Block Copolymer Samples Research Articles

Experimental investigations into additive manufacturing of styrene-ethylene-butylene-styrene block copolymers using solvent cast 3D printing technique

PurposeThis paper aims to discuss the successful 3D printing of styrene–ethylene–butylene–styrene (SEBS) block copolymers using solvent-cast 3D printing (SC-3DP) technique.Design/methodology/approachThree different Kraton grade SEBS block copolymers were used to prepare viscous polymer solutions (ink) in three different solvents, namely, toluene, cyclopentane and tetrahydrofuran. Hansen solubility parameters (HSPs) were taken into account to understand the solvent–polymer interactions. Ultraviolet–visible spectroscopy was used to analyze transmittance behavior of different inks. Printability of ink samples was compared in terms of shape retention capability, solvent evaporation and shear viscosity. Dimensional deviations in 3D-printed parts were evaluated in terms of percentage shrinkage. Surface morphology of 3D-printed parts was investigated by scanning electron microscope. In addition, mechanical properties and rheology of the SC-3D-printed SEBS samples were also investigated.FindingsHSP analysis revealed toluene to be the most suitable solvent for SC-3DP. Cyclopentane showed a strong preferential solubility toward the ethylene–butylene block. Microscopic surface cracks were present on tetrahydrofuran ink-based 3D-printed samples. SC-3D-printed samples exhibited high elongation at break (up to 2,200%) and low tension set (up to 9%).Practical implicationsSC-3DP proves to be an effective fabrication route for complex SEBS parts overcoming the challenges associated with fused deposition modeling.Originality/valueTo the best of authors’ knowledge, this is the first report investigating the effect of different solvents on physicomechanical properties of SC-3D-printed SEBS block copolymer samples.

Improved strength, creep resistance and recyclability of polyisoprene vitrimers by bottom-up construction of inhomogeneous network

Vitrimer elastomers bring huge chance to solve the recycling problem of conventional rubbers. However, their application is extremely limited by their lack of creep resistance. Although the crosslinking density can significantly affect the relaxation behavior of dynamic covalent networks, but limited by the tradeoff between mechanical strength and creep resistant properties. Here, we introduce inhomogeneous dynamic covalent network with regions of different crosslinking densities, in which the low crosslinking density mainly contribute to the creep resistance and the high crosslinking density contribute to the mechanical strength. In detail, block copolymers with polymyrcene and polyisoprene blocks and its control sample polyisoprene were prepared and epoxidized. The polymyrcene block is a double bond-rich block compared to polyisoprene block, which will become an epoxy group-rich block after epoxidation and a high cross-link density phase region after crosslinking with a dicarboxylic acid agent. Therefore, the cross-linked block copolymer will have an inhomogeneous dynamic covalent network, which were confirmed by the Multi-quantum (MQ) NMR tests, AFM images and tanδ measurement. And the heterogeneous structure becomes more obvious with the increased length of polymyrcene block. WAXD results show that cross-linked block copolymers have lower strain-induced crystallization onset strain and higher crystallinity, making them far stronger and tougher. In addition, block copolymer samples demonstrate lower creep and lower permanent set due to slow relaxation of the low crosslinking density regions. The recycling efficiencies of mechanical strength of block copolymer samples were higher than that of homopolymer. This work provides a useful approach for improving the mechanical properties and dimensional stability of vitrimer elastomers simultaneously.

Synthesis and self-assembly of fluorinated supramolecular mesogen-jacketed liquid crystalline polymer and its high-χ block copolymer constructed by hydrogen bonding

By connecting a fluorinated molecule 2,5-bis((4-(perfluorohexyl)benzoyl)oxy)benzoic acid (6DFP) to the poly(4-vinylpyridine) (P4VP) backbone through hydrogen bonding, we synthesized a new series of fluorinated supramolecular mesogen-jacketed liquid crystalline polymer (MJLCP) P4VP(6DFP)x, where x is the molar ratio of donor to acceptor. Polarized light microscopy and wide-angle X-ray scattering were used to investigate the liquid crystallinity of the resulting complexes. The results show that this kind of supramolecular MJLCP has good thermal stability, with the isotropization temperature of about 170 °C. Subsequently, by connecting the fluorinated molecule 6DFP to the commercially available coil−coil block copolymer (BCP) polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) chain also via hydrogen bond, we constructed a series of supramolecular rod−coil BCP PSmVn(6DFP)x, where m and n are the degrees of polymerization of PS and P4VP, respectively. PSmVn(6DFP)x exhibits a hierarchically ordered self-assembled structure. Owing to the introduction of fluorine atoms, the Flory-Huggins interaction parameter (χ) of such a supramolecular BCP is high. BCP sample with a low total degree of polymerization can still be ordered, and the periodic size can be as low as 11.5 nm. This work provides a new approach for the construction of small-sized structures by supramolecular BCPs via hydrogen bonding, which can be used as nanotemplates and nanoporous materials after selective removal of the small molecules.

Transition between tetragonal and hexagonal pattern in binary blends of ABC block copolymers with different chain lengths

The thin film morphology of binary blends of triblock copolymers (poly(isoprene - block - styrene - block - (2-vinylpyridine)) ISP after solvent vapor annealing (SVA) was investigated using AFM, GISAXS and TEM. Although bulk samples of binary ISP blends exhibit tetragonal pattern, thin films led either to tetragonal pattern or hexagonal pattern, depending on the annealing time. These transitions were attributed to the formation of non-synchronized wetting layers of I and P, leading to a variation of the inner composition in I and P during SVA. Surprisingly, the hexagonal morphology exhibited centered hexagons of I and surrounding hexagons of P, which is not predicted nor observed for neat block copolymer samples. Although the system must adopt the lowest P/S interface, our results suggest that the effect of chain length with marked difference in the studied blends is playing a major role. Particularly, the presence of long chains of I favors the formation of I domains with bigger size, in order to keep their conformation entropy loss as small as possible.

Two-dimensional (2D) small-angle X-ray scattering (SAXS) correlation spectroscopy for block copolymer consisting of microlamellar and liquid crystal (LC) structures

Thermally induced variation of an ABA type block copolymer including microlamellar and liquid crystal (LC) structures was probed monitored by two-dimensional (2D) small-angle X-ray scattering (SAXS). By taking an advantage of strong X-ray light source of a synchrotron radiation facility, i.e. Spring-8, time-resolved SAXS spectra of the block copolymer sample based on PEMA and BB-5(3-Me) was collected during heat treatment well below isotropization temperature of the LC structure. A substantial level of change in the spectral feature are observed when the sample is subjected to the applied temperature. Fine features of the spectral changes are readily analyzed by 2D correlation method, including conventional and hetero-spectral correlation analysis. Hetero-spectral 2D correlation analysis of the spectra collected along and perpendicular to the fiber axis elucidated details of the thermally induced variation of the microdomain structure of the copolymer. Namely, it was revealed that the heating of the copolymer sample first induces the decrease in the diffraction peak intensity at 0.32 nm−1 and 0.42 nm−1 in the spectra collected along the direction perpendicular to the fiber axis. Further heating eventually leads to the development of the peak at 0.27 nm−1 in the spectra measured along the direction parallel to the fiber axis. Above observation suggests that the applied temperature first result in the rotation of the periodical lamellar structure initially aligned to the direction perpendicular to the fiber axis. This rotation eventually leads to the appearance of the periodical lamellar structure along the direction parallel to the fiber axis.

Mixed morphology in low molar mass fluorinated block copolymers

New low molar mass (Mn ~ 20 kg mol−1) polystyrene-b-poly(methyl methacrylate-co-perfluorohexylethyl acrylate) (PS-b-P(MMA-co-FA)) block copolymers were synthesized all consisting of ~70 mol% PS block and ~30 mol% P(MMA-co-FA) block. The amount of FA counits in the latter block was increased (0.5, 1, 3 and 4 mol%) in order to enhance the incompatibility between the two blocks and to form different self-assembled nanostructures. The block copolymers were thermally annealed by Rapid Thermal Processing (RTP) over wide ranges of temperatures and times. Complementary SEM and AFM analyses evidenced that the introduction of FA counits above a critical content (~2 mol%) drove a self-assembly process through mixed morphologies. These were formed at a distance from the polymer–air interface and consisted of perpendicular cylinders of P(MMA-co-FA) in a PS matrix laying at the substrate– polymer interface, and surmounted PS stripes and PS dots. Modification by low amounts of FA produced block copolymer samples that self-assembled in new, mixed nanostructures, even though they possessed much lower molar masses than those of analogous well established PS-b-PMMA block copolymers.

Styrene-butadiene branched star-shaped asphalt modifiers: Synthesis and mechanical characterization

The synthesis and the corresponding characterization of styrene-butadiene (SB), branched, star-shaped copolymers was investigated as part of a research project on asphalt modification using polymers with precise molecular structures. The method of anionic polymerization was followed to prepare samples of block copolymers of SB, a synthesis method that controls chain-architecture, molecular weight distribution, monomer distribution, and the average molecular weight. The research studies are the synthesis of block copolymers including linear, three- and four-arms constructs, depending on the coupling agent used. The techniques of nuclear magnetic resonance (1NMR), differential scanning calorimetry (DSC), gel permeation chromatography (GPC), and rheology were carried out to characterize the copolymers. From the results of the 1NMR, DSC, and GPC analyses, all star-shaped copolymers investigated showed a similar block copolymer composition. Furthermore, the rheological behavior of one of the synthesized star-shaped copolymers was nearly the same as a four-branched commercial copolymer. Rheologically, the four-arm block copolymer sample had the largest storage modulus (G′) among the branched copolymers synthetized, indicating that such architecture produces a highly structured material. In regard to polymer-modified asphalt formulations, the three-branched copolymer architecture yielded better elastic behavior than the four-branch version. In summary, the findings of this investigation provide new insight about a polymer system that may offer advantages in industrial asphalt paving applications.

Photo‐responsive block copolymer containing azobenzene group: Synthesis by reversible addition‐fragmentation chain transfer polymerization and characterization

ABSTRACTThe design and synthesis of a new azobenzene‐based methacrylate monomer (Azo‐IEM) was demonstrated, and its polymerization behavior during reversible addition‐fragmentation chain transfer (RAFT) polymerization was investigated. Well‐defined homopolymer and amphiphilic block copolymer containing Azo‐IEM monomeric units were successfully prepared as evidenced by NMR and GPC analysis. Moreover, the photo‐triggered reversible isomerization of polymer products in selected solvents was investigated. Finally, TEM analysis showed that there were significant differences in the nanoparticle morphologies when the block copolymer samples were irradiated with different wavelengths of light (i.e., UV and visible). The size and shapes of the p(HEMA‐b‐Azo‐IEM) polymer capable of transitions upon changes in Vis/UV light exposure which prepared from MeOH/CHCl3 mixture solvent. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47870.

Towards fast nanopattern fabrication by local laser annealing of block copolymer (BCP) films

The nanopatterning of surfaces and thin films with pattern dimensions of less than 100 nm is challenging for laser processing in particular in the case of large-area, low-cost fabrication. Self-assembly processes, however, provide a mechanism of pattern generation in this dimensional range offering an alternative fabrication method. The current work focuses on high-temperature, short-time laser annealing of PS-b-PMMA block copolymer (PS-b-PMMA BCP: poly(styrene-block-methyl methacrylate)) films on fused silica samples to achieve self-assembly into vertical lamellas with periods of approximately 50 nm. BCP samples were irradiated with a focussed CO2-laser beam for studying the influence of the laser power PL and the scanning speed vs on the lamellae formation in BCP films. The formation of lamellae is observed in the centre of the laser track at sufficient laser irradiation (PL: 2 to 15 W, vs: 1 to 250 mms−1). With increasing laser irradiation, first the quality of the lamellas improves to a certain point but thereafter a partial degradation of the BCP and dewetting of the BCP film occurs. The partial degradation of the PMMA micro-phase of the ordered BCP results in a local self-developing process reducing the processing steps for nanopattern formation. The experimental results on laser-induced local self-assembly with irradiation times below 0.1 s are discussed in relation to laser-induced temperature field simulations. Combining self-assembly capabilities of BCP with local heating by laser beams can provide a tool for direct writing of hierarchical nano-/microscale patterns that is useful for various applications mimicking bio-inspired structures.

Chromatographic characterization of amphiphilic di- and tri-block copolymers of poly(ethylene oxide) and poly(ε-caprolactone).

Amphiphilic di- and tri-block copolymers based on poly(ethylene oxide) as a hydrophilic segment and poly(ε-caprolactone) as a hydrophobic part are synthesized by the ring-opening polymerization of ε-caprolactone while using poly(ethylene glycol)s and methoxy poly(ethylene glycol)s of varying molar masses as macro-initiators. The synthesized block copolymers are characterized with respect to their total relative molar mass and its distribution by size exclusion chromatography. Liquid chromatography at critical conditions of both blocks is established for the analysis of individual block lengths and tracking presence of unwanted homopolymers of both types in the block copolymer samples. New critical conditions of polycaprolactone on reversed phase column are reported using organic mobile phase. The established critical conditions of polycaprolactone extended the applicable molar mass range significantly compared to already reported critical conditions of polycaprolactone in aqueous mobile phase. Block copolymers are also analyzed at critical conditions of poly(ethylene glycol). Complete analysis of the di- and tri-block copolymers at corresponding critical conditions provided a fair estimate of molar mass of non-critical block besides information regarding presence of homopolymers of both types in the samples.

Depolarized Scattering from Block Copolymer Grains Using Circularly Polarized Light

The grain structure of ordered block copolymer materials affects their viscoelastic, adhesive, optical, and electrical properties. Depolarized light scattering has proven to be an important method for characterizing this grain structure. In this paper, we use both theory and experiments to demonstrate the relationship between grain structure and depolarized light scattering from ordered block copolymer samples performed with crossed circular polarizers. We model the sample assuming it comprises randomly oriented ellipsoidal grains with optic axes coincident with the ellipsoid axes. We show that the scattering pattern obtained using circularly polarized (CP) light is azimuthally symmetric, in contrast to that obtained using linearly polarized (LP) light which exhibits 4-fold angular modulation. The integrated scattered power in the CP case is twice as large as that in the LP case. By simultaneously fitting CP and LP light scattering data, we obtain robust measures of parameters that characterize grain stru...

Functionally integrated liquid crystalline photochromic triple block copolymer with locally light‐ and thermal‐controllable sub‐blocks

ABSTRACTPhotoorientation and reorientation processes induced by illumination of the samples with oppositely directed polarized light and by the thermal treatment were studied for the films of triblock copolymer pAzo10‐b‐pPhM80‐b‐pAzo10 consisting of a nematic phenyl benzoate сentral sub‐block (PhM, DP = 80) with two terminal smectic azobenzene sub‐blocks (Azo, DP = 10). For amorphized films of triblock copolymer, illumination with polarized light (λ = 546 nm) is shown to be by orientation of only Azo‐containing groups, but upon following annealing of the film, PhM groups are adjusted to the orientation of Azo fragments. It was found, that the subsequent illumination of the block copolymer sample with oppositely directed polarized light changes the orientation of azobenzene groups, while the orientation of phenyl benzoate groups is remained unchanged. Thus, the cyclic illumination of the triblock copolymer samples by the linear polarized light and subsequent thermal treatment make it possible to control and fix orientation of azobenzene and phenyl benzoate groups located in different sub‐blocks in the desired and independent manner. The comparison of these results with the data on random p(Azo7‐ran‐PhM30) copolymer of the similar composition revealed, that in the random copolymer, both Azo and PhM mesogenic groups are involved in the orientational cooperative process regardless of films process treatment. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 1602–1611

Assessing the Local Nanomechanical Properties of Self-Assembled Block Copolymer Thin Films by Peak Force Tapping.

The mechanical properties of several types of block copolymer (BCP) thin films have been investigated using PeakForce quantitative nanomechanical mapping. The samples consisted of polystyrene/poly(methylmethacrylate) (PS/PMMA)-based BCP thin films with different pitches both randomly oriented and self-assembled. The measured films have a critical thickness below 50 nm and present features to be resolved of less than 22 nm. Beyond measuring and discriminate surface elastic modulus and adhesion forces of the different phases, we tuned the peak force parameters in order to reliably image those samples, avoiding plastic deformation. The method is able to detect the changes in mechanical response associated with the orientation of the PMMA cylinders with respect to the substrate (parallel versus vertical). The nanomechanical investigation is also capable of recognizing local stiffening due to the preferential growth of alumina deposited by atomic layer deposition on BCP samples, opening up new possibilities in the field of hard mask materials characterization.

RAFT Dispersion Polymerization in Nonpolar Media: Polymerization of 3-Phenylpropyl Methacrylate in n-Tetradecane with Poly(stearyl methacrylate) Homopolymers as Macro Chain Transfer Agents

Poly(stearyl methacrylate) (PSMA) homopolymers, prepared by RAFT radical polymerization, have been employed in the RAFT dispersion polymerization (RAFTDP) of 3-phenylpropyl methacrylate (PPMA) in n-tetradecane. RAFTDPs yielded block copolymers with narrow molecular weight distributions and tunable compositions and allowed for ready access to different polymorphic nanoparticle phases. Polymerization of PPMA at 20 wt %, for a fixed PSMA average degree of polymerization (Xn) of 19, allowed for the in situ preparation of soft matter nano-objects with spherical, worm, and vesicular morphologies. For a fixed block copolymer composition increasing total solids (from 10 to 40 wt %) favored the formation of nanoparticles with higher ordered morphologies. For block copolymer samples that formed soft physical gels at ambient temperature, a macroscopic thermoreversible degelation–gelation phenomenon was observed. The fundamental reason for this was a worm-to-sphere morphology transition that was facilitated, in part...

ASAXS measurements with soft (tender) X-rays to control the contrast

The structure and properties of thin soft matter materials might be better examined in detail by scattering measurements when the contrast between the materials and penetration depth are tunable. In the so-called tender X-ray region, there are several elements of interest for small-angle scattering measurements, such as Mg, Al, Si, P, and S. We worked on GISAXS measurements at K absorption edges of Si and P to control contrast and penetration depth for thin block copolymer (SEBS) samples and phospholipid alloy systems comprising of phospholipid (PC, DPPC), cholesterol, and ganglioside, and SAXS at Al for Al alloys. The photon energy used in the present measurements is soft enough to give large anomalous effect in the real part of refractive indices for light elements, yet hard enough so that the scattering vector required for nanostructure analysis can be covered. By choosing the photon energy at the K absorption edge of Si, the contrast between Si substrate and polymer thin film can be suppressed, thereby suppressing dynamical effect in GISAXS intensity caused by reflected beam[1]. Combined with the depth sensitive analysis, this is useful to examine the nanostructures that are changing with the distance from the surface. Concerning the contrast change inside the thin films, change of the GISAXS intensities from PC (phosphatidylcholine)-cholestrol-ganglioside (GD1) films spin-cast on Si substrates have been examined at the K absortpion edge of P [2]. ASAXS for P has been examined by Stuhrmann and coworkers[3], but the number of works after them is not large. Present measurements using image plates showed that the hexagonal phase appearing in dried phospholipid alloy films suggests a contrast reversal with the photon energy.

Structural transitions in asymmetric poly(styrene)-block-poly(lactide) thin films induced by solvent vapor exposure.

Successive structural transitions in thin films of asymmetric poly(styrene)-block-poly(lactide) (PS-PLA) block copolymer samples upon exposure to tetrahydrofuran (THF) vapors have been monitored using atomic force microscopy (AFM) and both in situ and ex situ grazing incidence small-angle X-ray scattering (GISAXS). A direct link was established between the structure in the swollen state and the morphology formed in the dried state post solvent evaporation. This was related to the high incompatibility between the constituting blocks of the copolymer that thwarted the system from reaching the homogeneous disordered state in the swollen state under the specific conditions utilized in this study. Upon rapid solvent removal, the morphologies formed in the swollen state were trapped due the fast evaporation kinetics. This work provides a better understanding of the mechanisms associated with block copolymer thin film morphology changes induced by solvent vapor annealing.

Preparation, development and in vitro release evaluation of amphotericin B–loaded amphiphilic block copolymer vectors

The aim of this work is to design and develop a suitable polymeric formulation incorporating amphotericin B (Ampho B) in order to overcome its water insolubility problem. To this end, we have chosen the poly(isoprene-b-ethylene oxide) amphiphilic block copolymer (IEO) family. We investigate the self assembly behavior and the stability kinetics of IEO copolymer based nanostructures formed in HPLC grade water and in phosphate buffer saline (PBS). The IEO block copolymer samples investigated have different molecular weights and compositions. A gamut of light scattering techniques (static, dynamic and electrophoretic) were used in order to extract information on the size, ζ-potential and morphological characteristics of the structures formed, as a function of the molar ratio of incorporated lipophilic drug Ampho B. The amphiphilic character and the colloidal stability of the particular polymeric drug vectors indicate that these nanostructures can be utilized as effective containers for the particular hydrophobic drug. The incorporation of Ampho B led to alteration of the physicochemical and morphological characteristics of the pure polymeric carriers. It is observed that the in vitro release of Ampho B from the prepared vectors IEO-b:Ampho B was quite slow, while the IEO-a carriers did not release Ampho B.

Structure analysis of ethylene/1-octene copolymers synthesized from living coordination polymerization

A series of ethylene/1-octene random and block copolymer samples were synthesized via a living coordination polymerization catalyzed by bis[N-(3-methylsalicylidene)-2,3,4,5,6-pentafluoroanilinato] titanium(IV) dichloride/dMAO. The chain microstructures of the copolymers were elucidated by analytic TREF and DSC thermal fractionation techniques in this work. It was found that the living random copolymers possessed narrower intrachain composition distributions than those prepared from conventional metallocene catalysts. With the same short chain branching content, the melting temperature of living random copolymer was about 16°C lower than metallocene-catalyzed random copolymer. The living block copolymers were also studied in comparison with the olefin multiblock copolymer (OBC) produced from chain shuttling polymerization. The interchain composition distribution of OBC was found broader than living block copolymers. However, the crystal thickness distribution of OBC was narrower. The diblock copolymer had a bimodal distribution in the crystal thickness and the step triblock copolymer showed a trimodal distribution, in contrast to OBC’s single modal distribution.

Poly(methyl methacrylate)/poly(ethylene glycol)/poly(ethylene glycol dimethacrylate) micelles: Preparation, characterization, and application as doxorubicin carriers

ABSTRACTA crosslinked amphiphilic copolymer [poly(ethylene glycol) (PEG)–poly(methyl methacrylate) (PMMA)–ethylene glycol dimethacrylate (EGDM)] composed of PMMA, PEG, and crosslinking units (EGDM) was synthesized by atom transfer radical polymerization to develop micelles as carriers for hydrophobic drugs. By adjusting the molar ratio of methyl methacrylate and EGDM, three block copolymer samples (P0, P1, and P2) were prepared. The measurement of gel permeation chromatography and 1H‐NMR indicated the formation of crosslinked structures for P1 and P2. Fluorescence spectroscopy measurement indicated that PEG–PMMA–EGDM could self‐assemble to form micelles, and the critical micelle concentration values of the crosslinked polymer were lower than those of linear ones. The prepared PEG–PMMA–EGDM micelles were used to load doxorubicin (DOX). The drug‐loading efficiencies of P1 and P2 were higher than that of P0 because the crosslinking units enhanced the micelles' stability. With increasing drug‐loading contents, DOX release from the micelles in vitro was decreased, and in the crosslinked formulations, the release rate was also slower. An in vitro release study indicated that DOX release from the micelles for the linear samples was faster than that for crosslinked micelles. The drug feeding amount increased and resulted in an increase in the drug‐loading content, and the loading efficiency decreased. These PEG–PMMA–EGDM micelles did not show toxicity in vitro and could reduce the cytotoxicity of DOX in the micelles; this suggested that they are good candidates as stable drug carriers. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39623.

Thermoreversible Changes in Aligned and Cross-Linked Block Copolymer Melts Studied by Two Color Depolarized Light Scattering

A procedure for creating samples that can be repeatedly cycled between weakly aligned and strongly aligned states is described. Poly(styrene-b-isoprene) block copolymer samples were first shear-aligned and then cross-linked using a high energy electron beam. Samples with more than 1.0 cross-links per chain on average showed almost complete recovery of their initial alignment state even after 20 cycles of heating above the order–disorder transition temperature of the un-cross-linked block copolymer. Samples with 1.1 cross-links per chain, which showed over 90% loss of alignment on heating and almost 100% recovery of alignment on cooling, provided the best example of a reversible aligned-to-unaligned transition. Samples with lower cross-linking densities exhibited irreversible loss of alignment upon heating, while those with higher cross-linking densities exhibited less than 90% loss of alignment upon heating. Alignment was quantified by a technique that we call two color depolarized light scattering (TCDLS), an extension of the traditional depolarized light scattering experiment used to determine the state of order in block copolymers. Qualitative confirmation of our interpretation of TCDLS data was obtained by small-angle X-ray scattering and transmission electron microscopy.