Breadth of glass transition temperature in styrene/acrylic acid block,random, and gradient copolymers: Unusual sequence distribution effects

Block, random, and gradient copolymers of styrene (S) and acrylic acid (AA) are synthesized by conventional or controlled radical polymerization, and their glass transition temperature (T_g) behaviors are compared. The location and breadth of the T_gs are determined using derivatives of differential scanning calorimetry heating curves. Each S/AA random copolymer exhibits one narrow T_g, consistent with a single phase of limited compositional nanoheterogeneity. Block copolymers exhibit two narrow T_gs originating from nanophase separation into ordered domains with nearly pure S or nearly pure AA repeat units. Each gradient copolymer exhibits a T_g response with a ～50–56 °C breadth that extends beyond the upper T_g of the block copolymers. For copolymers of similar composition, the maximum value in the gradient copolymer T_g response is consistent with that of a random copolymer, which has an enhanced T_g relative to poly(acrylic acid) due to more effective hydrogen bonding when AA units are separated along the chain backbone by S units. These results indicate that gradient copolymers with ordered nanostructures can be rationally designed, which exhibit broad glass transitions that extend to higher temperature than the T_gs observed with block copolymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2842–2849, 2007     

Poly(propylene terephthalate) containing 4,4′-sulfonylbisphenol units: Effect of chemical composition on the physical-chemical properties

Copolyesters containing rigid aromatic units based on 4,4′-sulfonylbisphenol (bisphenol S) have been prepared by melt mixing poly(propylene terephthalate) (PPT) with an ethoxylated bisphenol S (sulfonyldiphenol). The insertion of the bisphenol units inside the polymer chain occurred quantitatively and no side reaction has been observed. The copolymers displayed good thermal stability. The main effect of copolymerization was a lowering in the degree of crystallinity and a decrease of the melting temperature with respect to PPT. On the contrary, an increment of T _g as the content of bisphenol S units increased due to the stiffening effect of the moieties deriving from bisphenol S. The Wood equation described well the correlation between T _g and composition.     

Infrared laser photoisomerization of 2-fluoroethanol in argon

Different products result from single-photon IR photolysis of 2-fluoroethanol in solid argon depending upon the vibrational mode that is excited. Irradiation of the OH stretch causes an interconversion of the two most stable isomers T₁ and G_g. Irradiation of one CH stretch results in the formation of significant yields of the less stable G₁ and T_g isomers. The isomers of 2-fluoroethanol can be photooriented in argon by IR irradiation.     

Magnetic properties of the quasi one-dimensional Heisenberg linear chain antiferromagnet: manganocene

Magnetic susceptibility measurements on the rhombic form of manganocene, Mn(C₅H₅)₂, are reported between 0.94 and 297.5 K. A pronouced minimum in the 1/x^corr_m versus T curve is located at T_min = 141 ± 1 K. The results are well reproduced by the solution of Fisher to the quasi one-dimensional Heisenberg linear chain modified such as to include interchain interaction for J/k = ?14 K, g = 2x = ?5 K. A less accurate approximation to the experimental results has been achieved in terms of the pair model (J/k = ?22.5 K, g = 2.0). The results are in excellent agreement with the zigzag chain structure of C₅H₅Mn units reported for the compound.     

CPS 758 Untersuchung des Mischungsgleichgewichts binärer Polymermischungen

The phase diagram of a binary polymer blend can be derived from the glass temperaturesT _g of the demixed phases under the following conditions:

1. The T_g's of the pure components are sufficiently different from one another.
2. TheT _g 's of the one-phase homogeneous mixtures can be determined and vary monotonically with composition.
3. The equilibrium state of the mixture is attained after sufficient long annealing at temperatureT.
4. The equilibrium state at the temperatureT can be frozen by quenching.

These conditions are examined for mixtures of polystyrene (PS) and tetra methyl-bis-phenol A-polycarbonate (TMPC). The phase separation kinetics is investigated with respect to size and composition of the co-existing phases. The co-existance curves (binodal with lower critical point) are determined for mixtures with various molar masses of the PS component. The problems concerning the cloud point curves are shortly discussed. BetweenT _g and the binodal the one-phase mixtures exist in a hindered thermodynamic state, because the crystallization of the TMPC component is a very slow process which requires very long annealing. With increasing amounts of PS in the mixture the crystallization half time of TMPC is lowered.     

Structure-property study of polyimides derived from PMDA and BPDA dianhydrides with structurally different diamines

A series of aromatic diamines were polymerized with two aromatic dianhydrides, pyromellitic dianhydride and 3,3^′,4,4^′-biphenyltetracarboxylic dianhydride, and the resulting poly(amic acid)s were thermally cyclodehydrated to aromatic polyimides. The polyimides were characterized by determining the glass transition temperatures (T_g), thermal stability, coefficients of thermal expansion, and wide-angle X-ray diffraction. Structure-property relationships are elucidated and discussed in terms of the structural fragments in the polymer chain. The PMDA-based polyimides generally revealed a higher T_g than the corresponding BPDA-based analogues. Generally, the dilution of the imide content by the insertion of oxyphenylene segments into the diamines significantly reduced the T_g. The introduction of m- or o-phenylene units into the polymer backbone usually resulted in a decrease in T_g. The attachment of pendant groups on the backbone may lead to decreased or increased T_gs, depending on the structure of pendant groups. As evidenced by X-ray diffraction, the polyimides derived from rigid, rod-like diamines or the diamines having two or three p-oxyphenylene showed a higher crystalline tendency. The presence of aliphatic pendant groups slightly reduced the thermal stability of the polyimides. The other structural changes did not show a dramatic influence on the thermal stability. Some polyimides obtained from p- or m-phenylenediamine had low thermal expansion coefficients below 2×10−5°C⁻¹.     

The glass transition temperature of polystyrene

A round robin test was performed to determine the reliability of values for the glass transition temperatureT _g as determined by DTA on polymers. Ten different instruments were involved. The test material was high molecular weight polystyrene. Values forT _g (midpoint) were reported in the range 107°C±2 K. The respective heat flow curves differed considerably in shape. In the literature aT _g of 100°C is often given for polystyrene. The discrepancy between this value and the value of 107°C found in the round robin test is due to three differences: the thermal history of the sample, the evaluation of the heat flow curves, and the effect of finite sample size.     

Synthesis and characterization of polyesters derived from succinic acid, ethylene glycol and 1,3-propanediol

Poly(ethylene succinate) (PES), poly(trimethylene succinate) (PTS) and their copolyesters with various compositions were synthesized through a direct polycondensation reaction with titanium tetraisopropoxide as the catalyst. The results of intrinsic viscosity and GPC have proven successful in preparing high molecular weight polyesters. The compositions and the sequence distributions of the copolyesters were determined by analyses of ¹H NMR and ¹³C NMR spectra. The sequence distributions of ethylene succinate units and trimethylene succinate (TS) units were found to be random. Their thermal properties were characterized using differential scanning calorimeter and thermal gravimetric analyzer. All of the copolymers exhibit a single glass transition temperature (T_g). There is no significant difference in the thermal stability among these polyesters. Wide angle X-ray diffractograms (WAXD) were obtained for polyesters which can be crystallized isothermally. The results of thermal analysis and the WAXD patterns indicate that the incorporation of TS units into PES significantly inhibits the crystallization behavior of PES. Additionally, the crystal pattern of PTS is quite different from that of PES. Dynamic mechanical properties of moldable polyesters were investigated using a Rheometer operated at 1 Hz. Below T_g, the incorporation of TS units into PES results in the decline of storage modulus. Above T_g, the effect of crystallinity on the storage modulus can be found.     

Thermal and dynamic mechanical investigations on poly[bis(benzimidazobenzisoquinolinones)]

A series of new semi-ladder poly[bis(benzimidazobenzisoquinolinones)], obtained by the polycondensation of dinaphthalene dianhydrides and aromatic tetraamines was investigated by TG, DSC and DMA methods. The influence of polymer structure on the thermal behaviour of the poly[bis(benzimidazobenzisoquinolinones)] was examined. The polymers were found to be thermally stable with T_d > 723 K in air and T_g ranging from 585 to 701 K. A good agreement was obtained in T_g values measured by DSC and DMA methods. It was found that some cross-linking processes occurred at temperatures above T_g. Some of the isothermal ageing curves were used to find the activation energies of isothermal cross-linking and decomposition.     

Glass transition study of blends of poly(N-methyldodecano-12-lactam) with poly(styrene-co-acrylic acid)

The blends of poly(N-methyldodecano-12-lactam) (MPA) with poly(styrene-co-acrylic acid) (PSAA) prepared from dioxane solutions were studied by differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR). The experimental DSC data of glass transition temperature T_g as a function of composition of amorphous phase were fitted for the as-prepared and re-scanned samples using theoretical approaches. The as-prepared blends show monotonic single-T_g dependence. The values of the Gordon-Taylor coefficient not far from unity suggest miscibility of the blend system in amorphous phase in the whole concentration range. As documented by FTIR, this miscibility is associated with hydrogen bonds between COOH groups of the acrylic acid units in PSAA molecules acting as the H-bond donor and CO groups of MPA acting as the H-bond acceptor. The T_g-dependencies obtained form the second runs have a profound sigmoid character. The Schneider treatment induced an idea of partial limited miscibility in the MPA/PSAA blends caused by prevalence of homogeneous contacts. The difference in T_g between the first and second run can partly be attributed to higher crystallinities in the former.     

Orientation and relaxation in uniaxially stretched styrene-co-methyl methacrylate random copolymers

Orientation and relaxation behavior in uniaxially stretched styrene-co-methyl methacrylate random copolymers was investigated. When compared at a reference temperature T = T_g + constant, orientation of methyl methacrylate units (MMA) decreases while styrene units orientation increases with a decrease in the styrene percentage. This behavior can be related to intermolecular interactions between MMA units and to the stiffness of styrene-MMA units, which do not undergo conformational changes upon stretching. Both monomer units relax the same in a given copolymer and chain relaxation increases when the styrene percentage increases. Orientation relaxation of styrene and MMA units can be reduced to two general relaxation master curves whatever the blend composition, when the results are compared at same monomeric friction coefficient. © 1994 John Wiley & Sons, Inc.     

Dynamic mechanical analysis of multiblock (segmental) polyesterimides

Thermal, deformation-strength, and dynamic mechanical properties of films of segmental polyesterimides prepared from pyromellitic anhydride, aromatic diamines, and poly(butylene adipate) (M _n = 1000) with hydroxy terminal groups were studied. The glass transition points T _g of the samples obtained are below 0°C. The dynamic elastic modulus curves at temperatures higher than T _g are characterized by a portion in which the modulus only weakly depends on temperature.     

Differential thermogravimetric curves for a mixture of evaporable and degradable chain oligomers

Since the boiling point of oligomers increases with increasing chain length, differential thermogravimetric (DTG) curves of polymerization products are uniquely related to the molecular mass distribution of the oligomers in the chain length region in which the degradation rate is less than the rate of evaporation. Degradation is manifested by narrow, chain length-invariant peaks of the DTG curves so that they are distinguishable from broad DTG bands due to the evaporation of the mixture of oligomers. The detachment of the terminal groups at a temperature T₁ and main chain scission at T_d > T₁ are accompanied by dimerization of macroradicals, evaporation of the dimers in the T₁ < T < T_d interval, and appearance of the full degradation peak at T ≈ T_d. The pattern of DTG curves based on these concepts has been calculated on the assumption of free convection in the boundary layer and a spatially uniform degradation in the melt. As an example, DTG curves for the products of tetrafluoroethylene polymerization in liquid solutions have been considered.     

Novel random poly(propylene isophthalate/adipate) copolyesters: Synthesis and characterization

Poly(propylene adipate) (PPA) and poly(propylene isophthalate/adipate) (PPI-PPA) random copolymers of various compositions were synthesized in bulk and characterized in terms of chemical structure and molecular weight. Furthermore, the thermal behavior was examined by thermogravimetric analysis and differential scanning calorimetry. All the polymers showed a good thermal stability. At room temperature they appeared as semicrystalline materials, except the copolymers containing 20 and 30 mol% of PI units: the main effect of copolymerization was a lowering in the amount of crystallinity and a decrease of melting temperature with respect to homopolymers. The crystalline phase of PPI and PPA was evidenced at high content of propylene isophthalate or propylene adipate units, respectively. Amorphous samples were obtained after melt quenching and an increment of T_g as the content of PI units is increased was observed. This behavior was explained as due to the stiff phenylene groups in the polymeric chain. The Wood equation was found to describe well T_g-composition data. Lastly, the presence of a rigid-amorphous phase was evidenced in the copolymers, differently from PPA homopolymer.     

Glass transition temperatures of stereoblock,isotactic and atactic polypropylenes of various chain lengths

The effect of sample molecular weight on the glass transition temperature has been examined for isotactic, stereoblock and atactic polypropylene samples. Asymptotic values of T₉ (∞) (isotactic) = 272°K, T₉ (∞) (atactic) = 266°K, and T_g (∞) (stereoblock) = 266°K were found. Deviation from T_g (∞) was observed when M?_n was below 10⁴; the dependence of T_g on M?_n has been discussed in relation to the Gibbs-DiMarzio treatment of the glass transition. The possible effects of both tacticity and crystallinity on T_g were examined; comparison of the data obtained with those of other workers was made. It was concluded that molecular order in polypropylene samples could affect T_g significantly and that this was particularly obvious in short chain stereoblock fractions.     

Glass transition temperatures of poly(itaconic acid ester)s containing pendant cycloalkyl rings

A series of poly(itaconic acid ester)s with pendant cycloalkyl rings, ranging in size from cyclopropyl to cyclododecyl, have been prepared. Two distinct groups have been synthesized; Group I derivatives have the ring attached directly to the main chain through an oxycarbonyl group and Group II polymers have a methylene unit inserted between the ring and the oxycarbonyl group. The glass transition temperatures, T_g, have been measured for polymers in each group. In Group I, T_g increased with ring size up to the dicyclohexyl derivative, but it then decreased with further increase in ring size. The decrease in T_g is due to the inherent flexibility of the ring which leads to internal plasticization of the sample. This effect appears to predominate over ring size in determining the magnitude of T_g, for 7–12 membered rings. Similar trends have been found in the Group II polymers, but the effect of the ring becomes less important the further it is moved away from the chain backbone.     

Phase transitions and relaxation processes in ethylene-vinyl acetate copolymers probed by fluorescence spectroscopy

The steady-state fluorescence of pyrene and anthracene are used to investigate the relaxation processes of several random ethylene-co-vinyl acetate copolymers, EVA, with defined comonomer compositions (EVA-9, EVA-18, EVA-25, EVA-33 and EVA-40). The temperature of the relaxation processes are compared with those of low-density polyethylene (LDPE) and poly(vinyl acetate) (PVAc). The polymer relaxation processes are assigned to T_g=300-310 K (glass transition temperature of the PVAc); T_α=270-300 K (relaxation processes of the ethylene units present in LDPE and EVA); T_g=220-250 K (glass transition of the LDPE and of the EVA); T_γ or T_β=160-190 K (relaxation processes of interfacial defects of methylenic chains of LDPE and rotation of the acetate group of the PVAc and the EVA); and T_γ=90-130 K (relaxation processes of small sequences of methylene units of LDPE and end groups of PVAc). An Arrhenius-type function was employed as an attempt to represent the experimental data of fluorescence intensity versus temperature above the γ-relaxation temperature. As obtained with other techniques, there is not a simple relationship between the polymer relaxation processes and the vinyl acetate content that can be explained by the morphology in these copolymers.     

Interactions and mobility of copper(II)-imidazole-containing copolymers

Poly(1-vinylimidazole-co-methyl methacrylate) copolymers (PVM) were obtained from copolymerization of 1-vinylimidazole and methyl methacrylate with 2,2^′-azobisisobutyronitrile as an initiator. The formation of random copolymers was substantiated by the glass transition temperature (T_g) and the proton spin-lattice relaxation time in the rotating frame (T^H_1ρ). Cu(II)-PVM complexes were prepared by mixing tetrahydrofuran solution of PVM and copper sulfate solution. The formation of coordination bond between PVM and Cu²⁺ ions was studied using differential scanning calorimetry, infrared and ¹³C solid-stated nuclear magnetic resonance spectroscopy. A single composition dependent T_g was obtained for the PVM copolymers, and that increased with increasing VI content. The T_g value of the Cu(II)-PVM complex was much higher than that of the PVM copolymer with the same composition. The T^H_1ρ of the VI units and MMA units in the copolymers and complexes had one value, and that in the complexes was much lower than that in the copolymers. The dramatic decrease in T^H_1ρ for the Cu(II)-PVM complexes was due to Cu(II) complexation and electron-nuclear dipolar interactions.     

Differential scanning calorimetry study of Ge1−xSnxSe2.5 glasses

The glass-forming tendency and specific heat in ice cold water-quenched Ge_1?xSn_xSe_2.5 glassy alloys with 0H _f, the heat ΔH _c associated with the crystallization of an amorphous phase and the glass transition temperatureT _g were deduced from the DSC curves. The composition dependence of glass forming ability,T _g and crystallization behavior has been discussed.