Steady-state fluorescence and NMR study on self-association behavior of poly(methacrylamides) bearing hydrophobic amino acid residues

Self-association properties of poly(N-methacryloylphenylalanine) and poly(N-methacryloyltryptophan) (pMPhe and pMTrp, respectively) were investigated by several characterization techniques, including steady-state fluorescence and NMR. These characterization data revealed similarities and distinctions of their self-association properties.The pH dependencies of association properties of pMPhe and pMTrp are practically the same. Apparent pK_a values for pMPhe and pMTrp were determined to be 5.7 and 5.8, respectively, by potentiometric titration. Steady-state fluorescence measurements at varying pH using pyrene as fluorescence probe indicated that, at pH≈5 (< apparent pH), hydrophobic microdomains were formed, while, at pH≈7 and 9 (> apparent pK_a), hydrophobic microdomains were not formed significantly. ¹H NMR spectra for both the polymers measured in D₂O exhibited that a significant fraction of aromatic rings in amino acid residues were located close to the polymer main chain, and that, at pH≈5, the mobility of the polymer main chain and the aromatic ring was extremely restricted.The polymer concentration (C_p) dependencies of association properties of pMPhe and pMTrp at pH≈5 are distinct. Steady-state fluorescence data at varying C_p indicated that pMPhe was more hydrophobic microscopically than pMTrp. Dynamic light scattering data indicated that pMTrp had a stronger tendency for interpolymer association than pMPhe did at pH≈5. It is concluded that the distinction in C_p dependency of the self-association properties of pMPhe and pMTrp is due to the differences in the bulkiness and the hydrophobicity of the substituents of amino acid residues.     

Alginate-g-PNIPAM-Based Thermo/Shear-Responsive Injectable Hydrogels: Tailoring the Rheological Properties by Adjusting the LCST of the Grafting Chains

Graft copolymers of alginate backbone and N-isopropylacrylamide/N-tert-butylacrylamide random copolymer, P(NIPAM_x-co-NtBAM_y), side chains (stickers) with various NtBAM content were designed and explored in aqueous media. Self-assembling thermoresponsive hydrogels are formed upon heating, in all cases, through the hydrophobic association of the P(NIPAM_x-co-NtBAM_y) sticky pendant chains. The rheological properties of the formulations depend remarkably on the NtBAM hydrophobic content, which regulates the lower critical solution temperature (LCST) and, in turn, the stickers’ thermo-responsiveness. The gelation point, T_gel, was shifted to lower temperatures from 38 to 20 °C by enriching the PNIPAM chains with 20 mol % NtBAM, shifting accordingly to the gelation temperature window. The consequences of the T_gel shift to the hydrogels’ rheological properties are significant at room and body temperature. For instance, at 37 °C, the storage modulus increases about two orders of magnitude and the terminal relaxation time increase about 10 orders of magnitude by enriching the stickers with 20 mol % hydrophobic moieties. Two main thermo-induced behaviors were revealed, characterized by a sol–gel and a weak gel–stiff gel transition for the copolymer with stickers of low (0.6 mol %) and high (14, 20 mol %) NtBAM content, respectively. The first type of hydrogels is easily injectable, while for the second one, the injectability is provided by shear-thinning effects. The influence of the type of media (phosphate buffer (PB), phosphate-buffered saline (PBS), Dulbecco’s modified Eagle’s medium (DMEM)) on the hydrogel properties was also explored and discussed. The 4 wt % NaALG-g-P(NIPAM₈₀-co-NtBAM₂₀)/DMEM formulation showed excellent shear-induced injectability at room temperature and instantaneous thermo-induced gel stiffening at body temperature, rendering it a good candidate for cell transplantation potential applications.     

pH-Controlled association of PEG-containing terpolymers of N-isopropylacrylamide and 1-vinylimidazole

Temperature- and pH-controlled association of terpolymers of N-isopropylacrylamide (NIPA) with 1-vinylimidazole (VI) and polyethylene glycol (PEG) has been investigated by light scattering and atomic force microscopy (AFM) in situ. The polymers contained 0-15 mol% VI and 0-2 mol% PEG. The phase transition temperatures (T_p) have been in the range of 32-45 °C and exhibited significant dependence on the pH of solution in the pH range between 5 and 8. The T_p of the polymers increased with increasing VI content and with decreasing pH, confirming major effect of VI ionization status on T_p. The presence of PEG grafts in the polymer structure had augmenting effect on the magnitude of pH-responsiveness and on the pH-independent colloidal stability of the polymer particles formed above T_p. Incorporation of VI into the polymer structure had similar, but pH-dependent effect on colloidal stabilization of the polymer particles. The size of the particles formed after the phase transition is driven by the association of the collapsed NIPA segments in the globule conformation and it decreased with decreasing pH. The phase transition temperature of the polymers could be adjusted to increase from temperatures below, to temperatures above body temperature upon decreasing pH from 7 to 6, suggesting that such polymers could provide a material platform for a variety of biomedical applications. AFM analysis in situ showed a fully reversible formation of particles in the solutions of the polymers above their T_p.     

Alkanol-Induced Micelles of a Very Hydrophilic EO–PO–EO Block Copolymer: Characterization by Spectral and Scattering Methods

The aqueous solution behavior of a PEO–PPO–PEO block copolymer (EO₁₀₃PO₃₉EO₁₀₃), was investigated in the presence of aliphatic alkanols (C₂, C₄, C₆ and C₈). The non-associated polymer chains remain extremely hydrated in water, but aggregation in the form of spherical micelles was evidenced, triggered by the interaction of polymer chains with hydrophobic alkanol. We assume that the hydrophobic interaction between the PPO block of the copolymer and alkanol promotes micellization, which increases further with the introduction of higher chain length species. The critical micellization temperature (CMT), as measured by UV–visible spectroscopy, indicates an interaction of polymer chains with the alkanol bearing a higher chain length, which triggers aggregation. The micelles were characterized by small angle neutron scattering to elucidate the size and related micellar parameters. The gradual increase in the alkanol content increases the aggregation number, though the micelles were spherical in shape. We conclude that ethanol, due to its preferential solubility in the aqueous phase, does not affect the aggregation. The alkanols with chain lengths of C₄–C₈ chain, interact with the PPO block through hydrophobic interaction and shifts the CMTs to lower values. The combined effect of inorganic salt (NaCl) and alkanols show enhanced micellar properties.     

Calculation of thermodynamic quantities for carbon tetrachloride (CCl4) close to the III–IV phase transition

We calculate the thermal expansion α _p , isothermal compressibility κ _T and the specific heat, C _p -C _v , as a function of pressure using the observed V-P data at room temperature close to the III–IV phase transition in CCl₄. Calculated κ _T , α _p and C _p -C _v decrease as the pressure increases from phase III to phase IV in this molecular crystal system, as expected. On the basis of our calculations of the κ _T , α _p and C _p -C _v , the Pippard relations are established close to the III–IV phase transition in CCl₄, which can be verified experimentally.     

Characteristics of zwitterionic sulfobetaine acrylamide polymer and the hydrogels prepared by free-radical polymerization and effects of physical and chemical crosslinks on the UCST

A zwitterionic sulfobetaine polymer, poly(N,N-dimethyl(acrylamidopropyl) ammonium propane sulfonate) (poly(DMAAPS)), and the hydrogels of this polymer were synthesized by free-radical polymerization in an aqueous redox system using a wide range of monomer concentrations (C_m). The resulting polymers were characterized in terms of polymer yield, intrinsic viscosity, molecular weight, gel fraction, and thermoresponsive phase-transition behavior. Parameters in the Mark–Houwink–Sakurada equation, including the molecular-weight exponent α, were determined for poly(DMAAPS) in 0.1 M NaCl aqueous solution. The physical state and transparency of the poly(DMAAPS) samples were strongly dependent on C_m and temperature. At higher values of C_m (i.e. above a critical molecular weight), poly(DMAAPS) became a gel comprising a physically crosslinked network consisting of entangled polymer chains and interchain associations of the zwitterionic groups. The poly(DMAAPS) solutions or gels exhibited a thermoresponsive phase transition with an upper critical solution temperature (UCST). The gels obtained were completely soluble in aqueous NaCl solution at ambient temperature as well as in water at temperatures above UCST. The effects of molecular weight, chemical crosslink density and copolymerization on the UCST were also elucidated.     

Association behavior of thermo-responsive block copolymers based on poly(vinyl ethers)

Thermo-sensitive nanosized structures have been prepared in water from poly(methyl vinyl ether)-block-poly(isobutyl vinyl ether) (PMVE-b-PIBVE) block copolymers. The composition and the architecture (diblock and triblock architectures) of the PMVE-b-PIBVE copolymers have been varied. The investigated copolymers had an asymmetric composition with a major PMVE block. While the PIBVE blocks are hydrophobic, the PMVE blocks are hydrophilic at room temperature and become hydrophobic above their demixing temperature (around 36 °C) as a result of the lower critical solution temperature (LCST) behavior. At room temperature, the amphiphilic copolymers aggregate in water above a critical micelle concentration, which has been experimentally measured by hydrophobic dye solubilization. The hydrodynamic diameter of the structures formed above the cmc has been measured by dynamic light scattering (DLS) while their morphology has been studied by transmission electron microscopy (TEM). ¹H NMR measurements in D₂O at room temperature reveal that the aggregates contain PIBVE insoluble regions surrounded by solvated PMVE chains. These investigations have shown that polydisperse spherical micelles are formed for asymmetric PMVE-b-PIBVE copolymers containing at least 9 IBVE units. For copolymers containing less IBVE units, loose aggregates are formed.Finally, the thermo-responsive, reversible properties of these structures have been investigated. Above the cloud point of the copolymers, the loose aggregates precipitate while the micelles form large spherical structures.     

Thermoresponsive core-shell-corona micelles of poly(ethyleneglycol)-b-poly(N-isopropylacrylamide)-b-polystyrene

Core-shell-corona micelles with a thermoresponsive shell self-assembled by triblock copolymer of poly(ethyleneglycol)-b-poly(N-isopropylacrylamide)-b-polystyrene (PEG₄₅-b-PNIPAM₁₆₈-b-PS₄₆) are studied by ¹H NMR, light scattering and atomic force microscopy. The thermoresponsive triblock copolymer, which has a relatively short hydrophobic PS block, can disperse in water at room temperature to form core-shell-corona micelles with the hydrophobic PS block as core, the thermoresponsive PNIPAM block as shell and the hydrophilic PEG block as corona. At temperature above lower critical solution temperature (LCST) of the PNIPAM block, the PNIPAM chains gradually collapse on the PS core to shrink the size and change the structure of the resultant core-shell-corona micelles with temperature increasing. It is found that there possibly exists an interface between the PNIPAM shell and PEG corona of the core-shell-corona micelles at temperature above LCST of the PNIPAM block.     

UV curable polyurethane dispersions from polyisocyanate and organosilane

UV curable polyurethane dispersions (UV-PUDs) have been synthesized from hexane diisocyanate (HDI) trimer and polytetramethylene ether glycol (PTMG) with different types of capping agents (2-hydroxyethylacrylate (HEA), pentaerythritol triacrylate (PETA), aminopropyl triethoxy silane (APTES)) and prepolymer chain length (M_p). The PUD cast films were tack free prior to cure and UV cure provided the film with high solvent and yellowing resistances, and high surface properties together with high mechanical strength. Regarding the effect of capping agent, PETA gave greater hardness, modulus, strength, and glass transition temperature (T_g) than HEA due to the greater crosslink density of the polymer, and smaller swelling at large M_p. Swelling was governed by the hydrophilicity at large M_p, but by the crosslink density at small M_p. As APTES partially replaces HEA gel fraction and T_g decreased due to the decreased crosslink density, whereas hardness and contact angle increased due to the filler and hydrophobic nature of the silicon compound. Notably, the thermal degradation temperature of the UV-PUD has been increased by about 30–40 °C with at 3% APTES.     

Studies on swelling behaviors,mechanical properties,network parameters and thermodynamic interaction of water sorption of 2-hydroxyethyl methacrylate/novolac epoxy vinyl ester resin copolymeric hydrogels

A series of the highly cross-linked hydrogels has been developed by the syntheses of bulk copolymers based on 2-hydroxyethyl methacrylate (HEMA) and novolac epoxy vinyl ester resin (NEVER). The resulting hydrogels were investigated on their equilibrium water content (EWC), swelling behaviors and tensile properties. Dynamic swelling behaviors of copolymeric hydrogels indicate that the swelling process of these polymers follows Fickian behavior. The EWC decreased and volume fraction of polymer in hydrogel (ϕ₂) increased with NEVER content increasing due to its hydrophobicity. The increase of ionic strength of swelling medium or temperature results in a decrease in EWC and an increase in values of ϕ₂. Young’s modulus and tensile strength of hydrogels, as well as effective cross-link density (v_e), increased as NEVER content increased or ionic strength of swelling medium increased, attributing to increasing interaction between hydrophobic groups and polymer–polymer interaction with an increase in NEVER content or in ionic strength. The polymer–solvent interaction parameter χ reflecting thermodynamic interaction was also studied. As NEVER content, ionic strength of swelling medium or temperature increased, the values of χ increased. The values of χ and its two components χ_H and χ_S varied with increasing T. The negative values and trend of the enthalpy and entropy of dilution derived from values of χ_H and χ_S, could be explained on the basis of structuring of water through improved hydrogen bonding and hydrophobic interaction.     

Thermo-responsive behavior of hybrid core cross-linked polymer micelles with biocompatible shells

Poly(2-(methacryloyloxy)ethyl phosphorylcholine)-b-poly(N-isopropylacrylamide-co-2-(N,N-dimethylamino)ethyl methacrylate) (pMPC-b-p(NIPAM/DMA)) was synthesized via reversible addition-fragmentation chain transfer (RAFT) controlled radical polymerization. Below the critical aggregation temperature (CAT), i.e., about 40 °C, the diblock copolymer dissolved in water as a unimer with a hydrodynamic radius (R_h) of ca. 10 nm. Above CAT the diblock copolymers formed polymer micelles with an R_h of ca. 40 nm, composed of a p(NIPAM/DMA) core and biocompatible pMPC shell due to hydrophobic self-aggregation of the thermo-responsive p(NIPAM/DMA) block. The pendent 2-(N,N-dimethylamino)ethyl group of DMA in pMPC-b-p(NIPAM/DMA) reduced HAuCl₄ to form gold nanoparticles (AuNPs) and could attach to their surfaces. The cores of these polymer micelles could be cross-linked above CAT by HAuCl₄, which upon being reduced generated AuNPs as cross-linking points to form core cross-linked (CCL) polymer micelles, as confirmed by UV-vis absorption and dynamic light scattering measurements. The CCL polymer micelles absorbed visible light at 532 nm because of surface plasmon resonances of the AuNPs. The R_h of the CCL polymer micelles remained at ca. 40 nm regardless of temperature.     

Light scattering and microcalorimetry studies on aqueous solutions of thermo-responsive PVCL-g-PEO copolymers

Dilute aqueous solutions of thermo-responsive poly(N-vinyl caprolactam)-graft-polyethylene oxide (PVCL-g-PEO) copolymers were studied by light scattering and high sensitivity differential scanning microcalorimetry. These copolymers are double hydrophilic at low temperatures, but become amphiphilic upon heating the solutions above the cloud point temperature of the PVCL segments (T_CP). The self-assembly properties of the copolymers are investigated by dynamic light scattering as a function of the temperature, degree of grafting and concentration. It was found that a certain critical polymer concentration is needed for the polymers to form stable aggregates. These structures are expected to consist of a hydrophobic PVCL core, stabilized by a hydrophilic PEO shell. The size of these aggregates increases with the degree of grafting. Microcalorimetry results revealed that the grafting of PVCL with hydrophilic PEO does not influence the phase transition enthalpy of PVCL.     

Structural aspects of the LCST phase behavior of poly(benzyl methacrylate) in room-temperature ionic liquid

The structure and lower critical solution temperature (LCST) phase behavior of well-defined poly(benzyl methacrylate) (PBnMA) solution using 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide, [C₂mim][NTf₂] ionic liquid (IL) as a solvent have been studied by dynamic light scattering (DLS) and small-angle neutron scattering (SANS) at various temperatures. The SANS profiles observed for fully deuterated IL ([C₂mim]-d₁₁[NTf₂]) containing PBnMA were kept practically unchanged in the temperature range between 298 and 363 K, while they suddenly changed at 363 K. This indicates that the LCST behavior of PBnMA-IL solution is a first-order phase transition, which is consistent with the DLS results. The SANS profiles below 363 K were well represented by the theoretical Debye scattering function with inter-molecular interaction and the radius of gyration, R_g was estimated to be almost constant, i.e., ∼45 Å. The SANS result obtained here was compared with those in aqueous PNIPAm solutions as a typical LCST system, and some differences between IL and aqueous solution systems are pointed out. It is found that thermodynamic quantities (ΔH_demix, ΔS_demix and ΔG_demix) from the homogeneous solution to the phase separation states strongly depend on the solvation of the PBnMA polymer by the IL ([C₂mim] cation and [NTf₂] anion). We propose an LCST phase separation mechanism in the polymer-IL solution.     

Mobilities of polymer liquids at constant temperature and at constant volume

Previously developed relationships between isomobility states and equilibrium p-v-T properties of vinyl polymers are extended to predict mobilities, μ, at constant temperature and at constant volume, with poly(vinyl acetate) as an example. At constant volume, μ changes by several orders of magnitude while the ‘internal pressure’ remains constant, suggesting that kinetic energy (temperature) dominates in governing μ. From μ at constant temperature the Vogel parameters, B and T₀, are found to increase with pressure, the former increasing linearly. A new Vogel type equation is developed in which one of the parameters, B_v, depends only on the chemical composition of the polymer. Both μ and its ‘activation energy’ at constant pressure, E_p, are shown to be constant at the glass transition.     

Depolarization current of a novolac p-fluorophenol-formaldehyde resin

A Novolac p-fluorophenol-formaldehyde (NFF) resin was prepared by condensation of p-fluorophenol with formaldehyde. DSC showed the glass transition effect or coinciding endothermal peak depending upon the thermal history of samples. It is supposed that the peaks are caused by breaking of the intermolecular bondings in the resin during the glass transition. The bondings are formed in the resin during the storage at room temperature. Thermally stimulated depolarization current (TSDC) measurements were carried out in the temperature range of 290 to 350 K, with the samples having an average number molecular weight M?_n of 375 and 434. TSDC curves mainly showed the dipolar relaxation α peaks. The influence of poling temperatures, the influence of M?_n, the activation energy E_a, and the physical ageing of the samples were investigated. Physical ageing was determined as the reciprocal polarizability R_p vs. time of ageing. Samples. with higher M?_n showed a higher glass transition temperature, a lower E_a, and a higher increase in R_p than the sample with lower M?_n. The increase in M?_n increased the rigidness of NFF samples. The effects are attributed to the strong hydrogen bonding. The comparison with analogous results in novolac phenol-formaldehyde resin without fluorine is given.     

Studies on heat capacity of cellulose and lignin by differential scanning calorimetry

Heat capacities (C_p) of wood cellulose, other natural celluloses having various crystallinities and of lignin are given for temperatures ranging from 330K to 450K using differential scanning calorimetry. The calculation of the C_p of completely crystalline cellulose is based on a two-state model of cellulose which assumes linearity between the crystallinity and C_p. The higher C_p found in the amorphous region compared with the crystalline region, is apparantly due to differences in the frequency of molecular vibration in these two areas. The glass transition of lignin was observed as a sudden increase in C_p at 400K. The precise T_g of lignin was dependent on the sample's origin, characterization, thermal history etc. When annealed at around T_g enthalpy relaxation occurs, and this can be detected as an endothermic peak in the C_p curve at the transition temperature. Moreover, the C_p in the glassy state was found to decrease with both annealing time and temperature, suggesting that rearrangement of the local conformation of lignin molecules occurs in the glassy state temperature range.     

pH-responsive nanosized-micelles based on poly(monomethylitaconate)-co-poly(dimethylaminoethyl methacrylate) and cholesterol side chains effect on pH change-induced release of piroxicam

Novel double hydrophilic poly(monomethylitaconate)-co-poly(N,N-dimethylaminoethyl methacrylate) (PMMI-co-PDMAEMA) synthesized via free radical polymerization of corresponding monomers with defined molar ratios in the presence of K₂S₂O₈ as an initiator in an aqueous solution. The resulting copolymer was subsequently converted to a cholesterol conjugate (PMMICholC₆-co-PDMAEMA) by esterification reaction with 6-cholesteryl-1-hexanol (CholC₆). Two copolymers self-assembled into micelles by simply adjusting the solution pH at room temperature. The non-conjugated polymer had a sharp transition at pH 5. TEM and DLS studies showed that both micelles were spherical in shape with a mean diameter around 85 and 26 nm, respectively. Piroxicam (PX) as a hydrophobic model drug was encapsulated into micelles. The results indicated that PMMICholC₆-co-PDMAEMA micelles were able to load more amounts of drug than PMMI-co-PDMAEMA micelles which could be attributed to the strong hydrophobic interactions of cholesterol molecules in the core. In vitro release studies demonstrated that PX release from PMMI-co-PDMAEMA micelles was significantly fast at physiological pH compared with mildly acidic pH 4.5. However, at pH 4.5, PMMICholC₆-co-PDMAEMA micelles, with core-shell-corona structure, released loaded drug molecules faster than pH 7.4 which contained a relatively steady drug release profile. In summary, cholesterol-modified micelles could be introduced as stable and effective pH responsive nanocarriers to make a promising system for enhancing the efficacy of hydrophobic drugs in cancer cells for improved cancer therapy.     

Effect of end-group modification,hydrophilic/hydrophobic block ratio and temperature on the surface,associative and thermodynamic behaviour of poly(ethylene oxide)-b-poly(butylene oxide) diblock copolymers in aqueous media

This study describes the surface, micellar, associative and thermodynamic properties of four diblock oxyethylene (E)/oxybutylene (B) copolymers with different hydrophilic block ends and various hydrophilic/hydrophobic ratios in aqueous media. The copolymers were denoted DE₄₀B₁₈, TE₄₀B₁₈, E₅₆B₁₉ and E₅₆B₇. The aqueous polymer solutions at various concentrations and temperatures were investigated by surface tensiometry and dynamic and static laser light scattering. Surface tension measurements were employed to detect the critical micelle concentration (CMC) as well as to calculate the surface-active and thermodynamic parameters of adsorption at the air/water interface. CMC values were also used to calculate the enthalpy of micellization (?H ⁰ _mic), free energy of micellization (?G ⁰ _mic) and entropy of micellization (?S ⁰ _mic). Similarly, various thermodynamic parameters for adsorption at the air/water interface were also deduced. Dynamic light scattering (DLS) was used to obtain the hydrodynamic radii (r _h) and volumes (υ _h) of the micelle at different temperatures, and hence the hydrodynamic expansion parameter (δ _h) was also estimated. Likewise, static light-scattering measurements enabled us to determine various parameters of the copolymer micelles, such as the weight-average molar mass (M _w), association number (N _w), thermodynamic radius (r _t), thermodynamic volume (υ _t), anhydrous volume (υ _a) and the thermodynamic expansion parameter (δ_t). Various thermodynamic and micellar parameters obtained from light scattering show that the micelles formed are spherical in shape and have rather soft interaction potentials at low temperature but become harder at higher temperature. Based on the different experimental results obtained, it can be said that various surface, micellar and thermodynamic parameters are dependent not only on the temperature and solution conditions but also on the hydrophobic/hydrophilic ratio and the end-group composition of the polymer. Modification of the hydrophilic end group of the polymer prominently affects various micellar properties. This effect can be assigned to the difference in polarity and the intermicellar charge effect.     

Correlation between crosslinking efficiency and spatial inhomogeneity in poly(acrylamide) hydrogels

Summary Elasticity and light scattering measurements were carried out on poly(acrylamide) (PAAm) hydrogels prepared from acrylamide (AAm) and N,N’-methylenebisacrylamide (BAAm) monomers under various reaction conditions. Elasticity tests showed that the crosslinking efficiency of BAAm ε_xl, that is the fraction of BAAm forming effective crosslinks decreases as the initial monomer concentration C_o is decreased. At C_o=3%, ε_xl was found to be 10^-2–10^-3, indicating that 99 to 99.9% of BAAm used in the hydrogel preparation are wasted in elastically ineffective links. Debye-Bueche analysis of the light scattering data showed that, irrespective of the gel synthesis conditions, the correlation length ξ, that is, the extension of inhomogeneities in the hydrogels is 10¹ nm. The extent of frozen concentration fluctuations in the hydrogels represented by 〈η²〉 decreases with increasing crosslinking efficiency of BAAm. The combination of the light scattering and the elasticity data of gels shows a direct correlation between the fraction of wasted crosslinker molecules during gelation and the spatial gel inhomogeneity.     

Intramolecular mobility and its role in the glass transition temperature of ionic polymers

The glass transition temperature of ionic polymers is found to depend on the molar ionic cohesive energy, the universal gas constant and a factor (n) that is related to intramolecular interactions. The polyphosphates, polyacrylates and X, Y-ethylene ionenes polymer families are shown to follow the equation interrelating the above-mentioned variables. The significance of n can be understood by deriving various rules of constant specific heat at T_g (ΔC_p). The results of this analysis show that approximately $\text{2}\text{3}$ of ΔC_p is attributable to intersegmental interactions, while $\text{1}\text{3}$ of ΔC_p is related to intramolecular forces. Similar relationships were established between the degrees of freedom of the polymer repeat unit and ΔC_p. These rules are shown to be related to Wunderlich's ‘bead’ concept.