One‐step synthesis of star‐block copolymers via simultaneous free radical polymerization of styrene and ring opening polymerization of ε‐caprolacton using tetrafunctional iniferter

Star‐block copolymers comprised of poly(styrene) (S) core and four poly(ε‐caprolacton) (ε‐CL) arms were synthesized by the combination of free radical polymerization (FRP) of S and ring opening polymerization (ROP) of ε‐CL in one‐step in the presence of tetrafunctional ineferter. The block copolymers were characterized by ¹H‐NMR and FTIR spectroscopy, gel permeation chromatography (GPC), and fractional precipitation method. ¹H ‐NMR and FTIR spectroscopy and GPC studies of the obtained polymers indicate that star‐block copolymers easily formed as result of combination FRP and ROP in one‐step. The γ values (solvent/precipitant volume ratio) were observed between 1.04–2.72 (mL/mL) from fractional measurements. The results show that when the initial S feed increased, the molecular weights of the star‐block copolymers also increased and the polydispersities of the polymers decreased. M_w/M_n values of the products were measured between 1.4 and 2.86 from GPC. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis of hyperbranched polymers via a facile self-condensing vinyl polymerization system - Glycidyl methacrylate/Cp2TiCl2/Zn

A facile self-condensing vinyl polymerization (SCVP) system, the combination of glycidyl methacrylate, Cp₂TiCl₂ and Zn, has been firstly used to prepare novel hyperbranched polymers, consisting of vinyl polymers as the backbone, and cyclic ester polymers (poly(?-caprolactone) or poly(l-lactide)) as the side chains. The polymerizations are initiated by the epoxide radical ring-opening catalyzed by Cp₂Ti(III)Cl which is generated in situ via the reaction of Cp₂TiCl₂ with Zn. The key to success is that the polymerizations can proceed concurrently via two dissimilar chemistries possessing the opposite active initiating species, including ring-opening polymerization (ROP) and controlled/living radical polymerization (CRP). We have demonstrated that this facile one-step polymerization technique can be applied successfully to prepare highly branched polymers with a multiplicity of end reactive functionalities including Ti alkoxide, hydroxyl and vinyl functional groups.     

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.     

Copolymerization of N-vinyl phthalamide with acrylate and methacrylate monomers and preliminary analysis of the stereochemistry of poly(N-vinyl phthalamide)

Summary N-Vinyl phthalamide was copolymerized with methyl methacrylate, isobutyl methacrylate or butyl acrylate. The copolymerizations were initiated free radically and it was necessary to conduct the polymerizations in solution or else insoluble products would result. In most cases the polymerizations preceded to relatively high conversions in a short time. The conversions necessitated the use of high conversion methods to calculate the reactivity ratios. The N-vinyl phthalamide was found to be the less reactive monomer in all cases. As part of this study, poly(N-vinyl phthalamide) homopolymer was synthesized by free radical initiation. While the ¹H-NMR spectrum yield very little information concerning polymer stereochemistry, the methine carbon resonance in the ¹³C-NMR spectrum displayed a sensitivity to polymer stereochemistry.     

Thermal characterization of poly(vinyl chloride) samples prepared by living radical polymerization: Comparison with poly(vinyl chloride) prepared by free radical polymerization

Poly(vinyl chloride) (PVC) samples were synthesized by a living radical polymerization (LRP) method and compared with commercial PVC prepared by the conventional free radical polymerization (FRP). The differences were assessed, for the first time, in terms of viscosimetry parameters and thermal analysis. The LRP method used to prepare the PVC‐LRP samples is the only one available to obtain this polymer free of structural defects, being of commercial interest in a view of preparing a new generation of PVC‐based polymer with outstanding performance. The polymerization temperature selected (35°C) to prepare the LRP samples is currently used in the industry to prepare PVC‐FRP grades with moderate to high molecular weight. Since the thermal stability is a direct consequence of the polymer structure, this study is of vital importance to understand the potential of new PVC‐LRP. The thermoanalytical measurements demonstrate an enhanced thermal stability of PVC‐LRP when compared with its FRP counterpart. The PVC‐LRP sample with very low molecular weight reveals a higher thermal stability than the most stable PVC‐FRP sample. It is the first report dealing with thermal analysis of PVC prepared by LRP. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

New chain transfer agents for free radical polymerizations

The palmitoyl ester of N-hydroxypyridine-2-thione displayed useful chain transfer properties in free radical polymerizations of methyl methacrylate and styrene. Retardation, however, accompanied the lowering of molecular weight in methyl acrylate and vinyl acetate polymerizations. 4-Methyl-3-palmitoyloxythiazol-2(3H)-thione had good chain transfer activity with methyl methacrylate, styrene and methyl acrylate. Although benzyl thionobenzoate exhibited virtually ‘ideal’ behaviour (chain transfer constant C_x ～1) in styrene and methyl acrylate polymerizations, it was ineffective in lowering molecular weight of poly(methyl methacrylate). Severe retardation was observed with vinyl acetate. Addition-fragmentation pathways are postulated for chain transfer.     

An exhaustive study of chain-length-dependent and diffusion-controlled free radical and atom-transfer radical polymerization of styrene

A finely tuned-up and high-performance Monte Carlo simulation, which takes diffusion-controlled and chain-length-dependent bimolecular termination reactions into account, is developed to thoroughly simulate and compare free radical (FRP) and atom transfer radical polymerization (ATRP) of styrene. It is found out that the termination rate constant falls and eventually plateaus upon the increase of the chain length of radicals. In addition, average termination rate constant greatly decreases during ATRP; nonetheless, it remains almost unchanged and smaller in FRP. Moreover, there is an accumulation of CuBr₂ in the reactor as the ATRP proceeds, while the concentration of CuBr decreases and finally plateaus. Polymer chains are entirely initiated at the beginning of the ATRP, whereas initiation of chains continues throughout the free radical polymerization up to the end of the reaction. Also, the dead polymers are much lower in concentration (only 20%) in ATRP as compared to FRP (about 50%). In addition, a shift (toward higher molecular weight) in the location of the peaks of molecular weight distributions can easily be seen for the ATRP system, whilst the chain length distribution of free-radically generated polymers remains the same throughout the free radical polymerization. The molecular weight distributions narrow as the atom transfer radical polymerization progresses. Finally, the simulation results correspond closely to the experimental data.     

Cyclohexene oxide mid‐chain functional macromonomer of poly(ε‐caprolactone): Synthesis,characterization, and photoinitiated cationic homo‐ and copolymerization

In this study, a novel well‐defined epoxy mid‐chain functional macromonomer of poly(ε‐caprolactone) (PCL) has been synthesized by ring‐opening polymerization (ROP) of ε‐caprolactone (ε‐CL) and epoxidation on workup with 3‐chloroperoxybenzoic acid. The ROP of ε‐CL monomer in bulk at 110°C, by means of a dihydroxy functional initiator namely, 3‐cyclohexene‐1,1‐dimethanol in conjunction with stannous‐2‐ethylhexanoate, (Sn(Oct)₂), yielded a well‐defined PCL with a cyclohexene mid‐chain group. The epoxidation of the cyclohexene (CH) mid‐chain group of PCL was performed using 3‐chloroperoxybenzoic acid. GPC, IR, and ¹H‐NMR analyses revealed that a low‐polydispersity macromonomer of PCL with the desired cyclohexene oxide (CHO) functionality at the mid‐chain was obtained. The photoinduced cationic polymerizations of this macromonomer yielded comb‐shaped and graft copolymers. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

One‐step,one‐pot photoinitiation of free radical and free radical promoted cationic polymerizations

We describe here a novel approach to photoinitiate free radical and cationic polymerizations concurrently, involving the use of benzoin in conjunction with an onium salt such as diphenyl iodonium or N‐alkoxy pyridinium salt. On photolysis, benzoyl radicals formed from the decomposition of benzoin initiate free radical polymerization of methyl methacrylate. The hydroxy benzyl radicals formed concomitantly are readily oxidized to the corresponding cation by the onium salt to initiate cationic polymerization of cyclohexene oxide in the same system. Evidence for two independent polymerizations was obtained from studies involving gel permeation chromatography, extractions, and infrared and proton nuclear magnetic resonance analysis of the polymers. The effect of the type of the onium salt on each polymerization was also investigated. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2389–2395, 2002     

热塑性聚氨酯合成过程中平均相对分子质量的变化

采用转矩流变仪模拟双螺杆挤出反应,分别在无催化剂和铋/锌复合催化剂作用下进行4,4′/2,4′二苯基甲烷二异氰酸酯/聚四氢呋喃醚二醇/1,4丁二醇本体聚合,合成热塑性聚氨酯(TPU)。在聚合过程中取样并采用凝胶渗透色谱法测定TPU的平均相对分子质量,根据重均相对分子质量与反应速率常数和时间的关联式,得到无催化剂作用下TPU重均相对分子质量与反应温度和反应时间的关联式,以及有催化剂作用下TPU重均相对分子质量与反应温度、反应时间及催化剂浓度的关联式。采用所得动力学参数拟合反应过程中TPU重均相对分子质量的变化,拟合结果与实验值吻合良好。     

微反应器在聚合反应中的应用

微反应器因其良好的混合和传热性能近年来开始应用到聚合反应中,并表现出巨大潜力。本文对微反应器在自由基聚合、离子聚合和逐步聚合中的应用进行了系统综述。相比于传统的釜式反应器,微反应器可以更好地调节聚合产物分子量和分子量分布、控制共聚组成和分子结构。在强放热聚合反应中,利用微反应器可以获得窄分子量分布的聚合产物;在扩散控制的聚合反应中,利用微反应器可以大大缩短反应所需时间。微反应器在聚合反应领域中的拓展依赖于对反应机理和微反应器特点的深入理解,相关的基础研究将成为这一领域发展的关键。     

Effect of different modified nanoclays on the kinetics of preparation and properties of polymer-based nanocomposites

Polymer-clay nanocomposites have been prepared by free radical and RAFT polymerizations. To investigate the effects of nanoclay content and its modification system on the kinetics of polymerization, two different commercial grades of clay including Na-MMT and Cloisite 30B have been used and a method has been developed for further modification of Na-MMT with two commercial modifiers containing either a long organic chain or a vinyl group. Also, kinetics of free radical and RAFT polymerizations of both styrene and methyl methacrylate in the presence of these nanoclays was studied. Morphology of the nanocomposites has been studied by XRD and the results have been assessed with TEM observations. Exfoliated structure was obtained for the nanocomposites with 1?wt.% of vinyl-containing clays. Thermogravimetric behavior of the nanocomposites has been studied by TGA. Incorporation of clays has resulted in an evident increase in thermal stability of both polymers.     

Kinetics of reversible addition–fragmentation transfer (RAFT) miniemulsion polymerization of styrene using dibenzyl trithiocarbonate as RAFT reagent and costabilizer

The roles of dibenzyl trithiocarbonate (DBTTC) as both costabilizer and reversible addition–fragmentation transfer (RAFT) reagent in RAFT miniemulsion polymerizations of styrene were investigated. The effectiveness of DBTTC costabilizer in retarding Ostwald ripening involved in the storage stability of miniemulsion is comparable to that of conventional low‐molecular‐weight costabilizers such as cetyl alcohol, but inferior to that of hexadecane. The major variables chosen for studying kinetics of RAFT miniemulsion polymerizations include the type of initiators and levels of DBTTC and surfactant. At a constant level of DBTTC, the rate of polymerization for benzoyl peroxide (BPO)‐initiated polymerization is slower than that for sodium persulfate (SPS)‐initiated polymerization. Furthermore, the polymerization rate decreases with increasing level of DBTTC for polymerizations initiated by BPO (or SPS). It is the monomer droplet nucleation that governs BPO‐initiated polymerizations. In contrast, for SPS‐initiated polymerizations, the probability for homogeneous nucleation to take place is greatly increased, especially for polymerizations with lower levels of DBTTC and higher levels of surfactant. © 2015 Society of Chemical Industry     

Comparison of reaction kinetics and gelation behaviors in atom transfer, reversible addition-fragmentation chain transfer and conventional free radical copolymerization of oligo(ethylene glycol) methyl ether methacrylate and oligo(ethylene glycol) dimethacrylate

The reaction kinetics and gelation behavior in atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer (RAFT), and conventional free radical copolymerizations (FRP) of oligo(ethylene glycol) methyl ether methacrylate (OEGMEMA) and oligo(ethylene glycol) dimethacrylates (OEGDMAs) were investigated and compared with respect to the polymerization rate, gel point, and the evolution of network with vinyl conversion. All the three systems experienced autoacceleration in the reaction rate but occurred at different regions of vinyl conversion, caused by diffusion-controlled radical reactions: termination in the FRP, addition in the RAFT, and deactivation in the ATRP, respectively. In the FRP, significant amount of gel materials was collected by solvent extraction far before the onset of macro-gelation detected by an abrupt increase in complex viscosity. However, in the RAFT and ATRP, no gels were found until the systems approached their macro-gelation points. The observation suggests limited intramolecular crosslinking/cyclization reactions in the ATRP and RAFT systems. This is because the slow growth of primary chains (ATRP and RAFT in hours versus FRP in seconds) allowed adequate chain relaxation and diffusion of reacting species. The gel materials thus synthesized by ATRP and RAFT are expected to be more homogeneous in network structure than that by FRP.     

Kinetic and structural studies of the polymerization of N,N′‐bismaleimide‐4,4′‐diphenylmethane with barbituric acid

Both the isothermal and non‐isothermal polymerizations of N,N′‐bismaleimide‐4,4′‐diphenylmethane (BMI) with barbituric acid (BTA) were investigated by the differential scanning calorimeter. The experimental results showed that the polymerizations of BMI with BTA were governed by the competitive Michael addition reaction and free radical polymerization mechanisms. Furthermore, the contribution of free radical polymerization becomes more important when the mole fraction of BTA decreases. ¹H NMR and ¹³C NMR measurements further support the coexistence of the Michael addition reaction and free radical polymerization mechanisms. A preliminary kinetic model that took into account the competitive Michael addition reaction and free radical polymerization mechanisms was developed. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Effects of solvent basicity on free radical polymerizations of N,N′‐bismaleimide‐4,4′‐diphenylmethane initiated by barbituric acid

The polymerizations of N,N′‐bismaleimide‐4,4′‐diphenylmethane (BMI) initiated by barbituric acid (BTA) carried out in a variety of solvents at 130°C were studied. The nitrogen‐containing cyclic solvents such as N‐methyl‐2‐pyrrolidinone acted as a catalyst to promote the formation of the three‐dimensional crosslinked network structure. By contrast, the polymerization in a cyclic solvent that did not contain nitrogen such as γ‐butyrolactone resulted in nil gel content. The higher the solvent basicity, the larger the amount of insoluble polymer species formed. The molar ratio of BTA to BMI also played an important role in the polymerizations. The resultant polymers, presumably having a hyper‐branched structure, exhibited much narrower molecular weight distributions than those prepared by conventional free radical polymerizations. The BMI polymerizations using BTA as the initiator could not be adequately described by conventional free radical polymerization mechanisms. A polymerization mechanism that took into account the generation of a ketone radical pair between BTA and BMI and the subsequent initiation, propagation and termination reactions was proposed. It was concluded that the nitrogen‐containing cyclic solvents were capable of participating in the ketone radical pair formation process, thereby increasing the extent of polymer crosslinking reactions. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Transport properties of natural gas through polyethylene nanocomposites at high temperature and pressure

Four titanium(IV) alkoxides, namely: Ti(IV) n-propoxide (1), Ti(IV) n-butoxide (2), Ti(IV) tert-butoxide (3), and Ti(IV) 2-ethylhexoxide (4), have been used as initiators in the bulk ring-opening polymerization (ROP) of ??-caprolactone (??-CL). The influence of the alkoxide group on the course of the ROP of ??-CL was investigated by means of ¹H-NMR and differential scanning calorimetry (DSC). The ¹H-NMR spectra confirmed that the ROP reaction of ??-CL proceeded via the widely accepted coordination-insertion mechanism for each of the four initiators. Isoconversional methods have been used to evaluate non-isothermal DSC data via the equations of Friedman, Kissinger-Akahira-Sunose (KAS) and Ozawa-Flynn-Wall (OFW). The kinetic studies showed that the polymerization rate for the four initiators (1-4) was in the order of 1?>?2????4?>?3. The lowest activation energies (40?C47, 42?C44, and 49?C52?kJ/mol for the Friedman, KAS and OFW methods respectively) were found in the polymerizations using Ti(IV) n-propoxide (1), while the highest activation energies (84?C107, 77?C87, and 80?C91?kJ/mol for the Friedman, KAS and OFW methods respectively) were obtained using Ti(IV) tert-butoxide (3). Differences in the rates of polymerization and the activation energies amongst the four initiators appeared to be governed mainly by the different degrees of steric hindrance in the initiator structure. These results represent important findings regarding the steric influence of the alkoxide groups on the kinetics of the ROP of ??-CL initiated by titanium(IV) alkoxides.     

Crosslinking diversity on network morphology,template binding,and template transport of molecularly imprinted polymers prepared via living radical polymerization

The objective of this work is to study the effects of altering the chain building blocks and the reaction on template binding and transport parameters of imprinted polymer gels. The characterization of imprinted poly(diethylaminoethylmethacrylate‐co‐hydroxyethylmethacrylate‐co‐polyethyleneglycol(n)dimethacrylate) polymer gels prepared via free (FRP) or living (LRP) radical polymerization with varying crosslinking monomer lengths (number of ethylene glycol repeat units of 1, ～4.5, ～9) and concentrations (1, 5, 10, 50%) is presented. All imprinted networks prepared via LRP exhibited significantly higher template binding affinities and capacities as well as significantly lower template diffusion coefficients compared to those prepared via FRP. Synthesizing imprinted polymers via LRP results in much smaller and relatively constant dispersities of polymer chains compared to imprinted polymers prepared via FRP. Therefore, LRP has a profound structural effect on the imprinted polymer network leading to increased homogeneity in the mesh structure which enhances the molecular imprinting effect. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3588–3599, 2013     

Isoconversional kinetic analysis of ring-opening polymerization of ε-caprolactone: Steric influence of titanium(IV) alkoxides as initiators

Four titanium(IV) alkoxides, namely: Ti(IV) n-propoxide (1), Ti(IV) n-butoxide (2), Ti(IV) tert-butoxide (3), and Ti(IV) 2-ethylhexoxide (4), have been used as initiators in the bulk ring-opening polymerization (ROP) of ε-caprolactone (ε-CL). The influence of the alkoxide group on the course of the ROP of ε-CL was investigated by means of ¹H-NMR and differential scanning calorimetry (DSC). The ¹H-NMR spectra confirmed that the ROP reaction of ε-CL proceeded via the widely accepted coordination-insertion mechanism for each of the four initiators. Isoconversional methods have been used to evaluate non-isothermal DSC data via the equations of Friedman, Kissinger-Akahira-Sunose (KAS) and Ozawa-Flynn-Wall (OFW). The kinetic studies showed that the polymerization rate for the four initiators (1-4) was in the order of 1 > 2 ≈ 4 > 3. The lowest activation energies (40–47, 42–44, and 49–52 kJ/mol for the Friedman, KAS and OFW methods respectively) were found in the polymerizations using Ti(IV) n-propoxide (1), while the highest activation energies (84–107, 77–87, and 80–91 kJ/mol for the Friedman, KAS and OFW methods respectively) were obtained using Ti(IV) tert-butoxide (3). Differences in the rates of polymerization and the activation energies amongst the four initiators appeared to be governed mainly by the different degrees of steric hindrance in the initiator structure. These results represent important findings regarding the steric influence of the alkoxide groups on the kinetics of the ROP of ε-CL initiated by titanium(IV) alkoxides.     

Propylene Solubility in Toluene and Isododecane

Propylene solubility in toluene and isododecane (2,2,4,6,6‐Pentamethylheptane, CA Registry# 13475‐82‐6) was measured at different temperatures and pressures, similar to the ones normally used to carry out propylene polymerizations through metallocene and Ziegler‐Natta catalysts. Experimental data were obtained with a gravimetric method, where experimental liquid phase compositions are measured at known temperature and pressure conditions. The experimental data were modeled with two different models: the Wilson excess Gibbs free energy model and an empirical model. Both modeling approaches may be recommended for analysis of kinetic data obtained for slurry propylene polymerizations in toluene and isododecane.