Synthesis and characterization of photo-cross-linked hydrogels based on biodegradable polyphosphoesters and poly(ethylene glycol) copolymers

Novel biodegradable hydrogels by photo-cross-linking macromers based on polyphosphoesters and poly(ethylene glycol) (PEG) are reported. Photo-cross-linkable macromers were synthesized by ring-opening polymerization of the cyclic phosphoester monomer 2-(2-oxo-1,3,2-dioxaphospholoyloxy) ethyl methacrylate (OPEMA) using PEG as the initiator and stannous octoate as the catalyst. The macrorners were characterized by H-1 NMR, Fourier transform infrared spectroscopy, and gel permeation chromatography measurements. The content of polyphosphoester in the macromer was controlled by varying the feed ratio of OPEMA to PEG. Hydrogels were fabricated by exposing aqueous solutions of macromers with 0.05% (w/w) photoinitiator to UV light irradiation, and their swelling kinetics as well as degradation behaviors were evaluated. The results demonstrated that cross-linking density and pH values strongly affected the degradation rates. The macromers was compatible to osteoblast cells, not exhibiting significant cytotoxicity up to 0.5 mg/mL. "Live/dead" cell staining assay also demonstrated that a large majority of the osteoblast cells remained viable after encapsulation into the hydrogel constructs, showing their potential as tissue engineering scaffolds.

Reactive compatibilization of polyamide 6 with isocyanate functionalized ethylene-propylene copolymer

Reactive compatibilization of ethylene-propylene copolymer functionalized with allyl (3-isocyanato-4-tolyl) carbamate (TAI) isocyanate (EPM-g-TAI) and polyamide 6 (PA6) was investigated in this paper, FTIR analysis revealed the evidence of a chemical reaction between the end groups of PA6 and EPM-g-TAI. Thermal, rheological, morphological, and mechanical properties of the resultant system were examined, DSC analysis indicated that the crystallization of PA6 in Pa6/EPM-g-TAI blends was inhibited, due to the chemical reaction that occurs at the interface of PA6 and EPM-g-TAI. Rheological measurement showed that complex viscosity and storage modulus of PA6/EPM-g-TAI were both dramatically enhanced compared to those of PA6/EPM at the same blending composition. After examining the morphology of both blending systems, smaller particile sizes, more homogeneous distribution of domains and improved interfacial adhesion between matrix and domains were observed in the compatibilized system. Mechanical properties such as tensile strength. Young's modulus, flexural strength and modulus, as well as notched and un-notched impact strength of PA6/EPM-g-TAI blends were also found to improve gradually with increasing the content of grafted TAI.

Functionalization of an ethylene-propylene copolymer with allyl (3-isocyanate-4-tolyl) carbamate

An ethylene-propylene copolymer (EPM) was functionalized with an iso cyanate-bearing unsaturated monomer, allyl(3-isocyanate-4-tolyl) carbamate (TAI), with dicumyl peroxide as an initiator in a xylene solution. Fourier transform infrared (FTIR) was used to confirm the formation of EPM-g-TAI. The peak at 2273 cm(-1), characteristic of -NCO groups in EPM-g-TAI, revealed evidence of grafting. The grafting degree was determined with both chemical titration and FTIR. The grafting degree could be adjusted, and the maximum was over 6 wt % without any gelation. The molar mass distribution of EPM-g-TAI was narrower than that of EPM. The rheological behavior of both EPM-g-TAI and EPM was investigated with a rotational rheometer. The apparent viscosity of EPM-g-TAI was higher than that of EPM and increased with an increasing grafting degree of TAI. Surface analysis by contact-angle measurements showed that contact angles of EPM-g-TAI samples to a given polar liquid decreased with an increasing grafting degree of TAI. We also obtained the dispersion component of the surface free energy (gamma(S)(d)), the polar component of the surface free energy (gamma(S)(d)), and the total surface free energy (gamma(S) = gamma(S)(d) + gamma(S)(p)) of the grafted EPM. These parameters increased with the enhancement of the grafting degree, which gave us a quantitative estimation of the polar contribution of the grafted TAI to the total surface free energy of EPM-g-TAI.

Toughening of nylon with epoxidised ethylene propylene diene rubber

Blends of nylon-6 and epoxidised ethylene propylene diene (eEPDM) rubber were prepared through reactive mixing. It is found that the toughness of nylon-6 can be much improved by this method, and that the particle size of eEPDM is much smaller than that of unexpoxidised EPDM (uEPDM) rubber in a nylon-6 matrix. This indicates that the epoxy group in eEPDM could react with a nylon-6 end group to form a graft copolymer which could act as an interfacial compatibiliser between the nylon-6 and the eEPDM rubber dispersed phase. (C) 1998 Elsevier Science Ltd. All rights reserved.

Thermal analysis of ethylene propylene copolymer-grafted-acrylic acid

The thermal properties of ethylene propylene copolymer-grafted-acrylic acid (EP-g-AA) were investigated by using differential scanning calorimetry (DSC). Compared with the ethylene propylene copolymer (EP), the peak values of the melting temperature (T-m) of the propylene sequences in the grafted EP changed a little, the crystallization temperature (T-c) increased about 8-12 degrees C, and the melting enthalpy (Delta H-m) increased about 4-6 J/g. The isothermal crystallization kinetics of grafted and ungrafted samples was carried out by DSC. Within the scope of the researched crystallization temperature, the Avrami exponent (n) of the ungrafted sample was 1.6-1.8, and that of grafted samples were all above 2, which indicated that the grafted monomer could become the crystal nuclei for the crystallization of propylene sequence. With increasing grafted monomer content, the crystallization rate of propylene sequence in grafted EP increased; it might be the result of rapid nucleation rate and crystal growth rate.

Toughened blend of polycarbonate and epoxidized ethylene propylene diene rubber

A super-tough polycarbonate (PC) blend was obtained by using epoxidized ethylene propylene diene (eEPDM) rubber as modifier. The notched Izod impact strength of PC/eEPDM (96/4) blend shows a great improvement, with a value about 25 times of that of pure PC. Finely and homogeneously dispersed rubber particles (0.2-0.8 mu m) in the PC matrix indicated good adhesion between the eEPDM rubber phase and the PC matrix. (C) 1997 Elsevier Science Ltd.

In situ epoxidation of ethylene propylene diene rubber by performic acid

In this paper, epoxidation of ethylene propylene diene rubber by in situ generated performic acid is discussed. The samples have been characterized by infra-red and H-1-nuclear magnetic resonance analyses. Quantitative analysis of the reaction products is made possible by using the methyl deformation band at 1377 cm(-1) as internal standard. The conversion of double bonds increases rapidly within the first 1 h, then gradually, over 2 h, has only a slight increase. The maximum conversion ratio of double bonds is about 70%. The relative content of epoxy groups has a top value at about 7 h. The side reactions are also discussed. (C) 1997 Elsevier Science Ltd.

Melt functionalization of ethylene-propylene copolymer: Structural investigation

An ethylene-propylene copolymer (EPM) has been functionalized with acrylic acid (AA) by means of a radical-initiated melt process. Different degrees of grafting have been obtained by varying the overall composition of the reaction mixture. The influence of the grafting degree on the structure has been investigated by differential scanning calorimetry (DSC), Fourier-transform infrared analysis (FTIR), and wide-angle x-ray scattering (WAXS) techniques. The results of the structural investigations suggest that the grafting preferentially occurs onto the ethylene sequences of EPM. After acrylic acid was grafted onto EPM, the grafted AA acted as nucleation agent; it caused an increase of crystallization temperature of propylene sequences of EPM-g-AA.

Binary alloys of nylon 1010 and ethylene-propylene copolymer: Chemical, morphological, and mechanical analysis

The modification of ethylene-propylene copolymer (EPM) has been accomplished by melt grafting of maleic anhydride (MAH) molecules promoted by radical initiators. The resulting EPM-g-MAH and EPM have been used to obtain binary nylon 1010/EPM or nylon 1010/EPM-g-MAH blends by melt mixing. It was found that the EPM-g-MAH copolymer used as the second component has a profound effect upon the properties of the resulting blends. This behavior has been attributed to a series of chemical and physicochemical interactions taking place between the two components. The interactions are due to the presence of the anhydride functionality on the copolymer and do not occur when this functionality is absent. The interaction has been confirmed by Fourier-transform infrared spectroscopy, differential scanning calorimetry, dynamic mechanical analysis, and scanning electron microscopic.

Toughening of poly(butylene terephthalate) with epoxidized ethylene propylene diene rubber

In this paper, unepoxidized ethylene propylene diene rubber (uEPDM) was first epoxidized with formic acid and H2O2, and then the epoxidized ethylene propylene diene rubber (eEPDM) was melt-mixed with PET resin in a Brabender-like apparatus. Toughening of PET matrix was achieved by this method. The dispersion of rubber particles and phase structure of the blends were also observed by SEM. It has been suggested that the epoxy groups in the eEPDM could react with PET end groups to form a graft copolymer which could act as an interfacial compatibilizer between the PBT matrix and eEPDM rubber dispersed phase. This is beneficial to the improvement of the impact performance of PBT. (C) 1997 Elsevier Science Ltd.

Preparation and characterization of ethylene-propylene copolymer grafted with acrylamido tertiary butyl sulfonic acid

Grafting of acrylamido tertiary butyl sulfonic acid (ATBS) onto ethylene-polypropylene copolymer (EPM) was carried out by using a reactive processing method. The grafting copolymer was characterized by means of WAXD, FT-IR, ESCA, and DSC. Improved thermal stability was observed for graft copolymer. Effects of the monomer and the initiator concentrations, reactive temperature, and time on grafting degree were investigated. (C) 1997 John Wiley & Sons, Inc.

Toughened poly(butylene terephthalate) by epoxided ethylene-propylene-diene-rubber

Blends of poly (butylene terephthalate) (PBT) and epoxided ethylene-propylene-diene terpolymer (EEPDM) were prepared. Their mechanical properties and morphology were studied by Izod impact test machine and scanning electronic microscope respectively, It was found that the notched Izod impact strength of blend PBT/EEPDM was as about 23 times as that of pure PET and about 10 times as that of blend PBT/EPDM at room temperature, The dispersed rubber particles were much smaller and the phase boundary was more blurred in blend PBT/EEPDM than in blend PBT/EPDM. The toughness of blend PBT/EEPDM was much more better than that of blend PET and PBT/EPDM, which was in good agreement with the difference between their morphologies.

Thermal analysis of ethylene-propylene copolymer-grafted-glycidyl methacrylate

The thermal properties of ethylene-propylene copolymer grafted with glycidyl methacrylate (EP-g-GMA) were investigated by using differential scanning calorimetry (DSC). Compared to the plain ethylene-propylene copolymer (EP), peak values of melting temperature (T-m) of the propylene sequences in the grafted EP changed a little, crystallization temperature (T-c) increased about 8-12 degrees C, and melting enthalpy (Delta H-m) increased about 4-6 J/g. The isothermal and nonisothermal crystallization kinetics of grafted and ungrafted samples was carried out by DSC. Within the scope of the researched crystallization temperature, the Avrami exponent (n) of ungrafted sample is 1.6-1.8, and those of grafted samples are all above 2. The crystallization rates of propylene sequence in EP-g-GMA were faster than that in the plain EP and increased with increasing of grafted monomer content. It might be attributed to the results of rapid nucleation rate. (C) 1996 John Wiley & Sons, Inc.

The determination of ethylene-propylene copolymer-grafted-glycidyl methacrylate by the contact angle method

The contact angles theta of some liquids on ethylene-propylene copolymer-grafted-glycidyl methacrylate (EPM-g-GMA) were measured. The critical surface tensions r(c) of EPM-g-GMA were evaluated by the Zisman Plot (cos theta versus r(L)), Young-Dupre-Good-Girifalco plot (1 + cos theta versus 1/r(L)(0.5)) and log (1 + cos theta) versus log(r(L)) plot. The following results were obtained: the r(c) values varied significantly with the estimation methods. The critical surface tension r(c) decreased with the increase of the degree of grafting of EPM-g-GMA.

Properties of ethylene-propylene copolymer/PA-1010 blends using ethylene-propylene copolymer-graft-acrylic acid as a compatibilizing agent

The modification of ethylene-propylene copolymer (EP) has been accomplished by radical EP-graft-acrylic acid (EP-g-AA) has been used to obtain ternary PA/EP/EP-g-AA blends by melt mixing. Different blend morphologies were observed by scanning electron microscopy; the domain size of the EP-dispersed phase in the polyamide 1010 matrix of compatibilized blends decreased compared with that of uncompatibilized blends. It is found that EP-g-AA used as the third component has a profound effect on the mechanical properties of the resulting blends. This behavior has been attributed to serious chemical interactions taking place between the two components. Thermal analysis shows that some thermal properties of PA in compatibilized PA/EP/EP-g-AA changed because of chemical reactions taken place during the blending process. Wide angle x-ray diffraction measurements also confirmed this result. (C) 1996 John Wiley & Sons, Inc.