Homopolymer Networks Research Articles

Randomly cross-linked amphiphilic copolymer networks of n-butyl acrylate and N,N-dimethylacrylamide: synthesis and characterization

Abstract Five randomly cross-linked amphiphilic copolymer networks (ACPN) were prepared via the free radical cross-linking copolymerization of the hydrophobic n-butyl acrylate (BuA) and the hydrophilic N,N-dimethylacrylamide (DMAAm), in the presence of a small amount (5 mol% with respect to the sum of BuA plus DMAAm monomers) of the hydrophobic 1,6-hexanediol diacrylate (HexDA) cross-linker, initiated by 4,4ʹ-azobis(4-cyanovaleric acid) in 1,4-dioxane at a 10 % w/v total monomer concentration. The five ACPNs differed in their BuA content, fixed at 10, 30, 50, 70 and 90 mol%. The two homopolymer networks, BuA and DMAAm, were also prepared using the same polymerization method. Thus, this study involved a total of seven polymer networks, forming a homologous series with BuA contents ranging from 0 to 100 mol%. These networks were characterized in terms of their degrees of swelling in tetrahydrofuran (THF) and water, their mechanical properties in water, and their adhesion to human skin. The degrees of swelling (DS) of the networks in THF were higher than those in water because THF is a non-selective solvent, whereas water is selective for the hydrophilic DMAAm units. The DSs in THF increased with the network content in the less polar BuA units, while the opposite was true for the DSs in water which decreased with the content in the hydrophobic BuA units from 11 (0 mol% BuA) down to 1.1 (100 mol% BuA). A maximum in the elastic modulus was observed for the hydrogel with 50 mol% BuA, reflecting the opposing effects of polymer composition in soft polymer (polyBuA) content and hydrogel water content. In contrast, the tensile strain at break increased monotonically with the hydrogel BuA content, reaching a remarkable ∼900 % for the hydrogel with 90 mol% BuA. Finally, the adhesion of the ACPNs, both in their dried and hydrated states, onto human skin was explored. The adhesion of the hydrated samples onto skin was stronger than that of the dried ones. The hydrated ACPN with 30 mol% BuA exhibited the strongest adhesion onto skin, attributable to the best combination of a rather high content in polar DMAAm units (70 mol%), and a rather low aqueous DS (∼2.5), with the low DS value causing only a small dilution in the DMAAm units participating in the polar interactions with skin. The present work demonstrates that, even in this synthetically simple ACPN system, the multiple effects of ACPN composition on a certain property, in some cases opposing and in some other cooperating, lead to a rather complicated behavior. In particular, as the BuA content increases, some properties display maxima (elastic modulus, stress at break and fracture energy of hydrated ACPNs, and adhesion of hydrated ACPNs onto skin) while some other properties exhibit monotonic increases (strain at break of hydrated ACPNs, and adhesion of dried ACPNs onto skin). Thus, the optimal ACPN for a particular application will highly depend on the property best-serving the particular application, e.g., the ACPNs with 30, 50 and 90 mol% BuA for strongest wet adhesion to skin, stiffest hydrogel response, and highest hydrogel extensibility and toughness, respectively.

Controlled Synthesis of a Homopolymer Network Using a Well-Defined Single-Component Diels-Alder Cyclopentadiene Monomer.

Cyclopentadiene is known for its high reactivity and propensity to dimerize, making monomer synthesis and polymerization notoriously challenging. In fact, despite its long history and compelling chemistry, only two reports have appeared in the literature since the first attempt to homopolymerize cyclopentadiene by Staudinger in 1926. Herein, we present a strategy not only to synthesize, isolate, and homopolymerize a well-defined tetracyclopentadiene monomer but also to de-cross-link the network homopolymer. Mechanical properties are also investigated, including creep-recovery, shape memory, and tensile behaviors. Interestingly, the tensile test reflects a tough and elastic material, in contrast to prior Cp-based homopolymer networks. This work provides a versatile platform to access and study new cyclopentadiene-based and better-defined homopolymer networks with potential applications ranging from shape memory polymers to degradable thermosets.

Correlation between effective charge density and crosslinking efficiency of dicarboxylic acid containing highly anionic networks

By investigating the relationship between the swelling and deformation properties, an attempt was made to establish a correlation between microstructure and charge density of anionic polyacrylamide/itaconic acid (PAAm/ITA) hydrogels. The effective charge density of network dominated the microstructure of PAAm/ITA hydrogels. The porosity of anionic hydrogels increased with addition of diprotic ITA, and resulting microstructure determined the swollen state deformation. Based on effective charge density, the swelling gradually increased and maximum swelling was achieved with 14% ITA, while there was a 24-fold increase in gel volume relative to homopolymer network. The relationship between elasticity and crosslinking density was explained using Rubber elasticity theory on deformation behavior. A variety of factors that affect swelling and elasticity was explored such as effective charge density, crosslink density of anionic network as well as pH of solution and surfactant type. The equilibrium volume swelling ratio in water scales with network charge density by the relation φV ∝ feff1.17, while the dependence of reduced modulus with equilibrium gel volume was found to be Gr≈(φV)−0.28 indicating that equilibrium swollen PAAm/ITA hydrogels are in Gaussian regime. An empirical relationship has been found implying that by varying amount of ITA, the crosslinked structure and crosslinking density can be effectively controlled. PAAm/ITA hydrogels showed good reversible characteristics during repeated oscillations between pH 11.2 and 2.1, which is important for controlled drug delivery system. Rapid water penetration of PAAm/ITA hydrogels with internal morphology and high swelling resulting from the presence of ITA revealed internal adsorption sites for methyl violet and methylene blue. The adsorption kinetics followed a pseudo-second order and showed a two-stage intra-particle diffusion model. The results will contribute to the determination of correlation between anionic structure and properties for efficient and economical design of anionic materials for specific uses and industrial scale-up.

Highly conductive and mechanically robust nanocomposite polymer electrolytes for solid-state electrochemical thin-film devices

Abstract Ionic liquid-based polymer electrolyte composites (PECs) with high mechanical strength and ionic conductivity were fabricated by using a semicrystalline homopolymer network. Morphological, mechanical, and electrical properties of semicrystalline homopolymer-based PECs were investigated over the composition range of 10–50 polymer wt%. The PECs consisted of poly(vinylidene fluoride) (PVDF) and a room-temperature ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMI][TFSI]). The amorphous PVDF chains were solvated by the liquid electrolyte and interconnected the phase-separated PVDF crystalline-domains, acting as physical crosslinks. The ionic conductivity and specific capacitance of the homopolymer PECs were found to be very high, ranging from 0.4 to 4.9 mS/cm and from 2.6 to 9.1 μF/cm2, respectively. The elastic moduli of the PECs that range from 4 to 38 MPa were also greater than those of PECs prepared by using other polymeric networks. These PECs were successfully applied as electrolyte membranes in electrical double layer supercapacitors and as high-capacitance gate insulators in electrochemical thin-film transistors. These results provide detailed systematic data for fabricating high-performance solid polymer electrolytes for electrochemical thin-film devices.

Thermally-Induced Actuation of Magnetic Nanocomposites Based on Oligo(ω-Pentadecalactone) and Covalently Integrated Magnetic Nanoparticles

AbstractThe incorporation of inorganic particles in a polymer matrix has been established as a method to adjust the mechanical performance of composite materials. We report on the influence of covalent integration of magnetic nanoparticles (MNP) on the actuation behavior and mechanical performance of hybrid nanocomposite (H-NC) based shape-memory polymer actuators (SMPA). The H-NC were synthesized by reacting two types of oligo(ω-pentadecalactone) (OPDL) based precursors with terminal hydroxy groups, a three arm OPDL (3AOPDL, Mn = 6000 g mol·1-1) and an OPDL (Mn =3300 g · mol-1) coated magnetite nanoparticle (Ø = 10 ± 2 nm), with a diisocyanate. These H-NC were compared to the homopolymer network regarding the actuation performance, contractual stress (σcontr) as well as thermal and mechanical properties. The melting range of the OPDL crystals (ΔTm,OPDL) was shifted in homo polymer networks from 36 °C – 76 °C to 41°C – 81 °C for H-NC with 9 wt% of MNP content. The actuators were explored by variation of separating temperature (Tsep), which splits the OPDL crystalline domain into actuating and geometry determining segments. Tsep was varied in the melting range of the nanocomposites and the actuation capability and contractual stress (σcontr) of the nanocomposite actuators could be adjusted. The reversible strain (εrev) was decreased from 11 ± 0.3% for homo polymer network to 3.2±0.3% for H-NC9 with 9 wt% of MNP indicating a restraining effect of the MNP on chain mobility. The results show that the performance of H-NCs in terms of thermal and elastic properties can be tailored by MNP content, however for higher reversible actuation, lower MNP contents are preferable.

Development of a Nonelectrolytic Selectively Superabsorbent Polymer

Highly absorbent polymers capable of trapping large volumes of organic liquids are attractive materials for cleaning up toxic chemical spills. Here we report development of a homopolymer network using N-butyl-N-phenylacrylamide with poly(ethylene glycol) dimethacrylate as the cross-linker, that absorbs a variety of organic liquids by swelling. The nonelectrolytic basis of this polymer allows it to be used in areas where organic liquids and water coexist in the form of an emulsion. We demonstrate that this new polymer swells up to 20× in nonpolar organic liquids and up to 33× in more polar organic liquids but has negligible swelling in water. Consequently, this novel selectively superabsorbent polymer has potential use in a broad range of applications to capture and remove hazardous materials.

Swelling of Random Copolymer Networks in Pure and Mixed Solvents: Multi-Component Flory–Rehner Theory

A generalized extension of Flory-Rehner (FR) theory is derived to describe equilibrium swelling of polymer networks, including copolymers with two or more chemically distinct repeat units, in either pure or mixed solvents. The model is derived by equating the chemical potential of each solvent in the liquid and gel phases at equilibrium, while assuming the deformation of the network chains is affine. Simplifications of the model are derived for specific cases involving homopolymer networks, copolymer networks, pure solvents, and binary solvent mixtures. With reasonable assumptions, the number of polymer-solvent interaction parameters that must be determined by experiments can be reduced to two effective parameters (θ1 and θ2), which describe the net interactions between water/copolymer (θ1) and ethanol/copolymer (θ2), respectively. Experimental measurements of the swelling of random copolymer networks of n-butyl acrylate and 2-hydroxyethyl acrylate in water, ethanol, and a 100 g/L ethanol/water mixture are utilized to validate the model. For a random copolymer network, θ1 and θ2 can be obtained by fitting the three-component FR model to equilibrium swelling data obtained in the pure solvents. Predicted solvent volume fractions for swelling in water-ethanol mixtures obtained by inserting fitted values of θ1 and θ2 into the four-component FR model are in reasonable agreement with experimental measurements.

Interpenetrating polymers supported on microporous polypropylene membranes for the transport of chromium ions

Abstract Modifying polypropylene membranes with interpenetrating polymer networks (IPNs) through the incorporation of poly(glycidyl methacrylate-N-methyl- d -glucamine) (P(GMA-NMG)) was performed by in situ synthesis via radical polymerization. The surface of the polypropylene membrane was activated by hydrophilic grafted polyelectrolyte, and then, pressure injection was used for the impregnation of the reactive solution in the membrane. Two types of pore-filled membranes were synthesized, chelating interpenetrating homopolymer networks of P(GMA-NMG), and chelating-ion exchange interpenetrating polymer networks (e.g., P(GMA-NMG)/P(AA), P(GMA-NMG)/P(AMPSA), and P(GMA-NMG)/P(ClVBTA)). After their synthesis, the modified polypropylene membranes were characterized using techniques such as the electrokinetic potential, SEM, FT-IR, and Donnan dialysis to corroborate the chromium ion transport. The P(GMA-NMG) and complex network membranes exhibited a hydrophilic character with a water-uptake capacity between 20% and 35% and a percentage of modification between 4.0% and 7.0% in comparison with the behavior of the unmodified polypropylene membrane. Hexavalent chromium ions were efficiently transported from the food chamber at pH 9.0 when the 65.2% MTA1 P(ClVBTA) homopolymer IPN membrane and 48.5% MTAG P(GMA-NMG)/P(ClVBTA) IPN membrane were used. Similarly, hexavalent chromium ions were removed from the food chamber at pH 3.0 when MTAG (63.30%) and MTA1 (35.68%) were used in 1 mol·L− 1 NaCl solution as the extraction reagent.

Anionic amphiphilic model conetworks synthesized by end-linking of tetra-arm copolymers

Abstract Highly homogeneous block and random amphiphilic conetworks (APCNs) of sodium acrylate (NaA) and methyl acrylate (MA) with the same composition (NaA/MA ∼ 2/1) were synthesized via end-linking reaction between tetra-arm copolymers of tert-butyl acrylate and MA by copper-catalyzed azide-alkyne cycloaddition followed by the removal of the protecting tert-butyl group and neutralization. Measurement of the degrees of swelling in saline (Qs) and in pure water (Qpw) showed that the ratio of Qs to Qpw for the random APCNs was similar to that for homopolymer networks of NaA, whereas it was significantly smaller for the block APCNs. The result indicated that hydrophobic interaction between PMA blocks was induced by added salt. Taking advantage of the salt-responsive property of the block APCNs, their ability to capture and release a hydrophobic compound was investigated by confocal laser scanning microscopy using fluorescein as a probe molecule.

Collapse Dynamics of Core–Shell Nanogels

Stimuli-responsive core–shell nanogels display collapse properties which are determined by both the core and the shell. We examine the equilibrium properties and the detailed structural changes during a collapse transition of polymer core–shell nanoparticles using Brownian dynamics simulations. Gel particles with randomly distributed cross-linking nodes are created. The influence of the cross-linking degree, core/shell mass ratio, and the strength of the interparticle attractive interaction on the collapse behavior is investigated. Both collapsed core and collapsed shell structures are considered and compared with collapsed homopolymer networks. The transition time was found to be reduced with increasing cross-linking degree and inversely related to the depth of the Lennard-Jones potential. Similar to the kinetics of single chain collapse, there is an initial formation of clusters, in this case near cross-linking nodes, and a subsequent coarsening to form a compact globule. Where the nanogels were collapsed into a compact core, the deformation was found to be essentially symmetric, with a significantly slower relaxation time for the shell units compared to the core collapse transition time. Reducing the core size, the shell units were less affected by the presence of a collapsing core. For the system with a collapsing shell, our simulations reveal in some cases an inversion, with the shell compressing and eventually squeezing out the core units. This effect was more pronounced with decreasing cross-linking degree and core/shell mass ratio.

Molecular dynamics in polymer networks containing caprolactone and ethylene glycol moieties studied by dielectric relaxation spectroscopy

Copolymer networks with methacrylate main chain and caprolactone and ethylene glycol side groups were obtained by free radical copolymerisation of caprolactone methacrylate (CLMA) and poly(ethylene glycol) methacrylate (PEGMA). Dielectric relaxation spectroscopy was used to analyse molecular mobility of the different groups in the system. Only one main dielectric relaxation process was found in CLMA/PEGMA copolymer networks, located between those of the corresponding homonetworks, indicating that the system does not present phase separation. The copolymers show a secondary relaxation process at temperatures below −50°C, which can be assigned to the overlapping of the corresponding secondary processes for the homopolymer networks; one of them was related to the local mobility of caprolactone units in CLMA and the second one was assigned to the twisting motions within ethylene glycol moiety in PEGMA. Besides the relaxation processes, the mobility of space charges has been analysed by means of conductivity and electric modulus formalisms.

Novel “core-first” star-based quasi-model amphiphilic polymer networks

Novel quasi-model networks based on “core-first” star (co)polymers have been synthesised. The polymeric networks (gels) were based on the hydrophilic, thermo- and pH-responsive 2-(dimethylamino)ethyl methacrylate (DMAEMA) and the non-ionic, hydrophobic methyl methacrylate (MMA). Specifically two homopolymer networks and three amphiphilic polymer networks were synthesised based on two block and one statistical “core-first” star copolymers. The precursors to and the extractables of the networks were characterised using Gel Permeation Chromatography and proton Nuclear Magnetic Resonance to determine the molecular weight, polydispersity and composition. The degrees of swelling (DSs) of the networks were then determined in both aqueous and organic solvents. The DSs in organic solvents and non-acidic water were dependant only on the composition of the conetworks while the DSs in acidic water were also affected by the architecture of the conetworks. Finally the networks were evaluated in terms of their ability to absorb and deliver hydrophilic and hydrophobic compounds that were used as “model drugs” and interestingly it was observed that the architecture of the networks, and not just the composition of the networks, affected the release of the compounds.

Synthesis and Characterization of End-Linked Amphiphilic Copolymer Conetworks Based on a Novel Bifunctional Cleavable Chain Transfer Agent

A novel bifunctional bis(hemiacetal ester) chain transfer agent (CTA), 1,2-bis[1-(4-cyano-4-methyl-1-oxo-4-(phenylcarbonothioylthio)butanoxy)ethoxy]ethane (CMPTBEE), appropriate for the reversible addition–fragmentation chain transfer (RAFT) polymerization of methacrylate monomers, was successfully synthesized and used for the preparation of a family of 10 hydrolyzable end-linked polymer (co)networks. The family comprised three methyl methacrylate (MMA) homopolymer networks with different degrees of polymerization, 100, 150, and 200, and seven end-linked amphiphilic polymer conetworks of MMA and 2-(dimethylamino)ethyl methacrylate (DMAEMA) with a constant overall degree of polymerization equal to 200 but various compositions and architectures. The agreement of the experimentally measured molecular weights with the theoretically expected ones and the low molecular weight dispersities of the linear precursors to the (co)networks indicated successful control of the polymerization. All (co)networks were characterized in terms of their sol fraction and in terms of their degree of swelling in THF. The value of the former was found in the range between 4 and 50%, whereas that of the latter was around 13%. The presence of the hemiacetal ester groups allowed the hydrolysis of the most hydrophilic, DMAEMA-rich conetworks. The resistance to hydrolysis of the other (co)networks could be attributed to the large hydrophobic blocks surrounding and protecting from hydrolysis the hemiacetal ester groups of the CTA residue in the conetworks.

Microphase separation in cross-linked polymer blends

We investigate the behaviour of randomly cross-linked (co)polymer blends using a combination of replica theory and large-scale molecular dynamics simulations. In particular, we derive the analogue of the random phase approximation for systems with quenched disorder and show how the required correlation functions can be calculated efficiently. By post-processing simulation data for homopolymer networks we are able to describe neutron scattering measurements in heterogeneous systems without resorting to microscopic detail and otherwise unphysical assumptions. We obtain structure function data which illustrate the expected microphase separation and contain system-specific information relating to the intrinsic length scales of our networks.

Poly(ethylene glycol)‐based amphiphilic model conetworks: Synthesis by RAFT polymerization and characterization

AbstractPoly(ethylene glycol) (PEG)‐containing quasi‐model amphiphilic polymer conetworks (APCNs) were prepared by reversible addition fragmentation chain transfer (RAFT) polymerization using α,ω‐bis(2‐cyanoprop‐2‐yl dithiobenzoate)‐PEG as a bifunctional RAFT macrochain transfer agent (macro‐CTA) and stepwise additions of a hydrophobic monomer and a crosslinker (crosslinker: macro‐CTA = 10:1, reaction time 24 h). Three different types of monomers, methyl methacrylate (MMA), n‐butyl acrylate and styrene, were employed as the hydrophobic monomers, whereas ethylene glycol dimethacrylate, ethylene glycol diacrylate and 1,4‐divinylbenzene served as the respective crosslinkers. PEG homopolymer hydrophilic quasi‐model networks were also prepared by RAFT‐polymerizing the three crosslinkers directly onto the two active ends of the PEG‐based macro‐CTA. From the three ABA triblock copolymers prepared, the MMA‐containing one was obtained at the highest polymerization yields. The crosslinking yields of the three ABA triblock copolymers with the corresponding crosslinkers were higher than those of the PEG‐based macro‐CTA with the same crosslinkers. The degrees of swelling (DSs) of all conetworks were measured in water and in tetrahydrofuran (THF). The DSs of the APCNs in THF were higher than those in water, whereas the reverse was true for the DSs of the hydrophilic homopolymer networks. Finally, the aqueous DSs of the APCNs were lower than those of the corresponding hydrophilic homopolymer networks. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7556–7565, 2008

Block Polyelectrolyte Networks from Poly(acrylic acid) and Poly(ethylene oxide): Sorption and Release of Cytochrome C

A new family of block polyelectrolyte networks containing cross-linked poly(acrylic acid) (PAA) and poly(ethylene oxide) (PEO) was synthesized by copolymerization of acrylic acid and bisacrylated PEO (10 kDa). Two materials with different PEO/PAA ratios were compared with a weakly cross-linked PAA homopolymer network. The networks bound a cationic protein, cytochrome C, due to the polyion coupling, leading to the network contraction. After binding the protein the block polyelectrolyte networks were more porous compared to a homopolymer network, facilitating protein absorption within the gel. The protein was released by adding Ca2+ ions or a polycation. Ca2+ ions migrated within the gels and reacted with PAA chains, thus displacing the protein. The polycation transfer into hydrogels, as a result of polyion substitution reactions, was inhibited by the excess of PEO chains in the block polyelectrolyte networks. Overall, these findings advance development of functional polyelectrolyte networks for immobilization and controlled release of proteins.

Swelling behavior of responsive amphiphilic gels

We study the equilibrium swelling degrees of an amphiphilic microgel which consists of two different types of constituents: hydrophobic (H) and hydrophilic (P) monomers. Using Flory-type theories, scaling arguments, and variational calculations, we investigate the influence of the number of cross links and cross-linking types on the equilibrium swelling behavior. We show that amphiphilic microgels exhibit discrete swelling degrees which are more pronounced than for homopolymer networks as the fraction of hydrophobic components in the gel changes. The heterogeneous cross links between different types of monomers prevent a complete phase separation and stabilize the gel at relatively high fraction of H monomers. Disorder in the arrangement of the monomers as well as the cross-linking positions is treated in the framework of the variational principle. The method developed here is also applied for designed networks which display well-defined conformational transitions. Such macrogels can be used for drug loading or release under specific environments. We provide scaling results for specifically constructed networks that are confirmed by our variational theory.

Group transfer polymerization in the bulk: linear polymers and randomly cross-linked networks

Linear homopolymers and randomly cross-linked homopolymer networks of 2-(dimethylamino)ethyl methacrylate of various molecular weights (MWs) were synthesized by group transfer polymerization in the bulk. 1-methoxy-1-(trimethylsiloxy)-2-methyl propene was used as the initiator, while tetrabutylammonium bibenzoate served as the catalyst. Ethylene glycol dimethacrylate was the cross-linker used for the network synthesis at an 8-fold molar excess with respect to the initiator. Gel permeation chromatography in tetrahydrofuran was used to characterize the linear homopolymers in terms of their MW and molecular weight distribution (MWD). Although the experimental MWs did not match the theoretical MWs, they were reasonably close to them. The MWDs were rather broad with polydispersity indices ranging between 1.5 and 1.9. The monomer conversion was relatively high, ranging from 97% to 74% for theoretical degrees of polymerization (DPs) from 5 to 500. No polymerization was observed for an attempted DP of 1000. Networks with molar ratios of monomer to initiator (nominal DPs) from 5 to 200 were prepared, while an attempted synthesis with a nominal DP of 500 did not yield a network. The networks were characterized in terms of their degree of swelling in water and the effects of DP, pH, salt concentration and temperature were investigated.

Randomly cross-linked homopolymer networks: synthesis by group transfer polymerization in solution and characterization of the aqueous degree of swelling

Randomly cross-linked homopolymer networks of 2-(dimethylamino)ethyl methacrylate (DMAEMA) of various average degrees of polymerization (DPs) between cross-links were synthesized by group transfer polymerization (GTP) in tetrahydrofuran (THF), using 1-methoxy-1-(trimethylsiloxy)-2-methyl propene (MTS) as the initiator, ethylene glycol dimethacrylate (EGDMA) as the cross-linker (eightfold molar excess with respect to the initiator), and tetrabutylammonium bibenzoate (TBABB) as the catalyst. Networks with monomer-to-initiator molar ratios of 5, 10, 20, 50, 100 and 200 were synthesized successfully, while an attempted synthesis with a monomer-to-initiator molar ratio of 500 did not produce a network. The networks were characterized in terms of their degree of swelling (DS) in water and the effects of DP, pH, salt concentration and temperature were investigated. Moreover, the aqueous degrees of swelling determined in this study of random networks were compared to the aqueous degrees of swelling of model networks also synthesized by GTP and using a similar procedure.

Characterization of hydrophilic networks synthesized by group transfer polymerization

Group transfer polymerization was used to synthesize several series of hydrophilic random and model networks. Cationic random networks were prepared both in bulk and in tetrahydrofuran (THF) using a monofunctional initiator and simultaneous polymerization of monomer and branch units, while a bifanctional initiator was employed in THF for the synthesis of model networks comprising basic or acidic chains. Upon polymerization of the monomer, the latter initiator gives linear polymer chains with two “living” ends, which are subsequently interconnected to a polymer network by the addition of a branch unit. Homopolymer network star polymers were also synthesized in THF by a one-pot procedure. The synthesis involved the use of a monofunctional initiator and the four-step addition of the following reagents: (i) monomer, to give linear homopolymers; (ii) branch unit, to form “arm-first” star polymers; (iii) monomer, to form secondary arms and give “in-out” star polymers; and, finally (iv) branch unit again, to interconnect the “in-out” stars to networks. Different networks were prepared for which the degree of polymerization (DP) of the linear chains between junction points was varied systematically. For all networks synthesized, the linear segments, the “arm-first” and the “in-out” stars were characterized in terms of their molecular weight (MW) and molecular weight distribution (MWD) using gel permeation chromatography (GPC). The degrees of swelling of both the random and model networks in water were measured and the effects of DP, pH, and monomer type were investigated.