基于ATRP/CuAAC反应的降冰片烯类大分子单体的制备

利用原子转移自由基聚合合成了聚丙烯酸叔丁酯聚苯乙烯嵌段共聚物,通过取代反应在聚合物末端修饰叠氮基团,随后采用铜催化的叠氮-炔基环加成反应将含有炔基的顺-5-降冰片烯-外-2,3-二酸酐衍生物与嵌段共聚物偶联,得到大分子单体,最后通过大分子单体的开环易位聚合,制备了具有"Y"形的聚合物。通过核磁共振波谱仪、凝胶渗透色谱仪、原子力显微镜等研究了聚合物的结构与形貌。结果表明:通过活性可控聚合技术可以得到设计良好的具有复杂拓扑结构的聚合物。     

Radical polymerization approach for ring opened oxanorbornene anhydride based macromonomers

In this work, we synthesized end group functionalization of the cis-Norbornene-5-6-endo-dicarboxylic anhydride species via the ring-opening metathesis polymerization (ROMP) of oxanorbornene derivatives generated a chiseled poly(cis-Norbornene-5-6-endo-Dicarboxylic anhydride) acrylate macromonomer. Further, acrylate oxanorbornene based macromonomer further polymerized via reversible addition fragmentation chain transfer (RAFT) polymerization technique. Chain transfer is exhibited in the structure during the radical polymerizations so that free radical polymerization could also be used to comb structure copolymers with a PDI value below 1.2 with the help of acrylate oxanorbornene. Atomic force microscopy reveals the comb shape of branched polymer brushes structure. This method involves polymerizable end-group attachment to a macromonomer, and the backbone of the comb polymer is created in a second step of the polymerization. We believe that this kind of comb structured polymers can be considered for different biological applications.     

Honeycomb-like polymeric films from dendritic polymers presenting reactive pendent moieties

In this paper we describe the fabrication of honeycomb-shaped polyurethane films from dendritic side-chain polymers presenting reactive pendent units. Two novel functional polyurethanes, poly(urethane-co-acylurea) (PU-PACY) and polyurethane-co-azetidine-2,4-dione containing polyurethane (PU-PAZ), were synthesized. The waxy dendrons featured focal urea/malonamide linkages favorable for hydrogen bonding and peripheral alkyl chains. These intermolecular forces caused two functional PUs to undergo phase separation and self-assembly. This resulted in honeycomb-like films with well-controlled surface roughness characterized in terms of the ratio of rim width (W) to the pore size (D), i.e. W/D. The PU-PAZ film had a higher contact angle (CA) and a lower value of W/D than did the PU-PACY analogue, due to the presence of relatively more hydrophobic azetidine-2, 4-dione functionalities in the former film. Subsequent chemical modification of the PU-PAZ films through reaction with a hydrophobic poly(oxyalkylene)amine enhanced the CA from 113 to 134°. Further physical modification through a peeling-off process rendered the film surface with a three-dimensional (3D) rod-co-valley-structure having feature dimensions on a submicrometer scale. The 3D rod-co-valley–like film exhibited superhydrophobicity with a CA of 151°. The films also displayed excellent solvent-resistance after crosslinking with a diamine. Through hydrophobic or hydrophilic chemical modification, we could readily manipulate the surface properties of these honeycomb-like films with controllable surface roughnesses and reactive functionalities.     

Synthesis and characterization of triptycene type cross-linker and its use in photoinduced curing applications

A novel triptycene type diacrylate cross-linker, triptycene hydroquinone diacrylate (THDA) was synthesized from the reaction of triptycene hydroquinone with acryloyl chloride and characterized. The photocuring behaviour and the reaction kinetics of the synthesized cross-linker were investigated by means of photo-differential scanning calorimetry (photo-DSC) experiments. Formulations containing monofunctional (meth)acrylate monomers, namely glycidyl methacrylate (GMA), 2-hydroxyethyl acrylate (HEA), 2-hydroxyethyl methacrylate (HEMA), and 2-ethylhexyl methacrylate (EHMA), cross-linker, THDA and 2,2-dimethoxy-2-phenylacetophenone (DMPA) as a photoinitiator were irradiated. A conventional cross-linker without triptycene unit such as hydroquinone diacrylate (HDA) was used under the same conditions for comparison. The effects of the structure of the monofunctional monomer and triptycene moiety on the photopolymerization kinetics were evaluated and discussed.     

High-pressure atom transfer radical polymerization of methyl methacrylate for well-defined ultrahigh molecular-weight polymers

The feasibility of high-pressure atom transfer radical polymerization (ATRP) for synthesizing well-defined polymers of extraordinarily high molecular weights was demonstrated. ATRP of methyl methacrylate (MMA) under pressures up to 500 MPa was investigated at 60 °C. The addition of a small amount of a Cu(II)Cl₂/ligand complex along with the general benefits of high pressure of enhancing propagation and suppressing termination brought about an excellent control of polymerization even with an extremely low concentration of ATRP initiator. For example, there was produced PMMA with a number-average molecular weight M_n of 3.6 × 10⁶ and a polydispersity index of 1.24, which had never been achieved by conventional ATRP.     

Photopolymerization of N-vinylcarbazole in dichloromethane in the presence and absence of free radical photoinitiators

The photopolymerization of N-vinylcarbazole in dichloromethane was investigated, both in the presence and absence of free radical photoinitiators. The steric microstructure of the poly(N-vinylcarbazole) (PVK) samples produced was monitored as a function of temperature qualitatively, using ¹H n.m.r. and quantitatively, using glass transition temperature measurements. The activation enthalpy and entropy differences between isotactic propagation when the previous diad was syndiotactic and syndiotactic propagation when the previous diad was isotactic (ΔH³_s/i-ΔH³_i/s) and (ΔS³_s/j-ΔS³_i/s) respectively were obtained from plots of log X_i/X_sversus 1/T for the free radically and cationically polymerized components of the PVK samples. Values for (ΔH³_s/i-ΔH³_i/s) and (ΔS³_s/i-ΔS³_i/s) of ?2.65 kJ mol^?1 and ?11.7 J mol^?1 grad^?1 respectively were found for free radically polymerized fractions and +260 J mol^?1 and ?0.3 J mol^?1 grad^?1 for cationically polymerized fractions.     

Advances in RAFT polymerization: the synthesis of polymers with defined end-groups

This paper provides an overview and discusses some recent developments in radical polymerization with reversible addition-fragmentation chain transfer (RAFT polymerization). Guidelines for the selection of RAFT agents are presented. The utility of the RAFT process is then illustrated with several examples of the synthesis of polymers with reactive end-groups. Thus, RAFT polymerization with appropriately designed trithiocarbonate RAFT agents is successfully applied to the synthesis of narrow polydispersity carboxy-functional poly(methyl methacrylate) and primary amino-functional polystyrene. Methods for removing the thiocarbonylthio end-group by aminolysis, reduction and thermal elimination are discussed. It is shown that the thiocarbonylthio end-group can be cleanly cleaved by radical induced reduction with tri-n-butylstannane, to leave a saturated chain end, or by thermolysis, to leave an unsaturated chain end.     

The influence of the photophysics of 2-substituted thioxanthones on their activity as photoinitiators

The polymerization of methyl methacrylate photoinitiated by thioxanthones (TXs) substituted in the position 2 of the chromophore ring in the presence of 2-(N,N-diethylamino)ethanol has been investigated. The photoinitiation efficiency of these systems is highly dependent on the structure of the 2-substituent. At high amine concentrations, compounds with electron-withdrawing substituents appear as more efficient photoinitiators. The photophysics of the ketones was studied in the polymerization medium. These data show that the singlet excited state of TXs is deactivated by the amine with a rate constant near the diffusional control limit. The triplet rate constants for quenching by the amine and the monomer are highly dependent on the ketone structure. Compounds with electron-withdrawing substituents in the position 2 are more reactive. These studies allow to simulate the dependence of the photoinitiation efficiency with the amine concentration and indicate that the active radicals are produced by the interaction of the ketone triplet with the amine.     

Radical entry mechanisms in redox-initiated emulsion polymerizations

The mechanisms and kinetics of radical entry in emulsion polymerizations utilizing redox initiation are investigated using polymerization rate data obtained by reaction calorimetry and electrospray mass spectroscopy analysis of initiator-derived aqueous-phase products. These data have been used to evaluate an initiation scheme for redox-initiated emulsion polymerizations of common monomers such as styrene and methyl methacrylate based around the oxidant, tert-butyl hydroperoxide. Redox initiators are broadly classed by the solubility of their radical products: Hydrophilic radicals enter by propagating to a critical degree of polymerization to become surface-active whilst more hydrophobic radicals may enter particles directly. When direct entry is applicable (the hydrophobic case), initiation efficiency will always be very high.     

Benzophenone-di-1,3-dioxane as a novel initiator for free radical photopolymerization

Benzophenone-di-1,3-dioxane (BP-DDO), a novel photoinitiator for free radical polymerization, was synthesized and characterized. The photopolymerization kinetics of BP-DDO was studied by real-time infrared spectroscopy (FT-IR). When this photointiator was used to efficiently initiate polymerization of acrylates and methacrylates, there was an optimum cure rate with the increase in BP-DDO concentration. Both the polymerization rate and final conversion increased with the increase in light intensity. The kinetics study of photopolymerization of TMPTA showed that BP-DDO was a more effective photoinitiator than benzophenone and benzophenone/ethyl-4-dimethylaminobenzoate (EDAB).     

Modeling methyl methacrylate free radical polymerization in nanoporous confinement

Nanoconfinement of methyl methacrylate free radical polymerization is known to impact the molecular weight and molecular weight distribution of the polymer produced, with results in the literature generally indicating an increase in molecular weight and a concomitant decrease in polydispersity index. In the present work, the mathematical model described by Verros et al. (2005) for free radical bulk polymerization of methyl methacrylate is extended to account for polymerization in nanopores. The model of Verros et al. (2005) incorporates diffusion effects and is capable of describing the conversion and the number- and weight-average molecular weights of the resulting poly(methyl methacrylate) as a function of polymerization time and process conditions. The model is extended by incorporating the effect of nanoconfinement on diffusivity using the scaling reported in the literature. The calculations indicate that nanoconfinement will lead to higher molecular weights and lower polydispersity, and the gel effect will occur earlier. The results are compared to experimental work and implications discussed.     

The role of radical polymerization in the production of thermoregulating microcapsules or polymers from saturated and unsaturated fatty acids

The microencapsulation of linoleic (LinA), oleic, erucic, and palmitic acids (PAs) from styrene and divinylbenzene were studied by using the suspension‐like polymerization technique. All materials exhibited a spherical shape, with a particle size between 166 and 416 μm. The phase change material (PCM) content decreased with the presence of double bonds in the fatty acid molecule. The thermal energy storage (TES) capacity of the microcapsules (MC) containing saturated PA was the highest (123.30 J g^?1). Whereas, the lowest TES capacity was observed for the LinA. TES capacity values from unsaturated fatty acid materials and the high particle yield indicated that these kinds of acids played two different roles, as PCM and also as monomers, in the radical polymerization processes. At high initiator concentrations, the unsaturated fatty acids were observed to react. This was confirmed by Fourier transform infrared where the peak assigned to the C?C bond disappears in the spectrum of MC. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45970.     

Synthesis and characterization of well-defined comb-like branched polymers

Well-defined comb-like branched polymers having one branch in each repeating unit have been successfully synthesized by the coupling reaction of living polystyrene (PS) and polyisoprene (PI) anions with 1, 1-diphenylethenyl (DPE) groups along PS backbone prepared via atom transfer radical polymerization (ATRP) of 4-vinylbenzyloxy benzophenone (Sc) followed by Wittig reaction. The resulting comb-like branched polymers were characterized by IR, ¹H-NMR, gel permeation chromatography (GPC) and static light scattering (SLS) in detail. The effect of living chains and DPE group molar ratio on grafting efficiency was discussed. The results show the coupling reaction of living chains and DPE groups was highly effective, and the coupling efficiency can be controlled via the feed molar ratios of living chains and DPE groups. Moreover, the effect of molecular weights of backbone (PSe) and PSLi or PILi on grafting efficiency was also discussed. The results show that when excess living polymers were used, the almost quantitative grafting efficiency could be achieved. __________ Translated from Acta Polymerica Sinica (China), 2007, (3): 203–208 [译自: 高分子学报]     

Preparation of a series of photoinitiators and their use in the thermal curing of epoxide and radical polymerization of acrylate

A series of photoinitiators, quaternary ammonium tetraphenylborate salts (QA Salts-BPh₄) with various chromophores, have been synthesized and characterized by elemental analysis (EA), ¹H NMR and IR. The photochemistry and photophysics of QA Salts-BPh₄ have been investigated by UV spectroscopy. The formation of triethylenediamine (TEDA) and phenyl free radical in the photolysis of QA Salts-BPh₄ was ascertained by mass spectrometric method. Their reactivity in the thermal curing of epoxide resin such as EPON827 and radical polymerization of acrylate monomers such as trimethylolpropane triacrylate (TMPTA) was studied. It is found that the relative initiator efficiency of QA Salts-BPh₄ is related to the structure of chromophore.     

Synthesis and characterization of star-like microgels by one-pot free radical polymerization

A one-pot free radical polymerization process was used to prepare methyl acrylate/ethylene glycol dimethacrylate (MA/EGDMA) and methyl methacrylate/ethylene glycol dimethacrylate (MMA/EGDMA) polymers. The role of monomer and crosslinker reactivity ratios in producing different network structures was demonstrated. While both systems produced branched polymers that exhibited low intrinsic viscosities with little variation across a wide range of molecular weights, the star-like microgels formed between a less reactive monomer (MA) with a more reactive crosslinker (EGDMA) gave lower bulk solution viscosities than the more statistical polymers formed between similarly reactive monomers and crosslinkers (MMA and EGDMA). This paper presented a simple and cost-effective synthetic route for the production of polymers with high molecular weight and low viscosity with considerable potential for industrial-scale processing.     

Kinetics of free radical polymerization probed by dielectric relaxation spectroscopy under high conductivity conditions

Polymerization kinetics of tri-ethylene glycol dimethacrylate (TrEGDMA)/2,2-azobis-isobutyronitrile (AIBN) mixtures (0.1% w.t.) at different temperatures was investigated by using dielectric relaxation spectroscopy. The dielectric spectra at the polymerization temperatures studied are dominated by high conductivity leading us to employ the electric modulus representation in order to extract information about the evolution of the system during isothermal reaction. An intense peak appears in the imaginary component of the complex dielectric modulus which is related to conductivity. The variation of the strength of this peak and of its relaxation time with the polymerization time allows us to determine the polymerization degree evolution and the moment in which vitrification is attained, which can be compared with results obtained by temperature modulated DSC in a previous work (Viciosa MT, Hoyo JQ, Dionísio M, Gómez Ribelles JL. Journal of Thermal Analysis and Calorimetry 2007; 90:407-414).The study was completed with a detailed analysis of conductivity carried out in the unreacted system using both dielectric modulus and conductivity representations.     

Magnetic field effects on the free radical solution polymerization of acrylamide

Systematic polymerization experiments quantified magnetic field (MF) influences on the free radical solution polymerization of acrylamide for various polymerization conditions. The type of initiation, the initiator concentration, the monomer concentration, and the viscosity of the aqueous medium were the subject of variation. The initiator efficiency (Φ) increased up to 60% and the initiator exponent of the overall rate expression raised from 0.1 to 0.28 when a weak MF of 0.1 T was applied to photochemical initiation. However, no appropriate effect was observed for thermal initiation. Kinetic analysis proved a reduction of the termination rate coefficient (k_t) up to 40%. Photochemically initiated polymerizations in media of enhanced viscosity revealed the highest increment of the initiator efficiency ratio Φ^MF/Φ and the most pronounced reduction of k_t^MF/k_t. On the contrary, the propagation rate coefficient (k_p) and the monomer exponent were not influenced by MF. Despite considerable increase of the polymerization rate in MF, no reduction of the molar mass was found. Compensation of increased Φ^MF and decreased k_t^MF are suggested as explanation. The singlet-triplet intersystem crossing mechanism for radical pairs served to explain the MF effects.     

Trapping polystyrene radicals using nitrones: Synthesis of polymers with mid-chain alkoxyamine functionality

Polystyrene radicals were formed in the presence of NtBPN under a variety of reaction conditions and reactant ratios, forming polymer dimers of twice the molecular weight of the monobrominated polystyrene (PStBr) precursors. The polystyrene radicals were generated by the activation of the monohalogentated polystyrene precursors, prepared by atom transfer radical polymerization (ATRP). The extent of radicals trapped by the nitrone, and therefore containing mid-chain alkoxyamine functionality, was determined by thermolysis of the polymer dimers, with the C-O bond in this functionality being cleaved and reverting the chains back to the approximate size of the precursors. Polymer dimers could also be formed simply by radical-radical combination of the chain-ends, which is conventional atom transfer radical coupling (ATRC) and thus contains a head-to-head C-C bond, rendering them inert to thermolysis under conditions that cleave the C-O bond. It was found that near quantitative alkoxyamine mid-chain functionality could be achieved by activating the PStBr in the presence of 10 equivalents of nitrone, 5 equivalents of copper bromide, and 2 equivalents of copper metal. Further reducing the amount of copper metal led to incomplete coupling, while increasing the equivalents beyond 2 generated polymer dimers with less than quantitative mid-chain functionality. Monochlorinated polystyrene (PStCl) precursors gave much poorer coupling results compared to reactions with PStBr, which is consistent with the stronger C-Cl bond resisting activation and the formation of the polystyryl radicals.     

Deacetylation behavior of binary blend films of cellulose acetate and various polymers

For binary blend films of cellulose acetate (CA) and various polymers, the elution behavior of the polymers from the CA films in different environments (i.e., soil, water) was examined. For the CA film containing poly(ethylene glycol) (PEG), the PEG eluted to the periphery of the film completely. On the other hand, polyvinylpyrrolidone blended with CA remained in the CA film. A CA film containing acrylic acid was prepared, and this film was heated. The elution of acrylic acid was inhibited by its polymerization. These results suggested that the internal polymers were capable of remaining in the CA film by polymer entanglement. Second, we examined the deacetylation and biodegradation behavior of CA films containing polymers with a phosphoric acid moiety in the side chain, such as poly(2‐hydroxyethyl methacrylate phosphoric acid ester) [poly(HEMA‐P)]. Poly(HEMA‐P) had the ability to deacetylate the CA, and the biodegradation rate of the CA films containing poly(HEMA‐P) increased in comparison with that of the nonadditive CA films. The elution of internal 2‐hydroxyethyl methacrylate phosphoric acid ester was inhibited by the copolymerization with 2‐hydroxyethyl methacrylate or crosslinking. In the case of both 2‐hydroxyethyl methacrylate phenyl phosphoric acid ester and 10‐methacryloyloxydecyl dihydrogen phosphate, the acetone‐soluble polymers were obtained by radical polymerization in a mixture of acetone and water. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1816–1823, 2006