Block copolymers and polymer-modified bitumen obtained therefrom

Abstract

Disclosed herein are linear block copolymers of the formula A-B-A' or A-B*B-A', wherein blocks A and A' are polystyrene blocks, block B is a poly(conjugated diene) block, and * is a coupling agent having a vinyl content of 10-60 mol%. The block copolymers have a polystyrene content of 20-35 wt%, relative to the total weight of the block copolymer, and a molecular weight of 200,000-300,000 g / mol. The block copolymers are useful with a variety of grades of bitumen and are valuable for producing homogeneous polymer-modified bitumen compositions having an effective combination of properties (e.g., acceptable viscosity, good elastic response to applied stress, and low irrecoverable creep compliance). The combination of vinyl content and polymerization technology allows for high solution concentrations during polymerization without resulting in excessively high processing viscosities.

Description

TECHNICAL FIELD

[0001] The present invention relates to block copolymers and their use in the production of polymer modified bitumen and derived bitumen compositions. BACKGROUND

[0002] It is known to use bitumen in the manufacture of materials for highway and industrial applications, such as asphalt. Bitumen is the primary hydrocarbon binder used in the field of road construction and civil engineering. In order to be used as a binder in these various applications, bitumen is expected to have certain mechanical properties, such as viscoelastic, adhesive and / or cohesive properties. The mechanical properties of bitumen and binder compositions comprising bitumen are measured by standardized tests, such as determining the softening point T sp , penetration and other rheological properties.

[0003] Polymer modified bitumen has been used to improve properties. However, there is still a need for enhanced binder formulations to further improve the performance of bitumen mixtures, such as improving the elastomer response, reducing fatigue cracking, reducing low temperature cracking and reducing rutting caused by load factors, weather conditions, etc., to improve the performance of the resulting road. SUMMARY

[0004] In one embodiment, a linear sequential block copolymer is disclosed. The block copolymer has the formula A-B-A' or (A-B)n-X-(B-A')m, where A and A' are polystyrene blocks, B is a poly(conjugated diene) block. n and m are > 1, and X is a coupling agent. The average vinyl content of block B is 10-60 mol%. The polystyrene content of the overall polymer is 20-35 wt%. The molecular weight of the copolymer is 200,000-300,000 g / mol.

[0005] In some embodiments, the block copolymer has the formula (A-B)n-X-(B-A')m, where the values of n and m are 1, and the block copolymer further comprises up to 25 wt% of a second block copolymer based on the total weight of the block copolymer, the second block copolymer having the structure (A-B)n-X-(B-A')m, where the values of n and m are > 1 and < 5.

[0006] In another embodiment, a polymer modified bitumen is disclosed. The polymer modified bitumen comprises or consists essentially of or consists of (i) a linear sequential block copolymer of the formula A-B-A' or (A-B) n -X-(B-A') m of the above, (ii) at least one base bitumen, and (iii) optionally at least one crosslinking agent.

[0007] In another embodiment, a method of making a polymer modified asphalt composition is described. The method comprises or consists essentially of or consists of forming a mixture of a block copolymer and an asphalt, optionally adding a crosslinking agent, mixing at 140-220 °C to form a polymer modified asphalt composition. The crosslinking agent can be based on a sulfur donor, a peroxide, or any other compound commonly used in the industry to crosslink styrene block copolymers in asphalt. DETAILED DESCRIPTION

[0008] The following terms as used in the specification have the following meanings:

[0009] "Molecular weight" refers to the styrene equivalent molecular weight (g / mol) of a polymer block or block copolymer. The molecular weight can be measured by gel permeation chromatography (GPC) using polystyrene calibration standards, as per ASTM 5296-19. The chromatograph is calibrated using commercial polystyrene molecular weight standards. The polymer molecular weight measured using a GPC so calibrated is the styrene equivalent molecular weight. When the styrene content of a polymer and the vinyl content of the diene segment are known, the styrene equivalent molecular weight can be converted to true molecular weight. The detector can be a combination of ultraviolet and refractive index detectors. The molecular weight expressed herein is measured at the peak of the GPC trace, which can be converted to true molecular weight, and is often referred to as the "peak molecular weight" (M p ) unless converted to true molecular weight as described above. The molecular weight cited refers to the "styrene equivalent peak molecular weight" unless converted to true molecular weight as described above.

[0010] The "vinyl content" of a polymer or block copolymer refers to the amount of vinyl groups produced when a conjugated diene is added via a 1,2- mechanism (resulting in an alkene or vinyl group adjacent to the polymer backbone). The vinyl content can be measured by nuclear magnetic resonance spectroscopy (NMR), typically expressed as mol% of conjugated diene moieties. The vinyl content in some embodiments can be tapered, present in blocks, or uniformly distributed. The vinyl content of a polymer can be controlled by the concentration of a microstructure control agent during polymerization at a constant temperature. If the dosage is constant, the vinyl distribution is substantially uniform. If the dosage is increased gradually during polymerization, the distribution is tapered. If the dosage is increased all at once, typically from zero to high, the vinyl is distributed in blocks that are low at the beginning and high at the end.

[0011] "Coupling efficiency" (CE) is expressed in % CE and is calculated from the GPC trace using the wt% of coupled polymer and the wt% of uncoupled polymer. The wt% of coupled polymer and uncoupled polymer is determined using the output of the differential refractometer detector. The signal intensity at a particular elution volume is directly proportional to the amount of material detected at that elution volume that corresponds to the molecular weight of a polystyrene standard. Thus, the area under the curve corresponding to the MW range of coupled polymer represents the wt% of coupled polymer, and the same for uncoupled polymer. The formula for % CE is:

[0012] 100 * (wt% of coupled polymer) / (wt% of coupled polymer + wt% of uncoupled polymer)

[0013] For example, if the coupling efficiency is 80%, the polymer will contain 20% diblocks and 80% triblocks and multi-arm blocks.

[0014] "Polystyrene content" or PSC refers to the weight percent of polymerized styrene in a block copolymer, calculated by dividing the sum of the molecular weights of all polystyrene blocks by the total molecular weight of the block copolymer. PSC can be determined using proton-NMR.

[0015] "Bitumen" and "asphalt" are used interchangeably to refer to the natural and manufactured forms of the material.

[0016] Asphalt (Europe) or "asphalt mixture" (USA) refers to the mixture of aggregate fraction and asphalt binder as the base material for the binder course of a road structure.

[0017] "Polymer modified asphalt" or PMA (USA) and "polymer modified bitumen" or PMB (Europe) refers to an asphalt binder, such as a "polymer modified bitumen" or "polymer modified asphalt" binder.

[0018] MSCR or "multiple stress creep recovery" test (also known as AASHTO TP70 and AASHTO MP19) refers to a creep and recovery test to assess the likelihood of binder permanent deformation without the need for separate tests such as elastic recovery, ductility, and force delay to indicate that the asphalt binder has been sufficiently polymer modified. In the MSCR test using a dynamic shear rheometer (DSR), an asphalt binder sample is subjected to a 1 second creep load followed by a 9 second recovery, with multiple stress levels of 0.1 and 3.2 kPa, 10 cycles at each stress level.

[0019] The present invention relates to a linear sequential styrene block copolymer (SBC) composition that is particularly optimized for performance grade paving applications using the multiple stress creep recovery (MSCR) test. The SBCs can be referred to herein as "linear sequential block copolymers" because even though the production method in some embodiments involves the use of a coupling agent to couple, the structure is sequential and the SBC compositions can include some multi-armed species.

[0020] Linear sequential styrene block copolymers (SBCs) The SBCs comprise linear block copolymers having the formula A-B-A' or (A-B)n X-(B-A')m, where X is a coupling agent, n and m are > 1.

[0021] The blocks A and A' are vinyl aromatic blocks having different molecular weights, where styrene is the major component, and a structurally related vinyl aromatic monomer selected from the group consisting of ortho-methylstyrene, para-methylstyrene, para-tert-butylstyrene, 2,4-dimethylstyrene, alpha-methylstyrene, vinyl naphthalene, vinyl toluene, vinyl xylene, 1,1-diphenylethylene, or combinations thereof is the minor component. In certain embodiments, the A and A' blocks have different molecular weights, a smaller block and a larger block, where the difference in MW of the smaller block and the larger block is 3000-8000, or preferably 3500-7000.

[0022] In some embodiments, the PSC of the SBC is 20-35 wt%, or 23-33 wt% or 27-33 wt% or 29-33 wt% relative to the total weight of the SBC.

[0023] The block B is a conjugated diene block, where the diene can be any conjugated diene. Alternatively, the conjugated diene has 4-8 carbon atoms. In some embodiments, the conjugated diene is substantially butadiene monomer or isoprene monomer, or butadiene monomer or isoprene monomer that includes a minor proportion (e.g., up to 10 wt%) of a structurally related conjugated diene (e.g., 2,3-dimethyl-1,3-butadiene, isoprene, 1,3-pentadiene, farnesene, myrcene, and 1,3-hexadiene). Alternatively, the conjugated diene block can be prepared using substantially pure butadiene or substantially pure isoprene. In some embodiments, the conjugated diene block includes a mixture of butadiene and isoprene monomers. In some embodiments, the conjugated diene block includes residual coupling agent.

[0024] In some embodiments, the vinyl content of block B is 20-60 mol%, or 25-55 mol%, or 35-45 mol%, or > 30 mol%, or < 50 mol%. It is recognized that the vinyl content is averaged and that by varying the addition of microstructure control agents, products can be produced with a gradual decrease or blocky and non-uniform vinyl content. In some embodiments, the vinyl content is regularly distributed across the conjugated diene block, or is distributed in a gradient across the conjugated diene block, or is present in different blocks of standard and high vinyl content, where standard refers to the level typically obtained when polymerizing without microstructure modifiers, thus less than 20%, or typically in the range of 7-15%, and high refers to the level obtained with microstructure modifiers, ranging from > 20%, such as 22-50% or 25-40%, or up to 75%. In some embodiments, the vinyl content of block B is controlled by the addition of microstructure modifiers and / or the order of addition and control of reaction temperature.

[0025] In some embodiments, the SBC has the formula A-B-A' or (A-B)n X-(B-A')m, where A and A' together form the polystyrene content of the block copolymer molecule, and m and n have a value of 1. In some embodiments, the SBC further comprises up to 20 wt% or < 25 wt% or 3-15 wt% of a block copolymer having the structure (A-B)n X-(B-A')m, where n and / or m is > 1, or has a value of up to 5, or is 2-4.

[0026] In some embodiments, the SBC has a molecular weight of 200,000-300,000 g / mol, or > 210,000 g / mol, or < 290,000 g / mol, or 220,000-270,000 g / mol.

[0027] Preparation of linear sequential SBCs The SBC can be prepared by sequential polymerization or by polymerization and coupling. Polymerization can be achieved by contacting the appropriate monomers with an organic alkali metal compound in a suitable solvent at temperatures ranging from -150°C to 200°C or > -100°C or 0°C to 110°C or < 150°C, or at ambient temperature.

[0028] In some embodiments, the block copolymer is prepared by anionic polymerization techniques, with sequential polymerization of styrene to form a polystyrene block, followed by continued polymerization by the addition of butadiene to form a butadiene block, and polymerization of styrene to form a third block. Sequential polymerization ensures that each polymer molecule contains smaller and larger styrene blocks, if desired, and coupling of the polystyrene-polybutadiene A-B and A'-B di-blocks with smaller and larger styrene blocks will result in a statistical distribution of different size styrene blocks on the molecule. Additionally, sequential polymerization minimizes the presence of residual di-block material.

[0029] In some embodiments, the block copolymer is prepared by polymerization and coupling. Coupling techniques can better control the size of the styrene blocks and reduce the viscosity of the polymer solution in the polymerization process, as the viscosity of the living polymer depends on the length of the two diblock living polymers due to the association of the living polymers. Lower viscosity allows higher concentration of polymer per batch, thus increasing the run speed and reducing the energy cost involved in the solvent removal process.

[0030] In embodiments for preparing SBCs with different vinyl aromatic blocks, the process starts with sequential anionic polymerization of styrene with an organic alkali metal compound to form a monomolecular weight polystyrene block, or by adding additional organic alkali metal compound during styrene polymerization to form a mixture of different molecular weight polystyrene blocks. The polymerization is continued by adding butadiene to form a portion of the target butadiene block, followed by addition of a microstructure modifier and subsequent addition of the remaining butadiene to form a diblock for coupling or a sequential polymer prior to the subsequent styrene addition. The butadiene polymerized prior to the addition of the microstructure modifier has a low vinyl content, while the butadiene polymerized after the addition of the microstructure modifier forms a different high vinyl portion in the polybutadiene block. The diblock can be coupled to complete a linear block copolymer with different high and low vinyl polybutadiene blocks.

[0031] In some embodiments, the coupling agent is selected from difunctional and polyfunctional molecules capable of coupling living anionic polymers, such as methoxysilane or halosilane, epoxide, adipate, benzoate, carbon dioxide, dimethyldimethoxysilane, dimethyldichlorosilane, diethyl adipate, and mixtures thereof. In some embodiments, the use of coupling agents with more than 2 functional groups can produce SBCs that are essentially linear products at suitable dosage levels, such as (A-B)nX-(B-A')m, where n and m have a value of 1, and very few (<20 wt% or <10 wt%) of n and / or m have a value >1.

[0032] In embodiments to increase the vinyl content of the conjugated diene portion of the SBC or to control the vinyl content of block B, a microstructure modifier is added and / or the reaction temperature is added and controlled sequentially. Examples of the modifier include, but are not limited to, polar compounds such as ethers, amines and other Lewis bases, and dialkyl ethers of diols. The most preferred modifier is selected from dialkyl ethers of ethylene glycol, which contain the same or different terminal alkoxy groups and optionally carry alkyl substituents on the ethylene group, such as monoglyme, diglyme, diethoxyethane, 1,2-diethoxypropane, 1-ethoxy-2,2-tert-butoxyethane, of which 1,2-diethoxypropane is most preferred.

[0033] Use of styrene block copolymers (SBCs) In some embodiments, the SBC is used to modify asphalt to provide a polymer modified asphalt (PMB) with improved physical properties at the same polymer concentration (weight) as compared to other types of block copolymers, as discussed further below.

[0034] Preparation of PMB The PMB composition can be prepared by mixing the linear sequential SBC with asphalt and other suitable components. Any type of asphalt can be used to prepare the PMB. This can be advantageous where the quality / composition / source of the asphalt can vary. A variety of additives can be used in conjunction with the block copolymer to form the PMB composition. Examples include non-polymeric additives, non-reactive polymers, and reactive polymers. Non-polymeric additives include acid-based additives, asphalt flux oil, liquid plasticizer, hydrogen sulfide scavengers, amine scavengers, acid anhydrides such as linear and cyclic acid anhydrides, sulfur sources, and combinations thereof. Examples of acid-based additives include one or more phosphoric acid and polyphosphoric acid.

[0035] Asphalt flux oil includes many types of oils used to modify asphalt and are the end products in the distillation of crude oil. They are non-volatile oils that are mixed with asphalt to soften it. They can be aromatic, paraffinic, or naphthenic. The asphalt flux oil can also be any renewable produced vegetable oil or bio-oil. Mixtures of two or more asphalt flux oils can also be used. The asphalt flux oil can also be a renewable oil of mineral or biological origin.

[0036] In one embodiment, the SBC and at least one base asphalt are first mixed, and then a sulfur-based crosslinking agent is optionally added to the mixture. Optionally, an acid-based additive can be introduced. The resulting mixture is mixed at a temperature of 140 °C - 220 °C or > 150 °C or < 200 °C to produce the PMB. High shear milling processes or low shear mixing processes known in the art can be used.

[0037] In some embodiments, the PMB composition comprises 1 - 15 wt% or 1 - 10 wt% or 2 - 6 wt% of the SBC, based on the total weight of the PMB composition.

[0038] Use of PMB compositions The PMB is used in applications including, but not limited to, asphalt pavements and roofing. Examples include road paving materials for new pavements, for pavement maintenance, and for pavement repair, in forms including hot mix asphalt, cold mix asphalt, warm mix asphalt, emulsified asphalt based bitumen (chip seal, slurry seal, micro surfacing, fog seal, etc.), asphalt crack filler, and tack coat.

[0039] The PMB is useful for applications where relatively low viscosity, low permeability, and high softening point T spRoofing applications. Examples include modified bitumen membranes, self-adhered membranes, impact resistant shingles, laminates, tile adhesives, shingle bodies, sheets or rolls, and clean-up asphalt or mastic applications.

[0040] In addition to paving and roofing applications, other applications include, but are not limited to, pipe coatings, sealants, sound barrier membranes, carpet or railroad structures.

[0041] Performance of polymer modified bitumen (PMB) For paving compositions, it was observed that PMBs made using linear sequential SBCs have advantageous %R MSCR.

[0042] The compositions exhibit better MSCR performance at a given wt% SBC in the PMB compared to PMBs made using other types of block copolymers of the prior art, such as star block copolymers or linear coupled block copolymers. Alternatively, the PMBs made can exhibit similar MSCR performance at lower polymer concentrations. Thus, the PMBs have higher efficiency based on the amount of polymer.

[0043] PMB compositions have superior performance, in part due to the elastomeric modified bitumen. One of the parameters that measures the effectiveness of the polymer in the PMB is the "% Recovery" (also referred to herein as "%R") measured using the MSCR (Multiple Stress Creep Recovery) test according to ASTM D7405 test method at a given shear stress. The %R value is defined by equation (1):

[0044] %R = 100 * (recoverable shear strain / peak strain) Equation (1)

[0045] where the recoverable shear strain is given by the difference between the instantaneous shear strain and the non-recoverable shear strain. The MSCR test is also a standard method to evaluate the rut resistance (especially at high temperatures) of asphalt mixtures produced using PMBs. To compare the effectiveness of a given PMB with a reference bituminous material, the parameter %R as described above can be used.

[0046] This parameter can also be used to study the influence of different variables on the overall performance of the PMB, such as the type of bitumen used to make the PMB, the curing temperature or curing time, the wt% of SBC in the PMB. The variability of bitumen can be caused by a number of factors, such as the source of the bitumen, the process used to make the bitumen, and the composition of the bitumen (blended components). When the bitumen grade varies, it is generally desirable to obtain a high %R value that does not vary much with the chemical nature of the bitumen, resulting in more stable performance under actual road / pavement conditions as well as conditions during road construction.

[0047] In some embodiments, the PMB made after crosslinking exhibits an improvement in %R of at least 10% or at least 12% or at least 15% or at least 20% at 3.2 kPa and 64°C relative to a PMB made with a linear coupled block copolymer having a molecular weight of 173,000 g / mol, a vinyl content of 10 mol%, and a polystyrene content of 31% measured at a polymer concentration of 3 wt% (“Comparative SBC”) according to ASTM D7405.

[0048] The PMB made also has a higher softening point Tm sp In some embodiments, the PMB after crosslinking has a softening point Tm sp (in degrees Celsius) that is at least 5°C higher than the Comparative SBC measured at a polymer concentration of 9 wt% according to ASTM D36. In some embodiments, the PMB made has a Tm sp that is at least 10°C higher than a PMB made with a linear sequential block copolymer having a MW of 150,000 g / mol, a vinyl content of 40%, and a polystyrene content of 30% measured at a polymer concentration of 9 wt% according to ASTM D36. Examples

[0049] The following non-limiting examples are provided to illustrate the performance of linear sequential SBCs and PMBs made therefrom. In the examples:

[0050] “RTFO” stands for Rotating Thin Film Oven.

[0051] “DSR” refers to Dynamic Shear Rheometer.

[0052] “ODSR” stands for Original Dynamic Shear Rheometer, indicating a test performed using a dynamic shear rheometer on unaged asphalt composition.

[0053] “MSCR” refers to Multiple Stress Creep and Recovery. In the MSCR test, the parameter %R represents the percent of recoverable strain and is used to assess the elastic recovery of polymer modified asphalt.

[0054] “Jnr” represents the non-recoverable creep compliance

[0055] “BBR m average” refers to the average m value measured using a Bending Beam Rheometer.

[0056] “BBR S average” refers to the average S value measured using a Bending Beam Rheometer.

[0057] δTc is given by the numerical difference between the low continuous grade temperature determined by the Bending Beam Rheometer (BBR) stiffness criterion (temperature at which the stiffness S equals 300 MPa) and the low continuous grade temperature determined by the BBR m value (temperature at which m equals 0.300).

[0058] G* • sin(δ) represents the SuperPave fatigue parameter.

[0059] "PAV" stands for Pressure Aging Vessel, which is used to simulate long term aging of asphalt binders.

[0060] Example of C260-2 block copolymer prepared: 34.5 kg of styrene was added to 1032 kg of cyclohexane at 40-50°C, followed by the addition of 0.88 kg of a 12% sec-butyllithium solution. The reaction was complete after 39 minutes. Thereafter, 169 kg of butadiene was added over 58 minutes. The polymerization was allowed to proceed for 77 minutes. Thereafter, a second portion of 34.5 kg of styrene was added over 10 minutes. The polymerization was allowed to proceed for 52 minutes, after which 63 grams of methanol were added to terminate the polymerization. After the reaction mixture was cooled, 0.2% of a phenolic antioxidant, based on the weight of the polymer, was added for stabilization. The product C260-2 was isolated by steam stripping to give white crumb.

[0061] Examples of block copolymers C260-8 and C275-1 These SBCs have an ABA' structure, where the difference in MW of the A and A' blocks is 5300 g / mol and 5100 g / mol, respectively. These were prepared by the same procedure as described above, with the addition of diethoxypropane after the polymerization of the styrene but before the addition of butadiene. The amounts and reaction conditions are listed in Table 1.

[0062] Table 1

[0063] Polymer C260-2 C260-8 C275-1 Styrene (kg) 34.5 34.5 30 Cyclohexane (kg) 1032 1032 1032 sec-Butyllithium solution (kg) 0.88 0.88 0.77 Reaction time (min) 39 64 63 Diethoxypropane (g) 0 204 204 Butadiene (kg) 169 169 179 Reaction time (min) 77 101 76 Styrene (kg) 34.5 34.5 30 Reaction time (min) 52 27 30 Methanol (g) 63 63 54

[0064] In addition to the SBCs described above, the following block copolymers were used (properties as shown in Table 2). These polymers have similar MWs to the polystyrene blocks.

[0065] U-119-X is a linear sequential block copolymer.

[0066] U-1101 is a linear triblock copolymer.

[0067] C246-8 is a star block copolymer.

[0068] U-1184 is a branched triblock (star) copolymer.

[0069] Table 2

[0070]

[0071] *CE - Coupling efficiency; PS - Polystyrene content; MW - Molecular weight x 1000 g / mol.

[0072] Examples of preparation of polymer modified bitumen In this example, each mixture was prepared by mixing 2.5 wt% of a ground form of the block copolymer and 97.5 wt% of the asphalt at 180°C for 1 hour under nitrogen protection in low shear mode. After 1 hour, 0.1 wt% elemental sulfur was added to the combination of asphalt and block polymer and mixing was continued at 180°C for 6 hours. The PMB mixtures were sampled for storage stability, RTFO DSR at 64°C, and MSCR testing. Results are shown in Table 3. The quantities "MSCR %R, 3.2 kPa, 64°C top" and "%R, 3.2 kPa, 64°C bottom" refer to the difference in %R between the top and bottom layers of the PMB mixture as measured according to ASTM D7173. Desirably, the PMB mixture has a low viscosity at 135°C, low separation (%R) values (negative values or close to 0) for the top and bottom layers, high RTFO DSR, and high RTFO MSCR.

[0073] Table 3

[0074]

[0075] All PMB samples had an acceptable viscosity of less than 3.0 Pa.s at 135°C. PMB samples 9 and 10 showed no phase separation upon storage. Sample 8 showed some phase separation upon storage. All PMB samples showed high RTFO DSR performance. PMB sample 9 showed the best combination of viscosity, phase stability, and MSCR performance. PMB with high MSCR performance (excellent elastic properties) can be valuable in paving applications. Using PMB with low viscosity or low block copolymer content can result in better overall performance and savings in material costs for roads.

[0076] The suitability of block copolymers C260-8, U-119-X, U-1101, and U-1184 in obtaining PMB formulations that pass the PG64E-22 / PG76-22 performance grade parameters was compared. For each polymer sample, 2 PMB samples were prepared, one with 3 wt% of the polymer and the other with 2 wt% of the polymer. In each case, the PMB formulation was prepared by mixing the indicated wt% of the polymer in ground form and asphalt at 180°C for 1 hour under nitrogen protection in low shear mode. After 1 hour, 0.1 wt% elemental sulfur was added and mixing was continued at 180°C for 8 hours. The difference in %R between the top and bottom layers of the PMB mixture as measured according to ASTM D7173 gave the storage stability.

[0077] Interpolated polymer dosage based on the following criteria: RTFO G* / sin(delta), 76°C = 2.2 kPa, Jnr, 3.2 kPa, 64°C < 0.5, see Table 5.

[0078] The data show that PMB compositions based on block copolymer C260-8 have better performance than PMB compositions made using block copolymers U-119-X, U-1101, and U-1184. For example, PMB composition 14 is more effective than PMB compositions 16, 18, and 20 based on the wt% of block copolymer to achieve a favorable MSCR%R.

[0079] Table 4

[0080]

[0081] Table 5: Interpolated polymer dosage based on the following criteria: RTFO G* / sin(delta), 76°C = 2.2 kPa, Jnr, 3.2 kPa, 64°C < 0.5

[0082]

[0083] From the interpolated value data, it can be seen that PMB obtained using block copolymer C260-8 shows the most favorable overall performance at the lowest wt% content of polymer in asphalt compared to polymer example U-119-X (a suboptimal polymer).

[0084] Even with a change in asphalt binder component, block copolymer C260-8 forms PMB with superior MSCR performance. Block copolymers C260-8 and U-1101 were selected for this study. For each polymer sample, 2 PMB samples were prepared, one sample with 3 wt% polymer and the other sample with 2 wt% polymer, using the same procedure as previously described. Interpolated polymer dosage based on the following criteria: RTFO G* / sin(delta), 76°C = 2.2 kPa, Jnr, 3.2 kPa, 64°C < 0.5 was determined. Data are shown in Tables 6 and 7.

[0085] Table 6

[0086]

[0087] Table 7: Interpolated polymer dosage based on the following criteria: Jnr, 3.2 kPa, 64°C < 0.5 to target PG 64E-28 grade

[0088]

[0089] Table 8 shows the Tg of PMB made using polymers C260-8, U-1101, and U-1184.sp PMB made with polymer C260-8 had the highest ring and ball T sp PMB made with linear order block copolymer C260-8 was valuable in paving applications with high ring and ball T sp .

[0090] Table 8

[0091]

[0092] Table 8 also shows that at a given polymer wt%, PMB based on polymer C260-8 had higher T sp than PMB samples based on block copolymers U-1101 and U-119-X in addition to showing %R improvement (see Table 4). Thus, PMB based on block copolymer C260-8 had high efficiency per unit weight of polymer.

[0093] Comparative performance of block copolymers C260-8, U-119-X and U-1101 at different asphalt grades (A, B and C) was also investigated. All mixtures were prepared under the conditions listed in Table 9.

[0094] Table 9: Preparation of formulations

[0095]

[0096] The performance of PMB 26-37 made from polymers C260-8, U-119-X and U-1101 is shown in Table 10. For different asphalt grades, PMB made from polymer C260-8 had satisfactory penetration T sp while producing relatively low viscosity. The % phase separation was determined as follows. Freshly prepared PMB was poured into a 1 liter metal can. The can was then capped and placed in an oven at 160°C for 5 days. The sample was then removed and quickly cooled to room temperature to solidify the PMB sample. The bottom of the metal can was then removed and the side of the can was heated until the PMB sample inside the can slid out. The PMB sample was probed from the bottom to the top with a needle to detect whether phase separation of the polymer had occurred in the sample (in a phase separated sample, the polymer floated to the top of the sample, significantly changing the physical properties of the top and bottom portions). The sample was then cut at a height with a hot knife to separate the polymer rich portion and the polymer lean portion. The weight of the polymer rich portion of the sample was then weighed, and this weight was divided by the total weight of the sample and converted to a percentage. 100% polymer rich indicated that the polymer remained completely dispersed throughout the sample. 50% phase separation indicated that the polymer rich phase accounted for 50% of the total sample weight after the test was completed. 100% polymer rich was the ideal test result.

[0097] Table 10

[0098]

[0099] The data show that PMB of Example 26 exhibits the highest T sp , permeability and viscosity, resulting in the best overall performance. PMB composition 26 has a T sp , permeability and viscosity.

[0100] Although the terms "comprising" and "including" have been used herein to describe various aspects, the terms "consisting essentially of and "consisting of" can be substituted therefor to provide more specific aspects of the application, and are also disclosed.

Claims

1. A polymer modified asphalt composition comprising: at least one asphalt; and 1-25 wt% of a block copolymer, relative to the total weight of the composition, wherein the block copolymer has the formula A-B-A' or (A-B)n - X - (B-A')m, wherein: A and A' are vinyl aromatic blocks having different molecular weights, and A and A' have a difference in molecular weight of 3000-8000 g / mol, B is a conjugated diene block having an average vinyl content of 20-60 mol%, n and m > 1, X is a coupling agent; wherein the block copolymer has a polystyrene content of 23-35 wt%, relative to the total weight of the block copolymer, and the block copolymer has a peak molecular weight of 220,000-270,000 g / mol; wherein the polymer-modified asphalt composition exhibits at least 10% improvement in recovery at 3.2 kPa and 64 o C after crosslinking, relative to a polymer-modified asphalt having a linear block copolymer with a molecular weight of 173,000 g / mol, a vinyl content of 10 mol%, and a polystyrene content of 31%, measured at a polymer concentration of 3 wt% according to ASTM D7405.

2. The polymer modified asphalt composition of claim 1, wherein the block copolymer has the formula (A-B)n - X - (B-A')m, wherein the values of n and m are 1.

3. The polymer modified asphalt composition of any one of claims 1-2, wherein the block copolymer further comprises up to 25 wt% of a second block copolymer having the structure (A-B)n - X - (B-A')m, based on the total weight of the block copolymer, wherein the values of n and m are > 1 and < 5.

4. The polymer modified asphalt composition of any one of claims 1-2, wherein the block B of the block copolymer has a vinyl content of 25-55 mol%.

5. The polymer modified asphalt composition of any one of claims 1-2, wherein the vinyl is distributed uniformly or in a gradient across the conjugated diene block B of the block copolymer.

6. The polymer modified asphalt composition of any one of claims 1-2, wherein the vinyl is distributed in one or more distinct blocks of the conjugated diene block B of the block copolymer having a vinyl content of < 20% or > 22%.

7. The polymer modified asphalt composition of any one of claims 1-2, wherein the block copolymer is prepared by any one of a process of sequential anionic polymerization or sequential anionic polymerization and then coupling.

8. The polymer modified asphalt composition of claim 7, wherein the block copolymer has the formula A-B-A', and wherein the block copolymer is prepared by sequential anionic polymerization.

9. The polymer modified asphalt composition of claim 7, wherein the block copolymer has the formula (A-B)n - X - (B-A')m, and wherein the block copolymer is prepared by sequential anionic polymerization and then coupling with a coupling agent.

10. The polymer modified asphalt composition of claim 9, wherein the coupling agent is selected from the group consisting of a methoxysilane, a halosilane, an epoxide, an adipate, a benzoate, carbon dioxide, and mixtures thereof.

11. The polymer-modified asphalt composition of claim 10, wherein the coupling agent is selected from the group consisting of dimethyldimethoxysilane, dimethyldichlorosilane, diethyl adipate, and mixtures thereof.

12. The polymer-modified asphalt composition of claim 7, wherein at least one microstructure modifier is added to the polymerization process to control the ethylene content of block B, and wherein the microstructure modifier is selected from the group consisting of ethers, amines, dialkyl ethers of diols, and mixtures thereof.

13. The polymer-modified asphalt composition of any one of claims 1-2, further comprising at least one crosslinking agent, and optionally other additives.

14. The polymer-modified asphalt composition of claim 13, wherein the composition is used in an asphalt paving product or an asphalt roofing product.

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