gel, the effects of p-benzoquinone addition and dose rate were studied in detail. Most of the polymerization is inhibited by p-benzoquinone at levels above 10^-2 mole/l. The GPC spectra of both graft polymers and homopolymers show two peaks. The high molecular weight material appears to have been formed by polymerization by a radical mechanism, because these peaks decrease as p-benzoquinone concentration increases; on the other hand, their low molecular weight polymers seem to be products of an ionic polymerization mechanism because those peaks are almost not affected by p-benzoquinone. The four GPC peaks differ in dose rate dependences of their polymerization rate. The dose-rate exponents of polymerization rate were obtained for the four GPC peaks. The behavior of the low molecular weight peaks of graft polymers and homopolymers were quite different, suggesting that the polymers differ considerably in formation mechanism.     

Effect of dicarboxy terminated polystyrene on strengthening immiscible polystyrene/poly(methyl methacrylate) interface

The fracture toughness between polystyrene (PS)/poly(methyl methacrylate) (PMMA) reinforced with reactive polymers, poly(glycidyl methacrylate) (PGMA) and dicarboxy or monocarboxy terminated PS (dcPS and mcPS), was measured by the asymmetric fracture test. Molecular weight effect of mcPS, although the molecular weight distribution is rather polydisperse, on the maximum achievable fracture toughness, G_max qualitatively agreed with the results of the monodisperse case^4,5). In the case of dcPS with M_w ≅ 142 K, G_max reached ca. 170 J/m² which is nearly 8 times higher than that of mcPS of molecular weight of about 150K. From the mechanical point of view, dcPS with a degree of polymerization (N) greater than the ratio of chain breaking force to monomeric friction force (f_b/f_mono) is more effective in enhancing the interfacial adhesion than mcPS since it provides two stitches to the interface. It was also shown by Monte Carlo simulation on reactive polymer system that the di‐endfunctional polymers are more effective than mono‐endfunctional polymers in reinforcing the week interface between immiscible polymers.     

Soft Matter Nanoparticles with Reactive Coronal Pentafluorophenyl Methacrylate Residues via Non‐Polar RAFT Dispersion Polymerization and Polymerization‐Induced Self‐Assembly

Soft matter nanoparticles exhibiting rich polymorphism with reactive pentafluorophenyl methacrylate (PFPMA) units in their coronae were prepared via non‐polar reversible addition‐fragmentation chain transfer dispersion polymerization and polymerization‐induced self‐assembly. Poly(stearyl methacrylate‐stat‐PFPMA) macro‐CTAs, containing up to 12 mol % PFPMA, were used in n‐octane and n‐tetradecane for the subsequent copolymerization of 3‐phenylpropyl methacrylate. Both formulations gave the full, common family of nanoparticles (spheres, worms, and vesicles) as determined by transmission electron microscopy. Reaction of the PFP ester repeating units in the coronal layer of spherical nanoparticles with benzylamine, tetrahydrofurfurylamine, N,N‐dimethylethylenediamine, and an amine functional methyl red dye yielded a new library of functional spherical nano‐objects. The success of the nucleophilic acyl substitution reactions was confirmed using a combination of ¹H/¹⁹F NMR and Fourier transform infrared spectroscopies as well as dynamic light scattering. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2326–2335     

Hyperbranched polymers generated from oxyanionic vinyl polymerization of commercially available methacrylate inimers

Hyperbranched polymethacrylates were prepared by means of oxyanionic vinyl polymerization of commercially available monomers, including hydroxyethyl methacrylate (HEMA) and poly(ethylene glycol) methacrylate (PEG‐MA). Hyperbranched polymethacrylates with high molecular weight were obtained with the complex of potassium hydride and 18‐crown‐6 as the initiator. The effect of 18‐crown‐6 is very important, and only oligomer can be obtained in the polymerization without 18‐crown‐6. The molecular structure of the hyperbranched polymers was confirmed with ¹H NMR and ¹³C NMR spectra. The ratio of initiator to monomer significantly affects the architecture of the resultant polymers. When the ratio of initiator to monomer equals 1 in the oxyanionic vinyl polymerization of HEMA, the degree of branching of the resulting polymer was calculated to be around 0.49. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3502–3509, 2005     

A Study on End Group Characterization of Poly(phenacyl methacrylate) Polymer Produced by Free Radical Polymerization

Free‐radical homopolymerization and copolymerization of phenacyl methacrylate (PAMA) with methyl methacrylate (MMA) was done using 2,2′‐azobis(isobutyronitrile) (AIBN) as the initiator in 1,4‐dioxane at 60°C. ¹H‐NMR and FT‐IR spectroscopy confirmed the existence of OCH₂ and CH signals and unsaturated structure and CN stretch at the chain end of low molecular weight poly(phenacyl methacrylate) [poly(PAMA)], respectively. The six‐membered ring with both ester and ether at the end group was detected by ¹H‐NMR. In the poly(PAMA), the end groups formed due to chain transfer reactions were found in large concentrations. The mechanism of the formation of end groups has been presented. The behavior of free radical polymerization of PAMA was compared with that of phenoxycarbonylmethyl methacrylate (PCMMA). The molecular weight distribution of the homo and copolymers was determined using gel permeation chromatography. Thermal properties of the polymers were determined using differential thermal analysis (DTA) and thermogravimetric analysis (TGA).     

Architecture of hyperbranched polymers consisting of a stearyl methacrylate sequence via a living radical copolymerization

The living radical photocopolymerization of 2-(N,N-diethyldithiocarbamyl)ethyl methacrylate (DCEM) as inimer and stearyl methacrylate (STM) as comonomer was carried out under UV irradiation. According to this method, we synthesized hyperbranched polymers (HP) consisting of a STM sequence having a long alkyl side chain. The gel permeation chromatography distribution of hyperbranched polymers had a unimodal pattern. The reactivity ratios (r(1)=0.79 and r(2)=0.81) were estimated by the Kelen-Tüd?s method (DCEM: [M](1) and STM: [M](2)). These values indicated that the two monomers showed almost equal reactivity toward propagating radical species. The radius of gyration (R(g)) and the hydrodynamic radius (R(h)) of copolymers were determined by static and dynamic light scattering (SLS and DLS), and the values of R(g)/R(h) changed from 0.79 to 1.59 with an increment of the feed amount of STM. These results indicated that the copolymer structures changed from hard spheres to loose branched molecules in solution.     

A Study on End Group Characterization of Poly(phenacyl methacrylate) Polymer Produced by Free Radical Polymerization

Free‐radical homopolymerization and copolymerization of phenacyl methacrylate (PAMA) with methyl methacrylate (MMA) was done using 2,2′‐azobis(isobutyronitrile) (AIBN) as the initiator in 1,4‐dioxane at 60°C. ¹H‐NMR and FT‐IR spectroscopy confirmed the existence of OCH₂ and CH signals and unsaturated structure and CN stretch at the chain end of low molecular weight poly(phenacyl methacrylate)[poly(PAMA)], respectively. The six‐membered ring with both ester and ether at the end group was detected by ¹H‐NMR. In the poly(PAMA), the end groups formed due to chain transfer reactions were found in large concentrations. The mechanism of the formation of end groups has been presented. The behavior of free radical polymerization of PAMA was compared with that of phenoxycarbonylmethyl methacrylate (PCMMA). The molecular weight distribution of the homo and copolymers was determined using gel permeation chromatography. Thermal properties of the polymers were determined using differential thermal analysis (DTA) and thermogravimetric analysis (TGA).