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Fast deformation of entangled melts is known to cause chain stretching due to affinelike straining of the entanglement network. Since the chain deformation may also result in perturbations of covalent bond angles and bond length, there are always possible enthalpic effects. In this study, we first subject polystyrene and PMMA of different molecular weights to either uniaxial melt extension or planar extension and subsequently impose rapid thermal quenching to preserve the chain deformation. Then, such pre-melt-deformed samples are annealed at various temperatures below the glass transition temperature Tg. During annealing, these samples can undergo appreciable contraction on a time scale much shorter than the alpha relaxation time. Significant retractive stress is observed when such contracting samples are held fixed during the annealing. The stress level can be nearly as high as the Cauchy stress produced during melt stretching. These observations not only allowed us to investigate glassy chain dynamics as well as the molecular nature of mechanical stress but may also suggest that pre-melt-stretched polymers can cause segmental mobilization in the glassy state. The available evidence indicates that the retractive stress is enthalpic in origin, associated with the conformational distortion at the bond level produced by melt stretching. [ABSTRACT FROM AUTHOR]

Monodispersed hairy nanocomposites with typical 2 nm (isophthalic acid)24Cu24 metal–organic polyhedra (MOP) as a core protected by 24 polymer chains with controlled narrow molecular weight distribution has been probed by imaging and scattering studies for the heterogeneity of polymers in the nanocomposites and the confinement effect the MOPs imposing on anchored polymers. Typical confined‐extending surrounded by one entanglement area is proposed to describe the physical states of the polymer chains. This model dictates the counterintuitive thermal and rheological properties and prohibited solvent exchange properties of the nanocomposites, whilst those polymer chain states are tunable and deterministic based on their component inputs. From the relationship between the structure and behavior of the MOP nanocomposites, a MOP‐composited thermoplastic elastomer was obtained, providing practical solutions to improve mechanical/rheological performances and processabilities of inorganic MOPs. [ABSTRACT FROM AUTHOR]

We carried out a large set of tests to establish a correlation between the molecular (network) structure (influenced by molecular weight, molecular weight distribution, and melt predeformation) and mechanical responses of several glassy polymers to uniaxial compression at different temperatures and different compression speeds. The experimental results show that to have ductile responses there must be an adequate chain network, afforded by the interchain uncrossability among sufficiently long chains. Specifically, polystyrene (PS) and poly(methyl methacrylate) of sufficiently low molar mass do not have chain network and are found to be very brittle. Binary PS mixtures are brittle at room temperature when the volume fraction of the high‐molecular‐weight component is sufficiently low (e.g., at and below 27.5%). Moreover, sufficiently melt‐stretched PS mixtures show brittle fracture when compressed along the same direction, along which melt stretching was made. All the experimental findings confirm that a robust chain network is also a prerequisite for yielding and ductile cold compression of polymer glasses, as is for extension. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 758–770 [ABSTRACT FROM AUTHOR]

We present the synthesis of poly(n-butyl acrylate)-g-poly(methyl methacrylate)(PnBA-g-PMMA) multigraft copolymersvia a grafting-through (macromonomer) approach. The synthesis wasperformed using two controlled polymerization techniques. The PMMAmacromonomer was obtained by high-vacuum anionic polymerization followedby the copolymerization of n-butyl acrylate and PMMAmacromonomer using reversible addition–fragmentation chaintransfer (RAFT) polymerization to yield the desired all-acrylic multigraftstructures. The PnBA-g-PMMA multigraftstructures exhibit randomly spaced branch points with various PMMAcontents, ranging from 15 to 40 vol %, allowing an investigation intohow physical properties vary with differences in the number of branchpoints and molecular weight of grafted side chains. The determinationof molecular weight and polydispersity indices of both the PMMA macromonomerand the graft copolymers was carried out using size exclusion chromatographywith triple detection, and the structural characteristics of boththe macromonomer and PnBA-g-PMMAgraft materials were characterized by 1H and 13C NMR. Matrix-assisted laser desorption/ionization time-of-flightmass spectrometry was employed for monitoring the macromonomer synthesis.Thermal characteristics of the materials were analyzed using differentialscanning calorimetry and thermogravimetric analysis. The mechanicalperformance of the graft materials was characterized by rheology anddynamic mechanical analysis, revealing that samples with PMMA contentof 25–40 vol % exhibit superior elastomeric properties as comparedto materials containing short PMMA side chains or <25 vol % PMMA.Lastly, atomic force microscopy showed a varying degree of microphaseseparation between the glassy and rubbery components that is stronglydependent on PMMA side chain molecular weight. [ABSTRACT FROM AUTHOR]

Comband centipede multigraft copolymers, poly(n-butylacrylate)-g-polystyrene (PnBA-g-PS) with PnBA backbones and PS side chains,were synthesized via high-vacuum anionic polymerization and miniemulsionpolymerization. Single-tailed and double-tailed PS macromonomers weresynthesized by anionic polymerization and Steglich esterification.Subsequently, the copolymerization of each macromonomer and nBA was carried out in miniemulsion, and multigraft copolymerswere obtained. The latex particles of multigraft copolymers were characterizedusing dynamic light scattering. The molecular weights of macromonomersand multigraft copolymers were analyzed by size exclusion chromatography.Moreover, the molecular weights and structures of macromonomers wereinvestigated by matrix-assisted laser desorption/ionization time-of-flightmass spectrometry and 1H nuclear magnetic resonance spectroscopy.The weight contents of PS in comb and centipede multigraft copolymerswere calculated by 1H nuclear magnetic resonance spectroscopy.The thermal properties of multigraft copolymers were characterizedby thermogravimetric analysis and differential scanning calorimetry.The microphase separation of multigraft copolymers was observed byatomic force microscopy and transmission electronic microscopy. Rheologicalmeasurements showed that comb and centipede multigraft copolymershave elastic properties when the weight content of PS side chainsis 26–32 wt %. Centipede multigraft copolymers possess betterelastic properties than comb multigraft copolymers with the similarweight content of PS. These findings are similar to previous resultson poly(isoprene-g-polystyrene) comb and centipedecopolymers made by anionic polymerization. [ABSTRACT FROM AUTHOR]

It has long been established that the coherent scattering intensity of neutrons by isotropic mixtures of hydrogenous and deuterated polymers of matching molecular weights is, to the first approximation, proportional to the single-chain structure factor of the polymer chain. The validity of this fundamental relation for equilibrium, undeformed polymer melts is well supported by the extensive experimental and theoretical investigations over the past several decades. The generalization of this relation to the case of nonequilibrium, deformed polymer melts, however, is not a trivial one. Despite its widespread usage in small-angle neutron scattering (SANS) studies of deformed polymer melts, the assumed proportionality between coherent scattering intensity and single-chain structure factor has received very little experimental scrutiny. This work quantitatively examines this issue through spherical harmonic expansion analysis of the anisotropic SANS spectra of deformed polystyrene melts of different levels of deuterium labeling. It is shown that the classical assumption works extremely well over a wide range of scattering wavevectors, where the isotropic component of the SANS spectrum and the leading term of structural anisotropy vary by more than two orders of magnitude. Image 1 • Application of the spherical harmonic expansion technique to quantitatively the SANS spectra. • Carefully designed and prepared experimental systems with identical melt structure and viscoelastic properties. • Confirmation of a fundamental assumption in SANS studies of deformed polymer melts. • Detailed exposition of relevant theoretical arguments. [ABSTRACT FROM AUTHOR]