Bifunctional initiators on the polymerization of vinyl acetate (original) (raw)
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Recent Advances in the Study of Multifunctional Initiators in Free Radical Polymerizations
Macromolecular Reaction Engineering, 2007
When reviewing the state of research completed on multifunctional initiators, there appears to be a lack of comprehensive studies following a systematic approach to understanding their behaviour in free radical polymerizations. Apart from a few exceptions, most studies have focused entirely on the free radical polymerization of styrene and neglected to examine the behaviour of the initiator in question with various other monomers. Additionally, some of the previous papers employ a less than ideal method of proving the rate benefits of
Journal of Applied Polymer Science, 2000
Monofunctional initiators are extensively used in free radical polymerization. To enhance productivity, a higher temperature is usually used; however, this leads to lower molecular weights. Bifunctional initiators can increase the polymerization rate without decreasing the average molecular weight and this can be desirable. A bifunctional initiator is an important issue to be investigated, and it is of great interest to industries. The objective of this work is to study polymerization reactions with mono-and bi-functional initiators through comprehensive mathematical models. Polystyrene is considered as case study. This work collects and presents some experimental data available in literature for polymerization using two different types of bifunctional initiators. Model prediction showed good agreement with experimental data. It was observed that the initial initiator concentration has a huge impact on the efficiency of initiators with functionality bigger than one and high concentrations of bifunctional initiator make the system behave as if it were a system operating with monofunctional initiator. V
Industrial & Engineering Chemistry Research, 2004
A comprehensive kinetic model is developed for the suspension free-radical polymerization of vinyl chloride (VC) initiated by a mixture of monofunctional and bifunctional initiators. The model predicts the monomer concentrations in the gas, aqueous, and polymer phases; the overall monomer conversion; the polymerization rate; the polymer chain structural characteristics (e.g., number-and weight-average molecular weights, short chain branching, and number of terminal double bonds); the reactor temperature and pressure; and the coolant flow rate and temperature in the reactor's jacket over the whole batch polymerization cycle. The capabilities of the model are demonstrated by a direct comparison of model predictions with experimental data on monomer conversion, number-and weight-average molecular weights, and reactor pressure. It is shown that high molecular weights and high polymerization rates can be obtained in the presence of a mixture of monofunctional and bifunctional initiators. Moreover, the use of bifunctional initiators results in a significant reduction of the polymerization time without impairing the final molecular weight properties of the polymer. To our knowledge, this is the first comprehensive kinetic modeling study on the combined use of monofunctional and bifunctional initiators on the free-radical suspension polymerization of VC. Taking into consideration the excellent agreement of the model predictions with the experimental measurements, the proposed model should find wide application in the design, optimization, and control of industrial poly(vinyl chloride) batch reactors.
Gas-free initiators for high-temperature free-radical polymerization
Journal of Polymer Science Part A-polymer Chemistry, 2000
Quaternary ammonium persulfates as free-radical initiators for high-temperature polymerization are synthesized and their shelf-life stability investigated. These initiators do not have gaseous byproducts and are therefore ideal for frontal polymerization, a process in which polymeric materials are produced via a thermal front that propagates through the unreacted monomer/initiator solution. Quaternary ammonium persulfate initiators offer additional qualities such as high solubility in organic media and low volatility, which are desirable for frontal polymerization. The initiators are synthesized using two procedures, and the initiating efficacy of the respective products is compared to a peroxide initiator in the frontal polymerization of 1,6-hexanediol diacrylate. Of all the quartenary ammonium persulfates synthesized, tricaprylmethylammonium (Aliquat) persulfate (APSO) is the best initiator for frontal polymerization because it is soluble in organic media, is very reactive, and does not produce volatile byproducts under decomposition. A study of the decomposition kinetics of APSO is performed, and frontal polymerization is proposed as a quicker analytical technique to assay the purity.
Macromolecules, 1994
We describe the use of poly(a-methylstyrene peroxide) (PaMSP), an alternating copolymer of a-methylstyrene and oxygen, as initiator for the radical polymerization of vinyl monomers. Thermal decomposition of PaMSP in 1,4-dioxane follows first-order kinetics with an activation energy (E,) of 34.6 kcal/mol. Polymerization of methyl methacrylate (MMA) and styrene using PaMSP as an initiator was carried out in the temperature range 60-90 OC. The kinetic order with respect to the initiator and the monomer was close to 0.5 and 1.0, respectively, for both monomers. The E, for the polymerization was 20.6 and 22.9 kcal/mol for MMA and styrene, respectively. The efficiency of PaMSP was found to be in the range 0.02-0.04. The low efficiency of PaMSP was explained in terms of the unimolecular decomposition of the alkoxy radicals which competes with primary radical initiation. The presence of peroxy segmenta in the main chain of PMMA and polystyrene was confirmed from spectroscopic and DSC studies. Ri't2.l values for PaMSP compared to that of BPO at 80 "C indicate that PaMSP can be used as an effective high-temperature initiator.
Bubble-Free Initiators for High Temperature Free-Radical Polymerization
Quaternary ammonium persulfates as free-radical initiators for high-temperature polymerization are synthesized and their shelf-life stability investigated. These initiators do not have gaseous byproducts and are therefore ideal for frontal polymerization, a process in which polymeric materials are produced via a thermal front that propagates through the unreacted monomer/initiator solution. Quaternary ammonium persulfate initiators offer additional qualities such as high solubility in organic media and low volatility, which are desirable for frontal polymerization. The initiators are synthesized using two procedures, and the initiating efficacy of the respective products is compared to a peroxide initiator in the frontal polymerization of 1,6-hexanediol diacrylate. Of all the quartenary ammonium persulfates synthesized, tricaprylmethylammonium (Aliquat) persulfate (APSO) is the best initiator for frontal polymerization because it is soluble in organic media, is very reactive, and does not produce volatile byproducts under decomposition. A study of the decomposition kinetics of APSO is performed, and frontal polymerization is proposed as a quicker analytical technique to assay the purity.
2015
Introduction Atom Transfer Radical Polymerization (ATRP), a controlled system reported by Matyjaszewski et. al. [1, 2] has been widely used for synthesis of end-functional, telethelic, block, graft and various polymers/copolymers with precisely controlled architecture [3,4]. The ATRP process, in which a free radical generates by the transfer of a halogen (typically bromine) from a dormant initiator or polymeric chain to a transition metal. This free radical then adds of monomer to yield polymer. Scheme 1: Mechanism of metal complex-mediated ATRP Although various type of initiators have been reported for ATRP, α-haloesters have been successfully employed for well-controlled ATRP to synthesis of various functional polymer or copolymers.[2,5-9] Structural adjustment of the α-haloesters initiator provides a handle to fine-tune the rate of initiation in the ATRP system. For instance, α-haloisobutyrates produce initiating radicals faster than the corresponding α-halopropionates due to better stabilization of the generated radicals after the halogen abstraction step. The polymerization of methacrylates with slow initiation was found to report using α-halopropionates.[10,11] Matyjaszewski et. al. reported the ATRP of styrene with vinyl chloroacetate and allyl chloroacetate as initiator using CuBr-bipyridine catalyst system.[5] The former was found as better initiator for styrene polymerization. The initiation and propagation rate of the polymerization depend on the structure of initiator as well as the generation and stability of the free radical. Although several papers have been reported to clarify the effect of the structure of the initiator on ATRP, [12, 13] it is an importance topic to investigate the efficiency of new initiators for ATRP. In this work, undecenyl bromopropionate (UBP) and allyl bromopropionate (ABP) initiators were synthesized and applied as initiators on ATRP of styrene under different conditions and the effect of-CH 2spacer between CH 2 =CH-and ester groups of the initiators was investigated. II. Experimental Materials: Styrene was purchased from Aldrich and it was purified by passing through an alumina column to remove stabilizer and then stirred with CaH 2 for 8 h and filtered. Finally it was stored in a Schelnk flask at 0 °C under nitrogen prior to use. Copper (I) bromide was purified by recrystalization in methanol and washed with ether. Bipyridine from Fluka, 2-bromopropenyl bromide, allyl alcohol and 10-undecen-1-ol were purchased from Aldrich and used without further purification. Triethylamine was distilled over CaH 2. All solvents were purified by distillation followed by refluxed with sodium and benzophenone. Polymerization procedure: Polymerization was carried out in a 50 mL Schelnk type reactor equipped with magnetic stirrer in nitrogen atmosphere. The reactor was charged with prescribed amount of CuBr and bipyridine. Three freeze-pump-thaw cycles were performed, and the tubes were sealed under vacuum with rubber septum. A required amount of degassed styrene and initiator were added with syringe. The reactor was
Gas-Free Initiators for High-Temperature Polymerization
Quaternary ammonium persulfates as free-radical initiators for high-temperature polymerization are synthesized and their shelf-life stability investigated. These initiators do not have gaseous byproducts and are therefore ideal for frontal polymerization, a process in which polymeric materials are produced via a thermal front that propagates through the unreacted monomer/initiator solution. Quaternary ammonium persulfate initiators offer additional qualities such as high solubility in organic media and low volatility, which are desirable for frontal polymerization. The initiators are synthesized using two procedures, and the initiating efficacy of the respective products is compared to a peroxide initiator in the frontal polymerization of 1,6-hexanediol diacrylate. Of all the quartenary ammonium persulfates synthesized, tricaprylmethylammonium (Aliquat) persulfate (APSO) is the best initiator for frontal polymerization because it is soluble in organic media, is very reactive, and does not produce volatile byproducts under decomposition. A study of the decomposition kinetics of APSO is performed, and frontal polymerization is proposed as a quicker analytical technique to assay the purity.
Radical polymerizations of some vinyl alkyl carbonates
Polymer, 1994
Some simple experiments have been carried out to assess the kinetics of the radical polymerizations of vinyl ethyl, vinyl tert-butyl, vinyl phenyl and vinyl benzyl carbonates at temperatures between 30°C and 60°C. It is shown that, contrary to some impressions given in the literature, the vinyl alkyl carbonates can be polymerized readily to give polymers of high molecular weight with conventional radical initiators (i.e. benzoyl peroxide and azoisobutyronitrile) provided that it is recognized that they polymerize relatively slowly owing, probably, to them having relatively low values of kp/klt/2. Therefore radical initiators must be used with these monomers at temperatures at which they will have relatively long half-lives. It is further shown that the low-temperature initiator, dicyclohexylperoxydicarbonate (DCHPC), favoured by previous workers for the polymerization of these monomers, offers no obvious advantages over the use of the more conventional initiators at higher temperatures, and that an alternative low temperature initiator, tert-butylperoxyneodecanoate, polymerizes vinyl alkyl carbonates with a facility equal to that of DCHPC.