Monomer-solvent Mixtures Research Articles

Optimization of thermoresponsive hydrogels based on oligomers with lower critical solution temperature (LCST) far below/above physiological temperatures for biomedical applications

Hydrogels with oligo(ethylene glycol) (OEG), oligo(propylene glycol) (OPG), and for the first time with combined OEG/OPG pendant chains within the methacrylate (MA) network, were synthesized and the swelling behavior, thermal properties, microstructure, and genotoxicity were investigated. Prior to hydrogel fabrication, an optimized method was developed for oligo(propylene glycol) methacrylate (OPGMA), i.e., oligomer with an LCST below a temperature at which synthesis occurs, indicating that proper preparation and tuning of reaction conditions were required. PEG6MA and PPG5MA homopolymers, as well as P(EG6/PG5)MA copolymer hydrogel, were produced by gamma radiation-induced polymerization and crosslinking of OEG and OPG monomers from the monomer-solvent mixture by using different water/ethanol composition as a solvent and by exposing the reaction mixture to various radiation doses. The combination of OEG and OPG pendant chains within the same network was advantageous in that it allowed an easy tuning of the phase transition temperature. Thus, the volume phase transition (VPT) at temperatures above 70 °C observed in the case of PEG6MA, and in the case of PPG5MA at temperatures below 15 °C, could easily be tuned close to physiological temperatures for P(EG6/PG5)MA hydrogel. Finally, all obtained thermoresponsive hydrogels showed non-genotoxic and non-cytotoxic properties, which indicate promising potential for biomedical applications.

Stimuli-responsive copolymeric hydrogels based on oligo(ethylene glycol) dimethacrylate for biomedical applications: An optimisation study of pH and thermoresponsive behaviour

Di(meth)acrylate (D(M)A) systems with pendant oligo(ethylene glycol) (OEG) chains are promising biomedical candidates. Homopolymeric P(OEG)D(M)A hydrogels have significant thermoresponsiveness demonstrated mainly at elevated temperatures which makes this class of materials unsuitable for bio-applications. Copolymerisation with less hydrophilic 2-hydroxyethyl methacrylate (HEMA) was performed in an effort to shift volume phase transition (VPT) closer to physiological temperatures and to widen their application as thermoresponsive materials. Various monomer-solvent mixtures, consisting of different mole ratios of OEGDMA and HEMA monomers (100/0, 50/50, 27.5/72.5, and 12.5/87.5) and water/ethanol as solvent, were exposed to gamma radiation up to 6, 12, 25, and 50 kGy. Furthermore, in an attempt to obtain multi- (thermo- and pH-) responsive hydrogels for biomedical applications new P(OEGDMA/HEMA/IA) terpolymers containing a small share (2.5, and 5 wt%) of itaconic acid (IA) were synthesised. The successful fabrication of the hydrogels was confirmed by gel measurements and FTIR spectroscopy. Swelling measurements indicated that obtained networks possessed tuneable thermal behaviour and swelling properties which could be significantly altered by hydrogel composition. The porous architecture was investigated using SEM, confirming swelling results. Cytotoxicity revealed relatively high cell viability for all hydrogels, indicating satisfactory in vitro biocompatibility. Therefore, new OEGDMA based hydrogels showed potential for biomedical applications.

Computer Simulation of Anisotropic Polymeric Materials Using Polymerization-Induced Phase Separation under Combined Temperature and Concentration Gradients.

In this study, the self-condensation polymerization of a tri-functional monomer in a monomer-solvent mixture and the phase separation of the system were simultaneously modeled and simulated. Nonlinear Cahn–Hilliard and Flory–Huggins free energy theories incorporated with the kinetics of the polymerization reaction were utilized to develop the model. Linear temperature and concentration gradients singly and in combination were applied to the system. Eight cases which faced different ranges of initial concentration and/or temperature gradients in different directions, were studied. Various anisotropic structural morphologies were achieved. The numerical results were in good agreement with published data. The size analysis and structural characterization of the phase-separated system were also carried out using digital imaging software. The results showed that the phase separation occurred earlier in the section with a higher initial concentration and/or temperature, and, at a given time, the average equivalent diameter of the droplets <dave> was larger in this region. While smaller droplets formed later in the lower concentration/temperature regions, at the higher concentration/temperature side, the droplets went through phase separation longer, allowing them to reach the late stage of the phase separation where particles coarsened. In the intermediate stage of phase separation, <dave> was found proportional to , where was in the range between and for the cases studied and was consistent with published results.

Impregnation and polymerization reinforcement of porous materials by liquid monomer-solvent mixtures

Effect of the composition of liquid monomer-solvent mixtures on the processes of impregnation and subsequent reinforcement of solid chalkstone samples by the monomer polymerization in pores was considered. Factors influencing the rate of the solution-monomer mixture penetration in pores of a solid were studied.

Net expansion of dried demineralized dentin matrix produced by monomer/alcohol saturation and solvent evaporation

The purpose of this work was to determine if nonaqueous methacrylate monomer/alcohol mixtures could expand dried collapsed demineralized dentin matrix. Thin disks (ca. 200 microm) of human dentin were demineralized and placed in wells beneath contact probes of linear variable differential transformers. The probes were placed on water-saturated expanded matrices to record the shrinkage associated with drying. Monomer mixtures containing hydroxyethyl methacrylate, 2,2-bis[4-(2-hydroxy-3 methacryloyloxy)propoxyphenyl] propane, or triethyleneglycol dimethacrylate were mixed with methanol or ethanol at alcohol/monomer mass fraction % of 90/10, 70/30, 50/50, or 30/70. They were randomly applied to the dried matrices to determine the rate and magnitude of expansion; then shrinkage was recorded during evaporation of the alcohols. The results indicated that matrix expansion was positively correlated with the Hoy's solubility parameters for hydrogen bonding forces (delta(h)) of the monomer/solvent mixtures (p < 0.001). Expansions were more rapid with methanol-containing than with ethanol-containing monomer mixtures. For the test solutions, triethyleneglycol dimethacrylate-containing mixtures produced the slowest rate of matrix expansion and hydroxyethyl methacrylate-containing mixtures the most rapid expansion. When the solvents were evaporated, the matrix shrank in proportion to the solvent content and the delta(h) of the monomer-solvent mixtures. The results indicate that expansion of dried, collapsed dentin matrices requires that the delta(h) of the mixtures be larger than 17 (J/cm(3))(1/2). The greater the delta(h) of the monomer solutions, the greater the rate and extent of expansion.

Enhanced biocompatibility of polyphosphazenes achieved by radiation grafting

This paper reviews the work recently carried out in the authors' laboratory on the radiation graft copolymerization of hydrophilic monomers onto polyphosphazenes. Kinetics of grafting by the mutual irradiation method at room temperature of monomer-solvent mixtures were followed. Hydrophilicity, structure, mechanical properties, biocompatibility and anticoagulating properties of the modified samples were reported. Some experiments on the grafted polymer, to which heparin was ionically bonded with a high yield, were also carried out.

Solvation effect in thermal decomposition of 2,2′‐azoisobutyronitrile

AbstractThe solvation effect in the thermal decomposition of a radical initiator (AIBN) in monomer–solvent mixtures is discussed. Equations were derived which comprise the initiator decomposition constant as a function of the monomer mole fraction for chosen types of solvation. In addition, equations were deduced presenting the concentrations and partial relative decomposition rates for the solvated initiator species as a function of the monomer mole fraction. The equations obtained were compared to the experimental literature data and possible dependences of decomposition constants on monomer concentration were simulated for various solvated species. The simulated relationships were found to be straight lines, curves of saturated type (possessing a plateau), S‐shaped curves, and maximum or minimum curves. © 1995 John Wiley &amp; Sons, Inc.

Radiation grafting of hydrophilic monomers onto poly[bis(trifluoroethoxy)phosphazene

The hydrophilic monomers dimethylacrylamide (DMAA) and acrylamide (AAm) were radiation grafted onto poly[bis-(trifluoroethoxy)phosphazene] (PTFP) for biocompatibility enhancement through direct irradiation of the polymer films immersed in monomer-solvent mixtures, and the progress of grafting was followed up to a large monomer depletion. The water absorption of the samples was found to increase as the amount of the grafted chains increased. The grafted chains, mainly confined in the film surface at high dose rates, progressively extend to the interior of the sample as the dose rate decreases. In the grafted samples the ultimate mechanical properties ε r and σ r were essentially preserved. The in vivo tests indicated an enhancement of surface biocompatibility in the PTFP-g-AAm samples and not in the PTFP-g-DMAA samples.

Investigation of radiation grafting of vinyl acetate onto (tetrafluoroethylene–perfluorovinyl ether) copolymer films

AbstractA study has been made of radiation‐induced grafting of vinyl acetate (VAc) on to (tetrafluoroethylene–perfluorovinyl ether) copolymer (PFA). Effects of grafting conditions such as inhibitor and monomer concentrations and irradiation dose on the grafting yield were investigated. In this grafting system, ammonium ferrous sulphate (Mohr′s salt) was added to the monomer‐solvent mixture to minimize the homopolymerization of VAc and the most suitable concentration was found to be 2.0 wt%. It was found that the dependence of the initial grafting rate on monomer concentration is of the order 1.5. The degree of grafting tends to level off at high irradiation doses due to the recombination of formed free radicals without initiating graft polymerization. Some properties of the prepared graft copolymer such as swelling behaviour, electrical conductivity, thermal and mechanical properties were also investigated. The electrical conductivity was improved by hydrolysis of poly(vinyl acetate) in the grafted chains to their respective vinyl alcohols. The tensile properties were improved by grafting; however, the elongation percent decreased. The DTA data showed thermal stability of such graft copolymers for temperatures up to 300°C, but stability decreased at higher temperatures.

Kinetics of Radical Polymerization. XLI. Kinetic Investigation of the Radical Polymerization of Methyl Methacrylate in Benzene and Bromobenzene

Abstract The present paper deals with the radical polymerization kinetics of the systems MU-AIBN-Bz-50°C and MMA-AIBN-BrBz-50°C. The rate of initiation and the k2/√k4 value were determined in a broad range of monomer concentrations. The initiation rate constant was found to be independent of the concentration of solvent and monomer. In the system MMA-Bz the k2/√K4 value does not change with dilution, while in the system MMA-BrBz it depends on the viscosity of the initial monomer-solvent mixture.

Etude calorimetrique de radiopolymerisations en phase solide

Radiation induced solid state polymerization of crystalline acrylonitrile and glassy monomer-solvent mixtures have been studied in an adiabatic calorimeter by means of heat effects associated with these reactions. This technique allows separation of reactions taking place during the irradiation at 77°K and those during warming up of irradiated samples. Evidence is given for “in-source” polymerization which leads to small conversions. The greatest part of the polymer is produced during warming up at temperatures close to phase transition temperatures (crystal-crystal, crystal-liquid, glass-supercooled liquid) i.e. when molecular motions are possible in the solid state. This observation leads to a proposal of a localization in “hot zones” of in-source polymerization.

Effect of solvents on the graft copolymerization by pre-irradiation technique

Grafting on polypropylene by pre-irradiation and exposure to some monomer-solvent mixtures has been investigated. The experimental results show that the mutual interactions between the polymeric matrix and the monomer-solvent mixtures are of the greatest importance.