PEO/PBT copolymers

Sakkers RJB, Dalmeyer RAJ, Wijn JR, and Blitterswijk CA. Use of bone-bonding hydrogel copolymers in bone An in vitro and in vivo study of expanding PEO-PBT copolymers in goat femora. J Biomed Mater Res, 2000, 49, 312-318. 

Reed AM and Gilding DK. Biodegradable polymers for use in surgery-poly(ethylene oxide) poly (ethylene terephthalate) (PEO/PET)copolymers 2. in vitro degradation [J]. Polymer, 1981, 22,499-504. Van Blitterswijk CA, Brink JVD, Eeenders H, et al. The effect of PEG ratio on degradation, calcification and bone bonding of PEO/PBT copolymer (Polyactive). Cell Mater, 1993, 3(1), 23-36. 

Rudder AM, Leenders H, and van Blitterswijk CA. Interface reactions to PEO/PBT copolymers (Polyactive) after implantation in cortical bone. J Biomed Mater Res, 1994, 28, 141-151. 

Roessler, Wilke A, Griss PM, and Kienapfel H. Missing osteoconductive effect of a resorbable PEO/PBT copolymer in human bone defects A clinically relevant pilot study with contrary results to previous animal studies. Biomed Mater Res (Appl Biomater), 2000, 53, 167-173. 

Beumer GJ, Van Blitterswijk CA, Bakker D, Ponec M. Cell-seeding and in vitro biocompatibility evaluation of pol3uneric matrices of PEO/PBT copolymers and PTJ.A. Biomaterials 1993 14 598-604. 

Therefore, research focused on the development of new membrane materials and up-scaling for production is still important. In that direction, and in order to understand better the membrane behaviour of PEO-PBT copolymers, the CO2 permeability (Table 12.1) were fitted to polynomial mathematical models (Equation 12.2), and plotted versus the molecular weight (M ) of the PEO block, as shown in Figure 12.2. 

Fowler B.O. Infrared studies of apatites. I. Vibrational assignments for calcimn, strontium, and barium hydroxyapatites utilizing isotopic substitution. Inorg. Chem. 1974 13 194-207 Gaillard M.L., van den Brink J., van Blitterwijk C.A., Luklinska Z.B. Applying a calcimn phosphate layer on PEO/PBT copolymers affects bone formation in vivo. J. Mater. Sci. Mater. Med. 1994 5 424 28... 

Figure 4.8 Selectivity for various gases relative to oxygen at 20 °C for a PBT-PEO block-copolymer [75].

Figure 12.1 presents the chemical structure of poly(amide-b-ethylene oxide) (commercial name Pebax ) and poly(ethylene oxide)-poly(butylene terephthalate) (PEO-PBT) (commercially known as Polyactive ). These copolymers with high content of PEO are hydrophilic and show excellent chemical resistance towards solvents. The solubility of these copolymers in different solvents is determined by the ratio of segmented blocks. Pebax MH 1657 is soluble only in few solvents and generally the polymer solution is prepared under reflux at high temperature and low polymer concentration by using n-butanol or a mixture of n-butanol/l-propanol, after cooling down to room temperature. 

Table 12.2 Thermal properties of PEO-PBT multi-block copolymers [Reprinted with permission 67] ...

Figure 12.3 Thermai gravimetric analyses of PEO-PBT multi-block copolymers. Reprinted with permission from Advanced Functional Materials, Tailor-made polymeric membranes based on segmented block copolymers for CO2 separation, by A. Car, C. Stropnik, W.

Over the last decade, Fakirov et al carried out extensive studies on the synthesis, structure, and physical properties of PEE based on PBT and PEO [18-21]. The investigations of the oriented PEE structure are particularly interesting [18,19,21,29,30,125-128,130,131]. Textile fibers have been obtained with the use of these copolymers [19]. The hardness of PEO-PBT based PEE changes with temperature and PEO molecular weight similarly to the PTMO-PBT block copolymers [129]... 

Table 2. Physical properties of PEO-6-PBT and PTMO-6-PBT copolymers with various degrees of branching [106]...

At constant PBT/PTMO composition, when the molar mass of PTMO block is >2000, partial crystallization of the polyether phase leads to copolymer stiffening. The properties of polyesterether TPEs are not dramatically different when PTMO is replaced by polyethers such as poly(oxyethylene) (PEO) or poly(oxypropylene). PEO-based TPEs present higher hydrophilicity, which may be of interest for some applications such as waterproof breathable membranes but which also results in much lower hydrolysis resistance. Changing PBT into a more rigid polymer by using 2,6-naphthalene dicarboxylic acid instead of terephthalic acid results in compounds that exhibit excellent general properties but poorer low-temperature stiffening characteristics. 

Some polymorphic modifications can be converted from one to another by a change in temperature. Phase transitions can be also induced by an external stress field. Phase transitions under tensile stress can be observed in natural rubber when it orients and crystallizes under tension and reverts to its original amorphous state by relaxation (Mandelkem, 1964). Stress-induced transitions are also observed in some crystalline polymers, e.g. PBT (Jakeways etal., 1975 Yokouchi etal., 1976) and its block copolymers with polyftetramethylene oxide) (PTMO) (Tashiro et al, 1986), PEO (Takahashi et al., 1973 Tashiro Tadokoro, 1978), polyoxacyclobutane (Takahashi et al., 1980), PA6 (Miyasaka Ishikawa, 1968), PVF2 (Lando et al, 1966 Hasegawa et al, 1972), polypivalolactone (Prud homme Marchessault, 1974), keratin (Astbury Woods, 1933 Hearle et al, 1971), and others. These stress-induced phase transitions are either reversible, i.e. the crystal structure reverts to the original structure on relaxation, or irreversible, i.e. the newly formed structure does not revert after relaxation. Examples of the former include PBT, PEO and keratin. 

Let us now discuss the microhardness of PBT block copolymers during the stress-induced polymorphic transition for some block copolymers this transition is rather smeared (Tashiro et al, 1986). An additional reason for performing this work is the fact that the copolymers of PBT with PEO had not then been studied with reference to polymorphic transitions. The very detailed structural characterization of the copolymers with PEO as mentioned above was expected to shed more light on the nature of the microhardness behaviour. 

After following the microhardness behaviour during the stress-induced polymorphic transition of homo-PBT and its multiblock copolymers attention is now focused on the deformation behaviour of a blend of PBT and a PEE thermoplastic elastomer, the latter being a copolymer of PBT and PEO. This system is attractive not only because the two polymers have the same crystallizable component but also because the copolymer, being an elastomer, strongly affects the mechanical properties of the blend. It should be mentioned that these blends have been well characterized by differential scanning calorimetry, SAXS, dynamic mechanical thermal analysis and static mechanical measurements (Apostolov et al, 1994). 

Poly(amide-b-ethylene oxide) copolymers were presented in 1990 as a promising membrane material [43]. These block copolymers were developed in 1972 but in 1981 began to be used for commercial purpose under the trade name Pebax , produced by ATOCHEM [44] (now ARKEMA). Another important group of segmented poly(ester)s used for membranes are block copolymers based on PEO and PBT (poly(butylene tereph-thalate), known under commercial name of Polyactive [45]. By changing the polyamide and polyether segment, molecnlar mass and the content of each block, the mechanical, chemical, and physical properties are nicely tnned as well [46]. 

On the other hand, pristine 4000PE055PBT45 copolymer showed two characteristic Tni values (40 °C for PEO and 213 for PBT, see Table 12.2). It is consistent with the microphase separated slnictme in block copolymers [91]. For the blend samples for the PEO crystalline phase was shifted to higher values when PEG is added into the polymer matrix (Figme 12.12a). These results are in contradiction to those observed in Pebax/PEG system reported earlier [24]. High PEG content slightly increases the crystallinity from 19% (pristine polymer) to 24% (blend with 50% of PEG). values of PBT... 

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