ESTER URETHANE COPOLYMER

A series of poly(ester-urethane) urea triblock copolymers have been synthesized and characterized by Wagner et al/ using PCL, polyethylene glycol, and 1,4 diisocyanatobutane with either lysine ethyl ester or putrescine, as the chain extender. These materials have shown the elongation at break from 325% to 560% and tensile strengths from 8 to 20 MPa. Degradation products of this kind of materials did not show any toxicity on cells. 

Another approach was attempted by Seppala and Kylma who reported the synthesis of poly(ester-urethane)s by condensation of hydroxyl terminated tel-echelic poly(CL-co-LA) oligomers with 1,6-hexamethylene diisocyanate (Scheme 33) [94]. The diisocyanate acts as chain extender producing an increase in molecular weight of the preformed oligomers. The authors claim that some of the copolymers present elastomeric properties. Using a similar method. Storey described the synthesis of polyurethane networks based on D,L-LA, GA, eCL,... 

Two different types of chain-extending agents were used, namely 4,4 -di-isophenylmethane diisocyanate (MDI) and phosgene, which lead to two different classes of copolymers, poly(ester-urethane)s and poly(ester-carbonate)s respectively. High molecular weight poly(ester-carbonate)s have earlier been prepared by the dichloroformate synthesis [12-13]. 

Guan JJ et al (2004) Biodegradable poly(ether ester urethane)urea elastomers based on poly(ether ester) triblock copolymers and putrescine synthesis, characterization and cytocompatibility. Biomaterials 25(l) 85-96... 

Polyurethanes were found to be biodegradable by the enzyme, fungi, and yeast studied. In the case of poly(ester-urethanes) a relation between the polyester chain length of the copolymer... 

Cohn, D. et al, 2006. PEO-PPO-PEO-based poly(ether ester urethane)s as degradable reverse thermo-responsive multiblock copolymers. Biomaterials, 27, 1718-1727. 

However, PLA can be pol5merized with diisocyanates to form poly(ester-urethane)s or with caprolactones to form poly(L-lactic acid-co-e-caprolactone-urethane)s. Such copolymers can be tailored as hard plastics or flexible elastomers and can have unique glass transition temperatures from -70°C to +60°C, tensile modulus from 2 MPa to 2000 MPa, and % strain from 1% to about 1000% (2). 

On W, Qiu H, Chen Z, Xu K. Biodegradable block poly(ester-urethane)s based on poly (3-hydroxybutyrate-co-4-hydroxybut5Tate) copolymers. Biomateiials April 2011 32(12) 3178-88. 

Bioresorbable poly(ester urethanes) have been developed by reacting lysine diisocyanate (LDI) with polyester diols or triols based on D,L-lactide, caprolac-tone, and other copolymers [45]. In these systems, aliphatic polyesters such as PLGA or PCL form the soft segments and the polypeptides form the hard segments [46]. A resorbable elastomeric poly(ester urethane) called Degrapol is available commercially. It is currently being used to develop porous scaffolds for tissue engineering applications. 

The copolymerization approach has successfully been applied for poly(ester-urethane)s by equipping the prepolymers with elastomeric properties by copolymerization. e-Ca-prolactone-lactic acid copolymers have been reported to result in a significant increase in the strain and the flexibility [62]. Table 3.2 shows the changes in the material properties that have been achieved by varying the prepolymer composition [50, 62]. 

Sirolimus+ EPC capture/ OrbusNeich Medical Inc, Ft. Lauderdale, FL Stainless steel SynBiosys polymer (2 bioabsorbable urethane-linked poly(ether ester) multiblock copolymers composed of glycolide, lactide, e-caprolactone, and polyethylene glycol prepolymer blocks). Anti-CD34 antibody cell captme coating on the luminal siu-face Approx. 5 pg/mm NA... 

In the study of spherulites formed in poly(ester urethane) multiblock copolymer [51], FTIR imaging was used to reveal valuable information about both the orientation of the polymer chain and the composition of the spherulites. This information was not available from the measurements obtained from atomic force microscopy or polarized light microscopy. A separate study has also demonstrated that linear polarized FTIR imaging is a powerful tool for the investigation of the crystalline and amorphous structures and chain orientation of spherulites of PHB and isotactic poly(propylene oxide) [52]. Recently, a novel multipolarization calculation method has been proposed and applied to obtain FTIR images showing band structure in poly(L-lactic acid) and PHB spherulites with the indication of local molecular chain orientation [53]. 

Wang W, Jin Y, Yang XN, Su ZH. Chain orientation and distribution in ring-banded spherulites formed in poly(ester urethane) multiblock copolymer. J Polym Sci B 2010 48 541-547. 

Block copolymers can contain crystalline or amorphous hard blocks. Examples of crystalline block copolymers are polyurethanes (e.g. B.F. Goodrich s Estane line), polyether esters (e.g. Dupont s Hytrel polymers), polyether amides (e.g. Atofina s Pebax grades). Polyurethanes have enjoyed limited utility due to their relatively low thermal stability use temperatures must be kept below 275°F, due to the reversibility of the urethane linkage. Recently, polyurethanes with stability at 350°F for nearly 100 h have been claimed [2]. Polyether esters and polyether amides have been explored for PSA applications where their heat and plasticizer resistance is a benefit [3]. However, the high price of these materials and their multiblock architecture have limited their use. All of these crystalline block copolymers consist of multiblocks with relatively short, amorphous, polyether or polyester mid-blocks. Consequently they can not be diluted as extensively with tackifiers and diluents as styrenic triblock copolymers. Thereby it is more difficult to obtain strong, yet soft adhesives — the primary goals of adding rubber to hot melts. 

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