Synthesis and characterization of trifluoromethyl substituted styrene polymers and copolymers with methacrylates: Effects of trifluoromethyl substituent on styrene

2-Trifluoromethyl styrene (2TFMS), 2,5-bis(trifluoromethyl) styrene (25BTFMS), and 3,5-bis(trifluoromethyl) styrene (35BTFMS) were synthesized. These styrenes were readily polymerized in bulk and also in solution using AIBN as a free radical initiator. The polymerization rate of these trifluoromethyl substituted styrenes and other monomers such as styrene (St), pentafluorostyrene (PFS) and 4-trifluoromethyl-tetrafluorostyrene (TFMTFS) were measured in benzene and dioxane by monitoring the ¹H NMR spectra of the double bond hydrogen. The order of polymerization rates was TFMTFS > 35BTFMS > 25BTFMS > PFS > 2TFMS > St. T_gs of styrene polymers with CF₃ substituted on the ortho position of the phenyl ring were much higher than those of the meta and para substituted styrenes due to the steric hindrance of the bulky CF₃ group close to the polymer main chain, which resulted in a decrease in the segment mobility of the polymer chains and an increasing T_g of the polymers. The copolymers of 2TFMS with methyl methacrylate (MMA) and also 25BTFMS with trifluoroethyl methacrylate (TFEMA) were prepared. T_gs of the copolymers were in the range of 120-145 °C and the copolymers were transparent and thermally stable. The copolymer films were flexible and exhibited high transmittance as the homopolymers of MMA and TFEMA. Thus, these copolymers may be utilized as novel optical materials.     

A study of blending and complexation of poly(acrylic acid)/poly(vinyl pyrrolidone)

Poly(acrylic acid) (PAA) and poly(vinyl pyrrolidone) (PVP) were chosen to prepare polymer complex and blends. The complex was prepared from ethanol solution and the blends were prepared from 1-methyl-2-pyrrolidone solution. DSC results show that the T_gs of the PAA/PVP blends lie between those of the two constituent polymers, whereas T_g of the PAA/PVP complex is higher than both blends and the two constituent polymers. TGA results show that degradation temperature, T_d, of PAA increases upon adding PVP in the blend, but thermal stability of the complex is higher than that of the blends as reflected by the higher T_d. Both FTIR and high-resolution solid state NMR show strong hydrogen bonding between PAA and PVP by showing significant chemical shift. The T_1ρ(H) measurement shows that the homogeneity scale for the blend is at ∼20 Å and that for the complex is ∼15 Å.     

Synthesis of high molecular weight poly(l-lactic acid) and poly(d-lactic acid) with improved thermal stability via melt/solid polycondensation catalyzed by biogenic creatinine

Stereoregular high polymers of poly(l-lactic acid) (PLLA) (M_w 1.2 × 10⁵, isotacticity 96.0%) and poly(d-lactic acid) (PDLA) (M_w 1.0 × 10⁵, isotacticity 98.6%) were successfully synthesized via melt/solid polycondensation (MP/SSP) using a biogenic catalyst creatinine (CR). The follow-up monitor of the polycondensation products with ¹³C NMR technique revealed that the polymerization of MP/SSP proceeded in a stereochemical controlled way throughout the whole process as evidenced by the constant high values of isotacticity (97.8–99.4%) of produced polymers. Thermogravimetric analysis demonstrated that the decomposition temperatures (T_d,init 324.3 °C, T_{d, 5%} 347.0 °C, T_{d, max} 400.2 °C) of PLLA synthesized with catalyst CR are over 100 °C above those of PLLA synthesized with catalyst SnCl₂·2H₂O.     

Synthesis and characterization of poly(amideimide)s from 4-(p-carboxyphenoxy)phthalic anhydride and 4-(p-carboxybenzoyl)phthalic anhydride

A series of poly(amideimide)s were prepared by the reaction of two new anhydride acidchloride monomers with aromatic diamines. 4-(p-Carboxyphenoxy)phthalic anhydride was synthesized by nucleophilic displacement reaction of N-methyl-4-nitrophthalimide with p-hydroxybenzoic acid, followed by hydrolysis. The tricarboxylic acid was converted to the corresponding anhydride acidchloride. 4-(p-Carboxybenzoyl)phthalic anhydride was synthesized by Friedel–Craft's acylation of toluene with N-phenylphthalimide-4-carbonylchloride, which was then converted to anhydride acidchloride of 4-(p-carboxybenzoyl)phthalic acid. The monomers were characterized by IR and NMR. Several PAI were prepared by the reaction of these anhydride acidchloride monomers with aromatic diamines. The inherent viscosities of the polymers were in the range of 0.42–0.58 dL/g. All polymers were soluble in polar aprotic solvents. The polymers showed good thermal stability and T_g values were in the range of 226–269 °C. X-Ray diffractograms of polymers indicate amorphous nature of these polymers.     

High molecular weight graft stabilisers for dispersion polymerisation of vinylidene fluoride in supercritical carbon dioxide: the effect of architecture

A group of high molecular weight graft stabilisers, both fluorinated and non-fluorinated, were synthesised by thermal ring-opening esterification of anhydride copolymers. These included poly(methyl vinyl ether-alt-maleic anhydride) and poly(maleic anhydride-octadecene) and were reacted with alcohols, including 1H,1H,2H,2H-perfluorooctanol, 1H,1H,2H,2H-perfluoro-dodecanol and 1-octanol. The stabilisers were fully characterised by ¹H, ¹⁹F and ¹³C nuclear magnetic resonance, diffuse reflectance Fourier transform infrared spectroscopy, and thermal analysis. Their phase behaviour in supercritical carbon dioxide (scCO₂), vinylidene fluoride (VDF), and a mixture of scCO₂/VDF was also studied using a variable volume view cell. Each stabiliser was tested for the dispersion polymerisation of VDF in scCO₂. The effect of the stabiliser architecture on the molecular weight and morphology of the poly(vinylidene fluoride) (PVDF) polymer product was investigated. Steric stabilisation effects were observed. Gel permeation chromatography and scanning electron microscopy were used for the characterisation of the molecular weight and morphology of PVDF polymers.     

NMR studies of thermo-responsive behavior of an amphiphilic poly(asparagine) derivative in water

The thermo-responsive behavior of a unique biocompatible polymer, poly(N-substituted α/β-asparagine) derivative (PAD), has been studied with several NMR methods. The ¹H and ¹³C solution NMR measurements of the PAD in DMSO-d₆ were used to investigate the isolated polymer and perform spectral assignments. By systematic addition of D₂O we have tracked structural changes due to aggregation and observed contraction of hydrophilic side chains. Solution and cross polarization/magic angle spinning (CP/MAS) ¹³C NMR approaches were implemented to investigate the aggregates of the PAD aqueous solution during the liquid to gel transition as the temperature was increased. At temperatures near 20 °C, all of the peaks from the PAD were observed in the ¹³C CP/MAS and ¹³C solution NMR spectra, indicating the presence of polymer chain nodes. Increasing the temperature to 40 °C resulted in a partial disentanglement of the nodes due to thermal agitation and further heating resulted in little to no additional structural changes. Deuterium T₁–T₂ and T₂–T₂ two-dimensional relaxation spectroscopies using an inverse Laplace transform, were also implemented to monitor the water–PAD interaction during the phase transition. At temperatures near 20 °C the dynamical characteristics of water were manifested into one peak in the deuterium T₁–T₂ map. Increasing the temperature to 40 °C resulted in several distinguishable reservoirs of water with different dynamical characteristics. The observation of several reservoirs of water at the temperature of gel formation at 40 °C is consistent with a physical picture of a gel involving a network of interconnected polymer chains trapping a fluid. Further increase in temperature to 70 °C resulted in two non-exchanging water reservoirs probed by deuterium T₂–T₂ measurements.     

Shape memory polymer system of semi-interpenetrating network structure composed of crosslinked poly (methyl methacrylate) and poly (ethylene oxide)

Shape memory semi-interpenetrating polymer networks (semi-IPNs) composed of crystalline poly (ethylene oxide) (PEO) and crosslinked poly (methyl methacrylate) (x-PMMA) have been investigated. The selected compositions show shape memory property with a reasonable fast recovery (recovery time ∼1 min) and shape recovery ratio of 99%. Effects of composition (x-PMMA/PEO = 80/20…60/40) and crosslinker (triethyleneglycol dimethacrylate) concentration (up to 6 wt.%) on the creep property were also studied. The recovery time of the semi-IPNs increased and the creep compliance decreased with increasing crosslinker concentration. The network structure containing PEO crystal was characterized by scanning electron microscopy (SEM). Differential scanning calorimetry (DSC) indicated that the PEO, present confined in the semi-IPN, melts at a lower temperature compared to the pure PEO. Dynamic mechanical analysis (DMA) showed a decrease in the glass transition (T_g) of the semi-IPN due to the phase mixing of amorphous PEO and PMMA. Both the glassy and rubbery moduli (E_g and E_r, respectively) were lower for the semi-IPNs than for the x-PMMA network. On the other hand, the E_g/E_r ratio was markedly increased for the semi-IPNs supporting an easy shaping along with a good shape fixing.     

Biobased poly(butylene 2,5-furandicarboxylate) and poly(butylene adipate-co-butylene 2,5-furandicarboxylate)s: From synthesis using highly purified 2,5-furandicarboxylic acid to thermo-mechanical properties

To synthesize high quality (co)polyesters derived from 2,5-furandicarboxylic acid (FA), an acetic acid refluxing/pH-swing method was proposed to purify FA. 2-Carboxyl furfural and other impurities were removed completely from FA with this method. Using highly purified FA, biobased polyester poly(butylene furnadicarboxylate) (PBF) and aliphatic-aromatic copolyesters poly(butylene adipate-co-butylene 2,5-furandicarboxy-late)s (PBAFs) were synthesized via melt (co)polycondensation. The (co)polyesters were characterized with GPC, FTIR, ¹H NMR, DSC and TGA, and their tensile mechanical properties were also assessed. The copolyesters possess random chain structure, monomer feed ratio-controlled copolymer composition and excellent thermal stability (T_d,5% > 340 °C) in full composition range. Both BA-rich and BF-rich PBAFs are crystalline polymers. The crystallizability decreases with composition, up to nearly amorphous at moderate ?_BF (40–60%). PBAFs with ?_BF no more than 50% exhibit obvious high-elastic deformation and rebound resilience, and possess tensile properties (E 18–160 MPa, σ_b 9–17 MPa, ε_b 370–910%) comparable to poly(butylene adipate). PBAFs with higher ?_BF behave like nonrigid plastics with low tensile moduli (42–110 MPa), moderate strength (30–42 MPa) and high elongation at break (310–470%). In comparison, PBF is a strong and tough thermoplastic having balanced mechanical properties, namely, much higher tensile modulus (1.9 GPa) and strength (56 MPa) and high elongation at break (260%). It seems necessary and effective to use highly purified FA for synthesizing high performance FA-derived (co)polyesters.     

Grafting of styrene/maleic anhydride copolymer onto PVDF membrane by supercritical carbon dioxide: Preparation,characterization and biocompatibility

Herein we report the surface modification of poly(vinylidene fluoride) (PVDF) microporous membrane via thermally induced graft copolymerization with maleic anhydride (Man)/styrene (St) in supercritical carbon dioxide (SC CO₂). SC CO₂, as a solvent and carrier agent, could accelerate mass transfer of monomers inside polymer matrixes and then facilitate the graft copolymerization on the surface of the membrane and within membrane pores, which were confirmed by FT-IR/ATR and XPS spectra together with SEM photographs. The effects of SC CO₂ pressure and temperature and the monomer concentration on the graft copolymerization were investigated. The modified PVDF membranes containing from 0 to 7 wt.% of grafted St–Man copolymer (SMA) were prepared and analysed in terms of surface microstructure, composition, hydrophilicity and biocompatibility. Solid-state ¹³C CP/MAS NMR and DSC indicated that the grafted SMA on the PVDF membrane had the alternative sequence structure and formed the different phases in the modified membrane, where the grafted SMA was associated with T_g of 122.8 °C and the PVDF matrix with T_m of 161.2 °C. The static contact angle measurements revealed that remarkable and permanent hydrophilicity was obtained upon grafting SMA. The experiments of BSA adsorption and cell growth also showed that the surface of SMA-based PVDF membrane has excellent biocompatibility.     

New copper(II) complexes of polyampholyte and polyelectrolyte polymers: Solid-state NMR, FTIR, XRPD and thermal analyses

Novel solid copper(II) complexes were obtained from the polyampholyte poly(EGDE-MAA-IM) and the polyelectrolyte poly(EGDE-MAA) polymers with copper salts at different concentration levels.The materials were characterized employing solid-state Nuclear Magnetic Resonance (NMR), Fourier Transform infrared (FTIR), X-ray powder diffraction (XRPD), differential scanning calorimetry (DSC) and thermogravimetry (TG).The reticulation induced by MAA in these materials against the poly(EGDE-IM) gel was analyzed by DSC. The coordination behavior of the carboxylic acid of MAA, compared to that provided by the imidazole ring, was studied through solid-state ¹³C NMR and changes in the FTIR spectra. The non-homogenous character of the doped and undoped materials was analyzed by the glass transition temperature (T_g), 2D ¹H-¹³C WISE NMR and proton spin-lattice relaxation time in the rotating frame (T^H_1ρ). In particular, the T^H_1ρ and T^H₁ values in the complexes decreased with the Cu(II) concentration, showing the high sensitivity of both parameters to the presence of a paramagnetic ion. Finally, the thermogravimetric studies indicated that the presence of the imidazole ring was decisive for the stability of the Cu(II) complexes and for the undoped polymers.     

Limits to expanding the PN‐F series of polyphosphazene elastomers

Mixed‐substituent fluoroalkoxyphosphazene polymers bearing ～15% 1H,1H,2H,2H‐perfluorooctan‐1‐oxy or 1H,1H,2H,2H‐perfluorodecan‐1‐oxy side groups together with trifluoroethoxy cosubstituent groups were synthesized. The low reactivity of the long‐chain fluoroalkoxides and their limited solubility in organic solvents prevented higher levels of substitution. Moreover, the sodium alkoxides with two methylene residues adjacent to the oxygen proved to be unstable in solution due to elimination of NaF and precipitation of side products, and this limited the time available for chlorine replacement reactions. The resulting cosubstituent polymers were characterized by proton nuclear magnetic resonance (¹H‐NMR), ³¹P‐NMR, ¹⁹F‐NMR, gel‐permeation chromatography, and differential scanning calorimetry. Unlike homo‐ or mixed‐substituent fluoroalkoxyphosphazene polymers, such as [NP(OCH₂CF₃)₂]_n (a microcrystalline thermoplastic, T_g ～ ?63°C, T_m ～ 242°C) or [NP(OCH₂CF₃)(OCH₂(CF₂)_xCF₂H)]_n (PN‐F, a rubbery elastomer, T_g ～ ?60°C, but no detectable T_m), the new polymers are gums (T_g ～ ?50°C, but no detectable T_m) with molecular weights in the 10⁵ g/mol rather than the 10⁶ g/mol range. POLYM. ENG. SCI., 54:1827–1832, 2014. © 2013 Society of Plastics Engineers     

Synthesis and electro-optic activities of novel polycarbonates bearing tricyanopyrroline-based nonlinear optical chromophores with excellent thermal stability of dipole alignment

Two series of novel electro-optic (EO) polycarbonates incorporating two kinds of tricyanopyrroline-based nonlinear optical (NLO) chromophores were designed and synthesized. These new polycarbonates were prepared through the facile copolymerization of diol NLO chromophores and bisphenol A bis(chloroformate), and the successful preparations were demonstrated by ¹H NMR and Fourier transform infrared (FT-IR) spectra. These polycarbonates possessed good thermal stabilities and also showed higher glass transition temperatures (T_g) in the range of 156–165 °C. After corona poling, the EO coefficients (r₃₃) of two poled polycarbonates films were up to 52 pm/V (PC-DTCPC-Ph-2) and 46 pm/V (PC-DTCPC-FPh-2) at the wavelength of 1310 nm. The higher T_gs endow the polycarbonates' poled films with good temporal stability of poling-induced dipole alignment, and the resulting poled films of PC-DTCPC-Ph-2 and PC-DTCPC-FPh-2 could retain 95% and 93% of the initial EO activities at 85 °C for more than 500 h respectively.     

Synthesis and properties of novel poly(tetramethylsilnaphthylenesiloxane) derivatives

Novel poly(tetramethylsilnaphthylenesiloxane) derivatives were synthesized and characterized by differential scanning calorimetry (DSC), thermogravimetry (TG), and X-ray diffraction analyses. Poly(tetramethylsilnaphthylenesiloxane) derivatives were obtained by condensation polymerization of the corresponding disilanol derivatives, i.e. 1,4-, 1,5-, 2,6-, and 2,7-bis(dimethylhydroxysilyl)naphthalenes, which were prepared by the Grignard reaction using chlorodimethylsilane and the corresponding dibromonaphthalene derivatives followed by the hydrolyses, catalyzed by palladium on charcoal. The obtained poly(tetramethyl-1,5-silnaphthylenesiloxane) was insoluble in common organic solvents; however, the other polymers exhibited the good solubility in common organic solvents, such as tetrahydrofuran (THF), chloroform, dichloromethane, and toluene. The introduction of tetramethyl-1,5-silnaphthylenesiloxane units into the resulting polymer was confirmed by ¹H NMR spectrum of the copolymer obtained by condensation copolymerization of 1,5-bis(dimethylhydroxysilyl)naphthalene with 1,4-bis(dimethylhydroxysilyl)naphthalene. It was revealed from the DSC and X-ray diffraction measurements that poly(tetramethyl-1,5-silnaphthylenesiloxane) and poly(tetramethyl-2,6-silnaphthylenesiloxane) exhibited the crystallinity; however, poly(tetramethyl-1,4-silnaphthylenesiloxane) and poly(tetramethyl-2,7-silnaphthylenesiloxane) were amorphous. The glass transition temperature (T_g) and the temperature at 5% weight loss (T_d5) of poly(tetramethylsilnaphthylenesiloxane) derivatives with dimethylsilyl group at 1-position of the naphthylene moiety were higher than those at 2-position of the naphthylene moiety. The T_g and melting point (T_m) of the present polymers were higher than those of poly(tetramethyl-1,4-silphenylenesiloxane).     

Synthesis and characterization of amphiphilic block copolymers from poly(ethylene glycol)methyl ether and 4-methyl-?-caprolactone or 4-phenyl-?-caprolactone

MPEG-b-PMCL and MPEG-b-PBCL diblock copolymers were synthesized by ring-opening polymerization of 4-methyl-?-caprolactone (MCL) or 4-phenyl-?-caprolactone (BCL) using monomethoxy poly(ethylene glycol) (MPEG, M_n = 550 or 2000 g mol⁻¹) as the macroinitiator and SnOct₂ as the catalyst. These copolymers were characterized by differential scanning calorimetry (DSC), ¹H NMR, ¹³C NMR, and gel permeation chromatography. The thermal properties (T_g and T_m) of the diblock copolymers depend on the composition of polymers. When larger amount of MCL or BCL was incorporated into the macromolecular backbone there was an increase in T_g. Their micellar characteristics in the aqueous phase were investigated by fluorescence spectroscopy, transmission electron microscopy (TEM), and dynamic light scattering (DLS). The block copolymers formed micelles in the aqueous phase with critical micelle concentrations (CMCs) in the range of 0.5-2.9 mg L⁻¹, depending on the composition of polymers. The lengths of hydrophilic segment influence the shape of micelle. The mean hydrodynamic diameters of micelles from DLS were in the range of 70-140 nm. The drug entrapment efficiency and the drug-loading content of micelles depending on the composition of block polymers were described.     

Synthesis of thermoresponsive block and graft copolymers via the combination of living cationic polymerization and RAFT polymerization using a vinyl ether-type RAFT agent

A novel vinyl ether-type RAFT agent, benzyl 2-(vinyloxy)ethyl carbonotrithioate (BVCT) was synthesized for various block copolymers via the combination of living cationic polymerization of vinyl ethers and reversible addition−fragmentation chain transfer (RAFT) polymerization. The novel BVCT–trifluoroacetic acid adduct play an important role to produce well-defined block copolymers, which is both as a cationogen under EtAlCl₂ initiation system in the presence of ethyl acetate for living cationic polymerization and a RAFT agent for blocks by RAFT polymerization. The resulting polymer, poly(vinyl ether)s, by living cationic polymerization had a high number average α-end functionality (≥0.9) as determined by both ¹H NMR and MALDI-TOF-MS spectrometry. In addition, this poly(vinyl ether)s worked well as a macromolecular chain transfer agent for RAFT polymerization. The RAFT polymerization of radically polymerizable monomers was conducted in toluene using 2,2′-azobis(isobutyronitrile) at 70 °C. For example, a double thermoresponsive block copolymer (MOVE₆₁-b-NIPAM₁₅₀) consisting of 2-methoxyethyl vinyl ether (MOVE) and N-isopropylacrylamide (NIPAM) was prepared via the combination of living cationic polymerization and RAFT polymerization. The block copolymer reversibly formed and deformed micellar assemblies above the phase separation temperature (T_ps) of poly(NIPAM) block in water. This BVCT is not only functioned as an initiator, but also acted as a monomer. When BVCT was copolymerized with MOVE by living cationic polymerization, followed by graft copolymerization with NIPAM via RAFT polymerization, well-defined graft copolymers (MOVE_n-co-BVCT_m)-g-NIPAM_x (n = 62–73, m = 1–9, x = 19–214) were successfully obtained. However, no micelle formed in water above T_ps of poly(NIPAM) graft chain unlike the case of block copolymers.     

Microwave-assisted polymerization process: A way to design new, high molecular weight poly(arylimidazole)s

In this paper, the microwave-assisted synthesis of high molecular weight poly(arylimidazole)s is described. These polymers were obtained by a one-pot polycondensation reaction involving a bis(α-diketone), an aromatic dialdehyde and ammonium acetate. Depending on the dialdehyde monomer, different poly(arylimidazole)s structures were synthesized. Structural characterization (¹H and ¹³C NMR), thermal properties (T_g, thermal stability) as well as a molecular weight determination of the polymers are reported.     

Reversible cross-linking reactions of alkoxyamine-appended polymers under bulk conditions for transition between flow and rubber-like states

Reversible cross-linking reactions of alkoxyamine-appended polymers with low glass transition temperature (T_g) were successfully carried out under bulk conditions. The low-T_g polymers with alkoxyamine units in the side chains were synthesised by radical copolymerisation of 2-ethylhexyl acrylate and two kinds of alkoxyamine-containing acrylate monomers. By heating the low-T_g polymers under bulk conditions at 100 °C, cross-linked polymers were formed by radical exchange reactions between alkoxyamine units, and a transition from a liquid-like flowable polymer state to a rubber-like polymer state was confirmed. A de-cross-linking reaction was also accomplished by radical exchange reactions between the cross-linked polymers and an added alkoxyamine-containing small molecule or stable nitroxyl radical, which resulted in transition to the flowable state again. The structural transition between low-T_g linear polymers and cross-linked polymers were characterised by ¹H and ¹³C NMR spectroscopy, Fourier transform infrared spectroscopy, rheology measurement, swelling experiment, and gel permeation chromatography measurement.     

Ring opening polymerization of 3-semifluoro- and 3-bromomethyloxetanes to poly(2,2-substituted-1,3-propylene oxide) telechelics for soft blocks in polyurethanes

The synthesis of hydroxy-terminated poly(2,2-substituted-1,3-propylene oxide) polyoxetane telechelics and co-telechelics bearing semifluorinated (-CH₂OCH₂(CF₂)_nCF₃) and functional bromomethyl pendant groups is reported. Characterization utilized ¹H NMR spectroscopy, temperature modulated DSC (MDCS), and gel permeation chromatography (GPC). Analysis of relative reactivity ratios for a 1:1 3FOx to BrOx feed indicates that in the early stages of reaction BrOx-BrOx dyad mole fraction is below the statistically predicted amount. However, a model suggests that the final telechelic dyad composition at complete reaction is not very different from a statistical copolymer. The co-telechelics have low T_gs (−33 to −39 °C) and molecular weight in a desirable range (M_w≈3-5 k). Telechelics were incorporated in polyurethanes (PUs) with isophorone diisocyanate (IPDI) and butanediol (BD) as the hard block. Characterization of polyurethane composition and bulk properties by ¹H NMR, MDSC, and GPC is described. The new polyurethanes hold promise for a ‘reaction on polymer’ approach to polyurethanes with functional soft blocks.     

Methacrylate-based polymer films useful in lithographic applications exhibit different glass transition temperature-confinement effects at high and low molecular weight

The effects of confinement on polymer films are important in applications related to photoresists. To optimize resolution, methacrylate polymers used in photoresists are often low molecular weight (MW). We use ellipsometry and fluorescence to study how the glass transition temperature (T_g) is affected by confinement in silica-supported films of low and high MW poly(1-ethylcyclopentyl methacrylate) (PECPMA) and poly(methyl methacrylate) (PMMA). With decreasing nanoscale thickness, T_g is nearly invariant for high MW (M_n = 22.5, 188 and 297 kg/mol) PECPMA but decreases for low MW PECPMA, with T_g – T_g,bulk = −7 to 8 °C in a 27-nm-thick film (M_n = 4.1 kg/mol) via ellipsometry and −15 °C in a 17-nm-thick film (M_n = 4.9 kg/mol) via fluorescence. Fluorescence studies using a 20-nm-thick dye-labeled layer in multilayer, bulk PECPMA films reveal a much greater perturbation to T_g in the free-surface layer for low MW PECPMA, which propagates tens of nanometers into the film. The effect of MW in single-layer monodisperse PMMA films is even more striking; T_g increases with confinement for high MW but decreases for low MW, with T_g – T_g,bulk = 9 °C in a 12-nm-thick film (nominal MW = 509 kg/mol) and −16 °C in a 17-nm-thick film (nominal MW = 3.3 kg/mol). The strong influence of MW on confinement effects in PECPMA and PMMA is in contrast to the previously reported invariance of the effect with MW in supported polystyrene films, reconfirmed here.     

Radically crosslinked branched poly(N-allylethylenimine) with lithium triflate as a solid state polymer electrolyte

Branched poly(N-allylethylenimine) (BPAEI), a solid state polymer electrolyte host, was synthesized by allylation of branched poly(ethylenimine) (BPEI). Allylation was essentially complete with the 2 and 1° nitrogen atoms of BPEI being mono-allylated and di-allylated, respectively, and with little or no quaternization. BPAEI can be radically cross-linked with and without lithium trifluoromethanesulfonate (LiTf) present to form free-standing, homogeneous, minimally hygroscopic films. BPAEI has a glass transition temperature (T_g) of −65 °C, as measured by differential scanning calorimetry (DSC), which increases with the concentration of initiator upon cross-linking using V-50 (2,2-azobis(2-amidino-propane) dihydrochloride) to −15 °C at a 10:1 nitrogen to initiator molar ratio (N:initiator). BPAEI with 20:1 N:Li⁺ (molar ratio) LiTf has a T_g of −48 °C, which increases with the concentration of radical initiator upon cross-linking using V-50 to 3 °C at 10:1 N:initiator. At compositions near 60:1 N:initiator, an unusual decrease in the rate at which T_g changes with cross-linking was observed, both with and without LiTf present, indicating that some undefined morphological changes occur. The effect of this morphological change resulted in the highest Ac conductivities at 60:1 N:initiator for all LiTf concentrations studied. At 20:1 N:Li⁺ LiTf and 60:1 N:initiator, the room temperature Ac conductivity was 1×10⁻⁸ S/cm which increased to 1×10⁻⁵ S/cm at 80 °C, the highest conductivity observed in the concentration ranges studied. Infrared spectroscopy (IR) showed that the concentrations of the individual ionic species present were largely independent of either LiTf concentration or cross-linking density, suggesting that changes in ion mobility, likely resulting from morphological changes, substantially control the ionic conductivity.