Thermoelastic and dielectric studies of poly(3,3-dimethyl oxetane) chains

Poly(3,3-dimethyl oxetane) was synthesized by ring opening polymerization of 3,3-dimethyl oxetane. Elongation experiments were performed on unswollen elastomeric networks prepared from this polymer over the temperature range 30–90°C. The changes in the tensile stress while the networks crystallized were examined at various elongations. From thermoelastic data which were free from the effects of network crystallization, the temperature coefficient of the chain dimensions was found to be 1.1 × 10^?3 K^?1 in the vicinity of 60°C. The dipole moment ratio and its temperature coefficient were also measured; the average values of these parameters at 30°C were 0.20₆ and 2.5 × 10^?3 K^?1, respectively. All of these experimental-configuration-dependent properties were critically interpreted in terms of the rotational isomeric-state model. In comparing theory and experiment, conclusions were obtained which confirm earlier results according to which gauche states about C—C skeletal bonds in poly(3,3-dimethyl oxetane) are strongly favored over the alternative trans states.     

Effect of molecular weight and temperature on the isothermal crystallization of poly(oxetane)

Poly(oxetane) fractions ranging in number-average molecular weights from 7800 to 157000 have been isothermally crystallized in the temperature range from –50 to 19 C, using dilatometric and calorimetric techniques. In both cases, reproducible isotherms were obtained with an Avrami exponent equal to three. The crystallization rate against crystallization temperature presents a maximum at –30 C. The level of crystallinity changes with molecular weight and the influence of this parameter on the rate of crystallization is pronounced. The crystallization temperature coefficient was studied using nucleation theory and it was found an slight increase in the basal interfacial free energy for the lowest molecular weight fraction. For the analysis of the temperature coefficient at the higher undercoolings, different approximations for the free energy of fusion and the transport term have been considered. The conclusion of this analysis is that, independently of these approximations, the obtained temperature coefficients are the same.     

Nonisothermal crystallization and melting behavior of a luminescent conjugated polymer,poly(9,9‐dihexylfluorene‐alt‐co‐2,5‐didecyloxy‐1,4‐phenylene)

The nonisothermal crystallization kinetics of a luminescent conjugated polymer, poly(9,9‐dihexylfluorene‐alt‐co‐2,5‐didecyloxy‐1,4‐phenylene) (PF6OC10) with three different molecular weights was investigated by differential scanning calorimetry under different cooling rates from the melt. With increasing molecular weight of PF6OC10, the temperature range of crystallization peak steadily became narrower and shifted to higher temperature region and the crystallization rate increased. It was found that the Ozawa method failed to describe the nonisothermal crystallization behavior of PF6OC10. Although the Avrami method did not effectively describe the nonisothermal crystallization kinetics of PF6OC10 for overall process, it was valid for describing the early stage of crystallization with an Avrami exponent n of about 3. The combined method proposed in our previous report was able to satisfactorily describe the nonisothermal crystallization behavior of PF6OC10. The crystallization activation energies determined by Kissinger, Takhor, and Augis‐Bennett models were comparable. The melting temperature of PF6OC10 increased with increasing molecular weight. For low‐molecular‐weight sample, PF6OC10 showed the characteristic of double melting phenomenon. The interval between the two melting peaks decreased with increasing molecular weight, and only one melting peak was observed for the high‐molecular‐weight sample. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 976–987, 2007     

Polymerization of some sulfur-containing oxetanes

Polymerization under the influence of boron trifluoride of 2-oxa-6-thia[3,3]spiroheptane gives two products: a linear polyether containing oxetane groups and a crosslinked polyether polysulfide. When the polymerization was carried out at ?3°C., up to 60% of soluble polysulfide is obtained. This does not prove that the thietane group polymerizes more rapidly than the oxetane group but rather that oxetane polymerization is inhibited by the presence of thietane groups. Polymerization under the influence of boron trifluoride etherate of 3,3-bis(mercaptomethyl)oxetane leads to a polyether containing free thiol groups. The degree of polymerization of the polymer, however, is low. In order to obtain higher degrees of polymerization several compounds with masked thiol groups were polymerized. 2-Oxa-6,7-dithia-6-thio[3,4]spirooctane and 2-oxa-6,8-dithia-7,7-dimethyl[3,5]-spirononane gave crosslinked products. The diacetate of 3,3-bis(mercaptomethyl)oxetane gave a linear polyether containing thiolacetate groups. Hydrolysis of this polymer leads to poly-3,3-bis(mercaptomethyl)oxetane with a softening temperature of 125–135°C.     

Effect of molecular weight on crystallization and rheological properties of poly(3,3-bis(azidomethyl)oxetane)

Various molecular weight of poly(3,3-bis(azidomethyl)oxetane) were prepared from 3,3-bis(chloromethyl) oxetane. The structure of those were confirmed by Fourier transform infrared, proton nuclear magnetic resonance spectral analysis and gel permeation chromatograph, meanwhile the properties were also compared by X-ray diffraction, differential scanning calorimetry and rheological analysis. The results indicated that increasing molecular weight weakened the crystallization ability of PBAMO and increased the glass transition temperature. Furthermore, the viscosity, shear stress, G′ and G″ of PBAMO increased gradually with increasing of the molecular weight.     

Effects of solvents on the crystallization of dilute poly(ethylene oxide) solutions

The crystallization kinetics of a poly(ethylene oxide) sample with molecular weight of 20 000 was studied in dilute solutions ofn-propanol,n-butanol andn-pentanol by dilatometric methods. The value of the Avrami exponent was observed to change with crystallization temperature in poorer solvents. The temperature coefficient of overall rate was analyzed according to the theory developed for polymer-diluent mixtures. Statistical analysis of data pertinent to overall rate temperature coefficient showed that the end surface free energy _en changes with the thermodynamic quality of the solvent. This is considered to be attributed to the loss in flexibility of polymer chains due to the intramolecular association displayed by poly(ethylene oxide) in its solutions of poor solvents.     

Influence of crystallization temperature,molecular weight,and additives on the crystallization kinetics of poly(ethylene terephthalate)

The spherulite growth rate, the maximum spherulite radius, and the overall rate of crystallization of poly(ethylene terephthalate) (PETP) were measured by means of scattering and transmission of depolarized light. The influence of crystallization temperature, molecular weight, and additives on the above-mentioned quantities was investigated. An expression has been derived for the spherulite growth rate of PETP as a function of crystallization temperature and the number-average molecular weight for M?_n in the range of 19,000 to 39,000.     

Synthesis,crystallization, and morphology of star‐shaped poly(ε‐caprolactone)

Six‐arm star‐shaped poly(ε‐caprolactone) (sPCL) was successfully synthesized via the ring‐opening polymerization of ε‐caprolactone with a commercial dipentaerythritol as the initiator and stannous octoate (SnOct₂) as the catalyst in bulk at 120 °C. The effects of the molar ratios of both the monomer to the initiator and the monomer to the catalyst on the molecular weight of the polymer were investigated in detail. The molecular weight of the polymer linearly increased with the molar ratio of the monomer to the initiator, and the molecular weight distribution was very low (weight‐average molecular weight/number‐average molecular weight = 1.05–1.24). However, the molar ratio of the monomer to the catalyst had no apparent influence on the molecular weight of the polymer. Differential scanning calorimetry analysis indicated that the maximal melting point, cold crystallization temperature, and degree of crystallinity of the sPCL polymers increased with increasing molecular weight, and crystallinities of different sizes and imperfect crystallization possibly did not exist in the sPCL polymers. Furthermore, polarized optical microscopy analysis indicated that the crystallization rate of the polymers was in the order of linear poly(ε‐caprolactone) (LPCL) > sPCL5 > sPCL1 (sPCL5 had a higher molecular weight than both sPCL1 and LPCL, which had similar molecular weights). Both LPCL and sPCL5 exhibited a good spherulitic morphology with apparent Maltese cross patterns, whereas sPCL1 showed a poor spherulitic morphology. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5449–5457, 2005     

Crystallization of poly(tetramethyl-p-silphenylene)-siloxane (TMPS) polymers. Part II

The crystallization kinetics and morphology of poly(tetramethyl-p-silphenylene)siloxane spherulites have been investigated over a temperature range of 25–130°C. The effect of molecular weight on the spherulitic growth rates, ranging from the monomer to molecular weights about 10⁶, is discussed in terms of conventional rate theory. Surface free energies of crystal growth are computed on the basis of a spherulitic model in which the polymer chains are presumed to be incorporated within the lamellar crystallites which are comprised in the spherulites. Mention is made of the change in mechanical properties with molecular weight.     

Poly[3,3-bis(hydroxymethyl) oxetane]—an analog of cellulose: Synthesis,characterization, and properties

Poly[3,3-bis(hydroxymethyl)oxetane], PBHMO, was prepared in high molecular weight (η_inh up to 5.2) by polymerizing the trimethylsilylether of 3,3-bis(hydroxymethyl)oxetane with the i-Bu₃Al–0.7 H₂O cationic catalyst at low temperature, followed by hydrolysis. PBHMO is crystalline, very high melting (314°C) and highly insoluble, much like its analog, cellulose. It is soluble in 75% H₂SO₄ at 30°C, being 65% converted to the acid sulfate ester; these conditions are useful for viscosity measurement, since the degradation rate is low and at least an order of magnitude less than for cellulose in this solvent. PBHMO can be prepared as oriented films and fibers using the lower melting diacetate (184°C) which can be melt or solution (CHCl₃) fabricated and then the oriented forms saponified to oriented PBHMO. BHMO can be directly polymerized to low molecular weight, perhaps somewhat branched, PBHMO (η_inh 0.1) with trifluoromethanesulfonic acid catalyst at room temperature. Poly(3-methyl-3-hydroxymethyloxetane), (PMHMO), prepared in high molecular weight (η_inh up to 3.8) by the same method used for PBHMO, is more soluble and lower melting (165°C) than PBHMO, appears to be atactic and can be compression molded at 195°C to a tough, clear film which is readily oriented. Copolymers of BHMO with MHMO are crystalline over the entire composition range with a linear variation of T_m with composition, a new example of isomorphism in the polymer area.     

Synthesis,crystallization kinetics,and spherulitic growth of linear and star‐shaped poly(L‐lactide)s with different numbers of arms

Well‐defined linear poly(L ‐lactide)s with one or two arms (LPLLA and 2LPLLA, respectively) and star‐shaped poly(L ‐lactide)s with four or six arms (4sPLLA and 6sPLLA, respectively) were synthesized and then used for the investigation of the thermal properties, isothermal crystallization kinetics, and spherulitic growth. The maximal melting temperature, the cold‐crystallization temperature, and the degree of crystallinity of these poly(L ‐lactide) polymers decreased with an increasing number of arms in the macromolecule. Moreover, the isothermal crystallization rate constant (K) of these poly(L ‐lactide) polymers decreased in the order of K_LPLLA > K_2LPLLA > K_4sPLLA > K_6sPLLA2, which was consistent with the variation trend of the spherulitic growth rate (G). Meanwhile, both K and G of 6sPLLA slightly increased with the increasing molecular weight of the polymer. Furthermore, both LPLLA and 2LPLLA presented spherulites with good morphology and apparent Maltese cross patterns, whereas both unclear Maltese cross patterns and imperfect crystallization were observed for the star‐shaped 4sPLLA and 6sPLLA polymers. These results indicated that both the macromolecular architecture and the molecular weight of the polymer controlled K, G, and the spherulitic morphology of these poly(L ‐lactide) polymers. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2226–2236, 2006     

The influence of molecular weight of the donor polymer on the solid-state behavior of interchain EDA complexes

N-(2-hydroxyethyl)carbazolyl methacrylate (HECM) and N-ethyl-3-hydroxymethyl carbazolyl methacrylate (HMCM-2) were polymerized by group transfer polymerization to varying molecular weights of somewhat narrow molecular weight distribution. The thermal behavior of the homopolymers and of their EDA complexes with poly(β-hydroxyethyl-3,5-dinitrobenzoyl methacrylate) (PDNBM-2) was studied as a function of molecular weight. The T_g′s of both polymers and their miscible complexes increase steadily as molecular weight increases and then become constant at about M _n = 6000. Both the PHECM–PDNBM-2 and PHMCM-2—PDNBM-2 systems are thermally reversible miscible networks over all polymer molecular weights. Miscibility is thermodynamically controlled over the entire range of molecular weights in the first system and decomplexation does not occur below the decomposition temperature. However, miscibility is thermodynamically controlled in the second system when the molecular weight of PHMCM-2 is less than 5000, and kinetically controlled for higher molecular weights. The decomplexation temperature or LCST of the PHMCM-2–PDNBM-2 system occurs below the decomposition temperature and increases with decreasing PHMCM-2 molecular weight, in agreement with theoretical predictions on the dependence of LCST on polymer molecular weight.     

Crystallization kinetics of metallocene type polypropylenes

The crystallization kinetics from the melt of metallocene type isotactic poly(propylenes) having the same chain defect concentration and molecular weights ranging from 68480 to 288430 have been studied by differential scanning calorimetry. The crystallization rates and the variation of the rates with crystallization temperature follow a pattern that is basically independent of molecular weight. This result contrasts with the molecular weight dependence on the crystallization rate observed in linear polyethylene, random ethylene copolymers as well as other semicrystalline systems.Most significant is the fact that the metallocene poly(propylenes) show apparently significantly higher _eu products than do the Ziegler type fractions of matched molecular weight and defect concentration. This difference can be interpreted as the metallocene type crystallites having higher effect on surface interfacial free energies than the Ziegler type, or can result from the two different chain types having different sequence propagation probabilities.The work at Florida State University was supported by the Polymer Program, National Science Foundation 94-19508. This support is greatfully acknowledged. MJG wishes to acknowledge support from the National Research Council of Argentina (CONICET).     

Isothermal crystallization behavior of poly(L‐lactide) in poly(L‐lactide)‐block‐poly(ethylene glycol) diblock copolymers

The crystal unit‐cell structures and the isothermal crystallization kinetics of poly(L ‐lactide) in biodegradable poly(L ‐lactide)‐block‐methoxy poly(ethylene glycol) (PLLA‐b‐MePEG) diblock copolymers have been analyzed by wide‐angle X‐ray diffraction and differential scanning calorimetry. In particular, the effects due to the presence of MePEG that is chemically connected to PLLA as well as the PLLA crystallization temperature T_C are examined. Though we observe no variation of both the PLLA and MePEG crystal unit‐cell structures with the block ratio between PLLA and MePEG and T_C, the isothermal crystallization kinetics of PLLA is greatly influenced by the presence of MePEG that is connected to it. In particular, the equilibrium melting temperature of PLLA, T, significantly decreases in the diblock copolymers. When the T_C is high so that the crystallization is controlled by nucleation, because of the decreasing T and thereafter the nucleation density with decreasing PLLA molecular weight, the crystallinity of PLLA also decreases with a decrease in the PLLA molecular weight. While, for the lower crystallization temperature regime controlled by the growth mechanism, the crystallizability of PLLA in copolymers is greater than that of pure PLLA. This suggests that the activation energy for the PLLA segment diffusing to the crystallization site decreases in the diblocks. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2438–2448, 2006     

Thermal degradation of a polyphenylimide-quinoxaline in air and under vacuum

Three samples of poly{2,2′-[N,N′-bis(1,4-phenylene)benzophenone-3,3′,4,4′-tetracarboxylimide-6,6′-bis(3-phenyl-quinoxaline)]} (PPIQ), were prepared, differing in molecular weights and polymer chain endings. Their thermal degradation in vacuo and in air was determined by isothermal weight loss measurements. As in the case of poly-[2,2′-(1,4-phenylene)-6,6′-bis(3-phenylquinoxaline)] (PPQ), the temperature coefficients of thermal degradation in air were independent of molecular weight. However, in contrast, the temperature coefficients were independent of the type of polymer endgroups. It is, therefore, concluded that, contrary to amino-terminated PPQ's, polymer chain-end unzipping of PPIQ is of minor importance during thermal-oxidative degradation.     

Isomorphic behavior of poly(aryl ether ketone) blends

Blends of various poly(aryl ether ketones) have been found to exhibit a range of miscibility and isomorphic behavior. This range is dependent on molecular weight; however, for poly(aryl ether ketones) with number-average molecular weight of 20,000, this range is about ±25% difference in ketone content. All miscible blends exhibit isomorphism, and all immiscible blends exhibit no evidence of isomorphism. The dependence of the glass transition temperature T_g versus composition exhibits a minimum deviation from linearity whereas the melting temperature T_m versus composition exhibits a pronounced maximum deviation from linear behavior. The crystalline melting point versus composition for isomorphic blends is considerably different than for random copolymers with isomorphic units. Homopolymers and random copolymers exhibit a melting point that is a linear function of ketone content (increasing ketone content increases T_m). For blends, the melting point is essentially the same as that of the higher melting constituent until high levels of the lower melting constituent are present. The observed melting point versus composition behavior will be interpreted using classical theory to calculate the components of the liquid and crystalline phase compositions. As a miscible blend is cooled from the melt, essentially pure component of the highest melting point crystallizes out of solution, as predicted by calculated solid-liquid phase diagrams. This occurs until the crystallization is complete owing to spherulitic impingement. At high concentrations of the lower melting constituent, lower melting points will be observed because the highest melting constituent will be depleted before the crystallization is complete. In many miscible blends involving addition of an amorphous polymer to a crystalline polymer, the degree of crystallinity of the crystalline polymer has been shown to increase. On the basis of evidence presented here, it is hypothesized that dilution by a miscible, amorphous polymer allows for a higher level of crystallinity.     

Crystallization behavior of poly(3,3-bisethoxymethyl oxetane) and poly(3,3-bisazidomethyl oxetane)

Two crystal modifications have been found for poly(3,3-bisethoxymethyl oxetane) [poly- (BEMO)] by wide-angle x-ray powder diffraction and differential scanning calorimetry, while only one modification has been found for poly(3,3-bisazidomethyl oxetane) [poly(BAMO)]. Melting temperatures for the two polymers were nearly the same, varying from about 70 to about 90°C depending on the thermal treatment; higher crystallization temperatures resulted in higher melting temperatures. The equilibrium melting temperature T was found to be 125 and 128°C for poly(BEMO) and poly(BAMO), respectively, by using the Hoffman-Weeks extrapolation procedure. Measurement of the melting-point depression of Poly(BEMO) and poly(BAMO) in dibutyl phthalate yielded enthalpy of fusion values of 2.25 and 12.8 kcal/mol, respectively. The percent crystallinity for poly(BEMO) and poly(BAMO), respectively, was calculated to be 55-60 and 13-30% based on DSC and x-ray analysis.     

The effect of molecular weight heterogeneity on the second virial coefficient of linear polymers in good solvents

The effect of molecular weight heterogeneity on the second virial coefficient A₂ in good solvents is studied for binary mixtures of monodisperse poly(α-methylstyrenes). It is concluded that A₂ for polymer mixtures passes through a maximum with variation of the mixing ration. From comparison with the data, it is concluded that no available theory quantitatively explains both the molecular weight dependence of A₂ of monodisperse polymer and the variation of A₂ of mixtures with the mixing ratio. The interpenetration function for two polymer coils with different molecular weights is discussed on the assumption that the thermodynamic interaction between two polymer coils in good solvents can be approximated by a hard-sphere model.     

Poly(dimethyl biphenylene)

Two methods were investigated for the preparation of poly(dimethyl biphenylene) in a search for polymers combining good solubility with sufficiently high chain extension to produce a lyotropic nematic phase. The Ullmann reaction was used to condense 4,4′-diiodo-3,3′-dimethyl biphenyl and the corresponding 2,2′-dimethyl derivative with copper, and 4,4′-dibromo-2,2′-dimethyl biphenyl was polymerized using the coupling reagent, bis(1,5-cyclooctadiene)nickel(0), developed by Semmelhack. The Ullmann polymers were completely soluble in CHCl₃ but only partially soluble in toluene, whereas earlier work had indicated similar polymers of higher molecular weight to be completely soluble in toluene. All the polymers produced were of low molecular weight and no evidence of the nematic phase was found by polarized light microscopy for CHCl₃ solutions over the concentration range 6.8–25% by weight.