Random copolymers of N-isopropylacrylamide and methacrylic acid monomers with hydrophobic spacers: pH-tunable temperature sensitive materials

Two series of random copolymers of N-isopropylacrylamide (NIPAAm) and comonomers derived from methacrylic acid with a different number of methylene units as hydrophobic spacers (n=4, 7 and 10) were synthesized via free radicals. The first series was prepared having the acid groups methoxy-protected while the second series have the acid groups free. The NIPAAm-copolymers of both series were prepared varying the comonomer content from 5 to 20 mol%. All the copolymers were characterized by FTIR, DSC, ¹H NMR and SLS. The aqueous solution behaviour of the copolymers having methoxy-protected acid groups shows that the comonomer increases the hydrophobicity of the copolymer chain and decreases its lower critical solution temperature (LCST). For the copolymers having free acid groups, hydrogen-bonding is responsible for a further decrease in the LCST of these copolymers in pure water. In buffer solutions, every acid comonomer have a critical ionization degree (α_crit) above which the LCST increases with increasing comonomer content while at an ionization degree lower than α_crit the LCST decreases with increasing comonomer content. In dependence of comonomer content, number of methylene units in the spacer and the pH of the buffer solution, the LCST of the copolymers can be varied widely, showing that these random copolymers have pH-tunable temperature sensitivity.     

The synthesis and solution behaviors of novel amphiphilic block copolymers based on d-galactopyranose and 2-(dimethylamino)ethyl methacrylate

A series of novel stimuli-responsive AB, ABA, and BAB type block copolymers based on 6-O-methacryloyl-1,2:3,4-di-O-isopropylidene-d-galactopyranose (MAIpGP:A block) and 2-(N,N-dimethylamino)ethyl methacrylate (DMAEMA: B block) were synthesized via ATRP techniques using ethyl 2-bromoisobutyrate (EBiB) as monofunctional ATRP initiator in the case of diblock copolymer and diethyl meso-2,5-dibromoadipate (DEDBA) as bifunctional ATRP initiator in the case of triblock copolymers. The PMAIpGP blocks of the AB, ABA, and BAB type linear block copolymers were converted to water soluble PMAGP blocks via deprotection process under mild acidic conditions. Both proton NMR and DLS studies demonstrated that block copolymers were temperature-sensitive, whereby the lower critical solution temperature (LCST) of polymers varied with the polymerization degrees of comonomers in the block copolymers. LCST was determined to be between ∼35 °C and 55 °C depending on the type and the comonomer compositions of the block copolymers. It was observed that an increase on the percentage of hydrophilic PMAGP block in block copolymer caused an increase on the LCST value as expected.     

Surface modification of lyocell fibres by graft copolymerization of thermo-sensitive poly-N-isopropylacrylamide

Thermo-sensitive poly-N-isopropylacrylamide (poly-NIPAAm) was grafted onto lyocell fibres using cerium ammonium nitrate (CAN) as initiator. The effects of initiation time, initiator concentration, monomer concentration and grafting time on the degree of grafting were investigated. A 15-60 min exposure time, 7.5 mM CAN solution concentration and a 0.5-1 mM NIPAAm monomer concentration were optimal for obtaining a maximum degree of grafting (60-70% at 24 h grafting time) of poly-NIPAAm on lyocell fibres. Higher degree of grafting was obtained increasing the grafting time, such as 120% at 72 h.The properties of the obtained poly-NIPAAm/lyocell copolymer were also investigated. Specifically, the effects of temperature and degree of grafting of poly-NIPAAm on the swelling behaviour of the copolymer were experimentally determined. Moreover, structural characterization, thermal behaviour and morphology of the poly-NIPAAm/lyocell copolymers were examined by Fourier Transform Infrared Spectroscopy (FTIR), Differencial Scanning Calorimetry (DSC) and Scanning electron microscopy (SEM) techniques, respectively.     

Preparation and sorption studies of polyester microsphere copolymers containing β-Cyclodextrin

Polyester copolymer sorbent materials that incorporate β-Cyclodextrin (β-CD) were prepared using water-in-oil (w/o) micro-emulsion conditions at variable β-CD: cross linker mole ratios; where the cross linker units were sebacoyl chloride (SCl) and terephthaloyl chloride (TCl). The copolymers were characterized using TGA, nitrogen adsorption, and NMR/IR spectroscopy. The dye-based sorption properties of the copolymers with p-nitrophenol (PNP) in aqueous solution were evaluated at pH 4.6 and 295 K using UV-Vis spectrophotometry. The uptake of PNP varied from 0.221 to 0.352 mmol/g, according to the nature of the cross linker and the copolymer mole ratio. The sorption capacity of SCl-based copolymers exceed that for TCl-based copolymers, and correlate with the relative swelling properties and hydrated surface areas of the sorbent frameworks. ¹H NMR spectroscopy of copolymers with low levels of linker content (i.e. SCl or TCl) indicate dual sorption sites for PNP (i.e. β-CD inclusion sites and non-inclusion (interstitial) linker domains). The existence of dual sorption sites is similarly concluded for copolymers containing higher levels of cross linker. Inclusion complexes are firstly formed between PNP and the β-CD inclusion sites of the copolymer; thereafter, PNP is adsorbed onto the linker domains of the copolymer sorbent framework.     

Morphology and temperature responsiveness–swelling relationship of poly(N‐isopropylamide–chitosan) copolymers and their application to drug release

Poly [N‐isopropylacrylamide (NIPAAm)–chitosan] crosslinked copolymer particles were synthesized by soapless emulsion copolymerization of NIPAAm and chitosan. An anionic initiator [ammonium persulfate (APS)] and a cationic initiator [2,2′‐azobis(2‐methylpropionamidine)dihydrochloride (AIBA)] were used to initiate the reaction of copolymerization. The chitosan–NIPAAm copolymer synthesized by using APS as the initiator showed a homogeneous morphology and exhibited the characteristic of a lower critical solution temperature (LCST). The copolymer synthesized by using AIBA as an initiator showed a core–shell morphology, and the characteristic of LCST was insignificant. The LCST of the chitosan–NIPAAm copolymer depended on the morphology of the copolymer particles. In addition, the chitosan–NIPAAm copolymer particles were processed to form copolymer disks. Then, the effect of various variables such as the chitosan/NIPAAm weight ratio, the concentration of crosslinking agent, and the pH values on the swelling ratio of chitosan–NIPAAm copolymer disks were investigated. Furthermore, caffeine was used as the model drug to study the characteristics of drug loading of the chitosan–NIPAAm copolymer disks. Variables such as the chitosan/NIPAAm weight ratio and the concentration of the crosslinking agent significantly influenced the behavior of caffeine loading. Two factors (pore size and swelling ratio) affected the behavior of caffeine release from the chitosan–NIPAAm copolymer disks. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3029–3037, 2004     

Copolymer of poly(4-vinylpyridine)-g-poly(ethylene oxide) respond sharply to temperature, pH and ionic strength

The stimuli-responsive copolymers with poly(ethylene oxide) (PEO) as side chain were prepared by free-radical copolymerization of methacrylamide end-capped PEO macromonomer and 4-vinylpyridine (4VP). Phase transition behavior of these copolymers of poly(4-vinylpyridine)-g-poly(ethylene oxide) (P4VP-g-PEO) was investigated as a function of polymer concentration, temperature, pH and ionic strength by monitoring the turbidity of the polymer solutions. The copolymers displayed sharp response to temperature and pH. The LCST of P4VP-g-PEO copolymer increased with the increase of PEO content and decreased with increasing pH due to the deprotonation of the pyridine ring, indicating well-tunable LCST. In addition, the LCST of P4VP-g-PEO9 presented a unique phase transition behavior with varying salt concentration, showing a minimum with 1 M NaCl solution at pH 6.0.     

ATRP synthesis and association properties of temperature responsive dextran copolymers grafted with poly(N-isopropylacrylamide)

Temperature responsive copolymers of dextran grafted with poly(N-isopropylacrylamide) (Dex-g-PNIPAAM) were prepared by atom transfer radical polymerization (ATRP) in homogeneous mild conditions without using protecting group chemistry. Dextran macroinitiator was synthesized by reaction of dextran with 2-chloropropionyl chloride at room temperature in DMF containing 2% LiCl. ATRP was carried out in DMF:water 50:50 (v/v) mixtures at room temperature with CuBr/Tris(2-dimethylaminoethyl)amine (Me₆TREN) as catalyst. Several grafted copolymers with well defined number and length of low polydispersity grafted chains were prepared. Temperature induced association properties in aqueous solution were studied as a function of temperature and polymer concentration by dynamic light scattering, fluorescence spectroscopy and atomic force microscopy (AFM). LCST, ranging from 35 to 41 °C, was significantly affected by number and length of grafted chains. The fine tuning of LCST around body temperature is an important characteristic not obtainable by conventional radical grafting of PNIPAAM. Well defined spherical nanoparticles were formed above the LCST of PNIPAAM. Hydrodynamic diameter was in the range 73-98 nm.     

Monomer reactivity ratios of N-isopropylacrylamide-itaconic acid copolymers at low and high conversions

Copolymers of N-isopropylacrylamide (NIPAAm) and itaconic acid (IA) having various compositions were synthesized using free radical solution polymerization in 1,4-dioxane at 50 °C with α,α′-azobisisobutyronitrile (AIBN) as initiator. The structures of the copolymers were confirmed by Fourier transform infrared (FTIR) spectroscopic technique. The copolymer compositions were determined by conductometric and potentiometric methods from the inflection points in the acid-base titration curves and by FTIR spectroscopy through recorded analytical absorption bands for NIPAAm (1620 cm⁻¹ for CO stretching of secondary amides) and for IA (1704 cm⁻¹ for CO stretching) units, respectively. Monomer reactivity ratios of IA (F₁)-NIPAAm (F₂) pair were estimated using the Finemann-Ross, the inverted Finemann-Ross, the Kelen-Tüdós and the extended Kelen-Tüdós graphical methods. The values ranged from 0.40 to 0.60 for r₁ and from 1.20 to 1.90 for r₂, depending on the conversion percentage, calculation methods of monomer reactivity ratios and determination methods of copolymer compositions. In all cases, r₁r₂ < 1 and r₁ < r₂ indicate the random distribution of the monomers in the final copolymers and the presence of higher amount of NIPAAm units in the copolymer than that in the feed, respectively.     

Synthesis of poly(styrene-b-dimethylsiloxane) multi-block copolymers via polyhydrosilylation reaction

Poly(styrene-b-siloxane) multi-block copolymers have been prepared by polyhydrosilylation reaction. Four copolymers have been synthesized by the reaction of α,ω-bis silane polydimethylsiloxanes with α,ω-bis allyl polystyrene. The latter has been obtained by the reaction of carboxy-telechelic polystyrene with allyl glycidyl ether. ¹H NMR and FT-IR analyses show that the polyhydrosilylation reaction is quantitative. The copolymer molecular weights were determined by SEC to be about 25,000 g/mol. The properties of these copolymers were characterized by DSC and DMA analyses. The rubbery plateaus of these copolymers are in the range of −115 °C to 85 °C.     

Poly(N-isopropylacrylamide) thermoresponsive cross-linked conjugates containing polymeric soybean oil and/or polypropylene glycol

Synthesis, characterization and solution properties of a new series of the PNIPAM-soybean oil and/or polypropylene glycol, PPG, conjugates (conjugates also referred to as co-networks) have been described. For this purpose free radical polymerization of NIPAM monomer was initiated by macroinitiators based on PSB and/or PPG in order to obtain PSB-g-PNIPAM, PPG-g-PNIPAM and PSB-g-PPG-g-PNIPAM cross-linked graft copolymers. The autooxidation of soybean oil under air at room temperature rendered waxy soluble polymeric soybean oil peroxide associated with cross-linked parts. The soluble polymeric oil macro-peroxide isolated from the cross-linked part was used to initiate the free radical polymerization of NIPAM to give PSB-g-PNIPAM cross-linked copolymer. To obtain PPG-macromonomeric initiator, PPG-MIM, PPG-bis amino propyl ether with Mn 400 (or 2000) Dalton was reacted with 4,4′-azo bis cyanopentanoyl chloride and methacryloyl chloride, respectively. PPG-MIM also initiated the free radical polymerization of NIPAM at 80 °C to yield PPG-g-PNIPAM cross-linked thermoresponsive product. In order to obtain PSB-g-PPG-g-PNIPAM cross-linked triblock copolymer, NIPAM was polymerized by using the mixture of two macroinitiators, PSB and PPG-MIM. PSB contents in the graft copolymers were calculated via elemental analysis of nitrogen in graft copolymers. Thermal analysis, SEM, FTIR and ¹H NMR techniques were used in the characterization of the products. The effect of polymeric soybean oil, PSB, and/or PPG on the thermal response rate of poly(N-isopropylacrylamide, PNIPAM, cross-linked-graft copolymers swollen in water has been investigated by means of swelling-deswelling and drug release behaviors against to temperature change. Lower critical solution temperatures (LCST) of the cross-linked PNIPAM conjugates (conjugates also referred to as co-networks) were determined from the curves of swelling degrees versus solution temperatures. The response temperature of the hydrophobically modified PNIPAM conjugates was reduced to 27 °C, 23 °C and 27 °C for PSB-g-PNIPAM, PPG-g-PNIPAM and PSB-g-PPG-g-PNIPAM, respectively. We have found that the graft copolymers were not pH-responsive. In addition, higher pH ranges cause the hydrolysis of the PSB ester linkages, quickly and makes the cross-linked graft copolymers soluble.The fastest shrinking of the gels was observed by loosing water between 65% and 98% at 50 °C.Methyl orange (MO), was used as a model drug, loaded into cross-linked graft copolymers to examine and compare the effects of controlled release at lower and higher temperatures of lower critical solution temperature (LCST).     

Synthesis and characterization of thermosensitive interpenetrating polymer networks based on N-isopropylacrylamide/N-acryloxysuccinimide, crosslinked with polylysine, grafted onto polypropylene

Interpenetrating polymer networks (IPNs) based on poly (N-isopropylacrylamide), (PNIPAAm) and poly (N-acryloxysuccinimide) (PNAS), grafted onto polypropylene (PP), were synthesized in three consecutive steps using ionizing radiation in the first and second steps and chemical reaction in third one. In the first step a thermosensitive graft copolymer of NIPAAm onto PP film was obtained by gamma radiation with a ⁶⁰Co source. The grafted side chains of PNIPAAm were then crosslinked with gamma radiation to give net-[PP-g-NIPAAm]. The secondary network was obtained in situ by chemical crosslinking between PNAS and polylysine (pLys). The PP-g-IPNs exhibited the lower critical solution temperature (LCST) at around 32 °C. Based on its thermoreversible behavior, this system could be used for immobilization of biomolecules. The phase transition temperature (LCST) and network properties of the IPNs were measured by swelling behavior. Additional characterization by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and infrared (FTIR-ATR) determinations are reported.     

Lower critical solution temperature control and swelling behaviour of physically crosslinked thermosensitive copolymers based on N-isopropylacrylamide

In this contribution we have developed thermosensitive polymer matrices based on N-isopropylacrylamide (NIPAAm). Preparation of the hydrogels involved photopolymerisation of a combination of NIPAAm, 1-vinyl-2-pyrrolidinone (NVP) and distilled water, in appropriate amounts and contained a UV-light sensitive initiator called 1-hydroxycyclohexylphenylketone. As NIPAAm monomer could be readily dissolved in mixtures of liquid NVP and distilled water, the use of organic solvents was not required in the polymerisation process. Furthermore, chemical crosslinking agents are not needed in the synthesis. By alternating the feed ratio, hydrogels were synthesised to have lower critical solution temperatures (LCST) in the vicinity of 37 °C. This ability to shift the phase transition temperature of the gels provides excellent flexibility in tailoring transitions for specific uses. The transition temperature of the pseudo gels was established using cloud point measurement and modulated differential scanning calorimetry (MDSC). The chemical structure of the xerogels was characterised by means of Fourier transform infrared spectroscopy (Ftir), while swelling experiments in distilled water indicate that the swelling and dissolution behaviour of the gels is strongly temperature dependent.     

Synthesis, characterization and metal uptake capacity of a new carboxymethyl chitosan derivative

Chemical modification of chitosan (Cs) and its derivatives via graft copolymerization can enhance their properties and consequently expands their potential applications. Carboxymethyl chitosan (CMCs) was prepared and characterized by FTIR spectroscopy, elemental analysis and X-ray diffraction. Graft copolymerization of N-acryloylglycine (NAGly) onto CMCs using 2,2-dimethoxy-2-phenyl acetophenone (PI) as photoinitiator was carried out under nitrogen atmosphere in aqueous solution. Evidence of grafting was confirmed by comparison of FTIR spectra of CMCs and the graft copolymers as well as the 2D-X-ray diffraction patterns, elemental analysis and the difference in solubility profiles before and after grafting. The effects of concentration of NAGly, PI and reaction time on the extent of grafting were investigated by determining the grafting percentage and grafting efficiency. With other conditions kept constant, the obtained optimum grafting conditions were: CMCs = 0.1 g, NAGly = 0.4 g, PI = 0.02 g and reaction time = 1 h. A preliminary study was then carried out to evaluate the capacity of the prepared new graft copolymer to uptake copper ions from aqueous systems. This preliminary investigation of the prepared graft copolymers showed that they may be tailored and exploited to expand the utilization of these systems in metal ions uptake and treatment of wastewater.     

Radiation grafting of NIPAAm and acryloxysuccinimide onto PP films and sequent crosslinking with polylysine

N-isopropylacrylamide (NIPAAm) and N-acryloxysuccinimide (NAS) were grafted from their binary mixtures in tetrahydrofurane (THF) and toluene solutions onto polypropylene (PP) films by the pre-irradiation oxidative method in air. Effects of pre-irradiation dose, dose rate, and monomer concentrations (NAS/NIPAAm) were studied. The grafted copolymers exhibited the lower critical solution temperature (LCST) at around 31 °C. Based on its thermo-reversible behavior, this system has been used for immunoassay, drug delivery, separation processes and immobilization of enzymes. N-acryloxysuccinimide (NAS) has been used as an active ester to bind proteins through amide bond formation with lysine, and because of this property, the grafted copolymer has been crosslinked with polylysine. Techniques used to characterize the films included differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), infrared (FTIR-ATR) and elemental analysis. Results on thermo-sensitivity are presented. This new system could find applications in vesicle immobilizations.     

The use of hydrophobic spacers in the development of new temperature- and pH-sensitive polymers

The preparation and characterization of two series of methacrylic acid derivative polymers is described. One series contains aliphatic spacers with one to ten methylene units, while the other series includes an aromatic ring with changes in the position of the acid, as spacer. Both series of polymers were obtained as methoxy-ester protected acid polymers and as polymers containing free acid groups in different amounts. pH-sensitive gels and temperature-sensitive N-isopropylacrylamide (NIPAAm) copolymers were prepared by using some of the monomeric structures described. The pH of the swelling transition of the gels changed from 3.5 up to 9.0 as a function of the spacer length and type. The lower critical solution temperature (LCST) of NIPAAm copolymers in water was lowered from 33.6°C to 6°C as a function of the co-monomer content and type. The observed changes in the pH of the swelling transition of gels and in the LCST of NIPAAm copolymers can only be explained if hydrophobic-hydrophobic and hydrogen-bonding interactions are considered in connection with the specific chemical structure of the monomers used.     

Thermo-responsive gelatin-functionalized PCL film surfaces for improvement of cell adhesion and intelligent recovery of gene-transfected cells

Efficient local gene transfection on a tissue scaffold is dependent on good cell-adhesion characteristics. In this work, the thermo-responsive gelatin-functionalized polycaprolactone (PCL) films were proposed for improvement of cell adhesion and intelligent recovery of gene-transfected cells. Functional copolymer brushes (PCL-g-P(NIPAAm-co-MAAS)) were first prepared via surface-initiated ATRP of N-isopropylacrylamide (NIPAAm) and methacrylic acid sodium salt (MAAS) from the initiator-funcationalized PCL surfaces. The pendant carboxyl end-groups of the PCL-g-P(NIPAAm-co-MAAS) surface were subsequently coupled with gelatin via carbodiimide chemistry to produce the thermo-responsive gelatin-functionalized PCL surface. The thermo-responsive gelatin-functionalized PCL film surface can improve cell adhesion and proliferation above the LCST of P(NIPAAm) without destroying cell detachment properties at lower temperatures. The dense transfected cells can be recovered simply by lowering culture temperature. The thermo-responsive gelatin-functionalized PCL films are potentially useful as intelligent adhesion modifiers for directing cellular functions within tissue scaffolds.     

Poly[(N-isopropylacrylamide-co-acrylamide-co-(hydroxyethylmethacrylate))] thermoresponsive microspheres: An accurate method based on solute exclusion technique to determine the volume phase transition temperature

Poly[(N-isopropylacrylamide-co-acrylamide-co-(hydroxyethylmethacrylate))] [poly(NIPAAm-co-AAm-co-HEMA)] copolymer was synthesized as a new thermoresponsive material possessing a lower critical solution temperature (LCST) around 37 °C in phosphate buffer, pH 7.4, at a solution concentration of 1%, w/v. The influence of polymer concentration on LCST was determined by cloud point measurements and by microcalorimetric analysis. The copolymer was transformed in hydrogel microspheres by suspension reticulation of OH groups with glutaraldehyde. The volume phase transition temperature (VPTT) of microspheres was determined by a new approach, which involves measurement of the increase in concentration of a blue dextran (BD) solution at different temperatures in the presence of dry microspheres. The minimum BD concentration that gives reliable and reproducible results was determined to be 1 mg/ml. However, the higher is the concentration of BD in solution the smaller is the error. Contrary to solution of the linear polymer which displays a sharp phase transition temperature, the dependence of water regain of the hydrogel with temperature lasts from 4 °C to 50 °C.     

The synthesis, characterisation, phase behaviour and swelling of temperature sensitive physically crosslinked poly(1-vinyl-2-pyrrolidinone)/poly(N-isopropylacrylamide) hydrogels

Physically crosslinked complexes of polyvinyl pyrrolidinone-poly (N-isopropylacrylamide) (PVP-PNIPAAm) were prepared by photopolymerisation from a mixture of the monomers 1-vinyl-2-pyrrolidinone and N-isopropylacrylamide. IR spectroscopy and calorimetry were used to characterise the resulting xerogels. By alternating the monomer feed ratio, copolymers were synthesised to have their own distinctive lower critical solution temperature (LCST). The transition temperature of the gels was established using cloud point measurement and modulated differential scanning calorimeter (MDSC). This ability to shift the phase transition temperature of the copolymers provides excellent flexibility in tailoring transitions for specific uses. Swelling experiments were performed on the copolymer disks in distilled water at varying temperatures to establish the behaviour of the gels above and below phase transition temperature. The results obtained show that below transition temperature, the gels are water soluble but above this temperature they are slightly less water soluble; significantly less water soluble; or water insoluble; depending on the composition and LCST of the gel.     

PP films grafted with N-isopropylacrylamide and N-(3-aminopropyl) methacrylamide by γ radiation: synthesis and characterization

Simultaneous grafting of N-isopropylacrylamide (NIPAAm) and N-(3-aminopropyl) methacrylamide hydrochloride (APMA) on polypropylene (PP) was investigated for obtaining interfaces that are stimuli-responsive under physiological conditions. A pre-irradiation method was optimized tuning the γ-irradiation dose, reaction time, temperature, and monomers concentrations. FT-IR ATR and XPS analysis of the grafted copolymers evidenced a greater content in NIPAAm than in APMA; the APMA/NIPAAm ratio increasing with the concentration of APMA in the reaction medium and when the grafting was carried out in 1 M NaNO₃. The grafted films were characterized regarding their thermal properties (DSC and TGA) swelling behavior and contact angle. Immersion of the pre-irradiated films in 1 M NIPAAm/0.5 M APMA aqueous solution rendered PP-g-(1NIPAAm-r-0.5APMA) which exhibited rapid and reversible transitions showing a LCST around the physiological temperature. By contrast, a greater content in APMA enhanced the hydrophilicity and prevented the shrinking of PP-g-(1NIPAAm-r-1APMA).     

Synthesis and properties of poly(aryl ether benzimidazole) copolymers for high-temperature fuel cell membranes

A series of poly(aryl ether benzimidazole) copolymers bearing different aryl ether linkage contents were synthesized by condensation polymerization in polyphosphoric acid (PPA) by varying the feed ratio of 4,4′-dicarboxydiphenyl ether (DCPE) to terephthalic acid (TA). As the ether unit content in the copolymer increased, the solubility of the copolymer in PPA and N,N′-dimethylacetamide/LiCl improved. For example 3–7 wt.% DMAc solution containing 2 wt.% of LiCl could be prepared from the copolymers. XRD studies revealed that the incorporation of flexible aryl ether linkages increased the chain d-spacings of the polymer backbones and decreased the crystallinity of the copolymers. Still, these copolymers having ether linkages showed reasonably good thermal/mechanical stability and high proton conductivity. For example, the copolymer with 30 mol% ether linkage had a tensile strength of 43 MPa (at 26 °C and 40% relative humidity) at an acid doping level of 7.5 mol H₃PO₄ and a proton conductivity of 0.098 S cm⁻¹ (at 180 °C and 0% relative humidity) at an acid doping level of 6.6 mol H₃PO₄.