Crystallization Behavior and Dynamic Mechanical Properties of Poly(ε-caprolactone)/Octaisobutyl-Polyhedral Oligomeric Silsesquioxanes Composites Prepared via Different Methods

Two octaisobutyl-polyhedral oligomeric silsesquioxanes(oib-POSS)reinforced biodegradable poly(ε-caprolactone)(PCL)composites were prepared via two different methods,i.e.,melt compounding and solution casting,which were named as m PCL/oib-POSS and s PCL/oibPOSS,respectively,in this work.Oib-POSS dispersed finely in both composites;moreover,oib-POSS aggregates were larger in m PCL/oib-POSS than in s PCL/oib-POSS.Despite the different preparation methods,oib-POSS obviously promoted the crystallization of PCL,especially in s PCL/oib-POSS,but did not modify the crystal structure of PCL.The storage moduli of PCL were improved significantly in both composites.PCL/oib-POSS composites with enhanced crystallization behavior and improved dynamic mechanical properties were successfully prepared through both methods;moreover,the solution casting method was more effective than the melt compounding method.     

Multiarm Star Poly(ε-caprolactone) with Hyperbranched Polyamidoamine as Core Capable of Selective Accommodating Cationic or Anionic Guests

Hyperbranched polyamidoamines(HPAs) were directly employed as macroinitiators to initiate the Sn(Oct)2 catalyzed ring-opening polymerization of ε-caprolactone(CL), resulting in multiarm star copolymers with poly(ε-caprolactone)(PCL) as shells and HPA as core(HPA-b-PCL). From 1H-NMR characterization it was deduced that both the primary amines and the secondary amide groups of HPAs could initiate the CL polymerization, and the initiation efficiency increased when more CL monomers were fed. The average arm-numbers of the obtained stars were in the range of 115-353. Differential scanning calorimetry measurements demonstrated that the melting and crystallization temperatures, fusion and crystallization enthalpy and the degree of crystallinity of the star polymers increased as the PCL arm length increased. HPAb-PCL stars could be used as nanocarriers to efficiently accommodate anionic dyes at acidic condition, while load cationic dyes at basic condition. Compared with the dye-loading behavior of multiarm star PCL with the neutral hyperbranched polyglycerol as core, it was deduced that HPA-b-PCL nanocarriers accommodated anionic dyes using the HPA core, while loaded cationic dyes using both the HPA core and the PCL shell. Dynamic light scattering analyses also supported such deduction. Furthermore, HPA-b-PCL nanocarriers could selectively load the anionic Eosin Y or the cationic methylene blue from their mixture at p H = 6 or 9, respectively, realizing their separation.     

Morphology, crystallization and mechanical properties of poly(ɛ-caprolactone)/graphene oxide nanocomposites

A series of nanocomposites based on poly(ε-caprolactone) (PCL) and graphene oxide (GO) were prepared by in situ polymerization. Scanning electron microscopy observation revealed not only a well dispersion of GO but also a strong interfacial interaction between GO and the PCL matrix, as evidenced by the presence of some GO nanosheets embedded in the matrix. Effects of GO nanofillers on the crystal structure, crystallization behavior and spherulitic morphology of the PCL matrix were investigated in detail. The results showed that the crystallization temperature of PCL enhanced significantly due to the presence of GO in the nanocomposites, however, the addition of GO did not affect the crystal structure greatly. Thermal stability of PCL remarkably increased with the addition of GO nanosheets, compared with that of pure PCL. Incorporation of GO greatly improved the tensile strength and Young’s modulus of PCL without a significant loss of the elongation at break.     

TRANSESTERIFICATION OF POLY(ETHYLENE TEREPHTHALATE) WITH POLY(ε-CAPROLACTONE)*

Transesterification of poly(ethylene terephthalate) (PET) with poly(ε-caprolactone) (PCL) was investigated bymeans of NMR spectroscopy, extraction experiments, differential scanning calorimetry (DSC) and phase contrast microscopy(PCM). The ~1H-NMR results show that transesterification takes place in the melt blends and leads to the formation of thePET-PCL copolyester with a chemical structure similar to ethylene terephthalate-ε-caprolactonc copolycster (TCL)synthesized directly from monomers. However, even in the blend that has been transesterified for 8 h, the random PET-PCLcopolyester, PET-PCL copolyester with long PET or long PCL segments and the unreacted PET and PCL homopolymersmay coexist. Due to the low mobility of PET and PCL chains and the high viscosity of the two macromolecules, thetransesterification proceeds with difficulty. Furthermore, PET is incompatible with PCL, the transesterification can onlyoccur at the interface or in the interfacial region between two phases, and finally the reaction can only reach a localequilibrium. These results indicate that in fact the transesterification in the melt blend between two incompatiblehomopolymers could not lead to the formation of completely random or typical block copolyesters.     

AN APPROACH TO SYNTHESIZE POLY(ETHYLENE GLYCOL)-b-POLY(ε-CAPROLACTONE) WITH TERMINAL AMINO GROUP via SCHIFF’S BASE AS AN INITIATOR

A new method to synthesize a degradable terminal amino group-containing copolymer,poly(ethylene glycol)-b- poly(ε-caprolactone)(MPEG-PCL-NH_2),was developed in the following three steps:(1)the ring-opening polymerization (ROP)ofε-caprolactone from the Schiff base prepared from benzatdehyde and ethanolamine(Ph-CH=NCH_2CH_2OH)used as an initiator to obtain heterobifunctional poly(ε-caprolactone)with one terminal Schiff base group and one hydroxyl group (HO-PCL-CH_2CH_2N=CH-Ph);(2)the coupling reaction of two reactive precursors,a hydroxy-terminated HO-PCL- CH_2CH_2N=CH-Ph andα-monocarboxy-ω-monomethoxy poly(ethylene glycol)(CMPEG)to synthesize MPEG-PCL- CH_2CH_2N=CH-Ph;(3)the conversion of the -N=CH-Ph end-group into NH_2 end-group by acidification of acetic acid to obtain MPEG-PCL-NH_2.The structures from the precursors to the terminal amino group-containing copolymer were confirmed by ~1H-NMR and their molecular weights were measured by gel permeation chromatography.The amphiphilic terminal amino group-containing copolymer could self-assemble into micelles in an aqueous system with PCL block as the core and PEG block as the shell.The micelle formation of the terminal amino group-containing block copolymer was studied by fluorescent probe technique and the existence of critical micellar concentration(cmc)confirmed the amphiphilic nature of the resulting copolymer.ESEM and DLS analysis of the micelles revealed a homogeneous spherical morphology and a unimodal size distribution.     

MOLECULAR WEIGHT DEPENDENCE OF THE MELTING BEHAVIOR OF POLY(ε-CAPROLACTONE)

Poly(ε-caprolactone) (PCL) with different molecular weights was synthesized and characterized by a gelpermeation chromatograph equipped with multiple detector. The melting behavior of PCL was also studied. It was found thatthe equilibrium melting points (T_m~0) of PCL samples depend on their molecular weights. Wide angle X-ray diffractionmeasurements (WAXD) and DSC measurements showed that the crystals of the high molecular weight PCLs were moreperfect than those of the low molecular weigh ones. These results demonstrate that the concentration of the end groups ofPCL chains is the main factor that influences the melting behavior. The fusion enthalpy per repeating unit (ΔH_u) wasdetermined to be 11.3 kJ/mol for PCL.     

In situ evaluation of cell cultivation on dynamically changed poly(ε-caprolactone) film caused by enzymatic degradation

In situ evaluation of cell cultivation on degrading poly(ε-caprolactone) (PCL) films was studied.New culture surroundings were constructed for cell growth by using PCL films as substrates and adding Pseudomonas cepacia lipase to accelerate biodegradation of PCL films.MTT experiments for 10 h indicated the low cytotoxicity of lipase solution with concentration up to 0.2 mg/mL for MG-63 cells growth on PCL films.With the optimized lipase concentration and degradation time,we studied cell growth behavior on dy...     

Solution Crystallization Behavior of Linear and Star-shaped Poly(ethylene glycol)-b-Poly(ε-caprolactone) Block Copolymers简

Lamellar crystals of diblock, triblock and four-arm poly（ethylene glycol）-b-poly（ε-caprolactone） （PEG-b-PCL） crystalline-crystalline copolymers were successfully obtained from their solution. Morphology and structure of lamellar crystals of crystalline-crystalline copotymers were investigated using tapping-mode atomic force microscopy （AFM） and selected area electron diffraction （SAED）. All of these samples showed the truncated-lozenge multilayer basal shapes with central screw dislocation or central stack, which were all obtained simultaneously from the oil bath. The diffraction pattern of PEG block lamellar crystal is attributed to the （120） diffracting planes and the pattern of PCL block lamellar crystal is attributed to the （1 I0） diffracting planes and （200） diffracting planes according to the SAED results. Four （110） crystal growth planes and two （200） crystal growth planes are discovered for the PCL blocks, but the （120） crystal growth planes of PEG blocks are hided in the figure of AFM. The crystalline structure of the four-arm copolymers （FA） is more disorder and confused than that of the diblock （DI） copolymer and the striated fold surface structures of lamellar crystals of four-arm copolymers （FA） are smoother than these of linear analogues, owing to the confused crystallization of blocks caused by the mutual restriction of blocks and the hindrance of the dendritic cores. In addition, the aspect ratio of FA is greater than that of the others. It is hypothesized that there are two reasons for the change of aspect ratios. First, the （200） diffracting planes of PCL crystals grew slowly compared to their （110） diffracting planes because of difference in the energy barrier. Secondly, edge dislocations on the （200） diffracting planes are also responsible for the variation of the aspect ratio. Consequently, the crystalline defects are augmented by the competing blocks crystallized simultaneously and the hindrance of the dendritic cores.     

Microwave-assisted Polymerization of ε-Caprolactone with Maleic Acid as Initiator and Drug Release Behavior of Ibuprofen-Poly(ε-caprolactone) System

Poly( ε-caprolactone)(PCL) with weight-average molar mass over 10000g/mol was synthesized by microwave-assisted ring -opening polymerization of ε-caprolactone(ε-CL) with maleic acid(MA) as initiator (2.45GHz,360W,85min),Ibuprofen-PCL controlled release system was prepared directly by the ROP of ε-CL in its mixture with ibuprofen.The release of ibuprofen from the system was sustained and steady.     

Enhanced <Emphasis Type="Italic">αγ</Emphasis>′ Transition of Poly(vinylidene fluoride) by Step Crystallization and Subsequent Annealing

Poly(vinylidene fluoride) (PVDF) exhibits pronounced polymorphs.Its γ phase is attractive due to the electroactive properties.The γ-PVDF is however difficult to obtain under normal crystallization condition.In a previous work,we reported a simple melt-recrystallization approach for producing y-phase rich PVDF thin films through selective melting and subsequent recrystallization.We reported here another approach for promoting the αγ'phase transition to prepare γ-phase rich PVDF thin films.To this end,a stepwise crystallization and subsequent annealing process was used.The idea is based on a quick generation of a large amount of α-PVDF crystals with some of their γ-PVDF counterparts at suitable crystallization temperature and then annealing at a temperature above the crystallization temperature for enhancing the molecular chain mobility to overcome the energy barrier of phase transition.It was found that crystallizing the PVDF melt first at 152 ℃ for4 h,then quenching to room temperature and finally annealing the sample at 160 ℃ for 100 h was the most efficient to produce γ-PVDF rich films.This is related to the melting and recrystallization of the α-PVDF crystals produced during quenching in the annealing process at 160 ℃,which favors the formation of γ-PVDF crystals for triggering the αγ'phase transition.     

Poly(4-vinylpyridine)：As a green, efficient and commercial available basic catalyst for the synthesis of chromene derivatives

Poly(4-vinylpyridine) is reported as a green,commercial available and efficient basic recyclable catalyst for the synthesis of chromene derivatives.This catalyst can be easily recovered by simple filtration and recycled up to 5 consecutive runs without any loss of its efficiency.     

Hydrothermal Synthesis,Crystal Structure and Properties of a New Binuclear Nickel(Ⅲ) Complex with 3-(Pyridin-2-yl)-1,2,4-triazole

A new binuclear nickel(II) complex Ni₂(HPT)_4(H₂O)₃ (1) has been hydrothermally synthesized with nickel hydroxide,3,4-pyridine dicarboxylic acid and 3-(pyridin-2-yl)-1,2,4-triazole (HPT) in the mixed solution (the volume ratio of methanol and water is 1:4).It crystallizes in tetragonal space group P4₂/n,with a=20.844(1),b=20.844(1),c=7.2463(7)A,V=3148.2(5)A³,D_c=1.587 g/cm³,Z=4,μ(Mo Ka)=1.257,F(000)=1544,the final GOOF=1.043,R=0.0437 and w R=0.1297.The crystal structure shows that the whole molecule consists of two nickel ions which are bridged by fourμ₂-η¹:η^0-3-(pyridin-2-yl)-1,2,4-triazole anions.The coordination environment of Ni(II) ion is Ni N₆,giving a distorted octahedral geometry.The thermal stability and fluorescent and magnetic properties of the complex were investigated.     

Photoluminescence and Electroluminescence Properties of 2,5-Bis[2,2′-bis(5-phenyl)-1,3,4-oxadiazole] Thiophene(T-OXD)and T-OXD/Poly(9-vinylcarbazole) Blends

The photoluminescence(PL) and the electroluminescence(EL) properties of a novel organic compound, 2,5-bis(2,2′-bis(5-phenyl)-1,3,4-oxadiazole(T-OXD), were studied in chloroform and in a solid thin film. The PL and the EL properties of T-OXD/poly(9-vinylcarbazole)(PVK) blends were also studied, which contained various contents of T-OXD. The PL maximum emission peaks of T-OXD/PVK blends show gradual bathochromtic-shift with the increase of the T-OXD content. The EL spectra of T-OXD/PVK devices are similar to their PL spectra, and all the EL maximum emission peaks show bathochromtic-shift compared with the corresponding PL spectra, which is ascribed to the formation of electroplex. The turn-on voltages for ITO/T-OXD:PVK/Al devices decreased from 13.5 V of the device cotaining 0.1% T-OXD(mass fraction) to 5 V of the device containing 5% T-OXD, which suggests that T-OXD improves the energy level match between T-OXD and PVK and enhances the emission efficiency. The experimental results indicate that T-OXD can be used as a good electron transporting material.