Dependence of the cyclization behavior of multifunctional network molecules on molecular size

The tendency for cyclization of nonlinear network molecules is quantitatively expressed by the cyclization probability, defined as the ratio of cyclization to total reaction rate. In contrast to branching, the rate of cyclization depends on the configurational statistical mechanics of segments joining functional groups. Direct integration of the joint configurational probability density in the subspace of encounters yields the distribution of the number of configurationally formed intramolecular functional group encounters (nearest neighbors). Statistically independent network segments are assumed to obey the Gaussian statistics. A recursive relationship for the distribution of chain lengths is developed, and it is shown that for large molecular sizes this relationship tends to a limiting distribution. Corresponding average and standard deviation follow power law dependence on degree of polymerization (DP). With these results, cyclization probabilities are explicitly expressed as functions of DP. When segmental diffusion is the rate controlling factor, cyclization is similar to short range (or primary) cyclization. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 861–870, 2005     

Role of molten fraction on the structural evolution in stretching and cooling of crosslinked low‐density polyethylene: Real‐time mechano‐optical measurements

We investigated the uniaxial deformation behavior of crosslinked low‐density polyethylene in partially and substantially molten states using a real‐time true stress–strain birefringence system. The stress–birefringence behavior exhibits a multiregime behavior during stretching and holding process. The details of this regime behavior are primarily governed by the degree of unmelted crystallinity as it has a dominant role in the long‐range structural connectivity. When the long‐range physical connectivity is present, a three‐regime nonlinear stress–optical behavior was observed. When the long‐range connectivity is substantially eliminated at higher temperatures, the regime I behavior disappears. Structural studies including cooling process reveal that the lower the proportion of molten material during stretching, the higher the concentration of fibrillar structure and the shorter are the lengths of the kebabs that exhibit twisted lamellae after solidification. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1825–1841, 2005     

Synthesis,isolation, and thermal behavior of polybutadiene grafted with poly(2,3,4,5,6‐pentafluorostyrene)

2,3,4,5,6‐Pentafluorostyrene (PFS) was copolymerized with polybutadiene (PB) in tetrahydrofuran using benzoyl peroxide as the initiator at 50, 60, and 80 °C. The copolymerizations follow typical radical polymerization kinetics and behavior. The grafting parameters were evaluated as a function of monomer conversion, initiator concentration, and/or temperature by gel permeation chromatography of directly injected copolymerization mixtures. The grafting efficiencies and grafting ratios are most consistent with a system that terminates by combination and whose graft sites are generated by hydrogen abstraction of allylic radicals by primary initiator radicals. Pure graft copolymers were isolated by extracting unreacted PB into hexanes and PPFS homopolymer into acetone. The similarity of the glass transition temperatures of the PPFS grafts and the corresponding extracted PPFS homopolymers confirms that their lengths are approximately equal. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2874–2891, 2005     

Synthesis and properties of sulfonated poly(arylene ether) containing tetraphenylmethane moieties for proton‐exchange membrane

A novel sulfonated poly(arylene ether) containing tetraphenylmethane moieties was successfully synthesized by the sulfonation of a designed parent polymer using chlorosulfonic acid as sulfonation agent. The sulfonation took place only at the para position on the pendant phenyl rings because of the specially designed parent polymer. The sulfonation degree can be easily controlled by using different ratios of sulfonation agent to polymer repeating unit. The position and degree of sulfonation were characterized by ¹H NMR and elemental analysis. The sulfonated polymers are highly soluble in common organic solvents, such as dimethylsulfoxide, N,N′‐dimethylacetamide, dimethylformamide, ethylene glycol monomethyl ether, and can be readily cast into tough and smooth films from solutions. The films showed good thermal and hydrolysis stabilities. Moreover, Fenton's reagent test revealed that the membrane exhibited superior stability to oxidation. The proton conductivities of the films were determined to be equivalent with Nafion® 117 under same conditions. The new polymer with sulfonic acid function on pendent phenyl rings can be potentially used as a proton‐exchange membrane for polymer electrolyte membrane fuel cell. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6411–6418, 2005     

Synthesis and self‐assembly of highly incompatible polybutadiene–poly(hexafluoropropylene oxide) diblock copolymers

A versatile coupling reaction for the preparation of polybutadiene–poly‐(hexafluoropropylene oxide) (BF) diblock copolymers is described. Six diblock copolymers with different block lengths were characterized by nuclear magnetic resonance spectroscopy and size exclusion chromatography; all six had total molecular weights below 15,000. Microphase separation of the block copolymers in the bulk state was established by small‐angle X‐ray scattering (SAXS) and differential scanning calorimetry. SAXS data suggest that the diblocks are characterized by an unusually large Flory‐Huggins interaction parameter, χ, on the order of 10. However, extraction of χ from the order–disorder transition gave large (order 1) but significantly different values, thereby suggesting that these copolymers are too small and too strongly interacting to be described by block copolymer mean‐field theory. Dynamic light scattering was used to analyze dilute solutions of the title block copolymers in four selective organic solvents; the sizes of the micelles formed were solvent dependent. The micellar aggregates were large and nonspherical, and this is also attributed to the high degree of incompatibility between the two immiscible blocks. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3685–3694, 2005     

Sequence analysis of poly (ether sulfone) copolymers by 13C NMR

Random and block copolymers of poly (ether sulfone) (PES) and poly (ether ether sulfone) (PEES) were synthesized by the nucleophilic polycondensation of 4,4′‐dichlorodiphenyl sulfone (DCDPS) with 4,4′‐dihydroxydiphenyl sulfone (DHDPS) and hydroquinone (HQ). Chemical structures of these copolymers were characterized by ¹³C NMR. The monomer molar fraction, sequential distribution, and degree of randomness of the copolymers were determined through analyses of the resonances of quaternary carbons in the DCDPS unit. Experimental results show that the molar fractions of the comonomer determined by ¹³C NMR analyses are close to the charged values in the synthetic step. Moreover, these copolymers, which were prepared by different polymerization methods, revealed different number‐average sequential length and degree of randomness. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1624–1630, 2005     

Synthesis and molecular structure analysis of nano‐sized methacryl‐grafted polysiloxane resin for fabrication of nano hybrid materials

The molecular structures of methacryl‐grafted polysiloxane resins from 3‐(trimethoxysilyl)propyl methacrylate (MPTS) and diphenylsilanediol (DPSD) were determined by theoretical computation and experimental measurement. The molecular structures obtained from theoretical computation coincided well with those from experimental measurement, and we found that the structural changes in the resins could be controlled by precursor compositions. While molecular weights and polysiloxane chain lengths of the resins increase with DPSD contents, their molecular sizes do not vary significantly. In the present study, molecular sizes and shapes of the resins with various compositions are hypothesized theoretically and proven experimentally. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 827–836, 2005     

Circular dichroism induced by the helical conformations of acylated chitosan derivatives bearing cinnamate chromophores

Through regioselective modifications, some acylated chitosan derivatives, O‐cinnamoyl chitosans with degree of substitution (DS) varying from 0.8 to 2.0 and N‐fatty acyl‐O‐dicinnamoyl chitosans with different fatty acyl chain lengths (C₂–C₁₂), were prepared, and their chiroptical properties in dilute solutions were investigated by circular dichroism (CD). Exciton coupling between two vicinal cinnamoyl chromophores appended to the helical mainchains gave rise to bisignate Cotton effects (CEs), which were used to deduce the absolute sense of the twisting structures in solution phase. It was found that the absolute helicities vary with DS, length of the fatty chain, and solvent property, but are nearly independent of thermal stimulus. The molecular interactions (hydrogen bonding and hydrophobic interaction) involved possibly in the self‐assembled ordered structures were discussed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1354–1364, 2005     

E‐glass/DGEBA/m‐PDA single fiber composites: New insights into the statistics of fiber fragmentation

The interfacial shear strength is a critical parameter for assessing composite performance and failure behavior. This parameter is usually obtained from a single‐fiber fragmentation test that induces sequential fracture with increasing strain of a single embedded fiber with output being the distribution of fragment lengths. An exact analytical form for the expected fragment length distribution is still not known. Such data are often fit empirically to Weibull, shifted‐exponential, or lognormal distribution functions. In this report, new insights into the sequential fiber fracture process are provided by detailed analyses of the fiber break locations along the length of the embedded fiber. From this approach, the high degree of uniformity of the break coordinate loci strongly suggests that there can be no mechanistic rationale for the use of the Weibull, or lognormal, or exponential functions to fit the fragment lengths. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2301–2312, 2009     

Modification of microstructures and physical properties of ultra high molecular weight polyethylene by electron beam irradiation

An ultra high molecular weight polyethylene was irradiated with the electron beam at dose levels ranging from 100 kGY to 1 MGy. The microstructures of the irradiated samples were characterized by FTIR, gel fraction measurement, DSC, and small‐ and wide‐angle X‐ray scattering. For the mechanical properties, a static tensile test and creep experiment were also performed. The crosslinking and the crystal morphology changes were the main microstructural changes to influence the mechanical properties. It was found that 250 kGy appeared to be the optimal dose level to induce crosslinks in the amorphous area and recrystalliztion in the crystal lamellae. At doses above 250 kGy, the electron beam penetrates into the crystal domains, resulting in crosslinks in the crystal domains and reduction in the crystal size and crystallinity. The static mechanical properties (modulus, strength) and the creep resistance were enhanced by the electron beam irradiation. The stiffness rather correlated with the degree of crosslinks while the strength with the crystal morphology. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3019–3029, 2005     

Synthesis and properties of highly branched polycations with an aliphatic polyether scaffold

Cationic polyelectrolytes with pyridinium and 1,2‐dimethylimidazolium functionalities based on a hyperbranched polyglycerol scaffold with a narrow polydispersity were prepared by a polymer analogous reaction in a one‐pot synthesis. By the variation of the spacer lengths between the cationic functionalities and polyether scaffold, a simple method was developed to adjust the charge density and flexibility of the polycations, as reflected by their glass‐transition temperature. The polyelectrolytes were further characterized in detail by ¹H NMR, ¹³C NMR, and IR spectroscopy, as well as thermogravimetric analysis. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4609–4617, 2005     

Synthesis of novel core‐crosslinked graft copolymers from crosslinked poly(mercapto‐thiourethane)

Crosslinked poly(mercapto‐thiourethane) was employed as a precursor for graft copolymer synthesis. The crosslinked stem polymer ( 1 ) was easily prepared by polyaddition of a bifunctional dithiocarbonate and piperazine under air atmosphere via oxidative coupling of mercapto group. Polymerization of styrene and methyl methacrylate in the presence of 1 yielded the corresponding crosslinked graft copolymers with high grafting weight percentages (>1800%). © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5097–5102, 2005     

Response of a biphasic poly(n‐hexyl isocyanate)/p‐xylene solution to applied high electric fields

The effect of a high electric field on a solution of a lyotropic liquid‐crystalline polymer, poly(n‐hexyl isocyanate) in p‐xylene, was studied. The application of a high‐voltage alternating‐current electric field to the biphasic solution resulted in an elongation of the nematic domains in the field direction, the degree of elongation varying approximately with the square of the electric field. At a constant field, the extent of elongation decreased, varying inversely with the frequency in an exponential fashion. The domain structure and thus the molecular orientation were examined to explain these electric field effects. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1124–1133, 2005     

Fundamental kinetic aspects of living radical polymerization and the use of gel permeation chromatography to shed light on them

The control achievable by living radical polymerization (LRP) is based on a kinetic balance of the activation–deactivation reversible reactions, which are specific to LRP, with conventional elementary reactions such as initiation, propagation, and termination. This work describes, as plainly as possible, how chains grow and how their polydispersity evolves as they experience activation–deactivation cycles and how these processes can be quantitatively analyzed by gel permeation chromatography. A comprehensive probability theory on the polydispersity indices of LRP polymers is presented. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4743–4755, 2004     

Hyperbranched polyesters based on polycondensation of 1,3,5‐tris(2‐hydroxyethyl) cyanuric acid and 3,5‐dihydroxybenzoic acid

A series of hyperbranched polyesters was produced by the condensation of the monomer 3,5‐dihydroxybenzoic acid with 1,3,5‐tris(2‐hydroxyethyl) cyanuric acid as a trifunctional central core. The monomer‐to‐core ratio was varied between 3 and 45. The resulting polymers were phenolic‐terminated polyesters. The degree of branching of the polyesters was calculated according to the method described by Fréchet and was found to be in the range of 0.7–0.8. The number‐average molecular weights calculated via ¹H NMR spectroscopic degree‐of‐polymerization values are in reasonable agreement with the predicted values derived from the monomer‐to‐core ratio for all prepared polyesters. Thermal and photophysical properties were also studied. Glass‐transition temperatures were determined by differential scanning calorimetry and were found to be relatively independent of the theoretical molar mass. The polyesters were found to be blue emitters, and the solutions exhibited intense fluorescence, with a maximum of 430 nm. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3278–3288, 2005     

Molecular dynamics of star‐shaped poly(L‐lactide)s in tetrahydrofuran as solvent monitored by fluorescence spectroscopy

Linear telechelic, α,ω‐ditelechelic, and star‐shaped tri‐, tetra‐, penta‐, and hexa‐arm poly(L ‐lactide)s (PLAs) fitted at every arm with pyrene end group have been prepared. Internal dynamics and mobility of the PLA chains in tetrahydrofuran solution at 25 °C, with regard to the number of PLA arms in one macromolecule and the individual arm average degree of polymerization, was followed by fluorescence spectroscopy. Analysis of both static and time‐resolved spectra of the star‐shaped polymers revealed dynamic segmental motion resulting in end‐to‐end cyclization, accompanied by an excimer formation. Probability and rate of the latter reaction increased with increasing number of arms and with decreasing their polymerization degree. Moreover, time‐resolved measurements revealed that for macromolecules containing few arms (2 or 3) the pyrene moieties are located in the interior of the star‐shaped PLAs, whereas in the instance of the higher number of arms (4–6) they are located at the periphery of the star‐shaped PLAs. Thus, increasing the number of arms leads to their stretching away from the center of the star‐shaped PLA macromolecule. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4586–4599, 2005     

Kinetically controlled phase transitions in liquid‐crystalline polymers. III. Influence of the molecular weight and annealing temperature on two‐dimensional K phase formation in a side‐chain polyacrylate

Narrow fractions of a side‐chain acrylate oligomer/polymer with phenyl benzoate side chains are separated in a broad range of the degree of polymerization (7 ≤ P_w ≤ 149). An examination of the phase behavior of the obtained fractions has shown that only the longer macromolecules can form the two‐dimensional K (TDK) mesophase, whereas oligomers of a shorter main chain form the conventional nematic phase only. A critical P_w value has been observed to be necessary for the TDK mesophase formation. The temperatures and enthalpies of liquid‐crystalline phase transitions have been studied as a function of the molar mass, and the phase‐growth kinetics for the TDK phase have been studied with an Avrami treatment. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2352–2360, 2005     

Design,syntheses, and characterization of new thermoplastic polyureas based on 3,4‐ethylenedioxythiophene

New thermoplastic polyureas labeled PUn (n = 2, 3, 4, 6, 7, 9, or 10), based on 3,4‐ethylenedioxythiophene (EDOT) with flexible aliphatic spacers, were synthesized and characterized for the first time. EDOT was chosen as a replacement for the aromatic phenyl group in conventional thermoplastics based on urea linkages to improve solubility without compromising the thermal properties. As synthesized, all the samples exhibited a semicrystalline nature. The glass‐transition and melting temperatures showed a strong dependence on the spacer length. A comparison of the thermal properties of these polyureas with the corresponding phenyl analogues indicated that EDOT was a viable heteroatomic analogue of the phenyl group to be inserted into the main‐chain polyureas without hampering their thermal stability. The polyureas with spacer lengths greater than hexamethylene formed transparent gels in N‐methylpyrrolidone, 1,1,2,2‐tetrachloroethane, and dimethyl sulfoxide. The molecular packing of the polyureas was assigned with wide‐angle X‐ray diffraction studies. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5823–5830, 2005     

Equation of state for high density solid and melt polyethylene

Pressure‐volume‐temperature (PVT) measurements for high‐density linear polyethylene (LPE) are studied experimentally over a temperature range of 290 to 470 K and pressures up to 3.1 kbar. For melt, the results can be represented by the Tait equation within the precision of the data. It is noticed that for each isotherm, an abrupt departure from the Tait representation occurs at a particular pressure. This is ascribed to onset of solidification due to pressure. Further, variation of the degree of crystallinity with pressure at various temperatures has been investigated. Finally, the PVT data has been analyzed in terms of the LJD cell theory in its original form without any modifications or simplifications of the cell potential. Satisfactory agreement is obtained between experiment and theory over the entire range of PVT data both in solids and melt states. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1618–1623, 2005     

Kinetic studies on the thermal polymerization of N‐chloroacetyl‐11‐aminoundecanoate potassium salt

A potassium salt of N‐chloroacetyl‐11‐aminoundecanoate was thermally polymerized to obtain the corresponding poly(glycolic acid‐alt‐11‐aminoundecanoic acid). A kinetic study was then performed that was based on isothermal and nonisothermal polymerizations performed in a differential scanning calorimeter. The complete kinetic triplet was determined (the activation energy, pre‐exponential factor, and integral function of the degree of conversion). A kinetic analysis was performed with an integral isoconversional procedure (free model), and the kinetic model was determined both with the Coats–Redfern method (the obtained isoconversional value being accepted as the effective activation energy) and through the compensation effect. The polymerization followed a three‐dimensional growth‐of‐nuclei (Avrami) kinetic mechanism. Isothermal polymerization was simulated with nonisothermal data. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1166–1176, 2005