Spontaneous polymerization and chain microstructure evolution in high-temperature solution polymerization of n-butyl acrylate

This study concerns understanding of the underlying mechanistic pathways in high temperature solution polymerization of n-butyl acrylate (nBA) in the absence of added thermal initiators. The particular system of interest is the batch polymerization of nBA in xylene at temperatures between 140 and 180 °C with initial monomer content between 20 and 40 wt%. A mechanistic process model is developed to capture the dynamics of the polymerization system. Postulated reaction mechanisms include chain-initiation by monomer (self-initiation), chain-initiation by unknown impurities, chain-propagation by secondary and tertiary radicals, intra-molecular chain-transfer to polymer (back-biting), chain-fragmentation (β-scission), chain-transfer to monomer and solvent, and chain termination by disproportionation and combination. The extent of the reactions is quantified by estimating the reaction rate constants of the initiation and the secondary reactions, based on a set of process measurements. The set of measurements considered in the parameter estimation includes monomer conversion, number- and weight-average molecular weights, and average number of chain-branches per chain (CBC). Effect of temperature on chain microstructures was observed to be most evident when microstructures are expressed in terms of their quantities per chain. The evolution of other microstructural quantities such as average number of terminal double bonds per chain (TDBC) and average number of terminal solvent groups per chain (TSGC) was then also investigated. Microstructural quantities per polymer chain (TDBC, TSGC, CBC) are defined based on combinations of ¹³C, ¹H NMR and chromatographic measurements. This study presents (i) a mechanistic explanation for the competing nature of short-chain-branch and terminal double bond formation (i.e. as temperature increases, number of chain branches per chain decreases and number of terminal double bonds per chain increases), (ii) quantitative insights into dominant modes of chain-initiation and chain-termination reactions, and (iii) mechanistic explanations for the observed spontaneous polymerization. The study also reports estimated Arrhenius parameters for second-order self initiation, tertiary radical propagation, secondary radical backbiting and tertiary radical β-scission reaction rate constants. Validation of the mechanistic process model with the estimated Arrhenius parameters and comparison of estimated parameter values to recently reported estimates are also presented.     

甲基丙烯酸甲酯的原子转移自由基沉淀聚合

以乙醇为溶剂,溴化亚铜(CuBr)为催化剂,溴乙酸乙酯为引发剂,1,10菲罗啉和N,N,N',N',N'-五甲基二乙烯基三胺(PMDETA)分别为配体的催化体系,进行了甲基丙烯酸甲酯的原子转移自由基沉淀聚合,通过GPC和称重量法对聚合物进行表征。结果表明,两种催化体系下MMA的转化速率较快,甲基丙烯酸甲酯的原子转移自由基沉淀聚合得到了较好的实现,得到了分子量分布较窄的聚合物。     

Controlled/living radical polymerization of styrene catalyzed by cobaltocene

Controlled/living radical polymerization of styrene has been achieved by atom transfer radical polymerization (ATRP) catalyzed by cobaltocene (PDI = 1.27-1.41). The effects of the initiators, temperatures and solvents were studied. The end group of PS-Br was characterized by ¹H NMR. Block copolymerization proved that the polymer end is still living and the PMMA-b-PSt block copolymer was synthesized.     

Influence of HMTA ligand in MMA AGET ATRP emulsion polymerization

Interactions of hexamethylenetetramine ligand in atom transfer radical polymerization initiated by activator generated by electron transfer were studied. Polymerization of methyl methacrylate was done using two-step experimental procedure in 2 L emulsion batch reactor at 50, 60, and 80°C. The selection of reactant ratios was quite challenging for a reactor of this size. Replicate runs were conducted for data reproducibility purpose. Gravimetry method and gel permeation chromatography were used to determine monomer conversion, Mn, and PDI of polymer samples. PMMA produced was also characterized by means of dynamic light scattering, Fourier-transform infrared spectroscopy and nuclear Magnetic Resonance spectroscopy. Results showed high monomer conversion up to 93% and Mn ranging 243–274 kg/mol with PDI from 1.45 to 1.60. Besides, combining HMTA with sodium dodecyl sulfate, an anionic surfactant, a well-controlled polymer with a lower Mn of 201 kg/mol and PDI of 1.56 was obtained in 3 hr reaction time.     

A cost-effective process for highly reactive polyisobutylenes via cationic polymerization coinitiated by AlCl3

The initiating system consisting of AlCl₃ with dialkyl ether such as di-n-butyl ether or diisopropyl ether has been successfully developed for providing a cost-effective process of synthesis of highly reactive polyisobutylenes (HRPIBs) with large proportion of exo-olefin end groups up to 93 mol% at temperatures ranging from −20 to +20 °C. The above dialkyl ethers played very important roles in promoting the directly rapid β-proton elimination from -CH₃ of the growing chain ends to create exo-olefin end groups and decreasing or even suppressing the carbenium ion rearrangements to form the double bond isomers. Very importantly, the highly reactive PIBs with 80-92 mol% of exo-olefin end groups, having low M_ns of 1300-2300 g mol⁻¹ and monomodal molecular weight distribution (M_w/M_n = 1.7-2.0) could be achieved at 0-20 °C. These results are comparable to those of commercial HRPIBs produced industrially by the best BF₃-based initiating system at far below 0 °C.     

纳米SiO_2/MMA无皂乳液聚合研究及其应用

以纳米 Si O2 为核 ,以 MMA为壳层单体 ,进行了无皂乳液聚合。研究了单体加入方式、引发剂用量、聚合反应温度等对无皂乳液聚合的影响。核壳产物对 PVC材料的力学性能有明显的提高。     

辐射接枝CR/MMA胶粘剂的研究

探索了一种无须溶媒和化学引发剂 ,利用γ射线来激发反应的CR/MMA接枝反应体系 ,及相关因素对该反应的影响 ,并获得了理想的接枝率。该实验的成功解决了在无苯低毒溶剂条件下化学接技CR/MMA反应法的接枝率偏低的问题 ,同时为解决氯丁橡胶粘合剂溶剂的毒性问题打开了一个新思路     

Syntheses of AB2 3- and AB4 5-miktoarm star copolymers by combination of the anionic ring-opening polymerization of hexamethylcyclotrisiloxane and nitroxide-mediated radical polymerization of styrene

AB₂ 3- and AB₄ 5-miktoarm star copolymers were prepared by combination of the anionic ring-opening polymerization (AROP) of hexamethylcyclotrisiloxane (D₃) and the TEMPO-mediated radical polymerization of styrene (St). Initially, two kinds of dendritic multifunctional initiators were prepared. One has a 4-bromobutoxy group and two TEMPO-based alkoxyamines and the other has a 4-bromobutoxy group and four TEMPO-based alkoxyamines. Treatment of the multifunctional initiators with tert-butyllithium gave the corresponding lithiobutoxy derivatives, and AROP of D₃ by the lithiobutoxy derivatives gave poly(D₃) with M_w/M_n of 1.07-1.12. Nitroxide-mediated radical polymerization of St by the poly(D₃)s at 120 °C gave AB₂ 3- and AB₄ 5-miktoarm star copolymers with M_w/M_n of 1.15-1.28. Their structures were analyzed by means of ¹H NMR and SEC measurements.     

A novel amphiphilic AB2 star copolymer synthesized by the combination of ring-opening metathesis polymerization and atom transfer radical polymerization

A new amphiphilic AB₂ star copolymer was synthesized by the combination of ring-opening metathesis polymerization (ROMP) and atom transfer radical polymerization (ATRP). Two different routes (methods A and B) were employed firstly to prepare the poly(oxanorbornene)-based monotelechelic polymers as the hydrophobic arm bearing dibromo-ended group via ROMP in the presence of two different terminating agents catalyzed by first generation Grubbs catalyst. The values of capping efficiency (CE) of the polymers were determined by NMR, which were 94% and 67% for methods A and B, respectively. Then, the dibromo-ended ROMP polymers were used as the macroinitiators for ATRP of 2-(dimethylamino)ethyl methacrylate (DMAEMA) to produce two hydrophilic arms. The prepared amphiphilic AB₂ star copolymers poly(7-oxanorborn-5-ene-exo,exo-2,3-dicarboxylic acid dimethyl ester)-block-bis[poly(2-(dimethylamino)ethyl methacrylate)] (PONBDM_n-b-(PDMAEMA_m)₂) with a fixed chain length of hydrophobic PONBDM and various hydrophilic PDMAEMA chain lengths can self-assemble spontaneously in water to form polymeric micelles, which were characterized by dynamic light scattering, atom force microscopy, and transmission electron microscopy measurements.     

Reverse ATRP of acrylonitrile with diethyl 2,3-dicyano-2,3-diphenyl succinate/FeCl3/iminodiacetic acid

The reverse atom transfer radical polymerization (RATRP) technique using FeCl₃/iminodiacetic acid (IMA) complex as a catalyst was applied to the living radical polymerization of acrylonitrile (AN). A hexa-substituted ethane thermal initiator, diethyl 2,3-dicyano-2,3-diphenylsuccinate (DCDPS), was firstly used as the initiator in this iron-based RATRP system. The polymerization in N,N-dimethylformamide not only shows the best control of molecular weight and its distribution but also provides rather rapid reaction rate with the ratio of [AN]:[DCDPS]:[FeCl₃]:[IMA] at 500:1:2:4. The rate of polymerization increases with increasing the polymerization temperature and the apparent activation energy was calculated to be 49.9 kJ mol⁻¹. The polymers obtained were end-functionalized by chlorine atom, and they were used as macroinitiators to proceed the chain extension polymerization in the presence of FeCl₂/IMA catalyst system via a conventional ATRP process. The resultant polyacrylonitrile fibers were obtained with the fineness at 1.16 dtex and the tenacity at 6.01cN dtex⁻¹.     

Comparison of thermomechanical properties of statistical, gradient and block copolymers of isobornyl acrylate and n-butyl acrylate with various acrylate homopolymers

Well-defined statistical, gradient and block copolymers consisting of isobornyl acrylate (IBA) and n-butyl acrylate (nBA) were synthesized via atom transfer radical polymerization (ATRP). To investigate structure-property correlation, copolymers were prepared with systematically varied molecular weights and compositions. Thermomechanical properties of synthesized materials were analyzed via differential scanning calorimetry (DSC), dynamic mechanical analyses (DMA) and small-angle X-ray scattering (SAXS). Glass transition temperature (T_g) of the resulting statistical poly(isobornyl acrylate-co-n-butyl acrylate) (P(IBA-co-nBA)) copolymers was tuned by changing the monomer feed. This way, it was possible to generate materials which can mimic thermal behavior of several homopolymers, such as poly(t-butyl acrylate) (PtBA), poly(methyl acrylate) (PMA), poly(ethyl acrylate) (PEA) and poly(n-propyl acrylate) (PPA). Although statistical copolymers had the same thermal properties as their homopolymer equivalents, DMA measurements revealed that they are much softer materials. While statistical copolymers showed a single T_g, block copolymers showed two T_gs and DSC thermogram for the gradient copolymer indicated a single, but very broad, glass transition. The mechanical properties of block and gradient copolymers were compared to the statistical copolymers with the same IBA/nBA composition.     

Additive effects of trialkylaluminum on propene polymerization with (t-BuNSiMe2Flu)TiMe2-based catalysts

Propene polymerization was conducted by [η³:η¹-tert-butyl(dimethylfluorenylsilyl)amido]dimethyltitanium combined with B(C₆F₅)₃ or methylaluminoxane (MAO) as a cocatalyst in the presence or absence of various trialkylaluminums: Me₃Al, Et₃Al, ⁱBu₃Al (triisobutylaluminum) and Oct₃Al (trioctylaluminum). In the case of living polymerization with B(C₆F₅)₃ at −50°C, addition of Oct₃Al and Et₃Al increased the propagation rate. Et₃Al also acted as a chain transfer reagent and selectively gave Al-terminated polymers, while Oct₃Al induced chain transfer reaction only in high concentration. Little polymer was obtained in the presence of Me₃Al or ⁱBu₃Al. When MAO was used as a cocatalyst, polymerization did not proceed at −50°C. The MAO system, however, showed high activity at 40°C and selectively gave low molecular weight polymers terminated with Al–C bonds. Contrary to the low temperature polymerization with B(C₆F₅)₃ at −50°C, the polymer yield was enhanced by the addition of Me₃Al and ⁱBu₃Al, while the molecular weight was reduced by Me₃Al and enlarged by ⁱBu₃Al. On the other hand, Et₃Al and Oct₃Al significantly decreased both the polymer yield and the molecular weight under these conditions. It was found that additive effects of trialkylaluminums were strongly dependent on polymerization temperature as well as on the structure of the alkyl group.     

Synthesis and sol-gel polymerization of [Si8O12](OCH3)8

Sol-gel polymerization of [Si₈O₁₂](OCH₃)₈ in an inert solvent under neutral conditions has been shown to yield very high-surface area silica xerogels [P. C. Cagleet al., Mater. Res. Soc. Symp. Proc. 180, 29 (1990)]. Two recent results relevant to this process are described here. First, a practical synthetic route to [Si₈O₁₂](OCH₃)₈ is described that allows multigram quantities to be conveniently prepared. Second, TEM studies are reported that confirm retention of the [Si₈O₁₂] cubic core structure in high-surface area, [Si₈O₁₂](OCH₃)₈ ^– derived xerogels.This paper is from the Second International Topical Workshop, Advances in Silicon-Based Science.     

Ring opening polymerization initiated by methylaluminoxane/AlMe3 complexes

The ROP of cyclic ethers, carbonates and esters in the presence of commercially available methylaluminoxane/trimethylaluminum system has been studied. MALDI-ToF end groups analysis indicates that in a majority of systems considered, the polymerization process is initiated by insertion of a monomer into the Al-O-Al bond, generating alkoxide species, which are active sites in coordination polymerization. The polymerization of six-membered carbonates proceeds selectively, forming linear polydiols with high yields at moderate temperatures. The polymerization of oxiranes and lactones is, however, accompanied by back-biting reactions leading to cyclic oligomers. The interaction of oxirane with aluminoxane electrophilic sites causes also the formation of cationic species, which initiate the polymerization of THF. The cationic species formed in those systems were trapped by triphenylphosphine and identified by ³¹P NMR spectra.     

Living polymerization of several substituted acetylenes by CpMoCl4-based catalysts

[(o-Trifluoromethyl)phenyl]acetylene polymerized in a living fashion in the presence of CpMoCl₄-cocatalyst-EtOH catalysts (Cp: cyclopentadienyl; cocatalyst: EtMgBr, Et₃Al, n-BuLi). The CpMoCl₄-EtMgBr-EtOH (1:2:2) catalyst was particularly effective, with which the M_w/M_n of the formed polymer and the initiation efficiency, [P^∗]/[Cat], were 1.06 and 7.6%, respectively. Further, [P^∗]/[Cat] increased up to 10-13% at low temperatures (e.g. 0 °C) of catalyst aging and monomer addition. [(o-Trimethylsilyl)phenyl]acetylene also provided polymer having narrow molecular weight distributions with CpMoCl₄-EtMgBr-EtOH (1:2:2). CpMoCl₄ was more stable to air and moisture than MoOCl₄ owing to the steric and electronic effects of the Cp ligand, while the activity of the CpMoCl₄-based catalysts were lower than that of the MoOCl₄-based counterparts.     

Biotechnological fabrication of LaMnO3-carbon catalyst for n-butanol conversion to ketones

An attempt to synthesize a hybrid carbon-based material for catalytic purposes was made using a biotechnological approach. The material consists of a carbon matrix in which LaMnO₃ nanocrystallites are dispersed. The perovskite-type oxide crystallites were synthesized in the carbon matrix by the transformation of lanthanum and manganese salts, which penetrated the living tissues of a plant due to the natural transport of metal ions. Cellulose/lignin rich plant stems were carbonized at 600-800 °C for 1-22 h, yielding a microporous carbon matrix in which nanocrystallites of the complex oxide were uniformly distributed. The plant (Salix viminalis) was selected because of its high tolerance to heavy metal ions. The formation of carbon matrix from organic precursor is a key factor in the synthesis of the complex inorganic nanocrystallites of high dispersion. The hybrid carbon-based materials were tested as catalysts for unconventional conversion of n-butanol to heptanone-4. The catalysts exhibited high selectivity and product yield, despite the extremely low content of LaMnO₃ (0.3% atomic). The paper proves that catalysis-oriented functionalization of carbons may begin at a very early stage through chemical modification.     

Controlled atom transfer radical polymerization of MMA onto the surface of high-density functionalized graphene oxide

We report on the grafting of poly(methyl methacrylate) (PMMA) onto the surface of high-density functionalized graphene oxides (GO) through controlled radical polymerization (CRP). To increase the density of surface grafting, GO was first diazotized (DGO), followed by esterification with 2-bromoisobutyryl bromide, which resulted in an atom transfer radical polymerization (ATRP) initiator-functionalized DGO-Br. The functionalized DGO-Br was characterized by X-ray photoelectron spectroscopy (XPS), Raman, and XRD patterns. PMMA chains were then grafted onto the DGO-Br surface through a ‘grafting from’ technique using ATRP. Gel permeation chromatography (GPC) results revealed that polymerization of methyl methacrylate (MMA) follows CRP. Thermal studies show that the resulting graphene-PMMA nanocomposites have higher thermal stability and glass transition temperatures (T_g) than those of pristine PMMA.     

AlCl3／D72树脂催化合成硬脂酸甲酯的研究

由AlCl3/D72树脂为催化剂,以硬脂酸与甲醇为原料催化合成硬脂酸甲酯。研究了催化剂的用量、酯化反应时间、酸醇物质的量比对酯化反应的影响。催化剂能使用多次催化效果较好。     

Solution homopolymerizations of n-butyl acrylate and styrene mediated using 2,2,5-trimethyl-4-tert-butyl-3-azahexane-3-oxyl (TITNO)

Use of Styryl-TITNO (the styrene alkoxyamine of 2,2,5-trimethyl-4-tert-butyl-3-azahexane-3-oxyl) as mediator for nitroxide-mediated polymerization (NMP) of n-butyl acrylate (BA) and styrene has been investigated at temperatures ≤110 °C. Very good control of molecular weight and molecular weight dispersity with no measurable loss of active chains, and no evidence of tails in the molecular weight distribution as conversion increases, was observed at 90 °C for BA and at 70 °C for styrene. The alkoxyamine dissociation equilibrium constant values determined for polyBA-TITNO (8.5 × 10⁻¹¹ mol L⁻¹ at 90 °C) and polystyrene-TITNO (3.1 × 10⁻⁹ mol L⁻¹ at 70 °C) are consistent with those required for control when using more established nitroxides that require higher temperatures to achieve these values. The lower optimum polymerization temperatures with Styryl-TITNO as mediator provide new opportunities for NMP and are especially significant for styrene since this appears to eliminate completely the complications from thermal initiation.