Vinyl acetate

About: Vinyl acetate is a research topic. Over the lifetime, 15970 publications have been published within this topic receiving 162142 citations. The topic is also known as: Ethenyl acetate & Ethenyl ethanoate.

Occurrence of head‐to‐head arrangements of structural units in polyvinyl alcohol

Abstract: Polyvinyl alcohol prepared by hydrolyzing polymerized vinyl acetate is partially degraded within a few minutes by reagents known to attack 1,2-glycol structures. The degree of degradation is limited, however, the final molecular weights of the degraded products being in the range of 3700 to 6500 (viscosity averages). The extent of degradation seems to depend solely on the temperature at which the vinyl acetate was polymerized. Mole percentages (based on the structural unit CH2CHOH) of 1,2-glycol structures, corresponding to head-to-head unit arrangements, have been computed from the degree of degradation with periodic acid. They increase from about 1.23% for polymerization at 25°C. to 1.95% at 110°C. The occurrence of head-to-head structures is attributed to occasional “abnormal” addition of monomer in the chain-growth phase of the polymerization. The activation energy for the abnormal addition reaction is 1250 calories higher than for the normal (preferred) addition; the steric factor for the abnormal addition is about one-tenth that for the normal addition.

Organo-Cobalt Mediated Living Radical Polymerization of Vinyl Acetate

Abstract: Vinyl acetate polymerization initiated by azo radical sources in the presence of cobalt(II) tetramesitylporphyrin ((TMP)CoII) shows an induction period followed by an organo-cobalt mediated living radical polymerization (LRP). The induction period corresponds to converting (TMP)CoII to an organo-cobalt porphyrin derivative (organo-Co(TMP)). Living character at low vinyl acetate conversion is demonstrated by a linear increase in molecular weight with conversion, relatively low polydispersity homopolymers, and formation of block copolymers with methyl acrylate ((TMP)Co-PVAc-b-PMA). Deviations from ideal LRP occur by radical termination and chain transfer events at moderate conversion of vinyl acetate (VAc). Mechanistic studies demonstrate that the VAc radical polymerization is controlled by a degenerative transfer mechanism that utilizes organo-cobalt complexes as the transfer agent. Kinetic studies are utilized in comparing radical polymerization of vinyl acetate and methyl acrylate that are mediated by or...

Heat Capacity and Other Thermodynamic Properties of Linear Macromolecules. VII. Other Carbon Backbone Polymers

Abstract: The heat capacity of poly‐1‐butene, poly‐1‐pentene, poly‐1‐hexene, polyisobutylene, poly(4‐methyl‐1‐pentene), polybutadiene, cis‐1, 4‐poly(2‐methylbutadiene), polycyclopentene, poly(vinyl fluoride), poly(vinylidene fluoride), polytrifluoroethylene, polytetrafluoroethylene, poly(vinyl chloride), poly(vinylidene chloride), polychlorotrifluoroethylene, poly(vinyl alcohol), poly(vinyl acetate), poly(α‐methylstyrene), poly(o‐methylstyrene), poly(o‐chlorostyrene) and a series of poly(vinyl benzoate)s is reviewed on the basis of 62 measurements reported in the literature. A set of recommended data has been derived for each polymer. Entropy and enthalpy functions have been calculated for poly‐1‐hexene, polyisobutylene, cis‐1, 4‐poly(2‐methylbutadiene), poly(vinyl chloride), and poly(α‐methylstyrene). This paper is seventh in a series which will ultimately cover all heat capacity measurements on linear macromolecules.

Distinction between esterases and lipases: a kinetic study with vinyl esters and TAG.

Abstract: The better to characterize enzymes hydrolyzing carboxyl ester bonds (carboxyl ester hydrolases), we have compared the kinetic behavior of various lipases and esterases against solutions and emulsions of vinyl esters and TAG. Short-chain vinyl esters are hydrolyzed at comparable rates by esterases and lipases and have higher limits of solubility in water than corresponding TAG. Therefore, they are suited to study the influence of the physical state of the substrate on carboxyl ester hydrolase activity within a large concentration range. Enzymes used in this study are TAG lipases from microorganisms, lipases from human and guinea pig pancreas, pig liver esterase, and acetylcholinesterase. This study also includes cutinase, a fungal enzyme that displays functional properties between esterases and lipases. Esterases display maximal activity against solutions of short-chain vinyl esters (vinyl acetate, vinyl propionate, and vinyl butyrate) and TAG (triacetin, tripropionin, and tributyrin). Half-maximal activity is reached at ester concentrations far below the solubility limit. The transition from solution to emulsion at substrate concentrations exceeding the solubility limit has no effect on esterase activity. Lipases are active on solutions of short-chain vinyl esters and TAG but, in contrast to esterases, they all display maximal activity against emulsified substrates and half-maximal activity is reached at substrate concentrations near the solubility limit of the esters. The kinetics of hydrolysis of soluble substrates by lipases are either hyperbolic or deviate from the Michaelis-Menten model and show no or weak interfacial activation. The presence of molecular aggregates in solutions of short-chain substrates, as evidenced by a spectral dye method, likely accounts for the activity of lipases against soluble esters. Unlike esterases, lipases hydrolyze emulsions of water-insoluble medium- and long-chain vinyl esters and TAG such as vinyl laurate, trioctanoin, and olive oil. In conclusion, comparisons of the kinetic behavior of carboxyl ester hydrolases against solutions and emulsions of vinyl esters and TAG allows the distinction between lipases and esterases. In this respect, it clearly appears that guinea pig pancreatic lipase and cutinase are unambiguously classified as lipases.