A continuous loop reactor was used for the production of 2‐ethylhexyl acrylate (2‐EHA), methyl methacrylate (MMA) and acrylic acid (AA) pressure sensitive adhesive by both emulsion and miniemulsion polymerization. Similar high monomer conversions were achieved in both processes, but striking differences in polymer architecture were found. A mathematical model was used to analyze these differences concluding that because the costabilizer suppressed monomer diffusion from miniemulsion droplets, the average polymer concentration in the polymerization loci was lower in the miniemulsion process. This resulted in less chain transfer to polymer, and hence in lower sol molecular weight and gel content.
Abstract A comparison of the dilatometrically determined rates of polymerization of pure meta-and pure para-divinylbenzenes confirms the previous observation that the meta isomer polymerizes more rapidly than the para isomer. This difference shows up also in the initiator square root rate dependencies, the gel times, and the conversions at gel point. The effect of added regulator (carbon tetrabromide) on the polymerization of the meta isomer is to decrease the gel time and conversion at gel time. 相似文献
Gel formation usually occurs in crosslinking systems during polymerization. The critical conversion in this process is dependent on the reactivity ratios of the different kinds of double bond in the system and on the tendency to cyclization. In this article a procedure for estimating the gel point for small amounts of a symmetric divinyl compound is shown in measurements of the degree of polymerization at different conversions. A method is also given to relate the reactivity ratio of the pendent double bonds to the amount of cyclization and to the degree of multiple crosslinking. In m-divinylbenzene/styrene the results indicate that about 10% of the pendent double bonds is consumed by cyclization due to backbiting of the primary chain, whereas an initial effective crosslink results in about seven multiple crosslink bonds. 相似文献
Post‐polymerization modification is based on the direct polymerization or copolymerization of monomers bearing chemoselective handles that are inert towards the polymerization conditions but can be quantitatively converted in a subsequent step into a broad range of other functional groups. The success of this method is based on the excellent conversions achievable under mild conditions, the excellent functional‐group tolerance, and the orthogonality of the post‐polymerization modification reactions. This Review surveys different classes of reactive polymer precursors bearing chemoselective handles and discusses issues related to the preparation of these reactive polymers by direct polymerization of appropriately functionalized monomers as well as the post‐polymerization modification of these precursors into functional polymers. 相似文献
The weight average degree of polymerization of vinyl acetate-divinyl adipate copolymers (low content of divinyl adipate) is measured at conversions up to 22%. From thisk13/k12 (rate constants of reaction of growing radicals with pendent double bonds and divinyl adipate double bonds, respectively) is calculated to be 0.28. A quantitative relation for the gel point (critical conversion) is given. 相似文献
The properties of polyacrylamide hydrogels synthesized with a novel hexafunctional (three double bonds) cross-linker, hexahydro-1,3,5-triacryloyl-s-triazine (1a), was evaluated and compared to the currently used tetrafunctional (two double bonds) cross-linker N,N-methylenebisacrylamide (Bis). A variety of characterization techniques that require very little sample preparation and data handling were chosen and include polymerization temperature profiles and conversions, water swelling, differential scanning calorimetry (DSC), polyacrylamide gel electrophoresis (PAGE), Gradiflow electrophoretic separation process and scanning electron microscopy (SEM). The alternative use of 1a compared to Bis results in polyacrylamide gels with larger pore sizes and a broad pore size distribution. 相似文献
