Effects of diluent on molecular motion and glass transitions in polymers. III. The system poly(vinyl acetate)–toluene

Dielectric measurements, differential thermal analyses (DTA), and broad-line proton magnetic resonance (NMR) measurements are reported on the system poly(vinyl acetate)–toluene. Four dielectric relaxations were observed between 80 and 400°K. From proton NMR measurements on solutions in toluene and in deuterated toluene, the relaxation processes can be assigned, respectively, to segmental motion of poly(vinyl acetate), α; motion of side group, β′ rotation of toluene, β; local motions of poly(vinyl acetate) and toluene, γ, in order of appearance with decreasing temperature. Two stepwise changes in DTA traces have been observed and can be assigned as glass transition points T_gI and T_gII. Comparison of these glass transition points with temperatures at which dielectric relaxation times for the α and β processes are 100 sec, indicate that segmental motion of poly(vinyl acetate) and rotation of toluene are frozen-in at T_gI and T_gII, respectively. Activation plots for the α process conform to the Vogel–Tamman equation. In terms of the parameters A, B, and T₀ of the equation, T_gI can be represented by an expression of the form T_gI ≈ T₀ + B/(A + 3). In the range of concentration above 50% by weight, A and B are almost independent of concentration but T₀ varies strongly. The nature of the secondary dispersions is also discussed.     

Diluent effects on molecular motions and glass transition in polymers. I. Polystyrene–toluene

The effects of diluent on molecular motions and glass transition in the polystyrene–toluene system was studied by means of dielectric, thermal, and NMR measurements. Three dielectric relaxations were observed between 80 and 400°K. On the basis of NMR measurements on solutions in toluene and in deuterated toluene, relaxation processes were assigned to segmental motions of polystyrene, rotations of toluene, and the local motions of polystyrene and toluene in order of appearance from the high-temperature side. The concentration dependence of the relaxation strength and of the activation energy for the primary relaxation (that at the highest temperature) show a step increment at about 50% by weight. The activation plots for the primary process were expressed by the Vogel–Tamman equation. With this equation, the temperatures at which the mean dielectric relaxation time becomes 100 sec is determined. This agrees well with the glass-transition temperature T_g and hence T_g in concentrated solution is expressed by in terms of the parameters A, B, and T₀ of the Vogel–Tamman equation. The values of A and B are, respectively, about 12 and 0.65 and independent of the concentration. The physical meaning of these parameters is discussed.     

Coupling of the overall molecular motion with the conformational transitions. II. The full rotational problem

The method proposed in the companion paper for analysing the coupling between overall and internal dynamics is applied to the study of the full rotational motion of a molecule with one internal degree of freedom. For systems characterized by a finite set of stable conformers determined by the minima of the intramolecular potential, a simplified time evolution operator of mixed type is derived, with the continuous diffusion equation and the generalized random walk operator representing the overall rotation and the internal dynamics, respectively. The dependence on the conformational state of the rotational diffusion tensor is one source of coupling between these two types of motion. Another source is represented by the recoil rotations acting on each subunit during a conformational transition. Both conformational-dependent rotational diffusion tensors and recoil rotations can be calculated from a model for the friction exerted by the solvent. Some applications of the theory are presented in relation to the butane molecule and the molecules having the structure of biphenyl, with particular emphasis on the calculation of the experimental observables in NMR and dielectric relaxation measurements.     

The crystallization of polymer–diluent mixtures

A theory pertinent to the nucleation of polymer-diluent systems for molecules of finite molecular weight has been developed. These results have been applied to the crystallization from polyethylene-α-chloronaphthalene mixtures using molecular weight fractions of polyethylene ranging from 4,000 to 250,000. This analysis is carried out over the composition range extending from pure polymer to a polymer fraction of 0.30. According to this theory, the interfacial basal free energy decreases as either the molecular weight or diluent concentration decreases.     

Functional polymers with cyclic ether moieties. II. Synthesis and properties of network polymers with tetrahydrofuran moiety

A tetrahydrofuran (THF)‐containing network polymer was prepared by the radical suspension copolymerization of a styrene (St)‐type monomer with THF moiety, St, p‐chloromethylstyrene, and divinylbenzene in a biphasic medium consisting of water and monochlorobenzene in the presence of acacia gum as a suspension stabilizer. The diameters of the obtained polymer beads ranged from 100 to 200 μm. The obtained network polymer showed higher swelling abilities in various organic solvents than a similarly prepared network polymer without THF moiety, and it was stable under oxidative, reductive, and basic conditions. In its derivations to polystyrene‐based resins with thioether alcohol and hydroxyl moiety, remarkable accelerations of reactions were observed as a result of the introduction of THF moiety. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 800–806, 2001     

Viscoelastic properties of entangled polymers. II. The interchain–intrachain entanglement model

Our earlier model of entangled chain dynamics represented the elastic effects at entanglement points as a coupling with the surrounding medium, which was propagated weakly to every other entanglement site on the parent chain. In this way, a great variety of linear viscoelastic phenomena could be successfully predicted, with the only significant deficiency being a quantitative failure in curve fitting the local minimum in dynamic loss modulus G″(ω). Here we introduce the “intrachain entanglement,” or the “internal entanglement,” in which the parent chain entangles directly with itself. Elastic forces between pairs of internal entanglements are assumed to be stronger than those with the medium (“external entanglement”). Predictions of the new model are compared with rheological data on monodisperse polystyrene. Good agreement is obtained between theory and experiment, including G″(ω).     

Exactly alternating silarylene–siloxane polymers. II. The condensation polymerization of arylenedisilanols and bisureidosilanes

A new method for the preparation of exactly alternating silarylene–siloxane polymers by the low temperature step-growth condensation polymerization reaction of arylenedisilanols and bisurei-dosilanes in chlorobenzene was investigated. To obtain high molecular weight products ¹H NMR spectroscopy and gel permeation chromatography were used to monitor the polymerization reaction. By using these procedures 12 different polymers were prepared from 1,4-bis(dimethylhydroxysilyl)-benzene, 4,4′-bis(dimethylhydroxysilyl)phenyl ether, bis(1,1-tetramethylene-3-phenylureido)-dimethylsilane, and bis(1,1-tetramethylene-3-phenylureido)-methylvinylsilane monomers. The polymers were obtained in high yields, purities, and molecular weights.     

Internal motion in organosilicon polymers. II. Dimethylpolysilazanes crosslinked through silicon

An investigation of the internal motion in organosilicon polymers by wideline nuclear magnetic resonance has been extended to a pair of dimethylpolysilazanes crosslinked through trifunctional silicon. The data suggest that there is considerable internal motion in all silazanes at 77°K. Evidence is presented for the presence of C₃ rotation of the methyl groups, as well as rotation or torsional oscillation of the Si(CH₃)₂ groups about the polymer backbone. Upon warming the NMR line is seen to narrow, and this is associated with the onset of additional motion, including chain translation and chain flexing or bending. Crosslinking through silicon increases the barrier to chain translation while decreasing the barrier to chain flexing or bending.     

Infrared spectroscopic studies of polymer transitions. III. Effects of sodium ion on glass transitions in styrene-based ionomers

The glass transition in styrene-based ionomers was investigated by means of infrared spectroscopy and differential scanning calorimetry (DSC). Transition temperatures were determined from the temperature dependence of the peak absorbances of the 1700 and 1745 cm^?1 bands. These transition temperatures agreed with glass transition temperatures (T_g) determined by DSC. With increasing degree of ionization, T_g and the enthalpy ΔH of the residual intermolecular hydrogen bonding increased. The values of T_g obtained were analyzed by the theory of Fox and Loshaek for the effect of crosslinks. It is concluded that sodium ions probably from ionic domains and act as crosslinks to reinforce the residual hydrogen bonding and may increase T_g. The absorbance at 1560 cm^?1 (ν_COO^?) did not change at T_g. This suggests that the glass transition observed here is not due to the onset of the mobility in ionic domains, as has been proposed for ethylene-based ionomers on the basis of dielectric measurements.     

Intumescent flame retardants for polymers. IV. The polycarbonate–aromatic sulfonates system

The mechanism of action of aromatic sulfonates as flame retardant (FR) agents on poly(bisphenol-A carbonate) (PC) has been investigated. These compounds are capable of inducing a self-extinguence in PC even when present in very low amounts (0.2–1%). Thermogravimetric and flash pyrolysis–GC–MS data show the thermal degradation rate of PC enhanced, and the distribution of the volatile pyrolysis products was modified by these additives. Oxygen Index (OI) and Nitrous Oxide Index (NOI) measurements indicate a FR condensed-phase mechanism of these additives. Traces of polymer surface temperature against time, measured under forced flame conditions, show that the expanded carbon layer formed in the combustion of polycarbonate–aromatic sulfonate blends produces a heat insulating effect toward the undecomposed bulk. The overall evidence leads us to conclude that aromatic sulfonates cause the flame extinguishment in polycarbonate by an intumescent phenomenon.     

Selective oxidation of tetrahydrofuran with molecular oxygen catalyzed by polyalumazane–platinum complexes

Tetrahydrofuran (THF) was oxidized selectively with molecular oxygen catalyzed by magnesium oxide-based polyalumazane-supported platinum complexes under mild conditions. The selective oxidation of C–H bond α to the oxygen atom of ether and the oxidative path to ester other than ring cleavage to carboxylic acid were controlled by carrying out the reaction at 60°C with nitroethane as solvent. The platinum loading and the reaction time greatly affected the yield of γ-butyrolactone whereas the selectivity always remained at 100%. 76.92% γ-butyrolactone was obtained with 0.2811 mmol platinum loading per gram support within 12 hr. The single product of the THF oxidation was confirmed by ¹H-nuclear magnetic resonance. X-ray photoelectron spectroscopy data also confirmed the more recent report on the activation of the C–H bond by the null valent platinum from the viewpoint of supported platinum catalyst. The oxidation path was also suggested.     

Structure of diepoxide–diamine network polymers. II. Soluble chemical species

Gel permeation chromatography has been used to separate diepoxide–diamine oligomers, produced at a variety of stoichiometric ratios, into individual chemical species. Probability theory has been applied to calculate expressions for the amounts of each of these compounds and close agreement has been found with the experimental results. In conjunction with previous conclusions, this provides compelling evidence in favor of a purely random reaction mechanism, contrary to the inhomogeneous network-forming mechanism suggested by other workers. The effect of adding an inert diluent prior to reaction has been investigated and it is evident that the fraction of intramolecularly formed bonds increases as the concentration of polymer decreases.     

Controlling molecular mobility and ductile–brittle transitions of polycarbonate copolymers

To control molecular mobility and study its effects on mechanical properties, we synthesized two series of poly(ester carbonate) and polycarbonate copolymers with different linkages: (B_xt)_n (x = 3, 5, 7, 9) and (B_xT)_n (x = 1, 3, 5, 7, 9), where t represents the terephthalate, T represents the tetramethyl bisphenol A carbonate linkages, and B is the conventional bisphenol‐A (BPA) carbonate. These two series of materials have distinct differences in their relaxation behaviors and chain mobility, as indicated by the π‐flip motion of the phenylene rings in the B_x blocks. Uniaxial tensile tests of the copolymers indicate that the brittle–ductile transition (BDT) temperatures of the copolymers are correlated to whether the γ‐relaxation peaks due to the B_x sequence is fully established. The materials possessing more fully established low‐temperature γ peaks give rise to a lower BDT. Also, the locations of the γ peaks are correlated to the ring flips of the B_x blocks of polymer chains. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1730–1740, 2001     

Kinetics and mechanism of the cationic polymerization of tetrahydrofuran in solution. I. THF–CCI4 system

Polymerization of THF in CCl₄ solvent was initiated with 1,3-dioxolan-2-ylium eations with AsF₆^?, PF₆^?, and SbF₆^? anions as well as with esters of fluorosulfonic and trifluoromethanesulfonic acids. With these esters polymerization proceeds with a marked acceleration period, due to slow initiation. The corresponding rate constants of initiation and their dependence on the polarity of the THF/CCl₄ mixture were determined. The rate constant of propagation on the macroion-pairs (k_p^±) of the polytetrahydrofurylium cation with AsF₆^?, PF₆^?, and SbF₆^? and CF₃SO₃^?, anions was found to be independent in CCl₄ solvent on the anion structure and given by the expression: k_p^± = 2.93 × 10^?2 exp {?4.7 × 10³/T} at [THF]₀ = 8.0M. This constant depends on the polarity of the polymerization mixture, and at 25°C for the THF-CCl₄ system, k_p^± = 1.78 × 10^?2 exp {?4.9/D}; thus, in CCl₄ at [THF]₀ = 8.0M, and at 25° k_p^± = 4.0 × 10^?21/mole-sec. In the polymerization with derivatives of CF₃SO₃H (able to form the corresponding macroester) the overall polymerization rate is much lower than that with complex anions because of the reversible conversion of the macroion-pairs into the macroester (internal return). The macroester is much less reactive than the macroionpair (10²–10³ times) in the monomer addition reaction. At [THF]₀ = 8.0M and at 25°C, 96.5% of the growing species exists in the macroester form. Polymerization of THF initiated with derivatives of CF₃SO₃H is a subject of a strong special salt-effect. At a sufficiently high ratio of [AgSbF₆] to [I]₀, where the initiator I is C₂H₅OSO₂CF₃, the overall polymerization rate is equal to that observed for the polymerization of THF on the macroion-pairs, since the internal return within the triflate ion-pair (the macroester formation) is eliminated and polymerization proceeds on the macroion-pairs with SbF₆- anions exclusively.     

Polyisobutylene-containing block polymers by sequential monomer addition. II. Polystyrene–polyisobutylene–polystyrene triblock polymers: Synthesis,characterization, and physical properties

New linear and three-arm star thermoplastic elastomers (TPEs) comprising a rubbery polysobutylene (PIB) midblock flanked by glass polystyrene (PSt) blocks have been synthesized by living carbocationic polymerization in the presence of select additives by sequential monomer addition. First, isobutylene (IB) was polymerized by bi- and trifunctional tert-ether (dicumyl- and tricumyl methoxy) initiators in conjunction with TiCl₄ conintiator in CH₃Cl/methylcyclohexane (MeCHx) (40/60 v/v) solvent mixtures at ?80°C. After the living, narrow molecular weight, distribution PIB (M?_w/M?_n = 1.1-1.2) has reached the desired molecular weight, styrene (St) together with an electron pair donor (ED) and a proton trap (di-tert-butylpyridine, DtBP) were added to block PSt from the living chain ends. Uncontrolled initiation by protic impurities that produces PSt contamination is prevented by the use of DtBP. PSt-PIB-PSt blocks obtained in the absence of additives are contaminated by homopolymer and /or diblocks due to inefficient blocking and initiation by protic impurities, and exhibit poor physical properties. In contrast in the presence of the strong ED N,N-dimethylacetamide (DMA) and DtBP the blocking of St from living PIB chain occurs efficiently and block copolymers exhibiting good mechanical properties can be prepared. Virgin TPEs can be repeatedly compression molded without deterioration of physical properties. The products exhibit a low and a high temperature T_g characteristic of phase separated PIB and PSt domains. Transmission electron microscopy of linear triblocks containing ～ 34 wt % PSt also indicates microphase separation and suggests PSt rods dispersed in a PIB matrix.     

Block polymers from isocyanate-terminated intermediates. II. Preparation of butadiene–ϵ-caprolactam and styrene–ϵ-caprolactam block polymers

Polystyrene–nylon 6 and polybutadiene–nylon 6 block copolymers have been prepared from isocyanate-terminated prepolymers. From extraction and fractionation data the products obtained were found to be mixtures of both homopolymers and pure block copolymer. The polybutadiene–nylon 6 copolymers are extremely pliable at ambient temperatures even at high ?-caprolactam contents (70–80 wt-%). This is true even though these copolymers show a crystalline melting point at 213°C similar to poly-?-caprolactam. Presumably this unusual behavior occurs because of the nature of the synthesis which renders the butadiene portion of these copolymers the continuous phase. Plasticity measurements indicate that pliability is dependent on the molecular weight of the block poly-?-caprolactam.     

Studies on the nature of multiple glass transitions in low acrylonitrile,butadiene–acrylonitrile rubbers

A study of the occurrence of multiple glass transitions in acrylonitrile–butadiene rubbers (NBR) has been made. Copolymerization theory was used to predict the change in comonomer composition with conversion for comonomer ratios both above and below the calculated azeotropic composition of 64% butadiene/36% acrylonitrile by weight. The results of these calculations suggested that multiple glass transitions, which occur only in NBR of less than 36% acrylonitrile, were due to an incompatibility of copolymer species of divergent comonomer compositions. This was shown by differential thermal analysis to be the case for various experimental polymers of known comonomer composition. A series of NBR's was prepared by incremental addition of acrylonitrile monomer during polymerization, and the resultant glass transition temperatures were evaluated. Results obtained showed that experimental samples which had single glass transitions also had a much narrower spread of comonomer species than the corresponding rubber polymerized with the use of full initial charge of both monomers. The data indicate that NBR's having a single glass transition, regardless of acrylonitrile content, may be prepared by incremental addition of acrylonitrile monomer during polymerization. Existing copolymerization theory appears to be adequate for predicting incremental monomer addition schedules suitable for the polymerization of NBR's having a single glass transition.     

The chemistry of THPC–urea polymers and relationship to flame retardance on wool and wool-polyester blends. I. Chemistry of THPC–urea polymers

Polymer formation from THPOH-urea, THPOH-dichloropropanol-urea, and THPC-urea was studied. Order and rate of urea addition were shown to influence insoluble polymer yields as well as polymer structure. The polymers were characterized by elemental analyses and infrared spectroscopy, and predominant structures proposed. The structures were correlated with thermogravimetric and differential scanning calorimetry data and probable thermal decomposition paths.