茂金属催化剂中丙烯/4-甲基-1-戊烯共聚物的结晶行为和性能,Macromolecules

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茂金属催化剂中丙烯/4-甲基-1-戊烯共聚物的结晶行为和性能
Macromolecules ( IF 5.1 ) Pub Date : 2023-02-10 , DOI: 10.1021/acs.macromol.2c02232
Miriam Scoti ₁ , Fabio De Stefano ₁ , Rocco Di Girolamo ₁ , Anna Malafronte ₁ , Giovanni Talarico ₁ , Claudio De Rosa ₁

Affiliation

全同立构聚丙烯 (iPP) 与 4-甲基-1-戊烯 (iPP4MP) 的共聚物使用高度等选择性均相有机金属催化剂制备，4-甲基-1-戊烯 (4MP) 浓度范围在约 1.7 至 14 mol% 之间。已在不同结晶温度下从熔体中结晶，以研究从晶体中排除的 4MP 共聚单体单元对 α 和 γ 形式结晶的影响。所有样品都以 α 和 γ 形式的混合物结晶，对于每个样品，γ 形式的分数随着结晶温度的升高而增加，以达到最大值 f γ ₍ max)，这取决于 4MP 浓度。与均聚物相比， f _γ中 γ 的最大分数(max) 随着 4MP 含量的增加而迅速增加，在 2.2 mol% 的低 4MP 浓度下达到 92% 的最高值，并随着 4MP 浓度的进一步增加而降低。将这些数据与在 iPP 与乙烯和丁烯的共聚物中形成的最大量 γ 形式的类似数据进行比较。这允许比较从晶体中排除缺陷的不同效果，这会中断规则的丙烯序列并缩短可结晶序列的长度，将缺陷包含在 α 和 γ 形式的晶体中，以及结晶的影响动力学。由于 4MP 共聚单体单元被排除在晶体之外，iPP4MP 共聚物的行为提供了唯一的中断效果，这是高效的，在接近 2 mol% 的低 4MP 浓度下产生最高量的 92% γ 形式。观察到的减少f _γ (max) 在较高的 4MP 浓度下是由于在这些 4MP 含量下 γ 形式的结晶速率太慢，导致动力学上有利的 α 形式的结晶。事实上，在这些共聚物中形成的 γ 型晶体存在高度缺陷，熔化温度低于 α 型，因此在高结晶温度下过冷度较低。这些结果表明，在含有大量结构缺陷的茂金属 iPP 共聚物中，由于短的规则丙烯序列，有利于 γ 形式的结晶，而在动力学上总是有利于 α 形式的结晶。

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Crystallization Behavior and Properties of Propylene/4-Methyl-1-pentene Copolymers from a Metallocene Catalyst

Copolymers of isotactic polypropylene (iPP) with 4-methyl-1-pentene (iPP4MP) were prepared with a highly isoselective homogeneous organometallic catalyst in a range of 4-methyl-1-pentene (4MP) concentrations between about 1.7 and 14 mol %. Crystallization from the melt at different crystallizations temperatures have been performed to study the effect of 4MP comonomeric units excluded from the crystals on the crystallization of α and γ forms. All samples crystallize in mixtures of α and γ forms, and for each sample, the fraction of γ form increases with increasing crystallization temperature to achieve a maximum value f_γ(max), which depends on the 4MP concentration. Compared to the homopolymer, the maximum fractional amount of γ form f_γ(max) rapidly increases with increasing 4MP content achieving the highest value of 92% at low 4MP concentration of 2.2 mol %, and decreases with a further increase of 4MP concentration. These data are compared with analogous data of the maximum amount of γ form that develops in copolymers of iPP with ethylene and butene. This allows comparing the different effects of rejection of defects from the crystals, which produces interruption of the regular propene sequences and shortening of the length of the crystallizable sequences, the inclusion of defects into crystals of α and γ forms, and the effect of the crystallization kinetics. Since 4MP comonomeric units are excluded from the crystals, the behavior of iPP4MP copolymers provides the sole interruption effect, which is highly efficient and produces the highest amount of γ form of 92% at low 4MP concentration of nearly 2 mol %. The observed decrease of f_γ(max) at higher 4MP concentrations is due to the too slow crystallization rate of the γ form at these 4MP contents that induces the crystallization of the kinetically favored α form. In fact, crystals of γ forms that develop in these copolymers are highly defective and show melting temperatures lower than those of the α form and, therefore, experience low undercooling at high crystallization temperatures. These results demonstrate that in metallocene iPP copolymers containing a significant amount of constitutional defects, the crystallization of the γ form is favored because of the short regular propene sequences, whereas the crystallization of the α form is always kinetically favored.

更新日期：2023-02-10

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