Acetate, polyvinyl linear

The solubility of vinyl acetate Increases linearly reaching 62J5 v/v in a 7% polyvinyl alcohol solution. However 11 hours had to be allowed to reach saturation so that a slow rate of solution may explain the... 

Recently, Brich and coworkers (40) reported the synthesis of lactide/glycolide polymers branched with different polyols. Polyvinyl-alcohol and dextran acetate were used to afford polymers exhibiting degradation profiles significantly different from that of linear poly-lactides. The biphasic release profile often observed with the linear polyesters was smoothened somewhat to a monophasic profile. Further, the overall degradation rate is accelerated. It was speculated that these polymers can potentially afford more uniform drug release kinetics. This potential has not yet been fully demonstrated. 

In order to estimate the branching factor e for polyvinyl acetate we have analyzed the SEC data obtained on sample PVAc-E4 using the MWBD method with various e values. This sample was synthesized under kinetically controlled conditions (isothermal, T = 60°C, [AIBN] = 10"5 g-mole/1, conversion level of 48.5 percent). The SEC measurements were made at 25°C in tetrahydro-furan. The Mark-Houwink coefficients used for linear polyvinyl acetate are those suggested by Graessley (21), namely K = 5.1 x 10"5 dl/gm and a = 0.791. The whole polymer M, Mj, and B j values obtained are listed in Table II. 

Fig. 5.18. Reduced compliance vs cM /qMc for solutions and undiluted sample of linear, narrow distribution polymers. The lines for polyethylene and (polydimethyl siloxane) are based on G (w) data as reported by Mills (204). Points are selected values for polyvinyl acetate solutions, O (176) and 9 (195), and undiluted 1,4 polybutadiene, (202) and - (203) The values of Mc were taken from Table 5.2...

Fig. 8.13. Dimensionless shear rate /30 locating the onset of shear rate dependence in the viscosity in narrow distribution systems of linear polymers vs cM/qM. Symbols for data on additional polymers are A for undiluted 1,4 polybutadiene (322), for undiluted poly(dimethyl siloxane) (323), and O for solutions of polyvinyl acetate in diethyl phthalate (195). The dotted lines indicate the ranges of for the intrinsic viscosity...

Eq. (5) in conjunction with Eqs. (8) and (9) have, so far, provided adequate representation of experimental isotherms6 32, which are characterized by an initial con vex-upward portion but tend to become linear at high pressures. Values of K, K2 and s0 have been deduced by appropriate curve-fitting procedures for a wide variety of polymer-gas systems. Among the polymers involved in recent studies of this kind, one may cite polyethylene terephthalate (PET) l2 I4), polycarbonate (PC) 19 22,27), a polyimide l6,17), polymethyl and polyethyl methacrylates (PMMA and PEMA)l8), polyacrylonitrile (PAN)15), a copolyester 26), a polysulphone 23), polyphenylene oxide (PPO)25), polystyrene (PS) 27 28), polyvinyl acetate 29) and chloride 32) (PVAc and PVC), ethyl cellulose 24) (EC) and cellulose acetate (CA) 30,3I>. A considerable number of gases have been used as penetrants, notably He, Ar, N2, C02, S02 and light hydrocarbons. 

The synthesis of branched polyvinyl acetate was based on the same method carboxyl-ended material was transformed to acid chloride with thionyl chloride and condensed with a linear copolymer of vinyl alcohol and vinyl acetate (155, 156). 

ABA ABS ABS-PC ABS-PVC ACM ACS AES AMMA AN APET APP ASA BR BS CA CAB CAP CN CP CPE CPET CPP CPVC CR CTA DAM DAP DMT ECTFE EEA EMA EMAA EMAC EMPP EnBA EP EPM ESI EVA(C) EVOH FEP HDI HDPE HIPS HMDI IPI LDPE LLDPE MBS Acrylonitrile-butadiene-acrylate Acrylonitrile-butadiene-styrene copolymer Acrylonitrile-butadiene-styrene-polycarbonate alloy Acrylonitrile-butadiene-styrene-poly(vinyl chloride) alloy Acrylic acid ester rubber Acrylonitrile-chlorinated pe-styrene Acrylonitrile-ethylene-propylene-styrene Acrylonitrile-methyl methacrylate Acrylonitrile Amorphous polyethylene terephthalate Atactic polypropylene Acrylic-styrene-acrylonitrile Butadiene rubber Butadiene styrene rubber Cellulose acetate Cellulose acetate-butyrate Cellulose acetate-propionate Cellulose nitrate Cellulose propionate Chlorinated polyethylene Crystalline polyethylene terephthalate Cast polypropylene Chlorinated polyvinyl chloride Chloroprene rubber Cellulose triacetate Diallyl maleate Diallyl phthalate Terephthalic acid, dimethyl ester Ethylene-chlorotrifluoroethylene copolymer Ethylene-ethyl acrylate Ethylene-methyl acrylate Ethylene methacrylic acid Ethylene-methyl acrylate copolymer Elastomer modified polypropylene Ethylene normal butyl acrylate Epoxy resin, also ethylene-propylene Ethylene-propylene rubber Ethylene-styrene copolymers Polyethylene-vinyl acetate Polyethylene-vinyl alcohol copolymers Fluorinated ethylene-propylene copolymers Hexamethylene diisocyanate High-density polyethylene High-impact polystyrene Diisocyanato dicyclohexylmethane Isophorone diisocyanate Low-density polyethylene Linear low-density polyethylene Methacrylate-butadiene-styrene... 

Acetylcholineesterase Miniaturized multichannel transduc-tor with planar Au electrode which was first covered with a choline-selective liquid membrane made from 66% PVC-polyvinyl acetate (PVA), 33% 2-nitrophenyl octyl ether plasticizer and 1% ion-pair choline phosphotungstate. A second layer of 2% AChE in the PVA-polyethylene dispersion was spread on the top. The electrode was used as working electrode versus Ag/AgCl for potentiometric measurement of Ch and ACh in 0.1 M Tris buffer at 7.4. Optimum pH range for the sensor was 7-9. The calibration graph was linear from 0.02-10 mm ACh and detection limit was 5 pM. Response time was 3-5 min. Sensor was suitable for determination of ACh in biological fluids. [86]... 

Fig. 2. Dimensionless ratio AsM/fa] for various polymers. Open circles, polyisobutylene 148). Upright triangles, poly(raethyl methacrylate) 40, 47, 5V, 59). Inverted triangles, polyvinyl acetate (62, 233). Squares, polystyrene 35,71, 73,148,206,208). Filled circles, atactic polypropylene 138). Crosses, linear polyethylene 26,152,256), The unfilled points were selected as specially reliable in 1957 by Orofino and...

Polyester Acrylic copolymers Alkali soluble polyvinyl acetate Linear polyester Stymer (styrene - maleic anhydride coplymer) Gelatin... 

These studies were extended to some related systems (20). In the hydrolysis of partially acetylated polyvinyl alcohtd Why linear allqrlsulfonic acids S, the catalytic efficiency increased with increasing length of the alkyl chain. More interesting is the acid hydrolysis of the vinyl acetate unit in water-soluble copolymers by polymer sulfonic acids. Tte catalytic efficfcnty was generally greater than in other systems... 

With loose structures of linear molecules the exponent for instance to cellulose nitrate in acetone, precipitated by water, to Polyvinyl acetate in toluene, precipitated by a methanol-water mixture-, and to the methyles-ters of polymethacrylic acid in benzene, precipitated by cyclohexane With compact spherical particles we must expect n-values in the neighbourhood of 2/3, since in this case only the outer surface of the particles is subject to the action of the medium. Examples can be found in some proteins. Finally, if the long-chain molecule shows a pronounced ramification or if the randomly kinked structure is comparatively close-packed, n may assume values between 0.7 and 1. This is shown for instance, by branched polystryrene h by acetyl-starch and by glycogene An accurate check on the value of n, however, is usually impossible. Husemann s experiments with glycogene, for instance, can be equally well described by n = 2/3 as by n — J (Fig. 5). This is due to the fact that the value of P in this method is not unlimited. In practice the upper limit of the molecular weight lies in the neighbourhood of 5.10, the lower limit lies in the further to be noted that the constant b in equation... 

Polyethylene (PE) is inherently less sensitive to oxidative attack than PP, but stabilization of PE is also mandatory for outdoor use. The stability varies with the type of polyethylene and manufacturing process. Linear low-density polyethylene (LLDPE) (1-octene comonomer) is significantly less sensitive to photooxidation than low-density polyethylene (LDPE) with comparable density and molecular weight [20, 21]. Generally, LDPE is less susceptible to photooxidation than high-density polyethylene (HDPE). The most fundamental difference between polyethylene homopolymers and polypropylene is the behavior of hydroperoxides toward photolysis. On photooxidation, hydroperoxides accumulate in PP, but decrease rapidly on UV exposure of PE. In copolymers of polyethylene with vinyl acetate, the stabihty depends on the content of vinyl acetate. The higher the content, the more the copolymers act like polyvinyl acetate, which is more susceptible to photooxidative degradation than polyethylene. 

PVA is a linear synthetic water soluble polymer with a pendant hydroxyl group (Fig. 8). Since the monomer, vinyl alcohol is not stable PVA is generally produced by the hydrolysis of polyvinyl acetate. The synthesis process is based on the partial replacement of ester groups in the vinyl acetate with hydroxyl groups and is done in the presence of anhydrous sodium methylate or aqueous sodium hydroxide. Commercial PVA grades are available with a high degree of hydrolysis. 

The linearity of a polyvinyl acetate resin can be controlled during the polymerization pro-... 

Maki-Arvela (1999) has developed a new polyolefin supported sulphonic acid catalyst for esterification of acetic acid with methanol. The esterification kinetics (pseudo-homogeneous) was modeled with a mechanistic rate equation, the parameters of which were determined by non-linear regression. The esterification rate constant of the most active modification of the new catalyst was 9.6 x 10 ° dm /(mol g min) at 328 K, which clearly exceeds the corresponding value obtained with a traditional (Amberlyst 15) polyvinyl benzene supported catalyst, 1.5 x 10 ° dm /(moP g min). 

---