Block copolymer stress-strain properties

Pedemonte E., Alfonso G.C., Dondero G., De C.F., and Araimo L. Correlation between morphology and stress strain properties of three block copolymers. 2. The hardening effect of the second deformation. Polymer, 18, 191, 1977. 

Figure 9. Comparison of stress-strain properties of the press-quenched films of HIBI block copolymers to those of homopolymer HB. Butadiene content is next...

Figure 11. Comparison of the stress-strain properties of the thermoplastic elastomer HBIB-27 to that of inverted block copolymer HIB1-29.

The mechanical and thermal properties of a range of poly(ethylene)/po-ly(ethylene propylene) (PE/PEP) copolymers with different architectures have been compared [2]. The tensile stress-strain properties of PE-PEP-PE and PEP-PE-PEP triblocks and a PE-PEP diblock are similar to each other at high PE content. This is because the mechanical properties are determined predominantly by the behaviour of the more continuous PE phase. For lower PE contents there are major differences in the mechanical properties of polymers with different architectures, that form a cubic-packed sphere phase. PE-PEP-PE triblocks were found to be thermoplastic elastomers, whereas PEP-PE-PEP triblocks behaved like particulate filled rubber. The difference was proposed to result from bridging of PE domains across spheres in PE-PEP-PE triblocks, which acted as physical crosslinks due to anchorage of the PE blocks in the semicrystalline domains. No such arrangement is possible for the PEP-PE-PEP or PE-PEP copolymers [2]. 

Novel sulfonated and carboxylated ionomers having "blocky" structures were synthesized via two completely different methods. Sulfonated ionomers were prepared by a fairly complex emulsion copolymerization of n-butyl acrylate and sulfonated styrene (Na or K salt) using a water soluble initiator system. Carboxylated ionomers were obtained by the hydrolysis of styrene-isobutyl-methacrylate block copolymers which have been produced by carefully controlled living anionic polymerization. Characterization of these materials showed the formation of novel ionomeric structures with dramatic improvements in the modulus-temperature behavior and also, in some cases, the stress-strain properties. However no change was observed in the glass transition temperature (DSC) of the ionomers when compared with their non-ionic counterparts, which is a strong indication of the formation of blocky structures. 

It was the objective of this work to investigate the effect of variation in block architecture (number and the order of the blocks) on the crystallinity level, morphology, the stress-strain and hysteresis behavior of this series of polymers. In addition, the composition ratio of the two block types is expected to play a crucial role in determining the bulk material properties of the block copolymers. This is related to the fact that the mechanical properties of block copolymer are typically influenced more substantially by the behavior of the continuous phase, as will be demonstrated.(1,22)... 

Likewise, the mechanical properties of the copolymers were nearly identical or even somewhat enhanced towards the polyimide homopolymer in terms of the modulus and tensile strength values [44,47]. For most of the block copolymers, the elongations to break were substantially higher than that of PMDA/ODA polyimide (Table 4). The shape of the polyimide stress-strain curve is similar to that of a work-hardened metal with no distinguishable yield point... 

Fisher124,125 has studied the stress-strain and optical properties of three SBS block copolymers containing, respectively, 31,40 and 49% polystyrene as a function of temperature. He has shown that these materials are two phase systems in which the polybutadiene chains form an elastomeric phase and the polystyrene chains a glassy phase acting as physical crosslinks. Fisher126 has also obtained electron micro-... 

If we look at Figure 21.3, we can see that there is an upper limit to the overall styrene content in the polymer if making a polymer to have rubbery properties is the desired outcome [66]. As the styrene content increases, the stress-strain response changes dramatically for these neat SBS polymers. At 53 and 65% styrene content, the polystyrene endblocks form the continuous phase in the phase-separated block copolymer, and these polymers behave more like polystyrene than a rubber at low strain. This low strain behavior is also shown at 39% styrene content, but a rubbery plateau begins to show at lower stress. 

Elongation to failure measured in tensile stress-strain measurements at room temperature (i.e., approximately 25 C) vary significantly as the composition of the polymer is varied from the glassy PS to the elastomeric PB (Figure 6). Also it is clear that the tensile properties of the random copolymer is significantly different from the same composition block copolymer. This difference is due, in part, to the differences in molecular weight (Table 1). 

Polycocyclotrimers were prepared by polycocyclotrimerization of difunctional isocyanates of variable chain length or difunctional isocyanate with monofunctional isocyanate. The stress-strain and viscoelastic properties of resulting polymers were determined. It was found that co-polycyclotrimers prepared from diisocyanates of the variable chain length had typical properties of phase separated block copolymers. 

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