Patent Application: US-201313962380-A

Abstract:
a method of preparing a malleable and / or self - healing polymeric or composite material is provided . the method includes providing a polymeric or composite material comprising at least one alkene - containing polymer , combining the polymer with at least one homogeneous or heterogeneous transition metal olefin metathesis catalyst to form a polymeric or composite material , and performing an olefin metathesis reaction on the polymer so as to form reversible carbon - carbon double bonds in the polymer . also provided is a method of healing a fractured surface of a polymeric material . the method includes bringing a fractured surface of a first polymeric material into contact with a second polymeric material , and performing an olefin metathesis reaction in the presence of a transition metal olefin metathesis catalyst such that the first polymeric material forms reversible carbon - carbon double bonds with the second polymeric material . compositions comprising malleable and / or self - healing polymeric or composite material are also provided .

Description:
provisional patent application no . 61 / 680 , 982 , filed on aug . 8 , 2012 , is incorporated by reference herein . in the methods and compositions provided , one or more homogeneous or heterogeneous transition metal olefin metathesis catalysts can be used . each catalyst can be any homogeneous or heterogeneous olefin metathesis catalyst , including but not limited to , a ruthenium - based olefin metathesis catalyst ( including the first and second generation of grubbs &# 39 ; catalysts , the first and second generation of hoveyda - grubbs catalysts , and various modifications of the above - mentioned ruthenium - containing olefin metathesis catalysts , such as the substitution of one or more ligands in these catalysts with other type of ligands ), any molybdenum - or tungsten - based olefin metathesis catalyst ( commonly referred to as the shrock &# 39 ; s catalysts ), various hetereogeneous olefin metathesis catalysts ( such as wo 3 / sio 2 or re 2 o 7 / sio 2 ), and combinations thereof . a polymeric material , composite material , or polymeric composition of the methods and compositions can comprise one or more olefin - containing polymers . any olefin - containing polymer can comprise an olefin - containing main chain . in some embodiments , any polymer can be polybutadiene , polyisoprene , butyl rubber , polynorbornene , polycyclooctene , polycyclooctadiene , unsaturated polyesters , polystyrene - b - polybutadiene , polystyrene - b - polybutadiene - b - polystyrene , various random / block / graft copolymers containing various levels of alkene functionality on either polymer backbones or side chains , as well as various modifications ( such as partial hydrogenation or functionalization , for example , by hydrosilation , alkene addition , or diels - alder reaction ) of the above - mentioned polymers , and combinations thereof . in some embodiments , the polymeric material can be a composite material having at least one of the above - mentioned alkene - containing polymers as the polymer matrix . composites can be formed by either physical blending or chemical bonding of organic , inorganic , semiconducting or metallic particles in various geometry and sizes with at least one of the above - mentioned alkene - containing polymers as matrix material . any polymer of the polymeric material or composite can comprise a polymer network . in the methods and compositions , healing can be considered to occur when the ultimate tensile strength of joined polymeric materials is ≧ 30 % of a control undamaged polymeric material . the inventor has reported the use of olefin metathesis for generating adaptive , malleable polymer networks . ( 35 ) introduction of low levels of the grubbs &# 39 ; second - generation ru metathesis catalyst into cross - linked pbd network makes it malleable at room temperature while retaining its insolubility . the malleability arises from ru - catalyzed olefin metathesis reaction , which covalently shuffles c — c double bonds in bulk network and rearranges network topology in response to external force . the inventor reasoned that the same mechanism can be employed to reversibly form c — c double bonds at fracture interfaces , which should result in strong covalent self - healing without the need of heat or light . to show that such a mechanism occurs , into a cross - linked pbd network ( cross - linking density ˜ 3 . 6 × 10 − 4 mol / cm 3 ) was loaded a second - generation grubbs &# 39 ; ru metathesis catalyst at 0 . 0050 , 0 . 0075 , and 0 . 010 mol % ( relative to the molarity of olefin ), respectively . for self - healing tests , a sample was first cut with a razor blade into two separate parts and the cut faces were pressed together . then the sample was let to heal in a teflon mold under different conditions . under moderate compressions ( 10 - 30 kpa ), two completely cut samples could heal effectively at room temperature or even under cooling conditions . in the following examples , detailed self - healing studies of this system under various conditions ( different catalyst loading , compression pressure , temperature , etc ) are described . firstly , the self - healing efficiency of pbd network loaded with different amounts of the ru catalyst ( fig2 ) was investigated . all cut samples were healed in mold at room temperature under 20 kpa of compression . at 0 . 010 and 0 . 0075 mol % ru catalyst loading , the cut samples self - healed completely and recovered their original mechanical properties after 1 hour and 3 hours healing , respectively ( fig2 a & amp ; b ). the quantitative healing was also evidenced by the observation that , during the tensile tests , the healed samples finally broke statistically at different positions instead of just at the healing interface . at the lowest catalyst loading ( 0 . 0050 mol %), the sample healed at a slower rate , but still recovered 95 % of the ultimate tensile strength after 6 hours of healing ( fig2 c ). as expected , higher catalyst loading accelerates the self - healing process because more ru catalyst should speed up olefin metathesis reaction at the healing interface . for all three samples , self - healing occurred faster in the beginning and then gradually leveled off ( fig2 d ). presumably , initial olefin metathesis reaction at the healing interface would contribute more effectively to new bonds formation between the two cut surfaces . with an increasing number of bonds forming between the healing surfaces , olefin metathesis reactions in later stage would contribute less to new bonds formation between the interfaces . as will be discussed later ( fig6 b ), the catalyst - free control pbd network only shows minimal healing capability ( vide infra ). next , the effect of compression pressure on self - healing efficiency of the materials was investigated . thus , 10 kpa , 20 kpa and 30 kpa of compression pressure was applied , respectively , to two freshly cut specimens with 0 . 0075 mol % of ru catalyst loading and let the sample heal at room temperature . as shown in fig3 , a moderate pressure is necessary for the healing and the sample heals more efficiently at higher compression pressure . for example , the strain at break recovered to respective 45 %, 78 %, and 90 % of the original sample after 1 hour of healing under compression pressure of 10 , 20 , and 30 kpa , respectively ( fig3 ). a couple of factors should be noted here . first , as a covalent 3d network , the cross - linked pbd chains have limited long - range translational mobility at the fracture interface to facilitate the healing process . second , as a very non - polar polymer for pbd , there are no strong molecular interactions to spontaneously attract the two cut surfaces together . third , the healing experiments were conducted at room temperature or under cooling conditions , without inputting any external energy in heat or light . given the microscopic roughness of the cut surfaces and the three factors discussed above , a moderate pressure is necessary to bring the two cut surfaces into molecular contact so that olefin cross metathesis between the two surfaces can occur . higher compression pressure ( fig3 a ) would bring the polymer chains from the two cut surfaces closer to each other , hence more efficient metathesis between the two surfaces and faster healing . to find out if such self - healing materials would be generally applicable at ambient conditions , the temperature dependence of their self - healing behavior was investigated . first , the temperature dependence of the ru catalyst activity was studied via bulk stress relaxation experiments ( 35 ) which shows that the relaxation time of the materials decreases with increasing temperature ( fig4 a ). quantitative correlation of viscosity - temperature data follows a simple arrhenius law ( 36 ) with activation energy of 25 . 8 kcal / mol , a value agreeing well with literature reported value ( 23 . 0 ± 0 . 4 kcal / mol ) for olefin metathesis reaction using the same catalyst ( 37 ) based on this activation energy value , the olefin metathesis reaction is estimated to accelerate by ˜ 5 times for every increase of 10 ° c . self - healing tests on a pbd sample were carried out at four different temperatures : 5 , 15 , 22 ( room temperature ) and 30 ° c . at constant catalyst loading ( 0 . 0075 mol %) and compression pressure ( 20 kpa ), the sample healed faster at higher temperature ( fig5 ). for example , while it takes three hours to fully heal the sample at room temperature ( fig5 b ), a slight heat ( 30 ° c .) enabled the sample to completely heal after only one hour ( fig5 a ). this can be attributed to the accelerated olefin metathesis reaction at higher temperature as discussed previously ( fig4 ). capitalizing the high healing efficiency of this system , we further tested healing at cooling condition . while cooling decreases the catalyst activity and slows down the healing process , the sample could still recover ˜ 94 % and ˜ 90 % of tensile strength at 15 ° c . after 9 hours ( fig4 c ) and 5 ° c . after 24 hours , respectively ( fig5 d ). to the inventor &# 39 ; s knowledge , this is the first example of a dynamic covalent polymer that can self - heal efficiently at sub - ambient temperature . the quantitative comparison of temperature - dependence for self - healing efficiency for this sample is shown in fig5 e . the effectiveness and high healing efficiency of this system was further demonstrated by the following experiment in which a ru - loaded sample healed with a corresponding control pbd sample with the ru catalyst removed by treating with vinyl ether . ( 37 , 38 ). it was reasoned that with one surface containing the ru catalyst , olefin metathesis reaction could still occur at the interface , forming new c — c bonds to connect with the other surface containing no ru catalyst . indeed , at room temperature and 20 kpa pressure , the ru - loaded sample healed with the ru - free samples with time ( fig6 a ). after three hours of healing , the sample recovered ˜ 80 % of the maximal strain . this offers a promising new strategy for healing mechanical damages : filling the crack of a normal catalyst - free pbd network with pbd containing a small amount of the ru catalyst , olefin metathesis between the catalyst - free surface of the fractured sample and the newly added ru - loaded pbd would result in covalent healing of the crack . in sharp contrast , two pieces of freshly cut ru - free control sample showed only minimal healing capability ( fig6 b , ˜ 15 % recovery of the maximal strain ). presumably , the minimal healing of the control sample could be due to diffusion of some long dangling polymer chains across the interface . ( 39 ) it should be noted that the cross - linked pbd networks used in this study contain minimal soluble polymers . the fraction of soluble polymers for ru - loaded pbd networks by repetitive extraction with a good solvent , n - heptane was quantitatively investigated . for example , for the most commonly used pbd samples in this study ( ru loading of 0 . 0075 mol %), 2 . 7 %, 1 . 0 % and 0 . 8 % weight loss , respectively , was observed after three cycles of 1 - hour extractions . based on this data , it was concluded that the contribution of diffusion of soluble polymers to healing should be insignificant , which agrees with the minimal healing observed for the control sample ( fig6 b ). lastly , the high effectiveness of olefin metathesis for self - healing is demonstrated by another experiment . instead of loading the ru catalyst to the bulk sample , a small amount of ru catalyst was applied only to the fracture surfaces of a pristine pbd network containing no ru catalyst . since healing occurs at the fracture interfaces , it was reasoned that only a small amount of ru catalyst at the fracture interface is necessary to catalyze the c ═ c bond metathesis between the two surfaces for healing . in one set of tests , 1 . 25 , 2 . 5 , and 5 . 0 μg of ru catalyst , respectively , was evenly applied onto both fracture surfaces ( 10 mm × 2 mm ), which were subsequently pressed together at 20 kpa for healing ( fig7 a ). in another set of experiments , the same total amounts of ru catalyst were applied to only one fracture surface , which was then pressed to a pristine pbd cut surface without any catalyst ( fig7 b ). visually , the colored ru catalyst resides only at the fracture interface . in both cases , the samples healed very effectively ( fig7 a & amp ; b ). in sharp contrast , the identical samples without applying any ru catalyst at fracture interfaces showed very minimal healing ( red curves in fig7 a & amp ; b ). besides further demonstration of the effectiveness of the healing method via olefin metathesis , this last result is significant for a few reasons . firstly , by applying ru catalyst only to fracture surfaces , self - healing can be achieved without introducing malleability into the bulk sample . as demonstrated previously , loading ru catalyst into a bulk pbd network makes it malleable . ( 35 ) while malleability is beneficial for some applications , shape persistence is desirable for some other applications . by applying a very small amount of ru catalyst only onto the fracture interfaces , this provides an option to achieve effective self - healing while maintaining shape persistence . indeed , no appreciable shape change for samples was observed during these healing tests . secondly , this new approach not only reduces the catalyst quantity , but , more importantly , offers a practical method to heal pristine pbd networks without requiring any pre - treatment for the bulk samples . in summary , this is a first reported example of olefin metathesis - mediated self - healing polymer based on dynamic exchange of strong covalent c — c double bonds . due to the high healing effectiveness and efficiency , for the first time a bulk polymer could effectively heal via dynamic covalent bond formation at sub - ambient temperature . by introducing a very low level of the grubbs &# 39 ; second - generation ru metathesis catalyst and applying a moderate pressure , a commodity pbd network self - heals effectively in air under various temperatures . the effect of concentration of catalyst , compression pressure and temperature on the self - healing efficiency of the material was investigated . it was also observed that the materials not only heal with themselves but also with control samples without any ru catalyst . furthermore , ru - free pbd samples can be healed effectively by applying a very small amount of ru catalyst only to the fracture surfaces , which allows self - healing to be achieved without compromising shape persistence . the approach is simple , effective , and potentially applicable to a wide range of olefin - containing polymers such as polyisoprene , butyl rubber , polynorbornene , and other polymers containing double bonds amenable for metathesis . given the strength of c — c double bonds , this method may offer the possibility of designing strong self - healing polymers . general . all the chemicals were obtained from commercial vendors and used as received without further purification . polybutadiene ( pbd ) was purchased from aldrich with an average mw of 200 - 300 kda , with 99 % of cis - 1 , 4 addition . grubbs &# 39 ; second - generation catalyst was obtained from the materia inc . as free samples . the ru - loaded samples and ru - free control samples were prepared following the same method as reported previously , ( 35 ) which is briefly described as follows . first , pbd was dissolved in dichloromethane ( dcm ) and then 1 % mole ( relative to the molarity of double bonds in pbd ) of benzyl peroxide was added to the polymer solution . the solvent was then evaporated at room temperature and the residue was molded in teflon mold and heated at 100 ° c . under vacuum for 6 h . the specimens ( 20 mm × 10 mm × 2 mm ) were then swelled in dcm and washed thoroughly to remove unreacted bpo and any byproducts . under cooling condition using an acetonenitrile / dry ice bath (− 42 ° c . ), the samples were then swelled in dcm solutions containing the grubbs &# 39 ; second - generation ru metathesis catalyst for 1 hour to incorporate different amount of the ru catalyst : 0 . 010 , 0 . 0075 , 0 . 0050 mol % ( relative to the molarity of olefin ), respectively . the specimens were then dried under vacuum at room temperature for 2 hours and finally subjected to self - healing tests . for control samples , the same ru - loaded specimens were quenched in vinyl ether at room temperature for 2 hours and then washed thoroughly with dcm to remove cleaved catalyst . ( 37 , 38 ) the specimens were then dried under vacuum at room temperature for 2 hours and subjected to self - healing tests . the tensile mechanical properties of the polymers were measured using an instron 3365 machine in standard stress / strain experiments . the specimens were extended at 100 mm / min at room temperature . stress - relaxation experiments ( fig4 ) were performed using a ta instru - ments dma q800 with attached cryo accessory . a constant strain of 10 % was applied at t = 5 min and then was maintained for 30 mins at 15 , 20 , 25 and 30 ° c . a ) for self - healing tests of ru - loaded samples : a sample loaded with a certain concentration of the ru catalyst ( 0 . 010 , 0 . 0075 or 0 . 0050 mol %) was first cut with a razor blade and the cut faces were pressed together right after being cut . then the samples were let to self - heal in a teflon mold under a certain compression pressure ( 10 , 20 or 30 kpa ) and at a certain temperature ( 5 , 15 , 22 ( room temperature ), or 30 ° c .) in air . after various healing times , the samples were subjected to stress - strain tests at room temperature at 100 mm / min pulling rate . b ) for self - healing tests of a ru - loaded sample with its corresponding ru - free control sample : a ru loaded sample ( 0 . 0075 mol % ru loading ) and a ru - free control sample were first cut with a razor blade . one piece of the ru - loaded sample and the other piece from its corresponding ru - free control sample were pressed together right after being cut . then they were let to self - heal in a teflon mold at 20 kpa of compression pressure at room temperature ( 22 ° c .) in air . the samples were then subjected to stress - strain tests at room temperature at 100 mm / min pulling rate . c ) for self - healing tests of the control samples : the ru - quenched controls ( before quenching , the sample was loaded with 0 . 0075 mol % of the ru catalyst ) was first cut with a razor blade and the cut faces were pressed together right after being cut . then they were let to self - heal in a teflon mold at 20 kpa of compression pressure at room temperature ( 22 ° c .) in air . the samples were then subjected to stress - strain tests at room temperature at 100 mm / min pulling rate . d ) for self - healing tests of pristine pbd samples with ru catalyst applied only at the cut surfaces : a pristine pbd sample was first cut with a razor blade . using a 25 μl micro syringe , a dcm solution of ru catalyst ( 0 . 5 mg / ml ) was applied onto both cut faces ( 2 . 5 , 5 . 0 or 10 μl each face ) or only one cut face ( 5 . 0 , 10 or 20 μl ) and then the cut pieces were let dry under vacuum for 5 min . the cut faces were then pressed together and were let to self - heal in a teflon mold at 20 kpa of compression pressure at room temperature ( 22 ° c .) in air for 3 hours . the samples were then subjected to stress - strain tests at room temperature at 100 mm / min pulling rate . e ) for self - healing tests of pristine pbd samples without any ru catalyst : a pristine pbd sample was first cut with a razor blade . the cut faces were then pressed together right after being cut and were let to self - heal in a teflon mold at 20 kpa of compression pressure at room temperature ( 22 ° c .) in air for 3 hours . the samples were then subjected to stress - strain tests at room temperature at 100 mm / min pulling rate . the ru - loaded samples ( with 0 . 010 , 0 . 0075 or 0 . 0050 mol % ru ) were swollen in n - heptane for 1 hour and then dried under vacuum for 12 hours . the weight loss was calculated from the weights of the initial samples and of the samples after swelling and drying . the same process was repeated three times for each sample . the percentage weight losses for all samples in three cycles of extraction are as follows : 4 . 8 %, 1 . 5 % and 1 . 7 % weight loss for the 0 . 010 mol % ru - loaded sample , 2 . 7 %, 1 . 0 % and 0 . 8 % weight loss for the 0 . 0075 mol % ru - loaded sample , and 1 . 1 %, 0 . 3 % and 0 . 4 % weight loss for the 0 . 0050 mol % ru - loaded sample . 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