Preparation of phenyl‐modified natural rubber in latex stage

Phenyl‐modified natural rubber was prepared in latex stage by bromination of deproteinized natural rubber followed by Suzuki‐Miyaura cross‐coupling reaction. First, the bromination of natural rubber was carried out using N‐bromosuccinimide in latex stage. The bromine atom content increased as amount of N‐bromosuccinimide increased. Second, the allylic bromine atom was replaced with a phenyl group using phenyl boronic acid in the presence of a palladium catalyst, according to the Suzuki‐Miyaura cross‐coupling reaction in latex stage. The resulting products were characterized by nuclear magnetic resonance (NMR) spectroscopy. Signal at 7.13 ppm was assigned to the phenyl group of the product, while signals at 3.98, 4.14, and 4.44 ppm were assigned to the remaining allylic brominated cis‐1,4‐isoprene units. The estimated phenyl group content and the conversion of the Suzuki‐Miyaura cross‐coupling reaction were 1.32 and 23.7 mol%, respectively. Glass transition temperature (T_g) of deproteinized natural rubber increased from ?62°C to ?46.7°C, when the phenyl group was introduced into the rubber.     

Latex‐state NMR spectroscopy for quantitative analysis of epoxidized deproteinized natural rubber

Method of quantitative analysis through latex‐state ¹³C NMR spectroscopy was established for in situ determination of epoxy group content of epoxidized natural rubber in latex stage. The epoxidized natural rubber latex was prepared by epoxidation of deproteinized natural rubber with freshly prepared peracetic acid in latex stage. The resulting epoxidized deproteinized natural rubber (EDPNR) latex was characterized through latex‐state ¹³C NMR spectroscopy. Chemical shift values of signals of latex‐state ¹³C NMR spectrum for EDPNR were similar to those of solution‐state ¹³C NMR spectrum for EDPNR. Resolution of latex‐state ¹³C NMR spectrum was gradually improved as temperature for the nuclear magnetic resonance (NMR) measurement increased to 70°C. Signal‐to‐noise ratio of latex‐state ¹³C NMR measurement was similar to that of solution‐state ¹³C NMR measurement at temperature above 50°C. The epoxy group content determined through latex‐state NMR spectroscopy was proved to be the same as that determined through solution‐state NMR spectroscopy. Copyright © 2017 John Wiley & Sons, Ltd.     

Preparation and properties of phenyl‐modified natural rubber

We prepared phenyl‐modified natural rubber using a two‐step process. In the first step, natural rubber was brominated using N‐bromosuccinimide in a dichloromethane solution of natural rubber. The amount of N‐bromosuccinimide controlled the bromine content. In the second step, a Suzuki–Miyaura cross‐coupling reaction of the brominated natural rubber with phenyl boronic acid in the presence of a palladium catalyst replaced the bromine atoms with phenyl groups. ¹H‐nuclear magnetic resonance and ¹³C‐nuclear magnetic resonance measurements characterized the products. The signals around 7 ppm in the ¹H‐nuclear magnetic resonance spectra of the products were assigned to the phenyl protons, and based on the assigned signals, the estimated conversion of the cross‐coupling reaction under mild conditions was more than 70 mol%. The amount of phenyl groups present affected both the loss tangent and the glass transition temperature of natural rubber, which increases from ?62°C to ?30°C. Copyright © 2015 John Wiley & Sons, Ltd.     

Investigation on thermoresponsive behavior of biodegradable poly(γ‐glutamic acid)‐graft‐L‐phenylalanine ethyl ester

The thermosensitivity of biodegradable and non‐toxic amphiphilic polymer derived from a naturally occurring polypeptide and a derivative of amino acid was first reported. The amphiphilic polymer consisted of poly(γ‐glutamic acid) (γ‐PGA) as a hydrophilic backbone, and L ‐phenylalanine ethyl ester (L ‐PAE) as a hydrophobic branch. Poly(γ‐glutamic acid)‐graft‐L ‐phenylalanine (γ‐PGA‐graft‐L ‐PAE) with grafting degrees of 7–49% were prepared by varying the content of a water‐soluble carbodiimide (WSC). γ‐PGA‐graft‐L ‐PAE with a grafting degree of 49% exhibited thermoresponsive phase transition behavior in an aqueous solution at around 80°C. The copolymers with grafting degrees in the range of 30–49% showed thermoresponsive properties in NaCl solution. A clouding temperature (T_cloud) could be adjusted by changing the polymer concentration and/or NaCl concentration. The thermoresponsive behavior was reversible. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012