Thermoresponsive UCST‐Type Behavior of Interpolymer Complexes of Poly(ethylene glycol) and Poly(poly(ethylene glycol) methacrylate) Brushes with Poly(acrylic acid) in Isopropanol

Upper critical solution temperature (UCST)‐type thermoresponsive behavior of poly(ethylene glycol)–poly(acrylic acid) (PEG–PAA) and poly(poly(ethylene glycol) methacrylate)–poly(acrylic acid) (PPEGMA–PAA) interpolymer complexes has been observed in isopropanol. For these investigations, PPEGMA and PAA with various average molecular weights have been synthesized by atom transfer radical polymerization. It has been found that both the PEG and PPEGMA have lower cloud point temperatures (T _cp) than its mixed polymer solutions with PAA, whereas PAA does not show such behavior in the investigated temperature range. These findings indicate the reversible formation of interpolymer complexes with variable structure and composition in the solutions of the polymer mixtures in isopropanol. Increasing the ethylene glycol/acrylic acid molar ratio or the molecular weight of either the PAA or the H‐acceptor PEG component of the interpolymer complexes increases the UCST‐type cloud point temperatures of these interpolymer systems. The polymer–polymer interactions by hydrogen bonds between PAA and PEG or PPEGMA and the correlations between T _cp and structural parameters of the components revealed in the course of these investigations may be utilized for exploring well‐defined UCST‐type material systems for various applications.

     

Effect of poly(dimethylsiloxane)-block-poly(oligo (ethylene glycol) methacrylate) amphiphilic block copolymers on dermal fibroblast viability and proliferation

Abstract

In this work, well-defined poly(dimethylsiloxane)-b-poly(oligo (ethylene glycol) methacrylate) (PDMS-b-POEGMA) amphiphilic block copolymers were synthesized and their effect on human dermal fibroblast were investigated. Anionic ring opening polymerization (ROP) and atom transfer radical polymerization (ATRP) were used to synthesis the block copolymers. The molecular weight of synthesized copolymers ranged from 1000 to 2300?Da by changing the number of both PDMS and POEGMA units. It was found that the copolymer having low molecular weight decreased the fibroblast viability and proliferation by inducing apoptosis. It was proved by flow cytometry and TUNEL assay that human dermal fibroblast experienced apoptosis after exposure to synthesized amphiphilic copolymers. The results of this work suggest the use of PDMS-b-POEGMA amphiphilic copolymers with low molecular weight for hypertrophic scars remediation.     

Physicochemical and biological properties of poly(ethylene glycol)-coupled immunoglobulin G. Part II. Effect of molecular weight of poly(ethylene glycol)

In order to obtain a stable human immunoglobulin G (IgG) preparation for clinical use, the chemical coupling of different molecular weights of poly(ethylene glycol)s (PEGs) to IgG molecules was achieved. The abilities of PEG-coupled IgGs (PEG-IgG hybrids) to aggregate were examined when they were subjected to such physicochemical treatments as interfacial exposure, heating, lyophilization, and acid treatment. It was found that the higher the molecular weight of PEG coupled, the more stable was the PEG-IgG hybrid obtained concerning interfacial exposure and heating. The hybrid was stable against lyophilization and acid treatment and its stability was independent of the PEG molecular weight. The decrease in antigen binding ability was suppressed as much as possible by the use of a small amount of PEG of higher molecular weight. The PEG-IgG hybrids were further assessed as a stabilizer for IgG. A limited degree of PEG coupling was required for the hybrids to achieve the most efficient stabilization of IgG: the optimal PEG contents of the hybrid were > 20 wt% (interfacial exposure), about 5'wt,?o (heating), 20 wt% (lyophilization), and 10 wt% (acid treatment) for PEG 5600. It was also confirmed that the PEG-IgG hybrid was superior to PEG and human serum albumin as a stabilizer.     

Hyper-branched poly(poly(ethylene glycol)methacrylate)-grafted surfaces by photo-polymerization with iniferter for bioactive interfaces

A new hyper-branched surface in which three species of architectures were constructed as stem chain, branched stem and twig chain-grafted branched chain of poly(poly(ethylene glycol)methacrylate) (poly(PEGMA)) by photo-polymerization using dithiocarbamyl group (DC) as iniferter was prepared and characterized. For these surfaces, radical copolymerization of styrene and an iniferter-activated chain that was previously synthesized was performed for using as base materials for surface coating. On a DC-activated surface, hyper-branched poly(PEGMA) was introduced by photo-polymerization and dithiocarbamylation. All modified surfaces were analyzed by X-ray photoelectron spectroscopy (XPS) and water contact angle measurements. Our results demonstrated that a highly hyper-branched graft architecture of poly(PEGMA) can be constructed on PU surface by photo-polymerization using dithiocarbamyl group as iniferter, in which first, second and third generation gave stem chain, branched chain and twig chain of poly(PEGMA), respectively. Our hyper-branched surfaces could be regulated by photo-irradiation time and might be controlled by feed amounts or other reaction conditions. This highly dense architecture of PEG chain with hydrophilicity and chain mobility, grafted on surface, is expected to be effectively utilized in bio-implantable substrates or micro- or nano-patterned surfaces for immobilization of bioactive molecules in biomedical fields.     

Preparation and antibacterial activity of silver-loaded poly(oligo(ethylene glycol) methacrylate) brush

Herein, we report on a robust approach to fabricate antibacterial nanocomposite coating simply by immersing poly(oligo(ethylene glycol) methacrylate) (POEGMA) brush into a silver perchlorate solution without using any external reducing agents. The POEGMA brush of 48.3?nm in thickness is prepared via surface-initiated atom transfer radical polymerization method. Field-emission scanning electron microscope and Raman measurements indicate that silver nanoparticles of 14?～?25?nm in diameter are successfully embedded into the POEGMA brush. Antibacterial activities of the resultant silver-loaded POEGMA brushes against both Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus are measured by zone of inhibition and colony-counting methods, respectively. The results show that the silver-loaded POEGMA coatings exhibit enhanced antibacterial efficiency compared to bare POEGMA brush. In order to elucidate their antibacterial mechanism, silver release behaviors of these silver-loaded POEGMA brushes are monitored via inductively coupled plasma mass spectrometry.     

AGET ATRP of Poly[poly(ethylene glycol) methyl ether methacrylate] Catalyzed by Hydrophobic Iron(III)–Porphyrins

Commercially available hydrophobic porphyrins are investigated as an environmentally friendly catalytic system for iron‐mediated atom transfer radical polymerization (ATRP) of poly(ethylene glycol) monomethyl ether methacrylate (PEGMA). Polymerizations in organic solvent are optimized using activators generated by electron transfer (AGET ATRP), based on iron(III)–porphyrin complexes, and tin(II) 2‐ethyl hexanoate or ascorbic acid as a reducing agent. Copper‐free PPEGMA macromolecules are obtained with high conversion, controlled molecular weight, and polydispersity index compared with standard copper‐based ATRP. The facile preparation and availability of the catalyst, together with its expected low toxicity, represent clear advantages for the synthesis of PPEGMA‐based materials for biomedical use.

     

Synthesis and properties of novel block copolymers containing poly(lactic-glycolic acid) and poly(ethyleneglycol) segments

A synthetic process for obtaining high-molecular-weight block copolymers containing poly(lacticglycolic acid) and poly(ethylene glycol) segments has been established. This process involves the reaction of poly(ethylene glycols) with phosgene, followed by polycondensation of the resulting ,ω-bis (chloroformates) with poly(lactic-glycolic acid) oligomers. The copolymers have been characterized for their molecular weight, solubility properties, water absorption and preliminarily thermal behaviour. All evidence points to the conclusion that the process described is a general one, enabling biodegradable polymers to be obtained tailor-made according to specific requirements.     

Microstructural pathway of fracture in poly(methyl methacrylate) bone cement

Mechanical failure of poly(methyl methacrylate) (PMMA) bone cement is linked to failure of cemented total joint prostheses. An essential step to minimize, if not eliminate, cement fracture is to understand the material characteristics controlling fracture resistance. At least four phases of bone cement can be identified that may affect the damage zone formation: pre-polymerized beads, interbead matrix polymer, BaSO₄, and porosity. Gel permeation chromatography (GPC) was used to determine the molecular weight (MW) distributions of the two polymer phases. Mechanical testing, scanning electron microscopy and light microscopy were used to analyse fracture mechanisms. Fatigue crack propagation of bone cement was distinctly different from rapid crack propagation. Microcracks defined the damage zone for fatigue fracture. The microcracks developed in the interbead matrix and not through the pre-polymerized beads. Light microscopy revealed evidence of craze formation on surfaces of fractured beads during rapid fracture, but not on fatigue surfaces. GPC analysis indicated an increase in MW from the bead phase alone to the fully cured bone cement, indicating a greater MW in the interbead matrix polymer. Increases of 36 and 176% were measured for two different bone cements, but the bulk of the polymer has an MW of less than 1 × 10⁶. Three factors were suggested to explain why the microcracks seem to prefer to grow in the interbead matrix: the presence of BaSO₄, shrinkage during the curing process, and the different polymerization processes of the bead and the interbead polymers. Pores had an affect on the microcrack formation as well, and did not need to be directly in front of the crack tip to interact with the damage zone. The pores seemed to act as nucleation sites for microcracks. The porosity-microcrack nucleation interaction may explain and reconcile the apparently disparate results concerning the effect of porosity on fracture toughness and fatigue life. Porosity may, however, also provide positive contributions to the fracture properties of bone cement by dispersing the energy at the crack tip, forming a larger damage zone, and effectively blunting the crack. The crack propagation mechanisms revealed by this research indicated the importance of microstructure in the fatigue failure of PMMA.     

Liquid Chromatography at Critical Conditions of Poly(propylene)

Liquid chromatography at critical conditions (LCCC) of poly(propylene) (PP) holds unique potential to further augment the understanding of molecular heterogeneities present in PP. The critical conditions for isotactic poly(propylene) (iPP) and syndiotactic poly(propylene) (sPP) have been identified using porous graphitic carbon as stationary phase and combinations of adsorption and desorption promoting solvents. It is found that 1,2,4‐trichlorobenzene is a stronger desorption promoting eluent compared to 1,2‐dichlorobenzene, while 2‐octanol shows a weaker adsorption promoting effect compared to 2‐ethyl‐1‐hexanol for all stereo‐isomeric forms of PP. The fraction of desorption promoting solvent needs to reach critical conditions decreased in a linear manner with the temperature. High temperature 2D liquid chromatography with infrared detection provides quantitative information about the fractions of the constituents (iPP and ethylene–propylene copolymer) of a model high impact PP sample at LCCC of iPP.

     

Crystallization Kinetics and Melting Behaviour of the Novel Biodegradable Polyesters Poly(propylene azelate) and Poly(propylene sebacate)

Novel biodegradable poly(propylene sebacate) (PPSeb) and poly(propylene azelate) (PPAz) polyesters were synthesized and fully characterized using WAXD, standard DSC, high‐rate DSC, and modulated‐temperature DSC. Multiple‐melting behaviour, observed for samples isothermally crystallized from the melt, was attributed to sequential melting–recrystallization–remelting. Study of isothermal and nonisothermal crystallization kinetics revealed a higher crystallization rate for PPSeb compared to PPAz. The Avrami and the Lauritzen‐Hoffman models were successfully applied to DSC measurements, using also data obtained after self‐nucleation, in order to diminish the effect of primary nucleation. Finally, the effective activation energy was estimated using the differential isoconversional method of Friedman.

     

Molecular calculations of poly(ethylene glycol) transport across a swollen poly (acrylic acid)/mucin interface

The transport of poly(ethylene glycol) chains than can promote mucoadhesion across the interface between lightly cross-linked poly(acrylic acid) and mucin may be analyzed as a function of molecular characteristics using theories of chain penetration in a dilute network. The fracture energy for the ensuing adhesive bond is proportional to the number of polymer chains crossing the interface, which, in turn, is related to the polymer volume fraction, the chain diffusion coefficient, and the degree of polymerization. Relevant calculations were performed for a number of cross-linked poly(acrylic acid) gels and three different types of poly(ethylene glycol) chains.     

Chain conformation and compatibility in polymer blends. A small-angle X-ray scattering study of the system poly(propylene glycol)-poly(methyl methacrylate)

The thermodynamic compatibility of dilute, solid solutions of poly(propylene glycol) (PPG) (mass-average molar mass M?_w = 3900 g/mol) in poly(methyl methacrylate) (PMMA) (M?_w = 550000 g/mol) was investigated by means of small-angle X-ray scattering. The results of the analysis show that PPG is molecularly dispersed in the solid, amorphous matrix of PMMA, and that the molecules display the typical statistical coil macroconformation of polymers in dilute, liquid solution, whereby the numerical value of the second virial coefficient seems to point to the unperturbed nature of the coils. This behaviour, consistent with the concept of “interpenetration of segments”, is in total agreement with the experimentally measured compositional variation of the glass transition temperature of the blends.     

聚乙二醇单甲醚-聚(D,L-乳酸)嵌段共聚物的研究

采用熔融缩聚反应合成一系列聚（D，L-乳酸）（PDLLA）／聚乙二醇单甲醚（mPEG）两亲性二嵌段共聚物（PEDLLA），采用IR、^1H-NMR、DSC、WAXD和TEM等手段分析和研究PEDLLA的结构与性能。实验结果表明，PEDLLA的结构和组成与设计相一致，结晶度和熔点均低于均聚物，且随着PEDLLA中PDLLA含量的增加，mPEG嵌段熔点降低，随着PDLLA嵌段相对分子质量的增大，PEDLLA降解速率增大。载药纳米粒呈核壳结构，载药量达30％。     

Solute transport analysis in pH-responsive,complexing hydrogels of poly(methacrylic acid-g-ethylene glycol)

We report on the preparation and properties of hydrogels of poly(methacrylic acid-g-ethylene glycol) that exhibit pH-responsive swelling behavior due to the reversible formation/dissociation of interpolymer complexes. Because of their nature, these materials may be useful in drug delivery applications. In this work, we studied the diffusional behavior of three solutes of varying molecular size in the complexing hydrogels as a function of solution pH. The ability of these gels to control the solute diffusion rates was strongly dependent on the molecular size of the solute and the environmental pH. The diffusion coefficients for solutes were calculated as a function of pH and were lower in acidic than neutral or basic media due to the formation of interpolymer complexes in the gels. However, the ratio of the solute radius to the network mesh size also was a significant factor in the overall behavior of these gels. The diffusion coefficient of the smallest solute, proxyphylline, studied only changed by a factor of five between the complexed and uncomplexed state. However, for the largest solute, FITC-dextran, which has a molecular radius ten times greater than proxyphylline, the diffusion coefficients of the drugs in complexed and uncomplexed gels varied by almost two orders of magnitude. These results are explained in terms of mesh size characteristics of the gels.     

Development of arginine-glycine-aspartate-immobilized 3D printed poly(propylene fumarate) scaffolds for cartilage tissue engineering

Abstract

Poly(propylene fumarate) (PPF) has known to be a good candidate material for cartilage tissue regeneration because of its excellent mechanical properties during its degradation processes. Here, we describe the potential application of PPF-based materials as 3D printing bioinks to create macroporous cell scaffolds using micro-stereolithography. To improve cell-matrix interaction of seeded human chondrocytes within the PPF-based 3D scaffolds, we immobilized arginine-glycine-aspartate (RGD) peptide onto the PPF scaffolds. We also evaluated various cellular behaviors of the seeded chondrocytes using MTS assay, microscopic and histological analyses. The results indicated that PPF-based biocompatible scaffolds with immobilized RGD peptide could effectively support initial adhesion and proliferation of human chondrocytes. Such a 3D bio-printable scaffold can offer an opportunity to promote cartilage tissue regeneration.     

Novel High and Ultrahigh Molecular Weight Poly(propylene) Plastomers by Asymmetric Hafnocene Catalysts

Summary: The novel asymmetric ansa‐complexes [1‐(9‐η⁵‐fluorenyl)‐2‐(2,5,7‐trimethyl‐indenyl)ethane]hafnium dichloride ( 7a ) and [1‐(9‐η⁵‐fluorenyl)‐2‐(2,4,6‐trimethyl‐indenyl)ethane]hafnium dichloride ( 7b ) were prepared and used as catalysts for propylene homopolymerization reactions after in situ activation. The synthetic route allows to separate the 4,6‐ and 5,7‐substituted ligand isomers before the complexation step. The orientation of the methyl groups to the “front” (4,6) or to the “back” (5,7) of the tetrahedral hafnocene dichloride species influences their performances in polymerization reactions. Whereas hafnocene ( 7b ) which bears trimethyl substitution at 2,4,6‐positions of the indenyl moiety exhibits only moderate activity, the 2,5,7‐trimethyl substituted structure ( 7a ) produces isotactic poly(propylene)s with high molecular weights (up to = 9.0 × 10⁵ g · mol^?1) and high activities [up to 3.2 × 10⁵ kg of PP (mol Hf × h)^?1]. A comparative analysis of polymerization data and mechanical behavior of 7a , and previously reported 6,7‐indenyl substituted complex 6b are reported.

Typical stress‐strain curves of different types of poly(propylene)s.     

Sulfonation of Poly(propylene) Films with Fuming Sulfuric Acid

Summary: Sulfonation is one of the most commonly used methods for the surface modification of polymers. In this study, the sulfonation of poly(propylene) (PP) films with fuming sulfuric acid has been investigated with the focus on the surface reaction. Analysis of the sulfonated PP films by X‐ray photoelectron spectroscopy (XPS), attenuated total reflectance (ATR) infrared spectroscopy, and chemical modification demonstrated the formation of C?C double bonds and sulfate groups in the sulfonation process. These results and a comparison with low‐density polyethylene (LDPE) films led us to propose a new sulfonation mechanism involving hydride abstraction and the formation of β‐sultones.

The here proposed mechanism of the sulfonation of poly(propylene) involves the formation of unstable β‐sultones.     

A facile method to fabricate thermo- and pH-sensitive hydrogels with good mechanical performance based on poly(ethylene glycol) methyl ether methacrylate and acrylic acid as a potential drug carriers

Abstract

A thermo- and pH-sensitive hydrogel was prepared by a facile free aqueous radical copolymerization of PEGMA and AAc without any crosslinkers for controlled drug delivery. The successful fabrication of hydrogels was confirmed by Fourier transform infrared spectroscopy (FT-IR) and thermo gravimetric analysis (TGA) measurements. The morphological, mechanical and swelling properties of the obtained hydrogels were studied systematically. The results showed that the morphological and mechanical behaviors of the resultant hydrogels were strongly affected by the content of AAc. Moreover, the obtained hydrogels showed an excellent thermo-, pH- and salinity sensitivities. Release profiles of 5-Fu were studied at different pH (gastric pH 1.2 and intestinal pH 7.4) and temperatures (25?°C and 37?°C). The results showed that the release is very low at pH 1.2/37?°C and high at pH 7.4/25?°C. The cytotoxicity of hydrogels to cells was determined by an MTT assay. The result demonstrated that the blank hydrogels had negligible toxicity to cells, whereas the 5-Fu-loaded hydrogels remained high in cytotoxicity for LO2 and HepG-2 cells. Results of the present investigation exemplify the potential of this novel thermo- and pH-sensitive hydrogel for the controlled and targeted delivery of the anti cancer drug 5-Fu.     

Preparation and properties of cryogel based on poly(hydroxypropyl methacrylate)

A novel supermacroporous poly(hydroxypropyl methacrylate) (p(HPMA)) cryogel was synthesized by cryogelation method at –16 °C. In this synthesis process, HPMA was used as a monomer, and N,N′-methylenebisacrylamide (MBAAm) was used as cross-linker; the reaction was carried out in the presence of redox initiator pair N,N,N′,N′-tetramethylene diamine (TEMED) and ammonium persulfate (APS). The effect of monomer concentration, cross-linker content, cooling rate, and dioxane co-solvent were determined with respect to the pore structure, mechanical behavior, swelling degree, and porosity of cryogel. The ESEM images indicate that the pore wall structure of cryogels was rough; moreover, small holes were present in the pore walls of cryogels. The result of compression test indicates that cryogels can be compressed by at least 80% without any breakdown. The result of swelling kinetics indicates that cryogels attain swelling equilibrium in 10 s. Furthermore, p(HPMA)-Cu²⁺ cryogel was prepared by loading Cu²⁺ ions on functionalized poly(hydroxypropyl methacrylate)-iminodiacetic acid (p(HPMA)-IDA) cryogel. We investigated the adsorption of bovine serum albumin (BSA) on cryogels. The results indicate that compared to Freundlich isotherm, Langmuir isotherm could more suitably describe the adsorption process of BSA on cryogels. Meanwhile, the adsorption capacity of p(HPMA)-Cu²⁺ cryogel was significantly greater than that of p(HPMA) cryogel. The maximum adsorption capacity of BSA on p(HPMA)-Cu²⁺ cryogel, which was treated with 1 M Cu²⁺ ions, was as high as 196.87 mg/g cryogel (equivalent to 20.48 mg/mL cryogel) at 25 °C and pH = 7.8; therefore, the maximum adsorption capacity of BSA on p(HPMA)-Cu²⁺ cryogel was 4.35 times higher than that of p(HPMA) cryogel. Thus, the adsorption capacity of cryogels was strongly influenced by Cu²⁺ concentration, moreover, temperature changes clearly affected the adsorption capacity of p(HPMA)-Cu²⁺cryogel. The adsorption capacity at 25 °C was twice as that at 15 °C. By calculating Gibbs free energy change (?G) of adsorption, we found that the adsorption process was spontaneous; moreover, adsorption process occurred better at higher temperature.     

Metallocenic Isotactic Poly(propylene) and its Copolymers with 1‐Hexene and Ethylene

A comprehensive study of the structure and properties has been performed for copolymers of propylene‐1‐hexene, CiPH, and propylene‐ethylene, CiPE, synthesized by an isotactic metallocene catalyst system. The comonomer content constitutes the most important factor affecting the structure and properties of these CiPH and CiPE copolymers, although the length of the comonomer is also very important. Thus, a considerable decrease in crystallinity is observed in the two kinds of copolymers as the comonomer content increases. The structure in the CiPH copolymers evolves, however, from the typical, monoclinic crystal lattice to mesomorphic‐like, ordered entities for the highest 1‐hexene molar fraction, whereas in the CiPE copolymers the structural evolution with molar fraction goes from a monoclinic lattice to an almost amorphous material. All of these variations in crystal structure significantly influence the viscoelastic and mechanical behavior of these CiPH and CiPE copolymers. Consequently, the location and intensity of the different relaxation mechanisms, as well as the rigidity parameters (storage and Young's moduli and microhardness) and deformation mechanism are strongly dependent upon composition.