丙烯腈与衣康酸在DMSO/H_2O中的聚合及聚合物性能表征

采用丙烯腈 (AN)与衣康酸 (IA)为共聚单体 ,以偶氮二异丁腈为引发剂在混合介质二甲基亚砜 水(DMSO H2 O)中自由基沉淀共聚合 ,合成了高分子量的聚丙烯腈 .通过正交设计方法研究了聚合反应条件 ,如反应温度、单体浓度、混合介质DMSO H2 O配比等对聚合反应的转化率的影响 ,还重点探讨了混合介质DMSO H2 O配比对转化率和粘均分子量的影响 .采用DSC ,TG ,IR等手段研究了PAN均聚物及 (PAN co IA)的结构与性能 .研究结果表明 ,增加反应温度 ,降低单体浓度 ,降低喂料AN IA配比中IA的含量 ,均有利于提高聚合反应的转化率 .AN与IA共聚反应的转化率随着反应介质中DMSO含量的增加而降低 ,同时聚合物的粘均分子量也降低 .对于喂料AN IA配比中IA含量相同的P(AN co IA)共聚物 ,高分子量P(AN co IA)共聚物比常规低分子量的放热峰起始温度低 ,放热峰宽     

云点法研究丙烯腈共聚体系反应活性及其与热稳定性能的关联

采用滴定实验法分别测试了衣康酸(IA)、丙烯酰胺(AM)、丙烯酸甲酯(MA)与丙烯腈(AN)一系列单体组成比时的云点;采用红外光谱、示差扫描量热分析和热失重分析研究了共聚单体的选择对共聚物热稳定化反应的影响和机理及其与共聚体系反应活性的关联.结果显示,IA、AM或MA的引入有利于提高AN聚合体系的云点,不同共单体用量构成的云点迹线斜率可以比较共聚体系反应活性,并对AN共聚体系组成的优化选择具有普适性;而AN与IA较高的共聚反应活性使得P(AN/IA)聚合物热稳定性能好,氰基未环化指数、环化反应起始温度及表观活化能低,环化反应速率快,这可能由于IA分子结构含有2个羧基,引发活性点较多,可以在低温条件下引发氰基环化形成更多的梯形结构.     

聚合反应介质对丙烯腈/衣康酸共聚物结构与性能的影响

利用混合溶剂沉淀聚合法研究了水/环丁砜(H_2O/TMS)等4种不同聚合反应介质对丙烯腈/衣康酸(AN/IA)共聚物的转化率、重均分子量(Mw)及分布(D)、表面微观形貌、竞聚率及链结构、聚合物热性能和纺丝性能的影响.结果表明,P(AN/IA)聚合物转化率随着混合溶剂中H_2O含量的增加,呈先升高后降低的趋势.P(AN/IA)的Mw与水/溶剂比例成线性增加的关系,其中,以H_2O/TMS作为混合反应介质所制备P(AN/IA)的Mw最大,D最小(小于2).AN与IA以H_2O/TMS为聚合介质时倾向于理想共聚,2IA链段分布几率仅为2.87%.以H_2O/TMS为聚合体系所制备P(AN/IA)结构疏松、颗粒粒径较小且易溶解,预氧化时环化反应放热速率低、放热区间宽,热稳定化阶段形成耐热梯形结构反应所需能垒小.P(AN/IA)/TMS纺丝溶液的表观黏度低,TMS为PAN的良溶剂.     

共聚单体对水相合成聚丙烯腈及其湿纺纤维结构与性能的影响

水相自由基聚合具有快速、高效的特点,是开发大规模、低成本的聚丙烯腈(PAN)基碳纤维原丝生产技术的首选工艺。本文采用该工艺制备了丙烯腈-衣康酸(P(AN-IA))和丙烯腈-醋酸乙烯酯(P(AN-VAc))两种共聚物,再经溶解和湿法纺丝将其制成纤维。采用傅里叶变换红外光谱仪(FT-IR)、场发射扫描电子显微镜(SEM)、旋转流变仪、旋转粘度计、X-射线衍射仪(XRD)和差式扫描量热/热重同步分析仪(DSG/TG)对比研究了两种共聚单体对水相合成PAN聚合物及其湿纺纤维结构与性能的影响。结果表明,与醋酸乙烯酯(VAc)相比,衣康酸(IA)降低了PAN聚合物的颗粒团聚程度和溶液粘度,显著提高了PAN纤维的截面圆整度和结构致密性,大幅降低了热稳定化反应起始温度、提高了热稳定性。这主要归因于IA的两个羧基基团。其改善了PAN聚合物的亲水性,使凝固过程更加缓和;减弱了氰基间的作用力,提高PAN分子链的运动性;能够诱导氰基在低温下发生环化反应。     

较高等规度丙烯腈成纤聚合物的合成

以无水氯化镁为添加剂,考察了不同条件下的丙烯腈聚合反应,研究了溶剂种类、聚合温度和氯化镁与丙烯腈的摩尔配比对聚合反应及聚合物等规度的影响,并确定了最佳反应条件,正己烷为溶剂,偶氮二异丁腈(AIBN)为引发剂,聚合温度为60℃,氯化镁与丙烯腈的摩尔比为2∶1.在此条件下,研究了单体浓度和引发剂浓度对丙烯腈(AN)均聚合、丙烯腈/衣康酸(AN/IA)二元共聚合和丙烯腈/衣康酸/丙烯酸甲酯(AN/IA/MA)三元共聚合反应的影响,并获得了较高等规度(三单元组全同分数30.2%～55.9%)的丙烯腈均聚物和共聚物.不同等规度的丙烯腈聚合物的热分析(DSC及TGA)表明,随着聚合物等规度的提高,聚合物的环化放热峰值温度向高温区移动,而且随着聚合物等规度的提高,环化放热峰变宽.随着聚合物等规度的提高,聚合物的热稳定性变差,热失重增加,碳收率降低.     

阻燃共聚酯/粘土复合物热降解动力学研究

用插层共聚方法合成了含磷共聚酯／粘土复合物。用热重(TG)方法考察热降解动力学。通过在空气中以不同的升温速率升温至设定温度,用Kissinger法和Hymn-Wall-Ozawa法对数据进行处理。结果表明,粘土组分含量较高的反应活化能较大,热稳定性较好。     

基于差示扫描量热法的火工品材料选型研究

通过综合分析差示扫描量热法(DSC)图谱及动力学数据,进行火工品中药剂外包覆材料的选型研究。采用DSC测试炸药与不同涂敷层材料在不同升温速率的热性质,利用Ozawa法和DSC曲线对比法,对几种涂敷层材料进行分析。炸药与丙烯酸清漆混合后,DSC曲线表观性征、峰温以及反应的活化能变化最小;炸药与快速固化剂混合后,峰温及活化能变化影响居中,DSC曲线表观性征在升温速率大时有较大变化;炸药与硅橡胶混合后,DSC曲线表观性征、峰温以及反应的活化能变化最大。从而确定丙烯酸清漆为最合适的炸药包覆材料。     

热塑弹性体热寿命和热降解动力学

利用热重法研究了聚苯乙烯/聚二烯烃/聚苯乙烯三嵌段共聚物(SIS,SBS,SI/BS)在氮气气氛条件下以不同升温速率β时热降解动力学及其热寿命。确定了热降解温度与升温速率的关系,求得了热降解过程的表观活化能和热降解速率常数,得到了不同失重率时的热寿命方程,计算出三种化合物在不同温度下的寿命。     

程序升温技术研究Mo/HZSM-5催化剂上甲烷无氧芳构化反应积炭的化学特性

对经过程序升温表面甲烷无氧芳构化反应(TPSR)后的Mo/HZSM-5催化剂上的积炭进行了程序升温加氢反应(TPH)和程序升温CO₂反应(TPCO₂),并对相应催化剂上的积炭进行了程序升温氧化反应(TPO)和热重(TG)实验.TPH实验及TPCO₂实验表明,H₂主要对高温烧炭峰发生作用.CO₂则可同时对这两种烧炭峰产生影响,对低温峰积炭的影响尤其明显.对不同Mo含量的催化剂进行上述实验的结果表明,Mo担载量的变化及不同的实验过程都会影响催化剂上两种温峰的积炭在总积炭量中所占的比例.由TG实验数据计算出的动力学结果说明,无论是TPH还是TPCO₂实验都可以降低烧炭过程的一级反应起始温度,并减少其活化能.此外,催化剂中Mo担载量的变化也会对开始温度和烧炭活化能产生明显影响.     

PPESK/PES共混物热性能及动态机械性能研究

采用熔融共混法制备了不同重量比例的新型含二氮杂萘酮结构聚芳醚砜酮(PPESK)与聚醚砜(PES)共混物.利用热失重(TGA)及动态热机械仪(DMTA)对该共混物的热性能及动态机械性能进行了研究.研究结果表明,在氮气氛围中,PPESK热分解分为两步反应进行,反应级数n=1,说明PPESK在氮气氛围中的热分解反应类型与β(升温速率)无关而与材料物性有关;采用Ozawa方法得出在15%热失重前,热分解活化能的平均值为240 kJ/mol;随着升温速率的提高,PPESK热降解速率有减缓趋势.在280℃以前,PPESK储能模量值随温度变化较小,保持在较高值,温度在280~330℃之间,储能模量值降低幅度突变.另外,PPESK中加入PES会降低其储能模量值及其热稳定性.     

DSC study of stabilization reactions in poly(acrylonitrile-co-itaconic acid) with peak-resolving method

The effect of itaconic acid (IA) content and heating rate on the stabilization reactions in poly(acrylonitrile-co-itaconic acid) (P(AN-co-IA)) was investigated by differential scanning calorimetry (DSC) with peak-resolving method. Increasing IA content was effective in decreasing the initial temperature and the heat evolved, and found to enhance oxidative reactions to some extent. While, promoting heating rate resulted in a shift of the exotherm to a higher temperature and a more rapid liberation of heat. The percentage of area of the first exothermic peak increased with increasing heating rate, which would be attributed to the enhancement of the free radical cyclization reactions.     

Mechanism and kinetics of the stabilization reactions of itaconic acid-modified polyacrylonitrile

The structural evolution and thermal behavior of polyacrylonitrile (PAN) homopolymer and copolymer [P(AN-IA)] containing about 1.5 mol% itaconic acid (IA) during stabilization in air were studied by Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC) and thermogravimetry (TG). A new parameter Es=A1595cm⁻¹/A2243cm⁻¹ was defined to evaluate the extent of stabilization. The kinetic parameters, viz. activation energy (E_a) and pre-exponential factor (A) of the stabilization reactions were calculated by Kissinger method and Ozawa method. FTIR analysis indicated that the cyclization of nitrile groups was initiated at a lower temperature by the IA comonomer and the stabilization proceeded at a more moderate pace in P(AN-IA) than in PAN, while an IA additive was found to be decomposed and failed to initiate the cyclization at a lower temperature. The improvement effect of IA comonomer on the stabilization reactions was further confirmed by the dynamic thermal analysis and kinetic study.     

Structure evolution mechanism of poly(acrylonitrile/itaconic acid/acrylamide) during thermal oxidative stabilization process

Polyacrylonitrile (PAN) polymers with different compositions were prepared by an efficient aqueous free-radical polymerization technique.Thermal properties of polyacrylonitrile homopolymer (PAN),poly(acrylonitrile/itaconic acid) [P(AN/IA)] and poly(acrylonitrile/itaconic acid/acrylamide) [P(AN/IA/AM)] were studied by Fourier transform infrared spectroscopy,X-ray diffraction,differential scanning calorimetry and thermogravimetry in detail.It was found that AM had the ability to initiate and accelerate thermal oxidative stabilization process,which was confirmed by the lower initiation temperature and broader exothermic peak in P(AN/IA/AM) as compared with that in P(AN/IA) and PAN.The intensity of heat releasing during the thermal treatment was relaxed due to the presence of two separated exothermic peaks.Accompanied by DSC analysis and calculation of the apparent activation energy of cyclization reaction,two peaks were assigned to the ionic and free radical induction mechanisms,respectively.The higher rate constant in P(AN/IA/AM) indicated that the ionic mechanism actually had a kinetic advantage at promoting thermal stability over the free radical mechanism.This study clearly show that the synthesized P(AN/IA/AM) terpolymers possess larger room to adjust manufacture parameters to fabricate high performance of PAN-based carbon fibers.     

衣康酸对聚丙烯腈原丝结构和性能的影响

控制单体配比 ,采用丙烯腈 (AN)与衣康酸 (IA)自由基溶液共聚 ,以偶氮二异丁腈为引发剂在溶剂二甲基亚砜中合成了聚丙烯腈原丝纺丝溶液 ,并纺制了碳纤维前驱体聚丙烯腈原丝 .通过元素分析、IR、DSC、13 C NMR等手段 ,讨论了共聚单体IA对共聚反应及聚丙烯腈原丝结构和性能的影响 .共聚反应时 ,共聚单体IA的加入量控制在AN/IA =98/2 (W/W )较合适 .利用IR谱 ,可定量分析IA在共聚中的摩尔分数 .经13 C NMR分析 ,随着共聚单体IR在共聚物中的摩尔分数的增加 ,共聚物的全同规整度增加 ,达到一定值后又呈下降趋势 .共聚单体IA能在较低温度时引发聚丙烯腈原丝的氧化、环化放热反应 ,且能减缓放热效应 .     

Thermal behavior of drawn acrylic fibers

The effect of stretching on the thermal behavior of acrylic fibers was investigated with differential scanning calorimetry (DSC), thermogravimetric analysis, and Fourier transform infrared spectroscopy (FTIR). In air atmosphere, the peak temperature of the dynamic DSC thermogram was significantly lowered from 289 to 273 °C when the gel fibers (undrawn) were drawn to a draw ratio of 11.2. However, the initiation temperature was unchanged at 202 °C. The shoulder in the region of 310–380 °C was gradually converted to a sharp peak during the drawing process. However, the dynamic DSC in nitrogen atmosphere did not change in all cases. In air atmosphere the total heat liberated, ΔH, for gel fiber was 851 J g^?1. However, upon drawing to 11.2, ΔH increased to 1580 J g^?1 showing an increase in the total chemical changes. An intimate relationship of chemical changes during the heating process was observed with FTIR of heated samples at various temperatures. The initiation of a DSC exotherm in air begins with nitrile cyclization, and subsequently dehydrogenation was initiated between 220 and 260 °C. An increase in the X‐ray orientation factor and sonic modulus gave a correlation between the stretching draw ratio and crystalline/overall molecular orientation. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2949–2958, 2003     

Thermo-chemical reactions and structural evolution of acrylamide-modified polyacrylonitrile

<正>Thermal properties of acrylonitrile(AN)-acrylamide(AM) copolymers for carbon fibers were studied by DSC and in situ FTIR techniques in nitrogen(N_2) and air flows.The cyclization mechanism and stabilization behavior of polyacrylonitrile(PAN) were discussed.In N_2 flow,it was found that AM had the ability to initiate and accelerate cyclization process,which was confirmed by the fact that the initiation of nitriles shifted to a lower temperature.Compared to AN homopolymer,the initiation temperature of cyclization was ahead 32 K by introducing 3.59 mol%AM into the copolymer.The exothermic reaction was relaxed due to the presence of two separated exothermic peaks.Accompanied by DSC,in situ FTIR and calculation of activation energy,the two peaks were proved to be caused by ionic cyclization and free radical cyclization,respectively,and the corresponding cyclization mechanism was proposed.With increasing in AM content,the ionic cyclization tends to be dominant and the total heat liberated first increases and then decreases.For AN homopolymer,the activation energy of cyclization is 179 kJ/mol.For AN-AM copolymer(containing 3.59 mol%AM),the activation energy of ionic cyclization is 96 kJ/mol and that of free radical cyclization is 338 kJ/mol.In air flow,similar cyclization routes occur and the difference is the contribution of oxidation.The oxygen in environment has no remarkable effect on cyclization of AN homopolymer but retards the cyclization of AN-AM copolymers.For AN-AM copolymer with 3.59 mol%AM,the cyclization temperature is postponed 10℃in air.     

Thermal decomposition and kinetics studies on the 2,2-dinitropropyl acrylate–styrene copolymer and 2,2-dinitropropyl acrylate–vinyl acetate copolymer

In the present work, kinetics of thermal decomposition of 2,2-dinitropropyl acrylate–styrene copolymer (DNPA/St) and 2,2-dinitropropyl acrylate–vinyl acetate copolymer (DNPA/VAc) was investigated by differential scanning calorimetry (DSC). The influence of the heating rate (5, 10, 15, and 20 °C min^?1) on the DSC behavior of the copolymer was verified. The results showed that, as the heating rate was increased, decomposition temperature of the copolymer was increased. Also, the kinetic parameters such as activation energy and frequency factor of the copolymer were obtained from the DSC data by the isoconversional methods proposed by Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO). Average activation energy obtained by KAS and FWO methods for the thermal decomposition reaction of DNPA/St and DNPA/VAc are 157.38 ± 0.27 and 147.67 ± 0.57 kJ mol^?1, respectively. The rate constants for thermal decomposition calculated from the activation parameters showed the structural dependency. The relative stability of two copolymers under 50 °C was in this order: DNPA/St > DNPA/VAc. The results of thermogravimetry (TG) analysis revealed that the main mass changes for DNPA/St and DNPA/VAc occurred in the temperature ranges of 200–270 °C. The DSC-FTIR analysis of DNPA/St indicates that the band intensity of nitro and other groups increased haphazardly from 230 °C due to thermal decomposition.     

碳酸乙烯酯溶剂中丙烯腈的聚合行为

以碳酸乙烯酯为溶剂,偶氮二异丁腈（AIBN）为引发剂,采用溶液自由基聚合的方法对丙烯腈(AN)均聚合、丙烯腈/衣康酸(AN/IA)二元共聚及丙烯腈/衣康酸/丙烯酸甲酯(AN/IA/MA)三元共聚合进行了研究。 考察了反应温度对丙烯腈均聚合,以及聚合单体浓度对丙烯腈共聚合的影响,在60 ℃合成了相对分子质量高于4.5×105、单体转化率高于85%的丙烯腈均聚物及共聚物。 采用正十二烷基硫醇（DDT）和甲酰基哌啶（FP）作为链转移剂,对AN均聚物、AN/IA及AN/IA/MA共聚物的相对分子质量进行调控,考察了链转移剂浓度对聚合物相对分子质量和单体转化率的影响。 结果表明,w(DDT)为0.25%时（以单体质量计）,聚合物相对分子质量可有效调节到1×105,而单体转化率保持在80%以上。     

Curing and thermal behaviour of DGEBA using mixture of biuret and 4,4′-diaminodiphenylsulfone

Curing behaviour of DGEBA was investigated in the presence of varying molar ratio of biuret and 4,4′-diaminodiphenylsulfone (DDS) by means of Differential scanning calorimetery. The multiple heating rate method (5, 10, 15 and 20 °C min⁻¹) was used to study the curing behaviour of epoxy resins. The peak exotherm temperature was found to be dependent on the heating rates, structure of biuret as well as on the ratios of biuret:DDS used. Ozawa method was used for calculating the activation energy of curing reaction. The thermal stability of the isothermally cured resins was evaluated by recording the thermogravimetric traces in nitrogen atmosphere. All the samples were stable up to 330 °C.