PE Block Research Articles

Control of the confined and unconfined crystallization in glassy-crystalline poly(vinylcyclohexane)- b-poly(ethylene)- b-poly-(vinylcyclohexane) triblock copolymer in solution

The influence of the solvent evaporation rate on the crystallization of the poly(vinylcyclohexane)- b-poly(ethylene)- b-poly(vinylcyclohexane) (PVCH–PE–PVCH) triblock copolymer with the high T g of PVCH segment in chloroform was investigated. The competition between the crystallization of PE block and the vitrification of PVCH in the triblock copolymer was controlled through changing the solvent evaporation rate in the solution system at different temperatures ( T e). It was found that the melting temperature ( T m) of PVCH–PE–PVCH samples increased with increasing the T e when the T e was lower than the solvent boiling point (bp), depending on the crystalline temperatures. However, when T e was just a little above the solvent bp, two melting peaks, which corresponding to the fusion of the confined and unconfined crystals, respectively, were observed on the DSC curves of the samples. As T e increased to be higher temperature, only one lower melting peak, which corresponding to the fusion of the confined crystals, existed for each samples. It was also found that the crystallinity ( X c) of the samples decreased gradually when T e was lower than the solvent bp, and then decreased suddenly when T e was just a little above the solvent bp, finally reached a plateau (about 13.5%) at higher T e. The changes in X c of the samples depend on the evaporating time in the solution. The results should be related to the competition between the crystallization of PE block in solvent and the vitrification of PVCH block with the solvent evaporation. Furthermore, the competition was controlled through changing the solvent evaporation rate. The confined and unconfined crystallization of the samples could be freely adjusted.

Confinement effects on the crystallization and SSA thermal fractionation of the PE block within PE- b-PS diblock copolymers

Well defined polyethylene- b-polystyrene (PE- b-PS) diblock copolymers have been synthesized by anionic polymerization in a wide composition range, keeping the length and the microstructure of the PE block constant. These copolymers provide a model system to study the confined crystallization of PE. A fractionated crystallization behavior (i.e., multiple exotherms are observed upon cooling from the melt) was observed for the PE block within block copolymers with 26% and 11% PE (i.e., E 26 S 74 105 and E 11 S 89 244 diblock copolymers, where the subscripts indicate the composition in wt% and the superscript the molecular weight in kg/mol). For confined PE, annealing is always observed when the material is self-nucleated. In the case of E 11 S 89 244 , most of the PE spheres crystallize at very large supercoolings, a behavior previously reported in the literature and associated with homogeneous nucleation. However, in our case, the peak crystallization temperature (i.e., T c = 46.6 °C) is much lower (16 °C) than that reported for similar size PE nano-droplets but in diblock copolymer whose second block is chemically different to PS. We therefore conclude that the nature of the interphase between the two neighboring blocks may be responsible for such low temperature nucleation, since this T c is still quite high with respect to the vitrification temperature of PE (in comparison with other polymers whose homogeneous nucleation temperature has been found close to T g), a fact that could indicate that the homogeneous nucleation temperature has not been reached because surface (or interfacial) effects can dominate. Thermal fractionation takes advantage of the distribution of methyl sequence length in hydrogenated polybutadiene in order to produce by successive thermal annealing a distribution of lamellar thickness within each PE block. Such a distribution of thermal fractions is affected by confinement and therefore these experiments demonstrate the influence of morphological restrictions on the crystallization of the PE block within the PE- b-PS diblock copolymers. As the PE content in the copolymer decreases, topological confinement effects limit the size of the lamellar crystals that can be formed within the reduced dimensions of the microdomains (MD). By the use of the Gibbs-Thomson equation and the thermal fractionation results, a distribution of crystalline lamellar thickness within each MD was obtained and the orientation of the chains within the MD was deduced.

Confined Discotic Liquid Crystalline Self-Assembly in a Novel Coil−Coil−Disk Triblock Oligomer

An asymmetric ABC coil-coil-disk triblock oligomer, based on polyethylene-block-poly- (ethylene oxide)-block-pentakis(pentyloxy)triphenylene (PE-b-PEO-b-P5T or EEO-P5T), was successfully synthesized by coupling a hydroxyl-terminated PE-b-PEO diblock oligomer and 2-hydroxy-3,6,7,10,11- pentakis(pentyloxy)triphenylene using oxalyl chloride. The structure and morphology of the supra- molecular self-assembly in bulk EEO-P5T were studied by differential scanning calorimetry, small- and wide-angle X-ray scatterings, polarized light microscopy, and transmission electron microscopy. The PE block crystallized into interdigitated, extended chain crystals with a chain-tilting angle of 23° from the lamellar normal. The peak melting temperature (Tm) of the PE crystals was at 93.8 °C. The PEO block remained in the amorphous state because of its both ends being tethered to other two blocks and the mismatch of the cross-section areas at the PE-PEO and PEO-P5T interfaces. Bilayer P5Ts, sandwiched between amorphous PEO layers, exhibited a nematic columnar (Ncol) to nematic discotic (ND) transition at ca. 23 °C. Intriguingly, the ND to isotropic (or vice versa) transition was observed to coincide with the melting (or crystallization) of the PE block.

Self-assembly and crystallization behavior of a double-crystalline polyethylene- block-poly(ethylene oxide) diblock copolymer

The self-assembly and crystallization behavior of a well-defined low molecular weight polyethylene- block-poly(ethylene oxide) (PE- b-PEO) diblock copolymer was studied. The number-average degrees of polymerization for the PE and PEO blocks were 29 and 20, respectively. The molecular weight distribution was 1.04 as determined by size-exclusion chromatography. The PE- b-PEO sample exhibited two melting points at 28.7 and 97.4 °C for the PEO and the PE crystals, respectively. The crystallization of the PE blocks was unconfined, while the crystallization of the PEO blocks was confined between pre-existing PE crystalline lamellae, as demonstrated by simultaneous small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) studies. In the fully crystalline state, both PE and PEO blocks formed extended-chain crystals with PE chains tilted ∼22° from the lamellar normal and PEO chains parallel to the lamellar normal, as evidenced by two-dimensional WAXD study of shear-oriented samples. Regardless of hydrogen bonding among hydroxyl chain ends in the PEO blocks, interdigitated, single-crystalline layer morphology was observed for both PE and PEO crystals. The partial crystalline morphology, where the PE crystallizes and the PEO is amorphous, had the same overall d-spacing as the fully crystalline morphology. A double-amorphous PEO layer sandwiched between neighboring PE crystalline layers was deduced based on a chain conformation study using Fourier transform infrared. The confined crystallization kinetics for PEO blocks was investigated by differential scanning calorimetry, which could be explained by a heterogeneous nucleation mechanism. The slower crystallization rate in the PEO-block than the same molecular weight homopolymer was attributed to the effects of nanoconfinement and PEO chains tethered to the PE crystals.

Crystallization and structure formation of block copolymers containing a glassy amorphous component

AbstractFormation of higher‐order structure in crystallization from microphase‐separated melts was studied for polystyrene–polyethylene (PS–PE) diblock copolymers and PS–PE–PS triblock copolymers with time‐resolved synchrotron small‐angle X‐ray scattering (SR–SAXS) techniques. The PE block was crystallized at temperatures when the PS block was in the glassy state. In both crystallization and melting processes, only the peak intensity in the SR–SAXS curve changed, however, the peak positions including higher‐order peaks did not change. This means that the microphase‐structure in the crystalline state was completely the same as that in the molten state. These behaviors were observed regardless of any melt microphase structure. Also, once a stable microphase structure was formed in the molten state, the structure was not changed even if crystallization and melting were repeated. Behavior of crystallization from such microphase‐separated melts was also studied. Apparent activation energies of crystallization were high for all block copolymers, compared with that for the PE homopolymer. In particular, the triblock copolymers showed higher apparent activation energies than the diblock copolymers. Both degrees of crystallinity and Avrami indices were greatly suppressed in crystallization from the cylindrical domain. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4199–4206, 2004

Morphology of melt-quenched poly(ε-caprolactone)- block-polyethylene copolymers

The morphology of a melt-quenched crystalline–crystalline diblock copolymer, poly(ε-caprolactone)- block-polyethylene (PCL- b-PE), was studied by small-angle X-ray scattering and transmission electron microscopy. The melting behavior of PCL- b-PE was also investigated by differential scanning calorimetry. The melting temperature of PCL blocks, T m,PCL, was ca. 55 °C and that of PE blocks was ca. 96 °C. Therefore, the PE block always crystallized first during quenching from the microphase-separated melt into various temperatures T c below T m,PCL to yield an alternating structure composed of PE lamellae and amorphous layers (PE lamellar morphology), and subsequently the crystallization of PCL blocks started at T c after some induction period. The PE lamellar morphology was preserved after the crystallization of PCL blocks at low crystallization temperatures ( T c<30 °C), that is, the PCL block crystallized within the PE lamellar morphology. At high crystallization temperatures (45 °C> T c>30 °C), on the other hand, the crystallization of PCL blocks destroyed the PE lamellar morphology to result in a new lamellar morphology mainly consisting of PCL lamellae and amorphous layers (PCL lamellar morphology). The PE crystals were fragmentarily dispersed in the PCL lamellar morphology.

Anisotropic Deformation Behavior of the Oriented Nanostructure of a Semicrystalline Terblock Copolymer with Multi-Scale Orderings

A highly oriented nanostructure of poly(styrene)-b-(ethylene-alt-propylene)-b-(ethylene) (PS/PEP/PE) semicrystalline terblock copolymer was deformed under tensile loading. Roll casting process oriented the microdomains of the terpolymer. Hexagonally ordered PS cylinders subsequently guided the crystallization of the PE block occurring in between the PS cylinders, resulting in the molecular chain orientation of the PE blocks perpendicular to the PS cylinder axis. The structure change of the terblock copolymer under deformation was monitored using Simultaneous Wide Angle X-ray Scattering (WAXS) and Small Angle X-ray Scattering (SAXS). The samples with the load parallel and perpendicular to the cylindrical axis of the PS show their mechanical failures at the strain of approximate 100 % and 210%, respectively. The anisotropic mechanical behavior was interpreted by interplay of the different types of the nano scale domains

Crystallization in Microdomains of a Block Copolymer Comprising Semicrystalline Block Observed by Simultaneous Measurement of SAXS and WAXS with H v‐SALS or DSC

Semicrystalline block copolymers provide us with a fascinating model for studying the kinetics of crystallization. We performed the simultaneous measurement of small‐ (SAXS) and wide‐angle (WAXS) x‐ray scattering (SWAXS) with differential scanning calorimetry (DSC), or SWAXS with small‐angle light scattering (H v‐SALS). The specimen used was polyethylene‐b‐poly(ethylene propylene) (PE‐b‐PEP) with the molecular weight of 44,200. The PE block has the melting point (T m) at 108°C. We observed the time evolution of crystallization in the lamellar microdomains of PE‐b‐PEP after a temperature drop from 180°C (≫T m) to a variety of temperatures slightly below T m. The exothermic signal was observed by DSC right after the temperature drop, while the four‐leaf‐clover pattern of H v‐SALS and the SAXS peaks due to the lamellar microdomains were observed several minutes after the temperature equilibration. The WAXS peaks of (110) and (200) reflection were almost simultaneously detected with the H v‐SALS and the SAXS peaks at crystallization temperature of 100°C. With the crystallization temperature closer to T m, the WAXS crystalline signals showed up with longer time lag after the H v‐SALS and the SAXS peaks began to appear. Interestingly, these phenomena are interpreted as that long‐range order of density fluctuation up to the order of micrometers was generated prior to the formation of crystals with partially ordered phase rather than the instantaneous crystalline nucleation.

Toughening of polylactide by melt blending with linear low‐density polyethylene

AbstractMelt blending of polylactide and linear low‐density polyethylene (LLDPE) was performed in an effort to toughen polylactide. In addition, two model polylactide‐polyethylene (PLLA‐PE) block copolymers were investigated as compatibilizers. The LLDPE particle size and the impact resistance of binary and ternary blends were measured to determine the extent of compatibilization. For the amorphous polylactide (PLA), toughening was achieved only when a PLLA‐PE block copolymer was used as a compatibilizer. For the semicrystalline polylactide (PLLA), toughening was achieved in the absence of block copolymer. To decrease the variability in the impact resistance of the PLLA/LLDPE binary blend, as little as 0.5 wt % of a PLLA–;PE block copolymer was effective. The differences that were seen between the PLA and PLLA binary blends were investigated with adhesion testing. The semicrystalline PLLA did show significantly better adhesion to the LLDPE. We propose that tacticty effects on the entanglement molecular weight or miscibility of polylactide allow for the improved adhesion between the PLLA and LLDPE. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3757–3768, 2003

Nanostructures, Semicrytalline Morphology, and Nanoscale Confinement Effect on the Crystallization Kinetics in Self-Organized Block Copolymer/Thermoset Blends

This work reports the first instance of self-organized thermoset blends containing diblock copolymers with a crystallizable thermoset-immiscible block. Nanostructured thermoset blends of bisphenol A-type epoxy resin (ER) and a low-molecular-weight (Mn = 1400) amphiphilic polyethylene-block-poly(ethylene oxide) (EEO) symmetric diblock copolymer were prepared using 4,4‘-methylenedianiline (MDA) as curing agent and were characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM), small-angle X-ray scattering (SAXS), and differential scanning calorimetry (DSC). All the MDA-cured ER/EEO blends do not show macroscopic phase separation but exhibit microstructures. The ER selectively mixes with the epoxy-miscible PEO block in the EEO diblock copolymer whereas the crystallizable PE blocks that are immiscible with ER form separate microdomains at nanoscales in the blends. The PE crystals with size on nanoscales are formed and restricted within the individual spherical micelles in the nanostructured ER/EEO blends with EEO content up to 30 wt %. The spherical micelles are highly aggregated in the blends containing 40 and 50 wt % EEO. The PE dentritic crystallites exist in the blend containing 50 wt % EEO whereas the blends with even higher EEO content are completely volume-filled with PE spherulites. The semicrystalline microphase-separated lamellae in the symmetric EEO diblock copolymer are swollen in the blend with decreasing EEO content, followed by a structural transition to aggregated spherical micellar phase morphology and, eventually, spherical micellar phase morphology at the lowest EEO contents. Three morphological regimes are identified, corresponding precisely to the three regimes of crystallization kinetics of the PE blocks. The nanoscale confinement effect on the crystallization kinetics in nanostructured thermoset blends is revealed for the first time. This new phenomenon is explained on the basis of homogeneous nucleation controlled crystallization within nanoscale confined environments in the block copolymer/thermoset blends.

Crystallization in ABC Triblock Copolymers with Two Different Crystalline End Blocks: Influence of Confinement on Self‐Nucleation Behavior

AbstractThe influence of different confinements active during crystallization within polybutadiene‐block‐polyisoprene‐block‐poly(ethylene oxide) (PB‐b‐PI‐b‐PEO) and the corresponding hydrogenated polyethylene‐block‐poly(ethylene‐alt‐propylene)‐block‐poly(ethylene oxide) (PE‐b‐PEP‐b‐PEO) triblock copolymers on the self‐nucleation behavior of the crystallizable PEO and PE blocks is investigated by means of differential scanning calorimetry (DSC). In triblock copolymers with PEO contents ≤ 20 wt.‐% crystallization of PEO is confined within small isolated microdomains (spheres or cylinders), and PEO crystallization takes place exclusively at high supercoolings. Self‐nucleation experiments reveal an anomalous behavior in comparison to the classical self‐nucleation behavior found in semicrystalline homopolymers. In these systems, domain II (exclusive self‐nucleation domain) vanishes, and self‐nucleation can only take place at lower temperatures in domain IIISA, when annealing is already active. The self‐nucleation behavior of the PE blocks is significantly different compared with that of the PEO blocks. Regardless of the low PE content (10–25 wt.‐%) in the investigated PE‐b‐PEP‐b‐PEO triblock copolymers a classical self‐nucleation behavior is observed, i.e., all three self‐nucleation domains, usually present in crystallizable homopolymers, can be located. This is a direct result of the small segmental interaction parameter of the PEP and PE segments in the melt. As a consequence, crystallization of PE occurs without confinement from a homogeneous mixture of PE and PEP segments. Self‐nucleation regimes of a block copolymer showing confined crystallization by means of DSC.magnified imageSelf‐nucleation regimes of a block copolymer showing confined crystallization by means of DSC.

Role of Block Copolymers on Suppression of Droplet Coalescence

Block copolymer reduces particle size in immiscible polymer−polymer blends by suppressing droplet coalescence and by aiding droplet breakup through reduced interfacial tension. In this paper we separated coalescence from breakup and studied suppression of coalescence by block copolymers in a model blend composed of polystyrene (PS), high-density polyethylene (HDPE), and polystyrene−polyethylene (PS−PE) block copolymer. Coalescence was examined by monitoring particle size change vs shear strain while varying the shear rate, block copolymer concentration, molecular weight, and symmetry (coil size ratio of blocks). Even 0.5% PS−PE block copolymer significantly suppressed coalescence of HDPE droplets in a PS matrix. Assuming all of the PS−PE molecules were at the interface, the minimum concentration of block copolymers required to prevent coalescence under shear was found to be about 0.2 chain/nm2 at a coalescence shear rate of 0.1 s-1 for PS−PE with a molecular weight of 20−20 kg/mol. We found that this minimum concentration decreased with shear rate and with increasing molecular weight of PS−PE. We also found that, with the total molecular weight being the same, a PS−PE with a larger PS block suppressed HDPE particle coalescence more efficiently than one with a smaller block. These results indicate that steric repulsive interactions due to the presence of block copolymer at the interfaces are more important than those due to interfacial tension gradients.

Thermal and self‐nucleation behavior of molecular complexes formed by p‐nitrophenol and the poly(ethylene oxide) end block within an ABC triblock copolymer

We have been able to prepare a molecular complex between the poly(ethylene oxide) block of a poly(ethylene)-b-poly(ethylene-alt-propylene)-b-poly(ethylene oxide) triblock copolymer and p-nitrophenol (PNP). The composition of the copolymer employed was: 24% PE, 57% PEP and 19% PEO in weight percent. The pure copolymer exhibited a nonconventional thermal behavior since the PEO block displayed a fractionated crystallization process during cooling. The PEO block /PNP complex did not show any apparent crystallization during cooling, instead cold crystallization during heating was observed and an approximately 30 °C increase in melting point as compared to the neat PEO block within the copolymer. This caused an overlap in the melting regions of the PE block and the PEO block/PNP complex. The self-nucleation of the PE-b-PEP-b-PEO/PNP complex is very different from that of the neat triblock copolymer. An increased capacity for self-nucleation of the PEO block was produced by the complexation with PNP and therefore the three self-nucleation domains were clearly encountered for both the PE block and for the PEO block/PNP complex. Self-nucleation was able to show that the two crystallizable blocks can be self-nucleated and annealed in an independent way, thereby ascertaining the presence of separate crystalline regions in the triblock copolymer. Through the use of PNP, both the crystallinity and the melting point of the PE-b-PEP-b-PEO block copolymer employed here can be substantially increased. Similar results were obtained by complexation of the same ABC triblock copolymer with resorcinol.

Crystallization of the polyethylene block in polystyrene-b-polyethylene-b-polycaprolactone triblock copolymers, 1. Self-nucleation behavior

The self-nucleation of branched polyethylene chains of different degrees of chain mobility was studied. The polyethylene block (PE block) within poly(styrene-b-ethylene-b-caprolactone) triblock copolymers (SEC) of varying compositions was studied. Differential scanning calorimetry was used to determine the self-nucleation domains as a function of the self-nucleation temperature (Ts). The self-nucleation behavior of PE chains within SEC block copolymers was found to be anomalous in comparison to the classical self-nucleation behavior exhibited by homopolymers. When the degree of chain constraint is high, as in the case where the SEC copolymer only contains 15% of PE, domain II (only self-nucleation domain) completely disappears and annealing can take place before self-nucleation occurs. This means that chain constraint complicates the self-nucleation process and this situation persists until, upon decreasing the self-nucleation temperature (Ts), annealing has generated crystals that are big enough to act as self-nuclei for the less restricted portions of the chain. If the PE content in the copolymer is very low (15%), two crystal populations can be distinguished. This may reflect the differences in diffusion of the PE chain segments close to the interfaces with the other two blocks and those segments that are close to the middle of the PE block. The influence of chain constraint on determining the difficulty of the chains to self-nucleate was further explored using a crosslinked low-density polyethylene (XLDPE). In this case, crosslinking junctions instead of covalent links with other blocks restrict chain mobility. Nevertheless, a similar difficulty in self-nucleation was found as in the case of the PE block within SEC triblock copolymers in contrast to neat LDPE, a polymer that exhibited the classical self-nucleation behavior with the usual three domains.

Crystallization of the polyethylene block in polystyrene-b-polyethylene-b-polycaprolactone triblock copolymers, 1. Self-nucleation behavior

The self-nucleation of branched polyethylene chains of different degrees of chain mobility was studied. The polyethylene block (PE block) within poly(styrene-b-ethylene-b-caprolactone) triblock copolymers (SEC) of varying compositions was studied. Differential scanning caloriometry was used to determine the self-nucleation domains as a function of the self-nucleation temperature (T s ). The self-nucleation behavior of PE chains within SEC block copolymers was found to be anomalous in comparison to the classical self-nucleation behavior exhibited by homopolymers. When the degree of chain constraint is high, as in the the case where the SEC copolymer only contains 15% of PE, domain II (only self-nucleation domain) completely disappears and annealing can take place before self-nucleation occurs. This means that chain constraint complicates the self-nucleation process and this situation persists until, upon decreasing the self-nucleation temperature (T s ), annealing has generated crystals tha are big enough to act a self-nuclei for the less restricted portions of the chain. If the PE content in the copolymer is very low (15%), two crystal populations can be distinguished. This may reflect the differences in diffusion of the PE chain segments close to the interfaces with the other two blocks and those segments that are close to the middle of the PE block. the influence of chain constraint on determining the difficulty of the chains to self-nucleate was further explored using a crosslinked low-density polyethylene (XLDPE). In this case, crosslinking junctions instead of covalent links with other blocks restrict chain mobility. Nevertheless, a similar difficulty in self-nucleation was found as in the case of the PE block within SEC triblock copolymers in contrast to neat LDPE, a polymer that exhibited the classical self-nucleation behavior with the usual three domains.

Synthesis and fractionation of syndiotactic-polystyrene/polyethylene copolymers with C 5H 5TiCl 3 catalysts

Highly stereoregulated syndiotactic-polystyrene/polyethylene (s-PS/PE) block copolymers with variable ethylene block lengths are synthesized using the sequential monomer feed scheme with C 5H 5TiCl 3 catalyst. The copolymer, after removing the atactic portion, is separated into two fractions by tetrahydrofuran (THF). The insoluble fraction contains a highly stereoregulated s-PS block linked with PE blocks, while the soluble fraction also contains a highly stereoregulated s-PS block but separated randomly by a shorter or isolated ethylene unit. For the I-fraction, r E=25±5 and r S=1.9±0.3, and for the S-fraction r E=0.4±0.1 and r S=0.34±0.15. These results are compared with prior studies, where mainly random type PS/PE copolymers with low styrene stereoregularity and rigio-irregular styrene and polyethylene are produced. Apparently, both the sequential feed scheme coupled with the use of a lower reactivity metallocene catalyst facilitated the switching of catalytical sites with the majority product being of block nature.

Miscibility and phase structure of at-polypropylene/ethylene- block-(ethylene- co-butylene)- block-ethylene-copolymer blend

Miscibility and phase structure in blends of atactic-polypropylene (aPP) with poly[ethylene- b-(ethylene- co-butylene)- b-ethylene] (E-b-EB-b-E) containing different butylene content in the mid-block were investigated by differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and field emission type scanning electron microscopy (FE-SEM). In DSC measurement, blends showed single glass transition temperature in no relation to the blend composition and the butylene contents of mid-block in the block copolymers. On the other hand, the melting point of PE block in the block copolymers was not varied systematically with variation of the blend composition with no relation to the butylene content. From these results, it is assumed that aPP dissolves in the EB block in the copolymers. In morphological observation, it was revealed that all blends have the islands–sea structures containing PE domain. In the blends using the high butylene content copolymer, it was observed that PE domain became smaller than that of neat block copolymer. On the other hand, in the lower butylene content copolymer, the microphase structure was not observed but fine dispersed phase separated structures were observed in the blends of aPP and the copolymer.

Crystallization of tethered polyethylene in confined geometries

Ordered poly(ethylene)-poly(vinylcyclohexane) (PE-PVCH) block copolymers are employed to study the crystallization of tethered PE in confined geometries. The high Tg of the PVCH component of these materials forces PE chains to crystallize in well-defined geometries dictated by the mesophase structure of the block copolymer. Effects of chain tethering on crystallization are examined through comparison of singly-tethered PE chains in PE-PVCH (EV) diblocks and doubly-tethered PE in PVCH-PE-PVCH (VEV) triblocks. Crystallinity is independent of the block copolymer mesophase structure in both the EV and VEV systems, although crystallinity in VEV depends on the molecular weight of the PE block of the copolymer. Melting temperature data indicate that spatial confinement reduces crystallite size in EV and VEV, and that the double tethering of PE chains in VEV reduces crystallite size further through topological constraints. Crystal nucleation and growth depend strongly on the type of microstructure in both EV and VEV block copolymers. Differences in the overall rate of crystallization are correlated with the dimensional continuity of the PE microdomains. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37:2053–2068, 1999

Crystallization of tethered polyethylene in confined geometries

Ordered poly(ethylene)-poly(vinylcyclohexane) (PE-PVCH) block copolymers are employed to study the crystallization of tethered PE in confined geometries. The high Tg of the PVCH component of these materials forces PE chains to crystallize in well-defined geometries dictated by the mesophase structure of the block copolymer. Effects of chain tethering on crystallization are examined through comparison of singly-tethered PE chains in PE-PVCH (EV) diblocks and doubly-tethered PE in PVCH-PE-PVCH (VEV) triblocks. Crystallinity is independent of the block copolymer mesophase structure in both the EV and VEV systems, although crystallinity in VEV depends on the molecular weight of the PE block of the copolymer. Melting temperature data indicate that spatial confinement reduces crystallite size in EV and VEV, and that the double tethering of PE chains in VEV reduces crystallite size further through topological constraints. Crystal nucleation and growth depend strongly on the type of microstructure in both EV and VEV block copolymers. Differences in the overall rate of crystallization are correlated with the dimensional continuity of the PE microdomains. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37:2053–2068, 1999

Antinucleation Effect of the Polyethylene Block on the Polycaprolactone Block in ABC Triblock Copolymers

Polystyrene-block-poly(ethylene-co-butylene)-block-poly(ε-caprolactone) triblock copolymers (SEC) were prepared by hydrogenating polystyrene-block-polybutadiene-block-poly(ε-caprolactone) triblock copolymers (SBC) previously prepared by sequential anionic polymerization. The effect of the crystallization of the polyethylene block (PE) upon cooling from a phase-segregated melt on the crystallization process of the adjacent polycaprolactone block (PCL) was investigated by means of differential scanning calorimetry and polarized optical microscopy. It was found that there was no nucleation effect of the PE block on the PCL block under controlled cooling conditions in the DSC. On the contrary, an antinucleation effect was detected when nucleation of the PCL block crystals within the SEC triblock copolymers was attempted. It was demonstrated that such an antinucleation effect was induced by the annealing of the polyethylene block crystals of the SEC copolymers. By the application of the successive self-nucleation and annealing technique (SSA) the possibility of producing a distribution of lamellar thickness within the PCL and the PE blocks of the SEC triblock copolymers was shown. These results, together with the spherulitic morphology displayed by the SEC copolymers with more than 50 wt.-% PCL, are consistent with previous morphological observations in SBC triblock copolymers. Those observations indicate that the chain stems within the lamellar crystals in the PCL blocks could be perpendicular to the interphase of the block copolymer domains, even though the crystallization occurred from a heterogeneous melt.