Particle Formation in Emulsion Polymerization: Particle Number at Steady State

Abstract

The number of particles formed in batch emulsion polymerization over wide ranges of emulsifier and initiator concentration has been investigated by computer simulation with a mathematical model developed in a previous paper. The influence of particle coagulation is also considered. The results show that, at low emulsifier concentration, the steady-state particle number N _s is governed by homogeneous nucleation so that N _s increases slowly with increasing emulsifier concentration [S]. In this range, N _s increases with increasing monomer polarity. The steep rise in N _s with emulsifier concentration after [S] exceeds a critical value suggests a transition from homogeneous nucleation domination to micelle nucleation. The slope of the N _s vs [S] relationship increases as the particle coagulation rate constant K_f increases. The power x in the empirical relationship N _s ? [S]^x decreases with increasing polarity of monomer in this region. At very high micelle concentration, insufficient radical generation and the increasing tendency for particle coagulation cause N ₂ to be less dependent on emulsifier concentration. These phenomena have been reviewed by Vanderhoff and confirmed by the experimental data presented by Sutterlin. The particle number increases with increasing initiator concentration [I] when [S] is above the CMC. As [I] continues to increase, however, N _s becomes relatively constant. Experimental data for styrene, butyl acrylate, and methyl acrylate from the literature are compared with the model predictions. Agreement between the theoretical predictions and the experimental data is evident over a wide range of emulsifier and initiator concentrations.     

Interpenetrating polymer networks from the novel bismaleimide and cyanate containing naphthalene: Cure and thermal characteristics

The novel interpenetrating network bismaleimide-triazine polymers were derived from A bismaleimide, viz. 2,7-bis(4-maleimidophenoxy)naphthalene (BMPN), and a dicyanate ester, viz. 2,7-dihydroxynaphthalene dicyanate (DNCY), possessing similar backbone structures. The cure process of the blends including of 0.11 mmol/mol Fe(AcAc)₃ and 2% nonyl phenol is characterized by DSC and in situ FTIR. The DSC curves show two-stages curing process for the mixture systems including of 0.11 mmol/mol Fe(AcAc)₃ and 2% nonyl phenol. In the in situ FTIR spectra of cured resin, the absorption peak of the CCH bending vibrations decreases continuously until the end of cure reaction after that of the OCN group disappears mostly. These illuminate that the structure of IPNs can be formed due to the respective polymerization of two monomers for mixtures. Interlaced patterns are seen obviously in the region by SEM for IPNs BT resins. Thermal stabilities of cured resins are characterized by TGA. The pure polyDNCY, polyBMPN and typical IPNs BT resins show good thermal stability.     

链延长型芳杂环双马来酰亚胺树脂的合成及性能

从分子结构出发,设计合成了含酞/芴Cardo环结构、1,3,4-噁二唑不对称结构共计3类10种新型链延长型双马来酰亚胺(BMI),采用核磁共振(NMR)、红外光谱(IR)、示差扫描量热仪(DSC)、热失重分析仪(TGA)、动态力学分析仪(DMA)等技术表征了BMI树脂的化学结构、固化行为以及固化物的热稳定性和动态力学性能,探讨了分子结构与性能关系.研究结果表明含酞(芴)Cardo结构BMI在普通低沸点有机溶剂中具有良好的溶解性能;含1,3,4-噁二唑结构BMI由于具有不对称分子结构导致两端官能团反应活性存在明显差异;3类BMI的固化物均具有优异耐热性和热稳定性.     

超支化聚硅氧烷改性双马来酰亚胺树脂的研究

将共聚改性与端氨基超支化聚硅氧烷(HBPSi(N))的合成一步完成,建立了一步法制备改性双马来酰亚胺树脂(记为B/D/H(N))的方法.以N,N′-4,4′-二苯甲烷双马来酰亚胺(BMI)、二烯丙基双酚A(DBA)组成的体系(记为B/D)为对比,探讨了HBPSi(N)含量对B/D/H(N)树脂性能的影响.研究结果表明,HBPSi(N)含量对B/D/H(N)树脂的性能有重要影响.少量HBPSi(N)的加入不仅可以显著提高固化物的韧性,而且能有效加快树脂的凝胶时间,同时大幅度提高固化树脂的耐热性、介电性能和耐湿性.这些性能的改善主要缘于HBPSi(N)的加入改变了交联网络的分子结构.B/D/H(N)体系优异的综合性能使之在制备先进树脂基复合材料、胶黏剂方面显示出很大的应用潜力.     

Thermal Properties Improvement of Bismaleimide Resin by a New Phosphorus‐containing Polycyclic Bismaleimide

A new phosphorus‐containing polycyclic bismaleimide resin (BMPI) was prepared by the reaction of bis(3‐maleimidophenyl) methylphosphine oxide (BAMP) with benzene‐1,2,4,5‐tetracarboxylic dianhydride (BTD) and maleic anhydride (MA). BMPI was confirmed by infrared (IR), ¹H‐ and ¹³C‐NMR spectroscopies. Its thermal properties were carried out by a differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) that revealed that the polymers have excellent thermal properties in the high temperature region and a high char yield of up to 53～65%. Furthermore, three conventional bismaleimide resins were prepared from different phosphorus‐free bismaleimides for comparison, e.g. 4,4′‐bismaleimidodiphenylmethane (BDM), 4,4′‐bismaleimidodiphenylether (BDE), 4,4′‐bismaleimidodiphenylsulfone (BDS).     

烯丙基甲酚醚/双马来酰亚胺/二烯丙基双酚A共混体的热稳定性研究

双马来酰亚胺(BMI)/二烯丙基双酚-A(DABP-A)共混体树脂体系,具有高韧性和优异的耐热性能,但粘度大,导致加工工艺复杂,应用困难。而烯丙基甲酚醚(AMPE)含有活性基团,与上述树脂体系能发生交联反应,将其作为活性稀释剂,选择合适比例,能在减小粘度的同时,提高体系的机械强度和耐热性能。实验中将AMPE加入到BMI/DABPA树脂体系,并改变AMPE在树脂体系中的质量分数,测定质量分数与体系粘度、热稳定性等性能之间的关系,确定最佳的比例为AMPE∶BMI∶DABPA=10～20∶36∶29.2,而热失重实验也表明,复合材料热稳定性得到了进一步提高。该结论对于企业改进生产工艺,降低生产成本,提高产品质量,改善生产效益,具有重要意义。     

The application of thiol-ene reaction on preparing UV curable bismaleimide-containing liquid formulations

Thiol-ene reaction method was introduced to photopolymerize a new liquid formulation of commercial bismaleimide, as an alternative to traditional thermal cure method presently used for BMI in the industry. UV curing was shown to be an efficient method which promoted the reaction rate significantly and was able to achieve this at low temperatures (30-50 °C). The liquid formulation is stable and has low viscosity. The cure mechanism and cure kinetics were studied based on the data elucidated from the DPC and FTIR. The cured thin film can achieve very high thermal stability (∼400 °C) and BMI can retard the thermal degradation temperature and rate.     

Structural aspects of high temperature thermosets - Bismaleimide/propargyl terminated resin system-polymerization and degradation studies

Bispropargyl ether of bisphenol-A (BPEBPA), 4,4′-bismaleimido diphenyl ether (BMIE) and a blend consisting 60 mol% of BPEBPA and 40 mol% of BMIE are prepared. The materials are structurally characterized by FTIR. The curing characteristics of the monomers are measured by FTIR and DSC. The results indicated that BPEBPA-BMIE blend has low ΔH_cure (J g⁻¹) for the thermal polymerization and the whole temperature window for the exothermic curing reaction is shifted to lower temperature compared to BPEBPA. Borchardt and Daniels method is used to study the cure kinetics of the materials. The thermal curing of BMIE requires activation energy of 156.0 kJ mol⁻¹ whereas BPEBPA needs slightly higher activation energy (177.2 kJ mol⁻¹). From the TG studies, it can be concluded that the cured BPEBPA exhibits higher thermal stability than the cured BMIE due to the more complex network structure that are formed during thermal polymerization of BPEBPA. Dharwadkar and Kharkhanavala equation is employed to calculate the activation energy needed for the thermal degradation of the thermally cured materials. BPEBPA shows much higher activation energy (65.5 kJ mol⁻¹) for thermal degradation indicating the higher thermal stability over the other two materials (BMIE: 42.5 kJ mol⁻¹ and BPEBPA-BMIE blend: 46.9 kJ mol⁻¹). The isothermal degradation of cured materials is effected in nitrogen atmosphere for constant time interval (10 min). The detailed analysis of the degradation products by GC-MS revealed the formation of phenols and several substituted phenols. This finding hints that the competitive C-C and C-O scissions of the chromene ring units formed via the Claisen rearrangement of the aryl propargyl ether system present in BPEBPA is operative.     

含有给电子生色团的双马来酰亚胺与脂肪二胺的共聚合及其荧光光谱跟踪

我们曾合成了一系列含有给电子生色团的丙烯酰类单体 ,它的给电子本质主要是由氮原子 ,以Ｎ ,Ｎ 二甲基氨基苯基的形式所贡献[1～ 4] ,即 :Ｎ ( 4 Ｎ′,Ｎ′ 二甲氨基苯基 )马来酰亚胺 ,Ｎ ( 4 Ｎ′ ,Ｎ′ 二甲氨基苯基 )丙烯酰胺 ,Ｎ ( 4 Ｎ′ ,Ｎ′ 二甲氨基苯基 )衣康酰胺 ,甲基丙烯酸 (对 4 Ｎ ,Ｎ 二甲氨基 )苄酯 ,这些单体的荧光发射强度总是远远低于相同浓度聚合物的荧光强度 .为了区别所熟知的荧光浓度自猝灭 ,我们称这种现象为结构自猝灭效应 (ＳＳＱＥ) [1～ 5] .具有ＳＳＱＥ的丙烯酰类单体可表示为Ａ( =) Ｄ( ) 型化合物 …     

Viscoelastic phase separation in polyethersulfone modified bismaleimide resin

The polymerization-induced phase separation process of polyethersulfone (PES) modified bismaleimide resin, 4,4′-bismaleimidodiphenylmethane (BDM), was investigated by time resolved light scattering (TRLS) and scanning electronic microscopes (SEM). At the blends with 10 wt% and 12.5 wt% PES, a phase inversion structure was found by SEM. TRLS results displayed clearly the spinodal decomposition (SD) mechanism and the exponential decay procedure of scattering vector q_m, which followed Maxwell-type relaxation equation. The characteristic relaxation time τ for the blends can be described by the Williams-Landel-Ferry equation. It demonstrated experimentally that the phase separation behaviors in these PES modified bismaleimide blends were affected by viscoelastic effect.