Polyether macrodiol

Polyurethane elastomers, prepared from (i) polyether macrodiols that contain a reduced number of ether linkages compared with PTMO [poly(tetramethylene oxide)],... 

Segmented polyurethane elastomers, prepared from diisocyanates, macrodiols and chain extenders, are frequently used in the construction of implantable medical devices, such as cardiac pacemakers, heart valves, catheters, and heart assist devices, because of their excellent mechanical properties and haemocompatibility. Polyether macrodiols, such as poly(tetramethylene oxide) (PTMO), are used to prepare polyurethanes for implant, since they offer an increased resistance to enzymatic hydrolysis compared with polyester-based polyurethanes. 

In some of our recent papers we also made evidence that polyetheric PUs phase separate to a much greater extent than the corresponding polyester-based polymers [135]. This is consistent with previous smdies, that showed polyether macrodiols to give greater phase separation than polyester macrodiols [4, 14]. The reason is believed to be the availability of a >C=0 group on each monomer in a polyester for... 

A series of polyurethane-ureas (PUUs) has been synthesized by us, based on the aromatic diisocyanates DBDI or MDI. The materials were synthesized with two SS macrodiols, the polyether macrodiol PTMO or the polyester SS, PEA. 

Martin D.J., Warren L.A.P., Gunatillake P.A., McCarthy S.J., Meijs G.F., and Schindhelm, K. Polydimethylsiloxane/polyether-mixed macrodiol-based polyurethane elastomer. Biomaterials, 21, 1021, 2000. 

In the case of Fig. 7.6a the cluster formation and the size distribution can be influenced not only by chemical reactions but also by partial miscibility of the substructures during reaction. Polyurethane networks prepared from polyolefin instead of polyester or polyether as macrodiol, can serve as an example. In this particular case an agglomeration of hard domains takes place in the pregel stage, produced by a thermodynamic driving force. 

The processes described in Table 2 present a peculiar interest in the working out of new materials as polyurethanes. These last polymers are very often based on macro diols coming from polyethers or polyesters, a-co functional polyolefins being relatively uncommon. Hence, Rhein and Ingham [139] prepared macrodiols by ozonization of polyisobutylene in CC14 at... 

D. Martin, L. Warren, P. Gunatillake, S. McCarthy, G. Meijs, K, Schindhelm, Polydimethylsiloxane/polyether-mixed macrodiol-based polyurethane elastomers biostability. Biomaterials 21 (10) (2000) 1021-1029. 

Long-chain diols or macrodiols , generating the SS, are typically polyester or polyether diols, with molecular weights between 500 to 5 000, although in practice, molecular weights of 1 000 and 2 000 are primarily used. 

Common SS include polyethers, polyesters and polyalkyl glycols with glass transition temperatures in the range of -70°to -30°C. Commonly used macrodiols in the PUs synthesis are polyalkyl-diols, such as polyisobutylene diol [70], polybutadiene (PBU) [20, 71], or oligo-butadiene diols [72] as well as hydrogenated polybutadiene diol [20] polyether diols polytetrahydrofuran (PTHF or PTMO) [50-52], polyethylene glycol (PEG) or (PEO) [73], polypropyleneoxide (PPO) [73] or mixed blocks of them PEO-PPO-PEO [74] and PPO-THF [54] polyester diols poly(ethylene adipate) (PEA) [4,20], poly(butylene adipate) (PBA) [20, 73], and latterly polycaprolactone diol (PCL or PCD) [75], polyalkylcarbonate polyol [20] or mixed blocks of them, for example poly(carbonate-co-ester)diol [76], poly(hexamethylene-carbonate)diol [77], as well as poly(hexamethylene-carbonate-co-caprolactone)diol [78] and a mixed block copolymer of polyether and polyester blocks PCL-b-PTHF-b-PCL [79]. Examples schemes of macrodiols are shown in Eig. 1.9. 

In the materials with DBDI (Fig. 2.14(b)) the overall etched texture is much flatter. The regions of chemical segregation are more or less equally attacked. The material with DBDI does not show the precipitated crystals. A more detailed SEM description on the morphology of MDI and DBDI based PUs and mixtures of them, is made in section 2.3.2.2. where the materials are characterized and compared from two perspectives (a) effect of the SS macrodiol nature (polyester or polyether) (b) effect of type, and number of diisocyanates (crystallizing or not) and their order of introduction in the reaction synthesis. 

The morphology of a series of polyester or polyether PUs based on mixtures of diisocyanates has been also examined by ourselves by using the AFM technique. Example PUs that were smdied, based on the macrodiol PEA and chain extended with EG are depicted in Table 2.4. The molar composition of the materials was diisocyanate macrodiol chain extender = 4 1 3 giving an isocynate index I = 100. The preparation procedures in order to obtain PUs with single or mixtures of the diisocyanates MDI and/or DBDI has been described elsewhere [127,207]. 

Materials with MDI/BDO hard domains have been extensively investigated. A series of polyether PUs based on the diisocyanate MDI and macrodiol PTMO and extended with BDO was investigated by Abouzahr and Wilkes who reported that the Tg increased with the increase of the HS content [176]. 

The molecular weight influenced the PUs thermomechanical behaviour. The best results were obtained with Mw = 2000. The type of SS macrodiol (polyether PTHF or polyester PBA) also influenced the PU thermomechanical behaviour. Numerous phase transformations were observed in the material obtained with PBAiooo (curve 8) as compared to the material with PTHFiooo (curve 3). Both materials were based on the same chain extender, DEG and diisocyanate DBDI. 

The range of polymers was designed to reveal the roles of choice of macrodiol and of chain extender in determining the performance as an elastomer. The SS were the polyether PTHF and polyester PEA or PBA, of molar mass 2 000 g/mol. The chain extenders used in the synthesis were EG, BG or DEG. Mechanical tests included load-unload cycles at constant rate of extension, with measurement of hysteresis and strain recovery, and stress relaxation tests. 

There have been several previous studies of the effects of varying HS fraction on the mechanical properties of thermoplastic PUs. The purpose of our present study has been to investigate the role of other important structural features, as summarized above. This was achieved by us, by a systematic variation of the three chemical constituents diisocyanate, macrodiol and chain extender. Two diisocyanates were considered the frequently employed MDI, and its close relation DBDI, that is of special interest because of its tendency to crystallize on cooling from the melt in the presence of some chain extenders [60, 61, 67, 127, 135]. Three macrodiols were considered PEA, PTHE PBA. These were chosen because polyethers such as PTHF are well-known to promote phase-separation from the diisocyanates, while polyesters such as PEA and PBA have a greater affinity for the diisocyanate through... 

In a second stage of our study we compared the DAB and MDA based materials (PUDB and PUDM from above) with other PUUs obtained by using the same macrodiols, (polyester PEA or polyether PTMO) but the diamine chain extenders 2,5-bis-(4-amino-phenylene)-I,3,4-oxadiazole (DAPO) or 2,6-diaminopyridine (DAPy). The materials were obtained similarly as in the case of the TDA and MDA... 

Therefore while the hydrogen bonding did not necessarily enhance the PUs mechanical properties, it plays an essential role on the improvement of the materials performance as elastomers. Similar conclusions were obtained by us in other works, for materials obtained with the diisocyanate MDI and when using other macrodiols like the polyester PEA or the polyether PTMO [127,327,328]. 

Martin, D. J., Poole Warren, L. A., Gunatillake, P. A., McCarthy, S. J., Meijs, G. F.,and Schindhelm,K., PDMS/polyether mixed macrodiol based polyurethane elastomers Biostability, Biomaterials 21, 1021-1029 (2000). 

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