Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session X42: Semicrystalline Polymers |
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Sponsoring Units: DPOLY Chair: Ahmed Ismail, University of West Virginia Room: 345 |
Friday, March 18, 2016 8:00AM - 8:12AM |
X42.00001: Crystallization of atactic polystyrene. Yu Chai, James Forrest Atactic polystyrene is often used as an archetypical example of a material that has no crystalline ground state due to the lack of order in the arrangement of phenyl groups along the backbone. However, even in polymers with perfect Bernoullian (random) statistics, there is a probability that a given molecule will have larger blocks of a given stereoregularity. These blocks, in turn, could allow the formation of nanocrysalline domains. As a model system to investigate whether such blocks could lead to nanoscale crystallinity, we consider PS with Mw less than 1000 where there is a reasonable probability of a molecule having all meso or racemo diads . For the case of Mw 600, there are clear indications of crystal growth with two characteristic temperatures below which two different crystal species can nucleate and grow. Similar crystal growth and melting behavior is observed for Mw 1000. [Preview Abstract] |
Friday, March 18, 2016 8:12AM - 8:24AM |
X42.00002: Bisoxalamide Clarifiers to Improve Optical Performance of Polyethylene Resins Lin Wang, Martin Hill, Nestor Santos Jr, Andrew Banks, Jessica Huang, Ellen Keene, Rich Keaton The use of special nucleating agents, often referred to as clarifying agents, to improve optical performance of polyethylene is not widely used in the industry. A series of bisoxalamide compounds were synthesized and mixed with linear low density polyethylene (LLDPE) to test clarification effects. In this talk, we will discuss structure/property relationship of these molecules on optical and thermal properties of LLDPE. [Preview Abstract] |
Friday, March 18, 2016 8:24AM - 8:36AM |
X42.00003: Coincident Crystallization of PEO-$b$-PCL Copolymers with Similar Block Molecular Weights Ryan Van Horn, Natasha Brigham, Christopher Nardi Poly(ethylene oxide)-\textit{block}-poly(epsilon-caprolactone) (PEO-$b$-PCL) copolymers have garnered much attention for their use in the biomedical field due to their biocompatibility and the degradation of PCL. The applications of this polymer are heavily dependent on the polymer's physical properties, including crystalline content. One complicating factor is the relatively similar transition temperatures for PEO and PCL. We have studied the coincident crystallization behavior of 5k-5k and 10k-10k g/mol samples using FTIR. Both samples were isothermally crystallized at varying temperatures to track the development of crystallinity over time. Experiments showed that the crystallization of both blocks occurred nearly simultaneously over all temperatures. Each block's crystallization behavior was affected by the other block's crystallization. [Preview Abstract] |
Friday, March 18, 2016 8:36AM - 8:48AM |
X42.00004: Self Nucleation and Crystallization of Poly(vinyl alcohol) David Thomas, Peggy Cebe Polyvinyl alcohol (PVA) is a hydrophilic, biodegradable, semi-crystalline polymer with uses ranging from textiles to medicine. Film samples of PVA were investigated to assess crystallization and melting behavior during self-nucleation experiments, and thermal degradation, using differential scanning calorimetry (DSC) and thermogravimetric (TG) analysis, respectively. TG results show that degradation occurred at temperatures close to the observed peak melting temperature of 223 C. Using conventional DSC, PVA was heated at a rate of 10 C/min to various self-nucleation temperatures, T$_{\mathrm{s}}$, within its melting range, briefly annealed, cooled and reheated. Three distinct crystallization regimes were observed upon cooling, depending upon self nucleation temperature. At low values of T$_{\mathrm{s}}$, below 227 C, PVA only partially melts; residual crystal anneals while new, less perfect crystals form during cooling. Between 228 C and 234 C, PVA was found to crystallize exclusively by self-nucleation. For T$_{\mathrm{s}}$ above 235 C the PVA melts completely. Fast scanning chip-based calorimetry was used to heat and cool at 2000 K/s, to prevent degradation. Results of self nucleation experiments using fast scanning and conventional DSC will be compared. [Preview Abstract] |
Friday, March 18, 2016 8:48AM - 9:00AM |
X42.00005: Folding of Polymer Chains in Early Stage of Crystallization Shichen Yuan, Toshikazu Miyoshi Understanding the structural formation of long polymer chains in the early stage of crystallization is one of the long-standing problems in polymer science. Using solid state NMR, we investigated chain trajectory of \textit{isotactic} polypropylene in the mesomorphic nano-domains formed via rapid and deep quenching. Comparison of experimental and simulated $^{\mathrm{13}}$C-$^{\mathrm{13}}$C Double Quantum (DQ) buildup curves demonstrated that instead of random re-entry models and solidification models, individual chains in the mesomorphic form $i$PP adopt adjacent reentry sequences with an average folding number of \textless n\textgreater $=$ 3-4 (assuming an adjacent re-entry fraction of \textless F\textgreater of 100{\%}) during mesomorphic formation process via nucleation and growth in the early stage. [Preview Abstract] |
Friday, March 18, 2016 9:00AM - 9:12AM |
X42.00006: Flow-Induced Crystallization of Poly(ether ether ketone). Behzad Nazari, Alicyn Rhoades, Ralph Colby The effects of an interval of shear above the melting temperature T$_{\mathrm{m}}$ on subsequent isothermal crystallization below T$_{\mathrm{m}}$ is reported for the premier engineering thermoplastic, poly(ether ether ketone) (PEEK). The effect of shear on the crystallization rate of PEEK is investigated by means of rheological techniques and differential scanning calorimetry (DSC) under a protocol of imposing shear in a rotational cone and plate rheometer and monitoring crystallization after quenching. The rate of crystallization at 320 \textdegree C was not affected by shear for shear rates \textless 7 s$^{\mathrm{-1}}$ at 350 \textdegree C, whereas intervals of adequate shear at higher shear rates prior to the quench to 320 \textdegree C accelerated crystallization significantly. As the duration of the interval of shear above 7 s$^{\mathrm{-1}}$ is increased, the crystallization time decreases but at each shear rate eventually saturates once the applied specific work exceeds \textasciitilde 120 MPa. The annealing of the flow-induced precursors was also investigated. The nuclei were fairly persistent at temperatures close to 350 \textdegree C, however very unstable at temperatures above 375 \textdegree C. This suggests that the nanostructures formed under shear might be akin to crystalline lamellae of greater thickness, compared to quiescently crystallized lamellae. [Preview Abstract] |
Friday, March 18, 2016 9:12AM - 9:24AM |
X42.00007: Fluoropolymer Microstructure and Dynamics: Influence of Molecular Orientation Induced by Uniaxial Drawing Daniel Miranda, Chaoqing Yin, James Runt Fluorinated semi-crystalline polymer films are attractive for dielectric film applications due to their chemical inertness, heat resistance, and high thermal stability. In the present investigation we explore the influence of orientation induced by uniaxial drawing on the crystalline microstructure and relaxation processes of poly(ethylene-tetrafluoroethylene) (ETFE), in order to ascertain how morphological control can benefit polymer dielectric design. When drawn below or near the T$_{\mathrm{g}}$, the crystallinity of the drawn films is unchanged, and oriented amorphous structures and crystalline microfibrils form at high draw ratios. This orientation slows segmental relaxation, reflected by an increase in the dynamic T$_{\mathrm{g}}$, and also delays the transition to the high temperature crystalline form of ETFE. When drawing above the T$_{\mathrm{g}}$, the films undergo strain-induced crystallization at high draw ratios. For these films an increase in the dynamic T$_{\mathrm{g\thinspace }}$is also observed, in addition to a second segmental relaxation process, appearing as a shoulder on the primary process. We propose that this represents a contribution from a rigid amorphous fraction, having slowed chain dynamics. [Preview Abstract] |
Friday, March 18, 2016 9:24AM - 9:36AM |
X42.00008: Structure of Poly(3-(2'-ethyl)hexylthiophene) (P3EHT) Containing Diblock Copolymers Controlled via Thermal Processing Emily Davidson, Rachel Segalman Poly(3-alkylthiophene)s with modified alkyl side chains crystallize confined within block copolymer microphases, serving as a good model system for the confined crystallization of semiflexible polymers. We hypothesize that the diblock structure may impose an equilibrium degree of crystalline conjugated chain folding which here is only accessible for small degrees of undercooling. Crystallization of these P3ATs in soft confinement drives microdomain expansion; here, we show that this expansion is minimized for crystallization at small degrees of undercooling. Upon heating, domains return to their melt structure over three distinct regimes. These regimes directly correspond to thermal features we assign to the relaxation of a rigid-amorphous fraction at the diblock interface, melt-recrystallization which reorganizes the degree of chain folding, and a final complete melting transition. [Preview Abstract] |
Friday, March 18, 2016 9:36AM - 9:48AM |
X42.00009: Annealing effects on the crystalline structures of syndiotactic polystyrene after the crystalline $\beta $ to $\alpha $ form structural transition induced by mechanical strain. Fuyuaki Endo, Atsushi Hotta The thermal effects on the polymorphic behavior of syndiotactic polystyrene (sPS) after the crystalline structural transition from $\beta $ to $\alpha $ were investigated. Our group has previously reported that $\beta $ form crystals of sPS could transform into $\alpha $ form crystals by mechanical strain at about 200°C. In this study, we investigated possible crystalline structural transitions of pre-stretched sPS by thermal treatments. More specifically, the samples containing $\beta $ form crystals were stretched at temperatures above the glass transition temperature (T$_{\mathrm{g}})$ before annealing. The crystalline structures in the sPS samples were characterized by Fourier-transform infrared spectroscopy and X-ray diffraction analyses. Before the annealing treatment, the samples stretched at near T$_{\mathrm{g}}$ possessed mesomorphic $\alpha $ form crystals, whereas the samples stretched at higher temperatures had more perfect $\alpha $ form crystals. It was also found that the mesomorphic $\alpha $ form crystals, produced by the mechanical strain at lower temperatures, could transform into perfect $\alpha $ form crystals by annealing, and that the amount of $\alpha $ form crystals slightly increased with the increase in the annealing temperature. [Preview Abstract] |
Friday, March 18, 2016 9:48AM - 10:00AM |
X42.00010: Investigating the Equilibrium Melting Temperature of Polyethylene Using the Non-Linear Hoffman-Weeks Analysis: Effect of Molecular Weight Hadi Mohammadi, Herve Marand The limiting equilibrium melting temperature for infinite molar mass linear polyethylene, $T_{m}^{o}$ , has been a point of controversy for about five decades. On one hand, Broadhurst and Flory-Vrij extrapolated melting data for short alkanes to a value of ca. 145$^{\mathrm{o}}$C. On the other hand, Wunderlich proposed a value of 141$^{\mathrm{o}}$C from melting studies of extended-chain PE crystals formed under high pressure. While a difference in $T_{m}^{o}$ by 4$^{\mathrm{o}}$C might seem superfluous, it has significant implication for the analysis of the temperature and chain length dependences of crystal growth kinetic data. In this work we estimate the equilibrium melting temperatures, $T_{m}$ for three linear narrow molecular weight distribution polyethylenes using the non-linear Hoffman-Weeks treatment. The resulting $T_{m}$ values thus obtained are significantly lower than these predicted by the Flory-Vrij treatment and are within experimental uncertainty indistinguishable from those reported by Wunderlich and Hikosaka et al. Our results also suggest that the constant C$_{\mathrm{2}}$ in the expression for the undercooling dependence of the initial lamellar thickness (l$_{\mathrm{g}}^{\mathrm{\ast }}=$ C$_{\mathrm{1}}$/$\Delta $T $+$ C$_{\mathrm{2}})$ increases linearly with chain length. [Preview Abstract] |
Friday, March 18, 2016 10:00AM - 10:12AM |
X42.00011: Free surfaces overcome superheating in simulated melting of isotactic polypropylene Qin Chen, Eric B. Sirota, Min Zhang, T.C. Mike Chung, Scott T. Milner The equilibrium melting point ($T_m$) is a challenging experimental benchmark for molecular dynamics simulation of polymer melting and crystallization. $T_m$ obtained from melting simulation of $\alpha$ phase isotactic polypropylene (iPP) can exhibit superheating of over 100$^{\circ}$C. Superheating has been attributed to the use of periodic boundary conditions and ultrafast simulated heating rates, both of which inhibit melting. We have developed a simple method to overcome superheating; we replace the periodic crystal structure with a periodic array of finite thickness slabs, separated by vacuum gaps. Thermal disorder at the slab surface promotes nucleation of the melt phase. Above $T_m$, we observe that the melting front advances into the crystal with a velocity proportional to $T-T_m$. This correspond to a quadratic rise in the system energy versus temperature, at constant heating rate. We obtain $T_m$ as the onset of this quadratic rise in energy, which give values consistent with experimental melting points for iPP oligomers. The same simulations allow reasonable estimates of the crystal-vacuum interfacial free energy, from the energy difference between crystalline slabs and periodic crystals. [Preview Abstract] |
Friday, March 18, 2016 10:12AM - 10:24AM |
X42.00012: Yield Stress Enhancement in Glassy-Polyethylene Block Copolymers. William Mulhearn, Richard Register Polyethylene (PE) has the highest annual production volume of all synthetic polymers worldwide, and is valuable across many applications due to its low cost, toughness, processability, and chemical resistance. However, PE is not well suited to certain applications due to its modest yield stress and Young's modulus (approximately 30 MPa and 1 GPa, respectively for linear, high-density PE). Irreversible deformation of PE results from dislocation of crystal stems and eventual crystal fragmentation under applied stress. The liquid-like amorphous fraction provides no useful mechanical support to the crystal fold surface in a PE homopolymer, so the only method to enhance the force required for crystal slip, and hence the yield stress, is crystal thickening via thermal treatment. An alternative route towards modifying the mechanical properties of PE involves copolymerization of a minority high-glass transition temperature block into a majority-PE block copolymer. In this work, we investigate a system of glassy/linear-PE block copolymers prepared via ring-opening metathesis polymerization of cyclopentene and substituted norbornene monomers followed by hydrogenation. We demonstrate that a large change in mechanical properties can be achieved with the addition of a short glassy block (e.g. a doubling of the yield stress and Young's modulus versus PE homopolymer with the addition of 25 percent glassy block). Furthermore, owing to the low interaction energy between PE and the substituted polynorbornene blocks employed, these high-yield PE block copolymers can exhibit single-phase melts for ease of processability. [Preview Abstract] |
Friday, March 18, 2016 10:24AM - 10:36AM |
X42.00013: On the structure and morphology of poly (vinylidene fluoride) nanoscrolls Gabriel Burks, Sarah Gleeson, Shan Mei, Hao Qi, Christopher Li Beyond its widely popular piezoelectric effect and $\beta $-phase molecular conformation, poly (vinylidene fluoride) PVDF also offers great intrigue as it relates to understanding its intrinsic crystallization behavior and morphological preference. It has been suggested that the $\gamma $-phase of PVDF adopts a highly regular scrolling lamellar habit which can be attributed to small differences in the folding volume of atomic level hydrogen and fluorine atoms resulting in the evolution of highly curved polymer lamellae. To date this scrolled morphology of $\gamma $-phase PVDF has been witnessed via high temperature melt crystallization of crystalline thin films and via severe chemical etching of PVDF bulk films. Here we show the first growth of free-standing $\gamma $-phase PVDF scrolls via the solution crystallization technique. Differential scanning calorimetry (DSC), X-Ray Diffraction (XRD), Fourier Transformed-Infrared Spectroscopy (FT-IR), and Atomic Force Microscopy (AFM) have been used to both characterize and to further understand the fundamental preferred crystalline habit of the $\gamma $-phase of poly (vinylidene fluoride). [Preview Abstract] |
Friday, March 18, 2016 10:36AM - 10:48AM |
X42.00014: Structure and Properties of Tactic Hydrogenated Polynorbornenes Adam B. Burns, Richard A. Register Tacticity is one of the most important structural parameters for determining the physical properties of a polymer. A high degree of steroregularity typically promotes crystallization, with different tacticities giving rise to differences in crystal structure, melting point, and degree of crystallinity. In polynorbornene (PN) made by ring-opening metathesis polymerization (ROMP), tacticity is determined by the relative configuration of the nonplanar cyclopentylene rings enchained in the backbone. Traditional ROMP initiators yield \textit{atactic} polymers ($a$PN); however, recent advances in catalyst design have produced both \textit{isotactic} and \textit{syndiotactic} PN. Newly reported \textit{cis,isotactic}- and \textit{cis,syndiotactic}-PNs were catalytically hydrogenated (abbreviated $i$hPN and $s$hPN, respectively) without altering the tacticity. The thermal and structural characteristics of $i$hPN and $s$hPN were studied by differential scanning calorimetry (DSC) and wide-angle x-ray scattering (WAXS) and compared to that of $a$hPN. Remarkably, all three polymers are semicrystalline, each with a distinct crystal structure. $i$hPN has a nominal melting point of 165 C, more than 20 C above that of $a$hPN. WAXS patterns of melt-drawn fibers of $i$hPN show few strong reflections indicative of either a highly symmetric unit cell or poor long-range order. $i$hPN fibers also exhibit a crystal-crystal transition near 130 C, which is not fully reversible on subsequent cooling. On the other hand, $s$hPN has a nominal melting point some 15 C below that of $a$hPN, and $s$hPN fibers show no evidence of polymorphism. [Preview Abstract] |
Friday, March 18, 2016 10:48AM - 11:00AM |
X42.00015: Crystallization and recrystallization behavior study on biopolymer composites with polymer grafted halloysite nanotubes Ya-Ting Hsieh, Ken Kojio, Atsushi Takahara We study the crystallization and recrystallization behavior of poly(lactic acid) (PLA) in PLA/halloysite composites. Specifically, we are interested in finding the additional effect of interface properties variation in composites except for enhancing filler dispersion. Halloysite nanotubes are grafted with polymer to create different surface properties at their surface. These polymer grafted halloysite nanotubes are then spread into PLA via solvent mixing. Using differential scanning calorimeter, we track and analyze the influence of halloysite surface properties on the crystallization and recrystallization behavior of PLA composites under several conditions. We also present investigations of polarizing optical microscopy, in-situ Fourier transform infrared spectroscopy, and in-situ synchrotron X-ray diffraction measurements. The investigations provide insight into interface effect on PLA composites. [Preview Abstract] |
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