Reversible crosslinking of polymers bearing pendant or terminal thiol groups prepared by nitroxide-mediated radical polymerization

Monomers or N-alkoxyamine initiators containing protected thiol groups are utilized to prepare polymers via nitroxide-mediated radical polymerization. Following thiol deprotection, the macromolecular properties of these polymers are manipulated, by adjusting the redox conditions to either form or cleave disulfide bonds, or irreversibly cap free thiols by the rapid addition to a maleimide Michael acceptor. Formation of disulfide bonds under dilute conditions results in intramolecular disulfide formation, resulting in internal polymer collapse. Alternatively, disulfide formation under high concentration results in intermolecular crosslinking of polymers to form networked macromolecular assemblies.     

Synthesis,characterization and rheological properties of three different microstructures of water-soluble polymers prepared by solution polymerization

Three different structures were synthesized via solution free radical polymerization. Polyacrylamides hydrophobically modified with small amounts of two different N′N-dialkylacrylamides [N,N-dihexylacrylamide (DHAM) and N,N-dioctylacrylamide (DOAM)] and two different N-alkylacrylamides [N-dodecylacrylamide (DAM) and N-hexadecylacrylamide (HDAM)] have been synthesized using two linear hydrophobic initiators with 12 (ACVA₁₂) and 16 (ACVA₁₆) carbon atoms and two di-substituted hydrophobic initiator with two chains of 6 (ACVA_di6) and 8 (ACVA_di8) carbon atoms derived from 4′4-azobis(4-cyanopentanoic acid) (ACVA). The polymers obtained were telechelic, multisticker and combined. The initiators, monomers and polymers synthesized were characterized by ¹H NMR and light scattering (LS). The rheological properties of these three different associative polymers were investigated using steady-state experiments. The effect of location and structure (linear or di-substituted) of the hydrophobic groups upon the viscosity of the polymer in solution was studied.     

Synthesis and characterization of telechelic polymers obtained by micellar polymerization

Summary The synthesis, characterization and rheological properties in aqueous solution of two telechelic polymers of different structures and size are reported: they are water soluble polyacrylamides, hydrophobically modified with linear and di-substituted hydrophobic initiators. The polymers were prepared via free radical micellar polymerization. The results of static light scattering (SLS), showed similar weight-average molecular weights (M_w) in all of the synthesized polymers. No signal corresponding to the presence of the hydrophobic group of the initiator could be observed by ¹H NMR; however, the presence of these hydrophobic groups was demonstrated using rheological measurements.     

Imprinted polymers prepared by aqueous suspension polymerization

The feasibility of preparing cholesterol‐imprinted polymers by aqueous suspension polymerization was investigated by the preparation of ethyleneglycol dimethacrylate and divinylbenzene‐based beads imprinted using cholesteryl(4‐vinyl)phenyl carbonate as the template. A low volatility porogen to replace a 4:1 hexane/toluene mixture was selected on the basis of solubility parameters and consisted of dioctyl phthalate/n‐decane 77:23 v/v. Beads were prepared using a range of porogen contents with the best results obtained at 5.5–6.5 mL /5 g of monomer. Uptake of cholesterol by suspension polymers was broadly similar to that of the corresponding “bulk” polymers, but suffered from higher nonspecific binding. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1841–1850, 2000     

Synthesis of binary mixed homopolymer brushes by combining atom transfer radical polymerization and nitroxide-mediated radical polymerization

This communication describes a novel strategy to synthesize binary mixed homopolymer brushes from mixed self-assembled monolayers (SAMs) on silica substrates by combining atom transfer radical polymerization (ATRP) and nitroxide-mediated radical polymerization (NMRP). Mixed SAMs terminated by ATRP and NMRP initiators were prepared by coadsorption of two corresponding organotrichlorosilanes from toluene solutions. Mixed poly(methyl methacrylate) (PMMA)/polystyrene (PS) brushes were synthesized by ATRP of MMA at 80 °C followed by NMRP of styrene at 115 °C. Corresponding ‘free’ initiators were added into the solutions to control the polymerizations. We have found that the brush thickness increases with molecular weight in a nearly linear fashion. For a series of binary brushes consisting of PMMA of molecular weight of 26,200 and PS of various molecular weights, we have observed a transition in water contact angles with increasing PS molecular weight after CH₂Cl₂ treatment. Moreover, binary mixed polymer brushes with comparable molecular weights for two grafted polymers undergo reorganization in response to environmental changes, exhibiting different wettabilities.     

Reactions of organoboron polymers prepared by hydroboration polymerization

Summary Organoboron polymers were prepared by hydroboration polymerization between various dienes and thexylborane. These polymers were reacted with -furyllithium followed by the treatment with acetic acid and then by the oxidative treatment to give the corresponding polyalcohols having primary and tertiary hydroxyl groups. The structures of the polyalcohols obtained were characterized by¹H-NMR compared with that for model compound, which was prepared by the reaction of dioctylthexylborane with -furyllithium. These conversions from organoboron polymers to polyalcohols include the migrations of two polymeric chains from boron atom to carbon and the ring-opening of furan ring.For parts I, II, and III, see references 4, 5 and 6, respectively.     

Reactions of organoboron polymers prepared by hydroboration polymerization

Summary Hydroboration polymerization of diolefin gives an organoboron polymer, which can be regarded as a polymer homologue of trialkylborane. The organoboron polymers obtained were reacted with ,-dichloromethyl methyl ether (DCME) followed by the oxidative treatment to produce the corresponding poly(alcohol)s in high yields.Part II: Polym. Bull. 25,1 (1991)     

Reactions of organoboron polymers prepared by hydroboration polymerization

Summary Organoboron polymers consisting of carbon-boron bonds in the main chains were prepared by hydroboration polymerization of various dienes with thexylborane. These polymers were reacted with α-furyllithium followed by treatment with acetic acid to give the corresponding poly(alcohol)s. This conversion includes the migrations of two polymeric main chains from boron atom to carbon and the reductive cleavage of carbon-boron bonds in the resulting boron-containing polymers. The structures of the poly(alcohol)s obtained were characterized by ¹H-NMR in comparison with that of model compound, which was prepared by the reaction of dioctylthexylborane with α-furyllithium followed by reductive treatment. The organoboron polymer prepared from 1,7-octadiene and thexylborane was also reacted with dichloromethyl methyl ether followed by acidolysis to form hydrocarbon polymer without obvious scission of polymeric main chain. See references     

Reactions of organoboron polymers prepared by hydroboration polymerization

Summary This paper describes a novel methodology for the preparation of poly(ketone). An organoboron polymer was prepared by polyaddition between thexylborane and 1,7-octadiene, which was reacted with potassium cyanide in the presence of trifluoroacetic anhydride. After oxidation of the reaction mixture, the corresponding poly(ketone) was obtained.     

Mechanical properties of cross-linked polymer particles prepared by nitroxide-mediated radical polymerization in aqueous micro-suspension

The compressive strengths of micron-sized, cross-linked poly(styrene-divinylbenzene) particles synthesized by conventional radical copolymerization (70 °C) and nitroxide (TEMPO)-mediated radical copolymerization (125 °C) in aqueous micro-suspension have been measured. In the conventional system, the breaking energies and the compressive strengths of the particles (after removal of unreacted monomer) remained approximately constant from low to high conversion, whereas in the NMP system, both quantities increased close to linearly with conversion. The results suggest that the network formation is more homogeneous in the NMP system than in the conventional system.     

Conducting polymers prepared by oxidative polymerization: polyaniline

Polyaniline (PANI) is one of the most intensively investigated polymers during the last decade. The establishment of the scientific principles allowing regulation of its properties, determining the potential application areas (alternative energy sources and transformers, media for erasable optical information storage, non-linear optics, membranes, etc.) is an important scientific problem. We have shown for the first time that the behavior of this polymer is subject to the same basic principles as the polymerization process itself. Both the polymerization of aniline and the subsequent transformations of polyaniline have to be regarded as typical redox processes, where the direction and establishment of equilibrium are dependent on the oxidation potentials and concentrations of the reactants (and also on pH of the medium, affecting the values of oxidation potential of the reactants). Such an approach allows us to identify the oxidative polymerization of aniline (and presumably of thiophene and pyrrole) as a new area in cationic polymerization, wherein the conditions of initiation, propagation and termination of the chains can be expressed by means of the electrochemical potential of the system. Furthermore, this allows an elucidation of the key problems related to the main types of transformations of this polymer (the so-called oxidative and non-oxidative doping of polyaniline). It also gave us a reason to suggest a novel original classification of the numerous potential application areas of PANI.     

Viscoelastic properties and morphological characterization of silica/polystyrene nanocomposites synthesized by nitroxide-mediated polymerization

Polystyrene (PS) chains with molecular weights comprised between 15,000 and 60,000 g/mol and narrow polydispersities were successfully grown from the surface of silica nanoparticles by nitroxide-mediated polymerization (NMP). Small angle X-ray scattering was used to characterize the structure of the interface layer formed around the silica particles, and at a larger scale, dynamic light scattering was used to determine the hydrodynamic diameter of the functionalized silica suspension. In a second part, blends of PS-grafted silica particles and pure polystyrene were prepared to evaluate the influence of the length of the grafted PS segments on the viscoelastic behavior of the so-produced nanocomposites in the linear viscoelasticity domain.Combination of all these techniques shows that the morphology of the nanocomposite materials is controlled by grafting. The steric hindrance generated by the grafted polymer chains enables partial destruction of the agglomerates that compose the original silica particles when the latter are dispersed either in a solvent or in a polymeric matrix.     

原位乳液聚合聚苯胺/聚甲基丙烯酸甲酯复合物及其表征

以DBSA为乳化剂和掺杂剂,在水介质中采用原位乳液聚合法制备出了聚苯胺/聚甲基丙烯酸甲酯(PANI/PMMA)复合物。采用扫描电镜、红外光谱分析、紫外光谱分析、热失重分析、X射线光电子能谱分析对PANI/PMMA复合物进行了表征。结果表明:复合物产物粒径在80～120nm;电导率可达到10-2S/cm,接近于乳液聚合得到的DBSA掺杂态PANI;乳化剂DBSA以掺杂剂和稳定剂两种状态存在于复合物中。     

Amphiphilic gradient poly(styrene-co-acrylic acid) copolymer prepared via nitroxide-mediated solution polymerization. Synthesis, characterization in aqueous solution and evaluation as emulsion polymerization stabilizer

A well-defined, amphiphilic poly(styrene-co-acrylic acid) copolymer was synthesized in a single step by nitroxide-mediated controlled free-radical copolymerization of styrene and acrylic acid, without protection of the acid groups: M_n=6500 g mol⁻¹, M_w/M_n=1.5 and a composition of F_AA=0.70±0.03 in acrylic acid. In addition to the good control over molar mass and molar mass distribution, the copolymer exhibited a narrow composition distribution with a slight gradient. Such copolymer was an efficient stabilizer for the emulsion polymerizations of styrene and of mixtures of methyl methacrylate and n-butyl acrylate, until 45 wt% solids. A low amount (typically 3-4 wt% based on the monomer(s)) was needed for a good stabilization. This is approximately a decade lower than the required amount of random, amphiphilic copolymers prepared via conventional free-radical polymerization. The performances were, however, below those of analogous diblock copolymers, but the great advantage is the very easy synthetic procedure.     

Synthesis and characterization of the novel inimer-containing fluorene units and preparation of blue light-emitting polymers

The novel inimer-containing fluorene units was successfully synthesized and characterized. Hyperbranched homopolymer and copolymers with methyl methacrylate (MMA) were prepared by the novel inimer via atom transfer radical polymerization where CuBr/1,1,4,7,10,10-hexamethyltriethylenetetramine (HMTETA) were used as catalyst. The copolymerization of inimer and MMA was performed under different ratio of the initial inimer/MMA and the inimer acted as not only the branched point (BP) but also the functional groups which emit blue light. The number-average molecular weight (M _n) and polydispersity index (PDI) of polymers are in the ranges (3.6–18.4) × 10³ and (1.3–2.8), respectively. Thermal gravimetric analysis (TGA) results showed all polymers had good thermal stabilities. The number of the inimers acted as branched point in the copolymer backbone is estimated by ¹H NMR spectra and UV–Vis absorption spectra.     

Synthesis and characterization of homo- and copolyimides prepared from two-step polymerization

Homopolyamic acids and copolyamic acids were prepared from four dianhydrides and three diamines. Copolyimides could be arranged in sequence through different reaction processes, such as alternating, block, and random. Polyamic acids were subsequently converted into corresponding polyimides by the solid-phase imidization. Polyimide derivatives were characterized by viscosity, thermal stability, mechanical properties, and solubility. The extent of polymerization might be influenced by the nucleophilicity of a diamine and the electrophilicity of a dianhydride. In gel permeation chromatography, molecular weight distribution of polymers was 2.5–3.0. The thermal stability of polymers decreased with increasing the ratio of a more flexible component, and alternating copolyimides showed slightly better than corresponding random and block ones. The melting temperatures of all polyimide derivatives did not exist on the differential scanning calorimetry curves, and the results were proof that the X-ray diffraction curves. Polymers derived from bis[4-(3-amino phenoxy)phenyl]sulfone dissolved well in some polar solvents. Alternating copolymers represented a better solubility than the corresponding random and block ones. All polymers had good mechanical properties, both tensile and elongation. The kinetics of imide formation could be also dependent on the structure and reactivity of reagents. The kinetics of cyclo-dehydration was described by the first-order kinetics up to relatively high conversion but deviated from the first-order kinetics at high conversion followed by the second-order kinetics. © 1996 John Wiley & Sons, Inc.     

Synthesis, characterization and third-order non-linear optical properties of novel fluorene monomers and their cross-conjugated polymers

We designed and synthesized two novel fluorene monomers of D-A-D (donor-acceptor-donor) type (M1 and M2), and their two corresponding polymers (PM1 and PM2) and a copolymer (CPM). These high molecular weight, film-forming polymers were obtained from metal-free, superacid-catalyzed reactions of the monomers with N-phenylisatin. The cubic NLO response (χ⁽³⁾) for these new compounds, in solid thin films, was measured through the use of third-harmonic generation (THG) Maker-Fringes technique at IR wavelengths given values of the order of 10⁻¹² esu from which, the corresponding second hyperpolarizabilities (γ) were estimated to be of the order of 10⁻³³ esu for monomers and 10⁻³¹ esu for polymers. Second hyperpolarizabilities have also been estimated theoretically at B3LYP/6-31G(d) level of theory in gas phase and related with the electronic structure of the synthesized molecules.     

Synthesizing and characterization of comb-shaped carbazole containing copolymer via combination of ring opening polymerization and nitroxide-mediated polymerization

The macro-TEMPO agent (poly(4-glycidyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl), PGTEMPO) was synthesized by anion ring-opening polymerization (ROP) of 4-glycidyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl (GTEMPO) using potassium t-butoxide as the initiator. The comb-shaped copolymer, PGTEMPO-g-PVBK, was prepared via nitroxide-mediated free radical polymerization (NMP) using PGTEMPO as macro-TEMPO agent and 9-(4-vinylbenzyl)-9H-carbazole (VBK) as the monomer. The polymerizations showed characteristics of “living”/controlled behavior. The optical properties, thermal analysis and electrochemical properties of the comb-shaped copolymers were investigated. The fluorescence and ultraviolet intensity and cyclic voltammetries of the comb-shaped copolymers with different molecular weight showed a regular order.     

Synthesis,characterization and rheological properties of three different associative polymers obtained by micellar polymerization

Summary We report the synthesis, characterization and rheological properties in aqueous solutions of three different water-soluble associative polymers (AP’s) (telechelic, multisticker and combined). Polymer chains consisting of water-soluble polyacrylamides, hydrophobically modified with low amounts of N,N-dihexylacrylamide and a linear hydrophobic initiator. These have been prepared via free radical micellar polymerization. We compare the properties of these different polymers, with respect to the localization of the hydrophobic groups, using steady-flow experiments. In the semidiluted regime we clearly differentiate two different zero-shear viscosity (η₀) -vs- concentration (C) behaviors; a first semidiluted regime unentangled, where the viscosity increases strongly and directly with c and a second regime entangled, where the viscosity increases proportionally to C⁴, independently of the localization of the hydrophobic group.     

Styrenation of air-blown linseed oil by nitroxide-mediated radical polymerization

Styrenation of air-blown linseed oil by a nitroxide-mediated radical polymerization (NMRP) technique is described. In this technique, air-blown linseed oil bearing hydroperoxide groups was used as a macroinitiator in NMRP of styrene in the presence of 2,2′,6,6′-tetramethylpiperidinyl-1-oxy (TEMPO). The effects of various parameters, such as the amount of TEMPO and hydroperoxide groups, were investigated in terms of molecular weight and polydispersity. For comparison, a copolymer sample of air-blown linseed oil with styrene was also prepared in the absence of TEMPO. The film properties of all samples were determined according to the related standards and were compared with respect to surface protection. Samples prepared by the NMRP technique exhibited relatively narrow polydispersity and better film properties compared to those of the samples obtained by the conventional method.