Isotactic Polypropylene with (3,1) Chain-Walking Defects: Characterization, Crystallization, and Melting Behaviors

Abstract

Using two living nickel α-diimine complexes (rac-1 and rac-4) activated with methylaluminoxane (MAO), isotactic polypropylene (iPP) samples containing five types of regiodefects were synthesized. Both isolated and successive groups of (2,1) and (3,1) enchainments were identified by solution-state 13C NMR spectroscopy. The extended monomer and bulky nature of these defects add some restraints to the crystallinity level that can be achieved in these polymer samples. The complex based on a cumyl-derived ligand, rac-4, produces higher molecular weight iPP with a higher content of bulky defects than rac-1. Melting temperatures and crystallinity levels of rac-4-derived iPP are accordingly lower than the polymers obtained from rac-1. Although the nature of the chain-walking defect is similar to the addition of the ethylene unit, the difference in polymer properties is profound. At equivalent point defects per total monomers (X B), iPP samples with chain-walking defects display lower melting temperatures and much lower degrees of crystallinity than random 1-alkene copolymers, including those with comonomers excluded from the crystal lattice such as the 1-hexene and 1-octene counits. Furthermore, iPP containing (3,1) regiodefects develops significantly higher contents of the γ-polymorph than any other iPP or random copolymer with a matched X B composition. The experimental evidence is consistent with shorter crystallizable sequences for iPP with chain-walking defects based on (3,1) enchainments. Taking crystallizable and noncrystallizable total units as the basis to compute point defects, the properties of (3,1) iPP adhere to the basis of exclusion equilibrium theory, indicating that the defects are random-bulky or generated in a random fashion but of a defined extended/multimonomer nature.

Non‐isothermal crystallization of Ziegler Natta i‐PP‐graphene nanocomposite: DSC and new model prediction

“…The i ‐PP backbone defect types can be divided into conventional stereodefects, and 2,1 and 3,1 regiodefects. The Z‐N and metallocene i ‐PPs usually show the stereodefects, whereas late Ni diamine catalysts, because of the chain walking property, generate both defect types . Some commercial metallocene i ‐PPs have also been reported to exhibit either defect type .…”

“…The butyl branch of a propylene‐1‐hexene statistical copolymer, unlike the pendant ─CH 3 in i ‐PP, is knowingly excluded from the crystalline region. Therefore, if the regiodefect i ‐PP shows a comparable or lower melting point and crystallinity than the reference propylene‐1‐hexene copolymer, the following can be concluded: The above defects are random and they exclude the crystalline region. They can be regarded as co‐units that impart a copolymer characteristic to the i ‐PP chain. Flory's thermodynamic exclusion equilibrium theory will also apply to regiodefect i ‐PP …”

“…The percent crystallinity was determined using Cycle 3 DSC output and the following relation: , where ΔH f and ΔH f ° (207 J/g) are the heats of fusion of the experimental sample and the perfect (defect‐free) i ‐PP crystal (of infinite lamellar thickness and molar mass), respectively; and X GnP is the weight fraction of GnP added to the experimental composites. Table reports the above thermal properties.…”

Trials and tribulations of designing multitasking catalysts for olefin/thiophene block copolymerizations

“…We initially selected Ni precatalyst C1 (Chart ), which was chosen based on its reported living, chain‐growth olefin polymerization behavior as well as its ability to synthesize P3HT with a targeted number‐average molecular weight ( M n ) and moderate dispersity (Đ) . Due to the high sensitivity of the olefin polymerization to coordinating substrates, including thiophene and THF, we synthesized the polyolefin block first, followed by polythiophene.…”

Crystalline Isotactic Polar Polypropylene from the Palladium‐Catalyzed Copolymerization of Propylene and Polar Monomers

“…[15] Analysis of the obtained polymer by 13 CNMR spectroscopy revealed that the control over regioregularity was almost absolute. [16,17] According to our preliminary theoretical calculations, [18] the high regioregularity can be attributed to the selective 1,2-insertion of propylene.I ti s worth noting that other, previously reported, propylene polymerization catalysts based on Group 10 metals,f or example,n ickel complexes, [19,20] require low temperatures (< À60 8 8C) to achieve control over the regioregularity. Moreover,the stereoregularity of the polypropylene obtained with 1d (entry 4) was much improved (mm = 0.49; Figure 1b) relative to that obtained with 1a or 1c (entries 1or3).…”