Crystallizable hard segments

The work reported here is concerned with the syntheses and properties of polyether-ester block copolymers containing poly (tetramethylene ether) units of molecular weight of approximately 1000 as the amorphous polyether blocks and a variety of esters as the crystallizable hard segments. The purpose of this study is to correlate changes in synthesis and properties of these thermoplastic and elastomeric copolymers with changes in the concentration and nature of the ester segments, particularly the types of diol and diacid. 

Structural studies on polyurethane elastomers with crystallizable hard segments... 

Thermoplastic copolyester elastomers are multiblock copolymers built up from so-called short crystallizable hard segments and long flexible segments. Owing to such chemical structure, TPEEs exhibit unusual combination of thermoplastic and elastomeric behavior. Physical and mechanical properties of these copolymers strongly depend on the chemical composition and the molecular structure... 

Illustration of fine structure expected in elastomeric fibers, composed of blocks of crystallizable hard segments and non-crystallizable coiled soft segments. 

These effects are not unique to copolymers in the isophthalate/ terephthalate system but are the expected results of copolymerizing the crystallizable tetramethylene terephthalate hard segment with any relatively lower-melting short-chain diol ester segment. The apparent eutectic at a 4GT mole fraction of 0.25 represents the condition where there are few short-chain diol ester segments present of either type having sufficient length to crystallize. 

There is no filler reinforcement of the polyurethane akin to the reinforcement which takes place when reactive or particulate fine particle size fillers are added to non-strain-crystallizable millable elastomers. Fillers in polyurethane reduce strength approximately in proportion to their volume they too, however, increase stiffness and hardness and are cheaper to use for this purpose than additional diisocyanate which gives the same result through hard-segment increase. 

Because of its rapid crystallization, PBT is very suitable for use as crystallizable segment in multiblock copolymers, which belong to the class of thermoplastic polyester elastomers (TPEEs). PBT-based block copolymers have been synthesized and studied in detail in the last thirty years. The commercial PBT block copolymers mostly possess a polyether, e.g. poly(tetramethylene oxide) (PTMO), or aliphatic polyester amorphous phase. Thermoplastic poly(ester-ether) elastomers, based on PBT and PTMO were developed by DuPont, and commercially introduced on the market in 1972, under the trade name Hytrel . Extensive investigations on the synthesis of block copolymers based on PBT rigid (hard) segments and various new... 

Phillips, R.A. and S.L. Cooper, Phase separation in crystallizable multiblock poly(ether-ester) copolymers with poly(tetramethylene isophthalate) hard segments. Polymer, 35(19) p. 4146.1994. 

Block copolymers based on hard segments of crystallizable poly((R)-3-hydroxybutyrate-co-(R)-3-hydroxyvalerate) (PHBV) and switching segments of hyperbranched three-arm poly(3-caprolactone) were proposed by Xue et al. (2010) as biodegradable SMPs for fast, self-deploying stents. Those containing copolymer with 25 wt% PHBV demonstrated almost complete self-expansion at 37°C within just 25 s, which is much faster than current self-deployable stents. 

Lendlein and Langer (2002) demonstrated this concept using multiblock copolymers based on hard segments of crystallizable oligo(p-dioxanone) diol and switching segments of oligo(s-caprolactone)diol. Fibres of this... 

---