【作者】 王明；

【导师】 向明；

【作者基本信息】 四川大学 ， 高分子科学与工程， 2022， 硕士

【摘要】 聚丁烯-1合金（PB-A）是在聚丁烯-1均聚物（PB-1）的基础上发展而来的一种釜内合金,它是由1-丁烯和丙烯通过“序贯聚合工艺”制备而成,其中“丙烯相”的含量通常低于10%。与PB-1相似,PB-A也是一种线性多晶型聚合物,具有优异的抗蠕变性能、耐环境应力开裂性能,在高温下也能保持良好的机械性能,广泛应用于高压热水管道的制造。相对于聚乙烯、聚丙烯等聚烯烃材料,PB-A的结晶速率比较慢,材料加工成型后在室温下还会发生亚稳态晶型Ⅱ向热力学稳定态晶型Ⅰ的固-固相转变,较慢的结晶速率和自发而不可逆的晶型转变延长了PB-A的成型周期,限制了其广泛应用与发展。此外,由于“丙烯相”的存在,PB-A的结构更为复杂,其结晶特性和晶型转变与PB-1有明显差异。而PB-A分子结构和冷却过程对其结晶及晶型转变的影响研究相对较少,聚合过程中的结构调控以及加工制造缺乏理论基础,因此对PB-A这一方面的研究格外重要。本论文以PB-A为研究对象,并与PB-1对比,探究了其结构对结晶成核、晶体生长、结晶速率及晶型转变的影响;探讨了冷却过程对PB-A和PB-1结晶及晶型转变的影响;利用闪速差示扫描量热法（Flash DSC）可控、超快的扫描速率研究了PB-A和PB-1在高降温速率下的结晶过程。主要的研究内容和结果如下:1.深入研究了PB-A的聚丙烯相与分子结构对其结晶及晶型转变的影响。通过溶液分级得到独立的聚丙烯相和丙烯共聚单体含量相近、分子量和可结晶序列长度不同的三个聚丁烯级分,利用高温凝胶渗透色谱（HT-GPC）、核磁共振碳谱(¹³C-NMR)、差示扫描量热法（DSC）和连续自成核退火（SSA）等发现PB-A中的“丙烯相”主要以两种形式存在,一是分散于树脂中的独立聚丙烯相,其质量分数为4～5%,重均分子量约为1×10⁶ g/mol,熔点为159.1℃,结晶度为35.6%;另一种是以共聚单体的形式无规分布于分子主链上的“丙烯单元”,含量为2～3 mol%。通过常规DSC、偏光显微镜（POM）研究了聚丙烯相对PB-A结晶及晶型转变的影响,结果表明,聚丙烯相能提高PB-A的成核温度和成核密度,加快结晶速率,同时其也能促进PB-A的晶型转变。而无规分布于分子链上的“丙烯单元”会改变PB-A的可结晶序列结构,较长的可结晶序列能加快PB-A的球晶生长速率与结晶速率,对晶型转变也有明显的促进作用。另一方面,PB-A中高分子量组分和可结晶序列较长的组分同时存在且含量越高,树脂的成核温度越高、成核密度越大、形成的晶片更厚、晶片厚度分布更均匀。PB-A的分子结构也强烈影响其晶型转变,分子量的降低或较长可结晶序列含量的增加都能加快晶型转变,但与分子量的作用相比,较长的可结晶序列对晶型转变的促进作用更明显,可结晶序列较长的PB-A在转变过程中形成的晶型Ⅰ和晶型Ⅱ的晶片更厚,完成转变后形成的晶型Ⅰ也更完善。因此为了提高PB-A树脂的结晶和晶型转变速率,需要在聚合过程中尽可能使较长可结晶序列分布于高分子量的组分中。2.详细探讨了降温速率和过冷度对PB-A结晶及晶型转变的影响,同时与PB-1对比。利用常规DSC的可控降温,发现PB-A在10℃/min和50℃/min的慢速降温条件下结晶全部形成晶型Ⅱ,而在淬火的快速冷却过程中发现PB-A能直接形成15～20%的晶型Ⅰ。慢速降温过程中形成的晶型Ⅱ需要更长的时间完成晶型转变,提高降温速率,转变速率加快。通过改变结晶温度获得不同的过冷度,过冷度较低（结晶温度较高）时,PB-A与PB-1的结晶和晶型转变速率都较慢。当结晶温度为25℃时,PB-A和PB-1初始的晶型转变表现出较快的速率,升高或降低结晶温度,初始转变形成的晶型Ⅰ结晶度都会降低。PB-A和PB-1在室温下完成晶型转变后形成的晶型Ⅰ结晶度随结晶温度的升高而增大。当结晶温度为0℃时,PB-A和PB-1的晶型转变最快,升高或降低结晶温度,转变速率都会减慢。与PB-1相比,采用不同冷却过程得到的PB-A晶型转变更快。结构不同的PB-A的晶型转变与晶型Ⅰ的完善程度也有差异,聚丙烯相含量较低、较长的可结晶序列含量较高的PB-A的晶型转变较快,完成转变后形成的晶型Ⅰ结晶度较高。采用不同冷却过程得到的PB-A和PB-1在室温下放置7天后仍有少量残留的晶型Ⅱ难以转变,晶型转变末期的转变速率非常慢。PB-A和PB-1以10℃/min降温结晶再在室温下放置7天后形成的晶型Ⅰ晶面间距最小,晶体结构更完善,而当结晶温度为液氮温度时,PB-A和PB-1在室温下放置7天后形成的晶型Ⅰ晶面间距最大。采用不同冷却过程得到的PB-A和PB-1晶型转变形成的晶型Ⅰ晶胞参数相近。3.利用Flash DSC深入探究了PB-A和PB-1在高降温速率下的结晶过程。PB-A和PB-1在快速降温后的升温过程中会发生冷结晶,且降温速率、过冷度与树脂结构对其冷结晶都有显著影响。聚丙烯相含量较高、较长可结晶序列含量较低时,PB-A从熔体降温至-50℃后,升温时在-13℃发生焓松弛。PB-A发生冷结晶的临界降温速率为15 K/s,冷结晶温度随降温速率的提高而升高,冷结晶热焓随降温速率的提高、过冷度的升高而增大,冷结晶主要形成晶型Ⅱ,晶型Ⅱ的熔融焓随降温速率的提高、过冷度的降低而增大。聚丙烯相含量较低、较长可结晶序列含量较高时,PB-A从熔体降温至-50℃后,升温时在-7℃发生焓松弛。PB-A发生冷结晶的临界降温速率为15 K/s,冷结晶热焓随降温速率的提高、过冷度的升高而增大,冷结晶能形成晶型Ⅱ和部分晶型Ⅰ,晶型Ⅰ的含量随降温速率的提高而增加。当PB-A从熔体降温至0℃时,形成的晶型Ⅰ含量最多,晶型Ⅰ的熔点最高,当从熔体降温至-50℃或-20℃时,晶型Ⅰ的含量会略微减少,而从熔体降温至40℃或70℃时,晶型Ⅰ的含量和熔点都最低。PB-1从熔体降温至-50℃,升温时在-6℃发生焓松弛。PB-1发生冷结晶的临界降温速率为35K/s,冷结晶热焓随降温速率的提高、过冷度的升高而增大,冷结晶主要形成晶型Ⅱ,晶型Ⅱ的熔融焓随降温速率的提高、过冷度的降低而增大。含有“丙烯相”的PB-A冷结晶能力更强,“丙烯相”可以提高PB-A的链段运动能力,从而促进其构象旋转和晶型Ⅰ的形成。PB-A和PB-1慢速降温时通过熔体结晶形成晶型Ⅱ,而快速降温时通过冷结晶形成晶型Ⅱ,冷结晶形成的晶型Ⅱ的晶体结构排列相对松散,非晶区的自由体积较大,可能有利于晶型Ⅱ晶区内链段的运动,使其更容易转变为晶型Ⅰ。更多还原

【Abstract】 Polybutene alloy（PB-A）is a kind of in-reactor alloy developed on the basis of polybutene-1 homopolymer（PB-1）,which is prepared by“sequential polymerization”of 1-butene and propylene,and the“propylene phase”content is usually less than10%.Similar to PB-1,PB-A is also a kind of linear polymorphic polymer,which possesses excellent creep resistance and environmental stress cracking resistance.It can also maintain good mechanical properties at a high temperature,so it is widely applied to the manufacture of high-pressure hot water pipes.Compared with polyolefin materials such as polyethylene and polypropylene,the crystallization rate of PB-A is relatively slow,and the solid-solid phase transition from metastable formⅡto thermodynamically stable formⅠoccurs at room temperature after the processing of PB-A.The slow crystallization rate as well as the spontaneous and irreversible crystal transformation prolongs the processing period of PB-A and restricts its wide application and development.In addition,due to the existence of“propylene phase”,PB-A has a more complex structure,therefore its crystal property and crystal transformation are obviously different from PB-1.However,the investigation about the influence of molecular structure and cooling process of PB-A on its crystallization and crystal transformation is relatively few,and there is no theoretical basis for the structure regulation in the polymerization and the processing of PB-A,so the research on PB-A in these aspects is particularly important.In this paper,compared with PB-1,PB-A was taken as the research object.The structure of PB-A and its effect on the crystal nucleation and growth,crystallization rate and crystal transformation were investigated.Additionally,the influence of cooling process on the crystallization and crystal transformation of PB-A and PB-1were discussed.The crystallization process of PB-A and PB-1 at high cooling rates were studied by the controllable and ultrafast scanning rate of Flash differential scanning calorimetry（Flash DSC）.The main contents and results of the research are as follows:1.The effects of the polypropylene phase and molecular structure of PB-A on its crystallization and crystal transformation were studied thoroughly.The independent polypropylene phase and three polybutene fractions with similar propylene comonomer content,different molecular weight and different length of crystallizable sequence were obtained by solution fractionation.That the“propylene phase”in PB-A mainly existed in two forms was discovered by high temperature gel permeation chromatography（HT-GPC）,nuclear magnetic resonance carbon spectroscopy(¹³C-NMR),differential scanning calorimetry（DSC）and successive self-nucleation and annealing（SSA）.The first was the independent polypropylene phase dispersed in the resin,whose weight fraction was 4～5%.Additionally,the weight-average molecular weight,melting point and crystallinity of polypropylene phase were 1×10⁶ g/mol,159.1℃and 35.6%,respectively.The other was the“propylene unit”randomly distributed on the main molecular chain as the comonomer,and the comonomer content was 2～3 mol%.The effect of polypropylene phase on the crystallization and crystal transformation was investigated by conventional DSC and polarized light microscope（POM）.The results showed that polypropylene phase could increase the nucleation temperature and nucleation density of PB-A.Polypropylene phase could also accelerate the crystallization rate and crystal transformation of PB-A.The“propylene unit”randomly distributed on the molecular chain could change the structure of crystallizable sequences of PB-A,thus affecting the crystallization and crystal transformation.Longer crystallizable sequence was able to accelerate the crystal growth rate and crystallization rate of PB-A,and it could also promote the crystal transformation.On the other hand,when the high molecular weight components and the components with longer crystallizable sequences existed simultaneously and their contents were larger,the nucleation temperature and the nucleation density of the resin were both higher.In addition,the lamellae were thicker and its thickness distribution was more uniform.The molecular structure of PB-A could also intensively affect its crystal transformation.The reduction of molecular weight and the increase of the content of longer crystallizable sequences could accelerate the crystal transformation.However,compared with the effect of molecular weight,the longer crystallizable sequence had a more obvious promotion on the crystal transformation.PB-A with longer crystallizable sequences had higher melting points of formⅠand formⅡ,so the lamellae of formⅠand formⅡwere thicker,and formⅠafter transformation was more perfect as well.Therefore,in order to accelerate the crystallization and crystal transformation of PB-A resin,it is necessary to distribute longer crystallizable sequences in the components with a high molecular weight during the polymerization as far as possible.2.The influence of cooling rate and undercooling degree on the crystallization and crystal transformation of PB-A was discussed in detail,comparing with PB-1.It was found that PB-A crystallized into formⅡunder slow cooling conditions of10℃/min and 50℃/min by controllable cooling of conventional DSC,and formⅠwith a crystallinity of 15～20%could generate directly in the rapid cooling process.FormⅡgenerated in the slow cooling process needed longer time to complete the crystal transformation,and increasing the cooling rate could accelerate the transformation rate.The crystallization temperature was changed to obtain different undercooling degree.The crystallization and transformation rate of PB-A and PB-1were slower when the undercooling degree was lower（the crystallization temperature was higher）.While the crystallization temperature was 25℃,the initial crystal transformation of PB-A and PB-1 exhibited a faster rate,and the crystallinity of formⅠgenerated in the initial transition decreased with the increase or decrease of the crystallization temperature.The crystallinity of PB-A and PB-1 increased with the rise of crystallization temperature.The crystal transformation of PB-A and PB-1 was the fastest at room temperature when the crystallization temperature was 0℃,and the transformation rate slowed down with the increase or decrease of the crystallization temperature.Compared with PB-1,PB-A obtained by different cooling processes owned a faster crystal transformation rate.PB-A with different structures also had different crystal transformation and perfection degree of formⅠ.PB-A with a lower polypropylene phase content and a higher content of longer crystallizable sequences had a faster crystal transformation rate and a higher crystallinity of formⅠafter transformation.There was still a small amount of residual formⅡthat was difficult to transform to formⅠin PB-A and PB-1 obtained by different cooling processes after placing at room temperature for 7 days,and the transformation rate at the end of crystal transformation was extremely slow.When PB-A and PB-1 were cooled at10℃/min and then placed at room temperature for 7 days,formⅠgenerated with the smallest crystal plane spacing and the most perfect crystal structure.However,when the crystallization temperature was the temperature of liquid nitrogen,the crystal plane spacing of formⅠgenerated after 7 days at room temperature of PB-A and PB-1 was the largest.The formⅠlattice parameters of PB-A and PB-1 obtained by different cooling processes were similar.3.The crystallization process of PB-A and PB-1 at high cooling rates was investigated by Flash DSC.The cold crystallization of PB-A and PB-1 occurred during the heating process after rapid cooling,and the cooling rate,the undercooling degree and the structure of resins had significant effects on the cold crystallization.When the polypropylene phase content was higher and the content of longer crystallizable sequences was lower,the enthalpy relaxation of PB-A occurred at-13℃after cooling from melt to-50℃.Its critical cooling rate of cold crystallization was15 K/s,and the cold crystallization temperature increased with the increase of cooling rate.The cold crystallization enthalpy increased with the increase of cooling rate and undercooling degree.FormⅡmainly generated during the cold crystallization,and the melting enthalpy of formⅡincreased with the increase of cooling rate and the reduction of undercooling degree.When the polypropylene phase content was lower and the content of longer crystallizable sequences was higher,the enthalpy relaxation of PB-A occurred at-7℃after cooling from melt to-50℃.Its critical cooling rate of cold crystallization was also 15 K/s,and the cold crystallization enthalpy increased with the increase of cooling rate and undercooling degree.FormⅡand partial formⅠcould generate during the cold crystallization,and the formⅠcontent increased with the increase of cooling rate.The content and the melting point of formⅠwere the highest when PB-A was cooled from melt to 0℃.When PB-A was cooled from melt to-50℃or-20℃,the formⅠcontent decreased slightly.The content and melting point of formⅠwere the lowest while cooled from melt to 40℃or 70℃.The enthalpy relaxation of PB-1 occurred at-6℃after cooling from melt to-50℃.Its critical cooling rate of cold crystallization was 35 K/s,and the cold crystallization enthalpy increased with the increase of cooling rate and undercooling degree.FormⅡmainly generated in the cold crystallization,and the melting enthalpy of formⅡincreased with the increase of cooling rate and the reduction of undercooling degree.PB-A containing the“propylene phase”possessed stronger cold crystallization ability,and the“propylene phase”could enhance the mobility of chain segments,thus promoting the conformation rotation and the formation of formⅠ.PB-A and PB-1 generated formⅡthrough melt crystallization during slow cooling,while they generated formⅡby cold crystallization during fast cooling.The crystal structure of formⅡgenerated during the cold crystallization was relatively loose,and the free volume of the amorphous region was larger,which may facilitate the mobility of the chain segments in the crystalline region of formⅡand make it easier to transform into formⅠ.更多还原