Soluble hyperbranched copolymer via initiator-fragment incorporation radical copolymerization using a trivinyl monomer

The initiator-fragment incorporation radical polymerization was extended to a copolymerization system of a trivinyl monomer. The copolymerization of trimethylolpropane trimethacrylate (TMPTM) as a trivinyl monomer with α-methylstyrene (MSt) was examined at 70 and 80 °C in toluene using dimethyl 2,2′-azobisisobutyrate (MAIB) of high concentrations as initiator. When the concentrations of TMPTM, MSt and MAIB were 0.30, 0.60 and 0.50 mol/l, the copolymerization proceeded homogeneously without gelation at 80 °C to yield soluble hyperbranched copolymer in a yield of 65%. The copolymer formed for 8 h consisted of 37 mol% of the TMPTM unit, 42 mol% of the MSt unit and 21 mol% of the methoxycarbonylpropyl group as initiator-fragment, where 22% of the vinyl groups of the incorporated TMPTM units remained unreacted. The copolymer showed an upper critical solution temperature (32 °C on cooling) in a tetrahydrofuran(THF)-water [44:10 (wt/wt)]. Reflecting the hyperbranched structure, the viscosity of a copolymer solution in toluene was very low. The porous film was prepared directly by casting a THF solution of the hyperbranched copolymer on a cover glass. The copolymer molecules are radially arranged on the surface layer of the spherical pores as showed by polarized optical microscope imaging.     

Formation of soluble hyperbranched polymer through the initiator-fragment incorporation radical copolymerization of ethylene glycol dimethacrylate with N-methylmethacrylamide

The copolymerization of ethylene glycol dimethacrylate (EGDMA) as a divinyl monomer with N-methylmethacrylamide (NMMAm) as a water-soluble monomer was carried out at 70 and 80 °C in N,N-dimethylformamide (DMF) using dimethyl 2,2′-azobisisobutyrate (MAIB) of high concentrations as initiator. When the concentrations of EGDMA, NMMAm and MAIB were 0.15, 0.50 and 0.35 mol/l, the copolymerization proceeded homogeneously with no gelation at 80 °C to give soluble copolymer in a yield of 50%. EGDMA was polymerized more rapidly than NMMAm as shown by Fourier-transform near infrared spectroscopy. The copolymer formed for 8 h consisted of 20 mol% of EGDMA unit, 47 mol% of NMMA unit and 33 mol% of methoxycarbonylpropyl group unit as MAIB-fragment. The copolymer formed at 80 °C for 30 min showed an upper critical solution temperature (34 °C on cooling) in methanol. The intrinsic viscosity of the copolymer formed for 2 h was very low (0.11 dl/g) at 30 °C in DMF despite high weight-average molecular weight [3.1×l0⁶ by multi-angle laser light scattering (MALLS)]. The copolymer exhibited a very low second virial coefficient (4.2×l0⁻⁶) as determined at 25 °C in DMF by MALLS. The individual copolymer molecules were observed as nanoparticles of 7-20 nm diameter by a transmission electron microscope. These results show that the resulting copolymers are of hyperbranched structure.     

Synthesis and characterization of soluble hyperbranched polymer via initiator‐fragment incorporation radical polymerization of divinylbenzene with dimethyl 2,2′‐azobisisobutyrate

The homopolymerization of divinylbenzene (DVB) as an excellent crosslinker (0.20 mol/L) with dimethyl 2,2′‐azobisisobutyrate (MAIB) proceeded homogeneously without any gelation at 80°C in benzene when the MAIB concentrations as high as 0.30–0.50 mol/L were used, yielding soluble polymers. In the polymerization at the concentrations of [DVB] = 0.20 mol/L and [MAIB] = 0.50 mol/L, the polymer yield increased with time and leveled off over 90 min. The molecular weight and molecular weight distribution increased with polymer yield. The vinyl groups of DVB were observed to be almost completely consumed in about 80 min, by FT near‐IR spectroscopic analysis. The homogeneous polymerization system involved ESR‐observable polymer radical, the concentration of which increased with time up to 3.4 × 10^?5 mol/L. The polymer formed in the polymerization for 2 h consisted of 46 mol % of DVB unit and 54 mol % of the methoxycarbonylpropyl group as MAIB fragment, indicating that an initiator‐fragment incorporation radical polymerization proceeds in the present polymerization. The polymer was soluble in benzene, tetrahydrofuran, ethyl acetate, chloroform, acetone, and N,N‐dimethylformamide, while it was insoluble in n‐hexane, acetonitrile, dimethyl sulfoxide, methanol, and water. The results of the multiangle laser light scattering and viscometric measurements revealed that the individual polymer molecules were formed as hyperbranched polymer nanoparticles. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 664–670, 2006     

Synthesis of monodisperse porous poly(divinylbenzene) microspheres by distillation-precipitation polymerization

Highly crosslinked monodisperse porous poly(divinylbenzene) (PDVB) microspheres were prepared by distillation-precipitation polymerization in acetonitrile containing up to 25 vol% of toluene as porogen with 2,2′-azobisisobutyronitrile (AIBN) as initiator in the absence of any stabilizer or surfactant. The porous polymer microspheres were formed through a precipitation manner during the distillation of the solvent from the reaction system. Monodisperse porous polymer particles with spherical shape and smooth surface were synthesized with diameters in the range of 1.86 and 3.06 μm, total porosity of up to 0.30 cm³/g and specific surface area as high as 762 m²/g. The growth procedure of porous PDVB microsphere was characterized by SEM technique for morphological observation and isotherm nitrogen adsorption for the determination of the special surface area and porosity. The resultant porous polymer microspheres had a novel structure with the gradual increasing of pore volume during distillation of the solvent out of the reaction system.     

Distribution function of hyperbranched polymers formed by AB2 type polycondensation with substitution effect

By kinetic model, the analytical expression of the distribution function for the hyperbranched polymers formed from AB₂ type polycondensation with substitution effect was derived. The results are compared to those for self-condensing vinyl polymerization of AB* monomers. Reaction becomes faster with the increasing reactivity of a linear B group. At any finite conversion of A group, both average degree of polymerization and dispersity increase with the increase of low rate constant, r (ratio of the reactivity of a linear B group to that of a terminal B group). However, the variation of these parameters is moderate if r>100 and they converge to respective limiting value. The average degree of polymerization and dispersity are much smaller than that of self-condensing vinyl polymerization of AB* monomers at the same conversion.     

Preparation and characterization of hyperbranched polymer grafted mesoporous silica nanoparticles via self-condensing atom transfer radical vinyl polymerization

Hyperbranched poly(2-((bromobutyryl)oxy)ethyl acrylate) (HPBBEA) was grafted onto the exterior surface of mesoporous silica nanoparticles (MSNs) by surface-initiated self-condensing atom transfer radical vinyl polymerization (SCATRVP). The MSNs with ATRP initiator anchored on the exterior surface (MSN-Br) were prepared by the reaction of 5,6-dihydroxyhexyl-functionalized MSNs (MSN-OH) with α-bromoisobutyryl bromide. Afterwards, MSN-Br was utilized as initiator in the SCATRVP of inimer BBEA, resulting in core-shell nanoparticles with MSN core and HPBBEA shell (MSN-g-HPBBEA). The molecular weight of HPBBEA increased with the increasing ratio of BBEA to MSN-Br. In view of the high density of bromoester groups on the surface of HPBBEA shell, MSN-HPBBEA was used to initiate the successive polymerization of (2-dimethylamino-ethylmethacrylate) (DMAEMA), forming core-shell nanoparticles MSN-g-HPBBEA-g-PDMAEMA. The resultant products were characterized by FT-IR, NMR, HRTEM and thermogravimetric analysis (TGA), etc. The pH-responsive property of MSN-g-HPBBEA-g-PDMAEMA was characterized by measuring the hydrodynamics radius at different pH values, and this core-shell nanostructure may have potential applications in biomedicine and biotechnology.     

Kinetic analysis of A2 + AB + B3 hyperbranched polymerization approach

This work theoretically deals with the kinetics of the hyperbranched polymerization with A₂, AB and B₃ monomers. The analytical expressions of the size distribution function and the various molecular parameters of the resulting hyperbranched polymers were derived. The structure and molecular parameters of the products depend on the monomer feed ratios and the conversion of groups. Gelation is easy to occur if the monomer feed ratio of A₂ to B₃ (λ) is in the range of 3/4 ≤ λ ≤ 3. The addition of AB monomer can increase the conversion of A or B groups and enhance the number-average degree of polymerization at the critical gelation point. On the other hand, excessive AB monomer will results in a small degree of branching for the products. A small λ and a suitable β value favor to form the hyperbranched polymers with certain degree of branching.     

An effective multipurpose building block for 3D electropolymerisation: 2,2′-Bis(2,2′-bithiophene-5-yl)-3,3′-bithianaphthene

Novel thiophene-based oligomer, 2,2′-bis(2,2′-bithiophene-5-yl)-3,3′-bithianaphthene (TX), was designed and synthesized, and its electrochemical and spectral properties characterised. TX was readily polymerised electrochemically to form well organized conducting homopolymer films on various solid electrode substrates. Moreover, it was successfully used for deposition by electropolymerisation of electrochemically active thin films of co-polymers with three different monomers of functionalised bis(2,2′-bithienyl)methane derivatives. It appeared that TX was an effective crosslinker and 3D promoter in these electropolymerisations involving co-monomers intrinsically showing limited aptitude for the electropolymerisation or forming polymer films of low conductivity. This attractive TX ability stems from combination of its (i) high conjugation efficiency in each of the two planar moieties, (ii) intrinsic 3D structure on account of the presence of the central node, and (iii) intrinsic regioselectivity in electropolymerisation on account of the positions of the two available free α-thiophene sites.     

Morphology control of poly(2,2′-phenylene-5,5′-bibenzimidazole) by reaction-induced crystallization during polymerization

Morphology control of polybenzimidazoles was examined by reaction-induced phase separation during polymerization. Polymerizations of 3,3′-diaminobenzidine with terephthalic acid or diphenyl terephthalate were carried out in poor solvents. The morphology of the precipitated poly[2,2′-(1,4-phenylene)-5,5′-bibenzimidazole] (PpBBI) was significantly influenced by the polymerization conditions, and the aggregates of nano-scale PpBBI fibers were obtained by the polymerization at a concentration of 3-5% and 320-350 °C in dibenzyltoluene. The average diameter of the fibers was ca. 50 nm and inherent viscosities of the precipitates were 0.35-0.58 dL g⁻¹. They possessed high crystallinity and thermal stability. The oligomers were precipitated first by the reaction-induced crystallization to form the highly crystalline lath-like crystals at an initial stage of polymerization. Then the lath-like crystals were split into disentangled aggregates of fine fibers with maintaining the high crystallinity. The polymerization mainly proceeded when the oligomers were registered into the crystals. The obtained aggregates of nano-scale fibers could be recognized as nonwoven fabrics. Morphology control of poly[2,2′-(1,3-phenylene)-5,5′-bibenzimidazole] was also examined and particles were mainly formed.     

Studies on the development of branching in ATRP of styrene and acrylonitrile in the presence of divinylbenzene

Branching atom transfer radical polymerization (ATRP) of styrene and acrylonitrile was attempted in the presence of divinylbenzene targeting toward soluble branched copolymer. The kinetics and the development of branching with monomer conversion were studied in detail. Gas chromatography (GC), gel permeation chromatography (GPC) coupled with multi-angle laser light scattering (MALLS), proton nuclear magnetic resonance (¹H NMR) spectroscopy and intrinsic viscosity determination were used to monitor the polymerization process and characterize the obtained copolymer. Analysis of conversion of reactants, the growth manner of molecular weight with monomer conversion and GPC traces proved that the primary chains with low polydispersity formed mainly at the early stage and then were linked in a statistical manner to start the branching at the middle or late stage. The more the branching agent was used, the earlier the branching occurred, and too much higher level of branching agent resulted in gelation. For the selected ratio of [t-BBiB]/[DVB]/[St]/[AN] = 1/0.9/15/15, with monomer conversion less than 40%, primary chains with low polydispersity formed from the polymerization of St, AN and DVB, and only a part of the primary chains contained pendent vinyl group. When monomer conversion was up to 40%, the pendent vinyl groups participated in polymerization, resulting in the linking of the primary chains statistically to start the branching. The branching became significant at monomer conversion up to 50%, giving rise to a steep increase in molecular weight and width in molecular weight distribution. As the polymerization proceeded, the polymer composition gradually approached the feed composition, identifying the obtained branched copolymer provided some gradients are in its primary chains. Finally, branched copolymer bearing about six primary chains was prepared at monomer conversion near to 80%, its absolute weight average molecular weight was about 8.87 × 10⁴.     

Synthesis and electrochemical characterization of bis(3,4-ethylene-dioxythiophene)-(4,4′-dinonyl-2,2′-bithiazole) comonomer

The synthesis and characterization of a novel donor acceptor donor type bis(3,4-ethylene-dioxythiophene)-(4,4′-dinonyl-2,2′-bithiazole) comonomer and its electrochemically prepared polymer on carbon fiber, Pt button and ITO plate is reported in this paper. Cyclic voltammetry of the polymer in 0.1 M Et₄NBF₄/CH₂Cl₂ exhibits a very well defined and reversible redox processes and this co-monomer can be either p-doped or n-doped. The half-wave oxidation potentials of the polymer (E_1/2) were observed at 0.303 and 0.814 V versus Ag/AgCl. The polymer is electrochromic; the onset for the π-π^* transition (E_g) of 1.75 eV with a λ_max at 2.15 eV and the homogeneous and high quality film of the polymer is stable of its optical properties offering fast switching time which is less than 0.25 s. The morphological studies reveal that the polymer was deposited as a continuous and very well adhering film to surface of the carbon fiber microelectrode. All these properties make this polymer favorable for use in electronic devices.     

Synthesis and characterization of hyperbranched azobenzene-containing polymers via self-condensing atom transfer radical polymerization and copolymerization

We report on the synthesis of an azobenzene-containing inimer 6-{4-[4-(2-(2-bromoisobutyryloxy)hexyloxy)phenylazo]phenoxy}hexyl methacrylate (I) and used it to prepare hyperbranched homopolymer and copolymers by self-condensing vinyl polymerization (SCVP) and copolymerization (SCVCP) with its precursor 6-{4-[4-(6-hydroxyhexyloxy)phenylazo]phenoxy}hexyl methacrylate (M) using atom transfer radical polymerization (ATRP). Depending on the comonomer ratio, γ=[M]₀/[I]₀, branched polymethacrylates with number-average weights between 8000 and 20,000 and degree of branching (DB) between 0.08 and 0.49 were obtained by SCVCP, as evidenced by GPC and ¹H NMR analysis. In addition, the photochemical properties of the polymers were also studied by UV-vis spectra and found the structure of polymers affect obviously the trans-cis isomerization properties of the branched polymers.     

Synthesis and properties of organosoluble polyimides based on 2,2′-diphenoxy-4,4′,5,5′-biphenyltetracarboxylic dianhydride

A novel method for the preparation of 2,2′-diphenoxy-4,4′,5,5′-biphenyltetracarboxylic dianhydride have been investigated. This new dianhydride contains flexible phenoxy side chain and a twist biphenyl moiety and it was synthesized by the nitration of an N-methyl protected 3,3′,4,4′-biphenyltetracarboxylic dianhydride and subsequent aromatic nucleophilic substitution with phenoxide. The overall yield was up to 75%. The dianhydride was polymerized with five different aromatic diamines to afford a series of aromatic polyimides. The polyimide properties such as inherent viscosity, solubility, UV transparency and thermaloxidative properties were investigated to illustrate the contribution of the introduction of phenoxy group at 2- and 2′-position of BPDA dianhydride. The resulting polyimides possessed excellent solubility in the fact that the polyimide containing rigid diamines such as 1,4-phenylenediamine and 4,4′-oxydianiline were soluble in various solvents such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, dimethyl sulfoxide and chloroform. The glass-transition temperatures of the polymers were in the range of 255-283 °C. These polymers exhibited good thermal stability with the temperatures at 5% weight loss range from 470 to 528 °C in nitrogen and 451 to 521 °C in air, respectively. The polyimide films were found to be transparent, flexible, and tough. The films had a tensile strength, elongation at break, and Young's modulus in the ranges 105-168 MPa, 15-51%, 1.87-2.38 GPa, respectively.     

Controlled chain branching free radical polymerization manipulate with trithiocarbonates

Soluble, branched (methyl) methacrylate copolymers have been prepared via facile, one‐step, batch solution free radical polymerizations taken to high conversion. Methyl methacrylate (MMA) or methacrylate has been copolymerized with the branching comonomer (BCM) using a trithiocarbonate (TTC) to inhibit gelation. The BCMs employed were tripropylene glycol diacrylate (TPGDA) and trihydroxymethylpropyl triacrylate (TMPTA). Soluble branched copolymers containing unreacted double bonds have been produced and characterized by ¹H‐NMR spectroscopy. These two brancher monomers have been shown to produce regularly branched material with the small molar mass distributions in the presence of TTC. The results of DSC and Mark–Houwink constant α analyses support the production of the branched architectures. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

二乙烯基苯/聚二甲基硅烷改良聚碳硅烷合成工艺的研究

在传统的合成体系中加入适量的二乙烯基苯,通过常压高温自由基聚合反应,获得了产率较高、可纺性优良的先驱体聚碳硅烷。采用正交实验设计研究了反应温度、升温速率、二乙烯基苯的质量分数、裂解温度和保温时间五个因素对聚碳硅烷产率的影响。方差分析表明,在反应温度为420℃、二乙烯基苯的质量分数为1·5%、升温速率为6℃/h、裂解温度为530℃、保温时间为5h条件下,可以得到粗产率为50%的黄色透明固态聚碳硅烷;各因素对聚碳硅烷产率影响的显著性依次为:升温速率>反应温度>二乙烯基苯的质量分数>保温时间>裂解温度。     

Gelation in the radical polymerization of dimethyl diallyl ammonium chloride

Within the framework of an irreversible aggregation model on a sample of polydimethyl diallyl ammonium chloride, we demonstrated that gelation occurred on a transient part from the autoacceleration stage until the dopolymerization stage. During part of the autoacceleration, the polymer solution was in a sol state on the segment of autoacceleration. Therefore, the use of the term gel effect in reference to the beginning of the reaction did not seem quite justified. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1394–1396, 2004     

Effect of feed rate on structure of hyperbranched polymers formed by stepwise addition of AB2 monomers into multifunctional cores

Hyperbranched polymers generated from the copolymerization of AB₂-type monomers slowly added into trifunctional C₃ cores under various feed rates were investigated by a kinetic model. The dependences of average molecular weight, polydispersity, degree of branching (DB), and number of structural units of the hyperbranched polymers on the feed rate were calculated by a generating function method. It was found that the final PDI can be attained below 1.5 by a slow addition with the parameter of feed rate, φ, less than 1. While the AB₂ monomers fed quickly, the system with a lower content of the C₃ cores results in a broader molecular weight distribution. A high DB, about 0.66, can be achieved by addition of a small amount of C₃ cores at φ lower than 10.