A novel polymeric shape memory system of chemically cross-linked polycyclooctene (PCO) was developed and characterized. PCO was synthesized via ring-opening metathesis polymerization of cyclooctene using the dihydroimidazolylidene-modified Grubb's catalyst. After dicumyl peroxide was added to PCO, the mixture was compression-molded into a film and further cured through chemical crosslinking upon heating. The chemically cross-linked PCO samples were fully characterized using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and wide-angle X-ray scattering (WAXS) in order to gain insight into the rapid shape memory behavior. We observe that the transition temperature of PCO is tunable through the change of the trans/cis ratio of vinylene groups. A fast shape memory behavior was observed, where the primary stress-free shape was recovered within 1 s on immersion in hot water above the melting point of the crystalline PCO phase. In contrast with glassy shape memory polymers, chemically cross-linked PCO behaves as an elastomer capable of arbitrary shaping above the sharp melting temperature of the PCO crystalline phase and subsequent shape fixing during crystallization.

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The effect of the microstructure on the phase behavior of mixtures of polybutadiene (PB) and poly(ethylene-co-1-butene) (PEB) with polystyrene (PS) has been investigated. A series of PBs with 1,2-addition content ranging from 7 to 93% were synthesized by anionic polymerization, and a portion of each was subsequently hydrogenated to yield PEB. Polymer pairs with blend compositions from 10 to 90 wt % were cast from toluene for each of the 16 PS/PB pairs and 7 PS/PEB pairs. Laser light scattering was used to obtain cloud point measurements, which were then used to construct phase diagrams. It was found that, for constituent components with equivalent degrees of polymerization, PS/PEB pairs give rise to higher upper critical solution temperatures than PS/PB pairs, indicating that PS/PEB pairs are less miscible than PS/PB pairs. Experimental phase diagrams were curve-fitted to theoretical phase diagrams predicted from the Flory−Huggins theory with the expression for the interaction parameter α:  α = a + b/T + cφPS/T, where α is related to the Flory−Huggins interaction parameter χ by χ = αV r, where V r is the molar reference volume, T is the absolute temperature, and φPS is the volume fraction of PS in the mixture. α values for PS/PB mixtures increase with increasing 1,2-addition (miscibility decreases) while α values for PS/PEB mixtures decrease (miscibility increases) with increasing 1-butene content. Using these α values, the Helfand−Wasserman theory was applied to predict the order−disorder transition temperatures of PS-block-PB and PS-block-PEB copolymers with varying 1,2-addition and 1-butene content, respectively.

The important role that the order-disorder transition temperature (TODT) of a block copolymer plays in the compatibilization of two immiscible homopolymers is demonstrated, using the model ternary blend systems consisting of a polystyrene-block-polybutadiene (SB diblock) copolymer and two immiscible homopolymers, polystyrene (hPS) and polyisoprene (hPI). For the study, SB diblock copolymers having different microstructures were employed. We investigated via transmission electron microscopy (TEM) the morphology of the blends. We found that an SB diblock copolymer was very poorly distributed at the interface between hPS and hPI in an hPS/hPI/SB ternary blend when the specimen was annealed at a temperature below the T ODT of the block copolymer, while a more uniform distribution of the SB diblock copolymer was observed when a specimen was annealed at a temperature above its TODT. We have shown that the miscibility (or the interaction parameter) between the hPI and PB block in an SB diblock copolymer plays a decisive role in controlling the morphology at the interfaces between hPS and hPI. We conclude that a block copolymer must be designed, such that its TODT is below the targeted melt blending temperature, in order for the block copolymer to be able to act as an effective compatibilizing agent for two immiscible homopolymers. This conclusion is supported further by investigating the tensile properties and morphology of ternary blends consisting of polypropylene (PP), hPS, and polystyrene-block-poly(ethylene-co-1-butene)-block-polystyrene (SEBS triblock) copolymer (Kraton G1650), which were prepared by melt blending at 200 °C in a batch mixer. That is, little improvement in the tensile properties of the ternary blends was observed when Kraton G1650 was added to PP/hPS binary blends. This observation is explained by a very poor distribution, observed by TEM, of Kraton G1650 at the interface between PP and hPS in the ternary blend. This is attributed to the very high T ODT, estimated to be above 350 °C from currently held mean-field theory, of Kraton G1650 compared to the melt blending temperature employed.

The morphology of A/B/(C-block-D) ternary blends was investigated by transmission electron microscopy (TEM), and its implications in the compatibilization of two immiscible homopolymers A and B with a C-block-D copolymer are discussed. Emphasis is placed on the thermodynamic requirements and the role of order-disorder transition temperature (T ODT) of block copolymer for compatibilization. For the investigation, the following model ternary blends were prepared: (i) 63/27/10 PS/PB/(PRMSblock-PI) with PS denoting polystyrene, PB denoting polybutadiene, PRMS denoting poly(R-methylstyrene), and PI denoting polyisoprene; (ii) 63/27/10 PPO/PP/(PS-block-PEB) with PPO denoting poly(phenylene oxide), PP denoting polypropylene, and PEB denoting poly(ethylene-co-1-butene); and (iii) 63/27/10 PMMA/ PP/(PRMS-block-PI) with PMMA denoting poly(methyl methacrylate). Blend specimens were prepared by melt blending in a Mini-Max mixer at temperatures above and below the T ODT of block copolymer. The TEM images of ternary blends showed a uniform distribution of (i) PRMS-block-PI layer on the surface of PB droplets dispersed in the PS matrix and (ii) PS-block-PEB layer on the surface of PP droplets dispersed in the PPO matrix only when melt blending was carried out at a temperature above the TODT of block copolymer. The formation of a uniform interphase between two immiscible homopolymers is attributed to the attractive thermodynamic interactions existing (i) between homopolymer PB and PI block in the 63/27/10 PS/PB/(PRMS-block-PI) ternary blend and (ii) between homopolymer PPO and PS block and between homopolymer PP and PEB block in the 63/27/10 PPO/PP/(PS-block-PEB) ternary blend. The present study indicates that the T ODT of block copolymer, in relation to melt blending temperature, determines whether the block copolymer can play the role of an effective compatibilizing agent even when thermodynamic requirements (attractive interactions) for compatibilization are satisfied. Thus, we have concluded that attractive thermodynamic interactions alone are not sufficient for compatibilization of two immiscible homopolymers unless the T ODT of block copolymer is lower than melt blending temperature, because the viscosity of block copolymer in an ordered state (at T < TODT) is a few orders of magnitude higher than that in the disordered state (at T > TODT). That is, the mobility of block copolymer plays an important role in the compatibilization of two immiscible homopolymers.