| Polyurethane materials play an important role in today’s social life.It can be found in the fields of house furnishing,transportation,architecture,sporting and so on.Polyurethane materials generally have high hardness,good elasticity,aging resistance,wear resistance,low temperature resistance and other advantages.And various polyurethane materials have their own characteristics;therefore,polyurethane materials can meet a variety of needs.The diversity of functions and properties of polyurethane materials are attributed to the diversity of choice of synthetic materials.Although there are mainly three types of polyurethane synthetic materials,including diisocyanates,polyols and chain extenders,the selection of different monomers in each category may change the properties of polyurethane materials.For example,polyurethane materials synthesized from aromatic diisocyanates are stronger than those with aliphatic diisocyanates,but they are more prone to yellowing.Polyurethane materials synthesized from polyether polyols are more flexible than those synthesized from polyester polyols,but they have poor oxygen resistance.And polyurethane materials with binary amine chain extenders have stronger molecular polarity and can form more hydrogen bonds than those with dialcohol chain extenders.In addition,the structure,molecular weight and other properties of each synthetic material may also affect the properties of polyurethane materials.At the same time,modifiers and various additives added in the synthesis process will have a certain impact on the properties of polyurethane materials,so polyurethane materials can have a wide variety of characteristics for many applications.There is a polyurethane material called acrylate modified waterborne polyurethane coating.It is featured by the introduction of acrylic structure at the end of polyurethane chain.In this way,the double bonds attached to the polymer backbone could induce crosslinking reaction under ultraviolet light,thus solidifying the liquid coating into a film.This ensures that with use of less solvent,coating can be liquid in the preservation,transport and before being used,but it can be shaped into films after being used to achieve the function of the coating.This product is considered to be an environmentally friendly coating.From the perspective of the application process of acrylate modified waterborne polyurethane coating,acrylic structure is only introduced at the end of the polyurethane molecular chain,which can be transformed from liquid to solid under ultraviolet light.We were inspired by that,it is suggested that if acrylic acid structure is introduced into the main structure of polyurethane,its properties can be regulated by adjusting its content and controlling its crosslinking degree.Based on this,this thesis attempts to synthesize acrylate type polyurethane and study the relationship between structure and properties of polyurethane.First,we chose hexamethylene diisocyanate(HDI),polycaprolactone(PCL),3,3’,5,5’-tetramethyldiphenyl acrylate resin(TMBPEA)as the raw materials to synthesize a series of polyurethane with double light energy acrylate by adjusting the feed ratio,and then treated them by UV crosslinking.After that,we performed X-ray diffraction test,tensile test and so on to find that the crystallization property of polyurethane in this thesis could be affected by adjusting the feeding ratio of raw materials and controlling the crosslinking degree,thus affecting its’ tensile property.With the increase of PCL feeding proportion,the degree of crystallinity of polyurethane increases from 33.01% to 69.60%,Young’s modulus increases from 89.79±5.74 MPa to 224.88±5.22 MPa,tensile strength increases from 9.04±1.26 MPa to 12.98±0.33 MPa,and strain at break increases from 499.09±88.38% to 776.51±67.39%.Meanwhile,the shape recovery rate of polyurethane increases from 6.2% to 86.2%.After UV crosslinking,the crosslinking degree of polyurethane increases from 37.94±0.56% to 69.30±1.08%,the degree of crystallinity decreases from 64.12% to 25.81%,Young’s modulus decreases from 104.27± 7.01 MPa to 18.74± 1.30 MPa,the tensile strength decreases from 14.06± 0.94 MPa to 7.27± 1.48 MPa,and stain at break increases from 55.44±3.78% to 68.22±11.43%.Therefore,we believed that we could control the properties of polyurethane materials more precisely by controlling the feed ratio and the degree of crosslinking.Secondly,we used PCL with lower molecule weight to synthesize the same kind of polyurethane.Compared with the one which had same feed ratio but higher molecule weight of PCL,the degree of crystallinity of polyurethane with lower molecule weight of PCL decreases to 49.01%.And Young’s modulus,tensile strength and stain at break decreases to 142.98±2.46 MPa,7.83±0.12 MPa and 246.52±115.88% respectively,and the shape recovery rate is 86.7%.On this basis,we used dicyclohexylmethane 4,4’-diisocyanate(HDMI)instead of hexamethylene diisocyanate(HDI),and(3-trifluoromethyl)phenyl hydroquinone epoxy arylate resin(3F-PQEA)and 1,1,1-tris(4-hydroxyphenyl)ethane(THE)instead of 3,3’,5,5’-tetramethybiphenyl epoxy arylate(TMBPEA)respectively,in order to explore the influence of different structure on the properties of polyurethane materials.We found that,after replacing HDI with HMDI to introduce aliphatic ring structure,the degree of crystallinity of polyurethane decreases from 45.21% to 32.95%,Young’s modulus decreases from 189.93± 13.37 MPa to 19.81± 5.27 MPa,tensile strength decreases from 11.36± 2.23 MPa to 6.37± 1.46 MPa,the strain at break decreases from 537.77±104.26% to 527.25±178.08%,and the shape recovery rate is 41.0%.After replacing TMBPEA with 3F-PQEA for changing the position of benzene ring while maintaining the content of benzene ring,the degree of crystallinity of polyurethane decreases to 5.51%,in the meantime,Young’s modulus and tensile strength respectively decrease to 1.52± 0.13 MPa and 4.64± 0.87 MPa,but strain at break increases to 804.57±63.34%,and the shape recovery rate is 68.4%.And after replacing TMBPEA with THE,the polyurethane material becomes crosslinked polymers.We found that the crystallinity and Young’s modulus of polyurethane decrease to 5.30% and 5.64±0.26 MPa,the tensile strength and strain at break increase to 17.31±.65 MPa and 640.27±73.66%,and the shape recovery rate is 13.4%.The above results show that the reducing molecular weight of PCL,the introduction of the structure of aliphatic ring structure and the introduction of the benzene ring on the branched chain while ensuring the content of the benzene ring is basically unchanged will reduce the mechanical properties of polyurethane materials.Compared with acrylate polyurethane block copolymers,crosslinked polyurethane has better toughness. |
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