Structure–property relationships of poly(vinyl alcohol). II. The influence of molecular regularity on the crystallization–dissolution temperature relationships of poly(vinyl alcohol)

Dissolution temperatures T_s have been determined for poly(vinyl alcohol) (PVA) samples of varying tacticity as a function of crystallization temperatures T_c. From the values of T_s and T_c, one can obtain values of (T_m)_∞, the dissolution temperature of crystals of infinite stepheight. (T_m)_∞ is a characteristic property of a given sample. This method of characterization is very sensitive and reliable for detecting differences in molecular regularity among PVA samples. The variation of (T_m)_∞ with stereoregularity is attributed in part to differences in hydrogen-bonding characteristics. Determinations of the crystallinities of solution-crystallized PVA have shown that stereoregularity in PVA does not result in higher crystallizability.     

Isotactic poly(pentene-1): Form III

A new crystalline form of isotactic poly(pentene-1) was obtained from dilute solution in amyl acetate. We have designated it as form III. The morphology and structure of isothermally crystallized samples were investigated by electron microscopy and electron and x-ray diffraction. This crystalline modification can be indexed on an orthorhombic unit cell (cell dimensions: a = 21.20 ± 0.05 Å, b = 11.48 ± 0.05 Å, c = 14.39 ± 0.05 Å (fiber axis) and probable space group P2₁2₁2₁).     

Soret Coefficients for Aqueous Polyethylene Glycol Solutions and Some Tests of the Segmental Model of Polymer Thermal Diffusion

A thermogravitational cell is used to measure Soret coefficients (s) for dilute binary aqueous solutions of ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, and polyethylene glycol (PEG) fractions with average molecular weights from 200 to 20,000 g-mol^–1. The cell design allows the top and bottom halves of the solution column to be withdrawn and injected into a high-precision HPLC differential refractometer detector for analysis. Previously reported mutual diffusion coefficients D and the measured Soret coefficients are used to calculate thermal diffusion coefficients D _T. s and D vary with the PEG molecular weight M as M ^+0.53 and M ^–0.52, respectively; hence, D _T = sD is essentially independent of M. The segmental model of polymer thermal diffusion predicts D _T = D_seg U _S/RT ², where D _seg is the segment diffusion coefficient, U _S the solvent activation energy for viscous flow, R the gas constant, and T the temperature. The predicted D _T values, although independent of M, are too large by a factor of five. Additional tests of the segmental model are provided using literature data for polystyrene + toluene, n-alkane + CCl₄, and n-alkane + CHCl₃ solutions. Agreement with experiment is not obtained. In particular, the measured D _T values for the alkane solutions are negative.     

Thermoelasticity of networks in swelling equilibrium with mixed diluents: Specific polymer-diluent interactions

Thermoelasticity studies of poly(vinyl alcohol) networks swollen in aqueous glycol indicate that the effects of specific polymer-diluent interactions diminish at high swelling, much as in the situation of poly(vinyl alcohol) in pure water reported earlier. In 20% glycol, the ratio of the energy component f_e of the force to the total force f was found to be ?0.59 at high swelling. Swelling was controlled by the degree of network crosslinking. Evidence that f_e/f could be determined under the condition of a null thermal expansion coefficient was not obtained; in fact, the contrary was indicated.     

Synthesis of polyester having pendent hydroxyl groups via regioselective dehydration polycondensations of dicarboxylic acids and diols by low temperature polycondensation

In this article, we describe the one‐step synthesis of polyesters having pendent hydroxyl groups by Lewis acid‐catalyzed, regioselective, dehydration polycondensations of diols (glycerol and sorbitol) and dicarboxylic acids [tartaric acid (TA) and malic acid (MA)] containing pendent hydroxyl groups, using low temperature polycondensation technique. Direct polycondensations of TA or MA and 1,9‐nonanediol catalyzed by scandium trifluoromethanesulfonate [Sc(OTf)₃] successfully yielded linear polyesters having hydroxyl functionality (M_n = ca. 1.0 × 10⁴). To demonstrate the reactivity of the pendent hydroxyl group, a glycosidation was performed. Poly(nonamethylene L ‐malate) showed significant higher biodegradability, compared with poly(nonamethylene L ‐tartrate) or poly(nonamethylene succinate). Stable poly(nonamethylene L ‐tartrate) emulsion could be prepared using poly(vinyl alcohol) as the surfactant, although emulsions consisting of poly(nonamethylene succinate) were unstable and phase‐separated within a few days. Furthermore, direct polycondensations of TA and diethylene glycol (DEG) or triethylene glycol (TEG) successfully produced water‐soluble polyesters having hydroxyl groups. This new polycondensation system may be extremely effective not only for advanced material design using functional monomers but also for effective utilization of biomass resources as chemical substances. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5747–5759, 2009     

Effects of amorphous poly(vinyl acetate) on crystalline morphology of poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid)

The amorphous and crystalline phase behavior, spherulite morphology, and interactions between amorphous poly(vinyl acetate) (PVAc) and poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid) (PHBV) were examined using differential scanning calorimetry, polarized-light optical and scanning electron, atomic-force microscopy (DSC, POM, SEM, AFM), and small-angle X-ray scattering (SAXS). The PHBV/PVAc blend was found to be miscible with an almost linear T _g-composition relationship, indicating perfect homogeneity. Interaction parameter by melting point depression is a negative value of χ = −0.32, suggesting quite favorable interaction strength. With the intimate interaction between the amorphous PVAc and crystalline PHBV polymers, effects of PVAc on the spherulitic morphology of PHBV are quite significant. Owing to the higher T _g of PVAc (than that of PHBV), the spherulite growth rate of PHBV was depressed by increasing PVAc content in blends. Neat PHBV exhibits ring-banded spherulites when crystallized at T_c = 60 ~ 110^° C {T_{\rm{c}}} = {6}0\sim {11}0^\circ {\hbox{C}} ; however, with increasing PVAc content in the blends, the temperature range at which the PHBV/PVAc blends exhibit ring-banded spherulites remains similar but the regularity increases, and the inter-ring spacing significantly decreases. In addition, the spherulite size and ring-band patterns therein are strongly dependent on T _max (190 vs. 220 °C, respectively, for erasing prior nuclei), from which the blends were quenched to a T _c (60–110 °C) for crystallization. For PHBV/PVAc blends crystallized at the same T _c from different T _max, higher T _max tends to erase nuclei, leading to larger spherulites. However, such larger spherulites owing to higher T _max are not necessarily packed with thicker lamellae.     

Copolymers of vinyl fluoride

Vinyl fluoride was polymerized by photochemical initiation in a continuous-flow cylindrical reactor at room temperature and at pressures of up to 30 atm. Copolymers with vinyl acetate were prepared in order to improve the solubility and processability of poly(vinyl fluoride) (PVF). The copolymers were hydrolyzed to the corresponding vinyl alcohol copolymers and yielded hydrophilic films that are strong and flexible only when swollen by water. It was found that on hydrolysis the T_g, T_m, and heat of fusion as well as degree of crystallinity increased. It was suggested that PVF and the copolymers with vinyl alcohol are isomorphous.     

Charge density effects in salt‐free polyelectrolyte solution rheology

Solution rheology of 2‐vinyl pyridine and N‐methyl‐2‐vinyl pyridinium chloride random copolymers in ethylene glycol was studied over wide ranges of concentration and effective charge. The fraction of quaternized monomers α and the fraction of monomers bearing an effective charge f of these copolymers were measured using counterion titration and dielectric spectroscopy, respectively. Ethylene glycol is a good solvent for neutral poly(2‐vinyl pyridine), with very few ionic impurities. The viscosity η and relaxation time τ of dilute and semidilute unentangled solutions exhibit the scaling with concentration and effective charge expected by the Dobrynin model. Reduced viscosity data are independent of concentration in dilute solution, giving an intrinsic viscosity that depends on effective charge, and the experimental data obey the Fuoss law in the semidilute unentangled regime. Scaling concentration with the overlap concentration (c/c*) reduces these data to common curves, and c* ～ f ^?12/7 as predicted by the Dobrynin model, where f is the fraction of monomers bearing an effective charge. While the overlap concentration depends strongly on effective charge until counterion condensation occurs, the entanglement concentration c_e is surprisingly insensitive to effective charge, indicating that entanglement effects are not understood using the Dobrynin model. The terminal modulus G = η/τ depends only on the number density of chains G = ckT/N for c* < c < c_e, and G ～ c^3/2 for c > c_e independent of the effective charge. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2001–2013, 2006     

The observation of a sub(gel-sol) transition in PVC/DOP gels

Dynamic viscoelastic measurements on poly(vinyl chloride)/dioctyl phthalate gels have been carried out in parallel-plate shear mode. Two transitions are observed: the well-known gel-sol transition at temperature T_f, which probably corresponds to the beginning of fusion of crystalities, and a transition, at a temperature below T_f, denoted as T_s and corresponding to phase separation. The sub(gel-sol) T_s temperature is manifested as the transition from the first plateau zone to a second plateau in log G' versus temperature plots. Other techniques like polarizing microscopy and DSC measurements are not adequate for the detection of T_s.     

Correlation of crack patterns and ring bands in spherulites of low molecular weight poly(<Emphasis Type="SmallCaps">l</Emphasis>-lactic acid)

Only a single type of circular circumferential crack is conventionally reported for poly(l-lactic acid) (PLLA). In this study, PLLA samples were found to exhibit as many as four crack types of different directions and patterns, which cannot be feasibly explained simply by the directional difference in coefficients of thermal expansion. Depending on crystallization temperature (T _c), PLLA crystallizes into ringless or ring-banded spherulites, whereas the crack patterns are dramatically different in these two types of spherulites. In ring-banded spherulites of PLLA crystallized at intermediate T _c, two uniquely different crack types are present: (1) twin circumferential cracks coinciding with the dark–bright and bright–dark boundary and (2) radial short-segmental voids coinciding on the bright bands in spherulites. The radial short-segmental cracks on the bright band of ring-banded spherulites may be caused by PLLA crystals of radial direction with various twisting that contract laterally upon cooling. Only circumferential cracks are present in PLLA crystallized into ringless spherulites, where concentric continuous circumferential cracks are present in the ringless spherulites at low T _c with finer lamellae, but discontinuous and irregular circumferential cracks are present in the ringless spherulites at high T _c with coarse lamellae. Although all cracks are triggered by cooling from T _c, all evidences indicate that the crack patterns and types are highly associated with the lamellar orientation, patterns, and coarseness in spherulites.     

1H NMR relaxation study of polymer-solvent interactions during thermotropic phase transition in aqueous solutions

The dynamic-structural changes and polymer - solvent interactions during the thermotropic phase transition in poly(vinyl methyl ether) (PVME)/D₂O solutions in a broad range of polymer concentrations (c = 0.1-60 wt.-%) were studied combining the measurements of ¹H NMR spectra, spin-spin (T₂) and spin-lattice (T₁) relaxation times. Phase separation in solutions results in a marked line broadening of a major part of polymer segments, evidently due to the formation of compact globular-like structures. The minority (∼15%) mobile component, which does not participate in the phase separation, consists of low-molecular-weight fractions of PVME, as shown by GPC. Measurements of spin-spin relaxation times T₂ of PVME methylene protons have shown that globular structures are more compact in dilute solutions in comparison with semidilute solutions where globules probably contain a certain amount of water. A certain portion of water molecules bound at elevated temperatures to (in) PVME globular structures in semidilute and concentrated solutions was revealed from measurements of spin-spin and spin-lattice relaxation times of residual HDO molecules.     

The relation between the microphase separation transition and the glass transition in diblock copolymers

The microphase separation transition (MST) has been studied for short chain diblock copolymers poly(styrene-b-isoprene) and poly(styrene-b-mma). A detailed analysis of small-angle x-ray scattering (SAXS) profiles in the homogeneous phase allows determination of the interaction parameter and the spinodal temperature T_s of the MST. T_s for the PS/PI diblocks is found to be lower than the glass transition temperature of their hard blocks. This results in a coupling of the MST and the glass transition. Using both structural (SAXS) and thermal differential scanning calorimetry (DSC) methods it is shown that an endothermal peak found in the DSC diagrams is related to the combined effect of the MST and the glass transition. © 1992 John Wiley & Sons, Inc.     

Formation of interpenetrated spherulites based on miscible crystalline polymer blends

The morphology and formation process of interpenetrated spherulites of poly(butylene succinate)/poly(vinylidene choloride‐co‐vinyl chloride) (PBSU/PVDCVC) blends were investigated by confocal laser scanning microscopy (CLSM). CLSM images showed that the dense fibrils of PBSU spherulites penetrated into the sparse PVDCVC spherulites. For a blend with PBSU content 50% and crystallization temperature T_c = 368 K, the simultaneous growth of PBSU and PVDCVC spherulites was observed. After PBSU fibrils collided with PVDCVC spherulites, they kept growing through PVDCVC spherulites. For a blend with PBSU content 30% and T_c = 363 K, PBSU started to nucleate after PVDCVC spherulites filled the whole space.     

Propagation/depropagation equilibrium and structural factors in the radiation degradation of poly(olefin sulfone)s

The principal volatile products observed after γ irradiation of nine different poly(olefin sulfone)s in the solid state were the two comonomers, i.e., the respective olefin and sulfur dioxide. An exponential increase in yield, G(volatile products), with increasing irradiation temperature, T_irr, was observed for each copolymer through the ceiling temperature, T_c, for the corresponding propagation/depropagation equilibrium. Thus the G value increased by ca. 3 orders of magnitude from T_irr = 0.7 T_c to T_irr = 1.3 T_c for all of the poly(olefin sulfone)s. Depropagation sensitivity was considered to be best measured by G(SO₂) since radiation induced, cationic homopolymerization of the product olefin occurred to a variable extent. Five of the poly(olefin sulfone)s had similar rates of depropagation at their respective T_c's but the polysulfones of 1-hexene, cyclohexene and 2-butene showed anomalously high depropagation rates. This may be related to greater steric hinderance to segmental chain mobility in the polysulfones of the 1,2 disubstituted olefins. Poly(1-hexene sulfone) appears to be anomalous, as in other respects.     

Modeling the vapor–liquid equilibria of polymer–solvent mixtures: Systems with complex hydrogen bonding behavior

The vapor–liquid equilibria of binary polymer–solvent systems was modeled using the Non-Random Hydrogen Bonding (NRHB) model. Mixtures of poly(ethylene glycol), poly(propylene glycol), poly(vinyl alcohol) and poly(vinyl acetate) with various solvents were investigated, while emphasis was put on hydrogen bonding systems, in which functional groups of the polymer chain can self-associate or cross-associate with the solvent molecules. Effort has been made to explicitly account for all hydrogen bonding interactions. The results reveal that the NRHB model offers a flexible approach to account for various self- or cross-associating interactions. In most cases model's predictions (using no binary interaction parameter k_ij = 0) and model's correlations (using one temperature independent binary interaction parameter, k_ij ≠ 0) are in satisfactory agreement with the experimental data, despite the complexity of the examined systems.     

Viscoelastic behaviors and molecular motions of highly syndiotactic poly(vinyl alcohol) fibers

The viscoelastic behavior and molecular motion of highly syndiotactic poly(vinyl alcohol) (S‐PVA) fibers with a dyad syndiotacticity (r) of 69% were studied by dynamic mechanical thermal analysis and wide‐angle X‐ray diffraction and compared with those of atactic poly(vinyl alcohol) (A‐PVA) fibers with r = 54%. The β_c dispersion, based on the molecular motion of the chain molecules in the crystalline regions, was observed for A‐PVA around 120–140 °C, and the only primary (α_c) dispersion was observed for S‐PVA around 180 °C. The thermal expansion coefficients for the a and c axes of the A‐PVA crystal changed discontinuously around 120 °C, which corresponded to the β_c dispersion. For S‐PVA, the coefficient for the (002) plane changed discontinuously around 100 °C, similarly to A‐PVA, but that for the (100) plane remained unchanged between 20 and 220 °C. These results showed that the intermolecular hydrogen bonding of S‐PVA was stronger in the direction of the a axis than in the other directions, suppressing the β_c dispersion. The storage modulus and thermal expansion coefficient of the (020) plane (molecular axis) of S‐PVA decreased markedly around 180 °C, and this indicated that the α_c dispersion was due to the torsional motion of the molecular chains in the crystalline regions. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 800–808, 2004     

Miscibility and thermal stability of poly(vinyl alcohol)/chitosan mixtures

The miscibility and the thermal behaviour of chitosan acetate (ChA) with poly(vinyl alcohol) (PVA) have been investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA). Chitosan is blended with poly(vinyl alcohol) in acetic acid solution and this solution is cast to prepare the blend film. From thermal curves the thermal transitions: T_g, T_m and characteristic temperatures of decomposition: T_di, T_max have been determined and compared. The influence of the degree of PVA hydrolysis on the thermal properties of blend systems has been discussed.Based upon the observation on the DSC analysis, the melting point of PVA is decreased when the amount of ChA in the blend film is increased. Though some broadening of the transition curves could be noticed (DSC, TGA and DMA), the obtained results suggest that in the solid ChA/PVA blends the components are poorly miscible. Only PVA sample with relatively low DH = 88% and hence low degree of crystallinity shows partial miscibility with ChA of relatively low molecular weight.     

Critical surface tension of poly(vinyl butyral) and poly(vinyl benzal) multilayers and its relation to their surface orientation. I. Effect of surface pressures during deposition

Critical surface tensions γ_c of poly(vinyl butyral) and poly(vinyl benzal) multilayers built up by the Langmuir-Blodgett method were measured with polyhydric alcohols and n-alkanes. The γ_c values of both polymer multilayers increased with increasing pressures of the piston oils used to control pressures of polymers on the water surface during deposition. The γ_c value of poly(vinyl butyral) multilayers built up to lower pressure of the piston oil was approximately consistent with a crystalline hydrocarbon surface, while the γ_c value of the multilayer built up to higher pressure of the piston oil was approximately consistent with a—CH₃ rather than a ? CH₂ ? CH₂? surface. All results for γ_c values of poly(vinyl benzal) multilayers were very close to the γ_c value of benzene ringrich surface. The γ_c value of the multilayer built up to lower pressure of the piston oil almost coincided with the γ_c value for amorphous polystyrene, while the γ_c value for the multilayer built up to higher pressure of the piston oil was in fair agreement with γ_c for an aromatic ring edge in the crystalline state. Values of γ_s^d, the dispersion force contribution to the surface free energy of multilayers calculated by Fowkes' relation, were in fair agreement with the corresponding observed γ_c values, respectively. It is concluded from these measurements that orientations and surface structures in both polymer multilayers are affected by pressure change of piston oils. The properties on monolayers of two polymers at a air-water interface and on barium stearate multilayers are also presented.     

Internal plasticization of poly(vinyl) chloride using glutamic acid as a branched linker to incorporate four plasticizers per anchor point

Internal plasticization of polyvinyl chloride (PVC) using thermal azide‐alkyne Huisgen dipolar cycloaddition between azidized PVC and electron‐poor acetylenediamides incorporating a branched glutamic acid linker resulted in incorporation of four plasticizing moieties per attachment point on the polymer chain. A systematic study incorporating either alkyl or polyethylene glycol esters provided materials with varying degrees of plasticization, with depressed T_g values ranging from ?1 °C to 62 °C. Three interesting trends were observed. First, T_g values of PVC bearing various internal plasticizers were shown to decrease with increasing chain length of the plasticizing ester. Second, branched internal plasticizers bearing triethylene glycol chains had lower T_g values compared to those with similar length long‐chain alkyl groups. Finally, thermogravimetric analysis of these internally plasticized PVC samples revealed that these branched internal plasticizers bearing alkyl chains are more thermally stable than similarity branched plasticizers bearing triethylene glycol units. These internal tetra‐plasticizers were synthesized and attached to PVC‐azide in three simple synthetic steps. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 1821–1835