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。     

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。     

电位滴定法测定聚酰胺酸固相热环化动力学

针对二步法合成聚酰亚胺的固相热环化过程,采用改进的自动电位滴定法和GPC测定了反应的剩余聚酰胺酸含量及相对分子质量随反应时间及反应温度的变化。结果表明:聚合物平均相对分子质量随热处理时间和温度的增加而逐步增大,相对分子质量分布指数则呈现先增后降的变化趋势。聚合物剩余聚酰胺酸的质量分数随热处理时间增加而逐渐降低,并出现初期的快速和后期的慢速2个阶段。提高热处理温度,则环化速率明显增大,环化程度亦增大。采用两步一级动力学模型关联并得到了2个阶段的热环化动力学参数,快速和慢速阶段的活化能较为接近,而指前因子和过渡熵相差较大。     

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。     

利用反应结晶制备大颗粒硫酸钾的研究

为解决国产硫酸钾粒度小的问题,采用软钾镁矾和氯化钾为原料,分别以不同的加料速率、搅拌速率、反应温度、加入晶种的量进行了反应结晶实验。研究结果表明,随加料速率的增大,硫酸钾晶体的成核速率和生长速率增大,产品平均粒径减小;随搅拌速率的增大,成核速率增大,生长速率减小,产品平均粒径减小;晶体成核速率和生长速率受温度影响较小;随着加入晶种量的增大,晶体成核速率先减小后增大,生长速率先增大后减小,并首次建立了硫酸钾反应结晶动力学模型。在优化条件下,实验产品的平均粒径最大可达394.3μm。     

N-烷基化聚羟基羧酰胺类超分散剂的合成

以蓖麻油酸、12-羟基硬脂酸等为原料,在催化剂和保护气体存在下,合成聚羟基羧酸酯,再用N,N-二甲基丙胺合成了标题化合物。反应温度对产品的聚合度影响小,随反应时间的延长,聚合度增加,适合的聚合度为n=6,适合的反应时间为16-18小时。实验结果表明SnCI2·H2O在摩尔比为0.0006时,就显示了催化活性。     

纤维素在离子液体中的溶解特性研究

测定了纤维素在不同结构的离子液体——1-烯丙基-3-甲基咪唑氯化物([AMIM]Cl)和1-丁基-3-甲基咪唑氯化物([BMIM]Cl)中的溶解度和溶解速率。结果发现:相同条件下,纤维素在[AMIM]Cl中具有较大的溶解度和较快的溶解速率;随着纤维素聚合度的增大,相同条件下,纤维素在离子液体中的溶解度降低。进一步通过WXRD、FT-IR、13C NMR和黏度法分析了溶解前后纤维素的化学结构、结晶结构和聚合度,结果表明:纤维素在离子液体中的溶解属于直接溶解,纤维素经离子液体溶解和再生后,晶型由纤维素I转变为纤维素II;溶解时间和温度对再生纤维素的聚合度有较大的影响,随着溶解时间的延长和溶解温度的提高,再生纤维素聚合度降低。     

工艺条件对合成聚酰胺酸的影响

预制聚酰胺酸是合成聚酰亚胺的关键。本文通过对聚酰亚胺前躯体聚酰胺酸特性黏数的测定,分析讨论加料顺序、单体配比、反应时间、反应温度四个因素对聚酰胺酸特性黏数的影响,确定聚酰胺酸的优化工艺条件,为制备耐高温聚酰亚胺纤维提供了基础。     

聚乙二醇与二氯亚砜反应合成氯代聚乙二醇过程研究

以吡啶为缚酸剂,二氯亚砜为氯化试剂对不同聚合度的聚乙二醇(PEG)进行端羟基取代,研究了反应过程中缚酸剂用量、反应温度、时间和聚乙二醇聚合度等条件对PEG转化率和氯代聚乙二醇(PEGCl)收率的影响;采用羟值测定、傅里叶变换红外光谱、核磁共振氢谱等技术对PEGCl的结构进行了分析。结果表明,在二氯亚砜、吡啶和聚乙二醇摩尔比为6:6:1时,PEG基本全部转化;在反应温度35~45℃,PEGCl的收率较高;随着反应时间延长,PEG转化率逐渐提高,但若反应时间过长则生成较多副产物,使PEGCl收率降低;当聚乙二醇聚合度较高时,氯化反应速率更快。经分析红外光谱和核磁共振氢谱表征可知,所得产物纯度较高。     

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。     

Effect of thermal history during drying and curing process on the chain orientation of rod-shaped polyimide

Chain orientation in polyimide (PI) film is influenced by the thermal history during drying and curing process. The amount of residual solvent and the degree of imidization, among other factors, play a major role in determining the chain orientation during the process. In the present study, poly(amic acid), the precursor of PI, coated on the glass substrate was imidized to PI through different drying and curing protocols. On the way of complete imidization, the residual solvent concentration and the degree of imidization were characterized using confocal Raman spectroscopy. The poly(amic acid) began to imidize quickly while retaining more solvent in the film as the initial drying temperature increased. The degree of in-plane chain orientation in fully imidized PI film made by different process protocols was compared using polarized Raman spectroscopy. The fully imidized PI showed the lowest degree of in-plane chain orientation when it was processed by the protocol with the highest drying temperature. The difference in the degree of in-plane chain orientation among different PI films significantly influenced the in-plane thermal expansion coefficient, while no significant change in crystallinity or glass transition temperature was observed.     

Effects of various factors on the formation of high molecular weight polyamic acid

The reaction of pyromellitic dianhydride (PMDA) and aromatic diamine in an aprotic solvent such as dimethylacetamide (DMAc) gives a solution of poly(amic acid). The effects of certain variables on the polymerization and some additives on the stability and imidization of the poly(amic acid)s were studied. It was found that the addition of PMDA portionwise to the solution of diamine always keeps the excess diamine in solution and enables one to obtain the highest molecular weight of poly(amic acid). When the addition process was reversed, either by the change or dehydration of solvent, a high molecular weight was not attained. The inevitable water in the solvent or the reaction medium is the major factor, and the more the water content in the solvent or the reaction medium, the larger is the probability of destruction of PMDA during the reaction and hence low molecular weight is obtained. If very pure monomers were used in the polymerization, the 1:1 of molar ratio is the optimum value. Excess diamine or dianhydride results in the exchange reaction with poly(amic acid) and causes a rapid degradation of polymer chain. This exchange reaction was proved by NMR measurements. The presence of electrophilic agents or the nucleophilic agents containing active protons in the poly(amic acid) solution promotes the decomposition of polymer and causes the brittleness of polyimide film in the curing process. Using acetic anhydride (A) to convert the poly(amic acid) to polyimide, pyridine (P) can protect the polymer chain from the nucleophilic attack by the anhydride. The mixture with proper ratio of A/P (1/1–15/1) can be used as good dehydrating agents. Meanwhile, according to the results to the results of experiments, we suggested the probable reaction mechanisms about how the water, amine, and anhydride destroy the polyamic acid chains.     

Pervaporation separation of aqueous mixtures using crosslinked poly(vinyl alcohol), I. Characterization of the reaction between PVA and amic acid

For the purposes of new membrane material development for pervaporation separation based on crosslinked polyvinyl alcohol (PVA), IR spectroscopy and DSC were used to characterize the crosslinking reaction and the imidization of the (PVA)-amic acid system. The IR spectra and the thermal analysis were performed on specimens that had been reacted for several different times at 150°C. The crosslinking reaction between the hydroxy groups of PVA and the carboxylic groups of amic acid was faster than the imidization of the amic acid. The best reaction times were about 30 min for the crosslinking reaction and 90 min for the imidization. The effects of the reaction time and the amic acid content on the thermal and mechanical properties have also been investigated.     

Kinetics of imidization of poly(amic acid) in miscible and immiscible polymer blends

Blends of commercial poly(amic acid), LARC-PAA polymer were prepared with thermoplastic polyimide P84. The blends were shown to be miscible over a certain composition range. Chemical imidization of LARC-PAA in the blends leads to phase separation. Thermal imidization of LARC PAA in the blends was carried out in the solid state. Miscible compositions of the blend remained miscible after imidization and showed a single glass transition for each blend. Immiscible compositions after imidization remained immiscible and showed two glass transition temperatures in the DSC scans. The kinetics of thermal imidization of PAA to polyimide (PI) in the solid state were studied using FTIR. In the immiscible blend the kinetics remained unaffected while in the miscible state the rate of imidization became faster than that of the pure PAA.     

Modeling of imidization kinetics

We investigated the applicability of a new kinetic model to the polyamic acid imidization process, which has been generally represented as involving two steps, fast and slow, with specific rate constants due to the existence of kinetically nonequivalent amic acid states. A time dependent nonlinear function of the form sech(-at) for the rate expression allowed us to simulate the general features of the imidization process. In the early stage, it is almost a constant, in accordance with the process of imidization of highly active amic acid groups, which is eventually limited by the chemical conversion of amic acid groups into imide rings. In the final stage, the reaction rate decreases exponentially because it is controlled by the conversion rate of amic acid groups from inactive to active states. Overall reaction rate is determined by the change in the rate-determining stage, and thus eventually exhibits a sharp drop in reaction rate. Comparison showed good agreement with experimental data. Activation energies calculated from the new model were in good agreement with those obtained from the first order model. The applicability of the model was further assessed by modeling a process involving two separate imidization processes. Simulation results showed good quantitative and qualitative correlations with experimental data. The model is also in good agreement with another complicated model.     

共聚型聚酰亚胺热亚胺化动力学研究

为考察共聚体系的热亚胺化动力学,今以4,4’-二氨基二苯醚(ODA),均苯二酐(PMDA),3,3’,4,4’-二苯酮二酐(BTDA)为单体合成共聚型聚酰胺酸(PAA),通过差示扫描量热分析(DSC)法测量PAA亚胺化动力学,并通过红外光谱分析仪 FT-IR 分析聚酰亚胺(PI)亚胺化程度,万能试验机测试共聚物力学性能.结果表明:随着柔性二酐(BTDA)的引入,聚合物分子链柔性增强,DSC图谱上反应出亚胺化反应相对平缓.动力学数据显示,二酐共聚体系亚胺化反应活化能最小,端基间碰撞克服的能垒最低,有利于亚胺化的进行.     

Polyimide nanocomposites: Comparison of their properties with precursor polymer nanocomposites

A precursor poly(amic acid) was obtained by solution polymerization of pyromellitic dianhydride and benzidine in N, N‐dimethylacetamide. Poly(amic acid)/Organoclay hybrids were prepared by the solution intercalation method with dodecylamine‐montmorillonite. A polyimide hybrid was obtained from poly(amic acid) hybrid by heat treatment at various temperatures. The film type polyimide hybrids showed better thermal properties than poly(amic acid) hybrids. Also, the thermal stability of the two polymer hybrids were enhanced linearly with increasing clay content from 0 to 8 wt%. Tensile properties and gas barriers of the hybrids, however, were enhanced remarkably compared to pristine polymers. Intercalations of the polymer chains in clar were examined through wide angle X‐ray diffraction (XRD) and electron microscopy (SEM and TEM). Transmission electron microscopy revealed that a partially exfoliated structure had been obtained from polyimide/organo‐clay hybrids.     

电位滴定法在聚酰亚胺合成中的应用

未完全环化的酰胺酸对聚酰亚胺的性能有重要影响,用电位滴定法可直接测定其含量。对常规的电位滴定装置进行了改进,用VB语言编写了上位机操作软件,实现了滴定控制、数据采集和处理等功能,建立了一套自动电位滴定测试系统,可用于测定二步法合成聚酰亚胺过程中剩余聚酰胺酸的含量。测定结果表明:数据的重现性好、灵敏度高,且操作方便,为进一步开展聚酰亚胺合成及其亚胺化动力学研究提供了可行的途径。     

Thermal imidization behavior of aromatic poly(amic dialkyl ester) precursors derived from biphenyltetracarboxylic dianhydride

Summary Poly(amic dialkyl ester) precursors of high performance poly(4,4-oxydiphenylene biphenyltetracarboximide) (BPDA-ODA) and poly(p-phenylene biphenyltetracarboximide) (BPDA-PDA) were synthesized and their thermal imidizations were investigated isothermally and nonisothermally by thermogravimetry. All precursors showed a two-step imidization behavior, fast imidization at early stage and slow imidization at intermediate and later stage. Kinetic parameters were estimated from the conversion versus time plots with the first-order rate equation. The imidization behaviors observed were interpreted with considering the T_g variation, the natures of alkyl leaving group and precursor backbone, and the flexibility of polymer chain. In addition, the onset temperature of imidization and T_g of precursors were estimated from the imidization kinetic data.     

PHASE SEPARATION OF POLY(AMIC ACID-CO-IMIDE) SOLUTION

Poly(amic acid-co-imide) (PA-I) is an intermediate for preparation of polyimide from polyamic acid (PAA). Phase separation does not appear for the solution until a certain imidization degree. The experimental results of a rotation viscometer and FT-IR analysis showed that the critical point of phase separation (CPPS) was related to the imidization methods (thermal or chemical imidization) and the backbone structures (flexible ODPA-ODA or semi-rigid PMDA-ODA). Phase separation time is shorted with the increase of the initial PAA concentration, acetic anhydride amount, or temperature. When phase separation occurs, the solution viscosity increases, while the imidization degree is almost constant as the initial PAA concentration rises. The greater the chain mobility, the higher the imidization degree at phase separation point. At CPPS, higher imidization degree and lower solution viscosity are obtained in the thermal imidization than in the chemical imidization; ODPA-ODA system exhibits higher imidization degree and better solubility than that of PMDA-ODA system.