聚酰胺酸薄膜表面热亚胺化动力学研究

采用均苯四甲酸二酐(PMDA)与4,4’-二氨基二苯醚(ODA)为单体,聚合得到表观黏度为1800m Pa·s的聚酰胺酸(PAA);通过衰减全发射红外光谱(ATR-FTIR)对聚酰胺酸凝胶膜表面亚胺化动力学进行了研究,结果表明:亚胺化程度随时间的增加和温度的升高而增大,并出现初期的快速和后期的慢速两个阶段。此外,由于薄膜下表面含有较多的残留溶剂,使其酰亚胺化程度高于上表面。用两步一级动力学模型进行关联,得到了相关的动力学参数。     

长链聚酰亚胺的制备与表征

以长链二胺4,4' 二(4 氨基苯氧基)二苯砜(BAPS)为单体,采用两步法分别与二酐PMDA、ODPA、BPADA合成了3种链长的聚酰亚胺。实验利用GPC监测0 05mol/L聚酰胺酸(PAA)的数均聚合度(Xn)及相对分子质量分布随缩聚时间的变化关系,结果表明该反应为一逐步缩聚反应,缩聚速率随二酐电子亲和性(EA)的递增而增加;与预聚体聚酰胺酸相比,热处理环化得到聚酰亚胺其数均分子质量( Mn)和特性粘度[η]均有所下降,而分布指数(D)增大。此外还利用红外光谱(FTIR)、差分扫描量热法(DSC)、热重分析(TGA)等对聚酰亚胺进行了表征,结果表明聚酰亚胺(PI)的玻璃化温度(tg)和热分解温度(td)随着聚合单元长度的增加而降低。     

热塑性聚酰亚胺微电子薄膜的制备

以微电子业所急需的聚酰亚胺薄膜为背景,采用一种热塑性聚酰亚胺树脂(TPI),实验测定了聚合物溶液特性、干燥工艺及热拉伸性能。在化学环化过程中聚合物溶液粘度随时间逐步增大;15 h后粘度和重均相对分子质量及分布趋于稳定。薄膜溶剂含量在干燥初期急剧下降,干燥速率随干燥温度升高而增大。TPI树脂表现出良好的热塑拉伸性能,当温度高于其玻璃化温度时,最大拉伸比随升温速率降低而增大,而随拉伸载荷增加呈现出先增后降。TPI薄膜经拉伸处理后其力学性能得到明显提高,综合性能与日本钟渊TP E薄膜相当。     

聚酰胺酸薄膜热环化过程热分析

用差热扫描量热仪(DSC)和傅立叶红外光谱仪(FTIR),考察了梯度升温过程中聚酰胺酸PAA[由4,4-二胺基二苯醚(ODA)和3,3,4,4-二苯醚四酸二酐(ODPA)制备]薄膜环化度和玻璃化温度(Tg)随反应温度的变化。结果表明,随着温度的升高,聚合物薄膜的亚胺化程度和Tg不断增大,且各恒温点的薄膜Tg均高于反应温度。另外,由亚胺化程度与Tg的关系曲线可见,在环化程度低时,薄膜Tg增长缓慢;随着亚胺化程度继续增高,薄膜的Tg迅速增大。用热环化过程中分子活动性的变化解释了酰亚胺化反应过程中环化速率的变化。     

聚酰胺酸相对分子质量对亚胺化速率的影响

以邻苯二甲酸酐为封端剂,控制合成了3种相对分子质量的聚酰胺酸,利用改进的电位滴定法对经热处理的聚酰胺酸的亚胺化程度进行了测定。实验结果表明:随着聚合度的增大,聚酰胺酸的特性粘数逐渐增大;聚合度为1的聚酰胺酸的链段运动能力强,反应速率快;聚合度为6的聚酰胺酸反应速率稍大于聚合度为18的聚酰胺酸,但在反应初期较聚合度为18的慢,且它们的剩余聚酰胺酸的质量分数较为相近。     

热处理过程中聚酰亚胺纤维结构与性能的演变

以联苯二酐与2,5-二(4-氨基苯基)嘧啶、4,4-二氨基二苯醚进行共聚,制备高相对分子质量的聚酰胺酸(PAA)纺丝原液,采用湿法纺丝、热环化、热拉伸制备共聚聚酰亚胺(PI)纤维,研究了热处理过程中PI纤维结构与性能的演变过程。结果表明:当热环化温度高于300℃时,PAA基本环化形成PI结构;在热拉伸作用下,PI纤维的凝聚态结构更加规整,且随拉伸倍数的提高,纤维的晶区取向度增加,同时伴随着力学性能的提升;当热拉伸倍数为2.00时,所得PI纤维的力学性能最佳,其拉伸强度及拉伸模量分别可达到21.8 cN/dtex和642.7 cN/dtex。     

聚酰胺酸合成工艺与聚酰亚胺膜制备及表征

聚酰亚胺是一类新型高性能的聚合物材料,是由聚酰胺酸脱水环化而成,因此高分子量的聚酰胺酸是获得高性能PI的前提。探讨了聚酰胺酸合成过程中的影响因素,得出了合成高分子量的聚酰胺酸的最佳工艺条件为:均苯四羧酸二酐与4,4' 二氨基二苯醚摩尔比为1.015～1.020∶1,反应温度20℃,反应时间为3h,聚酰胺酸在N 甲基 2 吡咯烷酮中的特性粘度为0.62dL/g左右。采用热转化法将聚酰胺酸脱水环化制备成均苯型聚酰亚胺膜,通过差示扫描量热法、红外光谱等进行了表征,其玻璃化转变温度为365～385℃,拉伸强度达192.4MPa,表明得到的聚酰亚胺膜具有优良的机械性能。     

碳气化反应的机理及热分析动力学研究

采用热分析（TG、DTG、DSC）技术,进行不同升温速率（10℃/min,,20℃/min,30℃/min）下碳气化反热分析研究。结果表明：在线性升温条件下,碳气化反应分为反应放热的缓慢阶段和吸热的快速阶段。慢速气化阶段呈现放热的原因是CO2在固体碳表面发生吸附作用热大于气化反应热。通过Coats-Redffen法求解动力学参数,得出慢速和快速气化阶段的活化能分别为65.68～33.38kJ·mol-1和159.26～105.58kJ·mol-1,并随升温速率的提高而降低。     

聚酰胺酸纺丝溶液的流变性能研究

由均苯四酸二酐(PMDA)和4,4'-二氨基二苯醚(ODA)在N,N-二甲基乙酰胺(DMAc)中共聚合制得聚酰亚胺前驱体——聚酰胺酸的纺丝溶液,采用哈克流变仪研究了溶液的流变性能。结果表明:聚酰胺酸溶液属于切力变稀的非牛顿流体;溶液的表观黏度随溶液温度的升高而降低,随溶液浓度的升高或聚合物特性黏度的增大而增大。溶液温度的升高、浓度的降低或聚合物特性黏度的减小均使得聚酰胺酸溶液呈现切力变稀行为的临界剪切速率变大,使得溶液的非牛顿指数增大,同时使得溶液的结构黏度指数减小。溶液的黏流活化能随剪切速率的增加或随溶液浓度的增高而下降。     

聚酰胺酸溶液的流变性能研究

采用锥板粘度计研究了聚酰胺酸溶液的流变性能及其粘度的影响因素。结果表明:聚酰胺酸溶液属于非牛顿假塑性流体,还具有负触变性流体的特征。聚酰胺酸溶液的粘度随剪切速率的增加而减小,随浓度的增加而增大,随温度的升高而降低,随存放时间的延长而下降;质量分数为15％的聚酰胺酸溶液的粘流活化能为20．83 kJ／mol。     

Modeling the imidization kinetics of AFR700B polyimide

AFR700B imidization was monitored using Fourier transform infrared spectroscopy (FTIR) by following the increase in the carbon-nitrogen bond of imide groups displayed by the 1360 cm⁻¹ band over several isotherms. Imidization occurred until ∼300°C (572°F). This was confirmed by the presence of water up to 300°C (572°F) in thermogravimetric analysis-mass spectroscopy (TGA-MS) data. First, reaction kinetics were described by first-order kinetics with a fast and slow region of reaction. However, this model did not accurately describe the data in the transition from the fast to the slow reaction region. Imidization is kinetically controlled at short times. However, when the monomers rapidly react to form a high molecular weight polymer gel, imidization is controlled by diffusion. Therefore, a second-order kinetic/diffusion model was used to describe the imidiation kinetics. This resulted in a substantial improvement in the fit of the data. The kinetic/diffusion model can also be used to describe imidization in polyimides other than AFR700B.     

有机蒙脱土对环氧树脂固化反应动力学的影响

2wt％的有机蒙脱土（OMMT）显著影响环氧树脂／六氢苯酐固化体系的非等温固化反应动力学,可促进低温主固化过程,但对高温固化阶段有延迟作用。根据Mfilek最概然模型选择法采用Kissinger方程对两个DSCN化峰分别进行模拟,发现环氧树脂低温主固化峰与高温固化峰均属自催化反应,总反应级数均为15左右。所采用的分峰模拟法可描述整个固化反应过程,对较为复杂的高分子固化反应动力学研究具有指导意义。     

Thermal and kinetic study of radical polymerization I. Melt state bulk polymerization of acrylamide by DSC

Radical‐initiated bulk polymerization of acrylamide in the presence of potassium persulfate in the melt phase has been investigated by differential scanning calorimetry (DSC). The method presented here has been carried out in isothermal condition. This not only saves energy and time but also has some less probable side effects. Side effects such as evaporation and imidization could affect the final yield and properties of the obtained product. Different temperatures have been examined for isothermal polymerization to find out the optimum temperature with complete conversion of acrylamide to its corresponding polymer. During the polymerization process, high‐molecular‐weight polyacrylamide is being produced without any significant loss in total yield. The molecular weight was determined by inherent viscosity measurement. Also, no side reaction such as imidization resulting in partial insolubility or crosslinked product was being observed. It is noteworthy that we believe DSC studies show the existence of living radicals that has not been reported before. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2335–2340, 2003     

Synthesis and processing of PMR-15/LaRC-TPI semi-IPN systems

To improve the fracture toughness of PMR-15 polyimide and to alleviate its high susceptibility to microcracking induced by thermal cycling, a thermoplastic polyimide, LARC-TPI, was incorporated to form a sequential semi-interpenetrating polymer network (semi-2 IPN). The imidization kinetics of LARC-TPI in the semi-IPNs were studied using a thermal gravimetric analyzer. Both the solvent and the glass transition temperature of the semi-IPN were found to have significant effects on the imidization kinetics. The kinetics could be modeled by a two-step reaction: the first step being a second-order reaction followed by a second step, which is a first-order diffusion-controlled reaction. Differential scanning calorimetry was chosen to investigate the curing of PMR-15 and PMR-15/LARC-TPI semi-IPNs. The curing process was well correlated by a first-order reaction kinetics, which suggested that the reverse Diels-Alder reaction of the Norbornene end group was the rate controlling step. The glass transition temperatures of these semi-IPNs were again found to play important an important role in dictating the curing kinetics. A higher proportion of LARC-TPI or a higher glass transition temperature of the semi-IPN prepolymer tended to result in a slower curing reaction. The optimum molding cycle of PMR-15 and PMR-15/LARC-TPI semi-IPNs were then determined from the obtained kinetics. © 1995 John Wiley & Sons, Inc.     

Solvent effect on the curing of polyimide resins

The effect of the solvent 1-methyl-2-pyrrolidinone (NMP) on the curing of polyimide resins synthesized from pyromellitic dianhydride (PMDA) and 4,4′-oxydianiline (ODA) has been investigated. Three polyimide precursors, i.e., the polyamic acid (PAA), with controlled amount of NMP were prepared. The study was aimed first to independently investigate the decomplexation process, which involved the evolution of hydrogen-bonded NMP from PAA, without interference from imidization. This was accomplished by TGA at varying heating rates using different solvent content in PAA. The observed one-stage decomplexation process suggested that the complex formation of NMP and PAA was not the same as the model compound studied by others. An average value of 150 kJ/mol for the activation energy of the decomplexation process was obtained. The study then sought to identify the effect of the decomplexation on the imidization kinetics by employing DSC at several drying temperatures and also varying heating rates. This allowed one to control the extent of plasticization that occurred to facilitate the imidization process. Our DSC data showed that over-drying PAA resulted in prolonged imidization due mainly to the lack of plasticization by decomplexed NMP. The estimated enthalpy of imidization and that of decomplexation were 114 KJ/mol and 53 kJ/mol NMP, respectively. Finally, the imidization kinetics was independently investigated using FTIR, without the interference from decomplexation process. The results indicated that there were four stages during the entire imidization process. Up to a temperature of 150°C, less than 20% of amide groups had reacted to give imide groups and the reaction was slow. Most of the imidization took place between 150 and 180°C with conversion as high as 90%. The imidization process was completed after the temperature was further raised to 250°C. Above 250°C, the reverse reaction became more significant (due probably to configurational and packing preference) and resulted in a lowering of final conversion back to 80%. © 1992 John Wiley & Sons, Inc.     

The forced gas sweeping process for semibatch melt polycondensation of poly(ethylene terephthalate)

The experimental and modeling studies are presented on the melt polycondensation of poly(ethylene terephthalate) by a gas sweeping process. In this process, low molecular weight prepolymer is polymerized to a higher molecular weight polymer in a molten state at ambient pressure as ethylene glycol is removed by nitrogen gas bubbles injected directly to the polymer melt through a metal tube. In the temperature range of 260–280°C, the rate of polymerization by the gas sweeping process is quite comparable to that of conventional high vacuum process. The effects of nitrogen gas flow rate and reaction temperature on polymerization rate and polymer molecular weight were investigated. Polymer molecular weight increases with an increase in gas flow rate up to certain limits. A dynamic mass transfer–reaction model has been developed, and the agreement between experimental data and model simulations was quite satisfactory. The effect of ethylene glycol bubble nucleation on the polymerization has also been investigated. It was observed that the presence of nucleated ethylene glycol bubbles induced by the bulk motion of polymer melt has negligible impact on the polymerization rate and polymer molecular weight. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1388–1400, 2001     

Evolution to similarity solutions for polymerization and depolymerization with microwave radiation

The kinetics of polymerization and depolymerization are critical in understanding the stability and characterization of polymers. The kinetics of simultaneous polymerization and degradation of poly(methyl methacrylate) have been investigated by varying the initiator concentration and monomer concentration under the influence of microwave energy. Microwave radiation initially polymerizes the monomer, then degrades the resulting polymer and the polymer attains an equilibrium molecular weight distribution with a polydispersity of two. To understand more fully the kinetics, the molecular weight distribution (MWD) is represented as a gamma distribution; the random degradation rate coefficient is assumed to vary linearly with molecular weight and the polymerization rate coefficient is assumed to be independent of molecular weight. The change of the MWD with time is studied by continuous distribution kinetics; the solutions obtained depict the change of the average molecular weight, polydispersity and the gamma distribution parameters with time. Experimental data indicate that reaction rates are enhanced by microwave radiation and the MWD approaches a similarity solution within 10 min for all the investigated cases. The model satisfactorily predicts the change of the MWD with time. © 2001 Society of Chemical Industry     

Biodegradable Polymers, 9. Technologically Relevant Aspects of Kinetics and Mechanism of Ring‐Opening Polymerization of L,L‐Dilactide

Poly(L ‐lactide) is manufactured by a cascade process comprising the fermentation of glucose substrate, oligomerization of L ‐lactic acid, cyclization depolymerization to L ,L ‐dilactide and ring‐opening polymerization of the cyclic diester. The process development requires detailed knowledge of kinetics, thermodynamics and reaction mechanism in all process stages. This paper aims to show the influence of micro‐ and macrokinetic factors on the course of the ring‐opening polymerization and the molecular parameters of the formed polyester. Monomer conversion and molecular weight of the polyester are determined by chemically active process parameters, like kind and concentration of catalyst and initiator, respectively, reaction temperature or presence of cocatalysts as well as by the intensity of mixing of the polymerizing melt. The highest polymerization rate is observed in presence of tin octoate, but this catalyst leads to a fast degradation of the formed polymer.     

Numerical analysis of a reactive extrusion process. Part I: Kinetics study on grafting of vinylsilane to polyethylene

For controlling a reactive extrusion process in the subsequent study. the model equations of reaction kinetics and shear viscosity were studied. We focused on a free radical reaction between the molten polyethylene and vinylsilane. The kinetics model was expressed as a reaction rate equation with an apparent rate constant. The shear dependent of reacted polyethylene was formulated by employing the modified Cross model proposed in our early study. In addition, the average molecular weight was considered to correlate the shear viscosity with the reaction kinetics, leading to a series of rheo‐kinetics formulas. The experiments were carried out in a specific batch mixer suitably designed for sampling in arbitrary periods. Their reaction conversions, molecular weight distributions, and shear viscosity were measured, respectively, with an induced coupled plasma (ICP) emission spectrochemical analyzer, a high temperature gel permeation chromatography (GPC), and a capillary rheometer. Determining the parameters in each model, a simulator is set to investigate an engineering extrusion process.