Influence of structural parameters on the degradation of ultrahigh‐molecular‐weight vinyl‐type network‐polymer precursors during elution through size exclusion chromatography columns

Network‐polymer precursors obtained in various crosslinking monovinyl/divinyl copolymerization systems, including benzyl methacrylate/1,6‐hexanediol dimethacrylate, benzyl acrylate (BzA)/1,6‐hexanediol diacrylate (HDDA), and vinyl benzoate/divinyl adipate, were subjected to degradation during elution through size exclusion chromatography (SEC) columns, although the copolymerizations were conducted under specified conditions where the factors for the greatly delayed gelation from the Flory–Stockmayer gelation theory were reduced. The most remarkable degradation was observed for the BzA/HDDA copolymerization, which provided prepolymers with the most flexible backbone chains. Thus, the BzA/HDDA precopolymers were chosen, and their degradation behavior during elution through SEC columns was explored in detail as one of the representatives of vinyl‐type network‐polymer precursors. The results were correlated with the structural parameters of network‐polymer precursors, including primary polymer chain length, branched structure, and multiple crosslink or network structure. The degradation became more remarkable with decreased primary polymer chain length, that is, the increment of branching, whereas reduced degradation was observed with the incorporation of loop and network structures into the prepolymer. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 577–582, 2003     

Kinetic model for crosslinking free radical polymerization including diffusion limitations

A kinetic model for crosslinking free radical polymerization is derived to predict the effect of temperature, inhibitor concentration, and initiator concentration on the rate of cure. The model is based on evidence from the literature that termination and comonomer reactivity differences can be ignored in many crosslinking free radical systems. Because of the complexity of the crosslinking chemistry, empirical relationships are used for decreasing initiator efficiency and radical mobility during cure. A sequential parameter fitting procedure is devised for isothermal curing data, and predictions are affirmed with both divinyl benzene and vinyl ester resin at several temperatures and concentrations of initiator and inhibitor. The key advantages of this kinetic model over previous models are its accuracy at high conversions and its ability to predict the effect of inhibitor and initiator concentrations on the rate of cure. This model is readily applicable to process modeling in the polymer composites manufacturing industry, which largely uses unsaturated polyester and vinyl ester resin matrices.     

A general kinetic method to predict sequence length distributions for non-linear irreversible multicomponent polymerizations

A method to predict the sequence length distribution (SLD) for homogeneous non-linear irreversible multicomponent polymerizations is described. With more than two monomers, it also predicts chain length distributions of the sub-domains containing a prescribed sub-set of the repeating units, but in all possible orderings. Its goal is the analysis of polymerization systems involving complex kinetic schemes in an automated way. The radical terpolymerization of two vinyl monomers with a divinyl monomer and a radical copolymerization including branching by transfer to polymer and by propagation on terminal double bonds are considered as case studies showing the interest of our approach. Finally, the concept of gelation of sequences is presented and discussed in comparison with the related and better known gelation of the population of polymer molecules.     

Crosslinking kinetics in emulsion polymerization

Network formation in free-radical polymerization is investigated both from experimental and theoretical points of view. In a bulk free-radical crosslinking copolymerization, the radical concentration increases significantly due to a decrease in the bimolecular termination rate. Some fraction of radicals is trapped during the course of network formation, and the reactivity of the radicals in liquid state is completely different from that in solid state (trapped radicals) in terms of both propagation and termination. In emulsion crosslinking polymerization, the crosslinking density tends to be fairly high even from the start of the polymerization. The crosslinking density development is substantially different from that in bulk and solution polymerizations, in which the crosslinking density increases with time, at least in the earlier stages of polymerization. Due to the elastic contribution of free energy change, the monomer concentration in the polymer particles is lower than for linear emulsion polymerizations as long as the monomer droplets exist, resulting in an enhanced tendency toward crosslinking reactions.     

拟三元自由基交联共聚合统计动力学模型与模拟

以甲基丙烯酸甲酯 /二甲基丙烯酸乙二醇酯自由基交联共聚合为研究对象 ,考虑到单烯与双烯自由基交联共聚合过程第 3种双键———悬挂双键的影响 ,在低双烯单体用量下简化为拟三元自由基共聚合 ,引入具有Arrhenius性质的交联影响因子 ,建立拟三元自由基交联共聚合动力学模型 .经自由基本体和溶液共聚试验验证了拟三元自由基交联共聚合动力学模型 ,通过数值仿真讨论了平均交联密度随转化率的变化关系 ,比较了本体共聚和溶液共聚条件下平均交联密度的变化规律     

丙烯酸酯改性水性聚氨酯皮革涂饰剂研究进展

综述了近年来丙烯酸酯改性水性聚氨酯(PUA)皮革涂饰剂的改性方法,包括共混交联法、溶液聚合法、种子乳液聚合法和互穿网络聚合法。讨论了PUA复合乳液及漆膜结构与性能的关系,提出了水性皮革涂饰剂的发展趋势。     

聚氨酯-丙烯酸酯复合乳液的研究进展

文中介绍了聚氨酯-丙烯酸酯复合乳液的制备方法,其中包括物理共混,交联共混,互穿网络乳液聚合,核一壳乳液聚合及乳液共聚法。同时从交联改性,有机硅改性,氟改性,纳米改性,环氧树脂改性等5个方面对改性聚氨酯-丙烯酸酯复合乳液的研究进展进行了综述。     

Novel flexible network polymers consisting of oligomeric primary polymer chains originated in the mechanistic discussion of multiallyl crosslinking polymerization

Summary It is well known that allyl monomers polymerize only with difficulty and yield polymers having low molecular weights, i.e., oligomers. Inevitably, free-radical multiallyl crosslinking polymerization provides network polymers consisting of oligomeric primary polymer chains, i.e., having abundant dangling chains. This led to the development of novel flexible network polymers such as amphiphilic network polymers (I) consisting of short primary polymer chains and long crosslink units with opposite polarities, simultaneous interpenetrating networks (II) consisting of both polyurethane (PU) and polymethacrylate (PM) networks with oligomeric primary polymer chains, and network polymers (III) consisting of centipede-type primary polymer chains. Thus, the solution copolymerizations of benzyl methacrylate with tricosaethylene glycol dimethacrylate in the presence of lauryl mercaptan yielded I consisting of nonpolar, short primary polymer chains and polar, long crosslink units. The opposite type of I was prepared by the copolymerization of 2-hydroxyethyl methacrylate, a polar monomer having a hydroxyl group, with heneicosapropylene glycol dimethacrylate, a nonpolar monomer having a poly(oxypropylene) unit. The equimolar polyaddition crosslinking reaction of poly(methyl methacrylate-co-2-methacryloyloxyethyl isocyanate) with tri(oxytetramethylene) glycol, leading to PU networks, and the free-radical crosslinking copolymerization of methyl methacrylate with tri(oxytetramethylene) dimethacrylate in the presence of CBr₄, leading to PM networks, were progressed simultaneously, providing II formed via the topological crosslink between PU and PM network structures. The post-copolymerizations of oligomeric allyl methacrylate/alkyl methacrylate precopolymers, having different amounts of pendant allyl groups and different molecular weights, with allyl benzoate/vinyl benzoate monomer mixtures were conducted to give III.     

A molecular weight model in vinyl chloride–divinyl monomer suspension copolymerization before the gel point

In this paper, a molecular weight model in the vinyl chloride (VC)–divinyl monomer suspension copolymerization was derived from the mechanism of VC two-phase polymerization, with pseudokinetic constant method and the theory of the moments of chain length distribution. Furthermore, the behavior of average polymerization degree was simulated with the model at varied experimental parameters. The simulation phenomena were discussed in detail. It is concluded that our model can be useful to predict the behavior of DP_w and to look inside the crosslinking mechanism in the VC–divinyl monomer copolymerization. © 1995 John Wiley & Sons, Inc.     

链式交联聚合的凝胶/溶胶分配理论模型

针对间歇法链式交联聚合体系中交联的不均匀性,推导出适于该体系的凝胶含量模型,并应用于氯乙烯-邻苯二甲酸二烯丙基酯悬浮共聚体系,由实验数据回归求得模型参数K。结果表明,模型可很好地描述聚合条件与聚合产物凝胶分率的关系。     

Seeded emulsion polymerization of vinyl chloride. A new approach to mechanism and kinetics

Some peculiarities concerning the mechanism and the kinetic behaviour of the vinyl chloride emulsion polymerization are described. Seeded emulsion polymerizations in the presence of an adequate mixture of anionic and non-ionic surfactants were carried out in order to avoid the micellar initiation. New kinetic parameters were determined from the experimental data as follows: (i) MSA, the minimum surface area of polymer seed particles necessary to capture all ion-oligoradicals generated in aqueous phase at a given initiator concentration; (ii) MCCI, the maximum critical concentration of initiator per unit surface of polymer particle under which the formation of new polymer particles is avoided; (iii) PVR₁, the polymer volume per active growing radical, necessary to be within the particle for 1 s. It was found that the average number of propagating radicals per particle, n, depends on the size of the polymer particle, as a resultant of entry and exit and then of the initiation and termination reactions. The practical consequences of the accurate control of the polymer particles growing during seeded emulsion polymerization of vinyl chloride were emphasized.     

Dimension of heterogeneous network architecture formed in emulsion cross-linking copolymerization

The mean-square radius of gyration Rg² and the graph diameter D of highly heterogeneous network polymers formed in emulsion vinyl/divinyl copolymerization are investigated to find a linear relationship, Rg² = a D. The proportionality coefficient, a, is dominated by the cycle (circuit) rank, k_c, or the number of intramolecular cross-links. The magnitude of a is slightly larger than that for the random cross-linked network polymers, but the functional form of a (k_c) is simply proportional to that for the random networks proposed earlier. This relationship makes it possible to determine Rg² based on D and k_c, enabling quick estimation of Rg² for large network polymers. It is found that the contraction factor g of the present heterogeneous network polymer is larger than that for the homogeneous networks formed through random cross-linking of polymer chains. The ratio of these two contraction factors is kept constant, irrespective of the magnitude of k_c.     

Photopolymerization kinetics,photorheology and photoplasticity of thiol–ene–allylic sulfide networks

BACKGROUND: Thiol–ene networks are of interest due to their facile photopolymerization and their open network structure. In this work, an allylic disulphide divinyl ether monomer is reacted with tetrathiol and divinyl ether monomers, which allows the network structure to permanently change in shape if stressed while under irradiation. We also study the photo‐differential scanning calorimetry (DSC) kinetics and photorheology during cure and the dynamic mechanical properties after cure. RESULTS: The heat of polymerization is similar for the thiol–ene systems and suggests ca 80% conversion of the vinyl ether groups. An increase in the initiator concentration increases the photocure rate as expected. The activation energy for photopolymerization is 7.6 kJ mol^?1. DSC and rheometry studies show that the polymerization kinetics is slowed by the addition of the allylic disulfide divinyl possibly due to the formation of less reactive radicals. However, as shown by dynamic mechanical thermal analysis, the network structure is not changed very much by addition of this monomer. If radicals are generated by irradiation of a photoinitiator in the network while a stress is being applied, the polymer will permanently deform depending on the fraction of 2‐methylenepropane‐1,3‐di(thioethyl vinyl ether) in the network, due to a bond interchange reaction. CONCLUSION: The rate of thiol–ene reaction is slowed by the addition of the allylic disulfide divinyl ether. Photoplasticity is observed in the networks containing the allylic disulfide groups. Further work is required to optimize the extent of photoplasticity in these systems. Copyright © 2007 Society of Chemical Industry     

Understanding multivinyl monomer photopolymerization kinetics through modeling and GPC investigation of degradable networks

Multivinyl monomers that react to form highly crosslinked, biodegradable networks are being developed as scaffolds for tissue engineering and vehicles for drug delivery; however, this work demonstrates their usefulness in characterizing better the complexities of the kinetics and structural evolution during crosslinking photopolymerization. The molecular weight distributions (MWDs) of the degradation products of networks formed through the free radical photopolymerization of multivinyl monomers validate a novel kinetic model to test hypotheses as to the important kinetic mechanisms during crosslinking. The kinetic model, in conjunction with the experimental results for the degradable network, provides insight into the fundamental termination mechanisms (i.e. chain length dependent termination (CLDT), chain transfer to either a unimolecular species or polymer, and the accumulation of persistent radicals) that control the MWD of the backbone kinetic chains throughout the polymerization. Specifically, the importance of CLDT during autoacceleration and the impact of light intensity on the MWD of the backbone kinetic chains are presented.     

丙烯酸酯改性水性聚氨酯的研究进展

介绍了聚氨酯/丙烯酸酯(PUA)复合乳液的制备方法,包括物理共混、交联共混、复合乳液共聚、核/壳结构乳液共聚法及互穿聚合物网络(IPN)法等,同时从无机纳米粒子改性、氟改性、有机硅改性和环氧树脂(EP)改性等方面对改性PUA复合乳液的研究进展进行了概述。     

水性聚氨酯／聚（丙烯酸丁酯-丙烯腈）互穿聚合物网络的研究

以甲苯二异氰酸酯（TDI-80）、聚醚二元醇（N220）、丙烯酸丁酯（BA）和丙烯腈（AN）为主要原料,采用无皂种子乳液聚合法制备了具有核壳结构的水性聚氨酯／聚（丙烯酸丁酯-丙烯腈）乳液互穿聚合物网络（LIPN）。通过红外光谱仪、热重分析仪、透射电镜、粒度仪等分析手段研究了产物的结构与性能。结果表明,与未改性的水性聚氨酯分散液相比,改性后的聚氨酯分散液的粒径均有所增大,乳液的黏度变化不大。胶膜的硬度和耐水性以及热稳定性显著提高,拉伸强度先增大后减小,断裂伸长率下降。HDDA的引入,形成了具有化学交联的核一壳互穿网络结构的聚合物,表现出明显的互穿协同效应,使WPU与乙烯基聚合物分子链具有较高的相客性。     

Experimental study of emulsion polymerization with crosslinking

Herein is reported the results of an extensive experimental investigation of the kinetics of emulsion polymerization as affected by crosslinking in the polymer particles. The model monomer system, methyl methacrylate (MMA) and ethylene glycol dimethacrylate (EGDMA), was chosen for this study due to its earlier comprehensive investigation in bulk polymerization. Standard recipes with sodium dodecylsulfate (SDS) as anionic emulsifier and potassium persulfate (KPS) as initiator were used for the batch emulsion polymerizations. Results, which clearly show the effect of crosslinking on the kinetics, are discussed in detail. These include swellability of polymer particles by monomer; polymer particle nucleation rates, below and above the critical micelle concentration (CMC); average number of radicals per particle; and gel-sol levels. It was found advantageous to use electron spin resonance (ESR) to follow radical concentrations during crosslinking in polymer particles. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 935–957, 1997     

聚合物微凝胶的制备及其在不饱和聚酯改性中的应用

以苯乙烯和丙烯酸丁酯为单体，二乙烯基苯（ＤＶＢ）为交联剂利用乳液聚合法制备出聚合物微凝胶并研究了ＤＶＢ及乳化剂用量对聚合反应的影响，将所得到的微凝胶用于增进不饱和聚酯（ＵＰ）的流变性。试验证明聚合物微凝胶对提高ＵＰ的触变指数具有良好的效果。     

Molecular mass control in methacrylic copolymer latexes containing glycidyl methacrylate

Results are presented on the preparation and characterization of batch emulsion copolymers of butyl methacrylate and glycidyl methacrylate (GMA). The two main problems occurring during an emulsion copolymerization with GMA are partial hydrolysis of the epoxy groups and internal crosslinking of the latex particles formed. The influence of chain transfer agents (CTA) on the degree of crosslinking was investigated. Furthermore, the effect of reaction temperature and the addition of methacrylic acid on the sol/gel content of the polymer formed and on the rate of epoxy hydrolysis were investigated. It was found that lowering the reaction temperature did not increase the sol content; however, it significantly decreased the extent of hydrolysis. The addition of a CTA (especially CBr₄) increased the sol content of the polymer, and good control over the molecular mass was achieved. The addition of methacrylic acid showed that this monomer can be used without any complications with respect to the control of the sol content of the polymer formed. © 1996 John Wiley & Sons, Inc.     

The effect of kinetic chain length on the mechanical relaxation of crosslinked photopolymers

This work investigates the effect of kinetic chain length on the network structure of multi-functional (meth)acrylates. Two chain transfer agents, dodecanethiol and m-toluenethiol, were added to a series of crosslinking free radical polymerizations to decrease the kinetic chain length. Using near-IR spectroscopy and dynamic mechanical analysis, the effect of chain transfer on the polymerization rate and network properties (i.e. T_g and modulus) was investigated. The results suggest that macroradical chain length, which has been shown to play a role in the termination kinetics of crosslinking systems, may also impact the network properties of the formed polymer. With the addition of only 0.5-1 wt% chain transfer agent, differences in the polymerization rate and mechanical properties were observed in the crosslinking methacrylate systems. The polymerization rate was significantly suppressed and the T_g of the cured network was found to decrease by up to 10 °C, depending on the monomer formulation. The largest differences in the mechanical properties occurred in the systems with the lowest crosslinking density and diminished as the crosslink density of the cured polymer increased. Furthermore, the differences were less dramatic in the multi-EGDMA systems, that have some inherent ability to chain transfer, and were not discernable in the transfer dominated diacrylate systems.