聚氯乙烯结构缺陷和热不稳定性之间关系的研究 2.各种结构缺陷含量和热脱氯化氢速率之间的关系

 本工作采用溴加成法、酚解法、FTIR法及臭氧裂解法分别测定了五种不饱和蒸气压下聚合的PVC样品(u-PVC)和五种商品PVC样品(s-PVC)的总双键、总不稳定氯、孤立双键和内部双键的含量.通过研究结构缺陷和PVC的平均分子量及脱HCl速率的相互关系,揭示了不饱和总双键值,总不稳定氯和孤立双键含量彼此的相关性是建立在它们分别与1/M_n的相关性基础之上,从而得出了这三种定量值测得的主要都是端基烯丙基氯结构.根据三者对脱HCl速率的良好线性相关性,首次提出了端基烯丙基氯结构在HCl催化作用下异构化成内部烯丙基氯从而成为脱HCl速率主要原因的机理.     

聚氯乙烯结构缺陷和热不稳定性之间关系的研究——Ⅰ.在单体不饱和蒸汽压下聚氯乙烯的合成及其热稳定性与分子量之间的关系

聚氯乙烯(PVC)容易发生脱氯化氢的热降解。研究者普遍认为,这是由于PVC分子链中存在结构缺陷而引起的。对究竟何种结构缺陷是引起PVC热不稳定的主要根源这一重要问题,虽然已有许多研究者进行过研究,但由于他们得到的结果往往各不相同,因而迄今未能达到一个明确一致的结论。如Minsker认为羰基烯丙基氯结构是引发脱HCl的主要原因。但Starnes却持相反意见。Hjertberg在其报告中指出叔氯     

聚氯乙烯热降解过程中HCl脱除机理的理论研究

使用B3LYP/6-311++G(d,p)方法对聚氯乙烯(PVC)几种可能模型化合物在热降解过程中HCl的脱除机理进行了理论计算.计算结果表明:PVC在第一阶段热降解过程中脱氯形成HCl时主要进行的是协同反应;缺陷结构的支链(如—CH_2CH_2Cl,—CHClCH_3和—CH_3)能显著降低邻近碳位脱除HCl的反应能垒;热降解产物HCl对热降解反应有催化作用;更为显著的是脱除HCl之后形成的氯丙烯基■—CHCl—)能降低HCl形成的反应能垒,而氯丁烯基■—CHCl—)对HCl的脱除几乎没有影响.     

季铵盐固相催化使聚氯乙烯脱HCl

通过将季铵盐与聚氯乙烯(PVC)混溶成膜,使其在固相脱HCl,研究了催化剂对PVC脱HCl反应速度和产物结构的影响以及固相反应与温度、时间的关系.发现在催化性能上下基铵盐比乙基铵盐好得多,根据实验结果提出了季铵盐通过分解成叔胺实现催化的机理.     

山梨酸镧复合热稳定剂的制备及协同性能研究

以山梨酸, NaOH, La(NO_3)_3, Ca(NO_3)_2, Zn(NO_3)_2为原料,制备山梨酸镧、山梨酸钙和山梨酸锌热稳定剂,并通过机械共混,制备了复合稀土热稳定剂。采用刚果红试纸法和转矩流变法考察其协同效应,从中筛选出协同效果最好的复合稀土热稳定剂。通过红外光谱法探讨了复合稀土热稳定剂的热稳定机制。研究表明:山梨酸镧-硬脂酸钙的协同效果最好,最佳复配比例为1∶1,静态热稳定时间为56.25 min,动态热稳定时间为1709 s。山梨酸镧复合稀土热稳定剂主要通过吸收中和HCl和与不稳定的氯原子络合以抑制聚氯乙烯(PVC)脱HCl,从而起到稳定作用。     

聚氯乙烯树脂的不饱和度和热稳定性的关系

用紫外 可见光谱法表征了不同来源的聚氯乙烯树脂（ＰＶＣ）的热稳定性，用一氯化碘加成法测量了ＰＶＣ的总的双键含量，用红外光谱法测量了ＰＶＣ的孤立双键和共轭双键的相对含量．结果表明，ＰＶＣ在加工期间的初期着色行为和长期热稳定性并不直接相关，前者取决于ＰＶＣ分子链中共轭双键的含量，而后者则和孤立双键的含量有关     

含二苯甲酮结构的稀土配合物对PVC光稳定性能的影响

兼具热和光稳定性的稀土稳定剂,对降低聚氯乙烯(PVC)加工成本,提高PVC的生产效率和打开稀土稳定剂的应用领域具有重要的意义,因此,通过人工加速紫外老化实验和户外自然光老化实验,研究了2,4-二羟基二苯甲酮镧(LBP)、 2-苯甲酰苯甲酸镧(LBA)及三元复合稳定剂对PVC光稳定性能的影响。结果表明：添加含LBP和含LBA的两种三元复合稳定剂(LBP∶ZnSt₂∶PE=2∶1∶2, LBA∶ZnSt₂∶PE=1∶1∶3)的PVC片材,人工紫外老化10 d后,失重率分别为2.7%和6.2%,自然光老化35 d后,拉伸强度保留率分别为87.6%和81.8%,复合稳定剂提高PVC的光稳定性能最佳。稀土稳定剂可以吸收PVC降解产生的氯化氢,降低氯化氢的浓度,从而减弱氯化氢对PVC降解的催化作用,抑制PVC脱去HCl形成双键,防止双键在氧作用下,形成过氧化物生成羰基化合物。     

TMPTA红外激光光聚合的实时动力学研究

采用实时FTIR研究了在红外激光照射下,阳离子菁染料-有机硼络合物1,3,3,1',3',3'-六甲基-11-氯-10,12-亚丙基吲哚三碳菁-正丁基三苯基硼引发的三羟甲基丙烷三丙烯酸酯(TMPTA)的光聚合反应动力学.研究发现,随激光功率的提高,单体的聚合速度与双键转化率均有显著提高.在临界浓度以下,引发剂的含量增加可以加快光聚合反应速率.样品厚度的增加明显降低双键转化率与聚合速度.计算结果表明,该体系的量子聚合效率为41.8mol/einstein.在17.0mW/cm²激光照射下TMPTA最高双键转化率可以达到80%.     

热稳定剂对PVC紫外光老化过程中微观结构及宏观性能演变的影响

通过UV-Vis、FTIR、DSC、以及色差、力学性能的测试表征,实时追踪分析了在紫外光老化过程中,含Pb、Sn以及Ca-Zn热稳定剂的PVC体系微观结构和宏观性能的演变过程.结果表明,在相同光老化条件下,PVC/Pb、PVC/Sn和PVC/Ca-Zn体系的微观结构变化规律基本一致,过程中主要的化学反应是,大分子吸收光能后,发生脱HCl生成共轭双键的反应、生成羰基的氧化反应、交联反应和降解反应;不同热稳定剂的作用,主要表现在对于微观结构变化的幅度和动力学过程的影响不同.相应地,3种体系的外观色差和力学性能的变化规律也相似,但色差的变化程度和速度以及老化后力学性能的保持率因所含热稳定剂的不同而不同,其中含Sn体系的颜色稳定性最好,含Pb体系的力学性能保持率最高。     

丁醇醛和丁醇酸热解形成CO和CO2机理的密度泛函理论研究

采用密度泛函理论方法B3LYP/cc-pVTZ,对模型化合物2,3,4-羟基丁醛的脱羰基和2,3,4-羟基丁酸的脱羧基反应机理进行了量子化学理论研究。对两种模型化合物分别设计了三种热解反应途径,计算了不同温度下各热解反应途径的标准热力学及动力学参数。计算结果表明,纤维素热解过程中CO₂和CO的逸出分别与脱羧基和脱羰基反应相对应,脱羧基和脱羰基反应均为分子内氢原子转移的协同过程。脱羰基反应是吸热反应,而脱羧基反应是放热反应。饱和丁醇醛的脱羰基反应反应能垒为288.8 kJ/mol,脱水后的不饱和烯醇醛的脱羰基反应能垒增大;饱和丁醇酸的脱羧基反应能垒较高,为303.4 kJ/mol,脱水后的不饱和烯醇酸的脱羧基反应能垒明显减小,这说明脱水有利于CO₂的生成。     

聚氯乙烯结构缺陷和热不稳定性之间关系的研究——Ⅰ.在单体不饱和蒸汽压下聚氯乙烯的合成及其热稳定性与分子量之间的关系

Five PVC samples (U-PVC) were prepared in water suspended system at monomer unsa-turation vapor pressure. The molecular weigh's and dehydrochlorination rates (De-HCl) of these samples and five commercial PVC samples (S-PVC) were determined. Experimental data showed that the thermal stabilities and molecular weights of U-PVC samples decreased wifh decreasing the monomer unsaturation vapor pressure (Pm/Po) in the preparation process. It was found also that there was a good linear correlation between 1/Mm, De-HCl and Pm/Po This result indicated the important role of the terminal structural defect in the dehydrochlorination of PVC.The mechanism of formation of terminal structural uefects was discussed.     

The Formation of Terminal Double Bonds in Vinyl Chloride Polymerization

The determination of double bonds in PVC is achieved with an increased accuracy in comparison with earlier methods by the addition of iodine monochloride (Wijs reaction) to PVC coupled with x-ray fluorescence analysis to determine the iodine content of the polymer. The number of double bonds per unit weight of polymer increases on increasing the polymerization temperature and is proportional to the number of polymer molecules. It is not affected, however, by the presence of the chain transfer agent tetrahydrofuran (THF). At the technically important polymerization temperatures of 30 to 80°C and in the absence of the chain transfer agent, 0.9 double bonds per polymer molecule are found. The number of double bonds per polymer molecule is lowered using the chain transfer agent THF. These results support the theory that the chain transfer to monomer and possibly the termination reaction are coupled with the formation of terminal double bonds. Contributions by internal double bonds formed by dehydrochlorination of the polymer during polymerization are excluded by investigating the Cl^θ content of the water phase in the oxygen-free VC suspension polymerization. No hydrogen chloride is formed. In IR spectra of PVC, the stretching vibration of the double bonds is detected at 1667 cm^?1 by the correlation of the double bond contents and the intensities of the absorption bands. The stretching vibration at 1667 cm^?1is in accordance with those of model compounds with a 1-chloro-2-alkene structure.     

Alkyne creation in aliphatic polymers: influence of side groups

In this article, we focus on the influence of side groups on terminal alkyne creation, in aliphatic polymers submitted to swift heavy ions, under vacuum. Terminal alkyne creation was compared in polyethylene and in substituted polymers. We selected two classes of side groups: alkyl groups, which differed in their length (polypropylene and polybutene) and allyl groups, which were linear (EPDMh) or cyclic (EPDMn). Irradiated samples were analyzed using Fourier transform IR spectroscopy, in the transmission mode, at room temperature. Alkynes are created when the electronic stopping power, (dE/dx)e, exceeds a threshold value. This threshold value was moderately influenced by the presence of an alkyl side chain but was clearly reduced in the presence of C=C bonds on the side chain. Nevertheless, in all-saturated polymers, below the (dE/dx)e threshold, terminal alkyne formation is observed after a latent dose, rather independently of the side-chain length and directly related to the formation of radiation-induced double bonds prior to alkyne formation. Under S ion irradiation, the radiation chemical yield G0 value obtained in EPDMh was 4 times the value of G0 in PE. This effect is understandable only if important energy transfers, from the backbone to C=C double bonds, are considered.     

Isomers of some vinyl and allyl compounds

The structures of two rotational isomers of styrene, methyl methacrylate, N-vinylpyrrolidone, and allyl benzoate found by AM1 calculations are discussed. Their formation is indicated by the presence of two minima on the curves of the rotation barriers around the C¹-C², C²-N³ and C(=O)-O, O-C(H₂) bonds. The structures of the isomers of allyl compounds were detected capable of providing the cyclization reaction and hydrogen atom elimination. It was found that both double bonds were of similar reactivity. The suggested structures of the isomers can participate in intermolecular interactions with the formation of self-associates and heteroassociates (molecular complexes) due to the presence of C=C and C=O groups with different degree of conjugation.     

Ungesättigte endgruppen in PVC—V reduktionsreaktion der modelle von ungesättigten endgruppen des PVC

Models for unsaturated endgroups in PVC (viz 3-chloropentene-1, 1-chloropentene-2, 2,3-dichloropentene-1, 1,3-dichloropentene-1, 1,2-dichloropentene-2 and 2,4-dichloropentene-1) were reduced with LiAlH₄ in THF. Gas chromatographic, i.r. and NMR analyses of the products showed that the chlorine atoms attached to saturated carbon atoms are substituted by hydrogen atoms during the reduction, while those attached to carbon atoms linked by double bonds are not changed. By Cotman's reduction method, the double bonds are not reduced. Therefore the branching degree determined by methods based on measurement of CH₃ groups in reduced PVC must be corrected so that the nature and number of unsaturated end-groups are taken into account. Some of these groups can be determined by measurements on the reduced polymer.     

对苯二胺和N-取代衍生物正离子自由基的共振喇曼光谱研究

本文中报道了对苯二胺和四种N-烷基取代衍生物正离子自由基的共振喇曼光谱, 揭示了自由基是具有明显C=C和C=N双键性质的半醌式结构, N原子上给电子基团的取代引起上述化学键振动峰低频移动, 反映出结构一端N上有烷基的自由基中与取代基直接相连的N原子失去一个p电子带正电荷, 并吸引环上的π电子形成一定程度C=N双键. 共振喇曼光谱随激发光波长的变化表明, 自由基的两个可见电子吸收带分别主要产生于环结构的π→π*和包含N原子结构的n→π*电子跃迁。     

8-甲氧基呋喃并[3′,2′:6,7]香豆素与烯烃的光环合加成反应的量子化学研究

我们用CNDO/Ⅱ方法UI对四甲基乙烯,偏甲基乙氧基乙烯,三甲基乙烯和丙烯睛等四个烯烃分子作了量子化学计算,它们的几何参数均采用pople标准数据。     

Improvement of Structural and Thermal Stabilities of PVC and Wood/PVC Composite by Zn and Pb Stearates,and Zeolite

Three different chemical stabilizers were introduced into neat PVC and a wood/PVC composite (containing 50 phr wood flour) to improve their thermal and structural stabilities. The changes in CIE yellowness index, polyene index, %wt loss, and decomposition temperature (T_d) were monitored. The effects of type and content of thermal stabilizers, thermal ageing time, and the presence of wood flour were our main interests. The experimental results suggested that the additions of Zn and Pb stearates into PVC and wood/PVC composite could improve the thermal stability of the PVC. At the test temperature of 177°C, the additions of Zn and Pb stearates could improve the thermal stabilities of PVC by retarding the upzipped reaction and by reducing the conjugated double bonds in PVC, Pb stearate being the most suitable for thermally stabilizing the PVC. Around the T_d range (～264°C), the addition of Zn stearate reduced the T_d value of PVC whereas that of Pb stearate had no effect on the change in T_d value. Zeolite loading could shift the T_d value of the PVC from 264 to 280°C. The addition of wood particles increased the polyene content and decreased the decomposition temperature of the PVC. The effect of wood flour on the thermal and structural changes of PVC overruled that of thermal stabilizer loading.