Hydroxyl-terminated Liquid Natural Rubber Research Articles

Effect of triblock copolymers based on liquid natural rubber and low molecular weight poly(lactic acid) on physical properties of poly(lactic acid)/natural rubber blend

Triblock copolymers of poly(lactic acid) (PLA) and natural rubber (NR) (PLA–NR–PLA) with different lengths of PLA end blocks were produced from hydroxyl-terminated liquid natural rubber (HTLNR) and low molecular weight PLA (pre-PLA). The HTLNR with a number-average molecular weight $$(\bar{M}_{\text{n}} )$$ ~ 28,000 g/mol obtained from photochemical degradation of NR and pre-PLA with varying molecular weight ( $$\bar{M}_{\text{n}}$$ ~ 3000, ~ 6500, ~ 9700 g/mol) was subjected to condensation polymerization. The compatibilizing effect of copolymers on the physical properties of the PLA/NR blend was studied using PLA/NR/PLA–NR–PLA blend ratios of 90/10/0, 90/9/1, 90/8/2 and 90/7/3 percent by weight (wt%). From the tensile testing results, elongation at break of the blends increased with an increase in the amount of triblock copolymer and with the length of the PLA end block. The blend without the copolymer showed elongation at break of 60.54%, whereas the blend with 3 wt% of PLA–NR–PLA prepared from pre-PLA with $$\bar{M}_{\text{n}}$$ of ~ 9700 g/mol showed elongation at break of 199.38%. This was about a 300% increase. The highest impact strength of 79.58 kJ/m2 (400% higher than neat PLA) was also found for the blend containing 3 wt% of PLA–NR–PLA with the longest PLA end block. A reduction in the diameter and well dispersion of the rubber particles in the PLA matrix were seen in micrographs taken with a scanning electron microscope. In general, after the addition of PLA–NR–PLA into a PLA/NR blend, the Tg of NR phase shifted to a higher temperature, whereas the Tg of the PLA phase decreased. The PLA–NR–PLA triblock copolymer with the longest PLA end block is possibly used as an effective compatibilizer for the PLA/NR blend.

Toughening of Bisphenol-A Diglycidyl Ether-based Epoxy by Modification with Hydroxyl-terminated Liquid Natural Rubber

Hydroxyl-terminated liquid natural rubbers (HTNRs), prepared by the Photo-Fenton reaction, were used to modify bisphenol-A diglycidyl ether-based epoxy (DGEBA). A chemical link between HTNRs and the epoxy resin was promoted employing toluene diisocyanate. The reactions between elastomers and epoxy resin were followed by FTIR. The mechanical properties of the composites were evaluated and the microstructure was investigated using scanning electronic microscopy. The results showed that the impact resistance of HTNR-modified DGEBA was superior to that of the pure epoxy resin. For the composites with HTNR, the impact resistance increased with elastomer concentration up to 2.5 parts per hundred parts of resin. Higher concentration of HTNR resulted in larger particles which gave lower impact values.

Synthesis and Characterisation of Hydroxyl-terminated Liquid Natural Rubber by Photo-Fenton Reaction

Hydroxyl-terminated liquid natural rubber (HTNR) was prepared by the photo-Fenton reaction, which was carried out in solution in the presence of H2O2/Fe(II) combined with UV irradiation. The HTNR obtained was characterized by GPC, FT-IR, 1H-NMR, 13C-NMR, DEPT-NMR spectroscopy as well as by chemical methods. A probable mechanism leading to the formation of HTNR was discussed based on the analytical data.

Synthesis of hydroxyl terminated liquid natural rubber by oxidative depolymerization of deproteinized natural rubber

Hydroxyl terminated liquid natural rubber (HTLNR) was prepared by the depolymerization of deproteinized natural rubber (DPNR) in mixture of toluene and water at 60oC for 24 hours in the presence of ammonium persulfate as an initiator and tetrahydrofuran (THF) as a homogenizing agent. GPC analysis revealed that the number-average molecular weight (Mn) and weight-average molecular weight (Mw) of HTLNR were found to be 4.334×103 g/mol and 11.702×103 g/mol, respectively, with polydispersity index (PDI) of 2.7. The chemical structure of HTLNR was determined by FTIR and 1H-NMR and 13C-NMR spectroscopic analysis. The mechanism of depolymerization and hydroxylation of NR to form HTNR based on the analytical data is also suggested in this study.

Synthesis and Characterization of Block Copolymer from Natural Rubber, Toluene-2,4-Diisocyanate and Poly(ξ-aprolactone) Diol-Based Polyurethane

A new type of polyurethane (PU) has been synthesized by using hydroxyl terminated liquid natural rubber (HTNR) and poly(e-caprolactone) (PCL) as a soft segment and toluene-2,4 diisocyanate (TDI) as a hard segment. This PU becomes a biodegradable and recyclable polymer. The PU samples were synthesized by solution polymerization. TDI/PCL polymerization was prepared in order to determine the appropriate NCO:OH ratio which evaluated from the molecular weight of derived PU and the ratios which were able to form a polymeric film. The suitable NCO:OH ratios were 0.84:1 – 1.20:1 and the Mn of the derived PUs was 3000-5500 g/mol determined by using GPC. PU from PCL-HTNR block copolymer was synthesized by varying molar ratio between PCL and HTNR. HTNR has been synthesized by epoxidation reaction and chain cleavage of natural rubber. The Mn of HTNR was in the range of 1700-8000 g/mol. 1H-NMR and FTIR were used to determine the functional group in order to verify the prepared HTNR and PU. Glass transition temperature and thermal decomposition of PU samples were investigated by using DSC and TGA, respectively.

Mechanical properties and fractography of block copolymers based on NR and MDI-based polyurethanes

Five series of block copolymers were synthesized from hydroxyl-terminated liquid natural rubber (HTNR) and polyurethane (PU) oligomers, from various diols and diphenyl methane-4,4′-diisocyanate (MDI). They were characterized by mechanical testing and fracture studies (SEM analysis). The block copolymer characteristics were assessed on the basis of the composition and the type of extender diols. Mechanical properties were found to be strongly dependent on the copolymer composition in all the series. Tensile properties were found to improve with the hard segment content. At low hard segment content samples resemble flexible elastomers whereas at high hard segment content they behave as rigid plastics. Where bisphenol A (BPA) is used as the extender diol sample rigidity was higher compared to the samples with aliphatic diols which is attributed to the presence of aromatic ring system in the former samples. Fracture mechanism was found to vary from ductile fracture to rigid and brittle fracture as the hard segment content increased. Fractography also shows the presence of some beads disposed on the sample surface which could be the uncombined polyurethane homopolymer fractions.

Synthesis and thermal studies of block copolymers from NR and MDI‐based polyurethanes

AbstractFive series of block copolymers based on natural rubber and polyurethane were prepared from hydroxyl terminated liquid natural rubber (HTNR) and polyurethane (PU) formed by the reaction of diphenyl methane—4,4′—diisocyanate (MDI) with a chain extender diol, viz., ethylene glycol (EG)/propylene glycol (PG)/1,4‐butane diol (1,4‐BDO)/1,3‐butane diol (1,3‐BDO)/bisphenol A (BPA), by solution polymerization. Structural characterization of the block copolymers was done by infrared (IR) analysis. Thermal studies and kinetic analysis on thermal degradation of the block copolymers were undertaken with the view of characterizing them. Energy of activation and entropy change for the degradation were determined and a probable mechanism for the solid state degradation was suggested which corresponds to a three dimensional diffusion mechanism. DSC analysis has been used for the study of microphase separation in the block copolymers. Thermal transition of the hard segment significantly varies with the extender diol which highlights the effect of extender diol structure on the chain stiffening mechanism. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Natural rubber–polyurethane block copolymers: Nonlinear structural variations with NCO/OH ratio

AbstractA series of segmented block copolymers was prepared by the chain extension of hydroxyl terminated liquid natural rubber (HTNR) with polyurethane oligomers derived from toluene diisocyanate (TDI) and 1,3‐butane diol at varying NCO/OH ratio. The previously reported two‐step method of synthesis was modified to get improved products. This was done by optimizing the formation of polyurethane oligomers in the first step of the synthesis. All the samples were characterized by solubility testing, DSC, tensile testing, etching studies, and SEM. The data obtained were correlated to the structural features of the block copolymers. It was found that NCO/OH ratio played an important role in determining the structural variations in the block copolymers. POLYM. ENG. SCI. 46:1812–1821, 2006. © 2006 Society of Plastics Engineers

Synthesis and characterization of block copolymers based on natural rubber and polypropylene oxide

AbstractSegmented block copolymers from different grades of hydroxyl terminated liquid natural rubber (HTNR) (Mn 3000, 8800, 10,000, and 17,000) and polypropylene oxide (PPO) (Mn 1000, 2000, 3000, and 4000) have been synthesized and characterized by spectral analysis, thermal analysis, scanning electron microscopy (SEM), and mechanical testing. The glass transition temperature of NR block was found to be at about −64°C, which is independent of the PPO whose transition is around 15°C. The thermogravimetric analysis (TGA) shows that the thermal degradation of the samples proceeded in two steps characteristic of the immiscible components. The inability of PPO segments to provide physical crosslinking and the subsequent formation of hard domains is reflected in the low tensile properties and tear properties. The amorphous nature of the PPO phase and its immiscibility with NR phase are evidenced by the SEM studies. The effect of molecular weight of PPO as well as HTNR on the properties of the block copolymers has also been discussed. © 2006 Wiley Periodicals, Inc. JAppl Polym Sci 103: 909–916, 2007

Swelling characteristics of NR/PU block copolymers and the effect of NCO/OH ratio on swelling behaviour

A series of (NR/PU) block copolymers (BCs) was prepared from toluene diisocyanate (TDI), 1,3-butane diol (1,3-BDO), and hydroxyl-terminated liquid natural rubber (HTNR), by solution polymerisation. The swelling characteristics of the BCs were investigated. Diffusion profile in various solvents and the sorption kinetics were studied. Arrhenius and thermodynamic parameters were evaluated from the diffusion data. Finally, the influence of NCO/OH ratio on the swelling behaviour was also studied. The equilibrium sorption value ( Q ∞) decreased with increasing NCO/OH ratio for all the BCs. The samples have higher uptake of solvents with solubility parameter within a small range centred about 9 (cal/cm 3) 1/2. Highly polar and non-polar solvents show minimum uptake. It was observed that polarity factor predominates in the solvent transport through the present block copolymer systems. The sorption behavior is also found to vary with the NCO/OH ratio employed in the preparation of polyurethane (PU) oligomers.

Synthesis and Characterization of Segmented Block Copolymers Based on Hydroxyl‐Terminated Liquid Natural Rubber and α,ω‐Diisocyanato Telechelics

AbstractSummary: Segmented block copolymers, consisting of non‐polar soft segments from hydroxyl‐terminated liquid natural rubber (HTNR) and polar hard segments from α,ω‐diisocyanato telechelics obtained by “criss‐cross”‐cycloaddition, have been synthesized. The block copolymer formation took place under relatively mild reaction conditions at 80 °C in dichloroethane in the presence of dibutyltin dilaurate as a catalyst. The resulting block copolymers were characterized by spectroscopic techniques (1H NMR, FTIR, UV‐vis spectroscopy) as well as GPC for molar mass determination. The block copolymers were compression molded in a hot stage press, and the resulting samples were characterized by DSC and stress‐strain measurement. The solubility and phase morphology of the materials have also been studied.Segmented block copolymer from HTNR and α,ω‐diisocyanato telechelicsmagnified imageSegmented block copolymer from HTNR and α,ω‐diisocyanato telechelics

Segmented block copolymers of natural rubber and bisphenol A-toluene diisocyanate oligomers

Segmented block copolymers were synthesized from hydroxyl-terminated liquid natural rubber and polyurethane oligomers based on Bisphenol A and toluene diisocyanate by one-shot and two-shot processes in solution. Structural features were characterized by infrared and nuclear magnetic resonance spectroscopic analysis. The spectra of the one-shot materials were identical with those of the two-shot materials, indicating their chemical identity. The soft segment Tg was well defined and almost invariant around −64°C, but the hard segment Tg varied from 75 to 105°C as the hard segment content increased from 30 to 60 wt %. Two relaxation temperatures were observed for each sample in dynamic mechanical analysis (DMA). These observations and the two-stage thermal decomposition by random nucleation mechanism, as investigated in thermogravimetric analysis unambiguously confirmed complete phase segregation in these materials. The scanning electron microscopy and optical micrographs showed well-defined domains dispersed in a matrix, indicating the two-phase morphology. Systematic changes in hardness and tensile properties with hard segment content were also observed. The samples behaved like soft elastomers at lower hard segment content, toughened plastics at high hard segment content, and rigid elastomers at intermediate compositions. Variations in hardness and tear strength were consistent with this behavior. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 706–721, 1999

Segmented block copolymers of natural rubber and propylene glycol‐toluene diisocyanate oligomers

AbstractSegmented block copolymers were synthesized from hydroxyl terminated liquid natural rubber (HTNR) and polyurethane oligomers based on 1,2‐propylene glycol and toluene diisocyanate (TDI) by one‐shot and two‐shot processes in solution. They were completely phase segregated. Structural features were characterized by infrared and nuclear magnetic resonance spectroscopies. The two‐phase morphology was deducted from thermal analysis and dynamic mechanical analysis (DMA). The soft segment glass transition temperature was about −64°C and the hard segment glass transition was between 70°C and 100°C depending on the polyurethane content. The two‐phase morphology was corroborated by a two‐stage thermal decomposition of the products. The morphology consisted of a heterogeneous dispersion of beads in a continuous matrix. The large size and the nature of the beads suggest that they are independent of the block copolymer structure and are formed by the agglomeration of the polyurethane homopolymers, which remain unbonded to the rubber chains during chain extension. At lower hard segment contents the materials behaved like quasi‐elastomers, and at higher hard segment contents, they were like tough plastics. At intermediate compositions they behaved as rigid elastomers. Variations in hardness and tear strength were consistent with this behavior.

Reinforcement of Natural Rubber from Hydroxyl-Terminated Liquid Natural Rubber Grafted Carbon Black. I. Grafting of Acyl Chloride Capped Liquid Natural Rubber onto Carbon Black

Abstract This paper deals with the grafting of acyl chloride capped liquid natural rubber (LNR–COCl) onto carbon black by the reaction of the acyl chloride group with the phenolic hydroxyl group on the surface. LNR–COCl was prepared by the reaction of hydroxyl-terminated liquid natural rubber (HTNR) with adipoyl dichloride. The percentage of grafting was estimated to be 18–21% depending on the grafting temperature and the molecular weight of HTNR used. It increased with an increase in the molecular weight of LNR–COCl. The LNR grafted onto carbon black was investigated by IR spectroscopy and by hydrolysis with a dilute THF solution of KOH. It was shown that LNR grafted onto the carbon black surface with ester bonds.

Segmented block copolymers based on liquid natural rubber

AbstractSegmented block copolymers were prepared from hydroxyl‐terminated liquid natural rubber (HTNR) and poly(ethylene oxide) (PEO). Toluene 2,4 diisocyanate (TDI) was used as the coupling agent for combining both types of segments. Keeping the molecular weight of HTNR constant, a series of materials were prepared using PEO with varying molecular weights. Their thermal and mechanical properties were evaluated. With increasing the PEO content, the properties vary from soft to rigid elastomers and rubber‐toughened plastics. This variation in properties is caused by the changes in the sample morphology, which depends on the relative fractions of the hard and soft segments. Water absorption capability of these block copolymers was determined. Hydrogels with water content approximately up to 80% were obtained.

Production of hydroxyl‐terminated liquid natural rubber—mechanism of photochemical depolymerization and hydroxylation

AbstractPhotochemical degradation of natural rubber yielded hydroxyl‐terminated liquid natural rubber (HTNR) when carried out in solution in presence of H2O2. Ultraviolet radiation from a medium pressure mercury vapor lamp and sunlight were found to be almost equally effective in bringing about the depolymerization and hydroxylation of natural rubber. The variations in the composition of the reagents and exposure time on the extent of depolymerization was conducted, and a suitable procedure for the large scale preparation of HTNR was described. A probable mechanism leading to the formation of HTNR as well as the side products is discussed based on the analytical data.