Semibatch Atom Transfer Radical Copolymerization of Styrene and Butyl Acrylate

Summary: Batch and semibatch butyl acrylate (BA) polymerizations are carried out using a heterogeneous atom transfer radical polymerization (ATRP) catalyst system, with excellent molecular weight (MW) control maintained at temperatures below 80 °C. A kinetic model, using rate coefficients from literature and catalyst solubility data from this study, provides a good representation of the experimental results, after modifying the model to account for the decrease in rate caused by intramolecular chain transfer. It is also demonstrated experimentally that well-defined random, gradient, and block styrene/BA copolymers can be synthesized by manipulating monomer feed profiles in the ATRP semibatch process.     

In Situ Semibatch Emulsion Polymerization of 2‐Ethyl Hexyl Acrylate/n‐Butyl Acrylate/Methyl Methacrylate/Cellulose Nanocrystal Nanocomposites for Adhesive Applications

Cellulose nanocrystals (CNCs) are safe, “green,” hydrophilic nanoparticles. CNCs are added in situ during a semibatch 2‐ethyl hexyl acrylate (EHA)/n‐butyl acrylate (BA)/methyl methacrylate (MMA) emulsion polymerization. As EHA is a more hydrophobic monomer, manipulation of the monomer feed composition allows for the evaluation of the effect of hydrophobicity on CNC distribution in the nanocomposite and ultimately on adhesive properties. The adhesive properties (loop tack, peel strength, and shear strength) of three different EHA/BA/MMA latex formulations are shown to simultaneously improve with increasing CNC loading. However, the hydrophobicity of the EHA leads to a nonuniform distribution of CNCs in the latex films. Comparison of the in situ polymerized nanocomposites to their blended counterparts is also made.     

High Temperature Semibatch Free Radical Copolymerization of Styrene and Butyl Acrylate

Summary: High temperature semibatch free radical solution copolymerizations of n-butyl acrylate (BA) and styrene (ST) were carried out over a range of copolymer composition. The significant increase in experimental polymer weight-average molecular weight with time, as well as the shift in the entire polymer molecular weight distribution, is explained by assuming fast β-scission of BA midchain radicals with an adjacent styrene unit, followed by subsequent addition of the resultant macromonomer to growing radicals. A mechanistic model including backbiting and β-scission, macronomer incorporation, long-chain branching, and propagation and termination penultimate effects was constructed in Predici; the model provides a good representation of the experimental data using rate coefficients taken from literature.     

在无机SiO2纳米粒子存在下的苯丙乳液共聚合

研究了在无机SiO₂纳米粒子存在下的苯丙乳液共聚合.选择了能使苯丙乳液稳定存在的乳化剂体系,研究了温度和SiO₂的加入对聚合过程转化率的影响,结果表明,SiO₂的加入对聚合过程有阻聚作用,使单体的转化率降低.SEM照片证明SiO₂粒子已经进入苯丙乳液粒子中,而且SiO₂的加入对乳液制成的膜断面形态有一定影响.实验发现在无机SiO₂纳米粒子存在下,苯丙乳液共聚合时有较多残渣出现,对此通过改进乳液聚合进行了有效地改善.同时对制成的复合材料进行了力学性能和热学性能的测定.     

醋酸乙烯酯及丙烯酸丁酯半连续法乳液共聚合

我们曾对丙烯酸丁酯(BA)与醋酸乙烯酯(VAc)一步法乳液共聚合机理进行过研究,并对其胶膜及胶乳性能进行了表征。结果表明一步法共聚乳胶粒具有类似于“核壳结构”的形态,其内核由BA含量高的共聚物组成,外壳基本是PVAc均聚物,对此用不同的方法进行了验证。在此基础上我们以VAc-BA进行了半连续法乳液共聚合,以与一步法相比较,从而探讨反应过程与胶粒结构及材料性能的关系。     

核壳乳液聚合法制备含氟硅丙烯酸酯乳液

以氟醇RfCH2CH2OH和乙烯基硅氧烷VTES为原料合成的氟硅单体,与甲基丙烯酸甲酯、丙烯酸丁酯在复合乳化体系中通过核壳乳液聚合制备了稳定的氟硅共聚乳液。对氟硅单体和氟硅丙烯酸酯共聚物的结构用红外光谱进行了表征,结果表明,得到了目标单体和共聚物。共聚物的TEM形态观察发现,乳胶粒子具有明显的核壳结构,平均粒径在125 nm左右。与丙烯酸酯共聚物相比,氟硅丙烯酸酯共聚物乳胶膜的吸水率降低至8.32%,热分解温度提高了23℃,耐溶剂性与氟硅单体的含量关系不大。     

干酪素存在下丙烯酸丁酯的乳液聚合及聚丙烯酸丁酯/干酪素核壳结构乳腔粒的形成

将丙烯酸丁酯(BA)在干酪素(CA)存在下使用异丁基过氧化氢(TBHP)为引发剂,采用无皂乳液聚合方法,通过接枝聚合制备了直径在150 nm左右具有核壳结构PBA/CA纳米复合微粒.探讨了反应温度、引发剂用量、BA和CA质量比等条件对单体转化率、接枝效率和乳胶粒粒径及其分布的影响,确定了制备此类复合乳胶粒的实验条件并对...     

Pulsed Initiation Polymerization Applied to Acrylate Monomers: Sources of Experimental Failure

Up to date, problems exist with the determination of k_p values with respect to acrylates. The pulsed laser polymerization (PLP) data published so far only give consistent values of k_p for temperatures below 30°C for acrylates. Recently, new insights in acrylate reactions seem to offer a plausible explanation for the failure of the pulsed initiation polymerization (PIP) experiment for acrylates that will be discussed here.     

Controlled Radical Ab Initio Emulsion Polymerization of n‐Butyl Acrylate by Reverse Iodine Transfer Polymerization (RITP): Effect of the Hydrolytic Disproportionation of Iodine

Summary: Controlled radical polymerization of n‐butyl acrylate by reverse iodine transfer polymerization (RITP) was achieved in ab initio emulsion polymerization to yield a stable and uncolored latex (particle diameter d_p = 106 nm). Hydrolysis of iodine, I₂, was responsible for an upward deviation from the targeted molecular weight = 10 400 g · mol⁻¹. The iodide concentration [I⁻] was followed by an iodide selective electrode and the amount of efficient iodine (33%) was successfully correlated with the experimental molecular weight = 31 000 g · mol⁻¹. Finally, a simplified mechanism of RITP in ab initio emulsion polymerization taking into account the iodine hydrolysis was proposed.

Evolution of molecular weight and polydispersity index in RITP of BuA in ab initio emulsion.     

Multiscale Modeling of Branch Length in Butyl Acrylate Solution Polymerization

Branch lengths resulting from both backbiting and intermolecular chain transfer to polymer are examined for the solution polymerization of butyl acrylate, using a rate‐equation model and ordinary differential equations. Backbiting is allowed to generate branches of varying length, according to a cumulative distribution function obtained from a lattice kinetic Monte Carlo simulation. About 8% of the branches produced by backbiting are 10 mers or longer. In contrast to common assumptions about the origins of short‐chain and long‐chain branches, the model indicates that nearly all of the long‐chain branches may be produced by backbiting, rather than intermolecular chain transfer to polymer.

     

甲基丙烯酸丁酯微波无皂乳液聚合

以过硫酸钾作为引发剂进行了甲基丙烯酸丁酯的微波无皂化乳液聚合，讨论了单体浓度和引发剂用量对单体转化率，粒子粒径及其分布的影响，并与常规乳液聚合进行了比较。结果表明，通过微波无皂乳液聚合，乳胶粒子的粒径分布没有明显变化，但是聚合速率大为增加。     

Stability of Emulsion Polymerization of New Fluorinated Acrylate Emulsion and Its Characterization

The new fluorinated acrylate emulsion was synthesized by using the intermediate perfluorous nonene and 2-hydroxyethyl methacrylate as the staring reactants via semi-continuous seeded emulsion polymerization. The structures, glass transition temperature, thermal property and water repellency of the fluorinated acrylate emulsion were characterized with FTIR, differential scanning calorimetry, thermal analysis, and contact angle meter. Influences of many factors such as the theoretical solid content, the temperature of the emulsion polymerization on the stability of the emulsion polymerization, the added amount of emulsifiers and the added amount of the initiator were studied. Results show that the stability of the emulsion polymerization is fairly good when the theoretical solid content is below 30% and the reaction temperature is 80°C and the added amount of emulsifiers and the initiator are 6.0–8.0% and 2.0% respectively. In comparison with the acylate emulsion, the thermal stability of the fluorinated acrylate emulsion is decreased but the water repellency of the fluorinated acrylate emulsion is greatly increased.     

A Density Functional Theory Study of Secondary Reactions in n‐Butyl Acrylate Free Radical Polymerization

In this work, secondary reactions involved in the free radical polymerization of butyl acrylate are investigated using quantum chemistry. First, various backbiting reactions are studied by adopting a simplified molecular model suitable for treating long polymer chains. The predicted reaction kinetics suggest the possibility of a radical migration along the poly(butyl acrylate) (PBA) chain as a consequence of subsequent j:j + 4 hydrogen abstractions, which are characterized by a low activation energy. Moreover, branching propagation and β‐scission reactions originating from mid‐chain radicals are investigated using a complete PBA model composed of five monomer units. The reaction kinetics involving short‐branch radicals are also examined, and a novel backbiting step leading to the formation of short branches is proposed.

     

Copolymerization of Tri-n-butyltin Acrylate and Tri-n-butyltin Methacrylate Monomers with Vinyl Monomers Containing Functional Groups

A new approach to obtaining thermoset organotin polymers, which permits control of crosslinking site distribution and, through it, a better control of properties of organotin antifouling polymers, is reported. Tri-n-butyltin acrylate and tri-n-butyltin methacrylate monomers were prepared and copolymerized, by the solution polymerization method with the use of free-radical initiators, with several vinyl monomers containing either an epoxy or a hydroxyl functional group. The reactivity ratios were determined for six pairs of monomers by using the analytical YBR method to solve the differential form of the copolymer equation. For copolymerization of tri-n-butyltin acrylate (M₁) with glycidyl acrylate (M₂), these reactivity ratios were n = 0.295 ± 0.053, r₂ = 1.409 ± 0.103; with glycidyl methacrylate (M₂) they were r₁ = 0.344 ± 0.201, r₂ = 4.290 ± 0.273; and with N-methylolacrylamide (M₂) they were r₁ = 0.977 ± 0.087, r₂ = 1.258 ± 0.038. Similarly, for the copolymerization of tri-n-butyltin methacrylate (Mi) with glycidyl aery late (M₂) these reactivity ratios were r₁ = 1.356 ± 0.157, r₂ = 0.367 ± 0.086; with glycidyl methacrylate (M₂) they were r₁ = 0.754 ± 0.128, r₂ = 0.794 ± 0.135; and with N-methylolacrylamide (M₂) they were r₁ ?4.230 ± 0.658, r₂ = 0.381 ± 0.074. Even though the magnitude of error in determination of reactivity ratios was small, it was not found possible to assign consistent Q,e values to either of the organotin monomers for all of its copolymerizations. Therefore, Q,e values were obtained by averaging all Q,e values found for the particular monomer, and these were Q = 0.852, e = 0.197 for the tri-n-butyltin methacrylate monomer; and Q = 0.235, e = 0.401 for the tri-n-butyltin acrylate monomer. Since the reactivity ratios indicate the distribution of the units of a particular monomer in the polymer chain, the measured values are discussed in relation to the selection of a suitable copolymer which, when cross-linked with appropriate crosslinking agents through functional groups, would give thermoset organotin coatings with an optimal balance of mechanical and antifouling properties.     

反相乳液聚合法制备丙烯酰胺-丙烯酸铵共聚物

以煤油为连续相,水为分散相,Span-80/Tween-80为复配乳化剂,过硫酸铵为引发剂,丙烯酰胺、丙烯酸和氨水为原料,采用反相乳液聚合法合成了丙烯酰胺-丙烯酸铵共聚物絮凝剂.考察了乳化剂种类及用量、引发剂浓度、单体浓度、EDTA用量、聚合温度等对共聚物特性黏数的影响.确定了最佳实验条件,利用FTIR对样品进行了表征.     

Initiation Efficiency Reduction in Semicontinuous Styrene and Butyl Acrylate Emulsion Copolymerization Reactions

The decrease of initiation efficiency (radical entry efficiency) during seeded emulsion copolymerizations of styrene and butyl acrylate with different residual monomer reduction strategies was evaluated. Experiments were carried out using 50 and 99wt.% of styrene in monomer feed stream. Simulations were performed with a detailed mathematical model of the process that takes into account the diffusion control of initiation, propagation and termination. Results showed that the radical entry into polymer particles is strongly influenced by the aqueous phase kinetics and by the monomer solubility in aqueous phase. Simulation results were compared to experimental results of residual monomer and showed that the residual monomer content can be reduced by a temperature increase at the end of the polymerization. However, an additional feeding of more initiator, even when combined with such an increase of temperature, did not lead to a smaller residual monomer content due, mainly, the kinetic of termination in aqueous phase and radical anchoring. A model that accounts for the reduction of initiator efficiency (free radical entry efficiency) was successfully used to explain the behavior of the experimental observations and was able to correctly predict the qualitative trends of the effectiveness of different residual monomer reduction strategies.     

Hydrophobic Monomers Recognize Microenvironments in Hydrogel Microspheres during Free-Radical-Seeded Emulsion Polymerization

The three-dimensional structure of nanocomposite microgels was precisely determined by cryo-electron micrography. Several nanocomposite microgels that differ with respect to their nanocomposite structure, which were obtained from seeded emulsion polymerization in the presence of microgels, were used as model nanocomposite materials for cryo-electron micrography. The obtained three-dimensional segmentation images of these nanocomposite microgels provide important insights into the interactions between the hydrophobic monomers and the microgels, that is, hydrophobic styrene monomers recognize molecular-scale differences in polarity within the microgels during the emulsion polymerization. This result led to the formation of unprecedented multi-layered nanocomposite microgels, which promise substantial potential in colloidal applications.