scholarly journals Investigation on the α/δ Crystal Transition of Poly(l-lactic Acid) with Different Molecular Weights

Polymers ◽  
2021 ◽  
Vol 13 (19) ◽  
pp. 3280
Author(s):  
Lei Zhang ◽  
Guoqun Zhao ◽  
Guilong Wang
Keyword(s):  
Molecular Weight ◽  
Lactic Acid ◽  
Crystal Form ◽  
Crystal Forms ◽  
Molecular Weights ◽  
X Ray Scattering ◽  
Crystallization Experiments ◽  
Weight Effect ◽  
Crystal Transition

Poly(l-lactic acid) (PLLA) crystal possesses a complex polymorphism, and the formation mechanism of various crystal forms has been a hot research topic in the field of polymer condensate matter. In this research, five kinds of PLLA with different molecular weights were prepared by ring-opening polymerization with strict dehydration operations and multistep purification treatments. Then, thin film isothermal crystallization experiments were carried out to obtain crystallized samples. Previous research has proven that the PLLA α crystal form is usually formed at a temperature above 120 °C and the PLLA δ (or α’) crystal form is usually formed at a temperature below 120 °C. However, in this research, the characterization results indicated that the PLLA crystal changed from δ form to α form with the decrease of molecular weight at a temperature of 80 °C. Considering the molecular weight effect, the paper argued that the transitions of the α/δ crystal form are not only associated with temperature, but also related to entanglement state before crystallization. The small-angle X-ray scattering of the PLLA crystal and rheology analysis of the PLLA melt before crystallization further proved the significant role of entanglement. Finally, we tentatively proposed the entanglement effect mechanism on the transitions of the α/δ crystal form.

Exopolysaccharides from lactic acid bacteria: Structural analysis, molecular weight effect on immunomodulation

2014 ◽  
Vol 68 ◽  
pp. 233-240 ◽  
Author(s):  
Utoomporn Surayot ◽  
Jianguo Wang ◽  
Phisit Seesuriyachan ◽  
Ampin Kuntiya ◽  
Mehdi Tabarsa ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Lactic Acid ◽  
Structural Analysis ◽  
Lactic Acid Bacteria ◽  
Weight Effect

scholarly journals How to Determine the Role of an Additive on the Length of Supramolecular Polymers?

2020 ◽  
Vol 02 (02) ◽  
pp. 129-142 ◽  
Author(s):  
Elisabeth Weyandt ◽  
Mathijs F. J. Mabesoone ◽  
Lafayette N. J. de Windt ◽  
E. W. Meijer ◽  
Anja R. A. Palmans ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Weight Control ◽  
Degree Of Polymerization ◽  
Supramolecular Polymers ◽  
Molecular Weights ◽  
Molecular Weight Control ◽  
A Chain ◽  
And Control ◽  
Supramolecular Polymerization

In polymer chemistry, modulation of sequence and control over chain length are routinely applied to alter and fine-tune the properties of covalent (co)polymers. For supramolecular polymers, the same principles underlying this control have not been fully elucidated up to this date. Particularly, rational control over molecular weight in dynamic supramolecular polymers is not trivial, especially when a cooperative mechanism is operative. We start this review by summarizing how molecular-weight control has been achieved in seminal examples in the field of supramolecular polymerizations. Following this, we propose to classify the avenues taken to control molecular weights in supramolecular polymerizations. We focus on dynamic cooperative supramolecular polymerization as this is the most challenging in terms of molecular weight control. We use a mass-balance equilibrium model to predict how the nature of the interaction of an additive B with the monomers and supramolecular polymers of component A affects the degree of aggregation and the degree of polymerization. We put forward a classification system that distinguishes between B acting as a chain capper, a sequestrator, a comonomer, or an intercalator. We also highlight the experimental methods applied to probe supramolecular polymerization processes, the type of information they provide in relation to molecular weight and degree of aggregation, and how this can be used to classify the role of B. The guidelines and classification delineated in this review to assess and control molecular weights in supramolecular polymers can serve to reevaluate exciting systems present in current literature and contribute to broaden the understanding of multicomponent systems.

Polyethersulfone polymers and oligomers — Morphology and crystallization

2012 ◽  
Vol 90 (10) ◽  
pp. 880-890 ◽  
Author(s):  
Abdelkader Benhalima ◽  
François Hudon ◽  
Finda Koulibaly ◽  
Christian Tessier ◽  
Josée Brisson
Keyword(s):  
Molecular Weight ◽  
Model Compound ◽  
Crystal Form ◽  
Low Molecular Weight ◽  
Structural Studies ◽  
X Ray Diffraction ◽  
Crystal Forms ◽  
X Ray ◽  
Diphenyl Sulfone ◽  
Induced Crystallization

Crystal forms of polyethersulfones (PES) were investigated by using a model compound and a low molecular weight oligomer. These are amorphous as-synthesized, and can undergo solvent-induced crystallization under the appropriate conditions. The model compound, 4,4′-bis(p-methoxyphenoxy)diphenyl sulfone, yielded monocrystals, and its structure was solved using X-ray diffraction. Conformational disorder is present, two conformers cohabiting in 55:45 proportions. This model compound, combined to previous structural studies published in the literature, served as a basis for conformational studies of polyethersulfone. Low molecular weight polymers submitted to solvent-induced crystallization resulted in a PES crystal form different from that previously published in the literature, as shown by powder X-ray diffraction.

Preparation and Characterization of Poly(lactic acid) with Different Molecular Weights by Thermal Hydrolysis

2013 ◽  
Vol 440 ◽  
pp. 19-24 ◽  
Author(s):  
Jun Yan Yao ◽  
Loogn Tak Lim ◽  
Yu Jie Li
Keyword(s):  
Molecular Weight ◽  
Lactic Acid ◽  
Hydroxyl Group ◽  
Poly Lactic Acid ◽  
Thermal Hydrolysis ◽  
Molecular Weights ◽  
Hydrolytic Reaction ◽  
Structures And Properties ◽  
Ft Ir

A feasible and effective method of thermal hydrolysis to prepare poly (lactic acid) (PLA) oligomers with different controlled molecular weight from PLA is presented in this paper. The thermal hydrolytic reaction was carried out by immerging PLA resin pellets in boiling distilled water for a certain period of time. Ester groups in PLA chains are hydrolytically degraded in the presence of water and thermal, so PLA oligomers with different molecular weight were prepared. The structures and properties of PLA oligomers were characterized by FT-IR, GPC, DSC, etc. The results showed that thermal hydrolytic reaction could effectively reduce the molecular weight of PLA, which declines with the increase of the thermal hydrolytic reaction time. Meanwhile, the content of terminal hydroxyl group, glass transition temperature, melting point of PLA oligomers prepared from thermal hydrolytic reactions exhibit gradual changes with the extension of the thermal hydrolytic time.

scholarly journals Synthesis, structure and thermogravimetric analysis of α,ω-telechelic polydimethylsiloxanes of low molecular weight

2017 ◽  
Vol 82 (12) ◽  
pp. 1395-1416 ◽  
Author(s):  
Aleksandra Tasic ◽  
Marija Pergal ◽  
Malisa Antic ◽  
Vesna Antic
Keyword(s):  
Molecular Weight ◽  
Thermogravimetric Analysis ◽  
Degradation Mechanism ◽  
Gel Permeation Chromatography ◽  
Polymer Chains ◽  
Low Molecular Weight ◽  
Dilute Solution ◽  
Molecular Weights ◽  
Dilute Solution Viscometry

A series of ?,?-telechelic polydimethylsiloxanes (PDMS), with predetermined molecular weights of about 2500 g mol-1, was synthesized by siloxane equilibration reaction. Syntheses were performed using octamethylcyclotetrasiloxane (D4) and various disiloxanes: hexamethyldisiloxane (HMDS), 1,1,3,3-tetramethyldisiloxane (TMDS), 1,3-divinyltetramethyldisiloxane (DVTMDS), 1,3-bis(3-carboxypropyl)tetramethyldisiloxane (DCPTMDS) and 1,3-bis(3-aminopropyl)tetramethyldisiloxane (DAPTMDS). The role of the disiloxane was to introduce terminal functional groups at the end of the polymer chains and to control the molecular weight of the polymers. Polymers with trimethyl, hydrido, vinyl, carboxypropyl and aminopropyl end-groups were obtained in this way. The structure of the ?,?-telechelic PDMSs was confirmed by NMR and IR spectroscopy. The molecular weights of the polymers were determined by 1H-NMR, gel permeation chromatography (GPC) and dilute solution viscometry. Thermogravimetric analysis (TGA) under nitrogen and air showed that the type of the terminal groups significantly influenced the thermal and thermo-oxidative stability, as well as the degradation mechanism of the ?,?-telechelic PDMSs.

Study on Chain Extension and Modification of Poly(Lactic Acid) by Isophorone Diisocyanate /Polyethylene Glycol

2012 ◽  
Vol 476-478 ◽  
pp. 2067-2070 ◽  
Author(s):  
Zhao Zhang ◽  
Guo Dong Fan ◽  
Hai Yan Yang
Keyword(s):  
Molecular Weight ◽  
Lactic Acid ◽  
Polyethylene Glycol ◽  
Chain Extension ◽  
Poly Lactic Acid ◽  
Isophorone Diisocyanate ◽  
Molecular Weights ◽  
Peg 400 ◽  
Peg 4000 ◽  
Better Than

Poly(lactic acid)(PLA)was end-capped by isophorone diisocyanate(IPDI) to get PLA-IPDI under the condition of temperature of 176°C and pressure of 0.090 MPa for 13 mins, and then the PLA-IPDI was chain-extended with different molecular weights polyethylene glycol (PEG)-400, PEG-600, PEG-800, PEG-4000 and PEG-6000 to produce a series of block copolymer PLA-IPDI-PEGs. when n(–OH)/n(–NCO)=1.5:1, the molecular weight of PLA-IPDI is maximum. All the copolymer PLA-IPDI-PEGs were characterized by GPC, FTIR, DSC and contact angle testing. The results show that the polymeric degree of PLA-IPDI-PEG-800 is the best and its molecular weight is the biggest. Tg of PLA-IPDI-PEG-800 is the lowest and its hydrophilicity is better than the others modification PLA-IPD-PEGs and pure PLA.

Polymorphs, hydrates and solvates of a co-crystal of caffeine with anthranilic acid

2014 ◽  
Vol 70 (1) ◽  
pp. 72-80 ◽  
Author(s):  
Nadeesh Madusanka ◽  
Mark D. Eddleston ◽  
Mihails Arhangelskis ◽  
William Jones
Keyword(s):  
Anthranilic Acid ◽  
Crystal Form ◽  
Related System ◽  
Crystal Forms ◽  
Solution Crystallization ◽  
Rich Diversity ◽  
Crystallization Experiments ◽  
Solvent Molecules ◽  
Zigzag Type ◽  
Channel Type

A polymorph screen on a new 1:1 co-crystal of caffeine, C8H10N4O2, with anthranilic acid, C7H7NO2, has revealed a rich diversity of crystal forms (two polymorphs, two hydrates and seven solvates, including two sets of isostructural solvates). These forms were prepared by liquid-assisted grinding and solution crystallization, and the crystal structures of nine of these forms have been solved using either single-crystal or powder X-ray data. The structures contain O—H...N and N—H...O hydrogen bonds through which caffeine and anthranilic acid molecules assemble to form zigzag-type chains. These chains can interact in an anti-parallel and offset manner to form cage- or channel-type skeletons within which solvent molecules can be located, giving rise to the diversity of forms observed for this co-crystal. In contrast, an equivalent series of liquid-assisted grinding and solution crystallization experiments with the closely related system of theobromine, C7H8N4O2, and anthranilic acid resulted in the formation of only one 1:1 co-crystal form.

A time-resolved SAXS study on the crystalline morphology of long-term stored isotactic polypropylene

2004 ◽  
Vol 37 (2) ◽  
pp. 295-299 ◽  
Author(s):  
Jun-Ting Xu ◽  
Yu-Jin Zhang ◽  
Zhi-Qiang Fan
Keyword(s):  
Isotactic Polypropylene ◽  
Crystal Form ◽  
Crystalline Morphology ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
Time Resolved ◽  
Crystal Forms ◽  
X Ray ◽  
X Ray Scattering

The crystalline morphology of a long-term stored metallocene isotactic polypropylene (mPP) has been studied with time-resolved small-angle X-ray scattering (SAXS), differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD), and compared with that of the freshly crystallized sample. It was found that both α and γ crystal forms occur in the long-term stored mPP, whereas freshly crystallized mPP contains only the α crystal form. Double SAXS peaks were observed for the long-term stored mPP, which can be assigned to the α and γ crystals. Based on the SAXS result, it is inferred that the crystal stacks of the α and γ forms in the long-term stored mPP are arranged according to the block mode.

X-Ray Diffraction Studies of Zwitterionic Associating Polymers

1989 ◽  
Vol 177 ◽  
Author(s):  
Y. Shen ◽  
C. R. Safinya ◽  
L. Fetters ◽  
M. Adam ◽  
T. Witten ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Long Range ◽  
Structural Phase ◽  
Range Order ◽  
Long Range Order ◽  
X Ray ◽  
Molecular Weights ◽  
X Ray Scattering ◽  
Associating Polymers ◽  
Ray Scattering

ABSTRACTWe have carried out x-ray scattering studies in melts of a series of linear polyisoprenes with highly polar sulfo-zwitterion groups at one end. The zwitterion end groups cause aggregation in good solvents for polyisoprene. The aggregation number depends strongly on the molecular weight of the polyisoprene tails and on the polarity of the solvent. Molecular mechanics simulations of the interactions between the zwitterion head groups suggest tubelike or diskline structures for the aggregates. Spherical structures are not energetically favorable. High resolution synchrotron x-ray scattering studies were carried out for six different (chain) molecular weights between 2000 and 23,000. For low molecular weights (between 2000 and 4000) a tubular structure is found with the tubes organized on a well-defined, two-dimensional triangular lattice with very large domain sizes >2000Å. A structural phase transition to a cubic (bcc) phase with long range order is observed to occur for molecular weights >10,000. The lattice spacing increase over the molecular range was between 95Å (for MW-2000) and 206Å (for MW-23,000). For the high molecular weight melts, annealing transforms the structure from (bcc) (with long range order) to an (fcc) disordered structure with short range order.

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