WO2025085612A1

WO2025085612A1 - Bioderived polymers from biogenic dienes

Info

Publication number: WO2025085612A1
Application number: PCT/US2024/051741
Authority: WO
Inventors: Frank S. Bates; Christopher J. Ellison
Original assignee: University of Minnesota Twin Cities; University of Minnesota System
Current assignee: University of Minnesota Twin Cities; University of Minnesota System
Priority date: 2023-10-17
Filing date: 2024-10-17
Publication date: 2025-04-24
Anticipated expiration: 2026-04-17

Abstract

Forming a recycled polymer blend includes melt blending recycled polyethylene and recycled polypropylene to yield a melt blend, and combining the melt blend with up to 10 wt% of a biogenic block copolymer to yield a recycled polymer blend. The recycled polymer blend includes recycled polyethylene, recycled polypropylene, and the biogenic block copolymer. Synthesizing the biogenic copolymer includes polymerizing biogenic butadiene, isoprene, or both to yield a biogenic copolymer. In some cases, synthesizing the biogenic block copolymer includes polymerizing biogenic butadiene to yield 1,4-poly(butadiene), reacting the 1,4-poly(butadiene) with an additional amount of biogenic butadiene to yield a 1,4-poly(butadiene)-block-1,2-poly(butadiene) diblock copolymer, coupling the 1,4-poly(butadiene)-block-1,2-poly(butadiene) diblock copolymer to yield a biogenic 1,4-poly(butadiene)-block-1,2-poly(butadiene)-block-1,4-poly(butadiene) triblock copolymer, and hydrogenating the 1,4-poly(butadiene)-block-1,2-poly(butadiene)-block-1,4-poly(butadiene) triblock copolymer to yield a polyethylene-block-poly(ethylene-ran-ethylethylene)-block-poly(ethylene) triblock copolymer.

Description

REPLACEMENT SHEET Attorney Docket No.: 09531-0546WO1 / UMN 2024-028 BIODERIVED POLYMERS FROM BIOGENIC DIENES CROSS-REFERENCE TO RELATED APPLICATION [0001] This application claims the benefit of U.S. Patent Application No.63/544,550 filed on October 17, 2023, which is incorporated by reference herein in its entirety. STATEMENT OF GOVERNMENT SUPPORT [0002] This invention was made with government support under CHE01413862 CHE1901635 awarded by the National Science Foundation. The government has certain rights in the invention. TECHNICAL FIELD [0003] This invention relates to bioderived polymers from biogenic dienes. BACKGROUND [0004] High-density polyethylene (PE) and isotactic polypropylene (iPP) offer many benefits, yet contribute to a rapidly growing reservoir of nearly indestructible waste, which ends up in landfills and the environment. Several approaches for addressing this crisis have been explored, such as chemical upcycling into feedstock chemicals (e.g., hydrogenolysis) and reintroduction of polyolefins into the economy through reprocessing. However, sorting polyolefin products in a recycle stream by flotation or optical methods is largely ineffective due to similar densities and virtually identical chemical structures (both are saturated hydrocarbons). Combining most PE and iPP products for reuse through melt blending results in phase separation leading to brittle and essentially useless materials due to poor interfacial adhesion, obviating an otherwise attractive approach to recycling. SUMMARY [0005] This disclosure describes anionic polymerization of biogenic dienes (e.g., biogenic butadiene) into block copolymers, with subsequent catalytic hydrogenation, yielding E and X blocks that are individually melt miscible with polyethylene (PE) and isotactic polypropylene containing 1 wt% of the triblock copolymer EXE of appropriate molecular weight results in mechanical properties competitive with the component plastics. Blend toughness is obtained through interfacial topological entanglements of the amorphous X polymer and semicrystalline zPP, along with anchoring of the E blocks through cocrystallization with the PE homopolymer. [0006] The effectiveness of PE-zPP multiblock copolymers in recycling polyethylene and polypropylene is attributed to at least two factors: (1) thermodynamic compatibility of the two block types with the homologous polyolefins leads to melt state interfacial activity in the phase separated blends; and (2) cocrystallization of the blocks with PE and zPP homopolymers binds the two phases together, reducing or eliminating interfacial debonding during deformation. Comparable toughening of PE and zPP blends after mixing small amounts (ca. 1 wt%) of a poly(ethylene)-Z>/oc -poly(ethylene-zzzzz-ethylethylene)-Z>/oc -poly(ethylene) triblock copolymer, denoted EXE, with commercial polyolefin homopolymers. The mechanism of interfacial strengthening combines topological entanglement of zPP melt-compatible and amorphous X center blocks with PE cocrystallizable terminal E blocks. This strategy eliminates the need to employ expensive organometallic catalysts, thus facilitating recycling of polyolefins through blending.

[0007] Although the disclosed inventive concepts include those defined in the attached claims, it should be understood that the inventive concepts can also be defined in accordance with the following embodiments.

[0008] Embodiment 1 is a method of synthesizing a biogenic copolymer comprising polymerizing biogenic butadiene, isoprene, or both to yield a biogenic copolymer.

[0009] Embodiment 2 is the method of embodiment 1, wherein the biogenic copolymer is a biogenic block copolymer.

[0010] Embodiment 3 is the method of embodiment 2, wherein the biogenic block copolymer is a biogenic multiblock copolymer.

[0011] Embodiment 4 is the method of embodiment 3, wherein the biogenic multiblock copolymer is a biogenic diblock copolymer or biogenic triblock copolymer.

[0012] Embodiment 5 is the biogenic copolymer formed by any one of the methods of embodiments 1-4.

[0013] Embodiment 6 is a method of synthesizing a biogenic block copolymer comprising: polymerizing biogenic butadiene to yield l,4-poly(butadiene); reacting the l,4-poly(butadiene) with an additional amount of biogenic butadiene to yield a l,4-poly(butadiene)-Z>/oc£-l,2-poly(butadiene) diblock copolymer; coupling the l,4-poly(butadiene)-/>/oc -l,2-poly(butadiene) diblock copolymer to yield a biogenic l,4-poly(butadiene)-£>/ocA'-l,2-poly(butadiene)-/>/oc£-l,4-poly(butadiene) triblock copolymer; and hydrogenating the 1 ,4-poly(butadi ene)-block- 1 ,2-poly(butadiene)-/>/oc - 1 ,4- poly(butadiene) triblock copolymer to yield a polyethylene-Z>/ocA>poly(ethylene-ra«- ethylethylene)-Z>foc -poly(ethylene) triblock copolymer.

[0014] Embodiment 7 is the method of embodiment 6, wherein each polyethylene block comprises up to 4 ethyl branches per 100 backbone carbon atoms.

[0015] Embodiment 8 is the method of embodiment 6 or 7, wherein the poly(ethylene-ra«- ethylethylene) block comprises about 70% to about 95% ethylethylene repeat units and about 30% to about 5% ethylene repeat units on a molar basis.

[0016] Embodiment 9 is the method of any one of embodiments 6-8, wherein the poly(ethylene-raH-ethylethylene) block is amorphous.

[0017] Embodiment 10 is the method of any one of embodiments 1-9, wherein the biogenic block copolymer is substantially free of homopolymer.

[0018] Embodiment 11 is the biogenic block copolymer formed by the method of any one of embodiments 6-10.

[0019] Embodiment 12 is a method of forming a recycled polymer blend comprising: melt blending recycled polyethylene and recycled polypropylene to yield a melt blend; and combining the melt blend with up to 10 wt% of the biogenic block copolymer synthesized by the method of claim 1 to yield a recycled polymer blend.

[0020] Embodiment 13 is the method of embodiment 12, wherein a weight ratio of the recycled polyethylene to the recycled polypropylene is in a range of 2:98 to 49:51 or 98:2 to 51:49.

[0021] Embodiment 14 is a recycled polymer blend comprising: recycled polyethylene; recycled polypropylene; and the biogenic block copolymer formed by the method of any one of embodiments 6-

10.

[0022] Embodiment 15 is the recycled polymer blend of embodiment 14, wherein recycled polymer blend comprises up to 10 wt% of the biogenic block copolymer.

[0023] Embodiment 16 is the recycled polymer blend of embodiment 15, wherein the recycled polymer blend comprises up to 5 wt% of the biogenic block copolymer.

[0024] Embodiment 17 is the recycled polymer blend of embodiment 16, wherein the recycled polymer blend comprises up to 3 wt% of the biogenic block copolymer.

[0025] Embodiment 18 is the recycled polymer blend of embodiment 17, wherein the recycled polymer blend comprises up to 1 wt% of the biogenic block copolymer.

[0026] Embodiment 19 is the recycled polymer blend of any one of embodiments 14-18, wherein a weight ratio of the recycled polyethylene to the recycled polypropylene is in a range of 2:98 to 49:51 or 98:2 to 51 :49.

[0027] Embodiment 20 is the recycled polymer blend of any one of embodiments 14-19, comprising a 30:70 blend of the recycled polyethylene and the recycled polypropylene and about 1 wt% of the biogenic block copolymer.

[0028] The details of one or more embodiments of the subject matter of this disclosure are set forth in the accompanying drawings and the description. Other features, aspects, and advantages of the subject matter will become apparent from the description, the drawings, and the claims.

BRIEF DESCRIPTION OF DRAWINGS

[0029] FIG. 1 shows a synthetic scheme for the preparation of EXE triblock copolymer from biogenic butadiene, where the fraction of ethylethylene repeat units in the E blocks (PE) is x ~ 0.06 and in the X blocks (PE/PEE) is y « 0.9.

[0030] FIGS. 2A-2H are representative atomic force microscope (AFM) phase images of neat PE/iPP blends (FIGS. 2A and 2E), and blends containing 1 wt% E91X93 (FIGS. 2B and 2F), E28X34E28 (FIGS. 2C and 2G), and EesXssEes (FIGS. 2D and 2H). The top and bottom rows depict PE:zPP compositions of 70:30 and 30:70, respectively. Light and dark domains correspond the /PP and PE. Reduction in the domain sizes with the addition of block copolymer is indicative of interfacial activity. [0031 ] FIG. 3 A shows representative stress-strain curves for neat PE and zPP homopolymers, and 70:30 blends containing 1 wt% block copolymer. The inset in FIG. 3A shows the stressstrain response of the uncompatibilized blend. FIG. 3B shows strain at break, £b, of compatibilized 70:30 PE:zPP blends as a function of block copolymer concentration. Error bars represent one standard deviation.

[0032] FIG. 4 A shows representative stress-strain curves for neat PE and zPP homopolymers, and 30:70 blends containing 1 wt% block copolymer. The inset in FIG. 4A shows the stressstrain response of the uncompatibilized blend. FIG. 4B shows strain at break, £b, of compatibilized 30:70 PE:zPP blends as a function of block copolymer concentration. Error bars represent one standard deviation.

[0033] FIGS. 5A and 5B shows scanning electron microscope (SEM) images obtained from cryo-fractured cross-sections of PE:zPP (70:30) blend following failure in tension at Sb ~ 10%, and PE:zPP (70:30) blend containing 1 wt% EesXssEes after failure at a ® 600, respectively. [0034] FIG. 6A depicts four thermal processing strategies, where slow cool = 1 °C/min and fast cool = 20 °C/min. 1) Slow cool zPP/slow cool PE from 180 to 30 °C (red/black lines). 2) Fast cool zPP/fast cool PE from 180 to 30 °C (teal/blue lines). 3) Slow cool zPP/fast cool PE; slow cool from 180 to 125 °C (red line) followed by fast cool from 125 to 30 °C (red line). 4) Fast cool zPP/slow cool PE; fast cool from 180 to 100 °C (teal line) followed by heating from 100 to 135 at 10 °C/min (teal line), isothermal annealing for 5 min at 135 °C (teal line) then slow cooling from 135 to 30 °C. FIG. 6B shows representative stress-strain curves obtained from PE: iPP (70:30) blends with 1 wt. % EesXssEes following different cooling recipes from the melt state.

[0035] FIGS. 7A-7D depict proposed mechanisms for block copolymer interfacial behavior in the melt state (FIG. 7A), and solid state (FIGS. 7B-7D). Fast cooling from the melt results in cocrystallization of E and PE, and entanglement of X with the amorphous portion of semicrystalline zPP (FIGS. 7B and 7C). A triblock architecture leads to topologically entrained X blocks and high interfacial strength (FIG. 7C). Diblocks present entangled but unconstrained X chains that can disengage from the interface under stress (FIG. 7B). Slow cooling (FIG. 7D) results in semicrystalline E blocks segregated from the PE morphology leading to poor interfacial strength. DETAILED DESCRIPTION

[0036] FIG. 1 shows a synthetic scheme for the preparation of EXE triblock copolymer from biogenic butadiene, where E and X are poly(ethylene-ran-ethylethylene) random copolymers with 6% and 90% ethylethylene repeat units, respectively. As used herein, a “biogenic” compound generally refers to a compound derived from biological sources, such as plants, rather than a fossil-based feedstocks, such as coal, oil, or natural gas. Unlike biogenic compounds, which are known to contain non-zero amounts of ¹⁴C, fossil-based feedstocks are free or substantially free of ¹⁴C.

[0037] Returning to FIG. 1, initiation of butadiene with sec-butyllithium in cyclohexane at 40 °C leads to a polymer containing 94 mol% 1,4-butadiene and 6 mol% 1,2-butadiene addition, referred to as 1,4-PB. Tetrahydrofuran (THF) is added to the living polymer solution at a molar concentration of [THF]: [Li] = 200:1, followed by addition of more butadiene monomer at 20 °C to produce a second 1,4-PB/1,2-PB statistical copolymer block with « 90% 1,2-PB content, denoted 1,2-PB. As used herein, “living polymer” generally refers to a polymer that grows without termination or chain transfer reactions, and thereby allowing control of molecular weight and structure. Following complete conversion of the monomer to polymer, a stoichiometric amount of di chlorodimethylsilane ([Cl-Si(CH3)2-Cl]:[Li] = 1:2) is used to couple the living diblock copolymer chains leading to predominately l,4-PB-Z>foc£-l,2-PB-6/ocA-l,4-PB triblock copolymer. Alternatively, termination of the living 1,4-PB or 1 ,4-PB-/)/ocC-l ,2-PB chains with acidic methanol results in homopolymer or diblock copolymer, respectively. Saturation of the block copolymers with hydrogen at 100 °C using a macroporous Pt/SiCE catalyst (or various other homogeneous catalysts) generates the desired products, EXE and EX, where the E block contains 1.5 ethyl branches per 100 backbone carbon atoms and the X blocks are statistical copolymers with about 90% ethylethylene and 10% ethylene repeat units. There is little homopolymer in the specimens, moreover, any such homopolymer would simply disperse into the PE domain during melt processing and have no influence on the blend properties. The coupling efficiency results in approximately 80 wt% of triblock copolymer as determined using SEC. ¹ H NMR and SEC traces of the saturated products demonstrate complete hydrogenation (> 99%) without degradation. The molecular characteristics of the saturated block copolymers are summarized in Table 1. All three block copolymers listed in Table 1 are microphase separated in the melt state up to 240 °C, as evidenced through dynamic mechanical spectroscopy measurements.

Table 1. Molecular Characteristics of EX and EXE Block Copolymers

a Subscripts x and y in E_xand X_y indicate number-average molecular weights in kg/mol. ^b Subscripts based on the molecular weight of the polybutadiene diblock copolymer prior to coupling. The molecular weight of the triblock copolymer is calculated based on tire molecular weight of the diblock. ^c Based on SEC using universal calibration with polystyrene standards, ¹ H NMR, and corrected for the addition of hydrogen. ^d Based on the molecular weight of the diblock prior to coupling. Tire lower molecular weight reflects about 80% coupling efficiency. ^e Volume fraction of X block based on 'H NMR, and assuming equal block melt densities. ^fBased on DSC measurements.

[0038] Blend Morphology. Polymer blends containing commercial high-density polyethylene (HDPE, referred to as PE) and isotactic polypropylene (zPP), both provided by the Dow Chemical Co., along with 0.5-5 wt% EXE or EX, were prepared using a recirculating twin screw microcompounder operated at 190 °C followed by molding into 0.5 mm thick films at 180 °C and subsequent cooling (~20 °C/min) to room temperature. Blend morphologies were characterized with atomic force microscopy (AFM) and scanning electron microscopy (SEM). FIGS. 2A-2H are representative AFM images obtained from blends of PE and zPP containing either 70% or 30% polyethylene (PE:zPP = 70:30 or 30:70, respectively) without (unmodified) and containing 1 wt% of E91X93, E28X34E28, or EesXggEes. Phase contrast is derived primarily from the difference in modulus between the two components, where the softer PE and stiffer zPP materials appear darker and lighter, respectively. Melt mixing results in droplet morphologies, where the block copolymer modified blends consistently show smaller domain sizes and narrower size distributions compared to the neat blends. These results evidence localization of block copolymer at the phase separated domain interfaces, which reduces the interfacial tension facilitating droplet breakup during mixing. Minor variations in the domain dimensions between the PE continuous and zPP continuous blends can be attributed at least in part to effects associated with differences in the homopolymer viscosities.

[0039] Mechanical Properties. Representative stress-strain curves obtained from neat PE and /PP homopolymers, and PE:zPP (70:30) blends with and without 1 wt% block copolymer, are shown in FIG. 3A. Both homopolymers are tough, exhibiting strains at break of £b ~ 450% (/PP) and a « 750% (PE). Blending these two polyolefins together results in a brittle plastic with L, « 10% (inset of FIG. 3 A). Adding 1 wt% of the EesXssEes triblock copolymer leads to full recovery of ductility with b » 600%, a mechanical signature of compatibilization. Substituting the E28X34E28 for EesXssEes ( 1% of the higher molecular weight triblock) or replacing the triblock with a relatively high molecular weight diblock (E91X93) at the same 1 wt% loading, results in significantly reduced blend toughness (sb < 40%). FIG. 3B illustrates the role of block copolymer concentration on tensile toughness for the three additives. Considerable ductility ( b > 200%) is obtained with just 0.5 wt% of EesXssEes, increasing to about 800% at a concentration of 5 wt%, roughly equivalent to that of pure PE. Both E28X34E28 and E91X93 exhibit modest benefits (fib « 200 %) at 3 wt% and about twice this value at 5 wt% loadings.

[0040] FIG. 4A summarizes the mechanical properties of /PP continuous (30:70 PE /PP) blends with 1 wt% of each of the three block copolymers, along with the uncompatibilized mixture. Here again, the unmodified mixture exhibits a reduced ductility (a ~ 50%) relative to the pure polyolefins. The increase in £b compared to the unmodified 70:30 blend (FIG. 3A) can be attributed to the dispersion of the more compliant PE as particles in a stiffer /PP matrix. And as before, adding 1 wt% of the EesXssEes triblock copolymer results in a strain at break (a « 550%) intermediate to the pure homopolymers. As shown in FIG. 4B, the dependence of the strain at break on block copolymer concentration for the 30:70 blends resembles what appears in FIG. 3B, with a couple of notable exceptions: diblock copolymer E91X93 promotes significantly greater toughness in the 30:70 blend at a concentration of 1 wt%, and EesXssEes affords nearly twice the strain at break at 0.5 wt% as was obtained with the 70:30 PE:zPP mixture.

[0041] Brittle fracture in uncompatibilized polyolefin blends has been attributed to interfacial failure when such composites are subjected to large deformations. As demonstrated by the SEM image in FIG. 5A, /PP particles appear to be cleanly separated from the PE matrix along the fracture surface in a failed 70:30 PE:/PP blend specimen (a ~ 10%). In contrast, the addition of 1 wt% EesXssEes suppresses interfacial failure during tensile deformation, resulting in drawing of both the matrix and particle domains without delamination up to the point of fracture (a ~ 600%), as seen in FIG. 5B.

[0042] Crystallization. The physical properties of semicrystalline polyolefins are related to the detailed molecular configurations associated with chain-folded crystalline morphologies. These in turn are determined at least in part by several factors, including the number of chain defects (e.g., the fraction of branches in PE or stereochemical irregularity in zPP) and the crystallization temperature, which is influenced by the rate of cooling from the melt state. The latter point was evaluated with the PE and zPP homopolymers by preparing rapidly (20 °C/min) and slowly (1 °C/min) cooled specimens, followed by tensile testing. The PE material exhibited a modest reduction in strain at break at the slower cooling rate (from a ~ 750% to a ~ 550%). However, when cooled at 1 °C/min, the zPP plastic became brittle, failing at a « 10% in contrast to a ~ 500% when cooled at 20 °C/min. A series of differential scanning calorimetry (DSC) experiments was conducted to observer the crystallization behavior of the PE and z'PP homopolymers as a function of cooling rate.

[0043] Both homopolymers crystalize (T_c) and melt (T_m) at slightly lower temperatures when cooled more rapidly: (z) dT/dt = 1 °C/min, T_C,PE = 119.9 °C, T_m,PE = 133.1 °C, and T_c,,pp = 128.5 °C, T_m,iP_P = 164.2 °C; (zz) dT/dt = 20 °C/min, T_C,PE = 117.0 °C, T_m,_PE = 130.2 °C, and T_wpp = 117.8 °C, Tmjpp = 161.4 °C. These trends are also reflected in the percent crystallinity: 63% versus 60% for PE and 58% versus 52% for zPP at the slower and faster cooling rates, respectively. The ductile to brittle transition associated with zPP as the cooling rate is lowered can be attributed to the increased crystallinity.

[0044] A molecular scale mechanism is proposed to explain the extraordinary toughness imparted to PE:zPP blends by the addition of small amounts of the EgsXssEes triblock copolymer. One aspect of this proposed mechanism includes cocrystallization of the E blocks with the PE homopolymer in the vicinity of the interfacial region between the phase separated domains. In order to probe such cocrystallization, two 1,4-PB homopolymers were synthesized and hydrogenated. These homopolymers are referred to as E35 and Ees, where the molecular weights were chosen to be similar to the E blocks in the two triblock copolymers (Table 1). DSC measurements show that these polymers have about 36% crystallinity with melting temperatures of T_m.E = 108-110 °C, following cooling from the melt at 20 °C/min, i.e., slightly higher than the melting temperatures of the E blocks in the pure block copolymers (Table 1). The difference in percent crystallinity and melting temperature T_m,PE - T_m,E ~ 21 °C can be attributed to the 1.5 ethyl branches per 100 backbone carbon atoms in the E polymer, which can result in segregation during melt crystallization in mixtures with the PE homopolymer. DSC experiments with blends of E35 and E65 containing PE demonstrate that these polymers largely cocrystallize when cooled from the melt at 20 °C/min, as evidenced by a depression of the principle melting temperature to T_m = 126-128 °C, and reduction in the percent crystallinity to 48%-50%, in mixtures containing 50% of either E polymer; a minority fraction (< 50%) of E segregates during solidification as indicated by a broad second melting endotherm at 108-110 °C in these blends. Mixtures containing 25% E and 75% PE exhibit almost no evidence of segregation after crystallization. Cooling these mixtures slowly (1 °C/min) somewhat increases segregation between E and PE during crystallization as evidenced by a slightly higher principal peak melting temperature (129- 130 °C) and a more distinct lower melting temperature (« 108 °C) endotherm in the 50/50 PE/E mixtures. These experiments show that, to a considerable extent, E35 and Ees cocrystallize with PE when cooled rapidly from the mixed melt state, with some degree of segregation in the solid state after slow cooling.

[0045] Analogous solidification experiments were performed with the 70:30 PE:zPP blend containing 1 wt% EesXssEes, guided by the thermal behavior determined for the two homopolymers. FIGS. 6A and 6B highlight the mechanical properties obtained following 4 different cooling and heating procedures. A tough blend (a ~ 600%) is obtained in the limit of fast cooling (20 °C/min) from the melt (180 °C) as described earlier. Reducing the cooling rate to 1 °C/min has a noticeable impact on the product, decreasing the strain at break to a « 25%. A third thermal history involved cooling from 180 °C at 1 °C/min (slow cool) to 125 °C followed by cooling at 20 °C/min (fast cool) to room temperature, designated “zPP slow cool/PE fast cool” in FIGS. 6A and 6B. This protocol, designed to produce crystalline zPP particles dispersed in a PE melt at 125 °C, with subsequent crystallization of PE (and E) while cooling slowly, results in a tough material, albeit with a somewhat reduced strain at break, a ~ 350%. In a fourth procedure, the entire blend was solidified by fast cooling from 180 °C to 100 °C (i.e., below the crystallization temperature of both PE and zPP), then was heated to 135 °C for 5 minutes (leaving fast cooled crystalline zPP dispersed in a PE melt), followed by slow cooling to room temperature. This process, referred to as “zPP fast cool/PE slow cool” in FIGS. 6A and 6B, results in a relatively brittle plastic with a ~ 30%.

[0046] Addition of a small amount (approximately 1 wt%) of an appropriately prepared EXE triblock copolymer to mixtures of commercially available polyethylene and polypropylene leads to remarkably tough materials, offering an approach to recycling these plastics. This finding is surprising because the X block, which is an amorphous polymer with a glass transition temperature T_g,x = -30 °C, cannot cocrystallize with zPP.

[0047] One factor in applying these compounds to compatibilization of PE and zPP is the segregation of the E and X blocks, which was verified using dynamic mechanical spectroscopy (DMS). Both pure EXE triblocks and the EX diblock display non-terminal low frequency elastic (G') and dynamic (G") moduli indicative of microphase separation up to 240 °C. Transport of the block copolymers to the interface between the phase separated PE and zPP domains during melt blending is therefore driven by thermodynamic compatibility of E and PE, and X and zPP. [0048] Interfacial activity of the EXE and EX block copolymers reduces the interfacial tension between PE and zPP in the melt state, similar to the behavior of a surfactant in contact with water and oil. In addition, localization of block copolymers at domain interfaces provides varying degrees of adhesion between the solid (semicrystalline) domains. Reduced interfacial tension is evident in the reduction in domain sizes relative to the unmodified mixtures apparent in the AFM images in FIGS. 2A-2H.

[0049] EXE triblock and EX diblock copolymers are configured at the domain interfaces as depicted in FIG. 7A. For the triblock molecular architecture, the X block forms a loop that extends into the liquid z'PP domain. Assuming Gaussian statistics, the radius of gyration of a flexible polymer is 7?_g = /4/V/6)^{1 2}, where N is the degree of polymerization and b is the statistical segment length. For the X block (and z'PP based on a 4-carbon repeat unit), Z>x = Z>ZPP = 0.58 nm, hence the X loop will project roughly D = 2R_S into the z'PP domain; for EesXssEes and E28X34E28, Dx ® 19 nm and 12 nm, respectively. Similarly, the E blocks will project into the PE melt roughly DE ~ 22 nm and 15 nm, respectively, based on Z>E = 0.80 nm (also with a 4-carbon repeat unit). Once formed, zPP chains will rapidly penetrate (“thread”) the X loop (“needle”) in order to maintain constant density, creating a state of entanglement with the homopolymer. For the zPP melt considered here, the melt molecular diffusion (reptation) time is r_r < 1 s. Estimating the X loop volume as Ex = (4/3 )7r/ _g ³ = 3.1 * 10³ nm³ with a melt density of p = 0.9 g/cm³yields roughly 10-20 zPP chains within a loop volume for EesXggEes, based on Y_n, /PP = 1 x 10^? g/mol and assuming the relevant metric is the number average molecular weight. M_n provides a conservative estimate of the “needle” size. The X blocks can be relatively narrow in dispersity. The molecular weights and dispersity of the zPP chains are factors in estimating how many of these polymers are entrained in a “needle”. The most relevant molecular weight for this purpose is believed to be M_n, since the number of zPP polymers contained in an X block coil volume is calculated. Since the entanglement molecular weight for polypropylene (and the X blocks) is M_e = 6,300 g/mol, the homopolymer chains associated with the X loop will be fully entangled. Maintaining the entropically favorable Gaussian coil configuration typically requires penetration of many iPP chains within the associated coil volume. Upon cooling, nucleation and growth of a chain-folded semicrystalline morphology typically requires local separation of the zPP and X chains, since the latter cannot crystallize. The X loops are believed to be entrained by the loops and bridging portions of the amorphous part of the semicrystalline zPP structure, creating topological constraints that bind the EesXssEes triblock copolymer to the zPP domain (see FIGS. 7C and 7D). An EX diblock architecture does not afford the same type of entrainment since the X block is immobilized only at one end (i.e., the EX block junction in FIG. 7B) and can escape confinement by wiggling out of the zPP entanglements in response to an applied load. However, the diblock will be interfacially active, as evidenced by the reduction in domain size shown for the blends containing E91X93 (FIGS. 2B and 2F). Such interfacial activity will not interfere with the “threading the needle” mechanism associated with the EXE triblock copolymer containing minor amounts of uncoupled diblock copolymer.

[0050] To support a stress across the interface, the E blocks are preferentially bound to the semicrystalline PE domains. This involves cocrystallization of E and PE, shown above to occur in blends of the two homopolymers. It is believed that, upon rapid cooling, a fraction of the E blocks are immobilized through crystallization with the homopolymer. This may involve actual mixing of crystalline E and PE stems within common lamellae (FIGS. 7B and 7C) or could result from entrained chain folded loops and bridges between separate crystalline E lamellae and PE lamellae. A certain fraction of the E blocks are typically fixed within the PE domain to withstand the forces created at the domain interface during deformation.

[0051] In the proposed toughening mechanism, zPP chains “thread-the-needle” formed by the looping X block in the melt state, which becomes topologically trapped upon crystallization of the homopolymer. Anchoring of the E blocks then results in interfacial adhesion. Support for this hypothesis is provided by the experimental results, especially in the limit of low concentrations of block copolymer (< 1 wt%).

[0052] As shown in FIG. 6, superior ductility (fib > 300%) can be obtained when PE crystallization occurs under fast cooling conditions, regardless of whether the zPP is cooled quickly or slowly. This implies that the threading-the-needle mechanism is not rate dependent. Disengagement of zPP during crystallization could occur if folding individual chains into growing lamellae drew them out of the X loop. However, this could involve collapse of the X loop, which would be entropically costly. It is believed that zPP crystallization captures the X loop in multiple chain-folded and bridging portions of the amorphous region of the semicrystalline zPP, creating topological crosslinks that stitch the block copolymer to the solid zPP domain. This mechanism is believed to be operative at considerably lower EXE molecular weights (see below). However, the E block is a factor as well.

[0053] FIGS. 6A and 6B show that slowly cooling the blends can lead to poor ductility. Most tellingly, fast cooling to 100 °C, with crystallization of PE and zPP, followed by melting of the PE (but not the zPP), and then slow crystallization of PE renders a material with a « 30%, which is almost indistinguishable from blends cooled continuously from 180 °C to room temperature at ~1 °C/min. E and PE cocrystallization near the domain interface is rate dependent. The extent of cocrystallization between E and PE will be smaller with slow cooling compared to fast cooling from the mixed melt state. Moreover, there appears to be an E block molecular weight dependence. The poor performance of E28X34E28 at low concentrations (FIGS. 3A-3B and 4A- 4B) is due at least in part to the reduction from 65 kDa to 28 kDa in the E block molecular weight.

[0054] Overall, the interfacial activity of the EXE triblock is not thought to be dependent on the blend composition (e.g., 70:30 PE:zPP versus 30:70 PE:zPP) in both limits acting as a macromolecular surfactant that lowers the interfacial tension while mechanically coupling the two domains through cocrystallization of E and PE, and topological entanglement of X and zPP. With respect to the behavior of the E91X93 diblock copolymer in the 30:70 PE:zPP blends (FIGS. 4A and 4B), it is observed that the fast-cooled mixture exhibits £b « 325% at 1 wt% loading. However, this block copolymer imparts no added toughness beyond the pure homopolymer blend at 0.5 wt%. This may reflect an increased E block molecular weight, combined with the role played by embedding lower modulus PE particles in a stiffer zPP matrix, reflected in the unmodified mixture (inset of FIG. 4A). Presumably, interfacial failure occurs through retraction and delamination of the X blocks, which are probably highly entangled in the amorphous region of the semicrystalline zPP domain.

[0055] Repurposing polyethylene (PE) and polypropylene (zPP) through blending requires economically tractable approaches to combining these plastics without sacrificing mechanical properties. Addition of 1 wt% of EXE triblock copolymers, containing PE and zPP melt miscible E and X blocks, generates ductile blends with a strain at break of a ~ 600%. Mechanically superior blends result from interfacial localization of the EXE triblock copolymer during melt mixing, which leads to X chains that are topologically entrained with semicrystalline zPP and E blocks that cocrystallize with the PE homopolymer upon rapid cooling.

Materials and Methods

[0056] Materials. Homopolymers zPP (H314-02Z, M_n = 100 kg/mol, D = 4.1, MFI = 2.0 g/10 min at 230 °C with 2.16 kg) and HOPE (DMDA-8904, M_n = 22 kg/mol, D = 3.8, MFI = 4.4 g/10 min at 190 °C with 2.16 kg) were both obtained from the Dow Chemical Company. A series of E-X block copolymers were synthesized using sequential anionic polymerization followed by catalytic hydrogenation. Cyclohexane (HPLC, Fisher Scientific) and tetrahydrofuran (THF) (HPLC, Fisher Scientific) were purified by passing through activated alumina columns.

Butadiene (> 99%, Sigma-Aldrich) was twice distilled from n-butyllithium (2.5M in hexanes, Sigma-Aldrich). Cyclohexane was first added to the reactor under an argon atmosphere, followed by sec-butyllithium (sBuLi, 1.4M in cyclohexanes, Sigma-Aldrich) and butadiene, which was allowed to react for 8 h at 40 °C. An aliquot of the living polymer was taken to determine the average molecular weight and dispersity. Then the reactor was cooled to 20 °C, and THF was added at a concentration of [THF]: [Li] = 200:1, followed by additional butadiene. After an additional 8 h, an aliquot of the diblock was removed from the reactor for analysis, and a stoichiometric amount of dimethyldichlorosilane (> 99.5%, Sigma-Aldrich) was added ([Cl] : [Li] = 1 : 1) and allowed to react for 3 days at room temperature. Polybutadiene homopolymers and diblock copolymers were prepared by terminating living polymers following the first and second stages using degassed methanol. The product was precipitated in cold methanol and dried under vacuum at 40 °C to constant weight. [0057] Polybutadiene (PB) polymers were dissolved in isooctane (> 99%, Fisher Scientific) at a concentration of 5 g/L and hydrogenated to E homopolymers, EX diblock, and EXE triblock copolymers, in a high-pressure reactor operated at 100 °C with 500 psi of H2 over a SiCh supported Pt catalyst (1 :5 catalyst-to-polymer (w/w)) for 24 h.(54) Catalyst was removed by hot filtration and the product was precipitated in cold methanol and dried under vacuum at 100 °C to constant weight.

[0058] The molecular weight and dispersity of the PB compounds were determined using room temperature size exclusion chromatography (SEC) at a concentration of 3-5 mg/mL with THF as the mobile phase and calibrated with polystyrene standards. The eluent flow rate is 1 mL/min, and the sample injection volume is 100 pL. The Mark-Houwink parameters used for the universal calibration are KPB= 2.52 x 10 ² mL/g, apB = 0.727, Kps = 8.63 x 10 ³ mL/g, and aps = 0.736.(55) The composition of the 1,4-PB and 1,2-PB blocks were determined by

NMR spectra obtained from 10% (w/w) CDCI3 solutions at 30 °C using a Bruker HD500 NMR spectrometer. The polybutadiene precursors and the hydrogenated products were examined by high-temperature SEC in tri chlorobenzene at 135 °C using an Agilent PL-220 instrument equipped with a refractive index detector to confirm a lack of chain degradation, and ’H NMR spectroscopy was performed with a Bruker HD500 instrument at 90 °C using deuterated toluene solutions to establish the extent of polymer saturation.

[0059] Blend Preparation and Tensile Test. Blends of PE, iPP, and 0.5-5 wt% block copolymers (weight fraction based on the weight of neat PE/zPP blends) were prepared using a recirculating 5 m DSM Xplore twin-screw microcompounder, with mixing for 8 min at 130 rpm at 190 °C. The blended materials were molded into 0.5 mm thick films at 180 °C employing a pressure of 4 MPa for 5 min with a Carver hot press. Unless otherwise stated, cooling water was used for quenching (~20 °C/min). Dumbbell-shaped tensile bars were prepared with a die cutter (ASTM DI 708, 5 mm gauge width, 22 mm gauge length). All tensile tests were conducted at room temperature (22 °C) using an Instron 5966 Universal Testing System operated at a crosshead speed of 22 mm/min (100%/min strain rate).

[0060] Atomic Force Microscopy. The morphology of neat and compatibilized PE:zPP blends were imaged using atomic force microscopy in dynamic mode (AFM; Bruker Nanoscope V Multimode 8, Digital Instruments Santa Barbara, CA open-loop system). Smooth imaging surfaces were obtained on pressed and annealed films using a cryo-ultramicrotome (Leica UC6) operated at -120 °C, first using a glass knife to create a cutting face, followed by sectioning of 500 nm thick slices with a diamond knife (Diatome), which were mounted on a silicon wafer. Samples were scanned in the repulsive regime using an n-type silicon tip cantilever (resonant frequency = 166 Hz, spring constant = 2 N/m, and radius = 8 nm). Captured images were processed using Gwyddion 2.56 open-source software to level the data, align rows, correct scarring, and adjust the contrast via histogram. Details regarding data handling are provided in Exhibit 1.

[0061] Fractography. Dogbone tensile specimens were cryo-fractured in liquid nitrogen, and the resulting cross sections were examined using a JEOL 6500 field emission SEM with 2 kV accelerating voltage and approximately 10 mm working distance. Specimens were affixed with carbon tape to a 90-degree pin stub mount and sputter coated with a 5 nm thick platinum conducting layer before imaging.

[0062] Thermal Analysis. Glass transition, melting and crystallization temperatures were determined using differential scanning calorimetry (DSC). 5-10 mg of sample was sealed in an aluminum pan and loaded in a TA QI 000 DSC instrument under a nitrogen atmosphere at gas flow rate 50 mL/min.

[0063] Rheology. Bulk rheological data were acquired for the three saturated block copolymers (E91X93, E28X34E28, and EesXssEes) using an ARES-G2 rheometer (Thermal Analysis Instruments, New Castle, DE) under nitrogen gas purge employing an 8 mm parallel plate geometry and a 0.5 mm gap. Frequency sweeps spanning 0.1 - 100 rad/s at a constant strain amplitude of 2% were conducted from 120 to 240 °C in 20 °C increments with 10 minutes between measurements for temperature equilibration. Master curves, referenced to 180 °C, were prepared using time-temperature superposition.

[0064] Although this disclosure contains many specific embodiment details, these should not be construed as limitations on the scope of the subject matter or on the scope of what may be claimed, but rather as descriptions of features that may be specific to particular embodiments. Certain features that are described in this disclosure in the context of separate embodiments can also be implemented, in combination, in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments, separately, or in any suitable sub-combination. Moreover, although previously described features may be described as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can, in some cases, be excised from the combination, and the claimed combination may be directed to a sub-combination or variation of a sub-combination.

[0065] Particular embodiments of the subject matter have been described. Other embodiments, alterations, and permutations of the described embodiments are within the scope of the following claims as will be apparent to those skilled in the art. While operations are depicted in the drawings or claims in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed (some operations may be considered optional), to achieve desirable results.

[0066] Accordingly, the previously described example embodiments do not define or constrain this disclosure. Other changes, substitutions, and alterations are also possible without departing from the spirit and scope of this disclosure.

Attorney Docket No.: 09531-0546WO1 / UMN 2024-028

BIODERIVED POLYMERS FROM BIOGENIC DIENES

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. Patent Application No. 63/544,550 filed on October 17, 2023, which is incorporated by reference herein in its entirety.

STATEMENT OF GOVERNMENT SUPPORT

[0002] This invention was made with government support under CHE01413862 CHE1901635 awarded by the National Science Foundation. The government has certain rights in the invention.

TECHNICAL FIELD

[0003] This invention relates to bioderived polymers from biogenic dienes.

BACKGROUND

[0004] High-density polyethylene (PE) and isotactic polypropylene (zPP) offer many benefits, yet contribute to a rapidly growing reservoir of nearly indestructible waste, which ends up in landfills and the environment. Several approaches for addressing this crisis have been explored, such as chemical upcycling into feedstock chemicals (e.g., hydrogenolysis) and reintroduction of polyolefins into the economy through reprocessing. However, sorting polyolefin products in a recycle stream by flotation or optical methods is largely ineffective due to similar densities and virtually identical chemical structures (both are saturated hydrocarbons). Combining most PE and zPP products for reuse through melt blending results in phase separation leading to brittle and essentially useless materials due to poor interfacial adhesion, obviating an otherwise attractive approach to recycling.

SUMMARY

[0005] This disclosure describes anionic polymerization of biogenic dienes (e.g., biogenic butadiene) into block copolymers, with subsequent catalytic hydrogenation, yielding E and X blocks that are individually melt miscible with polyethylene (PE) and isotactic polypropylene BIODERIVED POLYMERS FROM BIOGENIC DIENES

CROSS-REFERENCE TO RELATED APPLICATION

STATEMENT OF GOVERNMENT SUPPORT

[0002] This invention was made with government support under CHE 1901635 awarded by the National Science Foundation. The government has certain rights in the invention.

TECHNICAL FIELD

[0003] This invention relates to bioderived polymers from biogenic dienes.

BACKGROUND

[0004] High-density polyethylene (PE) and isotactic polypropylene (/PP) offer many benefits, yet contribute to a rapidly growing reservoir of nearly indestructible waste, which ends up in landfills and the environment. Several approaches for addressing this crisis have been explored, such as chemical upcycling into feedstock chemicals (e.g., hydrogenolysis) and reintroduction of polyolefins into the economy through reprocessing. However, sorting polyolefin products in a recycle stream by flotation or optical methods is largely ineffective due to similar densities and virtually identical chemical structures (both are saturated hydrocarbons). Combining most PE and zPP products for reuse through melt blending results in phase separation leading to brittle and essentially useless materials due to poor interfacial adhesion, obviating an otherwise attractive approach to recycling.

SUMMARY

[0005] This disclosure describes anionic polymerization of biogenic dienes (e.g., biogenic butadiene) into block copolymers, with subsequent catalytic hydrogenation, yielding E and X blocks that are individually melt miscible with polyethylene (PE) and isotactic polypropylene

Claims

Attorney Docket No.: 09531-0546WO1 / UMN 2024-028 WHAT IS CLAIMED IS: 1. A method of synthesizing a biogenic copolymer, the method comprising: polymerizing biogenic butadiene, isoprene, or both to yield a biogenic copolymer. 2. The method of claim 1, wherein the biogenic copolymer is a biogenic block copolymer. 3. The method of claim 2, wherein the biogenic block copolymer is a biogenic multiblock copolymer. 4. The method of claim 3, wherein the biogenic multiblock copolymer is a biogenic diblock copolymer or biogenic triblock copolymer. 5. The biogenic copolymer of claim 1. 6. A method of synthesizing a biogenic block copolymer, the method comprising: polymerizing biogenic butadiene to yield 1,4-poly(butadiene); reacting the 1,4-poly(butadiene) with an additional amount of biogenic butadiene to yield a 1,4-poly(butadiene)-block-1,2-poly(butadiene) diblock copolymer; coupling the 1,4-poly(butadiene)-block-1,2-poly(butadiene) diblock copolymer to yield a biogenic 1,4-poly(butadiene)-block-1,2-poly(butadiene)-block-1,4-poly(butadiene) triblock copolymer; and hydrogenating the 1,4-poly(butadiene)-block-1,2-poly(butadiene)-block-1,4- poly(butadiene) triblock copolymer to yield a polyethylene-block-poly(ethylene-ran- ethylethylene)-block-poly(ethylene) triblock copolymer. 7. The method of claim 6, wherein each polyethylene block comprises up to 4 ethyl branches per 100 backbone carbon atoms. 18 Attorney Docket No.: 09531-0546WO1 / UMN 2024-028 8. The method of claim 6, wherein the poly(ethylene-ran-ethylethylene) block comprises about 70% to about 95% ethylethylene repeat units and about 30% to about 5% ethylene repeat units on a molar basis. 9. The method of claim 6, wherein the poly(ethylene-ran-ethylethylene) block is amorphous. 10. The method of claim 6, wherein the biogenic block copolymer is substantially free of homopolymer. 11. The biogenic block copolymer formed by the method of claim 6. 12. A method of forming a recycled polymer blend, the method comprising: melt blending recycled polyethylene and recycled polypropylene to yield a melt blend; and combining the melt blend with up to 10 wt% of the biogenic block copolymer synthesized by the method of claim 1 to yield a recycled polymer blend. 13. The method of claim 12, wherein a weight ratio of the recycled polyethylene to the recycled polypropylene is in a range of 2:98 to 49:51 or 98:2 to 51:49. 14. A recycled polymer blend comprising: recycled polyethylene; recycled polypropylene; and the biogenic block copolymer formed by the method of claim 6. 15. The recycled polymer blend of claim 14, wherein recycled polymer blend comprises up to 10 wt% of the biogenic block copolymer. 16. The recycled polymer blend of claim 15, wherein the recycled polymer blend comprises up to 5 wt% of the biogenic block copolymer. 19 Attorney Docket No.: 09531-0546WO1 / UMN 2024-028 17. The recycled polymer blend of claim 16, wherein the recycled polymer blend comprises up to 3 wt% of the biogenic block copolymer. 18. The recycled polymer blend of claim 17, wherein the recycled polymer blend comprises about 1 wt% of the biogenic block copolymer. 19. The recycled polymer blend of claim 14, wherein a weight ratio of the recycled polyethylene to the recycled polypropylene is in a range of 2:98 to 49:51 or 98:2 to 51:49. 20. The recycled polymer blend of claim 14, comprising a 30:70 blend of the recycled polyethylene and the recycled polypropylene and about 1 wt% of the biogenic block copolymer. 20