Amphiphilic Networks Research Articles

Synthesis of novel amphiphilic pH-sensitive polyurethane networks through water-in-oil soap-free emulsion polymerization process. I. Microstructural differences and swelling behaviors

pH-sensitive amphiphilic networks are synthesized from urethane acrylate anionomer (UAA) precursor chains. The microstructures of these networks are very sensitive to the nature of and the amount of solvent used during crosslinking. Whereas dioxane forms relatively homogenous solution, water preferentially interacts with hydrophilic segment of UAA chains, causing the microphase separation between hydrophilic moieties and hydrophobic main chains. This microphase separation was locked-in by crosslinking reaction, enhancing largely the hydrophilicity of UAA networks and the hydrophobic aggregation. The UAA gels, prepared with water (UAAG) and/or dioxane (UADG), exhibit quite different swelling behaviors in the same dissolution medium because of their completely different microstructures. The improved hydrophilicity of UAAG gels due to the hydrophilic/hydrophobic microphase separation is confirmed by measuring the contact angle to water. These microphase-separated hydrophilic domains on UAA gel matrix, which are observed by scanning electron microscopy measurement, influence the mechanical property of dried UAA gels as well. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 2115–2127, 2000

Synthesis and properties of amphiphilic networks. 1: the effect of hydration and polymer composition on the adhesion of immunoglobulin-G to poly(laurylmethacrylate- stat-glycerolmonomethacrylate- stat-ethylene-glycol-dimethacrylate) networks

A series of hydrogels composed of varying fractions of dodecyl methacrylate (DM) and 2,3-dihydroxypropyl methacrylate (GM) were prepared using ethylene glycol dimethacrylate (EGDMA) as the cross-linking agent. The study found that for a series of gels with the same monomer ratio, bulk hydration could be controlled by adjusting the cross-link density. The ability to control cross-link density allowed the preparation of gels with the same bulk hydration but different ratios of the two monomers. The adsorption of IgG to the gels was investigated using ELISA. The aim of the project was to investigate the effect of the bulk hydration and polymer composition on IgG adsorption. The results show that for a series of gels with the same monomer ratio, there is a clear trend towards a reduction in protein adsorption as the bulk hydration and accompanying chain mobility of the gel increases. Studies on gels of the same bulk hydration but differing ratios of monomer show higher protein adsorption as the proportion of GM increases.

Amphiphilic networks. XIV

The synthesis and characterization of novel amphiphilic networks based on dimethylacrylamide and crosslinked by methacrylate telechelic three-arm star polyisobutylene (O(PIB-MA) 3 ) are reported. The networks are characterized by two M c 's and possess homogeneous' and heterogeneous crosslinks. The networks swell both in water and n-heptane which indicates a cocontinuous hydrophobic-hydrophilic microarchitecture. Water-swollen networks exhibit higher tensile strengths and elongations, than those made previously with linear MA-PIB-MA's of similar overall compositions (i.e., ∼1.0 versus ∼0.5 Mpa, and ∼300% versus ∼200%, respectively). The enhanced mechanical properties of the new networks are being exploited in biomedical applications.

Synthesis of novel amphiphilic pH-sensitive polyurethane networks through W/O soap-free emulsion polymerization process. II. Mechanical property and biphasic swelling behaviors

Amphiphilic urethane acrylate anionomer (UAA) chains exhibited very different solution properties in various solvents, such as water, dioxane, and dimethyl sulfoxide (DMSO). UAA chains showed a polyelectrolyte effect in a highly polar solvent, DMSO, but gave constant viscosity at various concentrations in aqueous solution, because of the microstructural difference of the UAA chain formed in solvents. In polar solvents (water and DMSO), the swelling of UAA networks prepared with water and dioxane strongly depended on the properties of the hydrophilic domains. In low and nonpolar solvents (dioxane and methylene chloride), the swelling of UAA networks was only dependent on the property of the hydrophobic segments. In the polar solvent medium, UAAG networks prepared with water exhibited greater swelling than UADG networks prepared with dioxane. Concerning swelling in a nonpolar solvent, however, UADG networks showed greater swelling than UAAG networks. This is because of the microstructural difference between these networks, which was confirmed by the mechanical property measurement. UAAG networks, having highly microphase-separated structures, had higher modulus and transition temperatures than the UADG networks, because of the microstructural difference between UADG and UAAG networks. Both the UAAG and UADG networks take up two immiscible solvents simultaneously within their hydrophobic and hydrophilic domains. Equilibrium swelling ratio of these networks in two immiscible solvents strongly depends on their hydrophilic/hydrophobic balance that is controlled by the type of solvent used in the network synthesis.

Synthesis and characterization of tubular amphiphilic networks with controlled pore dimensions for insulin delivery

A convenient laboratory process for the preparation of thin-walled (∼0.02 cm) tubular amphiphilic membranes has been developed. The membranes are suitable for implantation and isolation of pancreatic islets from immune responses. The process involves the simultaneous free radical copolymerization/crosslinking of dimethyl acrylamide (DMAAm) and methacrylate ditelechelic polyisobutylene (MA-PIB-MA) in narrow-bore (∼4 mm inner diameter) glass tubes horizontally rotating in a thermostated oven. The pore sizes of the membranes can be controlled by the length, i.e. molecular weight, of the hydrophilic poly(dimethyl acrylamide) (PDMAAm) segment (M c,hydrophilic). Pore sizes, M c,hydrophilic's, and molecular weight cut-off (MWCO) ranges of designed amphiphilic membranes were characterized in terms of Stokes (or viscosity) radii (R s) and the relationships between these parameters were evaluated. Membranes were designed to allow the rapid diffusion of molecules such as insulin (M n = 5733 g/mol, R s = 1.34 nm) but to be opaque to serum albumin (M n > 66 000 g/mol, R s > 3.62 nm) and larger proteins such as immunoglobulins. The diffusion coefficients (D) and permeabilities (P) of tubular and flat-sheet amphiphilic membranes have been compared and were found to be similar. Membrane pore size dimensions of the tubular devices were determined by the out-diffusion of commercially available protein markers of known molecular weights (M n = 6500-66 000 g/mol) and dimensions (Rs = 1.50-3.62 nm). It was found that the minimum Mc,hydrophilic or Rs that still allows the diffusion of insulin is ∼ 800 g/mol or ∼ 1.34nm, respectively, and that the maximum Mc,hydrophilic or Rs that prevents the ingress of antibodies is ∼ 5000 g/mol or ∼ 3.62 nm, respectively. According to diffusion experiments, the presence or absence of lightly crosslinked 1% calcium alginate does not affect the rate of diffusion of glucose and insulin through our tubules. These membranes are being used in vivo for encapsulating islet cells for implantation to correct type 1 diabetes.

Polytetrahydrofuran amphiphilic networks. I. Synthesis and characterization of polytetrahydrofuran acrylate ditelechelic and polyacrylamide-l-polytetrahydrofuran networks

A series of novel amphiphilic polyacrylamide-l-polytetrahydrofuran (PAm-l-PTHF) networks were prepared by the free-radical copolymerization of hydrophobic ditelechelic polytetrahydrofuran acrylate (PTHFDA) with hydrophilic acrylamide. PTHFDA was synthesized by acrylation of the corresponding hydroxycapped PTHF with acrylic acid in cyclohexane. After acrylation, there was no significant difference in the molecular weights and molecular weight distributions between the original PTHF and the resulting PTHFDA. Network structures and compositions were characterized by elemental analyses, Fourier transform infrared, differential scanning calorimetry, scanning electron microscopy, and swelling data. The networks can swell both in organic solvents and in water, which indicates that they are amphiphilic. The swelling of the networks in different solvents is composition-dependent. According to differential scanning calorimetry, scanning electron microscopy, and swelling tests, the networks have a microphase-separated and bicontinuous morphology. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3812–3820, 2000

Macromolecular engineering of polylactones and polylactides. XXV. Synthesis and characterization of bioerodible amphiphilic networks and their use as controlled drug delivery systems

Well-defined α,ω-methacryloyl poly-e-caprolactone (PCL) and poly(d,l)-lactide P(D,L)LA dimacromonomers have been synthesized by living ring-opening polymerization of the parent monomers initiated by diethylaluminum 2-hydroxyethylmethacrylate (Et2AlO(CH2)2OC(O)C(CH3)CH2) and terminated by reaction of the propagating Al alkoxide groups with methacryloyl chloride. These dimacromonomers have been copolymerized with a hydrophilic comonomer, i.e., 2-hydroxyethylmethacrylate, in bulk at 65°C by using benzoyl peroxide as a free-radical initiator. The swelling ability of the amphiphilic PHEMA/PCL or P(D,L)LA networks has been investigated in both aqueous and organic media. Effect of network composition and molecular weight of the dimacromonomer on the swelling kinetics and the equilibrium solvent uptake has been studied. Lipophilic dexamethasone acetate and the hydrophilic sodium phosphate counterpart have been incorporated into the amphiphilic gels and their release has been studied in relation to the gel characteristics. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2401–2411, 1999

New strategies for the synthesis of amphiphilic networks

Amphiphilic and hydrogel polymers are useful biomedical materials. This paper presents some recent work on new syntheses of such materials. Amphiphilic gels have been prepared by the Diels–Alder reaction of poly(ethylene glycol)s that contain acetylene dicarboxylate groups along the main chain, with furan-ended oligomers. Hexyl methacrylate oligomers with methacrylate end groups have been prepared. These have been copolymerized with hydrophilic monomers to yield segmented amphiphilic gels.

Amphiphilic networks XII: synthesis and characterization of quaternized amphiphilic networks derived from polyisobutylene-l-poly(2-(dimethylamino)ethyl methacrylate)

Polyisobutylene-l-poly(2-(dimethylamino)ethyl methacrylate) amphiphilic networks were quaternized by reaction with methyl iodide. Quaternization of the tertiary amine groups in the poly(2-(dimethylamino)ethyl methacrylate) (DMEAMA) segments was close to quantitative as determined by gravimetry and nitrogen and iodine analysis. The glass transition temperature of the DMEAMA phase strongly increased upon quaternization. The swelling behavior of the quaternized networks did not much vary with changing pH, while the non-quaternized parent amphiphilic networks exhibited a strong pH dependence. Swelling in n-heptane was greatly diminished in quaternized networks relative to the non-quaternized parent materials, even at high polyisobutylene contents.

Free Volume and Swelling Dynamics of the Poly[(2-dimethylamino)ethyl methacrylate]-l-polyisobutylene Amphiphilic Network by Positron Annihilation Investigations

The poly[(2-dimethylamino)ethyl methacrylate]-l-polyisobutylene (PDMAEMA-l-PIB) amphiphilic network (APN), a new class of cross-linked systems, was synthesized by the use of methacrylate−telechelic PIB obtained via quasiliving carbocationic polymerization. The swelling dynamics and the free volume changes of this APN was followed by simultaneous swelling and positron annihilation measurements. It was found that the lifetime of ortho positrons (o-Ps) increases with increasing swelling ratio (R), reaches a maximum at relatively low R, and decreases to a constant value at equilibrium swelling. These findings indicate the collapse of the hydrophobic PIB domains and expansion of the hydrophilic PDMAEMA phase in the network upon contacting with water. After reaching the maximum, the decrease of the lifetime parameter is caused by filling the free volume with water in the network. A striking observation was obtained for the o-Ps formation intensity as a function of time (or swelling ratio): the intensity rapidly decreases, and it reaches a minimum at very low R, at ∼10% of the equilibrium swelling ratio, and then increases to a constant value. These phenomena reveal important aspects of the structure of the free volume in the APN and provide fundamental information about the swelling dynamics. The minimum of the o-Ps intensity is reached at around 1:1 water/monomer units molar ratio in the network. Surprisingly, a similar phenomenon was observed when the monomer itself was mixed with water. Molecular modeling by ab initio calculations indicates that a 1:1 ringlike cluster may be formed between water and DMAEMA. On the basis of these results it is concluded that the surface of the free volume units in the APN become covered with water molecules quickly by interacting with the PDMAEMA chains at the beginning of swelling. This indicates that the free volume in the PDMAEMA-l-PIB APN is not composed of independent pores but of interconnected channels which allow rapid diffusion of water molecules to cover the surface of the free volume units. This fast process results in a quick surface structure reorganization, i.e., enrichment of the surface of the channels by PDMAEMA segments leading to the corresponding rapid decrease of o-Ps formation intensity, and to the simultaneous collapse of PIB domains yielding increase of free volume in the network and positron lifetime at the beginning of swelling. Results of this study also allow us to predict that the combined method presented here, i.e., simultaneous swelling kinetics and positron annihilation investigations, can be widely applicable for gaining new information on free volume structure, swelling dynamics, and interactions between material components and swelling agents for a large variety of networks, gels, polyelectrolytes, amorphous materials, blends, composites, etc.

Synthesis and characterization of amphiphilic networks obtained by copolymerization of poly(ethylene oxide) macromonomers with methylmethacrylate

Hydrogels whose elastic chains are constituted of hydrophilic Poly(ethylene oxide) (PEO) segments were obtained through free radical homopolymerization with methylmethacrylate (MMA) of α,ω-methacryloyloxy PEO macromonomers. This reaction can be conducted in water solution or in organic solvent. These networks were investigated as gels swollen to equilibrium in THF or in water. The influence of the preparation solvent on the properties of these networks was studied. The mechanical properties of the networks obtained in water are better than those of networks obtained under exactly the same conditions in organic solvents. This result can be explained by the preferential formation in water of micellar structures containing a higher concentration of polymerizable units. The influence of the concentration of the hydrophobic comonomer on the properties of these PEO networks was also examined.

Functionalized polymeric and oligomeric colloids

This paper reviews the author's work to date on functional colloids. Colloids with surface grafts of poly(N-isopropylacrylamide) have been prepared by a macromonomer technique. After removal of the anionic surfactant, the colloids displayed temperature-dependent stability. The preparation of functional colloids that are composed of dispersions of telechelic oligomers has been achieved by ozonizing latices of unsaturated polymers in which the particles were pre-swollen by a hydrophobic solvent. Enzyme immobilization has been carried out by reaction of aldehyde functional colloids with porcine pancreatic lipase. Functional colloids of carboxylic acid-ended oligomer have been further modified with furfuryl amine. The method has been found to be a useful clean technique for the preparation of telechelic oligomers with diene end-groups that can be reacted with dienophile-functionalized polymers. This Diels-Alder reaction yielded amphiphilic networks which may find uses as novel biomaterials. The paper also covers two alternative methods of preparing furan functional colloids of telechelic oligomers: that is, the use of difuran disulphide as a chain transfer agent in emulsion polymerization and the reaction of functional colloids composed of aldehyde functional telechelic oligomers with furfuryl amine. Finally, some preliminary results on the surface functionalization of polymer colloids via water-tolerant Lewis acids are presented.

Amphiphilic networks. XI. Mechanical properties and morphology

The bulk properties of two types of amphiphilic networks, poly(2-hydroxyethyl methacrylate)-l-polyisobutylene (PHEMA-l-PIB, H-network) and poly(N,N-dimethylacrylamide)-l-polyisobutylene (PDMAAm-l-PIB, A-network), have been investigated. Tensile strengths decreased considerably by swelling, and the decrease was more severe by swelling in water than in n-heptane. Elongations increased by swelling in water; however, the change was not consistent upon swelling in n-heptane. The hardness of dry networks decreased with increasing PIB content, while for wet networks it was similar to dry networks containing 85 wt % PIB. Small-angle X-ray scattering showed that average interdomain spacings decreased with increasing PIB content. According to dynamic mechanical thermal analysis (DMTA) the glass transition temperatures (Tg) of the respective hydrophobic and hydrophilic components shift toward each other with increasing PIB content. A “liquid-liquid transition” (Tll) above the Tg of the hydrophilic component was apparent by DMTA, but could not be found by differential scanning calorimetry (DSC). © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 901–910, 1997

Preparation of amphiphilic networks by Diels‐Alder reactions between oligo(butyl methacrylate) with furan end‐groups and a poly(ethylene oxide‐co‐acetylenedicarboxylate)

AbstractA butyl methacrylate oligomer with furan end‐groups was synthesized by ozonolysing a poly(butyl methacrylate‐co‐butadiene) latex. The end‐groups of this oligomer were amidated with aminomethylfuran to give a coagulated mass of derivatized oligomers. This furan functional oligomer was then mixed with poly(ethylene oxide‐co‐acetylenedicarboxylate) and heated at 60°C or 125°C. The material cured at 125°C was found to contain a higher gel fraction (55 wt.‐%) than that cured at 60°C (30 wt.‐%).

Novel amphiphilic polyurethane networks: gelation mechanism and swelling behaviors

Amphiphilic polyurethane gels can be prepared using poly(ethylene glycol)-modified urethane acrylate (PMUA) through two types of methods. When PMUA gels were prepared at an aqueous phase, droplet coalescence and gelation occurred at the same time, so the microstructure of these gels (UAHG) was similar to that of PMUA emulsion which was formed by the microphase separation between hydrophilic and hydrophobic domains. In the case of UAHG gels, as the composition ratio of water to PMUA increased, swelling in water increased, but swelling in dioxane was slightly decreased. For the other kind of PMUA gels prepared using dioxane through a conventional gelation process (UADG), swelling in dioxane greatly increased with increasing of the composition ratio of dioxane; however, swelling of these gels in water was very low. The difference in swelling behavior between UAHG and UADG gels was due to the difference of microstructures between these gels which also influenced the mechanical properties. Additionally, the microstructures of UADG and UAHG gels were able to be confirmed using scanning electron microscopy (SEM) and contact angle measurement. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 821-832, 1997

Structure of w/o-microemulsion templated polymer networks

The droplet phase of a water-in-oil microemulsion is used as a matrix to create amphiphilic polymer network structures from a poly(oxyethylene)-poly(isoprene)-poly(oxyethylene) triblock copolymer bearing polymerizable methacrylate end groups. Conductivity measurements and freeze fracture electron microscopy are used to obtain information about the structure of these gels. The droplet structure of the underlying microemulsion is only preserved for low droplet and polymer concentration. For higher concentrations the crosslinking reaction can induce the formation of a bicontinuous structure.

Water absorption in a polymeric network

Positron lifetime measurements were performed to study the swelling dynamics of an amphiphilic polymer network (APN). Lifetime spectroscopy proved to be suitable to investigate APNs. Very quick structural changes were indicated by lifetime parameters at very low swelling ratios. On the basis of the results a possible mechanism is proposed for the hydration of the investigated materials.

Synthetic approaches towards new polymer systems by the combination of living carbocationic and anionic polymerizations

AbstractThis study summarizes recent efforts to obtain by combination of living carbocationic and anionic polymerizations block copolymers which are potential precursors for building new well‐defined polymeric architectures with microphase separated morphology. Living carbocationic polymerization (LCCP) yields telechelic polyisobutylene (PIB) chains with a variety of useful endgroups, such as tert‐chlorine, isopropenyl, primary hydroxyl, tolyl etc. When tolyl‐ended PIB was used as precursor for macroinitiator of living anionic polymerization of 2‐(tert‐butyldimethylsilyloxy)ethyl methacrylate (tBuMe2SiOEMA), mixtures of homopolymers and block copolymers were formed due to incomplete lithiation of this chain end. In another approach a new functionalization method was developed by end‐quenching living PIB chains with 1,1‐diphenylethylene (DPE). In the presence of BCl3 a new telechelic PIB with 2,2‐diphenylvinyl (DPV) endgroups was formed. A corresponding DPV model compound was synthesized from 2‐chloro‐2,4,4‐trimethylpentane (TMPCl). Because of steric hindrance less than quantitative lithiation of this material occurred. Controlled deprotection of PtBuMe2SiOEMA obtained by living anionic polymerization (LAP) was utilized to prepare a precursor network composed of partially deprotected PtBuM2SiOEMA and hydroxyl‐telechelic PIB by using a diisocyanate crosslinker. After network formation deprotection with HCl was completed and a new amphiphilic network (APN) containing PIB and poly(2‐hydroxyethyl) methacrylate) (PHEMA) segments crosslinked by urethane linkages was obtained.

Synthesis strategies and properties of smart amphiphilic networks

AbstractThis paper briefly surveys recent developments in the field of amphiphilic networks (APN) which are a new class of crosslinked polymer systems consisting of covalently bonded hydrophobic and hydrophilic chain segments. The covalent bonds between immiscible hydrophobic and hydrophilic polymer chains prevent demixing and yield polymer networks with unique structure and properties. Telechelic macromonomers provide the basis for the first generation of APNs obtained by copolymerization of the macromonomer with selected low molecular weight monomers. Synthesis of a variety of APNs using methacrylate‐telechelic polyisobutylene (PIB) macromonomers prepared by living carbocationic polymerization (LCCP) and quantitative chain end derivatization is reviewed. The second generation of PIB‐based amphiphilic networks is prepared by crosslinking of well‐defined hydroxy‐telechelic PIB and partially deprotected silylated poly(2‐hydroxyethyl methacrylate) (PHEMA) precursor chains. Other opportunities providing better structural control of APNs by crosslinking of functional amphiphilic block copolymers (or precursors) obtained by combining living carbocationic and anionic polymerizations are outlined as well. Properties of APNs, such as control of swellability by composition, pH‐response of swelling, fast surface structure reorganization by contacting with solvent, morphology, sustained release of drugs and bio‐ and blood compatibility, are also summarized.

Extensional Flow in Two-Dimensional Amphiphilic Networks

A systematic investigation on the extensional flow properties of two polymerized amphiphilic monolayers is discussed. To perform those experiments a new method is developed that allows a direct rheological investigation by using a modified film balance device.