Isothermal crystallization of layered silicate/starch-polycaprolactone blend nanocomposites

The isothermal crystallization behavior of layered silicate/starch-polycaprolactone blend nanocomposites was studied by means of differential scanning calorimetry (DSC) measurements. The theoretical melting point was higher for the matrix than for nanocomposites. At low clay concentration, the induction time decreased and the overall crystallization rate increased acting as nucleating agent whereas at higher concentrations became retardants. Classical Avrami equation was used to analyze the crystallization kinetic of these materials. n values suggested that clay not only affected the crystallization rate but also influenced the mechanism of crystals growth. An Arrhenius type equation was used for the rate constant (k). Models correctly reproduced the experimental data.     

Polyiodized‐PCL as multisite transfer agent: Towards an enlarged library of degradable graft copolymers

Poly(ε‐caprolactone)‐based graft copolymers were prepared via a “grafting from” technique derived from iodine transfer polymerization. This copolymerization was done thanks to a poly(ε‐caprolactone‐co‐α‐iodo‐ε‐caprolactone) (PCL‐I), which was used as a multisite transfer agent. Styrene (Sty) and n‐butyl acrylate (n‐BuA) were firstly used as model monomers to establish the feasibility of using PCL‐I as multisite transfer agent, and investigate some general properties of the polymerization. The formation of PCL‐g‐PSty and PCL‐g‐P(n‐BuA) copolymers was confirmed by SEC and NMR analyzes of the copolymers before and after degradation of the PCL backbone. This method was extended to an acrylamide monomer, namely (N,N‐dimethyl) acrylamide (DMA), to prepare original amphiphilic copolymers with PCL as hydrophobic backbone and amido‐functionalized hydrophilic grafted chains. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5006–5016, 2009     

Mechanics and surface ultrastructure changes of poly(3-hydroxybutyrate) films during enzymatic degradation in pancreatic lipase solution

A study of in vitro biodegradation of poly(3-hydroxybutyrate) (PHB) in model conditions was performed. The porcine pancreatic lipase solutions at different concentrations in the two buffer systems (phosphate-buffered saline (PBS) and simulating body fluid (SBF)) were chosen as model biodegradation media. At first, optimal concentration of pancreatic lipase (0.25 mg/ml in PBS) was determined: in these media the decomposition of PHB films realized faster according to the data of gravimetric analysis. Differential scanning calorimetry showed an increase in the crystallinity of the samples (from 49% to 59%) after enzymatic degradation. These data are confirmed by method of nanoindentation, where the increase of the Young's modulus during the degradation (from 1.37 GPa to 4.4 GPa) was shown. This is due to the crystallization of the amorphous polymer component, and its decomposition and dissolving. During biodegradation three types of polymer ultrastructure changes were observed on the surfaces of the films: appearance of new lamellae, disappearance of lamellae and disintegration of lamellae into shorter fragments.     

Thermal Behaviour and Glass Transition Dynamics of Inclusion Complexes of α‐Cyclodextrin with Poly(D,L‐lactic acid)

Inclusion complexes (ICs) have been prepared by the host–guest interaction between α‐cyclodextrin (αCD) and poly(d,l ‐lactic acid) (PDLLA). This enables transformation of the amorphous polymer into a well organized channel‐type crystalline structure, as studied by wide angle X‐ray scattering (WAXS). WAXS experiments using synchrotron radiation allowed the evolution of this crystalline structure to be followed upon heating. The diffraction peaks disappeared above 320 °C, in a temperature region similar to the occurrence of thermal degradation, also investigated by thermogravimetric analysis. No glass transition could be detected in the IC using differential scanning calorimetry (DSC), but non‐conventional dynamic mechanical analysis measurements revealed the existence of loss factor peaks shifted to higher temperatures when compared with PDLLA. The relaxation plot of the IC was characterized by an Arrhenius behaviour with a high activation energy that could be consistent with the high geometrical confinement felt by the chains in the nanostructured organization.

     

Biodegradable Polymer Nanocylinders Fabricated by Transverse Fragmentation of Electrospun Nanofibers through Aminolysis

Biodegradable polymeric nanocylinders were fabricated by segmental degradation of electrospun nanofibers. Poly(L ‐lactic acid) (PLA) was electrospun to produce non‐crystalline nanofibers that were immediately treated with amino group‐containing strong bases to fabricate semi‐crystalline PLA nanocylinders with tunable aspect ratio. The formation of PLA nanocylinders was attributed to two concurrent events occurring during the aminolysis reaction: (i) development of stacked lamellae and (ii) transversely oriented degradation and fragmentation of the amorphous gaps between lamellae, both responsible for the fragmentation of PLA nanofibers into uniformly shaped nanocylinders. The aspect ratio of PLA nanocylinders was tunable by varying aminolysis time and controlling nanofiber diameter.

     

Biadhesive Peptides for Assembling Stainless Steel and Compound Loaded Micro‐Containers

Biadhesive peptides (peptesives) are an attractive tool for assembling two chemically different materials—for example, stainless steel and polycaprolactone (PCL). Stainless steel is used in medical stents and PCL is used as a biodegradable polymer for fabrication of tissue growth scaffolds and drug delivering micro‐containers. Biadhesive peptides are composed of two domains (e.g., dermaseptin S1 and LCI) with different material‐binding properties that are separated through a stiff peptide‐spacer. The peptesive dermaseptin S1‐domain Z‐LCI immobilizes antibiotic‐loaded PCL micro‐containers on stainless steel surfaces. Immobilization is visualized by microscopy and field emission scanning electron microscopy analysis and released antibiotic from the micro‐containers is confirmed through growth inhibition of Escherichia coli cells.     

Synthesis of a New PHEMA/PEO Enzymatically Biodegradable Hydrogel

Summary: We report the synthesis of a new enzymatically degradable gel based on PHEMA and PEO crosslinking macromonomer. The crosslinker contains the tripeptide sequence Gly‐Gly‐Leu, which is a substrate for proteases such as subtilisin or chymotrypsin. The crosslinker was obtained by the coupling reaction of succinyl‐glycyl‐glycyl‐leucine with 2‐aminoethyl‐terminated PEO chains ( = 3 400) and subsequent esterification of the hydroxyl endgroup with methacryloyl chloride. It was characterized by SEC and ¹H NMR. Enzymatic cleavage of the crosslinking macromonomer was showed by SEC. The macromonomer was copolymerized with HEMA to yield hydrogel that is stable in a physiological buffer. Enzymatic assay showed that this gel is degraded in the presence of a bacterial protease (subtilisin). The degradation is complete within 50 d at 37 °C. This new gel is a good candidate for drug‐delivery systems where the release can be triggered by the presence of bacterial proteases.

PHEMA crosslinked with MA‐PEG‐SucGGL‐PEO‐MA and its degradation by subtilisin.     

Melting Processing of Biodegradable Cellulose Diacetate/Starch Composites

Natural polymers and their derivatives are attracting increasing interest as promising biodegradable materials that can meet the environmental and recycling demands from society. This study prepared biodegradable composites of cellulose diacetate and starch, and examined their physical and thermal properties. In addition, the morphology of the composites was examined by scanning electron microscopy. For melt processing, epoxidized soybean oil, as a lubricant, and triacetine, as a plasticizer, were added to the composites. The optimal conditions for the preparation of the biodegradable composites were determined. Increasing the amount of starch in the composites resulted in further enhancement of the processability of cellulose diacetate. The tensile strength and Young's modulus decreased, and the amount of elongation and T_g value increased with increasing amount of starch.     

Branched polyphosphazenes with controlled dimensions

Using living cationic polymerization, a series of polyphosphazenes is prepared with precisely controlled molecular weights and narrow polydispersities. As well as varying chain length through the use of a living polymerization, amine‐capped polyalkylene oxide (Jeffamine) side chains with varied lengths are grafted to the polymer backbone to give a series of polymers with varied dimensions. Dynamic light scattering and size exclusion chromatography are used to confirm the preparation of polymers with a variety of controlled dimensions and thus hydrodynamic volumes. Furthermore, it is demonstrated how the number of arms per repeat unit, and thus the density of branching, can also be further increased from two to four through using a one‐pot thiolactone conversion of the Jeffamines, followed by thiol‐yne addition to the polyphosphazene backbone. These densely branched, molecular brush‐type polymers on a biodegradable polyphosphazene backbone all show excellent aqueous solubility and have potential in drug‐delivery applications. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4467–4473     

Organocatalysis applied to the ring‐opening polymerization of β‐lactones: A brief overview

Organocatalysis offers a number of prospects in the polymer community and presents advantages over metal based and bio‐organic methods. The use of organic molecules for performing chemical reactions is not a new concept, and any research into organocatalytic reactions builds on a respected history. Compared to the organocatalysis of large lactones, which began in the early 2000s, the examples presented here will demonstrate that few metal‐free initiating systems had been applied to β‐lactones well before the beginning of the current millennium. These metal‐free initiating systems present indisputable advantages over metal‐based processes. In the following paper, ring‐opening polymerizations (ROPs) of various β‐lactones for the preparation of poly(hydroxyalkanoate)s will be presented, as will the types of mechanisms involved, that is, zwitterionic and anionic, and cationic or supramolecular‐based ROPs. The advantages and drawbacks of the different technics will be discussed in the domain, which, for us, is important in the overall production of bioplastics. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 657–672