Branched polystyrene with abundant pendant vinyl functional groups from asymmetric divinyl monomer

Branched polystyrenes with abundant pendant vinyl functional groups were prepared via radical polymerization of an asymmetric divinyl monomer, which possesses a higher reactive styryl and a lower reactive butenyl. Employing a fast reversible addition fragmentation chain transfer (RAFT) equilibrium, the concentration of active propagation chains remained at a low value and thus crosslinking did not occur until a high level of monomer conversion. The combination of a higher reaction temperature (120 degrees C) and RAFT agent cumyl dithiobenzoate was demonstrated to be optimal for providing both a more highly branched architecture and a higher polymer yield.

Biosorption of Cd2+, Cu2+, Ni2+ and Zn2+ ions from aqueous solutions by pretreated biomass of brown algae

In this paper, marine brown algae Laminaria japonica was chemically modified by crosslinking with epichlorohydrin (EC1 and EC2), or oxidizing by potassium permanganate (PC), or crosslinking with glutaraldehyde (GA), or only washed by distilled water (DW). They were used for equilibrium sorption uptake studies with Cd2+, Cu2+, Ni2+ and Zn2+. The experimental data have been analyzed using Langmuir, Freundlich and Redlich-Peterson isotherms. The results showed that the biosorption equilibrium was well described by both the Langmuir and Redlich-Peterson isotherms.

Integrated processing-structure-property analysis on rubber in-mold vulcanization

On the basis of the quantitative relationship among rubber processing, structure and property, the methodology of the integrated processing-structure-property analysis on rubber in-mold vulcanization is presented, and then the temporal evolution and spatial distribution characteristics of silicone rubber hot processing parameters, crosslinking structure parameters and mechanical property parameters are obtained by means of the finite element method. The present work is helpful for optimizing curing conditions, and then the design of rubber vulcanization processes according to certain requirements can be done.

Numerical simulation of coil-helix transition processes of gelatin

Gelatin is widely used in food, pharmaceutical, and photographic industries due to the coil-helix transition, whereas the structural inhomogeneity considerably affects its essential properties closely connecting with the industrial applications. The spatially structural inhomogeneity of the gelatin caused by the uneven and unstable temperature field is analyzed by the finite element method during the cooling-induced coil-helix transition process. The helix conversion and the crosslinking density as functions of time and spatial grid are calculated by the incremental method. A length distribution density function is introduced to describe the continuous length distributions of two kinds of triple helices.

Cytotoxicity of liver targeted drug-loaded alginate nanoparticles

In this study, novel liver targeted doxorubicin (DOX) loaded alginate (ALG) nanoparticles were prepared by CaCl2 crosslinking method. Glycyrrhetinic acid (GA, a liver targeted molecule) modified alginate (GA-ALG) was synthesized in a heterogeneous system, and the structure of GA-ALG and the substitution degree of GA were analyzed by H-1 NMR, FT-IR and elemental analysis. The drug release profile under the simulated physiological condition and cytotoxicity experiments of drug-loaded GA-ALG nanoparticles were carried out in vitro. Transmission electron micrographs (TEM) and dynamic light scattering (DLS) analysis showed that drug-loaded GA-ALG nanoparticles have spherical shape structure with the mean hydrodynamic diameter around 214 +/- 11 nm.

Fabrication and characterization of microstructured and pH sensitive interpenetrating networks hydrogel films and application in drug delivery field

Novel microstructured and pH sensitive poly(acryliac acid-co-2-hydroxyethyl methacrylate)/poly(vinyl alcohol) (P(AA-co-HEMA)/PVA) interpenetrating network (IPN) hydrogel films were prepared by radical precipitation copolymerization and sequential IPN technology. The first P(AA-co-HEMA) network was synthesized in the present of IPN aqueous solution by radical initiating, then followed by condensation reaction (Glutaraldehyde as crosslinking agent) within the resultant latex, it formed multiple IPN microstructured hydrogel film. The film samples were characterized by IR, SEM and DSC. Swelling and deswelling behaviors and mechanical property showed the novel multiple IPN nanostuctured film had rapid response and good mechanical property. The IPN films were studied as controlled drug delivery material in different pH buffer solution using cationic compound, crystal violet as a model drug.

Effect of gamma-radiation on the thermal and mechanical properties of a commercial poly(butylene adipate-co-terephthalate)

BACKGROUND: Poly(butylene adipate-co-terephthalate) (PBAT) has attracted wide interest as a biodegradable polymer. However, its use is restricted in certain applications due to its low melting point.RESULTS: PBAT was treated using gamma-radiation. The radiation features were analyzed using Soxhlet extraction, and the ratio of chain scission and crosslinking and gelation dose were determined using the classical Charlesby-Pinner equation. The results showed that PBAT is a radiation-crosslinkable polymer. The degree of crosslinking increased with increasing radiation dose; the relation between sol fraction and dose followed the Charlesby-Pinner equation. Differential scanning calorimetry analyses showed that the melting temperature (T-m) and the heat of fusion (Delta H-m) of PBAT exhibited almost no change in the first scan. The second scan, however, showed a decrease in T-m and Delta H-m. The glass transition temperature of irradiated PBAT increased with increasing radiation dose.

Preparation and Physical Properties of LLDPE Grafted with Novel Nonionic Surfactants

Copolymers of linear low-density polyethylene (LLDPE) grafted with two novel nonionic surfactants, acrylic glycerol monostearate ester (AGMS) and acrylic polyoxyethylenesorbitan monooleate ester (ATW-EEN80), containing hydrophilic and hydrophobic groups and 1-olefin double bond were prepared by using a plasticorder at 190 degrees C. To evaluate the grafting degree, two different approaches based on H-1-NMR data were proposed, and FTIR calibration was showed to validate these methods. The rheological response of the molten polymers, determined under dynamic shear flow at small-amplitude oscillations, indicated that crosslinking formation of the chains could be decreased with increasing the monomer concentration. Their thermal behavior was studied by DSC and polarization microscope (PLM): The crystallization temperature (T-C) of grafted LLDPE shifted to higher temperature compared with neat LLDPE because the grafted chains acted as nucleating agents. Water and glycerol were used to calculate the surface free energy of grafted LLDPE films.

Crystallization Behavior and Mechanical Properties of Crosslinked Plasticized Poly(L-lactic acid)

Enhancing the stability of plasticized poly(L-lactic acid) (PLLA) with poly (ethylene glycol) (PEG) is necessary for its practical application. In this study, plasticized PLLA (PLLA/PEG 80/20 wt/wt) was crosslinked under I-ray (Co-60) in the presence of triallyl isocyanurate (TALC) as crosslinking agent. FTIR analysis revealed that PLLA, PEG, and TALC formed a cocrosslinking structure. Crystallization behavior and mechanical properties of the crosslinked plasticized PLLA were investigated by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), scanning electron microscopy (SEM), and tensile tests. Experimental results indicated that the crystallization behaviors of both PEG and PLLA in the blends were restrained after irradiation. The melting peak of PEG in the crystallized samples disappeared at a low irradiation doses about 10 kGy. Although PLLA still owned the behavior of crystallize, its cold crystallization temperature and glass transition temperature shifted to higher temperature. Mechanical properties of the plasticized PLLA were strengthened through crosslinking. Both yield strength and elastic modulus of the samples increased after crosslinking.

Thermal and mechanical properties of poly(epsilon-caprolactone) crosslinked with gamma radiation in the presence of triallyl isocyanurate

Poly(epsilon-caprolactone) was crosslinked by gamma radiation in the presence of triallyl isocyanurate. The influence of gamma-radiation crosslinking on the thermal and mechanical properties of poly(epsilon-caprolactone)/triallyl isocyanurate was investigated. Differential scanning calorimetry analyses showed differences between the first and second scans. Dynamic mechanical analysis showed an increase in the glass-transition temperature as a result of the radiation crosslinking of poly(epsilon-caprolactone). Thermogravimetric analysis showed that gamma-radiation crosslinking slightly improved the thermal stability of poly(epsilon-caprolactone). The 7 radiation also strongly influenced the mechanical properties. At room temperature, crosslinking by radiation did not have a significant influence on the Young's modulus and yield stress of poly(E-caprolactone). However, the tensile strength at break and the elongation at break generally decreased with an increase in the crosslinking level. When the temperature was increased above the melting point, the tensile strength at break, elongation at break, and Young's modulus of poly(epsilon-caprolactone) were also reduced with an increase in the crosslinking level. The yield stress disappeared as a result of the disappearance of the crystallites.

Crosslinked poly (epsilon-caprolactone) initiated by benzoyl peroxide

Poly(epsilon-caprolactone) (PCL) was chemically crosslinked with various amounts of benzoyl peroxide (BPO) The effect of BPO contents, crosslinking temperature and time on the crosslinking reaction was studied. The thermal, mechanical, and biodegradable properties of crosslinked PCL were also examined by DSC and DMA etc. The results showed that the melting temperature, crystallinity and glass transition temperature decreased with increase in BPO contents, while the crystallization temperature increased with increase in BPO content. The Young's modulus and elongation at break generally decreased with increase in BPO content. Moreover, the crosslinked PCL still had biodegradable ability.

A novel approach to synthesis of functional CPVC and CPE or graft copolymers - in situ chlorinating graft

A new process of graft copolymerization of poly(vinyl chloride) (PVC) and polyethylene (PE) with other monomers was developed. The grafted chlorinated poly(vinyl chloride) (CPVC) and chlorinated polyethylene (CPE) were synthesized by in situ chlorinating graft copolymerization (ISCGC) and were characterized. Convincing evidence for grafting and the structure of graft copolymers was obtained using FT-IR, H-1-NMR, gel permeation chromatography (GPC), and the vulcanized curves. Their mechanical properties were also measured. The results show that the products have different molecular structure from those prepared by other conventional graft processes. Their graft chains are short, being highly branched and chlorinated. The graft copolymers have no crosslinking structure. The unique molecular structure will make the materials equipped with special properties.

Reversible addition-fragmentation chain transfer mediated radical polymerization of asymmetrical divinyl monomers targeting hyperbranched vinyl polymers

Reversible addition-fragmentation chain transfer (RAFT) mediated radical polymerizations of allyl methacrylate and undecenyl methacrylate, compounds containing two types of vinyl groups with different reactivities, were investigated to provide hyperbranched polymers. The RAFT agent benzyl dithiobenzoate was demonstrated to be an appropriate chain-transfer agent to inhibit crosslinking and obtain polymers with moderate-to-high conversions. The polymerization of allyl methacrylate led to a polymer without branches but with five- or six-membered rings. However, poly(undecenyl methacrylate) showed an indication of branching rather than intramolecular cycles. The hyperbranched structure of poly(undecenyl methacrylate) was confirmed by a combination of H-1, C-13, H-1-H-1 correlation spectroscopy, and distortionless enhancement by polarization transfer 135 NMR spectra. The branching topology of the polymers was controlled by the variation of the reaction temperature, chain-transfer-agent concentration, and monomer conversion. The significantly lower inherent viscosities of the resulting polymers, compared with those of linear analogues, demonstrated their compact structure,

Synthesis of novel functional polyolefin containing carboxylic acid via Friedel-Crafts acylation reaction

The strong polar group, carboxylic acid, has triumphantly been introduced into ethylene and allylbenzene copolymers without obvious degradation or crosslinking via Friedel-Crafts (F-C) acylation reaction with glutaric anhydride (GA), succinic anhydride (SA) and phthalic anhydride (PA) in the presence of anhydrous aluminum chloride in carbon disulfide. Some important reaction parameters were examined in order to optimize the acylation process. In the optimum reaction conditions, almost all of the phenyls can be acylated with any anhydride. The microstructure of acylated copolymer was characterized by Fr-IR, H-1 NMR and H-1-H-1 COSY. All the peaks of acylated copolymers can be accurately attributed, which indicates that all the acylation reactions occur only at the para-positions of the substituent of the aromatic rings. The thermal behavior was studied by differential scanning calorimetry (DSC), showing that the melting temperatures (T(m)s) of acylated copolymers with GA firstly decrease slowly and then increase significantly with the increase of the amount of carboxyl acid groups.

Comparative study of PHBV/TBP and PHBV/BPA blends

In order to clarify the effects of phenols on properties of polyesters, the blends of poly[(3-hydroxybutyrate)-co-(3-hydroxyvalerate)] (PHBV) with 4,4'-dihydroxydiphenylpropane (BPA) and p-tert-butylphenol (TBP) were studied. The FTIR spectra revealed that there was strong hydrogen-bond (H-bond) interaction between PHBV and both phenols. By evaluating the fraction of H-bonded C = O in the blend, it was concluded that BPA showed a stronger tendency than TBP to form H-bonds with PHBV. Accordingly, BPA formed a stronger suppression than TBP on the crystallization of PHBV. When 30 wt% BPA or 50 wt% TBP were added into PHBV, the crystallization of PHBV was completely suppressed in the DSC cooling scan. As the phenol content was increased, the T-g of PHBV/TBP blend decreased while the T-g of PHBV/BPA blend increased. This difference indicated that TBP and BPA acted as plasticizer and physical crosslinking agent, respectively.