【作者】 邓清田；

【导师】 范志强； 傅智盛；

【作者基本信息】 浙江大学 ， 高分子化学与物理， 2008， 博士

【摘要】 聚丙烯(PP)是一种性能良好、用途广泛的通用高分子材料。为克服其性能的不足,用各种方法改性聚丙烯的工作一直受到学术界和工业界的高度重视,其中自由基引发PP接枝改性占有相当大的比重。PP的固相接枝聚合方法不需使用溶剂,反应条件温和,但仍存在一定程度的降解和交联等副反应,导致产物性能变差。已知固相接枝聚合主要发生于PP的无定型区,因而接枝产物的支化点分布及β-剪切、交联等副反应的程度将取决于PP链段在晶区和非晶区的分布状况。本论文试图通过改变PP聚集态结构来调控PP固相接枝聚合产物的链结构,探索制备高性能接枝物的新途径。首先,分别在110℃、130℃和150℃三个温度下对原生态球形多孔聚丙烯(N-PP)粒子进行了12小时等温退火处理,发现退火处理对聚丙烯的凝聚态结构有比较大的影响。DSC分析结果表明,退火处理对聚丙烯粒子的熔融过程有很大影响。随着退火温度的提高,聚丙烯的结晶度得到提高,晶片厚度分布变窄。而SEM、WAXD和压汞仪等的测试结果表明,退火处理并没有改变聚丙烯粒子原有的粒子形貌、结晶形貌和孔隙率。退火处理只是引起原生态聚丙烯粒子部分熔融和再结晶,使得结晶缺陷或者不完善部分趋于完善,其中150℃退火处理的效果最为明显。分别以经过150℃退火处理的聚丙烯(A-PP)和原生态聚丙烯(N-PP)为原料,以过氧化苯甲酸叔丁酯(TBPB)为引发剂引发了苯乙烯在PP粒子内的自由基固相接枝聚合,在较宽的引发剂用量范围内考察了两者在接枝过程中凝胶生成量、接枝率、接枝效率以及分子链降解反应的异同。发现退火处理、引发剂用量、反应温度、单体用量等因素对凝胶生成量、接枝率、接枝效率以及分子链降解反应都有影响。在反应温度为130℃时,随引发剂用量的增加,以A-PP为接枝原料所得产物的凝胶含量持续增加,而以N-PP为接枝基体所得产物的凝胶量达到一定程度后趋向于恒定。在引发剂用量为0～1%范围内退火处理对凝胶的生成有一定抑制作用,而在高引发剂用量范围内,其凝胶生成量同N-PP的凝胶生成量差别不明显。在反应温度为120℃时,退火处理引起的PP聚集态结构变化对凝胶生成的抑制作用更为明显。以N-PP为原料时,当引发剂用量超过1%时就开始有凝胶生成,而A-PP作为原料时直到引发剂用量达到2%才开始有凝胶生成。随反应温度的升高,凝胶生成量呈上升趋势。在适当苯乙烯用量范围内,凝胶生成量随苯乙烯用量加大而增加,再继续加大用量时则呈缓慢下降趋势,表明苯乙烯单体参与了凝胶生成过程。随反应温度升高,接枝率和接枝效率呈上升趋势,而随引发剂用量以及单体用量加大,接枝率先递增后趋于平衡。退火处理在低引发剂用量范围内对接枝率和接枝效率有一定抑制作用;在高引发剂用量时,由于苯乙烯参与了凝胶的生成,产物的接枝率反而有一定的提高。发现在固相接枝聚合过程中仍然有分子链降解反应发生。对PP粒子作退火处理或引入苯乙烯单体对降解反应均有抑制作用,特别是苯乙烯的引入在减轻分子链断裂的同时还伴随有部分分子链增长的过程。以DSC分析接枝产物的热性能发现,退火处理引起的PP聚集态结构变化对接枝产物的微观结构具有影响,N-PP的接枝产物比A-PP的接枝产物具有更多的接枝点,但其平均接枝链长度较后者更短。本论文的第二部分工作是比较系统地研究了在低引发剂用量(接枝产物中无凝胶成分)条件下引发苯乙烯与球形PP粒子的固相接枝聚合,探索通过固相接枝聚合制备长链支化聚丙烯(LCBed-PP)的可能性。通过温度梯度淋洗分级(TGEF)、GPC测试、熔体流变性能分析(ARES)、DSC以及红外光谱(IR)等分析手段,发现在苯乙烯接枝到PP链上的过程中有长支链形成,可以合成出长链支化聚丙烯。对TGEF级分的IR分析表明,接枝产物中几乎所有的PP链均带有聚苯乙烯支链,基本没有残留的PP均聚物链。苯乙烯参与了长支链的形成,并对长支链的形成有促进作用。反应温度、引发剂用量、单体用量以及反应时间等因素对长支链的形成也有影响。提高反应温度和引发剂用量有利于提高接枝效率,而单体用量在54.5%时有比较好的支化效果。反应时间对长支链的形成影响比较大,反应时间在10min以内所得产物的支化效果都不明显,经历20min以上聚合后产物含有明显的长支链结构。在苯乙烯存在下只需较低的引发剂用量,经历一定的反应时间就有长支链形成。本工作也考察了N-PP在相似条件下,反应时间对接枝效率的影响。发现以N-PP为原料的接枝产物中也含有长支链,只是N-PP在接枝聚合过程中分子链降解更加剧烈。接枝产物的力学性能测试结果表明,引入苯乙烯单元对接枝产物的拉伸性能和抗弯性能影响比较小。接枝产物的发泡试验结果表明,接枝产物的发泡材料泡孔比较均匀且没有破裂,这说明PP的熔体强度得到了提高,证明在接枝过程中有长支链的形成。以A-PP为原料制备的接枝产物的泡孔形态好于N-PP为原料制备的接枝产物。本论文还初步探索了以马来酸酐和苯乙烯为共单体与A-PP粒子进行接枝聚合,从而合成长链支化聚丙烯的可能性。研究结果表明,在TBPB用量为0.52%,苯乙烯加入量为64%的条件下,当马来酸酐的用量不超过10%时仍然有长支链形成。但是,马来酸酐的引入不利于长支链的生成,随马来酸酐用量的增加,支化效果明显下降。并且,马来酸酐的引入加剧了聚合物分子链降解。最后,根据本工作的实验结果和自由基反应机理,就退火处理引起的凝聚态结构变化对接枝聚合过程中凝胶生成、接枝率(接枝效率)、分子链降解等的影响进行了讨论,对此类固相接枝聚合反应的机理进行了阐述,也对苯乙烯接枝聚合过程、苯乙烯—马来酸酐共单体接枝过程中长支链形成的机理进行了初步探讨。更多还原

【Abstract】 Grafting polymerization of vinyl monomers with polyolefin is one of the most important ways to modify the properties of polyolefin materials. Modification of polypropylene (PP) by radical initiated solid-state grafting polymerization has been studied for many years. Because only the PP segments in the amorphous phase can be attacked by radicals to form the graft chains, the chain structure of grafting product will be changed when the crystallinity, lamella size and its distribution are changed. In this work, the phase morphology of nascent spherical PP granules was regulated by isothermal annealing treatment, and the annealed PP granules were then used as the matrix for grafting polymerization of styrene in solid state. Effects of annealing treatment on the grafting polymerization and structure of the graft copolymer were systematically studied. The products were found to have long chain branching structure, which markedly changed the rheological properties of PP. A mechanism model of the grafting polymerization was proposed to explain the effect of annealing treatment on the grafting copolymerization and the formation of long chain branched structures.Firstly, nascent PP granules were annealed respectively at 150°C, 130°C and 110°C for 12 hours at each temperature. DSC analysis results showed that the annealing treatment strongly influenced the phase morphology. As annealing temperature increased, the crystallinity of PP became higher and the lamellae thickness distribution became narrower. However, analysis results of SEM, WAXD, and mercury porosimeter demonstrated that the granule’s topological morphology, crystal form and porosity were almost intact after the annealing treatment. Annealing treatment only resulted in partial melting and recrystallizion of PP phase. The influence of annealing treatment at 150°C is most remarkable.Grafting copolymerization of styrene with annealed PP or nascent PP was performed, respectively, using tert-butyl perbenzoate (TBPB) as a radical initiator. The grafting degree, amount of gel, and degree of PP degradation were investigated. Experimental results demonstrate that factors such as annealing treatment, initiator concentration, amount of styrene and reaction temperature all showed strong effects on the grafting reaction. As the initiator concentration was increased, the content of gel formed at 130°C continuously increased when annealed PP was used as the matrix. Whereas, the content of gel based on nascent PP was firstly increased and then leveled off. When the initiator concentration was lower than 1%, the grafting product based on annealed PP matrix had lower gel content than that of nascent PP. At reaction temperature of 120°C, the difference in gel content was much remarkable between samples of nascent PP and annealed PP. Gel was formed in graft polymer from nascent PP at 1.0% TBPB feed, while there was no gel formed in graft polymer from annealed PP until 2.0% TBPB .With the increase of reaction temperature, the gel content, grafting degree and grafting efficiency all gradually increased. When reaction temperature was lower than 120°C, no gel was formed in the final products, but the grafting degree and grafting efficiency were also much lower than the samples prepared at 120°C and 130°C. With the increase of styrene concentration, the gel content and grafting degree increased at first and then decreased. However, the grafting degree and grafting efficiency of the products from annealed PP were slightly depressed at low initiator feed. Molecular weight analysis showed that significant degradation of the polymer chains also took place when either annealed PP or nascent PP were used as the matrix. The degradation reaction was depressed by using annealed PP as matrix, and (or) the introduction of styrene. In the presence of styrene, molecular weight of a part of polymer chains increased, implying that chain build-up or grafting reaction happened. DSC analysis demonstrated that there was differences in branch density and average length of graft chains between products from nascent PP and annealed PP. Grafting products based on nascent PP have higher branch density but shorter graft chains as compared with those based on annealed PP.Subsequently, a series of styrene grafting copolymerizations were conducted at low initiator concentration to prevent gel formation in the final products. Several kinds of analysis methods, such as temperature gradient extraction fractionation (TGEF), gel permeation chromatography (GPC), rheological properties measurement (ARES), differential scanning calorimetry (DSC) and infrared spectra (IR) were utilized to characterize the grafted samples. The analysis results demonstrate that long chain branching structure was formed in the grafting products. Styrene took part in the formation of long chain branches and played an important role. The formation of long chain branches was affected by factors such as reaction temperature, feed ratio of initiator, styrene feed and reaction time. Increases in reaction temperature and initiator feed were beneficial to the formation of long chain branches. During the process of grafting reaction, long chain branched structures were not formed until enough styrene was polymerizaed. It was also found that long chain branches can be formed at rather low initiator feed in the presence of styrene. In this work, we also investigated grafting copolymerization of styrene in nascent PP matrix. Experimental results exhibited that long chain branched structure could also be formed using this matrix, but polymer degradation was much more serious comparing with that of annealed PP. In addition, a series of graft copolymer samples were synthesized in larger scale, and their mechanical properties were measured. It was found that the mechanical properties of the grafting products were not deteriorated after the reaction, and in some cases even improved as compared to the unmodified PP. Grafting products based on annealed PP showed better mechanical properties than those of nascent PP. The foaming properties were also improved after the grafting eopolymerization, which evidenced the enhancement of melt strength.Under similar conditions as the styrene grafting copolymerization, styrene-co-MAH grafting copolymerization in annealed PP granules was also studied to introduce SMA branches into PP chains. Experimental results showed that long chain branches could also been formed when the MAH feed ratio was lower than 10% at 0.52% initiator and 64% of styrene feeds. The introduction of MAH was unfavorable to the formation of long chain branches. As the feed ratio of MAH increased, the effects of long chain branches in the graft copolymer declined. The introduction of MAH also made the degradation much serious.Finally, according to the experimental results and basic concepts of radical initiated grafting polymerization, a simplified mechanism model was proposed to elucidate the effect of PP annealing treatment on grafting degree, formation of gel and polymer chain degradation. The mechanism of long chain branches formation in the grafting processes was also proposed.更多还原