Molecular weight distribution of commercial PVC

The molecular weight distribution (MWD) of commercial suspension grade poly(vinyl chloride) (PVC) resins with K values from 50 to 93 and mass grade PVC resins with K values from 58 to 68 has been determined by size exclusion chromatography (SEC), using literature Mark‐Houwink coefficients. The MWD is characterized by the number average molecular weight (M_n), the weight average molecular weight (M_w) and the polydispersity (M_w/M_n). Our results for M_w are consistent with recently published data, but we find different results for M_n and consequently for M_w/M_n. The polydispersity of PVC increases with increasing K value. This effect can be explained by two mechanisms. The first mechanism is a reduced terminating reaction rate between two growing polymer chains (disproportionation) at higher molecular weight owing to the reduced mobility of the polymer chains. The second mechanism is long‐chain branching of molecules with high molecular weight which lets the molecules grow at two ends. For two examples graphs of the measured MWD are compared with the theoretically expected MWD.     

Molecular weight distribution of commercial emulsion grade PVC

At first glance the molecular weight distributions (MWDs) of suspension and emulsion grade PVC are very similar. However, studying the MWDs for both polymerization technologies in more detail reveals systematic differences that can be explained by the differences in the polymerization processes. The MWD of continuous emulsion PVC is broader than that of batch emulsion PVC, which, in turn, is broader than that of suspension PVC. When correlating molecular weight data to K values, it has to be considered that K values from resins including polymerization additives are different from the K value of the pure polymer. The knowledge of the differences in MWD may be helpful for estimating differences in other properties of the products.     

Ultra-high molecular weight PVC resins

Ultra-high molecular weight PVC resins have properties similar to conventional homopolymer resins, except for a few significant differences. Compounds utilizing these polymers display improved toughness qualities and utility in a wider temperature range. These upgraded properties, combined with the usual advantages of PVC such as colorability, processability, and chemical resistance, should permit these PVC compounds to enter markets previously excluded. New potential markets suggested are footwear utilizing the lighter weight advantage of these tougher compounds, automotive under-the-hood applications that employ the broader temperature properties, and replacements for elastomers in gasket and compounds used in automotive and appliance applications.     

Studies in the molecular weight distribution of epoxide resins. IV. Molecular weight distributions of epoxide resins made from bisphenol a and epichlorohydrin

The molecular weight distribution of epoxide resins made from bisphenol A and epichlorohydrin at high ratios of epichlorohydrin to bisphenol A are compared with the theoretically predicted distributions for two theoretical models: the “taffy” process A, the direct reaction of epichlorohydrin with bisphenol A; and the “taffy” process B, the self-polymerization of a monoglycidyl ether of bisphenol A followed by postglycidylation. At high ratios of epichlorohydrin to bisphenol A, process B is shown to give more low molecular weight products than process A. Deviations of the experimentally measured distributions from the theoretically predicted distributions for high epichlorohydrin/bisphenol ratios are attributed to the higher reactivity of epichlorohydrin to the phenolic compared with the aryl glycidyl ether functional group. Preliminary kinetic data are presented using a modified gel chromatographic method which enables the separation of most of the intermediates formed in this reaction.     

Molecular weight distribution in alkyd resins. Part III. Presence of microgel in alkyd resins

Alkyd resins which have the same overall chemical composition and the same degree of polymerization have been prepared from synthetic mixtures of mono-, di-, and triglycerides of linoleic acid, glycerol, and phthalic anhydride. The properties of these resins differend significantly. Microgel particles are present in all resins, but the quantity and size of the gel particules is a function of the glyceride composition. The concept of microgel is used to explain the solution and film forming properties of these resins. Examination of a range of commercially available alkyd resins has shown that microgel particles are present where the functionality is greater than two.     

Molecular weight distributions in epoxy resins

An exact procedure for calculating the weight-average and number-average molecular weights of epoxy resins made by the advancement process is presented. The calculation can take into account the presence of high molecular weight diepoxides and monofunctional epoxides in diglycidyl ether of disphenol A and indicates that the presence of the latter has a very significant effect. A model for the taffy process based on the overall reactions of the process was developed. Analytical solutions could be obtained if the dehydrohalogenation reactions were assumed to be fast. The predictions of the model are in good agreement with the observed values reported earlier.     

Molecular weight viscosity relationships for PVC

The inherent viscosity of PVC resin in compounds containing fillers and additives can be calculated accurately and conveniently from the weight average molecular weight or the peak molecular weight as measured by High Performance-Size Exclusion Chromatography (HP-SEC). Molecular weight/inherent viscosity relationships are shown for typical production PVC resins. The utility of HP-SEC instrumentation for the determination of IV for samples of commercial interest is demonstrated. Mark-Houwink coefficients from the literature were used to calculate a convenient conversion factor of 0.612, which can be used to convert the molecular weight measured relative to polystyrene by HP-SEC to the actual molecular weight for PVC.     

Molecular weight and solution viscosity characterization of PVC

As a means of developing the most accurate possible Mark-Houwink relationship possible for PVC, the literature Mark-Houwink coefficients for the weight average molecular weight (M_W) of PVC in THF are plotted and the derived “grand average” Mark-Houwink relationship (K = 15.56 × 10^?3 ml/g, a = 0.7690) is shown. High pressure-size exclusion chromatography (HP-SEC) data from two independent laboratories was used along with the “grand average” Mark-Houwink coefficients to calculate absolute number of average molecular weight (M_N) and weight average molecular weight values for PVC. An easy-to-use table has been developed to detail the relationships between M_N, M_W, K value, and inherent viscosity (I. V.).     

改性PVC树脂生产抗冲型管材

介绍了改进PVC管材性能的方法,简介了PVC-M管材优异的冲击性能、抗开裂性能、耐点载荷能力和可焊性。     

Molecular weight and molecular weight distribution from dynamic measurements of polymer melts

A method for determining the molecular weight distribution (MWD) of a polymer melt has been developed using the dynamic elastic modulus (G'), plateau modulus (G), and zero shear complex viscosity (η). The cumulative MWD was found to be proportional to a plot of (G'/G)^0.5 vs. measurement frequency (ω). Frequency (ω) was found to be inversely proportional to (MW)^3.4, as expected. Results were scaled to absolute values using the empirical relationship η ∝ (M?_w)^3.4, where M?_w is the weight-average MW. M?_w, M?_n (number-average MW) and M?_w/M?_n calculated from melt measurements were found to agree with size exclusion chromatography usually well within 10 percent for broad and bimodal distribution samples. M?_w/M?_n tended to be approximately 20 percent higher for narrow distribution samples (M?_w/M?_n < 1.2) because we did not account for a finite distribution of relaxation times from a collection of monodisperse polymer chains. We also did not account for the plasticizing effect of short chains mixed with long ones which caused peak positions to be closer together for Theological vs, size exclusive chromatography (SEC) determinations of MW for bimodal distribution blends.     

Plasticization of PVC with ethylene copolymer resins

Ethylene copolymer resin (ECR) modifiers, designed to be soluble in all proportions in PVC, form a wide variety of plasticized PVC blends. These solid, high molecular weight (Mw > 250,000) resin modifiers, unlike conventional liquid plasticizer, exhibit outstanding permanence in PVC. Compounding procedures, used for liquid plasticized PVC, are sometimes inadequate to produce homogeneous blends of PVC/ECR. A number of effective melt compounding techniques and a new family of ECR modifiers have been developed to produce homogeneous blends exhibiting many outstanding properties, including fluids/chemical resistance, high/low-temperature service, and weatherability.     

A DSC investigation on the stabilizer distribution in PVC blends

The distribution of a liquid organotin stabilizer between the phases of heterogeneous poly(vinyl chloride) (PVC) blends has been studied by differential scanning calorimetry (DSC). This method can be used even at low stabilizer concentrations. At concentrations > 1 wt.-% the stabilizer can be detected in both phases of a PVC/SAN (poly(vinyl chloride)/poly(styrene-co-acrylonitrile)) blend. At lower concentrations no stabilizer could be found in the SAN phase. Determination of the induction period of thermal degradation at 180°C under nitrogen atmosphere showed no loss of thermal stability for blends containing the stabilizer partly in the SAN phase. Kinetic measurements with the DSC indicate a migration of the stabilizer out of the SAN phase, PVC/PMA (poly(vinyl chloride)/poly(methyl acrylate)) blends showed no solubility of the stabilizer in the soft PMA phase.     

Molecular weight distribution and moments for condensation polymerization of monomers having reactivity different from their homologues

Molecular weight distributions and moments for condensation polymerization of monomer with unequal reactivities have been studied. When the monomer is more reactive than other species, the MWD curves are found to be different for even and odd mers. When the monomer is less reactive than other species, substantial amounts of unreacted monomer are left and a polydispersity index found by excluding the monomer is found to be a more appropriate representation of the dispersion of the curves. Values of this index at constant conversion are found to be larger or smaller depending on whether the monomer is more or less reactive compared with other homologues in the system, respectively.     

不同合成方法生产的高聚合度PVC树脂的性能比较

主要介绍了用低温法、扩链剂法以及加入内增塑单体共聚方法合成的高聚合度ＰＶＣ树脂在机械力学性能和熔融流变性等方面的区别。     

Thermal and rheological properties of polyethylene blends with bimodal molecular weight distribution

Polyethylene blends with bimodal molecular weight distribution were prepared by blending a high molecular weight polyethylene and a low molecular weight polyethylene in different ratios in xylene solution. The blends and their components were characterized by the high temperature gel permeation chromatograph (GPC), different scanning calorimetry (DSC), and small amplitude oscillatory shear experiments. The results showed that the dependence of zero‐shear viscosity (η₀) on molecular weight followed a power law equation with an exponent of 3.3. The correlations between characteristic frequency (ω₀) and polydispersity index, and between dynamic cross‐point (G_x) and polydispersity index were established. The complex viscosity (η^*) at different frequencies followed the log‐additivity rule, and the Han‐plots were independent of component and temperature, which indicated that the HMW/LMW blends were miscible in the melt state. Moreover, the thermal properties were very similar to a single component system, suggesting that the blends were miscible in the crystalline state. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Molecular weight distribution of Athabasca bitumen

A sample of whole Athabasca bitumen has been fractionated by preparative g.p.c. The weights of the fractions have been determined and their molecular weights measured by several methods. In contrast to previously published data, consistent results were obtained using different solvents (THF, be-nzene/water) and using different techniques (v.p.o., f.p.d. and g.c.-m.s.). This has resulted in an accurate definition of the molecular weight distribution of Athabasca bitumen.     

Compounds based on ultra-high molecular weight PVC resins for use in automotive applications

This paper reviews early work done in Japan and leads into recent domestic activities reviewing the current “state of the art.” The authors present original work covering the development of elastomeric PVC compounds for interior and exterior automotive compounds. Compound variations include variations in the molecular weight of the speciality resin component, effect of plasticizer level changes, and the addition of alloying polymers. Physical characteristics such as hardness, specific gravity, torsional modulus, tensile strength, elongation, compression set, and abrasion resistance are measured and reported. Rheology of the compounds are characterized and related to processing ease and compound surface characteristics, smoothness, gloss, etc., and evaluated in light of potential automotive applications. Weatherability for use in automotive exterior trim is discussed.     

PVC树脂的共混改性

分析了PVC共混改性的基本原理及特点,介绍了ABS、MBS、CPE、ACR、EVA等PVC树脂共混改性剂的主要牌号、改性效果及应用范围。     

Review of specialty PVC resins

World consumption of PVC was around 25 MM MT (55 billion pounds) in year 2001, second only to that of low density polyethylene. Only 10% of the PVC produced is classified as specialty PVC resins, while the other 90% is referred to as general purpose (GP) commodity resins. This paper tries to define what specialty PVC resins are, how they are produced, and their markets, applications, fabrication processes, and compounding as compared to those of GP resins.